technical repor1 3kw wind generator 2003

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Technical Report: Electrical Engineering

Student Information

Full Initials & Surname: R. Bester

Student Number: 206015259

Mailing Address for Reports: Cape Town Campus

Mr. L Khetla

Department of Co-operative Education

CPUT – Cape Town Campus

P O Box 652

Cape Town

8000

Project Information:

Report No: P1

Title of Project: The Assembly and Testing of a 3kW Axial Flux Air-core Wind

Generator

Field of Work: Design, Manufacturing, Assembly, Electrical Testing and Fault

Finding

Company Information

Company Name: Electrical Machines Laboratory

Department of Electrical Engineering

Stellenbosch University

Postal Address: University of Stellenbosch

Private Bag X1

Matieland

7602

Street Address: Room E166

Electrical Machines Research Dept of Electrical Engineering

Engineering Building Complex

University of StellenboschBanghoek Road

Stellenbosch

7600

Telephone No: 021 808 3890

Fax No: 021 808 3951

Email Address: [email protected]

Name of Mentor: Prof M.J. Kamper (M.Ing Stell PhD(Ing) Stell SMIEEE

MSAIEE Pr Eng

Tel No of Mentor: 021 808 4323

1

mailto:[email protected]

mailto:[email protected]



Table of Contents

Table of Contents ........................................................................................................... 2

Introduction .................................................................................................................... 3

Theoretical investigation ................................................................................................ 3

Practical Considerations .................................................................................................5

Manufacturing of the generator ................................................................................. 5

Testing ........................................................................................................................ 6

Control Circuit ............................................................................................................6

Erecting the generator onto the tower ........................................................................ 7

Fault finding ............................................................................................................... 7

Conclusions .................................................................................................................... 8

References ...................................................................................................................... 8

Tables ............................................................................................................................. 9

Figures ..........................................................................................................................10

......................................................................................................................................11

......................................................................................................................................18

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Introduction

I am an Electrical Engineering student from CPUT Cape Town doing my in-service

experimental training at the Electrical Machines Research Laboratory in the Electrical

Engineering Department at Stellenbosch University as a technical assistant.

This is my first Projects report.

I work in a post graduate research laboratory with post graduate students doing

research for their post graduate education. The students I am working with are

students busy with their MsC Eng degree or PHD Eng degree.

One of our main focuses is renewable energy in the form of environmentally friendly

electrical generation and we also spend a great amount of time in research and the

construction of electrical vehicles.

This project report is going to focus the assembly, erecting and testing a 3kW Axial

Flux Air Core Wind generator which powers a motor which drives a centrifugal

pump. This pump is going to pump water from a lower tank to an upper tank which is

situated in the lab and the amount of water pumped is going to be compared to the

wind speed at that specific time and the efficiency of the system is going to be

determined with this data.

In this report I am going to focus on the Wind generator driven pump system and

what my contribution to the project was and all of the areas that I was personally

involved in.

The system was designed by Edward Lenner who finished with his Msc Eng degree in

Electrical Engineering in 2008. Edward and I work under our mentor Prof. M.J.

Kamper.

Edward is currently employed at a mine in Gauteng and I was put in charge to

complete his pump system and retrieve valuable data from the various sensors for

research purposes.We communicate via email en telephone.

Theoretical investigation

The whole project is based on the simple fact that the standard 50Hz 3 phase

induction motors which is commonly used today can operate at variable speeds by

varying the supply voltage and frequency as long as a constant Voltage to Hertz ratiois used.

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This system is intended to replace the traditional wind pump system commonly found

in the agricultural sector. This system consists of a mechanical piston type of pump

driven with galvanized steel blades. This system is highly inefficient because of its

rugged construction.

This project replaces that system and consists of a turbine generator which generates a

varying voltage and frequency supply at variable wind speeds, induction motor which

drives the pump and a pump which pump the water.

Before designing the generator for the system we need to look at the behavior of the

other components or parts of the system as well. At first we look at the specific pump

performance curves (see fig. 1) to see where the working points for this specific pump

is. The working points on the graph are where the system curve intercepts the various

pump performance curves at certain speeds. The system curve is the total pressure

losses made up of the distance the fluid must travel which include friction and fittings

used in the pipeline. Now that we have the working points we can calculate themechanical- and input power of the pump by using the following formulas:

Mechanical power:

Ph = ρgQH

Where ρ = density of fluid

g = gravitational constant

Q = low capacity

H = head.

Input power:

Pin = Ph/л

Where л = efficiency.

The pump power must be matched to points where the turbine delivers optimum

power.

Fig. 2 is a graph that shows the characteristics of a 3kW, 3-blade turbine at certain

wind speeds. Optimum power points are indicated on the graph where the turbine is

most efficient. The input power of the pump is plotted on the graph and is known asthe load line. We want our system to operate as close to the optimum points as

possible at certain wind speeds. In other words we are trying to get the load line as

close as possible to the optimum points. The load line is shifted by playing with the

ratio of the poles between the motor and generator. The system will never operate at

the optimum power points because of the power losses in the motor and generator.

After calculating the input power of the pump the generator and induction motor can

be analyzed which deliver the mechanical power of the wind turbine shaft to the shaft

of the pump. The generator and motor must be sized according to the maximum

operating conditions of the turbine. The maximum wind speed on the graph in fig. 2 is11m/s. The maximum wind speed we are designing for is 10m/s which equals to a

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generator speed of 250 r.p.m therefore the generators power rating is going to be

2,2kW according to the graph because that is the maximum power the turbine can

deliver at 10m/s.

The motor used for the system is a 2,2kW induction motor with 2-poles because it

operates at lower frequencies. High frequencies cause unnecessary iron losses.

The power losses in the generator and motor must be known because the total input

power must be equal to the power required by the pump and the losses in the

generator and motor. This will help to choose the pole ratio between the motor and

generator.

The losses are calculated as follow:

R fe = 3E p² / Pfe

Where E p = volt drop over stator iron lossesPfe = Stator iron power loss.

After the calculations we find that 1:10 ratio causes the pump to operate closest to the

optimum operation points. This translates that the generator must have 20-poles. The

induced emf per phase of the generator follows a constant V/Hz ratio and is given by

the following equation:

Eƒ = 4.44NK wΦƒ

Where N = amount of turns

K w = winding factor

Φ = magnetic flux per pole and ƒ = operating frequency.

The maximum open circuit induced emf is calculated to be 400VL-L. That is for a

maximum speed of 250 r.p.m.

The system as whole is laid out in fig 3

Practical Considerations

Manufacturing of the generator

The coil width, coil height and the amount of turns of each coil were specifically

designed for this machine. All of these parameters influence the output voltage of the

generator.

The first step was to turn the windings on the winder using a Tufnell former on which

the copper enameled wires was turned on. This is shown in fig 4 and 5The specifications for the coils is as follows

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18 coils needed

200 turns per coil

0.8 mm diameter copper enameled grade 1 wire is used

After all 18 coils were wound; they were packed into a previously used mould in a

circle. 6 Coils was connected in series to with Farrell’s to form a phase. The 3 phaseswas then connected in a star configuration. This connection diagram is shown in fig 6

The next step was to reinforce the epoxy with weaving fiber-glass cloth. The mould

was closed up. The epoxy was mixed according to specific specifications and was

poured into the mould. After 24 hours the mould is set and is ready to be baked in a

oven. The dried stator is baked still in the mould at 100 degrees Celsius for 4 hours

and after that the heat is increased up to 110 degrees Celsius for 1 hour. The mould is

left to dry overnight. The next day the stator is taken out of the mould and inspected.

Part of the inspection process is to do a few measurements to check if everything is

correct. I used a multimeter and measured the resistance of each phase and I used a

LC meter to measure the inductance of each phase. Measurements were taken line toline and from line to neutral. The results are situated in table 1.

The phases are also connected to a megger to ensure that there are no short circuits or

leakage current between the phases. The completed stator is shown in fig 7

After the stator passed the inspection process, the generator assembly is started.

The permanent magnet rotor and is situated on both sides of the stator. A 1 mm air

gap is left between both sides of the stator and the rotor. The rotor and stator needs to

be lined up so that a 1mm air gap is present across both sides of the stator and is

uniform all around. This is done by inserting 1mm aluminum spacers between the

rotor and the stator and aligning them up. This part of the assembly is shown in fig 8.

Testing

After everything is aligned, the assembly is completed and more tests are done to

ensure that the generator gives out the correct voltage and that all 3 phases give a

sinusoidal wave which is 120 degrees apart from each other. This test is done by

connecting an oscilloscope to the phases and measuring the output voltage when the

generator is turned by hand. The results of the oscilloscope are shown in fig 9. After

the generator passed this test, I designed a control circuit which senses the output

voltage and frequency of the generator and uses these values along with contactor to

regulate the system and engage the load at the correct voltage range. If the voltageexceeds or drops below this voltage range, the load is disengaged. The system also

picks up the speed by sensing the frequency and breaks the system with resistive

braking if the generator were to spin out of control, bringing the speed down to the

regulated voltage.

Control Circuit

The load is engaged when the generator produces 170V.

The load is regulated between 140V and 280V. If the generator exceeds or falls below

this range, the load disengages. The frequency is monitored and kept between 20Hz

and 48Hz. If the frequency exceeds 51Hz or above, a contactor engages the resistive

braking which brings the overall speed down to a safe and manageable amount.

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The control circuit and the power circuit are shown in fig 10 and fig 11.

I designed the cover using a program called Autodesk Inventor. The drawing was then

sent fabrinox in Paarl to be manufactured. This drawing is shown in fig 12 and 13.

Erecting the generator onto the tower

After the control circuit is in place, the generator ready to be put on its tower. The

tower consists of a head on which the generator is mounted, a tail which keeps the

generator pointing into the wind. Attached to the generator are 3 fiberglass 1.8m

blades. These blades weigh only 6 kg each and are light enough to pick up speed with

the smallest of breeze.

The tower is designed to fold in the middle so that the generator can be assembled on

the ground and pulled up using a winch and rope.

This is shown in fig 14, fig 15, fig 16, fig 17, fig 18 and fig 19.

After the assembly is completed, the generator is connected to the control circuit. The

2.2kw load (3ph induction motor) is also connected to the load. Test was done earlier

in order to test the performance of this system and is show in table 2.

This setup is shown in fig 20.

A weather station is also mounted on the pole which senses and records wind speed

every minute and saves the data. A flow sensor is attached to the system and will

show how much cubic meter of water is pumped up to date. These data is going to beused over the next 6 months and we are going to establish the efficiency of this

system by comparing the amount of water pumped at which wind speed and

conclusions will be made after that

Fault finding

After some testing we ran into problems when the wind generator stopped. I was sent

to investigate and to find the fault in the system. I used a DC constant current supply

and I connected it between two phases. With this I measured the voltage and I

measured the current. With these two values I determined the resistance of all three

coils with the formula R = V/I

I discovered that there was a short circuit in two of the phases and that is the reason

why the blades do not turn, because a short circuit brakes the system electrically.

The reason I used a Constant current DC supply is because if you use a multimeter or

a megger, the readings is unstable and difficult to read due to the fact that the

generator rotates slightly and generates a voltage. The DC supply brakes the generator

and makes it stable enough to make accurate measurements.

We took the generator down from the pole and tested the generator and found the

there are no faults on the generator. Then I measured the cable coming from the

generator head and found that there is a short circuit between the blue and yellow

conductor.

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When we inspected the wire inside of the pole, we discovered that the cable got

damaged and was squashed at the point where the pole hinges. It pressed so hard on

the cable that a short occurred through the insulation.

We fixed that with insulation tape and giving the cable more slack by loosening the

glands a bit. After we fixed the cable, we assembled the generator back on the pole.And everything worked as it was intended to do

Conclusions

The generator was assembled successfully in time. A common problem is that a short

circuit can occurred due to vibration. The vibration sends the pole into oscillation and

if it reaches resonant frequency, the vibrations will cause the rotor to make contact

with the stator and cause a flashover and creates a short circuit. These vibrations canalso lead to mechanical failure of the system.

There are still quite a bit of vibration on the pole, but we will see how this will affect

the generator. And this can only be tested if the system runs for some time. The only

way we will know if the project is successful, is to let the system run for a couple of

months and compare the amount of flow to the amount of wind speed.

If this project is successful, it will attract the general public, government and the

private sector to invest in these types of technologies and this will create more

opportunities for further studies into this field of education.

I learned with this experience that theoretical concepts are not always successful in

practice. It takes trial and error to perfect a product up the point where it is reliable

enough to use in industry. I gained a huge amount of experience in taking

measurements and using equipment to solve problems. Skills that I will definitely use

in the future

References

Kamper, P. M. (2009, March 20). Wind generator principles. (R. Bester, Interviewer)

Lenner, E. C. (2008). Wind-Electric Pump System Design. Stellenbosch: Electrical

Machines Research Laboratory, Electrical Engineering Department, Stellenbosch

University.

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Technical crew

Pietro Petzer

Technical Officer

Andre Swart

Technical Officer

Marius Jumat

Technical Assistant

Ruan Bester

Technical Assistant

Tables

Resistance Inductance

Red – Yellow Line-to-line 17Ω 30.74mH

Yellow - Blue Line-to-line 17 Ω 30.87mH

Blue - Red Line-to-line 17 Ω 30.73mH

Red - Neutral 8.6 Ω 14.45mH

Blue – Neutral 8.7 Ω 14.34mHYellow - Neural 8.6 Ω 14.45mHTable 1: Measurements of the generator

Generator

Speed

(r.p.m)

Generator V

(V)

Generator I

(A)

Torque

Generator

Input (N.m)

Torque

Motor

Output(N.m)

Motor r.p.m

100 135 1.5 24 0.9 1175

110 150 1.6 25 1.2 1290

120 160 1.7 30 1.5 1400

130 170 1.8 36 1.78 1500

140 180 1.9 40 2 1610

150 195 2 45 2.33 1720

160 200 2.2 50 2.65 1830

170 215 2.42 54 3 1930

180 225 2.65 60 3.35 2040

190 230 2.9 67 3.65 2140

200 240 3.1 73 4 2240

210 250 3.4 80 4.3 2335

220 260 3.8 89 4.75 2430

230 265 4.15 98 5.15 2520

240 272 4.5 108 5.5 2600250 280 5 117 6 2700

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Wind Turbine

Permanent MagnetGenerator

3-PhaseInduction Motor Centrifugal

Pump

Table 2: Performance measurements of the motor and generator

Figures

Figure 1: Pump performance curve

Figure 2: Power speed characteristics of a 3-blade, 3kW wind turbine

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Figure 3: System layout



Figure 4: Turning a winding onto a former with a machine called "the winder"

Figure 5: Finished winding

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Figure 6: Connection diagram of the windings

Figure 7: Completed Stator

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Figure 8: Balancing the rotor and stator to ensure that a 1mm air gap is present on both sides

Figure 9: Testing with an oscilloscope to see if all phases are sinusoidal, are 120 degrees apart

and that the three voltages are of the same amplitude

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Figure 10: Control circuit

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Figure 11: Power circuit

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Figure 12: Base of the box which houses the control circuit

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Figure 13: Cover of box which houses the control circuit

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Figure 14: Completed generator

Figure 15: After the three 1.8 meter blades are put on, it is all held together with 6 brackets and

bolts

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Figure 16: The protective cover protects the generator from rain and improves aerodynamics

Figure 17: The pole hinges in the middle and can be hoisted up with a winch and by manpower

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Figure 18: The generator is lifted up very slowly

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Figure 19: The wind generator is in its final position

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Figure 20: A 2.2 kW 3ph motor is connected to a centrifugal pump which pumps water from a

lower tank to an upper tank

technical repor1 3kw wind generator 2003

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