practical exercise 3. measurement of the turbine machine

LVTS turbine machines

1

Study material

Turbine machines – laboratory exercises

Study material for the laboratory exercises

Authors:

Benjamin Bizjan

Marko Hočevar

Lovrenc Novak

Martin Petkovšek

Ljubljana, october 2016


2

Table of contents

Table of contents ................................................................................................................. 2 Introduction: Study order .................................................................................................... 3 Theoretical exercise 1. Control volume and Bernoulli's equation in turbine machines..... 5 Theoretical exercise 2. Measurement stations for measurement of integral

turbomachinery characteristics ......................................................................................... 15

Theoretical exercise 3. Similarity laws of turbomachinery .............................................. 20 Theoretical exercise 4. Velocity triangles at the inlet and outlet of turbine machinery

rotors ................................................................................................................................. 28

Practical exercise 1. Using data acquisition systems, vibration measurements on turbine

machines ........................................................................................................................... 37 Practical exercise 2. Measurement of the operating point of a turbine machine ............. 43

Practical exercise 3. Measurement of the turbine machine characteristic, the station for

the measurement of pump characteristics and cavitation ................................................. 48

Practical exercise 4. HE Hubelj ....................................................................................... 54 Laboratory exercise 5. Measurement of the water turbine characteristic ......................... 59 Practical exercise 6. Measuring the outlet velocity triangles of an axial turbine machine

with a five hole probe ....................................................................................................... 65

Practical exercise 7. A model of the Planica wind tunnel ................................................ 72

Appendix 1: Main types of water turbines and their characteristics ................................. 78 Appendix 2: The properties of hydroelectric power plants .............................................. 91

Appendix 3: The elements of hydroelectric power plants .............................................. 102 Literature ......................................................................................................................... 117


3

Introduction: Study order

There are two hours per week of laboratory work for the subject Turbinske machines.

Laboratory work instructions are available at the website of the Department for energy

engineering, www.fs.uni-lj.si/kes. Occasionally, the instructions are updated.

Study order for laboratory work

The LVTS laboratory is located in the old faculty building. The entrance is from the

faculty backyard through the green metal door, then you must proceed up the stairs to the

first floor. Students are divided into three separated groups, in which the lab work is

organized, one group at a time. The lab work exercises may be different from the

previous years, so the students are expected to obtain up-to-date instructions online. The

study process includes both theoretic (computational) exercises and practical laboratory

work exercises.

For every practical exercise, the assistant selects a different group of students responsible

for successful completion of the lab work. These students are required to present the

contets of the exercise to the fellow participating students, and assign the tasks to

individual students. They must assure that all the variables necessary for analysis are

determined by measurements or calculation (as required by the exercise).

The lab work takes place on industrial measurement setups and by using industrial

measurement equipment. Each student is responsible for his own safety at work and the

safety of other participants. Caution must be taken to safely and correctly connect and

power up the electrical appliances, and avoid contact with rotating or otherwise moving

parts of the lab appliances. Also, due to the lack of free space in the laboratory, students

must take additional care not to push the others in the direction of rotating machinery.

The students must immediately report any danger or irregularity (faulty electrical wiring,

improper fastening of rotating parts etc.) to the assistant.

Participation in the laboratory work is mandatory. In every exercise, presence of students

is checked by the assistant. Absence from the laboratory work is only allowed for medical

reasons, and should be announced in advance whenever possible, by contacting the

assistant by e-mail. In case of such justifiable absence, a student may be assigned another

subject-related activity, arranged by the assistant.

Some laboratory exercises take place outside of the facilities of the Faculty of mechanical

engineering, at an external institution. In this case, the students must comply with the

work and safety instructions issued by the external institution, as well as the instructions

of the administrator and assistant.

Study obligations


4

To successfully finish the laboratory work course of the subject Turbine machines,

students are required to participate in and successfully complete all of the laboratory

exercises. The results of each exercise must be presented as a report following the

instructions provided in this document and by the assistant, and successfully defended

following a presentation. Also, the knowledge of the computational exercises is checked.

A written test (colloquium) in the classroom is organized in the last week of the semester,

in the time reserved for the laboratory work.

In the process of lab work report preparation, the group of students to which the exercise

execution was assigned, must present the measurement procedure, as well as the results

of measurements and subsequent analysis. The presentation takes place at the end of the

semester.

Time plan for the laboratory work

11.10.2016 Introductory exercise

18.10.2016 Control volume and Bernoulli's equation in turbine machines

25.10.2016 Control volume and Bernoulli's equation in turbine machines

31.10.2016 Holiday

01.11.2016 Holiday

08.11.2016 meritev karakteristike vodne turbine

15.11.2016 meritev karakteristike vodne turbine

22.11.2016 merjenje zvočne moči aksialnega ventilatorja, Hidria Inštitut Klima

29.11.2016 merjenje zvočne moči aksialnega ventilatorja, Hidria Inštitut Klima

06.12.2016 meritev izstopnih trikotnikov hitrosti aksialnega turbinskega stroja s

petluknjično sondo

13.12.2016 meritev izstopnih trikotnikov hitrosti aksialnega turbinskega stroja s

petluknjično sondo

20.12.2016 meritev karakteristike turbinskega stroja

27.12.2016 meritev karakteristike turbinskega stroja

03.01.2017 Turboinštitut

10.01.2017 laboratory work defense

17.01.2017 written test (colloquium)


5

Theoretical exercise 1. Control volume and Bernoulli's

equation in turbine machines

When treating static fluids, only the fluid density and the location of the free surface are

needed. However, for treatment of fluid dynamics problems, in most cases we need to

know arbitrarily chosen state of flow variables, which are defined by the turbine machine

geometry, boundary conditions and laws of motion.

For the purpose of fluid motion analysis in turbine machines, three basic approches can

be taken:

1. Differential approach: searching for detailed flow description in each point (x,y,z) of

the flow field.

2. Control volume approach: in a limited finite area flow balance is established between

the flow entering the area and the flow exiting the area. Then, flow variables such as the

body force, torque or the quantity of transferred energy are calculated.

3. Experimental approach.

The following section will present the control volume approach, also known as the large

scale analysis.

All the laws of mechanics are written for a system, which is defined as a selected quantity

of mass, enclosed by a boundary, separating it from the surroundings. The laws of

mechanics explain the interaction between the system and the surroundings. The

boundaries of solid bodies are cleared and usually we do not even realize that the system

was enclosed by a boundary.

When utilizing the control volume approach, changes of an arbitrary flow variable are

written by the Reynolds transport theorem (Reynolds transport equation), similarly to

thermodynamic problems. This equation is used for mass, linear momentum, angular

momentum and energy, in order to derive the four basic equations for fluid dynamics in a

control volume. During the exercises of this subject, we will mostly evaluate the volume

flow rate Q or the mass flow rate m across selected boundaries.

For the measurement of energy characteristics of turbines, pumps and fans, normally two

flow planes are selected (high-pressure and low-pressure one).

Figure. Cases of selected control volumes


6

Figure. Selection of measurement planes for the measurement of turbine, pump or fan

characteristics.

There are many areas of applications for transport equations. The best known is the

Bernoulli's equation, which is a special case of the energy equation for steady flows.

Caution is requared with Bernoulli's equation as it is only valid in certain cases, namely

for a steady incompressible flow along the streamline, without friction, receiving or

performing work, and heat transfer.

Bernoulli's equation is as follows

constgzwp

gzwp

2

2

2

2

1

2

1

1

2

1

2

1

.

Figure. Bernoulli's equation.


7

Example: Pitot-Prandtl tube, two holes, one measures the total pressure and the other one

the static pressure. The difference between these is the dynamic pressure. The static

pressure is the pressure of the still ambient fluid, while dynamic pressure is the pressure

due to the flow velocity. Their sum is the total pressure.

An example of Bernoulli's equation applocation is the calculation of the fan characteristic

from the static to the total pressure or vice versa. Bernoulli's equation can be used in real

flows with the following modification (Y = specific work):

izgw

gzp

Ywgzp

22

12

2

222

111

...... unit [m

2/s

2]

Figure. Validity of Bernoulli's equation.

Example: Pump characteristic measurement at the location of installation into the

system. The pump operates in the operating point where the drag and work characteristics

intersect. In measurements where the pump is installed in the system, pressure

measurement is often impossible. This is why the pressure is measured on the pipeline at

a certain distance from the pump. In this measurement plane the flow is uniform across

the complete cross-section, without vortices etc. Therefore, when measuring this way, a

part of the pipeline is included in the pump's characteristic.

When considering the flow velocity in the pump characteristic of a pump or fan, the flow

velocity near the wall must be known. For the purpose of pressure measurements,

measurement locations (outlets) are designed with sharp edges.


8

Figure. A pump installed in a system

turbulent flow laminar flow

Example: Dynamic pressure of a pump (fan), application of the fan for room ventilation.


9

Exercise

A fixed control volume has three onedimensional oarts where the transport of matter

takes place. The flow is steady. Flow properties are given in the table. Calculate, how the

energy changes in the system defined by the control volume.

part type density

(kg/m3)

velocity

w (m/s)

area

A (m2)

Specific energy

e (J/kg)

1 inlet 800 5 2 300

2 inlet 800 8 3 100

3 outlet 800 17 2 150

Solution: We will write the energy equation for the control volume

AdeVdetdt

dE

apovrkvolumenk

2

sin..

3nw

.

The flow within the control volume is steady, therefore the first term on the right side of

the equation equals to zero, resulting in a zero value of the volume integral. The surface

integral consists of contribution from two inlet and one outlet surface.

333322221111 wAewAewAedt

dE

The system is losing energy with a power of 240 kW. As the fluid transitions across the

control surface was taken in consideration, the system must perform work in a way not

shown in the figure. In this particular case, the energy balance does not exist. However,

the mass balance must exist, which can be verified if energy is replaced by mass in the

Reynolds transport equation.


10

Exercise A pump pumps water from reservoir A to reservoir B. Calculate specific work per unit of

mass. Consider local losses and pipe drag, assume a square drag law. Both reservoirs are

open. The pump is under the lower reservoir.

Q = 60 l/s – volumetric flow rate

d1 = 200 mm – suction pipe

d2 = 150 mm – pressure pipe

z1 = 3 m – height difference between the pump axis and the lower reservoir (A) surface.

z2 = 32 m – height difference between the pump axis and the upper reservoir (B) surface.

l1 = 5 m – suction pipe

l2 = 35 m – pressure pipe

= 0.0165 – pipe drag coefficient

1 = 5 – sum of local loss coefficient in the suction pipe

2 = 15 – sum of local loss coefficient in the pressure pipe

Rešitev:

izgw

gzp

Yw

gzp

22

2

2

22

2

1

11

izgww

zzgpp

Y

2

)(2

1

2

212

12

p1 = p2 = 0, w1 = w2 = 0 3

1 2 2

1

0,061,91 /

0,1p

Q mw m s

S s m

3

2 2 2

2

0,063,4 /

0,075p

Q mw m s

S s m

2 2

1 21 22 1 2 1 1 2

1 2

2 2 2 2

2 2 2

2 2 2 2

2 2 2 2

( ) ( )2 2

10 (32 3 ) 5 1,91 35 3,40,0165 5 0,0165 15

0,2 2 0,15 2

290 9,87 108,95 408 ,

p pw wl lY g z z izg g z z

d d

m m m m m m m

s m s m s

m m m m Nm J

s s s s kg kg

Vaja

A centrifugal pump pumps 200000 kg/h of water from reservoir A to reservoir B, both of

them pressurized (pA = 1.5 bar and pB = 12.5 bar). The height difference of water levels is

10.2 m. Total losses amount to 100 J/kg. Determine specific work of the pump and

rerquired electric motor power, if its efficiency is 70%.


11

izgw

gzp

Yw

gzp

22

2

2

22

2

1

11

kg

J

kg

J

kg

J

kg

J

kg

Jm

s

m

kgm

Nmizgzzg

ppY

13001001001100

10010101000

1011)(

22

35

12

12

1 155,556 1300103,2

0.7

Pel

el el

P mY kg s J kgP kW

Exercise A venturi tube with a 100 mm throat is used to measure the airflow in a pipe with 200

mm diameter. What is the theoretical pressure difference between the pipe and venturi

tube throat, when the air flow rate is 0.3 m3/s? The density of air is 1.2 kg/m

3.

22

2

2

2

2

2

1

1

1w

gzpw

gzp

smD

Vw

smD

Vw

/2,384

/55,94

2

2

2

2

1

1

Pawwpp

8202

2

1

2

221

Exercise A pump pumps water from an irrigation channel 5 m above the field. The distance of the

fields from the channel is between l1=50 and l2=10000 m, the pipe diameter is 30 cm, and

the pipe drag coefficient is 0.02. Neglect the local losses in bends, valves etc. What is the

required specific work of the pump in both cases, if the desired flow rate is 0.3 m3/s?

izgw

gzp

Yw

gzp

22

2

2

22

2

1

11


12

2

2

2

2

2

2

2

22

22

2

2

2

2

2

2

2

22

21

22

3

2

2

212

2

221

59706020502

25,4

3,0

1000002,0510

9,191,30502

25,4

3,0

5002,0510

25,415,0

3,0

2)(

2

s

m

s

m

s

m

s

m

m

mm

s

mY

s

m

s

m

s

m

s

m

m

mm

s

mY

s

m

sm

m

A

Vw

w

d

lhhgY

w

d

lghYgh

Exercise

Calculate the force acting on the walls of a wind tunnel with dimensions 0.1x0.1x1 m, if

air flows through it with a flow rate of 1500 m3/h. What would be the force acting on the

wind tunnel walls, if the power of its air supply fan is reduced by 50%?

Exercise

A mixing pump for sewage slurry works with a characteristic Y = -200000Q2 + 1000Q +

30. Determine the drag characteristic of the pipeline and the operating point (pressure,

flow rate and hydraulic power) of the pump, mixing the liquid in a 5 m high reactor. The

suction pipeline of the pump is 0.5 m above the reactor floor. The outflow is 0.5 m above

the liquid surface in the tank. On the suction pipeline with d = 0.1 m and 1 = 0.02, there

is a valve with v=0.2. Assume the liquid density to be 1000 kg/m3.

42

2

2

4

42

2

1

2

2122

2

8,97269,4

8,9726)(8

2

mQs

mY

md

l

dm

wwppmQgHY

mQgH

YY

KC

gKC

izg

KCČ

Quadratic flow rate equation:


13

s

m

s

mY

s

m

a

acbbQ

QQ

QQQ

32

2

2

32

2,1

2

22

0135,08,97265,4

0135,02

4

01,2510008,209726

3010002000008,97269,4

Exercise

A city is supplied by water from a source with the flow rate of Q = 0.185 m3/s. The water

level at the source is 15 m above the level of collecting reservoir. The pipeline length

from the source to the reservoir is l = 2090 m, its diameter is d = 0.3 m, and the drag

coefricient is = 0.0165. Determine the pipeline characteristic and the required specific

work of a pump for a given flow rate Q. Local losses in the pipeline reresent 15 % of the

losses in straight pipeline sections. What would the flow rate be, if the pump was out of

operation due to the power failure? In this case, what would be the required pipeline

diameter to assure the same flow rate as when pump is in operation?

Exercise

Water flows through a fire hose with 10 cm hose diameter and 3 cm nozzle diameter, at a

rate of 1,5 m3/min. Assume an ideal flow and calculate the force, by which the screws

hold the nozzle attached to the hose.

konstgzvp

2

2

1

smA

Vv /183,3

1

1

smA

Vv /367,35

2

2

2

2

22

1

1

2

1

2

1v

pv

p

barvvp 2,6

2

1 2

1

2

21

)( 1211 vvmApFv NFv 4067

Exercise

A centrifugal pump pumps 75 m3/h of warm water, =971 kg/m

3. The manometer on the

pressure side measures an overpressure of pt=18.1 bar, while on the suction side the

underpressure is ps=141 mmHg. The manometer is located 1.1 m above the inlet coross-

section axis. The electric motor of the pump consumes electric power Pel=60 kW and has

94% efficiency. If the mechanical efficiency of the pump is 96%, calculate its hydraulic

efficiency. Inlet and outlet cross-sections are the same.


14

Exercise (EXCEL)

A radial fan operates with a characteristic 0029.52162.20316.0 2 VVpstat . The

flow rate in this equation is in v m3/h, and the static pressure difference is in mbar. The

air is sucked from the surroundings at ambient pressure, and pressurized into a pipe with

155 mm radius, where static pressure is measured. Draw the characteristic of static,

dynamic and total pressure.

Additionally, for the purpose of rotational frequency regulation, there is a pressure

measurement outlet on the spiral just before the flange at the fan's outlet. Determine

(draw) the characteristic of pressure measured by the regulating pressure transducer. The

spiral diameter is 30 mm. In both cases, assume that the air velocity is uniform

everywhere in the pipe.


15

Theoretical exercise 2. Measurement stations for

measurement of integral turbomachinery

characteristics

Measurement stations for measurement of integral turbomachinery characteristics are

divided in open and closed measurement stations. Open measurement stations are mostly

used for measurement of fan and compressor characteristics, while the closed stations are

used with pumps and turbines.

Open measurement stations

The following variables are measured:

- geometric values (D,B,β,……)

- volume or mass flow rate

- pressure difference (static or total pressure)

- rotational frequency of the rotor

- material properties (,….)

- torque or power on the shaft of the turbine machine

The procedure for measurement of integral work characteristics is given by the standard

ISO 5801 Industrial fans testing using standardized airways.

Variables of work

characteristics:

g

aero

o

g

o

t

P

Vp

nVgP

nVfp

),,(

),,(


16

11112 3 4

51

5

6

56

Figure. Measurement station for measurement of integral fan characteristics at

Turboinštit, Ljubljana. (1) orifice plate for flow rate measurement, (2) flow straigtener,

(3) auxiliary fan, (4) throttling latches, (5) settling chamber, (6) measured fan – a view

from the rear side.

Figure. Scheme of the measurement station for measurement of integral work

characteristics of fans in KGH Godovič.

Types of fan mounting

To measure integral work characteristics, fans are usually mounted in the measurement

station in a way which resembles the operating conditions. The properties of air at the fan

inlet must be known, or calculated from the ambient atmospheric conditions. Due to

variation of density between measurements, the machine's characterictic is often

recalculated to a typical density (in the case of air, usually to 1.2 kg/m3).


17

To reduce the effect of vortex before and after the fan to a minimum, pipe wall outlets for

pressure measurements are not located immediately on the fan's boundaries. Instead,

flow straighteners are installed between the fan and the outlets, and the actual fan

pressure is calculated by taking pipe losses in consideration.

Examples:

1. Fan at the pipe inlet, fan outlet into the pipe, throttling at outlet, no auxiliary fan:

2dst ppp

2. Fan in the pipe, fan inlet and outlet into the pipe, throttling at outlet, no auxiliary fan:

12 ddst pppp

3. Fan at the pipe outlet, throttling at inlet, no auxiliary fan:

1dst ppp

4. Fan for wall mounting, auxiliary fan at inlet, throttling in the settling chamber:


18

1dst ppp

Closed measurement stations

Closed-type stations are used mostly to measure integral work characteristics of pumps

and turbines. The measurement procedure is given by the standard IEC 60193. On closed-

type stations, the following tests and measurements are performed:

- energy characteristics in four quadrants at specified cavitation conditions

- cavitation characteristics according to stabdardized testing methods

- oscillaions of radial and axial forces on the rotor and stator

- pressure pulsations in the flow tract

- torque oscillations on the turbine machine shaft

- velocity profiles in the flow tract

Figure. Scheme of the measurement stations for testing Francis turbines, Turboinštitut

Ljubljana.


19

Figure. Measurement stations for testing Francis turbines, Turboinštitut Ljubljana.


20

Theoretical exercise 3. Similarity laws of

turbomachinery

The similarity theory is important to gain the understanding of turbine machine operation.

It is based on dimensional analysis, which is a formal procedure where a group of

parameters which describe a particular physical phenomenon, is reduced or changed to a

smaller number of dimensionless variable groups.

There are several important fields of application for the dimensional analysis: (1)

prediction of prototype operation based on experiments, performed on a scaled-down

machine - similarity, and (2) determining the most suitable type of a machine based on

the maximum efficiency, pressure, flow rate and rotational frequency, (3) prediction of

machine operation when the rotational frequency or density is changed.

There are several methods of determining dimensionless variables. Based on logical

reasoning and by using the Bernoulli's equation we are able to determine the exponents of

variables n, d and for the flow rate, pressure and aerodynamic/hydraulic power (table).

Table: Exponents of variables n, d in for flow rate, pressure and aerodynamic/hydraulic

power.

variable flow rate pressure aerodynamic,

hydraulic power

n n n2 n

3

d d3 d

2 d

5

1

604

,3

23 nD

Q

nd

Q

flow number

2

222222

602

,,

nD

Hg

dn

Hg

dn

H

pressure number

follows:

- the flow rate (volume or mass) is proportional to the rotational frequency

- the pressure is proportional to the square of the rotational frequency

- the power is proportional to the cube of the rotational frequency

Similar turbine machines have the same pressure and flow numbers.

Indexing by m and p (model, prototype). Model is also marked by s '.


21

D – exit on the shroud (Turboinštitut, Dm=0.35)

4

3

2

1

H

nQnq specific rotational frequency – pumps, nq= 25 (radial) to 150 (axial)

4

5

2

1

H

nPns specific rotational frequency – turbines, ns= 100-400 (Francis), 400-1000

(axial – Kaplan, tube/bulb)

Dimensionless parameter, specific speed4

5

2

1

gH

P

N s

NS is a function of the turbine's geometry, not its size. It is given for the point of

maximum efficiency.

For recalculation from the model to the prototype, hydraulic similarity must be assured.

Hydraulic similarity is assured, if two turbine machines are (1) dimensionally similar, if

(2) ratios of various forces acting between the fluid and the machine components, are the

same, and if (3) ratios of velocity components in each respective point of the model and

the prototype are the same, (i.e., if velocity triangles are the same).

A comment to (2): ratios of various forces acting between the fluid and the machine

components are defined by dimensionless similarity numbers:

- Reynolds number (inertia/viscosity),

5

1

Re

Re7.03.011 m

mp , valid for radial turbines

- Euler number (pressure/inertia),

- Thoma number (NPSE/E),

- Froude number (inertia/gravitation),

- Weber number (inertia/surface tension).

Usually it is impossible to attain testing conditions which would assure the model-

prototype equality for multiple dimensionless similarity numbers at the same time.

Therefore, equality is assured (or the required corrections are performed) for the

dimensionless number with the largest influence.


22

A comment to (3): ratios of velocity components are the same, if there is equality

between the model and the prototype for:

- flow number,

- pressure number,

- cavitation number.

Figure. Hill diagram, Vuzenica.


23

Exercise

A pump operates at 1 bar pressure and 100 m3/h flow rate. How do the pressure and flow

rate change, if rotational frequency of the rotor is increased from 1500/min to 1800/min?

hmn

nVV

barn

npp

/120

44,1

3

1

212

2

1

212

Exercise

Under optimal conditions, the turbine operates with 220 kW power. The turbine shroud

diameter is 1.3 m, the head (height difference) is 4.8 m, and the rotational difference is

1.66/s. Calculate the rotational frequency of a geometrically similar turbine with 0.65 m

shroud diameter and 7.5 m head. Calculate the power of this similar turbine. The turbine

efficiency is 90%.

'

'

1

222215,4

'

''

''

' sH

Hn

D

Dn

nD

H

nD

H

n

n

D

D

Q

Q

nD

Q

nD

Q '''

''

'3

33

49,0''''''

Q

Q

H

H

gHQ

QgH

P

P

49,0' PP =107.4 kW

Exercise

Calculate the ratio of power for a pump and a five times smaller model (D/D'=5), if the

head ratio is known (H/H'=4) and both pumps have the same efficiency.

'

'

2222 ''

'

'''

nD

H

nD

H

QgH

gHQ

P

P


24

505

25

'''

5

2

'

'

''''

3

3

22

n

n

D

D

Q

Q

H

H

D

D

n

n

n

n

D

D

H

H

200'''

QgH

gHQ

P

P

Exercise

A turbine machine model with diameter d operates with rotational frequency n and a fluid

of density . A similar machine of diameter d' operates with a rotational frequency n' and

a fluid of density '. Determine the ratios of flow rates Q/Q', specific energies Y/Y' and

powers P/P'. Assume that both turbine machines operate with the same efficiency.

Numerical data: d/d' = 2, n/n' = 0.5 in /' = 1.

'

'

4'''

''

'3

33

n

n

D

D

Q

Q

nD

Q

nD

Q

gHQpQP

gHY

n

n

D

D

H

H

nD

H

nD

H

1

'''''

'22

2222

Exercise

We designed a centrifugal pump model, which is supposed to achieve a flow rate of Q =

30 l/s at specific work of Y = 392.4 J/kg and rotational frequency n = 2900/min.

Hydraulic efficiency of the pump is h =0.84. Assume that all the specific work is

converted to pressure and perform the following calculations:

a) what is the pump specific speed?

b) what is the required pump power at its shaft,

c) if a motor with 7.36 kW is available for lab testing, what rotational frequency would

the pump have at this power,

d) what would be the flow rate, specific work and pump power of a pump, 2 -times

larger from the model and operating with the same rotational frequency,

e) what would be the specific speed of a double pump,

f) what would be the specific speed of a two-stage pump.

Solution:


25

a)

4

3

2

1

H

nQnq ,

4

3

2

1

)(gH

nQnq

b) /P p Q , p Y link specific work and pressure according to Bernoulli's equation

c) ' in '

Q

Q

n

n '' in

Y

Y

n

n ''2

3

3 ''

P

Pnn

d)

2''

''

d

dpp

3''

''

d

dQQ

5''

''

d

dPP

e) in a double pump, the liquid flows in from two sides

Q'''=2Q

4

3

2

1

2'''

H

Qnn q ,

4

3

2

1

)(

2'''

gH

Qnn q

f) in a two-stage pump, the fluid flows through the first and the second pump stage one

after another.

p'''=2p

4

3

2

1

2

'''

H

Qnn q ,

4

3

2

1

)2(

'''

gH

Qnn q


26

Exercise

A fan operates at a rotational frequency of 1750 rpm and a flow rate of 4.25 m3/s. A

larger, geometrically similar fan must be designed to achieve the same pressure

difference at 1440 rpm. Calculate the volume flow rate of the larger fan.

3nd

Q 21

22dn

Hg 21

2

2

2

2

1

2

1

2

1

1

dn

gH

dn

gH

2

2

2

1

2

1

2

2

n

n

d

d

822,0

1

2

1

1

2 n

n

d

d

3

22

2

3

11

1

dn

Q

dn

Q sm

n

n

n

nQ

d

d

n

nQ

dn

dnQQ /28,6 3

3

2

1

1

21

3

1

2

1

213

11

3

2212

Exercise (EXCEL)

Fan measurements (pressure, volume flow rate) were performed at the air density of =

1.14 kg/m3 and rotational frequency n = 48.6/s. Recalculate the measurement results to

the density of = 1.2 kg/m3 and rotational frequency of n = 50/s.


27

Exercise (EXCEL)

We want to measure the streamlines through the vacuum cleaner unit "Domel". The rotor

radius is r = 0,045 m and the rotor channel height is b = 0,008 m. As the vacuum cleaner

unit rotates at a very high speed, we would like to perform the measurement s with water.

Calculate the rotational frequency and the liquid flow rate of the vacuum cleaner unit, if

pressure is selected at 18 cm of water column and the water temperature is maintained at

40°C. At room temperature, kinematic viscosity of air is 1,57·10-5

m2/s, while the

corresponding values for water are 9.79E-7 m2/s at room temperature and 4,78·10

-7 m

2/s

at 40°C. Calculate the ratio of Reynolds numbers for all operating points. The air density

during the measurments was 1,164 kg/m3.

rotational

frequency

flow

rate

pressure

(1/min) (l/s) (kPa)

39232 47,08 2,39

39761 44,31 6,83

41132 37,51 14,77

41941 34,13 17,88

42834 30,04 20,99

44491 23,03 25,01

46730 16,03 28,12

48925 9,7 29,2

51648 4,15 29,13

53634 0 34,48


28

Theoretical exercise 4. Velocity triangles at the inlet

and outlet of turbine machinery rotors

Velocities in turbine machines will be defined as follows:

va – axial flow velocity – velocity in direction of machine's axis

vr - radial flow velocity - velocity in direction of radius vector

u - tangential velocity - velocity in direction of turbine machine rotor's circumference

vu – projection of the absolute flow velocity to the tangential velocity, whirl velocity

v – absolute flow velocity

vm – meridian flow velocity – a vector sum of the axial and radial flow velocity

w – relative flow velocity – relative velocity of the flow with respect to the turbine

machine blade's velocity

Indices 1 and 2 will mark the rotor inlet and outlet, respectively.

For ideal rotors we will assume that the inlet fluid flow angle will be the same to the inlet

angle of the turbine machine blade angle. The same assumption will be made on the

outlet, so that the outlet fluid flow angle will be the same as the blade outlet angle. In

reality, this is not true, therefore the corrections will be made taking in consideration the

blade thickness and total number. When considering these corrections, the blade angles

will be marked by index L.

Euler's equation 2211 uu vuvuY in general

1

2

1

2

2

1

22

tan

tan1

1

L

Lt

b

b

D

DuY

for turbines

2

1

2

1

2

2

12

2tan

tan1

L

Lč

b

b

D

DuY

for fans/pumps


29

Figure. Velocity triangles in an axial turbine machine.

Comparison: axial : radial turbine machine

- calculation of meridian velocities

- a change in radius causes affects the inlet and outlet tangential velocities

Exercise

Determine the inlet and outlet fluid flow angles for an axial turbine, defined by

specifications provided below. Calculate the angles for the diameter of the hub (DP) and

of the shroud (DV). Assume an ideal rotor.

Dp = 1.5 m

Dv = 2.5 m

Q = 6.2 m3/s

N = 500/min

Yteor = 850 J/kg

a)

2

5,1

60

5002

221

m

s

Duu

p

PP

39,3 m/s

2

5,2

60

5002

221

m

s

Duu V

VV

65,4 m/s

b)

97,1

)5,15,2(

2,64

4

222

3

22

sm

m

DD

Q

A

Qv

p

m

V

m/s


30

c)112211 uuuteor vuvuvuY

6,213,39

850

1

1 mkg

Js

u

Yv

p

pu m/s

134,65

850

1

1 mkg

Js

u

Yv

v

vu m/s

inlet:

2,5

6,21

97,1arctan1

1

1 p

pu

mp

v

vtg

6,8

13

97,1arctan1

1

1 v

vu

mv

v

vtg

4,6

6,213,39

97,1arctan1

11

1 p

pup

mp

vu

vtg

2,2

134,65

97,1arctan1

11

1 v

vuv

mv

vu

vtg

outlet: 902 p in 902v

9,2

3,39

97,1arctan2

2

2 p

p

mp

u

vtg

7,1

4,65

97,1arctan2

2

2 v

v

mv

u

vtg

Exercise

A pump has a rotor with following dimensions: d1 = 150 mm, D2 = 560 mm, b1 = 80 mm

and b2 = 60 mm. The blade angles are L1 = 19° and L2 = 26°.

a) Determine the pump's pressure number. Assume that all the specific work is converted

to pressure.

b) If the rotor's outer diameter is reduced by 5% by cutting the blade tips, by how much

will the flow rate, pressure and power of the pump be reduced? Perform calculations, as

though the pump geometry remained unchanged.

c) How must the rotational frequency of the cut rotor be changed, to attain the same

pressure difference as in the case of the original rotor? What would be the corresponding

flow rate of the pump?

d) Determine the pump's flow number, assume the angle of the relative flow velocity to

be the same to the blade angle.

a)222211 uuu vuvuvuY

2

1

2

1

2

2

12

2tan

tan1

L

L

čb

b

D

DuY


31

dnnru 2

)2,9(38,7tan

tan1

tan

tan1

1

2

2

2

2

1

2

1

2

2

12

2

22

2

2

2

2

1

2

1

2

2

12

2

2

2

22

2

22

2

2

Dn

b

b

D

DDn

Dn

b

b

D

Du

Dn

Y

Dn

p

Dn

gH

L

L

L

L

b) 53295,0' 22 DD mm

17,1'''

'3

2

3

2

3

2

3

2

D

D

Q

Q

nD

Q

nD

Q

2

2

2 2 2 '2 2

2 2 2

'1,11

' '

DgH gH H

n D n D H D

3,1'''

QH

HQ

P

PQpP

c) 2 2 2 '2 2 2 2 '2

2 2 2 2

' 1 1 '0,95

' '

gH gH n d

n D n D n D n D n d

11,1''

'3

2

3

2

Q

Q

nD

Q

nD

Q

d) 3

2nD

Q

222111 bDvbDvQ mm

2

2

1

2

1

1111

11

1

1

1 bDtgn

Q

bDnD

Q

nD

bD

Q

u

vtg m

1

1

2

1

2

1

1

2

1

2

1

3

2 D

btg

D

bDtg

nD

Q = 1,81

Exercise

A radial pump gives a specific work of 390 J/kg. Tangential fluid velocity is -4 m/s at the

inlet radius (144 mm) and 18 m/s at the outlet radius (360 mm). Determine both

tangential velocities.

2

1

2

1112211 uuuuteor vD

DuvuvuvuY


32

sm

vD

Dv

Yu

uu

C /95,7

2

1

2

1

1

smD

Duu /89,19

1

212

Exercise

A pump pumps 0.118 m3/s of water with 73 m head. Determine the fluid flow angle at the

rotor outlet, if the sum of losses is 20 %, b2 = 0.11D2, = 0.93 in n = 2900 min-1

.

7307310

2

s

mmgHY m

2/s

2

58,0290093,0

6073102

2

222

2

2

s

smm

n

gHD

Dn

gHm

158,011,014,3

118,0

11,02

3

2

22

2

s

m

D

Q

bD

Qvm

m/s

8860

58,0290014,3

602

2

2

222

nDDu

m/s

27,108,088

7302

2

2

222

ms

sm

u

YvvuY uu

m/s

6,8

6,6

1arctan2

2

22

u

m

v

vtg

7,0

6,688

1arctan2

22

22

u

m

vu

vtg

Exercise

A radial fan with inlet diameter of 0.075 m and outlet diameter of 0.15 m produces a

pressure of 1000 Pa at a rotational frequency of 4500/min. What should be the rotor

height ratio at the inlet and outlet, so that the relative fluid velocity angle at the inlet (1)

will be the same to the corresponding outlet angle (2). Draw velocity triangles. What

pressure difference is produced by the fan, if it rotates at 1.5 times of its original speed?

smnDD

u

smnDD

u

/325,35602

/66,17602

222

111


33

11

22

2

1

222

111

22

22

bD

bD

v

v

vbD

vbD

m

m

mm

smu

pv

vuY

u

u

/5,23325,352,1

10001

2

2

22

746,05,23325,35

66,17

15,0

075,0

tan

tan

22

1

2

1

1

2

22

1

11

22

22

1

2

1

22

2

1

1

22

22

1

11

u

u

um

m

u

mm

u

m

m

vu

u

D

D

b

b

vu

u

bD

bD

vu

u

v

v

vu

v

u

v

vu

v

u

v

Exercise

Determine and draw velocity triangles for a radial pump with following specifications:

D1 = 140 mm

D2 = 290 mm

b1 = 50 mm

b2 = 25 mm

z = 8 – number of blades

= 4 mm – blade thickness

Ll = 15o

L2 = 24o

Q = 0.05 m3/s

n = 1450 min-1

Solution:

6,1060

110

nDuu

m/s 22

60

232

nDuu

m/s


34

3,211

0 bD

Qv m

m/s

2,222

3 bD

Qv m

m/s

If the finite blade thickness is considered, the interblade cross-section area is reduced:

72,0sin

111

1 LD

z

91,0

sin1

22

2 LD

z

16,3111

1 bD

Qv m

m/s

4,2222

2 bD

Qv m

m/s

Now, we calculate the tangential component of the absolute velocity at the outlet:

7,34812

1

2

1

2

2

12

2

l

lč

tg

tg

b

b

D

DuY

J/kg

85,152

3 u

Yv č

u m/s

121

00

u

varctg m 5,16

1

11

u

varctg m

u

m

vu

varctg

32

22

u

m

vu

varctg

32

33

u

m

v

varctg

3

22

u

m

v

varctg

3

33

Exercise (written test 2, 2007/2008)

Consider a centrifugal pump with the following specifications:

D1 = 0.14m

D2 = 0.28m


35

b1 = 0.031m

b2 = 0.019m

= 0.004m

z = 5

1l = 18o

2l = 30o.

a) Determine the flow rate through the pump, if n = 1450 min-1

and if the volumetric

efficiency is v = 0.95! Assume 1 = 1l.

b) Calculate the pump's specific work Y, is the hydraulic efficiency is h = 0.87 and the

coefficient of the rotor imperfection is 0.72!

c) Calculate the energy difference (specific work), flow rate and power, if the pump

operates at n'=900 min-1

.

Determine and draw all velocity triangles!


36

Exercise

What should be the inlet and outlet blade angles to achieve the maximum efficiency of

the pump, if the following specifications are known:

Q = 0.0102 m3/s

Y = 501 J/kg

D1 = 0.12 m D2 = 0.35 m

b1 = 0.025 m b2 = 0.02 m

z = 7 (number of blades)

= 4 mm (blade thickness)

n = 1450 min-1

= 0.93 (total efficiency)

v = 0.99 (volumetric efficiency)

m = 0.98 (mechanical efficiency)

tr = 0.98 (efficiency due to the friction in labyrinths)

= 0.77 (coefficient of the rotor imperfection)

Solution:

Tangential velocities : smnD

usmnD

u /6.2660

/1.960

22

11

Blade thickness: 111

1sin

074.01

sin1

LLD

z

222

2sin

025.01

sin1

LLD

z

In equation for the meridian velocity, volumetric losses are also considered

2

222

2

1

111

1

sin

074.01

09.1

sin

074.01

09.1

L

v

m

L

v

mbD

Qv

bD

Qv

Inlet angle is obtained from a condition that 1 = 90°

1

1

11

sin

074.01

12.0tan

L

mL

u

v

By considering the relation between the functions sin in tan:

1

2

1

1

tan1

tansin

L

LL

,

a quadratic eq. is obtained for tan L1 : 000866.0tan227844.0tan926.0 11

2 LL

There are two solutions of this equation, but only one is relevant: L1 = 12,1o

To calculate the outlet angle, the hydraulic efficiency h must first be calculated:

trmvh

trmv

h

To calculate the blade outlet angle, the Euler's equation for a pump is used:

22

22

222tan

1L

m

huhu

vuvuY

We obtain a quadratic equation for tan L2 with solutions l2 = 17,85° and l2 = 14,97°.


37

Practical exercise 1. Using data acquisition systems,

vibration measurements on turbine machines

Introduction

In this practical exercise, the analog input of the measurement (data acquisition) card

must be connected to measure fan vibrations and the analog output to control the variable

frequency drive, which runs the fan. Vibrations are supposed to be measured on the fan

casing for different rotational frequencies of the fan.

Required prior knowledge:

- systems for data acquisition by a computer,

- using variable frequency drives,

- vibration measurement.

Analog-to-digital (A/D) converters

An analog-to-digital converter is a basic part of many measurement systems, for example

in measurement cards, digital multimeters (DMM), (micro)controllers etc. All of these

systems operate on the principle of voltage measurement. More advanced versions

include additional measurements of current, frequency and resistance, but in the end all of

these additional measurements are converted into voltage measurement. The basic

properties of measurement cards and digital multimeters are:

analog inputs

digital inputs

analog outputs

digital outputs

sampling frequency

sampling mode

resolution

input range

measurement uncertainty

timers

triggering

Measurement instruments with analog digital converters are used for measurements in

different environments, which is why their design and function are very different.

Usually, the A/D converter is in an integrated circuit, to which the other elements (user

interface, power supply etc.) are added.

a) analog inputs/outputs, digital inputs/outputs


38

Analog inputs are used for voltage measurements. By analog inputs, continuously

changing signals from sensors are acquired. For example, in flow measurement 0 V may

represent the flow of 0 m3/s, 1 V 1 m

3/s, ... and 10 V 10 m

3/s.

Analogue outputs are used for continuous control of devices. Analogue outputs are not

capable of producing large currents, which is why a proper interface (e.g. variable

frequency drive) must be used for connection to controlled devices.

Digital outputs are used for on/off regulation of devices (e.g. turning on/off a pump or an

electric heater), for synchronization of two measurement cards, for filter control. If the

digital signals are of the TTL type, it means that a current of a few mA can be produced

at the voltage of 5V. Similarly to analogue outputs, the digital outputs are not capable of

producing large currents, therefore relays or transistor amplifiers are used.

b) sampling frequency

The sampling frequency is the rate (speed) of conversion from analogue voltage values

into a digital form. According to the Nyquist sampling theorem, an observed

phenomenon can be sufficiently well described, if there are at least two samples per its

period. Example: If vibration measurement signal is acquired on a machine rotating by

3000 min-1

, the sampling rate must be at least 6000 min-1

(100 Hz). In practice, the

sampling rate should be set at about 5-10 times of the expected maximum signal

frequency of interest.

Typical sampling rates are 20-200 kHz for measurement cards and 1-100 Hz for DMMs.

To measure the so-called static variables, e.g. fluid temperature in a 100m3 process boiler,

one temperature reading every 10 seconds is sufficient. For vibration measurements, a

much higher sampling rate is required (e.g. 10000 Hz or more).

Figure. Sampling rate effect for analog signal acquisition. Above – adequate (sufficient)

number of sampling points per period to properly describe the measured signal, below –

inadequate (insufficient) number of sampling points per signal period due to the

undersampling. Measured values show an apparently slower rate of change of the same

measured variable.

c) sampling mode

The sampling mode can be serial or parallel. If signals from different inputs are read, a

multiplexer is used. The multiplexer is a device which combines different measurement


39

channels in series by sending their signals one after another to the A/D converter, causing

time lag between channels. Such system is used for measurements where the time lag is

not important. If the lag is important, the data acquisition device must be capable of

simultaneous acquisition (one A/D converter per each channel). Signals such as

temperature, pressure… are not sensitive to the time lag, because they change slowly.

In a DMM, there is a single A/D converter and the signals from different channels are

distributed to it by a relay multiplexer (mechanical switching).

In measurement cards there is usually also only one A/D converter, but an electronic

multiplexer is used for switching between signals (much higher switching speed in

comparison with mechanical switches).

d) analog input resolution

The resolution is the ratio of the maximum measurable value to the minimum measurable

value in the selected measurement range.

Normally, the resolution is 12, 16 or more (DMM 20, 22) bits. The resolution is the

number of levels which the measured voltage can take. In the case of 12 bit resolution

there are 212

= 4096 discrete levels, and the difference between two neighboring levels for

a 10 V voltage range is equal to

mVV

4.22

1012

The larger the number of levels which can be assumed by the measured values, the more

precisely the variable of interest can be measured. In practice, a 12 bit resolution is

sufficient for the majority of engineering measurements. At large sampling rates, the

resolution of measurement cards deteriorates.

Figure. Sampling of analog signals - resolution. Digitalization of the sine signal with 3 bit

resolution, which converts the input signal to n = 23 = 8 levels.

e) input range

The input range is the difference between the maximum and minimum voltage, which can

be accepted by the A/D converter. This range is usually –10 to 10 V, 0 to 10 V or 0 to 5


40

V. An unprotected measurement card is destroyed at around 35 V voltage. Better A/D

converters have a possibility of software variation of the measurement range (e.g. 12 bits

of resolution in the range 1-2V). For this purpose, an amplifier integrated in the

measurement card or the digital multimeter is used.

f) measurement uncertainty

The measurement uncertainty is usually discussed in connection with the A/D conversion

of analog inputs. Digital inputs only have two measurement levels, which is why it is not

possible to determine the measurement uncertainty in the same way. Different

manufacturers express the accuracy of installed A/D converters in different ways. We

will present two examples of measurement uncertainty definition: by Hewlett Packard

(Agilent) and National Instruments.

Hewlett Packard (Agilent): ( % % )absolute uncertainty reading error range error reading

National Instruments:

( % )

( )

absoluteuncertainty reading reading error

zerodrift sum quantization drift

The lower the measurement uncertainty, the better (more accurate) is the A/D converter.

The measurement uncertainty is usually larger than the measurement resolution. In the

case of analog inputs, the measurement uncertainty is determined in a similar way.

g) timers

The timers are used to measure the time, e.g. when measuring the time lag of an inductive

probe for rotational speed measurement. Certain flow meters, especially of rotary type,

have a pulsating output, e.g. one pulse per each turn or per a selected volume of liquid

throughput. The timers on measurement cards have a large resolution (usually 24 or 32

bits, 80 MHz).

h) triggering

The measurement card can be triggered by an external signal, e.g. from the rotational

speed sensor. This way, the measurement can be started by a signal originating from

observed phenomenon. Synchronization through external triggering is very quick. The

triggering channels are usually digital TTL.

Software

The software will be prepared by an assistant in the software package LabVIEW so that it

will allow measurements with a sampling frequency of 50 kHz, and writing data to disk.

Fan and variable frequency drive


41

A fan with a three-phase asynchronous electric motor is connected to a variable

frequency drive (VFD) Fuji Frenic, which is attached to the lab wall. The assistant will

configure the VFD so that it will be possible to regulate the rotational frequency of the

fan through an analog output on the measurement card (0-10V) connected to an analog

input of the VFD (the VFD's output frequency 0 Hz at 0 V and 60 Hz at 10 V). The

operation of such control can also be verified when the fan is not connected – check the

rotational frequency displayed on the screen of the VFD.

Vibration measurement

Measure vibrations on the casing of the selected fan. Install the acceleration sensor

(accelerometer) so that it will measure in direction perpendicular to the rotor axis. Screw

the accelerometer to the fan in order to be able to detect frequencies up to the reference

frequency of the sensor. Screw the sensor to the fan by first screwing the brass support,

and then screwing the sensor onto the support. Be careful not to damage the sensor, do

not touch the connector when screwing to avoid breaking it. The sensor can also be

attached by a magnet.

Calculate the equivalent velocities of the bearing casing and evaluate them according to

the standard ISO 10816. Calculate the equivalent velocity of the bearing casing vrms by

the following equation:

tvT

vrms

21,

where v(t) is the current velocity of the bearing casing and T is the total time of the

measurement.

Measuring equipment

For vibration measurements, use the accelerometer Bruel&Kjaer 4332 and the charge

amplifier Bruel&Kjaer 2635. On the amplifier, set the accelerometer sensitivity,

amplification and the size of the output physical unit. Connect the analog output of the

amplifier to the analog input of the measurement card. Ford regulation and data

acquisition use the measurement card National Instruments NI 6211, which is connected

to the computer through the USB port.


42

Figure. Accelerometer Bruel&Kjaer 4332 and the charge amplifier Bruel&Kjaer 2635.

Assignment

Determine which input on the VFD is intended for regulation with input voltage of 0-

10V. Connect the analog output of the measurement card to the selected input of the

VFD.

Connect the analog AC output of the vibration meter analog input of the measurement

card.

Measure fan vibrations at different rotational frequencies up to the nominal rotational

frequency and determine, if the resonance peak of the fan is located in this area. Present

the results according to the equation for the equivalent velocity of the bearing casing vrms.

Draw the power spectrum of the fan casing vibrations for the case of maximum vibrations

and evaluate them depending on the measurement type, settings and the measurement

equipment used.


43

Practical exercise 2. Measurement of the operating

point of a turbine machine

Introduction

In this practical exercise, the operating point of an axial fan Rotomatika HEF 500 will be

measured. The flow rate of air will be measured on the station for measurements on axial

fans by the traversing method, i.e. sequential velocity measurements in individual points

of the measuring plane in the complete cross-section.


- using variable frequency drives,

- using measuring transducers for measurement of static pressure,

- flow velocity and turbulent intensity measurement by a hotwire (HW) anemometer

- calculating the flow rate from velocity measurements by the traversing method

(measuring flow velocity on partial surfaces).

Measured variables

The following variables will be measured: flow rate, static pressure on the fan and

rotational frequency.

- flow rate measurement : it will be performed by the principle of measuring velocity in

multiple points across the cross section of the flow. Velocity will be measured in different

ways: (1) in different cross sections (inlet, outlet), by a different selection of points

(equidistant, by increasing the point density at edges, by rotating the velocity meter).

Velocity profile measurements can be made by different kinds of probes (Pitot probe,

five-hole probe, HW anemometer…). In this exercise, you will use a HW anemometer

and read the output data (velocity, turbulent intensity) from the LabVIEW software.

- static pressure measurement : hydraulic averaging in four points at the pipe wall.

For static pressure and orifice plate pressure measurements, three differential pressure

meters are available: two with a range of 0-10 mbar and one with a range of 0-100 mbar.

The fan is propelled by a three-phase asynchronous electric motor. The fan is installed in

the system in such way that sufficient resistance is provided by the system.

Rotational frequency measurement

Measure the rotational frequency of the test fan, use the manual laser rotational frequency

meter. Stick a reflective sticker (cat eye) on a turbine blade or paint the selected rotating

part of the machinery black or white color. You must assure a large contrast between the

fan rotor and the modified surface.

Selecting measurement locations

Measurement points can be elected by two methods, equidistantly or so that the point

density is larger at edges:

- equidistant: this method is useful, when we do not know the properties of the flow in the

measurement cross-section. It is used when there is a flow obstruction in close proximity


44

of the measurement cross-section (e.g. less that pipe 3 diameters upstream of the

measurement location), which disturbs the flow, e.g. vent, bend, expansion, contraction,

splitter etc.

- larger point density at edges: this method is used, if the flow in the selected cross-

section resembles the fully developed turbulent or laminar profile. This means that the

flow tract is obstruction-free at least 3 diameters before the measurement plane, and at

sufficient distance from the pipe inlet. The calculation procedure for the total flow rate

from velocities must be adjusted accordingly. The recommendations VDE 2640

(Netzmessungen in Strommungquerschnitten / Grid measurements in flow cross-section)

recommend selecting the points in such way that all the partial surfaces have the same

area. This means that the measurement locations are condensed near the edge.

Regardless of selected method, each measurement point must be assigned a partial

surface, so that the product of the partial surface area iS and velocity

iv represents the

volume flow rate through the selected partial surface. The total flow rate V is the sum of

partial flow rates:

i

ii SvV

The number of measurement locations is increased until we determine that the calculate

total flow rate no longer changes by further increasing the measurement grid density.

During velocity measurements with the HW anemometer, a time series of duration T is

recorded in a LabVIEW program. The time series is recorded with a high sampling

frequency (fs = 50-100 kHz). 2 important parameters are obtained from the time series:

mean velocity and turbulent intensity I:

/

1

1( )

a t fs

a

a

v v t tT

'vI

v

In above equations, v' is the RMS value of the fluctuating part of the velocity (defined as

at a given time t).

Assignment

1. Prepare a measurement scheme and comment on the selection of measurement

locations. Keep in mind that the choice of measurement locations determines the size of

the system treated as a black box.

2. Find the fan characteristics in the internet.

3. Compare measurements performed by different methods.

4. For each measurement, draw a 2D diagram of flow velocity across the measured

surface. If using the HW anemometer, also draw a diagram for the turbulent intensity.


45

5. Estimate, how well do the results of the operating point measurements agree with the

values provided in the online catalog of the manufacturer (Hidria).

Figure. Static pressure measurement on the pipe wall according to the standard ISO 5801,

design of the measurement outlet.

Figure. An example of velocity measurement location distribution according to the

standard ISO 5801 for determining the flow rate in standardized fan characteristics

measurement stations. The measurement points are more concentrated at the edge.


46

Figure. An example of an equidistant measurement location distribution,

recommendations VDE 2640 (Netzmessungen in Strommungquerschnitten).

Figure. An example of a non-equidistant distribution of measurement locations,

recommendations VDE 2640 (Netzmessungen in Strommungquerschnitten). In this case,

the measurement cross-section is only accessible from one point.


47

Figure. An example of a measurement location distribution, which is denser near the

edges, recommendations VDE 2640 (Netzmessungen in Strommungquerschnitten). Left:

circular cross-section. Right: rectangular cross-section.


48

Practical exercise 3. Measurement of the turbine

machine characteristic, the station for the measurement

of pump characteristics and cavitation

The exercises will be performed at the Faculty of civil and geodetic engineering,

Hajdrihova 28, at the Department of fluid mechanics (in the lab).

Introduction

In this exercise, the characteristic and operational range of a radial turbine machine must

be determined. For lab work, the pump KSB Etanorm 50-125 will be used. This pump

will propel the liquid through the cavitation measurement station. In the cavitation

station, a pipe is mounted at the location where the transparent plexi glass test section is

installed. Before and after the test section, isolation valves are installed. For pump

throttling, use the valve between the pump and the test section for cavitation. The pump

motor is connected to the variable frequency drive Mitsubishi, which is located in the

basement alongside the pump.


- using pressure transducers for measurement of static pressure,

- basics of flow rate measurements,

- the effect of pressure on pump operation, NPSH.

NPSH (net positive suction head)

Cavitation occurs in locations where the static pressure is lower that the liquid

vaporization pressure, usually due to low system pressure and high velocity. For pumps,

the following relation applies:

s PNPSH NPSH cavitation-free operation (NPSHP=NPSHr)

The system (pipeline conditions) must supply sufficient specific energy (high enough

pressure) to avoid cavitation conditions. NPSHP and NPSHr change with the pump flow

rate.

The cavitation reserve NPSHP (NPSHs) marks the actual NPSH of the pump (system),

while NPSHr marks the required cavitation reserve.


49

Figure. Operating range of a pump.

A general form of NPSE and NPSH for turbines and pumps

In accordance with standards ISO 60193 and ISO 60041 the basic parameter for

description of cavitation conditions in a turbine is the net positive suction energy NPSE.

NPSE relates to the suction side of a turbine machine and is in direct connection to the

occurrence of cavitation. NPSE represents the difference between the absolute specific

hydraulic energy at level 2 (consider the figure for selection of measuring planes) and

specific energy due to the vapor pressure pv at a certain reference level Zref (the reference

level usually corresponds to the center of the turbine or pump rotor).

Figure. Schematic representation of a hydraulic machine. Plane 1 is always overpressure

and plane 2 always underpressure. The flow flows in the direction of pump or turbine

arrow.

NPSE must be recalculated from the level 2 to the reference level of the turbine rotor. The

NPSE equation is as follows:


50

)(2

2

2

2

2

2 ZZgvpp

NPSHgNPSE refvabs

.

Similarly, NPSH (net positive suction head) denotes the total absolute net pressure height

(head) at a certain reference point with subtracted height of the water vapor pressure and

outlet losses. In relation to NPSE it is written by division with the gravitational

acceleration:

g

NPSENPSH .

Figure: Definition of levels and heads in a water turbine for calculating NPSE and NPSH.

Using NPSH in the exercise

In the case of a pump installed as in this exercise (consider the figure below), NPSH or

NPSH is written for the location of the pump inlet, i.e. at the inlet flange:

2

2

22 vppNPSHgNPSE vabs


51

Figure. Determining NPSE or NPSH by using Bernoulli's equation. The static absolute

pressure meter is installed above the measurement plane 0. As a result, it shows pressure

lower from the actual pressure at location 0 by the height contribution gH1.

If Bernoulli's equation is used for the commonly encountered case from above figure, it

can be assumed that kinetic energy of water in the plane marked by the point 0 is

negligible. At point 0 the static absolute pressure meter was installed. NPSE or NPSH at

point 0 is smaller from NPSE or NPSH at point 2 by the height contribution gH and

larger by the sum of losses (in the above equation, we assume that 02

2

0 v

):

izgvp

gHp abs

2

2

220

Bernoulli's equation, used for the above case, is inserted (

2absp) in the NPSE equation

and we obtain the net positive suction energy for the point at the pump inlet, i.e. at the

inlet flange:

izggHpp

NPSHgNPSE v

0


52

As we can see from the above equation, the velocity term is eliminated. To obtain p0, it is

necessary to insert the measured value of the static absolute pressure, increased by the

height contribution gH1.

Static pressure measurement

For pressure measurement, one differential and one absolute pressure transducer is

available. The absolute pressure transducer measures the pressure with respect to

vacuum, thus indicating about 1 bar at atmospheric pressure. Verify that the pressure

transducers are correctly connected and de-air them prior to the measurement. De-airing

is performed by unscrewing the cap on the opposite side of the pressure outlet by few

turns and letting the water push the air out. If the transducer is equipped by a valve, de-air

it by opening the valve. Note the height difference between the pump, pressure outlet and

pressure transducers. Also consider the difference between the inlet and outlet cross-

section, which results in different flow velocities in measuring planes according to the

Bernoulli's equation.

Before performing the exercise, prepare the measurement protocol in Excel so that you

will be able to already draw the pump characteristics during the measurement.

Measuring equipment

For the purpose of pressure measurement, an inductive flow meter ABB DL-43F is

installed in the experimental station. For pressure measurement you can use one

differential pressure transducer (ABB 2600T, range 6 bar) and one absolute pressure

transducer (ABB 2600T, range 6 bar). Enter the pressure and flow rate measurement data

manually in the Excel spreadsheet.

Measure the temperature by the Pt-100 sensor and the amplifier Agilent 34970A. Use the

four wire connection.

Determine efficiency by measuring electric power. Use the electric power meter

integrated in the variable frequency drive (VFD's control unit must be set correctly).

System for setting the pressure in the station

The pressure inside the measurement station is set by connection to the pneumatic system

or by a vacuum pump on the top of the upper reservoir. The vacuum pump is turned on

by a switch in the control panel, and by turning the valve on the top of the upper reservoir

at the same time. The valve at the top of the station must be switched to the correct

position (compressed air supply/vacuum pump/off/de-airing)

Take care of safety while working. Do not step on electric cables. If the water is

spilled on the floor, be especially careful when handling electric devices.


53

Figure. Station for measurement of pump characteristics and cavitation: measured is the

pump KSB Etanorm 50-125, the inductive flow meter ABB DL-43F is installed in the

basement in the uppermost position and is not visible in the image. The lower reservoir

serves as a settling and de-gassing chamber. The lower reservoir is connected to the upper

one by a pipe. The upper reservoir has a free surface, so that air can be pumped out of it

by a vacuum pump.

Legend: klet = basement, črpalka = pump, tlačni odjem = pressure outlet, frekvenčni

pretvornik črpalke = pump VFD, spodnji rezervoar = lower reservoir, zgornji rezervoar =

upper reservoir, pritličje = ground floor, vakuumska črpalka ) vacuum pump, komandna

plošča f. p. = VFD control panel, ventil = valve, tlačni pretvorniki = pressure transducers

Assignment

- draw the measurement station scheme,

- estimate, if the key elements of the station (diameters, lengths of straight sections at

measurement locations ...) are suitable for measurements,

- determine which measurement equipment is used and what its measurement uncertainty

is,

- measure the temperature of water in the cavitation station,

- measure the pump characteristics (pressure and efficiency) at VFD setting 50 Hz and 1

bar pressure in the upper reservoir, plus at two different underpressures; correct the

measured values with respect to density and dynamic pressure,

- compare measured characteristics with each other,

- compare measured characteristics with each other with the characteristic provided by

the manufacturer.


54

Practical exercise 4. HE Hubelj

Introduction

The purpose of this exercise is to familiarize with the turbine and accompanying systems

of HE Hubelj and measure its operating point.


- flow rate measurement,

- pressure measurement,

- basics of measurement data acquisition and A/D conversions.

HE Hubelj

HE Hubelj exploits the water from the river Hubelj. HE Hubelj has the following

specifications:

Start of operation: 1931

Gross head: 110 m

Mean flow rate: 2,80 m³/s

Total installed flow rate: 2,70 m³/s

Power: 2,100 MW

Turbine type: Francis

Annual production: 10.000 MWh

Figure. River Hubelj.


55

Figure. Left: the source and the damming of river Hubelj. Right: The gate for maintaining

biological minimum and the de-sanding gate. Visible behind (right corner) is the new

water supply plant.

Figure. The upper settling pool and its gate.

Figure. Head race tunnel (left) and the penstock (middle and right)


56

Figure. Bypass valve for drainage in the case of emergency shutdown, ball valve before

the turbine and its bypass.

Figure. Powerhouse, two Francis turbines of different sizes, two flywheels for isolated

(off-grid) operation, generator. Also visible is the stator opening regulation.


57

Figure. Excitation transformer (left) and transformer (right).

Figure. Connection (left panel) of the power plant part (right in the right panel) and the

dispatcher part (left in the right panel).

Figure. Power plant outlet (left), and the powerhouse building (right).


58

Figure. The old mechanical regulator (left), which had been used for power plant

regulation before the modern electronic regulator (right) was introduced.

Assignment

The contents of the exercise will be set in agreement with the SENG personnel, and will

only be known on the day of excursion.


59

Laboratory exercise 5. Measurement of the water

turbine characteristic

Introduction

The subject of measurement is the model axial turbine TC3. The model turbine TC3 is

one of the study (prototype) turbines manufactured for power plants on the lower Sava

and Mura river. The exercises will be performed at the Faculty of civil and geodetic

engineering, Department of fluid dynamics.


- measurement of turbine machine characteristics

- recalculation of turbine machine operating characteristics by the similarity theory

- using measuring transducers for measurement of pressure,

- using measuring transducers for measurement of torque,

- using electromagnetic flow meters

- measurement of electric power,

- measurement of rotational frequency.

Measurement station

The measurement station is of the open type with a pool in the basement. Three pumps

pump water in the first upper settling pool with a fixed vertical position. From there,

watrer flows into the second settling pool. The settling pools are of spilling type, meaning

that the excess water flows into the pool in the basement. Settling pools serve for accurate

head setting, as the water level height is accurately defined due to the spillway. The

second settling pool allows manual height adjustment, which simulatel the lake level

height above the surge tank level.

From the second settling pool the pipeline is connected to the turbine via a valve. The

valve is manually adjustable and allows water supply onto the turbine directly from the

pump or over both settling pools. From the turbine, water flows into the spilling tank, and

from there over a valve into the basement pool. The water level in the spilling tank is set

with a valve on the outlet pipeline. The valve is manually adjustable and is used to

maintain the lower water level, otherwise the outlet/outflow tube could be drained in case

of low flow rates.

The turbine is of axial type with a fixed rotor blade angle angle and dimensionless stator

(guide vane) opening. The rotor blade angle is ficed at 29°. Dimensionless stator opening

is A0=1,92. At larger flow rates, the resulting operating point lies right of the optimal

point. The optimal operating point for the TC3 turbine is at 20° rotor blade opening

angle and dimensionless stator opening A0=1,84. The dimensionless stator opening is

defined by the following equation:


60

V

VV

D

ZAA

0

,

where AV is the stator opening (lowest perpendicular distance between two neighboring

guide vanes), ZV the number of guide vanes and DV stator diameter.

Pressure outlets are located before and after the turbine. The upper and lower water levels

together with the flow regulation valve define the available head.

Figure. Hill diagram of the TC3 turbine.

The turbine is braked by a three-phase asynchronous electric motor (400V 0,75 kW,

1500/min) mounted on a flange. The regulation is carried out by a variable frequancy

drive Fuji Frenic Mega FRN 0.75 G1E-4E with 1500 W power. The VFD has an external

coil, chopper and braking resistance. The casing has bearings and is held in place by a

force meaurement cell FUTEK FSH00251 (10 lb force on a certain radius, which allows

for tubine torque measurement). Read the sensitivty from the sticker on the sensor. The

amplifier settings are: 10V bridge power supply, sensitivity range 1 mV/V to 10 mV/V.

The electromagnetic flow meter ABB Watermaster FEV 111 DN 150 with the current

output 4-20 mA is installed at the turbine inlet.

The thermometer is installed in the inlet tube. The thermometer is of resistance type Pt-

100 with four wire connection. The amplifier is Weidmuller Pro RTD, with voltage

output 0-10V.


61

In the electric box, there is a VFD with its equipment, power supply units, transducers,

measurement card and process computer. All electric metering devices are powered from

the electric box. On the bottom of the electric box there are jumpers where you can verify

individual device output values by a multimeter. On the inner side of the electric box

door there is an electric scheme, where you can find which jumper corresponds to which

measurement device.

For rotational frequency measrement, you can use the inductive sensor and transducer

Weidmuller WAS Pro Frequency. The inductive sensor is mounted at the electric motor.

All valves are controlled manually.

Figure. Scheme of the model bulbturbine at the Faculty of civil and geodetic engineering,

Department of fluid mechanics. The gray horizontal line represents the floor. The pool

and the water level regulation valve are located in the basement.


62

Figure. Turbine inlet – view through the inlet pipe, visible are the inlet guide vanes in

and the bearing casing.

Figure. A turbine with removed draft tube. Visible are the rotor and the stator..


63

Figure. Model turbine, Faculty of civil and geodetic engineering, Laboratory for

hydrotechnics.

Measuring equipment

The following measuring equipment is available at the measurement station:

- differential pressure transducer ABB 264DS with a range 0-6 bar (with a possibility of

setting to min. 0.06bar) for measurement of the turbine pressure drop,

- absolute pressure transducer ABB 264NS with a range 0-6 bar (with a possibility of

setting to min. 0.06bar), current output 4-20 mA, for measurement of the static absolute

pressure on the turbine,

- electromagnetic flow meter ABB Watermaster FEV 111 DN 150 with a current output

of 4-20 mA,

- inductive turbine rotational frequency meter with a transducer Weidmuller WAS Pro

Frequency,

- resistive thermometer Pt-100, type A, four wire connection, transducer Weidmuller

WAS RTD Pro, sensor sensor is mounted on the inlet pipeline,

- force measurement cell FUTEK FSH00251 10 lb with a bridge amplifier Weidmuller

WAS5 Pro Bridge with a current output of 4-20 mA or a voltage output of 0-10V for

torque measurement,


64

- measurement card, 16 channels, 16 bit resolution, National instruments NI USB 6212,

- process computer with 19" touch screen for data acquisition and measurement

monitoring.

Measurement procedure

If the turbine operates with selected (VFD controlled) rotational frequency, it can only

work with a certain flow rate for the given head (height difference between the upper and

lower water level). If you want to measure the characteristics or operating point of the

turbine, there are two possible approaches:

- vary the height difference between the upper and lower water level while maintaining a

constant rotational frequency, measure the flow rate through the turbine which changes as

a result,

- select a fixed height difference between the upper and lower water level, then vary the

rotational frequency of the turbine and measure the flow rate which changes as a result.

In this case, recalculate the obtained characteristics to a constant rotational frequency, as

in a power plant.

Choose the suitable water feeding pump(s). There are three feed pumps with flow rates

10 l/s, 20 l/s and 50 l/s, respectively. If you choose a too high feed pump flow rate, the

excessive water from the first settling pool returns to the basement pool over the spillway.

Assignment

1. Determine the operating point of the turbine in terms of the flow number and pressure

number.

2. De-air the system, determine thee turbine height and the height of pressure transducers.

3. Calculate flow rates and pressures which correspond to the hydraulic point defined by

the stator (guide vanes) and rotor blades opening angles.

4. Set the VFD so that it will maintain a constant rotational frequency of the turbine.

5. Measure friction in the bearings,

6. Measure the current operating point. Present the operating point as the head depending

on the flow rate. Take all dynamic pressures and losses in consideration (measure the

experimental station so that you can estimate the losses). Also take bearing friction in

consideration. In characteristics measurement, take note of the approximate flow rates at

which the turbine operates. To avoid damage to the turbine rotor, do not perform

measurements at very high flow rates.

7. Recalculate the operating point to the full-scale turbine.

8. In the exercise report, list all the measurement station settings and metering devices,

draw the experimental set-up scheme, describe the data analysis procedure (including the

equations), and present the results graphically.


65

Practical exercise 6. Measuring the outlet velocity

triangles of an axial turbine machine with a five hole

probe

Introduction

The purpose of this exercise is to measure the outlet velocity triangles of an axial turbine

machine. The measurements will be performed on a fan manufactured by Hidria

Rotomatika.


- flow velocity measurement by a five hole probe,


- measuring the rotational frequency,


Measuring station

The measurement station does not comply with the standards for fan characteristic

measurements, but is used due to the lack of space. The main difference with

standardized measurement stations is that the air in the chamber before the fan is not still.

The choice of the measurement station can be justified by a fact that the fans of this type

are normally installed in air conditioning units without a settling chamber before the fan.


66

Figure. Schematic view of the measurement station.

Five hole probe

The five hole probe allows the measurement of the flow velocity vector (all 3 Cartesian

velocity components). It is based on measuring the pressure difference on five holes in

the measurement volume.

Figure. Five hole probe – sensor part with holes for flow velocity component

measurement.


67

Figure. The five hole probe (positioned radially to the fan) is rotated around its lateral

axis by the angle , until the air flow to the probe becomes perpendicular. The angle is

read from the calibration curve.

During the measurements, the probe is rotated around its lateral axis, until it is

perpendicular to the local velocity vector. At this moment, p2 = p3 and the angle (yaw)

is read from the positioning table. The angle (pitch) is read from the calibration curve of

the five hole probe.

To determine all parameters, four pressure transducers are needed, pA to pD.

Pressure measurements: pA = p1-patm

pB = p1-p2

pC = p2-p3 =>0

pD = p4-p5

p1, p2, p3 and p4 are the pressure outlets on the five hole probe. pA, pB, pC and pD are the

readings of our pressure transducers.


68

Figure. Five hole probe, hole distribution.

Measurement procedure

The measurement procedure is as follows:

1. Determine , when p2 = p3, from the setting on the positioning table

2. Measure 21

54

pppp

3. Calculate by the calibration curve for

3,6579 +54,829x + 12,659x + 7,3545x- 28,787x - 9,0751x - 1,089x1)( 23456

21

54

xf

pp

ppf

4. Calculate the pressure ratio by the following calibration curve

1,013582 + 10.00344353 - 103,95666

+ 102,36451- 103,145655 - 102,147436 10314815,1

204-

306-407-509-610-

21

pp

pp st

5. Calculate the absolute velocity and velocity components (axial, tangential and radial)

sincossincoscos)(2

CCCCCCpp

C zyx

st


69

-40

-30

-20

-10

0

10

20

30

40

50

-1 -0,8 -0,6 -0,4 -0,2 0 0,2 0,4 0,6 0,8 1

(p4-p5)/(p1-p23) (-)

del

ta (

°)

Figure. Calibration curve for the angle δ.

0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

-50 -40 -30 -20 -10 0 10 20 30 40 50

delta (°)

(pt-

ps)

/(p1

-p2

3)

Pressure ratio (pt-ps)/(p1-p23) dependence on the angle δ, p2 = p3 = p23.


70

Measurement transducers and positioning table

The following differential pressure transducers will be used: Endress Hauser PD 235 with

0-1000 Pa range, 0.1% measurement uncertainty at 1000 Pa, current output 4-20 mA,

two-wire connection to the A/D converter.

Measurement transducers, computer and positioning system are electrically separated

from the measurement station by a separation transformer. The measurement station and

the positioning systems are grounded through the connecting cable of the electric motor.

The precision of the position setting is limited by the initial setting of the positioning

table, which should be aligned with the fan axis. When moving the positioning table

between different measurement points, the precision is better than 0.1 mm. The

positioning table is controlled by a serial RS 232 connection. In the control software, the

axis, length and velocity of the movement can be selected.

Data acquisition with LabVIEW software

1. Set the operating point. Select the desired flow rate, input the pressure.

2. Measure the rotational frequency of the blades (use the manual optical meter).

3. Move the five hole probe in the correct position, input in the correct window.

4. Measure pA, pB, pC and pD.

5. Determine From the positioning table setting, when p2 = p3, input value.

6. Toggle the key for data acquisition/writing to disk, wait for the averaging time to pass.

Figure. Measurement program in the LabVIEW software.


71

Assignment Measure velocity vectors at low fan speed and at maximum flow rate in five points on the

radius. Measure on the fan outlet and compare calculated velocity angles to the blade

angles on the same radius. Measure the blade angles manually.


72

Practical exercise 7. A model of the Planica wind tunnel

Introduction

The purpose of this exercise is to determine the operating point of the model Planica wind

tunnel.


- flow velocity measurement by a Pitot tube,



Planica wind tunnel

In construction of the Planica wind tunnel, the task of the work group at the Faculty of

mechanical engineering (FS UL) was to produce a wind tunnel model based on the

geometric shape produced by CFD computations (also performed at FS UL). The wind

tunnel model was intended to be a faithful representation of flow conditions in the actual

(full scale) wind tunnel in Planica. The model allows to:

- determine the total resistance characteristic of the system,

- determine the resistance of individual elements of the system,

- find the locations of flow separation,

- propose corrective measures for reduction of flow separation and total resistance

characteristics of the system,

- make a comparison to the CFD analysis.

The baseline conditions of the study were:

- known geometry of the aerodynamic system, skydiving section diameter of 3.6 m,

- available electric power for the fan section (1.8 MW),

- mean velocity in the vertical (skydiving) wind tunnel (180 km/h to 265 km/h) and

- mean velocity in the horizontal (ski jumping) wind tunnel (110 km/h to 150 km/h).

Homogeneous velocity profile was desired in both vertical and horizontal system section.


73

Figure. Left: Nordic center in Planica. The structure in the middle is the wind tunnel.

Right: aerodynamic model of the wind tunnel.

Model recalculation

The model recalculation is performed so that Reynolds number similarity is achieved.

Recalculation from the actual object (original, full scale) to the model is based on the

similarity theory. Two models are hydraulically similar, if dimensional, kinematic and

dynamic similarity is assured. In practice this is not possible, this is why we mostly want

to assure the same or at least similar Reynolds numbers.

An assumption can be made: let the size ratio model : original be 1:36. This satisfies the

following model conditions:

- sufficiently large test section for performing the measurements,

- manageable dimensions of the station,

- possibility of working medium temperature adjustment,

- low power of propulsion propellers,

Water will be used as the model's working medium.

In model calculations, the following parameters should allow changes and modifications:

- velocity,

- dimension – channel cross-section,

- dimension – human size (diameter),

- human cross-section,

- dynamic viscosity,

- drag force on a human 1 Planica / FS,

- drag force on a human 2 calculated from Cd,

- gravity force – buoyancy force,

- temperature,

- Reynolds number recalculated to the human diameter,

- Reynolds number recalculated to the channel diameter,

- power of fan/pump,

- flow rate,

- dynamic pressure at the testing section location,

- static pressure (numerical calculation at 180 km/h in the skydiving section),

- static pressure at selected velocity,

- total pressure of the fan,

- aerodynamic power of the fan,

- electric power of the fan (eta = 0.60).

Calculations are based on the assumption that the model ant the original must have the

same Reynolds numbers. On the model, this is most easily achieved by using hot water,

as the kinematic viscosity of water is much lower than the kinematic viscosity of air. At


74

the same time, we wanted the flow velocity in the test section (skydiving or ski jumping)

to be around 1 m/s, otherwise the flow visualization would not be possible.

To preserve the same Reynolds number (Re), very high fluid velocity and consequently

very high power on propeller shaft is needed. For this reason, we decided to sacrifice

complete similarity of Reynolds numbers by reducing Re by 50 times with respect to the

original wind tunnel. Consequently, velocity in the skydiving section was reduced to 1

m/s. The diameter of the cylindrically shaped ski jumping section was selected to be 10

cm. The 10 cm diameter allowed performing measurements and flow visualization, but

was also a good compromise regarding the propulsion (maximum required propulsion

power) and convenience.

Figure. Model recalculation in Excel.

Design of the model wind tunnel

The wind tunnel model is made of aluminum. Each part was 3D modeled in a shape,

suitable for milling. Each individual element is assembled from two parts, which was a

requirement of the milling procedure. The following parts are made of aluminum:

- fan section,

- bend 1 90°,

- confusor,

- bend 180°,


75

- bend 2 90°,

- skydiving section (contains a plexi glass window),

- ski jumping section (contains a plexi glass window),

- electric motor mounts and propeller mounts,

- return channel,

- propeller stator (manufactured by 3D printing).

The sealing between individual parts and part halves was carried out by a rubber seal

installed to the groove. The skydiving section was made from a single part using a CNC

turning machine, because the bore is circular. The ski jumping section has two side

windows sized 75x100 mm. For positioning of individual parts with respect to each other,

pins are used. Screwing was done with screws into aluminum, or by using threaded rods.

Some parts are large and have concave surfaces, which proved difficult for manufacturing

as splitting into pieces and turning was required. The model is located in the LVTS lab,

placed in a specially designed collection tray. The collection tray facilitates the placement

of the whole wind tunnel model inside it, allowing safe filling and draining of water.

Figure. Wind tunnel model for manufacturing with a CNC machine.

Propulsion section

The propulsion section of the model wind tunnel was designed before knowing the exact

type of fans to be installed in the full scale facility (actually, two fans 3.6m in diameter

and with 1 MW power each were installed). In this process, we were aided by the catalog

data of the Slovenian manufacturer Klima Celje for large axial fans with a stator (guide

vanes). The selected fan N-AVV-K-180/80-8 was recalculated by diameter and rotational

frequency with respect to the operating point requirements.


76

Figure. Catalog data for fans, which were used in design of the model wind tunnel.

In the following step, the propulsion screw (rotor) was chosen. Considering the model

scaling ratio of 1:36, a screw with 62.5 mm was selected. We also purchased drive shafts

of appropriate length and DC electric motors of appropriate power. Because the rotational

frequency of the drive was low, larger electric motors had to be chosen capable of such

operating regime.

We selected the screw Graupner 2308.65L with 0.034 m pitch and 0.065 m diameter,

which was later reduced to 0.062 m by turning process. At 50 rotations per second and

with both screws in operation, the available velocity in the ski jumping section was 1.44

m/s, not considering the slip. By taking slip in consideration, the velocity in the ski

jumping section will be between 1 m/s and 1.2 m/s. The screw can also be rotated with a

higher or lower rotational frequency. All the necessary equipment for powering the

electric motors is available at our lab.

The fans installed in the full size object have an adjustable axial stator. The function of

the stator is to direct the flow and thus reduce the tangential velocity component at outlet.

To achieve the same conditions on the wind tunnel model, same flow conditions had to

be assured at the propulsion section outlet (i.e. without tangential velocity). For this


77

purpose, measurements of outlet flow angles were conducted by a five hole probe. Based

on the measurement results, a constant 15° outlet angle was selected for the stator (guide

vanes). Later, the wind tunnel model was modified to allow interchanging of propulsion

screw stators.

Figure. Propulsion section.

Assignment

In this practical exercise, there are the following assignment:

- calculate the size and power of full scale fans, and determine the necessary rotational

frequency for levitation of a skydiver in the skydiving section,

- measure the operating point of the model wind tunnel (perform flow measurements by

measuring flow velocity with a five hole probe at the skydiving section inlet; perform

differential pressure measurements across propulsion screws; perform rotational

frequency measurements by a manual frequency meter),

- recalculate the obtained operating point of the wind tunnel model to the operating point

of the full scale wind tunnel in Planica; compare calculated values to actual data

As a guide in performing the five hole probe velocity measurements, consider the

instructions provided in "Practical exercise – Measuring the outlet velocity triangles of an

axial turbine machine with a five hole probe".

For the five hole probe measurements, the required equipment has been already prepared:

4 differential pressure transducers, a computer with a measurement card, connection box

and measurement software. For insertion of the five hole probe, a probe support is

already prepared on the wind tunnel and can be screwed in. The same 4 pressure

transducers can be used to measure the pressure difference across both fans. Connecting

plastic tubes are included.


78

Appendix 1: Main types of water turbines and their

characteristics

This appendix will overview different types of turbines: Pelton, Francis, Kaplan,

tube/bulb and other kinds of turbines.

Turbine classification

a) With regard to the type of the turbine:

- Pelton,

- Francis,

- Kaplan,

- tube/bulb and other turbines.

b) Hydroelectric power plants are classified by their operation :

- run-of-the-river (slo. pretočne),

- dammed/accumulation (slo. zajezne/akumulacijske),

- pumped-storage (slo. črpalno-zajezne)

Figure. Run-of-the-river (left, HE Krško) and dammed (right: HE Moste) power plants.

Criteria for water turbine classification with respect to the specific speed (ns)

Different kinds of turbines are used for different flow rates and heads.


79

Figure. Selection of turbines for different flow rates and heads. The diagram is given in

dimensional units.

Specific speed ns is a dimensional and also dimensionless parameter used to evaluate the

speed of turbine machines.

With the aid of variables nq or ns (specific speed) the turbines can be roughly classified

into three different groups: Pelton, Francis and Kaplan turbines, with the order on

appearance based on proportional increase of the specific speed. Pelton turbines cover the

area of large heads and low volumetric flow rates, Francis turbines the area of medium

heads and flow rates, and Kaplan turbines the area of low heads and large flow rates.

The turbine's rotational frequency n, volumetric flow rate Q available head H (height

difference between the upper and lower water level) are project parameters, which allow

the selection of the turbine type. Since there are several different definitions of ns, let us

provide the definition after ISO 60193 (Hydraulic turbines model acceptance tests):

Here, ns is specific speed, E specific hydraulic energy of the machine, n rotational

frequency, Q volumetric flow rate and H head (the height difference of water levels). The

values of Q, H and n used for calculation should be the ones defining the point of

maximum turbine efficiency (i.e. the expected most common values of these parameters).

In accordance to the upper definition ns is a dimensionless parameter.

Despite the standard ISO 60193, which requires the operating point of maximum

efficiency to be used for calculation of ns, some manufacturers use the point of nominal

or maximum power instead.


80

Some definitions of the specific speed omit the gravitational acceleration since it is

practically constant anywhere on Earth. In this case, the definition is not dimensionless

and the calculated values vary depending on the units used. The problem occurs with

American and UK manufacturers, which use imperial units such as gallons and feet. Also

used is a similar form of definition, in Slovenia (Turboinštitut, Litostroj) the following

equation is used [equation 1], where the rotational frequency must be input in [1/min],

while the head and the flow rate are given in SI units (the operating point with the

maximum efficiency is taken):

equation 1

The specific speed ns of a turbine defines the turbine's shape in a way so that it is

independent of the turbine's size. is the flow number and the pressure number. The

unit at the left side of the equation is [1/min], while the right side is without a unit.

The specific speed parameter also allows that the turbine is resized with respect to the

base design with known properties. The specific speed is also the main criterion for

suitability of a particular installation location with the turbine type.

According to [equation 1] the classification of turbines is as follows (Turboinštitut,

Litostroj):

- below ns = 70, Pelton turbines are used,

- from ns = 70 to ns = 350, Francis turbines are used,

- from ns = 350 to ns = 600, Kaplan turbines are used,

- above ns =600, bulb turbines are used


81

Figure. Turbine selection for different flow rates and heads. The flow rate is given by the

dimensionless number ns, as given by equation in the upper-right corner.

Pelton turbine

Historically, Pelton turbines have evolved from water wheels. A Pelton turbine (also

known as the Pelton wheel) is an impulse (slo. enakotlačna/impulzna) turbine with

tangential water flow to the turbine blades. The term impulse turbine means that the

pressure in the turbine casing is equal to the ambient pressure. Installation is vertical or

horizontal.

A traditional turbine design is such that the rotor rotates with 1/2 the velocity of the water

jet. Water exits the rotor blades (also known as buckets) with a very low velocity, so the

energy conversion efficiency is high. In practice, the water jet velocity is always slightly

higher so that the water is removed from the rotor area.

Pelton turbines are suitable for installation when the flow rate is low and the head is

large, i.e. from 50 m to 2000 m. For the operation of Pelton turbines, it is not advised that

the water level changes significantly.

The water exits the nozzle, where conversion from pressure to kinetic energy occurs.

Normally, there are 1-6 nozzles per a Pelton wheel. The jet is directed tangentially onto

the blades. Upon impact of the jet, kinetic energy is transferred to the blade. For design it

is important that the jet is deflected back from the blade, but does hit the next blade. The

rotor is spinning, which is why the central part of blades is partly cut out, forming a

splitter (divider) structure which separates the buckets in two symmetrical compartments.

The larger the number of nozzles, the more blades are exposed to the water jet

simultaneously, resulting in larger power of the Pelton turbine.

Turbine operation is regulated by moving the spear in the nozzle. The spear, which is

usually bulb shaped, is moved by the rod to which it is attached. The system can also

include a deflector, which prevents pressure surges in case of the rapid closing of the

nozzle (e.g. due to emergency shutdown). The deflector deflects the water jet for so long

that the spear completely closes the nozzle. There is a quantity regulation, meaning that

the quantity (flow rate) of water is changed. Such regulation is efficient starting from

very low turbine loads upwards (i.e. from 1/4 of the nominal load). For this reason, Pelton

turbines are used when the flow rate of water changes significantly.

The blades can be manufactured as a single part together with the turbine disk (blisk =

blade + disk). This solution has been commonly used in recent years, as nowadays rotors

are mostly manufactured by CNC machines.

To close the water flow on the supplying pressure pipeline (penstock), a valve is used,

just like with other turbine types. Closing the water flow from the upper reservoir on the

penstock, allows for a relative quick shutdown of the turbine and also for turbine

maintenance.


82

Figure. Pelton turbine, a drawing (left) and an image of a nozzle with the spear (right).

Figure. Pelton turbine, drawing (Ralston, Voith).


83

Figure. Pelton turbine rotor. Left: Pelton turbine from Walchensee, Germany. Center:

blisk - Pelton wheel manufactured by PRÄWEST. Right: detailed blade (bucket) view.

Francis turbine

A Francis turbine is a back-pressure/reactive (slo. nadtlačna) turbine of a radial - axial

design. It is used for medium flow rates and heads. Francis turbines have single

regulation, meaning that only guide (stay) vanes have an adjustable position for the

purpose of regulation, while the rotor blades are fixed. Francis turbines are reactive

turbines, meaning that the pressure of water is reduced as it passes the rotor blades.

Consequently, energy is transferred to the rotor and thus generator. Energy is transferred

to the rotor/generator by reducing the pressure and transferring the kinetic energy of

water.

In some rare cases, Francis turbines have the rotational frequency control. This means

that the rotational frequency can be varied, usually by a few % of the nominal rotational

frequency. In Slovenia, the only power plant with such regulation is HE Avče (from -2%

to +4%).

Francis turbines are used for heads from 20 to 500 m. Typical diameters are from 1 m to

10 m. Almost all Francis turbines are installed so that the axis of rotation is vertical.

Francis turbines have a high efficiency, often exceeding 93%, and cover a wide range of

flow ranges and heads. For these reasons, Francis turbines are the most commonly used

turbine type among the water turbines.

The main components of a Francis turbine are: (1) spiral casing, (2) fixed inlet guide

vanes (optional), (3) guide vanes (stator), (4) rotor, (5) draft tube, (6) shaft, (7) bearings,

(8) generator, etc. Most of these components are also used in Kaplan turbines. In the

following part of this chapter, individual parts of a Francis turbine will be used. Later (in

chapter 3) other parts necessary for safe and reliable operation of hydroelectric power

plants will also be described.

The spiral casing is installed around the turbine and connected to it through by a long

aperture. At inlet, the spiral casing is connected to the penstock or closing valve. Through

the aperture, water flows onto the guide vanes and then in the turbine. The spiral casing is

designed so that the fluid velocity is constant at all segments of the aperture. For this

reason, the diameter of the spiral casing is gradually reduced away from the inlet. In most

cases, the spiral casing of Francis turbines is poured in concrete.

The stator part consists of inlet guide vanes and guide vanes. The guide vanes have a

double function of converting the water pressure to kinetic energy and directing the flow

onto the turbine blades. The inlet guide vanes are usually distributed in two rows as fixed

inlet guide vanes and adjustable guide vanes in the second row. The angle of guide vane

rotation around the vane's base can be adjusted in order to reduce the water flow into the

turbine rotor. The guide vanes are connected to a guide ring, which allows all the vanes

to be rotated at the same time and by the same angle. The guide vanes are rotated by

hydraulic or servo motor propulsion. The guide vanes also allow to fully stop the water

flow onto the turbine rotor (during normal or forced shutdown, maintenance etc.).


84

The rotor (note that the terms stator and rotor are also used for the fixed and moving part

of a generator) rotates and converts the energy of water to the mechanical energy of the

shaft rotation. The rotor is mechanically linked to the shaft, which is attached to the

generator at the other end. The rotor has fixed blades, meaning that the turbine has single

regulation (regulation is only possible by rotation of guide blades).

The suction tube is the element installed below the rotor with a function of slowing the

water flow and leading the water towards the outlet facility (in pumped storage power

plants, the inlet-outlet facility). The flow must be slowed down, in order to lose its

available kinetic energy and convert it to pressure. According to Bernoulli's equation, the

energy of the flow is divided to pressure, velocity and head.

The other parts of hydroelectric power plants will be presented in chapter 3. At this point,

let us mention only the shaft, generator and bearings. The shaft is an element linking the

rotor to the generator. The bearings hold the rotor and the shaft in a horizontal and

vertical direction. Normally, a turbine has at least one carrier bearing (carries in the

vertical direction) and at least one guide bearing.

Apart from electricity production a Francis turbine can also be used for pumped storage

power plants. In the pumping mode of operation the turbine acts as a pump, pumping the

water from the lower accumulation to the upper accumulation. In the pumping mode,

when a sufficient amount of cheap electric energy is available, the generator operates as

an electric motor. This is mostly in the night time, when nuclear power plants produce

most of the electricity and the demand is low. By accumulating water, the lower and

upper accumulation serve as large sources of storing the unneeded electric energy. This is

one of several methods to temporarily store the surplus of electric power for later use.

Figure. Left: Francis turbine. Rotating parts (rotor and shaft) are shown in red color. The

stator (guide vanes and their regulating mechanism) is shown in green. Yellow color

represents the bearings and the light blue color the locations filled with water. Right:

pictured is a horizontal Francis turbine. Visible is the spiral casing and the outer part of

the stator. The mechanism for rotation of guide vanes is colored yellow.


85

Figure. Left: Francis turbine rotor, Three gorges power plant, China. Right: the rotor of

the pumped storage power plant Avče, measurements of cavitation erosion by a

measurement arm.

Figure. Left: turbine rotor transport, Guri, Venezuela, 10 × 730 MW + 4 × 180 MW + 3 ×

400 MW+ 3 × 225 MW + 1 × 340 MW. Right: hydroelectric power plant in Bratsk,

Russia, 18x250 MW.

Figure. Lowering the rotor in the machine shaft of the pumped storage power plant Avče.

Kaplan turbines

A Kaplan turbine is a reaction water turbine with adjustable rotor blades. It is a turbine

with double regulation, as the position of both guide vanes (stator blades) and rotor


86

blades can be adjusted. Historically speaking the Kaplan turbine is the evolution of the

Francis turbine for watercourses with low heads and high flow rates. Kaplan turbines are

normally used for heads between 10 m and 50 m and for power of up to 200 MW. The

nominal efficiency exceeds 90%, but can be lower in the case of very low heads and

small flow rates.

The inflow of water is carried out in the same way as with Francis turbines, i.e. through

the pressure pipeline (penstock) across the valve into the spiral casing, through the inlet

guide vanes and adjustable guide vanes. After the stator, the water turns downwards,

before reaching the rotor. This means both the inflow and outflow to/from the rotor are

axial, while the turbine as a whole has radial inflow and axial outflow. The rotor blades

have an adjustable blades. Blade angle adjustment is performed hydraulically, with

hydraulic oil flowing through the center of the shaft. The inflow of oil into the shaft is on

the upper side above the generator casing. The sealing of the oil system in the shaft must

be well made to prevent oil leakages into the river. Similarly to Francis turbines, the

water exits the rotor into the suction tube to the outlet.

The double regulation allows the operation of Kaplan turbines in a wide range of

operating points.

A special version of the Kaplan turbine is the propeller turbine, which has a similar

design, but with fixed rotor blades. Propeller turbines have single regulation with guide

vanes, like Francis turbines. Due to the simpler design and a higher rotational frequency,

propeller turbines are used to replace older Francis turbines installed in power plants with

lower heads (up to 10 m). A larger rotational frequency allows for a smaller and lighter

generator.

Figure. Left: a schematic view of a Kaplan turbine. Rotating parts (rotor, shaft and

generator) are shown in red color. The stator (guide vanes and their regulating

mechanism) and the hydraulic system for rotor blade adjustment are shown in green.

Yellow color represents the bearings, which are listed down from the top: upper generator

guide bearing, lower generator guide bearing, upper turbine guide/carrying bearing and

lower turbine carrying bearing. The parts of the turbine filled with water are shown in


87

light blue color. Right: Kaplan turbine rotor in Plave, Slovenia, well visible are the blade

pivots.

Tube turbines

The term tube turbines denote a group of several turbine subtypes: bulb turbine, turbine in

a shaft, S turbine and Saxo turbine. Tube turbines are a proper solution when the head is

lower than 30 m and have (in the recent years) almost completely replaced the low-head

Kaplan turbines. Due to very low heads, flooding of large areas by damming is no longer

necessary. Tube turbines can operate reversibly (e.g. in tidal power plants).

Some sources and authors treat tube turbines as a variation of Kaplan turbines, while the

others consider them as an independent water turbine type.

Among the various kinds of tube turbines, bulb turbines will be presented more

thoroughly while the other kinds will only be mentioned.

Tube turbines with a blub (bulb turbines)

A tube turbine with a bulb is an axial turbine with a horizontal shaft and axial water inlet

onto the rotor. It is equipped with a flat conical draft tube. Bulb turbines allow for a large

flow rate and consequently large power even for low heads. A direct drive generator is

installed in the watertight bulb, which is attached to the turbine's inlet guide vanes. The

bulbous shape of the generator casing gives the name to this particular turbine type.

The difference between a Kaplan and a bulb turbine is in the inflow of water onto the

turbine. Kaplan turbines have a radial inflow of water, while the inflow in bulb turbines is

axial. Both types of turbines have an axial outflow. Due to such installation the water

flow direction does not change significantly, allowing for a good efficiency and compact

size. The compact installation size considerably lowers the costs of construction works

and allows for a flexible installation.

The rotor of a bulb turbines has blades with adjustable angle, meaning that the turbine

regulation is double (regulation of guide vanes and turbine blades).

Bulb turbines lack the spiral casing and have a draft tube significantly different in shape

from draft tubes of Kaplan and Francis turbines.


88

Figure. A tube turbine with a bulb. Shown in red color are the rotating parts (rotor and

shaft).

Figure. A rotor of a bulb turbine.

Turbine in a shaft

The design is similar to bulb turbines, with a notable difference that the generator is

installed in the shaft of the flow tract. In the case of smaller power plants it is impossible

to have the generator enclosed in a watertight bulb within the flow. The generator is

usually linked to the turbine shaft through a geared transmission, which is installed in the

turbine shaft and enables generator rotation with a sufficiently high frequency despite the

slow turbine rotation. This way, the costs of manufacturing the generator are reduced,

making possible that even power plants with very low heads can operate profitably. A

design with direct transmission of torque between the turbine and the generator is also

possible.


89

Figure. Bulb turbine in a shaft.

S turbine

S Turbine is a variation of the bulb turbine. This type of turbine has a horizontal axis and

axial inflow of water onto the rotor. It is equipped with an S-shaped draft tube with one

or two bends. The shaft runs through the bend of the draft tube. This turbine type is

suitable for smaller hydroelectric plants with up to 10 MW power, which do not allow for

installation of the generator in a watertight bulb within the flow.

Figure. S-type tube turbine. The generator is installed outside of the turbine's flow tract.

Axial turbine with a vertical shaft – Saxo turbine

A Saxo Turbine is a variation of the bulb turbine, which in recent years has been a design

successfully used by Litostroj in Canada. This is a vertical axial turbine, which in its

upper part (between the inlet and the rotor) is similar to a tube turbine with an inlet bend

and a semi-axial stator. In the lower part (between the rotor and the end of the draft tube),

it is similar to conventional Kaplan turbines. The water flows onto the rotor in the axial

direction. The generator is installed above the turbine, with the shaft running through the

inlet bend. The suction tube can either be straight or with a bend. Saxo turbines can cover

the complete operating range of bulb and Kaplan turbines.


90

Figure. A scheme of a Saxo turbine. Source: Litostroj.


91

Appendix 2: The properties of hydroelectric power

plants

This section will present some properties of hydroelectric power plants, namely the

operating characteristics, hill diagram, operation of pumps/turbines, startup and shutdown

procedures etc. For a better understanding let us consider two variables which are a part

of the characteristics, namely the specific hydraulic energy and flow rate. Indices 1 and 2

mark the pressure and suction part of the machine, respectively, where specific hydraulic

energy is determined.

Figure. Schematic representation of a hydraulic machine. The flow flows in the direction

of the arrow for the pump or the turbine.

The specific hydraulic energy is a variable which gives the amount of specific energy that

water can transfer to the turbine:

21

2

2

2

121

2zzg

vvppE absabs

.

In above equation, 1absp and 2absp are the absolute pressures at measurement planes 1

and 2 and consist of two parts: (1) overpressure in the pipeline and (2) atmospheric

pressure. 1v and

2v are corresponding velocities. g is the average gravitational

acceleration. 21 zz is the height difference between both measurement planes. is the

average density of water.

Let us try to write the above equation in a simplified form.


92

For the sake of simplicity or historical reasons, often heights/heads are used instead of the

specific hydraulic energy. Under the assumption that the water flow velocity difference

1v -2v is insignificant, that the system has two free surfaces (1 and 2), and that

atmospheric pressures 1absp in 2absp on the free surface of water are approximately the

same, the equation can be rewritten as the dependence of the specific energy on the

geodetic height difference Hst (the difference between the upper and lower water level):

stgHzzgE 21 ,

The geodetic height difference between the upper and lower water level in hydroelectric

power plants is called static height difference Hst. The total pressure difference of a hydro

power plant Hb is the gross head, which follows from Hst and the kinetic energy

difference. Therefore, Hb is the static height difference, reduced by the fraction of energy,

represented by velocity increase from 1 to 2:

The net head Hn of a hydro power plant is obtained, if the gross head Hb is subtracted the

hydrodynamic losses in the inlet part until the turbine and the outlet part until the

lower accumulation:

The flow rate is the quantity of water, passing through planes 1 in 2. The flow rate

through both planes is assumed to be the same.

In the case of some power plants such as HE Plave and HE Doblar, the upper

accumulation is far from the powerhouse of the plant. Water flows through a long supply

tunnel (penstock). In this case, the sum of losses is relatively large and the water level in

the penstock is not the same on the inlet and outlet (it is different by the sum of head

losses from the upper equation).


93

Figure. Hydroelectric power plant Plave. Due to losses in the penstock, not all gross head

is available to the turbine.

Often, instead of the specific hydraulic energy, head or flow rate, dimensionless variables

are used: END (energy number, ND = non-dimensional), (flow number), Ψ (pressure

number), etc. Similarly, the dimensionless power (PND) can be defined, but many other

dimensionless numbers exist as well.

Characteristics and hill diagram of turbines

Properties of turbines are presented by characteristic diagrams and hill diagrams.

Depending on the type of regulation, three different types of turbines exist:

- turbines with single regulation

- turbines with double regulation

- turbines without regulation

Characteristics of turbines

A characteristic diagram or shortly turbine characteristics for single regulation turbines is

shown in the picture below. In the case of a single regulation turbine, measurements must

be taken in a sufficient number of operating points (for every selected dimensionless

specific energy EnD) so that the curves of constant efficiency, stator opening and power

can be drawn. Measurements on the measurement station are conducted by establishing

the selected dimensionless specific energy EnD on the boundaries of the turbine with the

air of an auxiliary pump. Then, the guide vanes/stator are opened and closed and for each

stator opening , we measure the flow rate (presented as the flow number on the

diagram), power and efficiency. Measurements are usually performed for a single

rotational frequency. Normally, the range of flow rates in which the turbine can operate is

prescribed.

A diagram in the image below can be used to obtain a chart with a three-dimensional

surface, also known as the hill diagram.


94

Figure. Characteristics of a single regulation turbine (e.g. Francis turbine). Measurements

are taken in a sufficient number of operating points (for every selected dimensionless

specific energy EnD) so that the curves of constant efficiency, stator opening and power

can be drawn. The index sp stands for "specified", as in the warranty tests the operating

points are selected for measurements and control of turbine operation. Source: ISO

60193.

Turbines with double regulation allow variation of the rotor blade angle (also known as

the rotor opening angle) in addition to the stator opening α. The characteristics of a

double regulation turbine is presented in the image below. In the process of determining

the characteristics, turbine power and efficiency are measured at different rotor blade

angles. This is due to the fact that on model turbines, it is easier to change the stator

opening than the rotor blade angle (in the latter case, the turbine must be disassembled).

Measurements on the measurement station are conducted by establishing the selected

dimensionless specific energy EnD on the boundaries of the turbine with the air of an

auxiliary pump. Then, the guide vanes/stator are opened and closed and for each stator

opening , we measure the flow rate (presented as the flow number on the diagram),

power and efficiency. Efficiency curves turn out to be fairly steep at a constant angle of

the rotor blade rotation . Over the peaks of these partial curves a common curve of

constant efficiency is drawn as an envelope (presented by a dashed line in the image

below). Measurements are usually performed for a single rotational frequency.


95

Figure. Characteristics of a double regulation turbine (e.g. Kaplan turbine). In every

measurement point (specific hydraulic energy/flow rate/stator opening), the rotor blade

angle is varied. Warranty and test ranges are determined based on the acceptance test

requirements. Source: ISO 60193.

In the case of an unregulated turbine (image below) power, flow rate and efficiency are

given at a selected rotational frequency. Measurements are conducted by variation of the

specific hydraulic energy and measurement of other variables.

Figure. Characteristics of an unregulated turbine. In this case, axes are inverted. The x

axis gives the dimensionless specific hydraulic energy End, while the y axis shows the

corresponding efficiency, flow rate and power. Source: ISO 60193.

Hill diagram


96

Characteristic – capability of a turbine as a hydraulic motor for driving the generator are

obtained by model measurements on test rigs, as presented above in the previous

subsection. Measured are basic characteristics: Q, M, and P. From characteristic

diagrams (such as the one presented in the above subsection), complex turbine

characteristics named the hill diagram can be obtained.

A hill diagram for turbines with single and double regulation are obtained by "slicing"

partial curves of efficiency and power. An example of a single regulation turbine

characteristics is shown in the image below (Francis turbine). The curves are shown for

different specific hydraulic energies End.

In the hill diagram for a double regulation turbine (Kaplan turbine, image below), the

curves of constant stator opening , constant rotor opening angle , constant efficiency

(shell/hill-shaped, hence the name hill diagram) and constant power can be seen.

The following turbine operational limits are evident from the hill diagram:

- maximum allowed flow rate,

- maximum power, which is mostly limited by the generator power,

- runaway curve at efficiency = 0.

The maximum power is specified due to the properties of the generator, which is only

capable of generating power up to the maximum allowed power. Exceeding the

maximum power limit would lead to a generator failure.

The runaway speed is the turbine speed at full flow rate and zero load. In the case of a

runaway event the turbine operation shifts very rapidly along the curve of the constant

stator opening (as set in the moment of losing the generator load) down until the runaway

curve. This means that both dimensional and dimensionless pressure across the turbine

are significantly reduced. In the case of Francis turbines, this means a transition to lower

flow rates, while in the case of Kaplan turbines, the flow rates may even increase,

depending on the direction of constant stator opening curves.

Shell diagrams can be either dimensional or dimensionless (flow number on x axis and

pressure number on y axis). In the case of dimensionless presentation, some parts of the

diagram are either relatively compressed or expanded with respect to the others, which is

why some customers require turbine manufacturers to provide both types of the hill

diagram.


97

Figure. A hill diagram for a turbine manufactured by Turboinštitut. Blue curves mark the

rotor blade/opening angles, red curves the stator opening, and thick black lines the curves

of constant efficiency. The diagram is shown in relative terms with 100% maximum

efficiency, as the manufacturers do not want to reveal the actual efficiencies of the

turbines they manufacture. Source: Turboinštitut.


98

Figure. A hill diagram for a single regulation turbine (Francis turbine). Shown are the

curves of constant efficiency and curves of constant stator opening . The guaranteed

range of operation is marked by gray color. Source: ISO 60193.

Qnd = , flow number (nd = non dimensional)

End = energy number,

= stator opening,

Qndmax = maximum allowed flow number,

EPmax = maximum allowed energy number for the prototype,

EPsp = agreed (specified) energy number for the prototype,

EPmin = minimum energy number for the prototype,

hM = hydraulic efficiency for the model.

Figure. A hill diagram for a double regulation turbine (Kaplan turbine). Source: ISO

60193. An additional feature in comparison with hill diagrams for single regulation

turbines is the rotor blade angle .

Pump/turbine operation in four quadrants (expanded range of operation)

Turbines and pumps can operate in four quadrants depending on the specific nominal

speed nED and the nominal flow rate QED. The four quadrants are defined with respect to

the value (positive or negative) of flow rate and rotational frequency. In the image below,

(a) marks the operation at the highest specified power and (c) the operation at the lowest

allowed power. The individual parts (quadrants) are:

bottom left – pump,

bottom right – reverse pump,

top left – turbine brake,

top right – turbine.


99

Some of the quadrants are further divided, for example the top left quadrant is divided to

the turbine part and turbine dissipative (brake) part, with the runaway curve (zero shaft

torque, generator is out of operation / disconnected from the power grid) separating them.

Above the runaway curve there is a pure turbine area, where turbines operate most of the

time (positive flow rate, rotational frequency and torque). Below the runaway curve is an

area of turbine dissipation (brake) with positive flow rate and rotational frequency, but

negative torque. Such operating conditions are rare though possible with some turbines,

but only occur in transitional flow regimes.

During the operation in the turbine regime, the turbine operates on one of the constant

stator opening () curves between the vertical lines, which mark the minimal and

maximal allowed power. In the case of emergency shutdown, the operating point slides

along the constant efficiency curve to the runaway curve (e.g., until the extreme upper-

right point in the graph). Then, as the guide vanes are closing, the operating point moves

along the runaway curve to the center of the coordinate system (zero flow rate and

rotational frequency).

Figure. Turbine operation in four quadrants. (a) marks the operation at maximum allowed

power and (c) at minimum allowed power. Source: ISO 60193.

Startup and shutdown of the power plant (normal and quick shutdown)

There are two types of the hydroelectric power plant shutdown, normal and quick

(emergency) shutdown. The startup procedure is always normal.

Power plant startup procedure

The startup procedure varies for different power plants. This subsection will present a

case of a Francis turbine for large heads and with an inverter. During the startup, the

following operation must be carried out:

- turning off creep detection,

- startup of auxiliary equipment (bearing cooling system etc.),

- turning on hydraulic machine pumps (initial bearing lubrication, usually disconnected

after approximately 10 minutes of operation),

- bypass valve opening to equalize the pressure before and after the ball valve,


100

- opening the ball valve,

- turning on the excitation breaker (breaker of the excitation transformer) and excitation

transformer,

- opening the stator (guide vanes), the water starts to flow through the turbine and the

turbine starts to rotate,

- closing the bypass valve,

- turning on the inverter (for example, pumped storage power plant Avče, which has such

inverter) or regulator (power plants without an inverter), in this moment internal turbine

regulation begins with the turbine still off-grid,

- turning on the synchronizer,

- turning on the generator breaker (generator switch), in this moment the generator starts

to operate and the power plant comes online,

- setting the minimal working power,

- turning on the working power regulator, which opens and closes the stator (also the

rotor blades on Kaplan turbines), and the inverter (if one exists), which means that the

power plant is online and its power is regulated,

- turning on the regulator of voltage and reactive power.

In the case if we want to start the pump/turbine in pumping regime, additional steps are

required. First, a brake must be set, then compressed air is supplied to the turbine (rotor is

rotated in air to minimize the startup current), and when the turbine is synchronized with

the grid, the de-airing valve is opened.

Normal power plant shutdown

The normal shutdown procedure varies for different power plants. This subsection will

present a case of a Francis turbine for large heads and with an inverter. During the normal

shutdown, the following operation must be carried out:

- turning off the working power regulator,

- turning off the regulator of voltage and reactive power,

- turning off the generator breaker (generator switch), which shuts down the generator

and disconnects the turbine from the grid,

- turning off the inverter,

- turning off the excitation,

- closing the stator (guide vanes) completely,

- turning on the stator short circuit switch,

- turning on the inverter, which serves for rotor braking in the stop sequence,

- turning on the electric braking with the aid of the inverter,

- turning on the main brakes (mechanical breaking),

- turning off the inverter,

- turning off the excitation transformer and excitation (turn off the excitation breaker)

- turning off the stator short circuit switch,

- closing the ball valve (after the stator has been fully closed),


101

- turning off the auxiliary systems,

- turning off the brake,

- activating creep detection.

Quick (emergency) power plant shutdown

A quick power plant shutdown is necessary, if there is a sudden loss of load on the

generator. This occurs in the case of transformer failure, power line damage, water break-

in or exceeding the critical vibration level. Then, since the generator is shut down

(offline), all the braking power on the turbine is lost, while the kinetic energy of water in

the penstock is very high, causing the generator and the turbine to accelerate. In an

emergency shutdown event, one must prevent the turbine from spinning so fast that

bearing or other turbine parts could be damaged or destroyed. A quick power plant

shutdown leads to large loads.

Some power plants (for example, HE Hubelj) have a safety bypass valve, which opens

(short-circuits) the pressure pipeline and the turbine outlet. Water is diverted past the

turbine and the main valve can be closed slowly.

Figure. Safety bypass valve in HE Hubelj (bottom left element in the image).

In power plants without the safety bypass valve, the flow of water must be closed with

the stator, rotor and the valve. This must be done slowly to prevent excessive pressure

fluctuations in the turbine and in the flow tract upstream of it. If the turbine is Kaplan-

type, the stator is closed while the rotor is opened.

The quick power plant shutdown presents one of the acceptance test performed when the

customer takes delivery of the turbine from the manufacturer. Quick shutdown tests are

usually, based upon the agreement between both parties involved, performed at different

loads, e.g. 60%, 75%, 90% and 100%, for a cold turbine (immediately after the startup

when the bearings are cold) and a warm turbine (after at least 30 minutes of operation).

The loads follow one after another until the 100% load is reached, unless the parameters

of vibrations and bearing casing movements have already been exceeded during previous

tests at partial loads.


102

Appendix 3: The elements of hydroelectric power plants

Intake system

The inflow system consists of the upper accumulation, dams and trash racks.

Dams

Dams are structures which hold the water for different purposes, including electricity

production. There are several types of dams: bulk, concrete, gravitational, arch, pillar or a

combination thereof.

Bulk dams (also known as rock-fill dams) are constructed by piling of rock material

around the central waterproof wall, which nowadays is usually made of concrete. These

are used in cases when a wide valley must be dammed. Bulk dams are gravitational and

are held in place by their own weight.

To dam deep and narrow gorges, a concrete dam is needed as only the concrete structure

is strong enough to withstand the pressure of water. The highest concrete dams exceed

300 m in height. The dam cross-section is usually triangular. Construction of large

concrete walls is complicated and slow, as the structure must be cooled during

construction. Concrete dams are gravitational (held in place by their own weight), arched

(curved in the shape of an arch and leaning on the sides to the valley banks which holds

them in place; used for damming high and narrow gorges) or pillar (the pillars have deep

and strong foundations which are supported by the ground), or a combination of different

types.

Apart from the main dam structure, the surrounding supporting area must also me

strengthened. For example, the dam of HE Medvode (60 m high, highest in Slovenia) is

located in an area where the river Sava created rapids in dolomite, which is mostly

cracked an full of cavities. To assure good foundations, the ground was stabilized by an

injection curtain. The unfolded width of the curtain is 190 m and extends until the

impervious base made of shale and sandstone, which lies in the depth between 27 m and

45 m.

To assure safe dam operation, the possibility of landslides into the accumulation must

also be assessed. The worst accident which happened due to ignoring the possibility of

such landslide happened at Vajont dam near Longarone, Italy. A part of the nearby hill

collapsed into the accumulation lake Vajont, causing a 200 m high tsunami wave.

Nowadays, larger dams usually have an equipment for detection of landslides.


103

Figure. Left: the concrete dam of HE Moste (arch-type), right: dam structure of HE

Medvode is a combination of pillar and gravity type, behind the accumulation Zbilje lake

can be seen.

Teeth and trash racks

The inlet from dams to the power plant channel or tunnel can be designed in different

ways, but is usually a part of the dam or the dam building. Different elements are used at

the inlet: teeth, trash racks etc.

The tooth holds all the floating or sinking debris. Due to the tooth, the inlet channel is

located a few meters below water level and above the bottom, which reduces the

possibility that larger pieces of wood would enter the power plant. The debris collecting

at the tooth must be cleaned with a cleaning machine.

The trash rack holds the dirt (tree leaves, stones, sand, gravel etc.) from travelling

through the turbine and damaging it. Some trash racks have a differential pressure meter.

If the differential pressure is too high, the rack must be cleaned with the cleaning

machines.

Figure. Left: The tooth of HE Medvode and the trash rack, the tooth holds the debris

while the rack is not visible (under the metal guardrail in the lower left part of the image).

Due to the tooth, the inlet channel is located about 3 m below the water level and above

the bottom, which reduces the possibility that larger pieces of wood would enter the

power plant. Middle and right: the inlet-outlet facility at the pumped storage power plant

Avče during construction and operation. The teeth are vertical and installed in a way

which prevents larger pieces of floating wood from being sucked into the power plant.


104

Figure. Left: exemplar trash rack on a small hydroelectric power plant.

Water supply system

The system for supplying the water from the upper accumulation to the turbine consists

of supply (head race) channels, supply tunnels, sand trap, gates, surge tanks, pressure

pipelines (penstocks) and closing elements. The water supply system is a continuation of

the inlet system and can be very large/long if the damming is far away from the

powerhouse. In run-of-the-river/accumulation power plants the water supply system is

short and incorporated in the dam structure.

Head race channels and tunnels

Head race channels and tunnels supply the water to the penstock, because in most cases

the dam is not located directly above the powerhouse, but some distance away from it.

The channels are open and are usually designed as excavated asphalt structures with low

inclination. The channels are made by drilling or blasting the rock and then covered with

concrete. Near the end of the head race channel/tunnel there is usually a sand trap, an

expanded section where flow velocity is reduced and the particles heavier than water

settle on the floor. Near the end of the head race channel/tunnel there is a surge tank.


105

Figure. Left: a head race tunnel during construction, visible are the individual layers of

concrete. Center: head race tunnel of the pumped-storage power plant Avče. Right: head

race tunnel of HE Hubelj.

Surge tank (surge chamber)

The function of the surge tank (also known as surge chamber) is to reduce pressure and

mass flow fluctuations in the penstock and head race tunnel caused by changes in load, to

within acceptable limits. A surge tank is an expanded part of the head race tunnel. When

pressure and mass fluctuations occur, water spills from the penstock into the surge tank,

where the water level is momentarily increased. The surge tank prevents the pressure

wave from propagating into the head race channel/tunnel, thus preventing damage and

spilling.

Behind the surge tank there is usually a gate chamber, which ends the relatively flat part

of the water supply system. Inside the chamber a gate is installed for the purpose of

closing the channel when the penstock must be drained for inspection and maintenance,

without the need of draining the head race channel. Behind the gate chamber, the

penstock begins.

Figure. Surge tanks. The surge tank of HE Moste is pictured in the rightmost image.

Penstock

A penstock is a pressure pipeline linking the gate chamber and the power plant. It ends

with a ball valve, in case the power plant has one. Longer penstocks have steel walls

capable of sustaining high water pressure within it. Apart from the static pressure, a

penstock must also withstand the additional pressure caused by quick shutdown of the

power plant. If the penstock is vertical, it is named a shaft. Penstocks are usually mounted

on pods, which can be fixed or sliding. Due to the (thermal) expansion penstocks include

expansion joints, where two pipes slide one inside another. Short penstocks (e.g. in run-

of-the-river power plants) are often made of concrete.


106

Figure. Left, center: the penstock of HE Hubelj (left) and an expansion joint on the

middle of it (center). Right: A cross-section across the turbine field of HE Solkan, the

penstock in between the inlet rack (4) and the turbine (8).

Bypass valve

A bypass valve is a valve used with some Francis turbines with a large head. It is

installed at the turbine inlet and intended to divert some water from the penstock past and

downstream of the turbine. In an event of quick (emergency) turbine shutdown the rate of

bypass valve opening is determined by the rate of guide vane closing, and reduces

pressure loads in the penstock due to formation of a pressure wave. The typical time of

bypass valve opening is a few seconds in an emergency shutdown event.

Larger power plants usually do not have the bypass valve.

Figure. Safety bypass valve in HE Hubelj (bottom left element in the image).

Ball valve and its bypass pipeline

A ball valve is an element used to close the penstock in a hydro power plant. It is

installed just before the turbine's spiral casing inlet.

The ball valve always closes when the power plant is shut down, and its closing is slow.

Ball valves are hydraulically operated, but also have a weight for emergency closing in an

event of a more serious malfunction of the power plant and its auxiliary systems. In the

case of the emergency shutdown, the ball valve starts to close together with the stator

(guide vanes), to prevent the turbine from accelerating to excessively high rotational


107

frequencies (i.e. runaway conditions). When the ball valve is closed, the turbine can be

opened because the water can be pumped out.

To open the ball valve, pressure across it must first be equalized. For this purpose, a

bypass is opened before opening the guide vanes, which results in equalization of

pressure before and after the valve.

Run-of-the-river power plants lack the ball valve and its bypass.

Figure. Left: the ball valve on pumped storage power plant Avče. Right, bypass on HE

Hubelj (horizontal pipe above the ball valve).

Gate

The purpose of the gate is to close the water flow onto the turbine. Gates are not used for

closing the water flow during normal shutdown events in everyday's operation, but for

shutdowns of longer durations, and overhaul. In the case of a run-of-a-river power plant,

the gate is lowered in the opening with a crane, usually in multiple parts. Such gates are

named segment gates. In the case of a dammed power plant, the gate is usually installed

at the end of the head race channel/tunnel behind the surge tank.

Turbine inlet gates, together with turbine outlet gates, enable the draining of the turbine

compartment in the run-of-the-river power plants.

Apart from gates in turbine fields, the run of the river power plants also have the gates on

the spillways.

Figure. Left: the gate of the turbine outlet at HE Dubrava. Right: the powerhouse area at

HE Plave with the gate chamber and the penstock, everything was excavated inside a hill.


108

Figure. Left: gates stacked at HE Medvode. Right: the location for inserting the gates.

Powerhouse equipment

The powerhouse is the facility where the turbines are installed. It can be a part of the dam

structure, or as a separated facility. For instance, the powerhouse of the pumped storage

power plant Avče is 80 m deep, to assure sufficient suction head of the pump-turbine

unit. In the following part of this chapter, the equipment installed in powerhouses will be

presented.

Figure. Left: the powerhouse of the pumped storage power plant Avče, view from the

generator casing upwards, yellow channels contain power lines from the generator to the

transformer. Right: the powerhouse of HE Dubrava, Croatia; the turbine is installed in the

hole below the elevator on the left side of the image.

Spiral casing

The spiral casing is an element for supplying the water to the inlet guide vanes and

adjustable guide vanes. It is designed so that the water outlet velocity is constant along its

perimeter. This is why the cross-section of the spiral casing is gradually reduced along

the perimeter as the water is gradually directed through the stator and onto the rotor.

In spiral casings of some turbines, pressure measurement outlets are installed to measure

the flow rate by the Winter-Kennedy method. The method is based on measurements of

the pressure difference on two locations in the spiral casing, which rises proportionally


109

with the flow rate. The method is usually calibrated during acceptance tests, when the

flow rate is measured by winged anemometers.

In the majority of the larger power plants, the spiral casing is poured in concrete. In

smaller power plants such as HE Hubelj, it is usually visible.

Inlet guide vanes and adjustable guide vanes

The inlet guide vanes direct the flow from the spiral casing towards the turbine and have

a fixed position. They have an important function of providing mechanical strength as

they link the upper and the lower part of the inner side of the spiral casing.

Figure. Left: fixed (inlet) and adjustable guide vanes at HE Solkan (Kaplan turbine).

Right: Guide vanes at HE Dubrava (bulb turbine). Outside of the flow tract, the guide vanes are connected by a guide ring which moves all

the vanes simultaneously and is steered by a hydraulic arm. In some cases, the guide

vanes can be mounted softly and equipped with micro switches. The micro switches

detect if a particular vane did not close completely during the shutdown procedure (e.g.

due to jamming by a tree branch). In this case, the operator can reopen and close the

guide vanes, possibly removing the jammed objects to be washed away by the water

flow.


110

Figure. Left: Guide ring (red color) on a bulb turbine HE Dubrava, Croatia. Right: guide

ring on the Kaplan turbine at HE Solkan, visible is the hydraulic arm for guide vane

steering, and the soft mounting of the vanes with micro switches (green color).

Rotor (runner) , turbine casing, sealing and air blowing system

The rotors (also known as runners) can be of different types (Pelton, Francis, Kaplan

etc.) The shaft can be horizontal or vertical, the latter design more suitable for higher

power ratings.

The turbine casing of the rotor is a thick steel plate installed above the rotor. Large

thickness is required because the turbine casing is exposed to high pressures. Within the

turbine casing, the sealing system is also installed.

The air blowing system has several different functions:

- it allows starting up large pumped storage power plants in the pumping regime (to avoid

excessive startup current, the pump-turbine starts pumping in air, forcedly blown in the

turbine compartment, which is only pumped out when the turbine reaches the desired

rotational frequency).

- it dampens the pressure pulsations in operation of Francis turbines at partial loads, when

a cavitation vortex appears in the suction cone and the bend. The vortex swings around

with approximately 1/3 of the rotational frequency of the runner and causes large

pressure, torque and electric power fluctuations as well as bearing vibrations.

Introduction of air (compressible medium) to water reduces the rigidity of the mixture,

the vent is only opened and the air enters by itself due to the suction in the flow tract.

- it dampens the water hammer effect during an emergency shutdown event (the vent lets

the air from the machine room into the suction part of the flow tract, reducing the

pressure fluctuations in the penstock).

Figure. Left: Kaplan turbine rotor, view from the lower side of the suction cone. Center:

holes in the rotor for blowing air, pumped storage power plant Avče. Right: turbine

casing of the same rotor.

Shaft

The shaft connects the turbine runner to the generator. The shaft is usually made of two

parts and as such, it can be divided to the turbine shaft (attached to the turbine's

rotor/runner) and the generator shaft (attached to the generator's rotor).


111

Figure. Left: turbine shaft of the pumped storage power plant Avče. The thick part visible

in the upper part of the image is the coupling between the turbine and generator shaft.

Right: the shaft of HE Solkan.

Bearings

The bearings in all larger hydro power plants are of the slide type. Each power plant has

at least one turbine bearing and one generator bearing. The guide bearings hold the

turbine in place in the radial direction and the carrying bearings support it in the axial

direction.

The bearings are made of segments with oil up to about the half of the segment height.

The function of oil is both cooling and lubrication of bearings. The red-colored blocking

elements in the image below (from HE Solkan) have a function of stabilizing the position

of each bearing segment in the axial direction. Besides, there is also a steel reinforcement

in the radial direction (shown in black color between the red blocking elements) which

also serves for setting the air gap (adjustable by a screw on the outer side of the bearing,

away from the shaft). In the image below, the holes in the axial direction on the bearing

segment No. 1 are used or disassembling the segment. The segment No. 2 has another

hole in the center, where the bearing temperature probe is installed (for monitoring and

protection purposes). Also visible from the below image are different bearing materials.

Adjacent to the shaft there is a thin layer of white metal, which protects the shaft in the

case of surface contact. Only the white metal is damaged because it is softer and has a

lower melting point, meaning that the segment can be easily repaired.

During operation an oil film is formed in the gap between the shaft and the bearing, and

is able to sustain itself without forced lubrication. On larger and more modern turbines,

the bearings are equipped with an oil pump for initial lubrication. This pump assures

sufficient bearing lubrication, while the turbine is stationary or starting to spin. If the

pump is turned in, the turbine can be rotated by hand if there is no water in the flow tract.

When the turbine reaches the normal operating conditions, the pump stops. The


112

lubrication oil is cooled in a water-cooled oil cooler, which is usually installed near the

bearing.

Figure. Segments of the turbine leading bearing at HE Solkan (detailed view shown in the

right). Black color marks the reinforcement, which serves as a support. Red color marks

the blocking elements, which assure a stable positioning of the bearing in the axial

direction. The image was taken with a removed bearing cover.

Figure. Left: water-cooled oil cooler at HE Medvode (blue color). Right: high-pressure

pump for initial bearing lubrication at HE Solkan, turbine shaft is visible on the left side.

Smaller hydro power plants have simpler bearings, such as HE Hubelj pictured below.


113

Figure. The bearings at HE Hubelj (colored yellow). Also visible is the flywheel, which is

used when the power plant runs separated from the remaining electric network.

Creep detection

Creep detection of the turbine shaft is a part of the turbine stator control system. Creep

detection is performed by a measuring device, which is able to measure very slow

rotation of the turbine shaft when the turbine is stopped. It can be a part of the rotational

frequency measurement system or a standalone instrument. If the turbine is rotating very

slowly even when the guide vanes are closed, this usually means that one or more vanes

are leaking (due to dirt, branches etc.). When the system senses a slow rotation, auxiliary

systems (bearing pups etc.) are turned on to prevent damage of the moving parts.

Figure. Creep detection at HE Solkan (light blue box). This turbine has another protective

device installed on the shaft: two screws that move radially out of their normal position

when the rotational frequency of the shaft reaches 120% of its nominal value, tripping the

switch in the front of the creep detection sensors. This initiates the emergency shutdown

sequence.

Inverter


114

Few power plants are equipped with an inverter (in Slovenia, only the pumped storage

power plant Avče). The inverter allows rotational frequency variation in a certain range,

for example from -4% to +4% of the nominal rotational frequency. This allows reaching a

better efficiency and more flexibility for adjusting the operation to current conditions in

the electroenergetic system and to the available quantity of water.

Brakes

The brakes are mechanical elements used to stop the turbine when it rotates very slowly

(before that point, the turbine is braked hydraulically by closing the guide vanes, or also

adjusting the rotor blade angle in the case of Kaplan turbines). When the turbine stops,

the brakes are released. After that, the turbine must remain still, which is monitored by

the creep detection system. If the runner starts to rotate by itself from the standstill, this is

usually due to the dirt jammed in the guide vanes, which prevents full closing. The

turbine must not rotate when not in operation, as such rotation can damage it. The brakes

are not intended to be used for permanent braking.

Generator and its electric equipment

The generator is a device where mechanical energy from the shaft is converted to electric

energy. A generator consist of a rotor and a stator. All the electric generators in power

plants operate on the principle of electric induction, where voltage is generated as a wire

passes the magnetic field. Lines. In smaller generators, the magnetic field is produced by

durable magnets, while in bigger units electromagnets (which require additional source of

current for excitation) are more common. Generators can be of synchronous or

asynchronous type.

In modern synchronous AC generators, the excitation current is produced from a

separated external source. Since the excitation current is much lower than the current in

the induced winding the excitation circuit is usually installed to the rotor of the generator

because the sliding rings are not suitable for conducting large currents.

Figure. Left: powerhouse and generator casing at HE Doblar II; rotor (center) and stator

(right) of the generator in HE Solkan during maintenance.

Other electric equipment includes the switchyard, distribution switchyard, transformers,

generator breaker, diesel power unit, batteries etc. The diesel power unit is constantly


115

heated to be always prepared for startup, when a backup power source is required for the

plant's own energy consumption. The own consumption of the power plant includes the

electric energy required for running the plant's systems, including those running when the

plant is out of operation. These are mostly the drainage pumps.

Figure. Diesel power unit at HE Medvode.

Other systems in the power plant

The other systems include the drainage system, different cooling systems, the system for

oil supply and cleaning etc. The drainage pumps operate constantly, as water usually

slowly breaks into the power plant building. The drainage pumps are a large source of the

plant's own consumption and must also operate when the power plant is offline and not

producing electricity.

Spillways and spillway gates

The spillway gates are similar to turbine gates. Depending on the type of the power plant,

often there are two spillway gates and can be of different types (e.g. segment gate, table

gate etc.) Segment gates are installed in place by a crane and is used, when water must be

drained from the table gate. Table gates have a function of closing the flow through the

spillway, when the flow rate is low enough and all the water passes the turbine. In the

case of increased flow rate, when the turbines cannot take all the water the table gate first

drops (low flow rate across the gate), then rises (high flow rate under the gate) or is fully

removed (the whole spillway is closed). The problem with flooding waters is that the

river flow carries large branches or even trees which can become stuck in the spillway,

greatly reducing the flow rate.

The water from turbine ways or spillways flows into the lower accumulation, where some

power plants have floating gates. These are hollow gates lowered by the crane into the

water of the lower accumulation, then they float to the place of installation, where they

are filled with water and being sunk as a result. Floating gates are used for the

maintenance of the outflow facility downstream of the power plant or under the waterfall

etc.


116

Figure: A cross section of the spillway at HE Solkan.

Power plants which must always sustain water flow to preserve the biological minimum

of the river, cannot completely stop the river flow. For this reason, not all the turbine

ways have gates.

Figure. Left: HE Solkan with two spillways and three turbine ways. Center: spillways of

HE Solkan during the floods in 2012. Right: a table gate with a hook design on the

spillway of HE Medvode.


117

Literature

- International standard, IEC 60193 Hydraulic turbines, storage pumps and pump-turbines

- Model acceptance tests, 1999.

- International standard, IEC 60041 Field acceptance tests to determine the hydraulic

performance of hydraulic turbines, storage pumps and pump-turbines, 1991.

- G. Krivchenko, Hydraulic Machines: Turbines and Pumps, CRC Press, 2nd edition,

1993

practical exercise 3. measurement of the turbine machine

Documents