common diesel generator protection of power systems in dp

Common Diesel Generator

Protection of power systems in DP

classified vessels.

By

Shuang Li

in partial fulfilment of the requirements for the degree of

Master of Science

in Electrical Sustainable Energy

at the Delft University of Technology,

to be defended publicly on Thursday July 14, 2016 at 9:00 AM.

Supervisor: Dr.ir. Marjan Popov TU Delft

Mr. Remmert Dekker Bakker Sliedrecht

Thesis committee: Prof.dr. Peter Palensky TU Delft

Dr.ir. Marjan Popov TU Delft

Dr. Armando Rodrigo Mor TU Delft

Mr. Remmert Dekker Bakker Sliedrecht

Abstract

For commercial and environmental reasons, DP vessel owners intend to operate with a

reduced number of diesel generator sets, which often operate at very low power levels, to

minimize the costs of fuel and maintenance.

The solution for these phenomena is that vessel’s power systems are operated under one

or more coupled bus-bars (closed Bus-Ties mode).

The classification societies are now providing special rules which make it possible for

suppliers of electrical systems to follow the above mentioned trend.

The consequence, however, for the suppliers of electrical systems is that the electrical

systems require much more complex and expensive control and protection systems than

before to obtain the same proven levels of safety and reliability of power systems with

separated bus-bars. (open Bus-Ties).

The protection circuits currently used are based on functional requirements of the

classification societies, where insufficient account has been taken of errors caused by the

diesel engine governor and generator AVR faults in closed bus tie mode. They occupy

15%~20% of all faults, according to the International Marine Contractors Association [1]. And

they are easy to cause a blackout in the vessel. For example, when 2 paralleled generators

are running online under low loading condition. Then a diesel engine is over fueling. The faulty

generator takes more load and the healthy generator takes less load. The healthy generator

takes reverse power, and will be tripped by protection. After tripping the healthy generator, the

faulty generator will be over frequency. At last, the faulty generator will trip, and a blackout

occurs.

The purpose of this "Common Diesel Generator Protection" is to detect the early stage

failures of diesel engine and generator in a power plant to avoid power interruption caused by

a so-called snowball effect (resulting in a blackout).

The other purpose of this master thesis is building a generator model with full excitation

system and diesel engine. Then, with the help of the test measurement from manufacturer and

vessel, tune parameters in diesel generator model and validate it. The validated diesel

generator model can be used for the further research in the company.

Preface

This report is the result of my master thesis as a master student in Electrical Sustainable

Energy master program. The work of the thesis is done at Bakker Sliedrecht, a marine power

system integrator, from November 2015 to July 2016. Many thanks are expressed to the

persons who helped and encouraged me during my thesis.

Firstly, I would like to thank Prof. Marjan Popov, who is my supervisor at the TU Delft, for his

guidance and many excellent suggestions to my thesis. Thank you for your patience and

encouragement.

Next, I would like to thank Remmert Dekker, who is the R&D manager at Bakker Sliedrecht

and also is my daily supervisor in the company. Thank you for giving me the opportunity to

have this thesis. Thanks for your encouragement when I met difficulties. Thanks for helping me

to arrange all affairs, which are related to my thesis, in the company.

At last, I want to thank the PHD candidate Lian Liu and Master student Meng Zhang for the

fruitful discussion about power system modeling.

Shuang Li

Sliedrecht, June 2016

Abbreviations

AGP Advanced Generator Protection

AVR Automatic Voltage Regulator

CDG Common Diesel Generator protection system

DGMS Diesel Generator & Monitoring System

DG Diesel Generator

DP Dynamic Positioning

IEC International Electro technical Commission

IEEE Institute of Electrical and Electronics Engineers

IMCA International Marine Contractor Association

OEL Over Excitation Limiter

PF Power Factor

PID controller Proportional Integral Derivative controller

PLC Programmable Logic Controller

UEL Under Excitation Limiter

Content

1. INTRODUCTION ................................................................................................ 1

1.1 Background ......................................................................................................... 1

1.2 Problem statement .............................................................................................. 2

1.3 Organization of the thesis ................................................................................... 3

1.4 Previous work ..................................................................................................... 4

2. MODELING OF MARINE POWER SYSTEM ..................................................... 6

2.1 Single diesel generator model ............................................................................ 6

2.1.1 Generator model ................................................................................................. 6

2.1.2 AVR and exciter ................................................................................................ 10

2.2 Diesel engine model ......................................................................................... 11

2.2.1 Engine model .................................................................................................... 12

2.2.2 Governor ........................................................................................................... 13

2.2.3 Emission control................................................................................................ 14

2.3 Consumer load.................................................................................................. 14

2.3.1 Constant impedance load ................................................................................. 14

2.3.2 Constant power load ......................................................................................... 15

2.4 Validation .......................................................................................................... 16

3. THREE PARALLEL DIESEL GENERATORS MODEL .................................... 20

3.1 Active and reactive power droop ...................................................................... 21

3.2 Load step test ................................................................................................... 22

3.3 Excitation system and prime mover faults simulation results ........................... 23

3.3.1 Excitation system faults simulation results ....................................................... 23

3.3.2 Prime mover faults simulation results ............................................................... 27

4. COMMON DIESEL GENERATOR PROTECTION DESIGN ............................ 29

4.2 Excitation system detection .............................................................................. 29

4.2.1 Mechanism ........................................................................................................ 29

4.2.2 Expected value calculation ............................................................................... 31

4.3 Prime mover detection ...................................................................................... 35

4.3.1 Mechanism ........................................................................................................ 35

4.3.2 Expected value calculation ............................................................................... 37

4.4 Voting system ................................................................................................... 37

4.5 Operation window ............................................................................................. 38

4.6 Deviation detection simulation results .............................................................. 39

4.7 CDG structure in simulation .............................................................................. 42

5. CDG VALIDATION ........................................................................................... 45

5.1 Test setup ......................................................................................................... 45

5.2 Test setup generator validation ........................................................................ 51

5.3 CDG test result ................................................................................................. 57

6. FUTURE WORK AND CONCLUSION ............................................................. 69

6.1 Future work ....................................................................................................... 69

6.2 Conclusion ........................................................................................................ 69

7. BIBLIOGRAPHY ............................................................................................... 71

APPENDIX A ........................................................................................................................... 73

APPENDIX B ........................................................................................................................... 74

APPENDIX C ........................................................................................................................... 82

APPENDIX D ........................................................................................................................... 90

APPENDIX E ........................................................................................................................... 91

1

1. Introduction

1.1 Background

The concept of marine electric power system was implemented around 100 years ago. And

it was not used commonly at that time. With the possibility to control an electrical motor with a

variable speed in a large power range with compact, reliable and cost-competitive solutions,

the marine electric power system became popular during 90’s.

With the development of azimuth thrusters, propulsion can force a vessel to move in all

directions. And with the number of the offshore application increasing, dynamic positioning

(DP) is proposed [2]. A dynamically positioned vessel means a unit or a vessel which

automatically maintains its position (fixed location or predetermined track) by means of

thruster force. Figure 1.1 shows a typical DP vessel.

Furthermore, around 10 years ago, in order to accomplish DP Class requirement (during DP

operation, the vessel can tolerate a single fault), open bus-tie configuration was used for the

power system. The open bus-tie configuration was to isolate generators in their own sections.

A single fault in the system only can influence the sub section, and cannot lead the vessel to

lose its DP operation [3].

Nowadays, because of the costs of the fuel and environment protection, vessel owners

would like to decrease the fuel consumption of their fleet. However, in an open bus-tie mode,

every generator is used to keep DP operation, which has a high fuel consumption and a high

noxious exhaust gas. That’s the reason why vessel owners would like to use closed bus-tie

mode, which does not require every generator to run and has lower fuel consumption than

open bus-tie mode [4]. Closed bus-tie mode becomes popular. And the new DNV GL DP class

DYNPOSER also opens up for DP2 and DP3 operation with closed bus-tie mode. Therefore,

the marine power system industry begins to modify the old system and investigate new system

to accomplish new DP Class requirements.

2

Figure 1.1 A DP pipe laying vessel from Subsea 7

1.2 Problem statement

As stated in the background, the closed bus-tie mode becomes recommended. However,

the fault and protection parameter settings become more complex in the closed bus-tie mode

than the open bus-tie mode, because each generator will affect each other and the system

becomes weak. Therefore, in order to have more researches and understanding on the closed

bus-tie mode, the company wants to have its own validated diesel generator model and

parallel generator sets model. The diesel generator model should include a brushless

generator, standard AVR and a diesel engine.

Moreover, the protection systems currently used are based on the functional requirements of

the classification societies, where insufficient account has been taken of errors caused by the

diesel engine governor and generator AVR faults in closed bus-tie mode. According to the

International Marine Contractor Association (IMCA), they occupy 15%~20% of all faults. And

they are easy to cause a blackout in the vessel. For example, when three paralleled

generators are running online under low load condition, a generator (Gen1) is over excited

after 20s. The situation of the example is shown in Figure 1.2.

3

Figure 1.2 Over excitation occurs on Gen1

The faulty generator (Gen1) takes more reactive power and the healthy generators (Gen2

and Gen3) take less reactive power. Then the healthy generators take reverse reactive power,

and will be tripped by the protection. After tripping the healthy generators, only the faulty

generator is online and the system voltage is only controlled by the faulty generator. At last, the

faulty generator will trip, due to overvoltage. The blackout occurs, and the vessel loses its DP

operation. The blackout also can result from prime mover faults. Therefore, in order to keep

pace with new DNV DP class standard, a system should be investigated to the protect system

from excitation system faults and prime mover faults. The company named it as CDG.

1.3 Organization of the thesis

The main contributions of the thesis are summarized here.

The single diesel generator model is described in Chapter 2. It describes each component

included in the model and gives all equations and block diagrams related to the model. The

model is built in Matlab Simulink. Validation of the generator model is done and the

comparisons between the test measurement and the model result are given.

In Chapter 3, the three parallel diesel generator sets model is built. In order to realize active

and reactive power load sharing, compensated active power droop and fixed reactive power

droop are used in the model. Different scenarios are simulated, which are a load step test, 7

kinds of excitation system faults and 5 kinds of prime mover faults.

4

In Chapter 4, a system named CDG, which can protect diesel generator sets from excitation

and prime mover faults, is proposed. The mechanism and functions of CDG are described.

The logical structure of CDG is given and transferred into the simulation model. At last, CDG is

tested under the different scenarios.

Chapter 5 shows that, in order to allow this system model to be commercially used later on,

a three parallel diesel generator sets test setup will be built to test CDG. The CDG model is

translated to PLC program. At last, CDG test result will be shown.

1.4 Previous work

For the modeling part, some researches have been done, which are focus on modeling of

marine diesel electrical power system. Hansen provided a model of a marine power system [5],

but diesel engine model is a one order model. And the saturation is not included in its

generator model. Pedersen uses Bond Graph to build a marine power system model [6]. But

Bond Graph language is not a recommended language by the classification society. The

marine power system model provided by Radan [7] has the same weakness as Hansen’s.

Regarding excitation and prime mover protection systems, some systems are proposed,

which are voting system [8], Advanced Generator Protection (AGP) [9] and ABB Diesel

Generator Monitoring System (DGMS) [10].

The voting system is to compare information collected from all online diesel generator sets.

If the information of one diesel generator set is not similar as the other diesel generator sets, it

is recognized as a faulty generator set. However, the voting system cannot be used when

there are only two diesel generator sets online and cannot find out a common fault on 2 or

more than 2 diesel generator sets.

Advanced Generator Protection (AGP) introduced by Cargill is used for the marine power

system with droop load sharing. If the active power and reactive power droops are known.

AGP uses a window around droop line to detect the conditions of the diesel generator sets. If a

diesel generator set goes out of this window, AGP will define it as a faulty generator. However,

this system may give the wrong response during normal operation. For example, a load step

can push the diesel generator set out of the windows of active power and reactive power droop.

And it can’t detect a small fault, which can keep all the generator inside the window. For a

heavy fault, healthy generators will also go out of the window to get a trip.

ABB designed DGMS (Diesel Generator & Monitoring System) to handle such faults by

using various types of algorithms as voting between three or more generators or looking at the

expected correlation between certain parameters that should follow each other in normal

situations, but not necessarily in faulty situations. The configuration of it is shown in Figure 1.3.

5

Figure 1.3 The configuration of DGMS

6

2. Modeling of marine power

system

This chapter is mainly focused on modeling a marine power system in Matlab Simulink. The

aim of modeling is to let the company have its own validated marine power system and the

company can use it for later research and project parameter setting. Furthermore, this model

should be improved to qualify the requirement of marine classification about marine power

system modeling. Therefore, the accuracy of the model should be high while the model

simulation speed is acceptable.

2.1 Single diesel generator model

The single diesel generator model consists of a brushless synchronous generator driven by

a diesel engine with controls. After building all components, the parameters of the model can

be calculated from the diesel engine and generator datasheets as well as the test

measurement. The model validation should be done as the requirements of the company. The

single diesel generator model is prepared for the three parallel diesel generators model.

2.1.1 Generator model

In the marine power systems, the brushless synchronous generator is mostly in use. Its

configuration is shown in Figure 2.

Figure 2.1 Configuration of brushless generator

7

The brushless generator consists of an exciter and a main generator. This section only

states the modeling of the main generator. The exciter will be described in Section 2.1.2.

The synchronous generator is a rotating machine. The relationship between torque and

rotating speed can be expressed by Newton’s second law for rotation, which is given by

Equation 2.1.

𝐽𝑔𝑑𝜔𝑟

𝑑𝑡= 𝑇𝑚𝑒𝑐ℎ − 𝑇𝑒𝑙𝑒𝑐 (2.1)

𝐽𝑔 is the moment of inertia of the generator.

𝜔𝑟 is the generator angular velocity.

𝑇𝑚𝑒𝑐ℎ is the mechanical torque from the diesel engine.

𝑇𝑒𝑙𝑒𝑐 is the electrical torque from the generator

The well known two-axis dq0-model is always used for modeling a synchronous generator.

In the two–axis dq0-model, 7 orders differential equations stating stator, rotor and damper

windings dynamics are included [11]. Saturation also is taken into account for this generator

model. Hysteresis and eddy current losses are represented by a speed dependent loss.

The transformations from abc to dq0 coordinates are shown in Equation 2.2, 2.3 and 2.4.

[

𝑒𝑑

𝑒𝑞

𝑒0

] = 𝑃𝑠 [

𝑣𝑎

𝑣𝑏

𝑣𝑐

] (2.2)

[

𝑖𝑑𝑖𝑞𝑖0

] = 𝑃𝑠 [

𝑖𝑎𝑖𝑏𝑖𝑐

] (2.3)

𝑃𝑠 =2

3

[ cos θ𝑒 cos( θ𝑒 −

2𝜋

3) cos(θ𝑒 +

2𝜋

3)

− sin θ𝑒 −sin(θ𝑒 −2𝜋

3) − sin(θ𝑒 +

2𝜋

3)

1

2

1

2

1

2 ]

(2.4)

𝑣𝑎, 𝑣𝑏, 𝑣𝑐 are the generator’s terminal voltage of phase a, b and c.

𝑖𝑎, 𝑖𝑏, 𝑖𝑐 are the generator stator current.

𝑒𝑑 is d axis stator voltage.

𝑒𝑞 is q axis stator voltage.

𝑒0 is 0 sequence stator voltage.

𝑖𝑑 is d axis stator current.

𝑖𝑞 is q axis stator current .

𝑖0 is 0 sequence stator voltage.

θ𝑒 is the angle between phase a and d axis.

8

According to the 7 orders generator model, the flux equations are shown in Equation 2.5,

2.6, 2.7, 2.8 and 2.9. The coupling inductance between damper winding and main field winding

is neglected.

𝜓𝑑 = −(𝐿𝑎𝑑 + 𝐿𝑙)𝑖𝑑 + 𝐿𝑎𝑑𝑖𝑓𝑑 + 𝐿𝑎𝑑𝑖1𝑑 (2.5)

𝜓𝑞 = −(𝐿𝑎𝑞 + 𝐿𝑙)𝑖𝑞 + 𝐿𝑎𝑞𝑖1𝑞 (2.6)

𝜓𝑓𝑑 = 𝐿𝑓𝑑𝑖𝑓𝑑 + 𝐿𝑎𝑑𝑖1𝑑 − 𝐿𝑎𝑑𝑖𝑑 (2.7)

𝜓1𝑑 = 𝐿𝑎𝑑𝑖𝑓𝑑 + 𝐿1𝑑𝑖1𝑑 − 𝐿𝑎𝑑𝑖𝑑 (2.8)

𝜓1𝑞 = 𝐿1𝑞𝑖1𝑞 − 𝐿𝑎𝑞𝑖𝑞 (2.9)

𝑖𝑓𝑑 is the rotor circuit current.

𝐿𝑓𝑑 is the self-inductance of rotor circuit.

𝐿1𝑑 is the self-inductance of d-axis damper winding.

𝐿1𝑞 is the self-inductance of q-axis damper winding.

𝜓𝑑 is the d-axis stator flux linkage.

𝜓𝑞 is the q-axis stator flux linkage.

𝜓𝑓𝑑 is the rotor circuit flux linkage.

𝜓1𝑑 is the d-axis damper winding flux linkage.

𝜓1𝑞 is the q-axis damper winding flux linkage.

The voltage equations are shown in Equation 2.10, 2.11, 2.12, 2.13 and 2.14

𝑒𝑑 =1

𝜔𝑏𝑎𝑠𝑒

𝑑𝜓𝑑

𝑑𝑡− 𝜓𝑞𝜔𝑟 − 𝑅𝑎𝑖𝑑 (2.10)

𝑒𝑞 =1


𝑑𝜓𝑞

𝑑𝑡+ 𝜓𝑑𝜔𝑟 − 𝑅𝑎𝑖𝑞 (2.11)

𝑒𝑓𝑑 =1


𝑑𝜓𝑓𝑑

𝑑𝑡+ 𝑅𝑓𝑑𝑖𝑓𝑑 (2.12)

𝑒1𝑑 =1


𝑑𝜓1𝑑

𝑑𝑡+ 𝑅1𝑑𝑖1𝑑 = 0 (2.13)

𝑒1𝑞 =1


𝑑𝜓1𝑞

𝑑𝑡+ 𝑅1𝑞𝑖1𝑞 = 0 (2.14)

𝜔𝑏𝑎𝑠𝑒 is nominal electrical angular speed.

9

In order to have a validated generator model, saturation also should be included.

The air gap flux linkage is calculated by Equation 2.15, 2.16 and 2.17.

𝜓𝑎𝑑 = 𝜓𝑑 + 𝐿𝑙𝑖𝑑 (2.15)

𝜓𝑎𝑞 = 𝜓𝑞 + 𝐿𝑙𝑖𝑞 (2.16)

𝜓𝑎𝑖𝑟 = √𝜓𝑎𝑑2 + 𝜓𝑎𝑑

22 (2.17)

𝜓𝑎𝑑 is d axis air gap flux linkage.

𝜓𝑎𝑞 is q axis air gap flux linkage.

𝜓𝑎𝑖𝑟 is air gap flux linkage.

After getting the air gap flux linkage, a saturation factor can be found, which is related to an

open circuit characteristic of the generator and the air gap flux linkage. The saturated induction

value can be calculated. They are shown in Equation 2.18, 2.19 and 2.20.

𝐾𝑠 = 𝑓(𝜓𝑎𝑖𝑟) (2.18)

If there is no saturation, Ks is a constant and equal to 1.

𝐿𝑎𝑑 = 𝐾𝑠 ∗ 𝐿𝑎𝑑𝑢 (2.19)

𝐿𝑎𝑞 = 𝐾𝑠 ∗ 𝐿𝑎𝑞𝑢 (2.20)

Moreover, the leakage inductance of a field circuit and a damper winding aren’t directly

given by the generator datasheet. In order to have a better understanding of the generator,

these values should be calculated. The time constants, transient inductance and sub transient

inductance of the generators are used to calculate those parameters [12] [13]. The calculation

equations are given in Equation 2.21, 2.22, 2.23, 2.24, 2.25 and 2.26.

𝐿𝑓𝑑𝑙 = 𝐿𝑓𝑑 − 𝐿𝑎𝑑 (2.21)

𝐿1𝑑𝑙 = 𝐿1𝑑 − 𝐿𝑎𝑑 (2.22)

𝐿1𝑞𝑙 = 𝐿1𝑞 − 𝐿𝑎𝑑 (2.23)

𝐿𝑓𝑑𝑙 = 𝐿𝑎𝑑 [(𝐿𝑑

′ −𝐿𝑙)

(𝐿𝑑−𝐿𝑑′ )

] (2.24)

𝐿1𝑑𝑙 = 𝐿𝑎𝑑𝐿𝑓𝑑𝑙

(𝐿𝑑" −𝐿𝑙)

[𝐿𝑎𝑑𝐿𝑓𝑑𝑙−𝐿𝑓𝑑(𝐿𝑑" −𝐿𝑙)]

(2.25)

𝐿1𝑞𝑙 = 𝐿𝑎𝑞 [(𝐿𝑎𝑞

" −𝐿1𝑞𝑙)

(𝐿𝑞−𝐿𝑞" )

] (2.26)

10

𝐿𝑓𝑑𝑙 is the rotor circuit leakage inductance.

𝐿1𝑑𝑙 is the d-axis leakage inductance.

𝐿1𝑞𝑙 is the q-axis leakage inductance.

𝐿𝑑′ is the d-axis transient inductance.

𝐿𝑑" is the d-axis sub transient inductance.

𝐿𝑎𝑞" is the q-axis sub transient inductance.

2.1.2 AVR and exciter

The automatic voltage regulator is designed to control the generator output voltage and the

reactive power output. Based on the recommendation from the AVR manufacturer, AVR and

the exciter model are built as the IEEE AC8B model [14] [15]. Its block diagram is shown in

Figure 2.2.

∑

+

VREF

-

VC

∑

VOEL

VUEL

+

+

Ka Ka

VRLMT/VTKA

0

∏

VT

KVHZ

VRLMT

0

∑

+

KVHZ

0

∏

FEX

FEX=f(IN)

FEX=f(IN)

KD

∑

-

+

∑ KE+

+

VX=VESE(VE)

EFD

IFD

Figure 2.2 Block diagram of an IEEE AC8B excitation system

Based on the requirements of the company, UEL, OEL, V/Hz limiter and softer starter should

also be added into the model.

Figure 2.3 and 2.4 show the block diagram of UEL and OEL [15]. The summing point type is

used for them. OEL and UEL both consist of outer loops and PI controller. Only the feedback

signals are different. The feedback signal of OEL is exciter current and the feedback signal of

UEL is the generator reactive power. Their outputs are added to the voltage set point of AVR to

control the AVR output. If the generator is over or under excited, the limiter outputs are

controlled by the reactive power set point or the exciter current with PI controller. Then their

outputs increase or decrease the set point of AVR to protect the generators.

11

∑ Kg-

+

+

∑1.5

0

1.5

0

VUELQ

QUEL_REF

Figure 2.3 Block diagram of under excitation limiter (UEL)

∑ Kg-

+

+

∑VREF

0

0VOEL

IEX

IOEL_REF

VREF

-1

Figure 2.4 Block diagram of over excitation limiter (OEL)

The V/Hz Limiter is designed to protect the generator from excessive magnetic flux that

results from low frequency or overvoltage. Its block diagram is shown in Figure 2.5. An

adjustable slope (KV/Hz) is to define the ratio between voltage and frequency. When the system

is in low frequency condition, the voltage reference is regulated by two parameters, the corner

frequency and an adjustable slope (KV/Hz). The adjustable slope (KV/Hz) defines the ratio

between voltage and frequency.

∑-

+

Generator Frequency

CornerFrequency

0

KVHZ ∏

VREF

VVHZ

Figure 2.5 Block diagram of V/Hz limiter

2.2 Diesel engine model

Many different kinds of prime mover are used in the marine power system, such as a

turbocharged medium speed diesel engine, a gas turbine and a steam turbine. However, the

most used prime mover in marine power system is the diesel engine. The diesel engine has

already been modeled by many kinds of models. The modeling complexity depends on the

applications in the model, which include the air-flow model, cylindrical combustion model and

system control. For Bakker Sliedrecht, only mechanical dynamics of the diesel engine should

be taken care of. And temperature, pressure and the cooling system should not be included.

12

The diesel engine model used here is based on the diesel engine model from L.Guzzella

and A. Amstutz [16], but doesn’t include temperature, pressure and cooling system. The

proposed diesel engine model is shown in Figure 2.6.

Figure 2.6 Configuration of diesel engine model

2.2.1 Engine model

The thermodynamic behavior is very difficult analyzing. Many papers have given many

models to simplify it. In this report, the mechanical torque is expressed as Equation 2.27, and

the thermal efficiency used here is a constant. In order to normalize the fuel mass flow, based

on the nominal torque, Equation 2.27 and 2.28, maximum mass of fuel flow injected into one

cylinder in one cycle can be calculated by Equation 2.29. After combining Equation 2.27 and

2.29, the normalized torque calculation is shown in Equation 2.30.

𝑇𝑚𝑒𝑐ℎ = 𝐻𝐿𝐻𝑉𝑚𝑓𝜂𝑡ℎ𝑒𝑟𝑚𝑎𝑙 (2.27)

𝜂𝑡ℎ𝑒𝑟𝑚𝑎𝑙 = 0.4 (2.28)

𝑚𝑓_𝑚𝑎𝑥 =𝑇𝑛𝑜𝑚𝑖𝑛𝑎𝑙

𝐻𝐿𝐻𝑉∗𝜂𝑡ℎ𝑒𝑟𝑚𝑎𝑙 (2.29)

𝑇𝑚𝑒𝑐ℎ =𝑚𝑓

𝑚𝑓_𝑚𝑎𝑥∗ 𝑇𝑛𝑜𝑚𝑖𝑛𝑎𝑙 (2.30)

𝐻𝐿𝐻𝑉 is the lower fuel heating value (42700 kJ/kg).

𝜂𝑡ℎ𝑒𝑟𝑚𝑎𝑙 is thermal efficiency.

𝑚𝑓 is the mass of fuel injected into one cylinder in one cycle.

The mass of fuel injected into one cylinder in one second is controlled by the governor. The

relationship between the mass of fuel injected into one cylinder in one second and that injected

into the diesel engine into one cylinder in one cycle is given in Equation 2.31.

Fuel Rack Position

Speed

Governor

Engine

(Thermo

dynamic)

Diesel engine output power

Output Torque

Speed Set point

Turbocharger

Emission control

(dP/dt control)

Fuel flow limit

13

𝑚𝑓 =𝑣∗2𝜋

𝜔𝑒�̇�𝑓 (2.31)

�̇�𝑓 is the mass of fuel injected into one cylinder in one second.

𝑣 is 2, if the number of strokes of diesel engine is 4.

𝜔𝑒 is the speed of the diesel engine

The mass of air injected into one cylinder in one second depends on the speed of the

turbocharger. Its calculation is given in Equation 2.32.

�̇�𝑎𝑖𝑟 = 𝑘𝑡𝑐𝜂𝑡𝑐𝜔𝑡𝑐 (2.32)

�̇�𝑎𝑖𝑟 is the mass of air into one cylinder in one second.

𝜂𝑡𝑐 is the efficiency of the turbocharger.

𝑘𝑡𝑐 is the mechanical factor of the turbocharger, which is related to dimension and

pressure ratio of the turbocharger.

The speed dynamic equation of the turbocharger is given in Equation 2.33.

�̇�𝑡𝑐 =1

𝐽𝑡𝑐(𝑇𝑡𝑐(𝑃𝑚𝑒𝑐ℎ) − 𝑇𝑡𝑐_𝑓(𝜔𝑡𝑐)) (2.33)

𝐽𝑡𝑐 is the inertia of the turbocharger

𝑇𝑡𝑐(𝑃𝑚𝑒𝑐ℎ) is the turbine torque. The turbocharger is driven by exhaust gas, and the

thermal and kinetic energy of exhaust gas are related with the diesel engine output power.

Therefore, the turbine torque is expressed as a function of diesel engine output power.

𝑇𝑡𝑐_𝑓(𝜔𝑡𝑐) is the friction of turbocharger which is related to the speed of turbocharger.

2.2.2 Governor

The governor is modeled by the PID controller and the droop control. The droop control is

prepared for active power sharing when generators are parallel [17]. The block diagram is

shown in Figure 2.7.

∑

+

-Speed sensor

Ka

PIDMAX

0

Droop Diesel engine output power

Speed setpoint Governor Output

-

Figure 2.7 Configuration of governor

14

Regarding PID controller, proportional gain, integral gain, derivative gain and derivative

filter time constant are set as the diesel engine manufacturer’s recommendation.

2.2.3 Emission control

Emission control is designed to prevent black smoke when a diesel engine is accelerating.

When there is a load step, the governor will give full fuel command to the fuel rack, because

the governor receives a positive speed error. However, because of the time delay of the

turbocharger, the rate of change of air flow cannot follow that of fuel. Then the ratio of fuel to

air becomes very large, and fuel cannot combust completely. The black smoke comes out.

Therefore, based on the recommended rate of change of power and maximum ratio of fuel

to air from datasheet of diesel engine [18], emission control limits maximum fuel flow quantity.

The equation of the ratio of fuel to air is shown in Equation 2.34. The maximum fuel flow

quantity is calculated by maximum ratio of fuel to air and the mass of air injected into one

cylinder in one second given by Equation 2.32. With the emission control, the diesel engine

doesn’t emit black smoke.

λ =�̇�𝑓

�̇�𝑎𝑖𝑟 (2.34)

λ is the ratio of fuel to air.

�̇�𝑓 is the mass of fuel injected into one cylinder in one second

�̇�𝑎𝑖𝑟 is the mass of air injected into one cylinder in one second.

Some types of diesel engine and governor don’t include the emission control. Therefore, an

enable input is used for the emission control.

2.3 Consumer load

The consumer load is also an important component of the single diesel generator model.

Two static load models are used in this chapter. They are the constant impedance and

constant power load.

2.3.1 Constant impedance load

The constant impedance load represents the passive loads, such as distribution network

and hotel loads. The active power and reactive power of it will be affected by voltage and

frequency variation. The constant impedance load can be represented by Equation 2.35 and

2.36. Based on the system nominal voltage, system nominal frequency, required active power

15

and required reactive power, the value of induction and resistance can be calculated as

Equation 2.37, 2.38 and 2.39.

𝑣 = 𝑖𝑍 (2.35)

𝑍 = 𝑅 + 𝑋𝑗 (2.36)

𝑅 =𝑣𝑛𝑜𝑚2

𝑃𝑠𝑒𝑡 (2.37)

𝑋 =𝑣𝑛𝑜𝑚

2

𝑄𝑠𝑒𝑡 (2.38)

𝑋 = 2𝜋𝑓𝑛𝑜𝑚𝐿 (2.39)

𝑣𝑛𝑜𝑚 is the system nominal voltage

𝑓𝑛𝑜𝑚 is the system nominal frequency

𝑃𝑠𝑒𝑡 is the active power set point under nominal voltage and frequency

𝑄𝑠𝑒𝑡 is the reactive power set point under nominal voltage and frequency

2.3.2 Constant power load

The variable frequency drive can be represented by a constant power load. The active

power and reactive power of constant power load cannot be influenced by voltage and

frequency variation. The dynamic equations of resistance and induction are shown in Equation

2.40, 2.41, 2.42 and 2.43.

𝑑𝑅

𝑑𝑡=

1

𝜏load(𝑃 − 𝑃𝑟𝑒𝑓) (2.40)

𝑑𝐿

𝑑𝑡=

1

𝜏𝑙𝑜𝑎𝑑(𝑄 − 𝑄𝑟𝑒𝑓) (2.41)

𝑍 = 𝑅 + 𝑋𝑗 (2.42)

𝑋 = 2𝜋𝑓𝐿 (2.43)

𝑃𝑟𝑒𝑓 is the active power set point

𝑄𝑟𝑒𝑓 is the reactive power set point

𝜏𝑙𝑜𝑎𝑑 is the time constant of constant power load

16

2.4 Validation

After building a completed diesel generator model, the model validation is the next step.

Because of not having enough measurement, until now, only generator model validation can

be realized and it can be accomplished by comparing the result of generator test with that of

simulation under same kind test.

First, based on the main generator datasheet and the exciter test, the parameters of main

generator and excitation system are input into the model. The datasheet of the generator is in

Appendix A.

Then, the generator voltage step test is used for the model validation. When the generator is

running at the nominal speed, a voltage step is given to the exciter stator. The test

configuration and measurement points (exciter stator current, main generator rotor voltage,

generator terminal voltage) are shown in Figure 2.8. And the test setup is shown in Figure 2.9.

G3~

E x c i t e r

E

A

V

V

Figure 2.8 Generator voltage step test configuration

17

Figure 2.9 Generator voltage step test setup

Furthermore, the same type of voltage step can be simulated in the model. After getting the

simulation results and the test measurements, the comparisons between them are shown in

Figure 2.10, 2.11 and 2.12.

Figure 2.10 Terminal voltage comparison

0.00

1000.00

2000.00

3000.00

4000.00

5000.00

6000.00

7000.00

8000.00

0 5 10 15

Term

inal

Vo

ltag

e(V

)

Time(s)

Terminal Voltage

Matlab Result

Measurement

18

Figure 2.11 Main generator rotor voltage comparison

Figure 2.12 Exciter stator current comparison

Because the three phase short circuit test is harmful to the generators, the vessel owner

doesn’t want to do this test. Therefore, we can’t get its waveform data. But we can get related

data from generator datasheet. In order to accomplish the short circuit comparison, first, we

can simulate the three phase short circuit test in the model. Then, based on the recommended

synchronous generator parameter measurement and calculation from IEEE [19] and IEC [20],

the simulation waveform, shown in Figure 2.13, can be transferred to the short circuit

-10

0

10

20

30

40

50

60

0 2 4 6 8 10 12 14

Mai

n G

en

era

tor

Ro

tor

Vo

ltag

e(V

)

Time(s)

Main Generator Rotor Voltage

Matlab Result

Measurement

-0.5

0

0.5

1

1.5

2

2.5

3

-1 1 3 5 7 9 11 13 15

Exci

ter

Stat

or

Cu

rren

t(A

)

Time(s)

Exciter Stator Current

Matlab Result

Measurement

19

parameters that are stated in the generator datasheet. Finally, after comparison, the results of

simulation fit those of the generator datasheet.

Figure 2.13 Simulation short circuit test current waveform

Because the diesel engine test measurement can’t be obtained, the validation of diesel

engine isn’t included in this thesis, which should be finished after this thesis.

Even though the diesel engine is not validated, the dynamic behavior of the diesel generator

under a constant power load step test should be investigated. A constant power load step is

implemented in a test and the simulation model. Its active power is 1MW and PF is 0.995.

There are two load steps shown in Figure 2.14. The first one is implemented on 65s and the

other one is on 90s.

Figure 2.14 Voltage and frequency comparison between simulation and measurement

Based on a constant power load step comparison, a small difference can be found. There

are two reasons resulting in this difference. The first one is that the diesel engine is not

validated, and more controllers should be added to the diesel engine model. The second

reason is that there is the different load value between simulation and practice, and we can’t

set completely the same value for both situations.

20

3. Three parallel diesel generators

model

After finishing the single diesel generator model, the three parallel diesel generators model

can be built. The three diesel generator sets are the same in it. The configuration of the three

parallel diesel generators model and the measurement locations are shown in Figure 3.1.

Besides connecting three single diesel generator models to the same bus, synchronization

function as well as active and reactive power sharing also should be added to the three parallel

diesel generators model [21]. Droop controls are built inside the AVR and the governor. In this

Section, the detail description of them will be given.

After building the whole three parallel diesel generators model, in order to understand the

behavior of the model, different scenarios are simulated. They are a constant impedance load

step test, 7 defined excitation system faults and 5 defined prime mover faults [22].

G3~

G3~

G3~

dP/dtlimit

dP/dtlimit

dP/dtlimit

Load Load Load

DG set1 DG set2 DG set3

Diesel Engine Output Power

Exciter Current

Active Power Reactive Power

Net Frequency Net Voltage

Figure 3.1: Three parallel diesel generators model configuration and measurement position.

21

3.1 Active and reactive power droop

In order to finish the active power and reactive power sharing in the three parallel diesel

generators model, the active and reactive power droop need to be built.

Regarding the active power droop, the compensated droop is used for it. Its slope is 4%.

The compensated droop controls the frequency of operation point as 60Hz by increasing or

decreasing the speed set point. The highest frequency on the droop line reaches when the

diesel engine takes no load, and the lowest frequency on the droop line reaches when the

diesel engine takes full load. The formula expression of active power droop is given in

Equation 3.1. Its diagram expression, when the generator takes no load, is given in Figure 3.2.

Droop% =No load frequency – Full load frequency

No load frequency ∗ 100 (3.1)

Figure 3.2 Active power droop

Regarding the reactive power droop, it uses fixed droop. Its slope is 5%. In the fixed reactive

power droop, the voltage set point doesn’t change with the operation point. The highest

voltage on the droop line reaches when the generator takes no reactive power, and the lowest

voltage on the droop line reaches when the generator takes the same value of reactive power

as the value of its rated apparent power. The formula expression of reactive power droop is

given in Equation 3.2. Its diagram expression is given in Figure 3.3.

Droop% =no reactive power voltage−full reactive power voltage

no reactive power voltage ∗ 100 (3.2)

0W; 60Hz

3,84MW; 57,6Hz

57

57.5

58

58.5

59

59.5

60

60.5

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

Fre

qu

en

cy(H

z)

Diesel Engine Output Power (MW)

Active Power Droop

22

Figure 3.3: Reactive power droop

3.2 Load step test

The load step test is implemented on the 3 parallel diesel generators model. The load used

in the test is a constant impedance load. The impedance value of load is calculated by the set

active power and reactive power under nominal frequency and voltage. A 3MW and PF = 0.95

load step is implemented at 20s. The dP/dt limitation of the load step is 1MW/s. The simulation

results of the load step test are shown in Figure 3.4. The oscillation of voltage in Figure 3.4

results from the AVR PID parameter setting.

4,1MVar; 6,6kV

0Var; 6,93kV

6.55

6.6

6.65

6.7

6.75

6.8

6.85

6.9

6.95

0 1 2 3 4 5

LL V

olt

age

(KV

)

Reactive Power(MVar)

Reactive Power Droop

23

Figure 3.4: Load step test simulation results

3.3 Excitation system and prime mover faults

simulation results

Understanding the behaviors of the generator during excitation system and prime mover

faults is an important step to build CDG. 7 kinds of excitation system faults and 5 kinds of

prime mover faults are simulated in this section.

3.3.1 Excitation system faults simulation results

In the excitation system fault simulation, before the faults, each generator is taking 2MW

constant impedance load (PF =0.95), and 7 kinds of excitation system faults are tested. The

first 3 faults are related to AVR. The other 4 faults are related to the exciter and generator rotor.

All excitation system faults are implemented only on DG set 1 (Gen1) at 20s.

24

Fault 1 and Fault2 are that the AVR output suddenly increases or decreases 10% AVR

output voltage and fixes. Fault 3 is that the AVR output increases to maximum. Figure 3.5

gives their configuration.

Figure 3.5: Fault 1, 2 and 3 configuration

The other 4 faults are short circuit or open circuit occurring on the exciter stator or the main

generator rotor. Figure 3.6 gives their configuration.

AVR

Fault4

Fault 5

Fault6

Fault 7

Exciter Current transducer

Figure 3.6: Fault 4, 5, 6 and 7 configuration

All excitation system faults scenarios are concluded below:

Fault 1: AVR output increases 10% and fixes.

Fault 2: AVR output decreases 10% and fixes.

Fault 3: AVR output increases to maximum.

Fault 4: Exciter stator open circuit.

Fault 5: Exciter stator short circuit.

Fault 6: Main generator rotor open circuit.

Fault 7: Main generator rotor short circuit.

Fault 1 and Fault 2 simulation results are shown in Figure 3.7 and 3.8. The other 5 faults

results are given in Appendix B.

AVR

Exciter

Stator

Fault 1/2: 1.1 or 0.9 times the AVR output before the fault Fault 3: Maximum output of AVR E

25

Figure 3.7: Fault 1(AVR increases 10% its output) simulation results

26

Figure 3.7: Fault 2(AVR decreases 10% its output) simulation results

We can find that, during excitation system faults, the reactive power of the faulty generator

deviates that of the healthy generators, meanwhile, the total reactive power doesn’t change,

because voltage has nearly no change. Furthermore, even though the faulty generator

absorbs or provides abnormal reactive power, the healthy generators still follow the reactive

power droop to maintain voltage. The exciter current has the same behavior as the reactive

power.

27

3.3.2 Prime mover faults simulation results

In the prime mover fault simulation, before the faults, each generator is taking 2MW constant

impedance load (PF =0.95), and 5 kinds of prime mover faults are tested. The first 2 faults are

related to governor. They are that the position of fuel rack will move up or down 20% of the

position before the fault and fixes. The other 3 faults are related to diesel engine. The diesel

engine suddenly takes no load (ex. The fuel pipe is blocked), full load or no speed (ex. The

piston is blocked) instantly. Prime mover faults will be implemented only in DG set 1 (Gen1) at

20s.

Prime mover fault scenarios are concluded below:

Fault 8: The position of fuel rack increases 20% and fixes.

Fault 9: The position of fuel rack decreases 20% and fixes.

Fault 10: The diesel engine takes full load.

Fault 11: The diesel engine takes no load.

Fault 12: The diesel engine is blocked instantly.

The Fault 8 and Fault 9 simulation results are shown in Figure 3.8 and 3.9. The other 3 faults

results are given in Appendix B.

28

Figure 3.8: Fault 8 (Diesel engine fuel rack increases 20%) simulation results

Figure 3.9: Fault 9 (Diesel engine fuel rack increases 20%) simulation results

29

Regarding prime mover faults, the active power of the faulty generator deviates that of the

healthy generators. Meanwhile, the total active power is almost constant, because voltage and

frequency have nearly no change. Even though faulty generator absorbs or provides abnormal

active power, the healthy generators still follow active power droop to maintain frequency.

Regarding exciter current, exciter current has the same behavior as active power after 21s.

However, between 20s and 21s, there is a dynamic period in exciter current.

4. Common diesel generator

protection design

With understanding the performance of faulty and healthy generators during the excitation

system and prime mover faults and concluding their characteristics, a protection method

especially for excitation system and prime mover can be found. The system is named as

Common Diesel Generator protection (CDG). It should include two parts. The first part is fault

detection, which can detect the faulty generator. The other part is the logical control of CDG to

decide the response of it.

For the first part, the main functions of fault detection in CDG are listed below:

1. Excitation system detection

2. Prime mover detection

3. Voting system

4. Operation window

They will be described in sub section 4.2, 4.3, 4.4, 4.5 and 4.6. The content of logical control

will be given in sub section 4.7.

4.2 Excitation system detection

4.2.1 Mechanism

Based on the excitation system fault simulation results in section 3.3, we can find out that

voltage, reactive power and exciter current will deviate from the value before the fault. It can be

named as the expected value and normal operation value.

After analyzing all excitation system faults simulation results, Table 4.1 and 4.2 conclude the

deviation and derivative of the faulty and healthy generator. The deviation is remarked by blue

30

boxes and derivative is remarked by purple boxes.

In the tables, 𝑄 means the actual reactive power. 𝑄𝑒𝑥𝑝 means the expected reactive

power. 𝑉 means the actual generator voltage. 𝑉𝑒𝑥𝑝 means the expected generator

voltage. 𝐼𝑒𝑥 means the actual exciter current and 𝐼𝑒𝑥_𝑒𝑥𝑝 means the expected exciter current.

Table 4.1 The performance of faulty generator during different kinds of situations

Table 4.2 The performance of healthy generator during different kinds of situations

By analyzing the tables above, we can sort these 8 conditions into 3 groups. The green

group is Normal Operation. The Orange group is AVR Dependent Fault. And the Red group is

AVR Independent Fault (generator internal fault).

In order to detect the faulty generator, we need find out the boundary of generator behavior

between normal and faulty operation, and the boundary between the faulty generator and

healthy generator during faults.

Conditions

𝑄

𝑑𝑄

𝑑𝑡

𝑄 − 𝑄𝑒𝑥𝑝

𝑉

𝑑𝑉

𝑑𝑡

𝑉 − 𝑉𝑒𝑥𝑝

𝐼𝑒𝑥

𝑑𝐼𝑒𝑥

𝑑𝑡

𝐼𝑒𝑥 − 𝐼𝑒𝑥_𝑒𝑥𝑝

Load step

>0

+

≈ 0

>0

-

≈0

>0

+

≈0

Fault1: AVR output increases 10%

>0

+

>0

>0

+

>0

>0

+

>0

Fault2: AVR output decreases 10%

>/<0

-

<0

>0

-

<0

>0

-

<0

Fault3: AVR output increases to maximum

>0

++

>0

>0

+

++

>0

++

>0

Fault4: Exciter stator Open circuit

<0

--

<0

>0

--

<0

=0

--

<0

Fault5: Exciter stator short circuit

<0

--

<0

>0

--

<0

>0

++

>0

Fault6:Main generator rotor short circuit

<0

--

<0

>0

--

<0

>0

++

>0

Fault7:Main generator rotor open circuit

<0

--

<0

>0

--

<0

>0

++

>0

Conditions

𝑄

𝑑𝑄

𝑑𝑡

𝑄 − 𝑄𝑒𝑥𝑝

𝑉

𝑑𝑉

𝑑𝑡

𝑉 − 𝑉𝑒𝑥𝑝

𝐼𝑒𝑥

𝑑𝐼𝑒𝑥

𝑑𝑡


Load step

>0

+

≈ 0

>0

-

≈0

>0

+

≈0

Fault1: AVR output increases 10%

>/<0

-

<0

>0

+

>0

>0

-

<0

Fault2: AVR output decreases 10%

>0

+

>0

>0

-

<0

>0

+

>0

Fault3: AVR output increases to maximum

<0

--

<0

>0

+

++

≈ 0

--

<0

Fault4: Exciter stator Open circuit

>0

++

>0

>0

--

<0

>0

++

>0

Fault5: Exciter stator short circuit

>0

++

>0

>0

--

<0

>0

++

>0

Fault6:Main generator rotor short circuit

>0

++

>0

>0

--

<0

>0

++

>0

Fault7:Main generator rotor open circuit

>0

++

>0

>0

--

<0

>0

++

>0

31

First, we discuss about the boundary of generator behavior between normal operation and

faults. Voltage, reactive power and exciter current will all follow the droop regulation and be

closed to the expected value. Only the voltage deviates from the expected value a little bit,

because of dynamic. However, during the faults, reactive power and voltage deviates from the

expected value a lot. Therefore, by analyzing the behavior of reactive power and voltage, the

boundary of generator behavior between normal operation and faults can be found.

Then, we discuss about the boundary of generator behavior between the faulty generator

and healthy generator during faults. We can find that voltage, reactive power and exciter

current of healthy generators can follow the droop regulation. However, voltage, reactive

power and exciter current of faulty generators doesn’t follow the droop regulation.

Furthermore, during the different groups of faults, the behaviors of generators are also

different. In the AVR Dependent Fault, the deviation and derivative of voltage, reactive power

and exciter current have the same direction. In the AVR Independent Fault, the deviation and

derivative of exciter current has the opposite direction to that of voltage and reactive power.

Therefore, we can have a clear boundary among healthy generators, a generator with AVR

Dependent Fault and a generator with AVR Independent Fault.

In derivative analysis, we also can find out that there is a same boundary between faulty

generator and healthy generator as deviation analysis. However, during the faults, some

transients occur in each parameter, which lead the boundary between the healthy and faulty

generator not be clear as that of deviation. Therefore, derivative detection cannot be a decisive

detection function.

Above all, we can use the characteristic of deviation and derivative during excitation system

faults to detect the faulty generator.

4.2.2 Expected value calculation

In this section, the calculation of expected value is discussed.

Expected reactive power

In normal operation, the reactive power of each generator will be controlled by reactive

power droop, and the whole reactive power online will be shared by generators evenly.

It means that the expected reactive power of each generator can be calculated by Equation

4.1.

𝑄𝑒𝑥𝑝 =𝑄𝑛𝑒𝑡

𝑛 (4.1)

32

𝑄𝑛𝑒𝑡 is the total reactive power online

𝑛 is the number of generators online.

Expected voltage calculation

In reactive power load sharing, we use fixed reactive power droop. Therefore, based on the

droop setting and expected reactive power of the generator, we can get the expected voltage.

The expected voltage can be calculated as Equation 4.2.

𝑉𝑒𝑥𝑝 = 𝑉𝑠𝑒𝑡 − 𝑄𝑒𝑥𝑝 ∗ 𝑑𝑟𝑜𝑜𝑝% (4.2)

𝑉𝑠𝑒𝑡 is the terminal voltage when the generator takes no reactive power.

Expected exciter current calculation

Figure 4.1 shows the simplified single line diagram of a brushless synchronous generator.

Eex

RexRf

E

Xd

Exciter Generator

Iex If

Figure 4.1 Brushless synchronous generator simplified single line diagram

According to the generator test, we know that the relation among exciter current (𝐼𝑒𝑥), exciter

rotor internal voltage (𝐸𝑒𝑥) and main generator rotor current (𝐼𝑓) is almost linear, and the exciter

has nearly no saturation in its operation region. Therefore, we can get the relationship shown

in Equation 4.3.

𝐼𝑒𝑥 ∝ 𝐸𝑒𝑥 ∝ 𝐼𝑓 (4.3)

When we talk about the relationship between the main generator rotor current (𝐼𝑓) and the

main generator internal voltage (𝐸), there is saturation between them. We can use linear line to

replace the saturation curve in generator operation region. It means that 𝑋𝑑 is constant in

certain operation region. The reason why 𝑋𝑑 is constant is that 𝑋𝑑 changes with the

saturation condition of air gap in the generator and, the saturation condition of air gap will keep

almost constant during operation, because the output voltage of generator changes very small

(AVR function and droop). In other words, the generator terminal voltage (not induced voltage)

is related to the flux in air gap. And flux in air gap determines the saturation level in air gap and

the value of 𝑋𝑑.

33

Figure 4.2 Synchronous generator open and short circuit characteristic curve

Furthermore, based on Figure 4.2 [23], using the Modified air gap line (Oc), we can find out

the value of 𝑋𝑑 under the rated terminal voltage. This value also can be found in the

datasheet of generator. It is named as Saturated 𝑋𝑑.

The active power and reactive power of the synchronous generator can be calculated by

Equation 4.4 and 4.5 [24].

𝑃 =|𝑉𝑡||𝐸|

𝑋𝑑𝑠𝑖𝑛𝛿 (4.4)

𝑄 =|𝑉𝑡|

𝑋𝑑(|𝐸|𝑐𝑜𝑠𝛿 − |𝑉𝑡|) (4.5)

𝑃 is the active power of the generator.

𝑉𝑡 is the terminal voltage of the generator.

𝛿 is the phase angle between terminal voltage and internal voltage.

𝑄 is the reactive power of the generator.

At steady state, based on the reactive power droop and constant 𝑋𝑑, we can get internal

voltage and main generator rotor current by combining Equation 4.4 and 4.5. Their calculation

are given in Equation 4.6 and 4.7,

𝐸 ≅ 𝐼𝑓 ∗ 𝑋𝑑 =√(𝑋𝑑𝑄+𝑉𝑡

2)2+(𝑃𝑋𝑑)2

Vt (4.6)

𝐼𝑓 = √(𝑃

𝑉𝑡)2 + (

𝑄

𝑉𝑡+

𝑉𝑡

𝑋𝑑)2 (4.7)

34

Equation 4.9 is obtained by using Equation 4.8 to replace 𝑉𝑡 in Equation 4.7. Now the

relationship between main generator rotor current (𝐼𝑓), active power (𝑃) and reactive power (𝑄)

is known.

𝑉𝑡 = 1.05 − 0.05 ∗ 𝑄 (4.8)

𝐼𝑓 ≈ √(𝑃

1.05−0.05∗𝑄)2 + (

𝑄

1.05−0.05∗𝑄+

1.05−0.05∗𝑄

𝑋𝑑)2 (4.9)

Then, based on Equation 4.9, we can plot the diagram of the main generator rotor current

and the reactive power under different active power (here we use 𝑋𝑑 as 1.1pu). The diagram

is shown in Figure 4.3.

Figure 4.3 The relation between the main generator rotor current and the reactive

power under different active power

According to Figure 4.3, the conclusion shows that under certain value of active power (𝑃),

main generator rotor current (𝐼𝑓) has the linear relation with reactive power (𝑄). Therefore,

based on Equation 4.3, we can conclude the relationship among active power (𝑃), reactive

power (𝑄), and exciter current (𝐼𝑒𝑥). It is shown in Equation 4.10.

𝐼𝑒𝑥 = [𝑆𝑙𝑜𝑝𝑒(𝑃𝑒𝑥𝑝) ∗ 𝑄𝑒𝑥𝑝 + 𝐼𝑛𝑡𝑒𝑟𝑐𝑒𝑝𝑡(𝑃𝑒𝑥𝑝)] (4.10)

The function “Slope” and “Intercept” can be decided by various PF load test measured data.

Equation 4.10 is only applied when the system uses the compensated active power droop. If

the fixed active power droop is used in the system, a factor related to the frequency should be

0

0.5

1

1.5

2

2.5

0 0.2 0.4 0.6 0.8 1

I f(p

u)

Q(pu)

1.0pu P

0.8pu P

0.6pu P

0.4pu P

0.2pu P

35

added. The relationship between the frequency and exciter current is shown in Equation 4.11.

𝑉𝑡 ∝ 𝐼𝑓 ∗ 𝑓 ∝ 𝐼𝑒𝑥 ∗ 𝑓 (4.11)

And the expected exciter current calculation changes from Equation 4.10 to 4.12.

𝐼𝑒𝑥 = [𝑆𝑙𝑜𝑝𝑒(𝑃𝑒𝑥𝑝) ∗ 𝑄𝑒𝑥𝑝 + 𝐼𝑛𝑡𝑒𝑟𝑐𝑒𝑝𝑡(𝑃𝑒𝑥𝑝)] ∗ 𝐶𝑜𝑛𝑠𝑡𝑎𝑛𝑡 ∗ 𝑓 (4.12)

4.3 Prime mover detection

4.3.1 Mechanism

Based on the prime mover fault simulation result in section 3.3, we can find out that

frequency, active power and exciter current will deviate from the value before the faults. It also

can be named as the expected value and normal operation value.

After analyzing all prime mover faults simulation results, Table 4.3 and 4.4 conclude the

deviation value and derivative of the faulty and healthy generator. The deviation is remarked

by blue boxes and derivative is remarked by purple boxes.

In the tables, 𝑃 means the actual active power. 𝑃𝑒𝑥𝑝 means the expected active power. 𝑓

means the actual generator frequency. 𝑓𝑒𝑥𝑝 means the expected generator frequency. 𝐼𝑒𝑥

means the actual exciter current and 𝐼𝑒𝑥_𝑒𝑥𝑝 means the expected exciter current.

Table 4.3 The performance of faulty generator during different kinds of situations

Conditions

𝑃

𝑑𝑃

𝑑𝑡

𝑃 − 𝑃𝑒𝑥𝑝

𝑓

𝑑𝑓

𝑑𝑡

𝑓 − 𝑓𝑒𝑥𝑝

𝐼𝑒𝑥

𝑑𝐼𝑒𝑥

𝑑𝑡


Load step

>0

+

≈ 0

>0

-

≈/< 0

>0

+

≈ 0

Fault8: Fuel rack increases 20%

>0

+

>0

>0

+

>0

>0

+

>0

Fault9: Fuel rack decreases 20%

>/<0

-

<0

>0

-

<0

>/=0

-

<0

Fault10: Fuel rack increases to maximum

>0

++

>0

>0

+

>0

>0

+

>0

Fault11: Diesel engine suddenly

takes no load

>/<0

--

<0

>0

--

<0

>/=0

--

<0

Fault12: Diesel engine has no

speed

>/<0

++/--

>/<0

>0

-

>/<0

>/=0

++/--

>/<0

36

Table4.4 The performance of healthy generator during different kinds of situations

Also, we can divide all conditions into three groups shown in the tables above. The green

group is Normal Operation. The orange group is Prime Mover Dependent Fault. The red group

is Prime Mover and Excitation System Dependent Fault. The red group will be discussed

separately. First we find the boundary of generator behavior between normal operation and

faults, and the boundary between the faulty generator and healthy generator during Prime

Mover Dependent Fault. During Normal Operation or Prime Mover Dependent Fault, active

Power (𝑃) and frequency (𝑓) of the healthy generators always follows the active power droop.

During Prime Mover Dependent Fault, active power and frequency of faulty generators change

in the same direction and don’t follow the active power droop.

In derivative analysis, we also can find out that there is the same boundary between faulty

generator and healthy generator as that in deviation analysis. However, during the fault, some

dynamics occur in each parameter, which lead the boundary between healthy and faulty

generator not to be clear as that of deviation. Therefore, derivative cannot be a decisive

detection function.

Furthermore, based on the simulation result and conclusion, even though exciter current

(𝐼𝑒𝑥) has the same behavior as active power (𝑃) in short time after the fault, the dynamic time

of exciter current after prime mover fault is so long that it is easy to lead CGD to have a wrong

response. Therefore, exciter current is not used as a detection parameter in the prime mover

detection.

At last, the red group fault is discussed. Because rotor is blocked, active power of the faulty

generator oscillates with net frequency. It isn’t suitable to be a detection parameter anymore.

However, the excitation system stops to work, because there is no speed on the rotor and no

voltage output from the exciter rotor. It means that during this fault, Orange group fault of

excitation system also exists in this fault. Therefore, we can use the detected method of the

excitation system orange group fault to detect this fault.

Conditions

𝑃

𝑑𝑃

𝑑𝑡

𝑃 − 𝑃𝑒𝑥𝑝

𝑓

𝑑𝑓

𝑑𝑡

𝑓 − 𝑓𝑒𝑥𝑝

𝐼𝑒𝑥

𝑑𝐼𝑒𝑥

𝑑𝑡


Load step

>0

+

≈ 0

>0

-

≈/< 0

>0

+

≈ 0

Fault8: Fuel rack increases 20%

>/<0

-

<0

>0

+

>0

>/=0

-

<0

Fault9: Fuel rack decreases

20%

>0

+

>0

>0

-

<0

>0

+

>0

Fault10: Fuel rack increases to maximum

</>0

--

<0

>0

+

>0

>0

+

>0

Fault11: Diesel engine suddenly

takes no load

>0

++

>0

>0

--

<0

>0

++

>0

Fault12: Diesel engine has no

speed

>/<0

++/

--

>/<0

>0

-

>/<0

>/=0

++/--

>/<0

37

4.3.2 Expected value calculation

In this section, the calculation of expected value is discussed.

Expected active power

In normal operation, the active power of each generator will be controlled by active power

droop, and the whole active power online will be shared by generators even.

It means that the expected active power can be calculated by Equation 4.13.

𝑃𝑒𝑥𝑝 =𝑃𝑛𝑒𝑡

𝑛 (4.13)

𝑃𝑛𝑒𝑡 is the total active power online

𝑛 is the number of generators online.

Expected frequency calculation

In active power load sharing, we use compensated droop. In compensated droop control, it

prefers to keep the frequency as 60Hz by changing the speed set point of the diesel engine.

Therefore, the speed set point, expected active power and active power droop should be used

for the expected frequency calculation. It is shown in Equation 4.14.

𝑓𝑒𝑥𝑝 = 𝑓𝑠𝑒𝑡 − 𝑃𝑒𝑥𝑝 ∗ 𝑑𝑟𝑜𝑜𝑝% (4.14)

𝑓𝑠𝑒𝑡 is the speed set point of the diesel engine

4.4 Voting system

The voting system is a function to help excitation system detection and prime mover

detection to detect the faulty generator. It can only be used when there are three or more than

three generators parallel online.

The mechanism of the voting system is that, each generator will compare with each other on

one parameter. If the system detects that there are some generators (less than the total

number of generators online) going to the opposite direction to the other generators, when the

deviation is larger than the setting value, the system will think the generators in the small group

as the faulty generators. The advantage of the voting system is that we can just use one

parameter to find faulty generator. However, the disadvantages are that the voting system is

not good at finding a common fault among 2 or more than 2 generators, and it cannot be used

in a two parallel generator sets system. Therefore, we prefer to use voting system as a

secondary detection method.

38

4.5 Operation window

During DP operation, the ship prefers to run under a smooth condition. It means that the

system should tolerate some small excitation system or prime mover faults. And the function of

the operation window is to define a tolerance region for the system. The operation window is

shown in Figure 4.4, the green area means a safe area. The dash yellow indicates the

boundary of the green area. And the red line is defined by the threshold of the primary

protection. Even if the excitation system detection or prime mover detection find the faulty

generator, the CGD will only give alarm and not trip the faulty generator, if all the generators

are in the green area. When the system doesn’t find the faulty generator, and one parameter

goes out of the red region, the bus tie circuit breaker should open immediately.

Figure 4.4 Operation window (PQ operation window on the top left, active power droop

on the top right, reactive power droop on the bottom)

Rated Power

Q (Kvar)

Terminal Voltage (V)

Q (Kvar)

P (Kw) P (kW)

Frequency (Hz）

39

4.6 Deviation detection simulation results

Based on the concepts described in section 4.1 and 4.2. The detection model of it is built.

Because deviation is a decisive parameter, the deviation of load step test, Fault 1, 2, 8 and 9

are given in Figure 4.5, 4.6, 4.7, 4.8 and 4.9. The deviation results of other faults are given in

Appendix C. The derivative results of all conditions are given in the folder.

Figure 4.5 Load step test, the deviation of parameters

40

Figure 4.6 Fault1 (AVR increases 10% its output), the deviation of parameters

Figure 4.7 Fault2 (AVR decreases 10% its output), the deviation of parameters

41

Figure 4.8 Fault8 (Diesel engine fuel rack increases 20%), the deviation of parameters

Figure 4.9 Fault9 (Diesel engine fuel rack decreases 20%), the deviation of parameters

42

The simulation results give us the same conclusion as Table 4.1, 4.2, 4.3 and 4.4. During the

load step test, the difference between measured exciter current and exciter current function

output is very small and is much smaller than the exciter current deviation during excitation

system fault. Therefore, the expected exciter current calculation is acceptable.

In Figure 4.8 and 4.9, during prime mover faults, even though the exciter current can give us

the right conclusion after 21s, the dynamics between 20s and 21s is so large that it is easy to

lead the system’s wrong response. Therefore, for safe aspect, exciter current will not be taken

into account to detect prime mover faults.

4.7 CDG structure in simulation

After building and testing the detection blocks of CDG, which are main functions of CDG,

voting system and dynamic window can be added to complete the CDG model. Figure 4.8

shows the logical structure of the prime mover detection with dynamic windows and voting

system. Figure 4.9 shows logical structure of excitation system detection with dynamic

window.

There are 3 deviation detection blocks to detect orange and red group faults in excitation

system and prime mover. Each deviation detection block has its own deviation level block to

determine how heavy the fault is. If the deviation remains in first level, there is no alarm from

CGD. If the deviation passes beyond the first deviation level and stay in the second deviation

level, the CDG gives alarm. CDG gives a tripping command, if one generator runs out of green

area of dynamic window or the deviation of the faulty generator excesses the second deviation

level.

According to the characteristic of derivative detection, the derivative detection is used to

detect heavy fault. If the derivative detection and deviation detection give alarms at the same

time, a trip command is sent out by CDG after a short time delay.

Because of the weakness of voting system, voting system will sent an alarm when one

generator is running out of green area of dynamic area. If the faults still are there after very

long time delay, the voting system sends a trip command.

The parameters of the whole system depend on the generator datasheet and the system

configuration.

43

Fig

ure

4.8

Config

ura

tion o

f excita

tion s

yste

m p

rote

ctio

n in

CD

G

44

Fig

ure

4.9

Config

ura

tion o

f prim

e m

over p

rote

ctio

n in

CD

G

45

5. CDG validation

According to the proposal of this master thesis, the CDG is supposed to be a commercial

production later. Therefore, the validation of CDG should be implemented. In order to finish

this step, a test setup for CDG should be built and CDG simulation block should be transferred

into PLC program. At last, the CDG can be tested by implementing excitation system and

prime mover faults on the test setup when the CDG PLC program is running.

5.1 Test setup

The setup consists of three generator sets, a main switch board and loads. The setup

configuration is shown in Figure 5.1.

Fig

ure

5.1

Config

ura

tion o

f CD

G te

st s

etu

p

46

Regarding the prime mover, because the company doesn’t have its own diesel engines for

tests, motors with frequency drives are used as prime movers to replace the diesel engines. 2

kinds of generators are used in the setup. The generator set 1 and 2 use one kind of generator,

which datasheet is given in Appendix D. The generator set 3 uses another kind of generator,

which datasheet is given in Appendix E.

Two pure resistors and a motor with frequency drive are used as loads in the setup. The

frequency drive can determines how much reactive power it requires. And the motor drives

another motor that determines the required active power and plays a role as a generator to

feed energy back to the system.

The synchronization function of this setup is realized by auto synchronization module. The

reactive power droop is same for all the generator sets. Its setting is shown in Figure 5.2.

However, generator set 3 has the different active power droop from generator set 1 and 2.

The reason why different active power droop uses for generator set 2 and 3 is that they can

always have the same per unit active power value. This kind of active power setting can

prevent the diesel engine from overload. The active power droop setting of generator set 1 and

2 is shown in Figure 5.3. And the active power droop setting of generator set 3 is shown in

Figure 5.4.

Figure 5.2 Setup reactive power droop.

0 kVar, 400V

36 kVar, 380V

375

380

385

390

395

400

405

0 5 10 15 20 25 30 35 40

Genera

tor

Term

inal V

oltage (

V)

Reactive Power(kVar)

Setup Reactive Power Droop

47

Figure 5.3 Generator 1 and 2 active power droop

Figure 5.4 Generator 3 active power droop

This is the final version of the test setup. The generator set 1 and 2 are new generators and

ordered from the manufacturer on April. The first new generator is in storage and delivered

very fast. However, the second new generator is not in storage and the delivery time of it is

very long. Therefore, in this master thesis, only generator set 2 and 3 are used to build two

parallel generator sets system. The three parallel generator sets system will be investigated

after this master thesis.

0 kW, 52 Hz

34 kW, 50 Hz

49.5

50

50.5

51

51.5

52

52.5

0 5 10 15 20 25 30 35 40

Fre

quency (

Hz)

Active Power (kW)

Generator 1 and 2 Active Power Droop

0 kW, 52 Hz

28.8 kW, 50 Hz

49.5

50

50.5

51

51.5

52

52.5

0 5 10 15 20 25 30 35

Fre

quency (

Hz)

Active Power (kW)

Generator 3 Active Power Droop

48

After building the two parallel generator sets setup, some photos are taken from the setup.

The generator set 2 is shown in Figure 5.4.

Figure 5.4 Generator set 2

The generator set 3 is shown in Figure 5.5.

Figure 5.5 Generator set 3

49

The drive cabinets for the motors are shown in Figure 5.6

Figure 5.6 Drive cabinets

The main switch board is shown in Figure 5.7

Figure 5.7 Main switch board

50

The motor load is shown in Figure 5.8

Figure 5.8 Motor load

51

5.2 Test setup generator validation

After building the test setup, the generators in the test setup should be validated by the

Matlab Simulink model. There are two reasons for these validations. The first one is that it is

easy to conclude the formula for expected value calculation. The second one is that more tests

will be done on this test setup after this Master Thesis, and these tests results are very useful

to understand and improve the generator model.

The test used to validate the generators on the test setup is the same test mentioned in

Section 2.4. In order to get more measurement points, a modification is done to the generator

2. A copper ring is added on the generator 2 rotor to measure the main generator rotor voltage.

The structure of the modification is shown in Figure 5.9.

Figure 5.9 Modification of generator 2

However, due to the structure of generator 3, this modification cannot be done on generator

3. Therefore, the measurement points of generator 2 are exciter current, main generator rotor

voltage and terminal voltage. The measurement points of generator 3 are exciter current and

terminal voltage. In the model, the diesel engine model mentioned in Section 2.2 represents

the motor with the variable frequency drive.

After doing tests on the generators and tuning the parameters of the generator models,

comparisons between the test results and the simulation results are concluded. Figure 5.10,

5.11 and 5.12 show the comparisons of generator 2, and Figure 5.13 as well as 5.14 show the

comparisons of generator 3

Brush

Rotor copper ring

52

Figure 5.10 Generator 2 terminal peak voltage comparison

Figure 5.11 Generator 2 exciter current comparison

53

Figure 5.12 Generator 2 rotor voltage comparison

Figure 5.13 Generator 3 terminal peak voltage comparison

54

Figure 5.14 Generator 3 exciter current comparison

According to figures shown above, the difference between test measurement and simulation

result is small. When the switcher turns off, spikes are found in Figure 5.10 and Figure 5.13.

They result from the measurement equipment.

The validation of AVR is not included in this report, because the AVR the generators use is

internal. Some parameters, such as PID parameter, are inaccessible.

After building validated generator model, we investigate the expected exciter current

calculation that is mentioned in Section 4.2.2. The different PF value load tests are done on

the simulation model and the test setup. On the setup, the different PF value load tests are

realized by the motor with frequency drive. 0.95, 0.9 and 0.87 PF value are used on the tests.

In the reactive power droop, 5 percent slope is used. In the active power droop, 0 and 4

percent are used. The measured and simulated results are concluded in Table 5.1, 5.2, 5.3

and 5.4.

55

Reactive power droop : 5%

Active power droop : 0%

PF

Active

power(kW)

Reactive

power(kVar)

Measured exciter

current(A)

Simulated exciter

current(A)

Deviation(%)

0.95

6.49 2.31 0.680 0.680 0.000

10.48 3.48 0.760 0.770 -1.316

14.50 4.64 0.874 0.875 -0.114

18.60 5.84 0.991 0.992 -0.101

22.65 7.06 1.103 1.116 -1.179

0.9

6.54 3.22 0.705 0.710 -0.709

10.50 4.97 0.815 0.819 -0.491

14.50 6.73 0.936 0.938 -0.214

18.63 8.51 1.068 1.071 -0.281

22.72 10.31 1.205 1.211 -0.498

0.87

6.55 3.76 0.724 0.729 -0.691

10.53 5.84 0.850 0.847 0.353

14.55 7.98 0.975 0.978 -0.308

18.63 10.10 1.117 1.119 -0.179

22.73 12.24 1.265 1.266 -0.079

Table 5.1 Generator 2 exciter current comparison 1



PF

Active

power(kW)

Reactive

power(kVar)

Measured exciter

current(A)

Simulated exciter

current(A)

Deviation(%)

0.9

6.53 2.94 0.640 0.644 -0.625

10.51 4.72 0.758 0.761 -0.396

14.50 6.53 0.886 0.892 -0.677

18.56 8.35 1.026 1.031 -0.487

22.69 10.16 1.176 1.181 -0.425

0.87

6.48 3.44 0.662 0.660 0.302

10.50 5.561 0.790 0.788 0.253

14.51 7.74 0.927 0.929 -0.216

18.60 9.94 1.075 1.080 -0.465

22.72 12.12 1.237 1.238 -0.081


56



PF

Active

power(kW)

Reactive

power(kVar)

Measured exciter

current(A)

Simulated exciter

current(A)

Deviation(%)

0.95

6.62 3.78 0.640 0.650 -1.563

10.57 5.85 0.743 0.743 0.000

14.60 7.93 0.851 0.855 -0.470

18.67 10.11 0.975 0.976 -0.103

22.76 12.24 1.112 1.107 0.450

0.9

6.59 3.22 0.679 0.683 -0.589

10.57 4.97 0.793 0.794 -0.126

14.58 6.72 0.923 0.920 0.325

18.62 8.51 1.063 1.059 0.376

22.73 10.31 1.217 1.211 0.493

0.87

6.62 3.32 0.695 0.703 -1.151

10.58 3.46 0.824 0.826 -0.243

14.56 4.70 0.968 0.962 0.620

18.61 5.85 1.119 1.112 0.626

22.67 7.07 1.292 1.270 1.703




PF

Active

power(kW)

Reactive

power(kVar)

Measured exciter

current(A)

Simulated exciter

current(A)

Deviation(%)

0.9

6.50 2.93 0.620 0.624 -0.645

10.48 4.73 0.740 0.745 -0.676

14.53 6.57 0.880 0.886 -0.682

18.59 8.39 1.035 1.036 -0.097

22.70 10.23 1.198 1.196 0.167

0.87

6.50 3.45 0.630 0.642 -1.905

10.49 5.57 0.770 0.776 -0.779

14.53 7.75 0.916 0.926 -1.092

18.60 9.93 1.090 1.086 0.367

22.71 12.16 1.269 1.257 0.946


57

5.3 CDG test result

After validating the generators and the expected value calculation, the CDG model in Matlab

Simulink can be transferred to PLC program. The PLC program is written in structure text. The

PLC hardware used here is from Bachmann. Its configuration is shown in Figure 5.15.

Figure 5.15 The PLC configuration

The basic parameter setting of CDG in PLC is concluded in Table 5.5.

Parameters Generator set 2 Generator set 3

Exciatation

System

Detection

Reactive Power First Level

Deviation

3kVar 3kVar

Reactive Power Second

Level Deviation

6kVar 6kVar

Voltage First Level

Deviation

1.5V 1.5V

Voltage Second Level

Deviation

2.8V 2.8V

Exciter Current First Level

Deviation

100mA 100mA

Exciter Current Second

Level Deviation

210mA 210mA

Prime

Mover

Detection

Active Power First Level

Deviation

3.4kW 2.88kW

Active Power Second Level

Deviation

6.8kW 5.76kW

Frequency First Deviation 0.2Hz 0.2Hz

Frequency Second

Deviation

0.45Hz 0.45Hz

Dynamic

Window

Highest Active Power

Boundary

30.6kW 25.9kW

Lowest Active Power

Boundary

0kW 0kW

Highest Reactive Power

Boundary

30.6kVar 30.6kVar

Lowest Reactive Power -2kVar -2kVar

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Boundary

Time Delay Alarm Time Delay 600ms 600ms

Trip Long Time Delay 1000ms 1000ms

Trip Short Time Delay 500ms 500ms

Table 5.5 The basic parameter setting of CDG

In Table 5.5, we can find out that the reactive power and voltage setting deviation doesn’t

follow the reactive power droop. Also, the active power and frequency setting deviation doesn’t

follow the active power droop. The reason why we use the nonlinear deviation setting is that

the dynamic responses of the generator sets during the faults may affect the performance of

CDG, and the nonlinear setting is to reduce the influence from dynamic responses of the

generator sets on CDG.

The voting system doesn’t include here, because it cannot be used when only two generator

are running parallel. It will be enabled, when three generator sets are running parallel.

After finishing the PLC program writing and setting, some kinds of excitation system faults

and prime mover faults can be implemented to test CDG. In order to prevent the setup from

damage, small faults are implemented on the setup. They are concluded below:

1. AVR set point of generator 3 increases 4V (1% of nominal voltage).

2. AVR set point of generator 3 decreases 4V (1% of nominal voltage).

3. AVR set point of generator 3 increases 8V (2% of nominal voltage).

4. AVR set point of generator 3 decreases 8V (2% of nominal voltage).

5. Speed set point of diesel generator 2 increases 15 rpm.

6. Speed set point of diesel generator 2 decreases 15 rpm.

7. Speed set point of diesel generator 2 increases 30 rpm.

8. Speed set point of diesel generator 2 decreases 30 rpm.

When the CDG finds the fault, it sends alarm and trip signals, but doesn’t give these signals

to the contactors. Because, the healthy generator takes a large load step after tripping, and

this setup doesn’t have fast load reduction protection to prevent generators from overload.

The alarm signal can be reset by CDG, if there is no faulty generator anymore. However, the

trip signal will be self-lock, and it should be reset manually. In the figures below, the

measurements use Y axis on the left side, and the alarm and trip signals use Y axis on the

right side, where 1 is for true and 0 is for false.

59

Figure 5.16, 5.17 and 5.18 show the behaviors of setup and response of CDG when the

AVR set point of generator 3 increases 4V.

Figure 5.16 Reactive power (the AVR set point of generator 3 increases 4V)

Figure 5.17 Voltage (the AVR set point of generator 3 increases 4V)

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Figure 5.18 Exciter current (the AVR set point of generator 3 increases 4V)

Figure 5.19, 5.20 and 5.21 show the behaviors of the setup and response of CDG when the

AVR set point of generator 3 decreases 4V.

Figure 5.19 Reactive power (the AVR set point of generator 3 decreases 4V)

61

Figure 5.20 Voltage (the AVR set point of generator 3 decreases 4V)

Figure 5.21 Exciter current (the AVR set point of generator 3 decreases 4V)

62


AVR set point of generator 3 increases 8V.

Figure 5.22 Reactive power (the AVR set point of generator 3 increases 8V)

Figure 5.23 Voltage (the AVR set point of generator 3 increases 8V)

63

Figure 5.24 Exciter current (the AVR set point of generator 3 increases 8V)


AVR set point of generator 3 decreases 8V.

Figure 5.25 Reactive power (the AVR set point of generator 3 decreases 8V)

64

Figure 5.26 Voltage (the AVR set point of generator 3 decreases 8V)

Figure 5.27 Exciter current (the AVR set point of generator 3 decreases 8V)

During the normal operation, small deviation is found in the reactive power, voltage and

exciter current. The reason why there is reactive power deviation is that generator 2 and 3 use

different kinds of AVR that have different measurement accuracy. Therefore, they lead the

generators not to share reactive power evenly. And the deviation in voltage results from the

unbalance reactive power load sharing. Moreover, in the normal operation, the deviation in

exciter current exists, and the values of it are larger than those in tables in Section 5.2. It is

because the generator temperatures are different among these tests, and magnetic hysteresis

works. Even though there are deviations during the normal operation, they are small and in

acceptable range.

65

When the deviation is larger than the first level deviation, the alarm will send out. When the

deviation is larger than the second level deviation or the generator runs out of dynamic window,

the trip alarm will send out. We can find that the response time of voltage is much shorter than

those of reactive power and exciter current. The alarm and trip signals are all triggered by

voltage deviation

Figure 5.28 and 5.29 show the behavior of the setup and response of CDG when the speed

set point of diesel generator 2 increases 15 rpm.

Figure 5.28 Active power (the speed set point of diesel generator 2 increases 15 rpm)

Figure 5.29 Frequency (the speed set point of diesel generator 2 increases 15 rpm)

66

Figure 5.30 and 5.31 show the behaviors of the setup and response of CDG when the speed

set point of diesel generator 2 decreases 15 rpm.

Figure 5.30 Active power (the speed set point of diesel generator 2 decreases 15 rpm)

Figure 5.31 Frequency (the speed set point of diesel generator 2 decreases 15 rpm)

67

Figure 5.32 and 5.33 show the behaviors of setup and response of CDG when the speed set

point of diesel generator 2 increases 30 rpm.

Figure 5.32 Active power (the speed set point of diesel generator 2 increases 30 rpm)

Figure 5.33 Frequency (the speed set point of diesel generator 2 increases 30 rpm)

68

Figure 5.34 and 5.35 show the behaviors of the setup and response of CDG when the speed

set point of diesel generator 2 decreases 30 rpm.

Figure 5.34 Active power (the speed set point of diesel generator 2 decreases 30 rpm)

Figure 5.35 Frequency (the speed set point of diesel generator 2 decreases 30 rpm)

In the normal operation, the deviation in active power is much smaller than the deviation in

reactive power. It is because the same kind motors and frequency drives are used for both

generator sets. And the response time of frequency is much shorter than that of active power.

The alarm and trip signals are all triggered by the frequency deviation.

69

6. Future work and conclusion

6.1 Future work

CDG is still a quite important protection system when the marine power system runs under

closed bus-tie configuration. Therefore, more researches are required for CDG. The Simulink

marine power system model also should be improved.

Regarding the diesel generator model, the diesel engine model is required to improve. It is

interesting to validate the dynamic performance of diesel engine and the fuel consumption of

the diesel engine. The paper from A. A. L.Guzzella and the delft model DE4A can be as the

reference.

Several kinds of AVR are used by Bakker Sliedrecht. Therefore, building validated AVR

models is also important. With the help of the validated AVR model, the company can tune the

PID parameters easily.

According to the CDG test results, some deviation in exciter current can be found during the

normal operation. This exciter current deviation results from the generator temperature and the

magnetic hysteresis. Therefore, the expected exciter current calculation should take the

generator temperature and the magnetic hysteresis into account.

In the master thesis, the PLC program and CDG setting are designed for 2 parallel

generator sets. The setup is designed as 3 parallel generator sets. Therefore, when the whole

setup finishes, the PLC program and CDG setting should be updated.

6.2 Conclusion

The closed bus-tie configuration in marine power system is a good method to help the

vessel owners to decrease fuel consumption. However, when the vessel is running under

closed bus-tie configuration, excitation system faults and prime mover faults can trigger a

blackout on the vessel. This master thesis is to design a system to detect the faulty generator

and prevent vessels from a blackout. This system is named as CDG.

In order to have a better understanding of the excitation system faults and prime mover

faults, validated diesel generator model and parallel diesel generator sets model are built. By

simulating many kinds of faults and normal operations, the performances of healthy and faulty

generators are concluded. By analyzing these performances, boundaries between healthy and

70

faulty generators are found. According to the boundary analysis, the CDG simulation block is

built and tested.

According to the aims of this master thesis, The CDG is designed for the commercial use.

Therefore, the validation of CDG is implemented. There are three steps to finish the CDG

validation. The first step is to build a two parallel generator sets setup. The second step is to

build validated generators and CDG model for the setups. The last step is to transfer the CDG

simulation block to PLC program and test CDG PLC program on the setup. Based on the test

results, the performance of CDG is in the expectation.

71

7. Bibliography

[1] IMCA, "A Guide to DP Electrical Power Control Systems," International Marine

Contractors Association (IMCA), 2012.

[2] A. J.S, "Marine System Analysis," Norwegain University of Technology, 2013.

[3] A. K. Adnanes, "Maritime Electrical Installations and Diesel Electric Propulsion," ABB

marine AS, 2003.

[4] D. R. Stig Olav Settemsdal, "DP3 Class power system solution for dynamically positioned

vessels," Dynamic Positioning Conference , 2007.

[5] Hansen, "Modelling and Control of Marine Power Systems," Norwegian University of

Technology, 2000.

[6] T. A. Pedersen, "Bond graph modelling of marine power system," Norwegain University of

Technology, 2009.

[7] D. Radan, "Integrated control of marine electrical power systems," Norwegian University

of Technology, 2008.

[8] P. Johannessen, "Advanced Failure Detection and Handling in Power Management

System," Dynamic Positioning Conference , 2009.

[9] S. Cargill, "A noval solution to common mode failure in DP Class 2 power plant," Dynamic

Positioning Conference , 2007.

[10] A. m. automation, "Diesel Generator Monitoring System (DGMS)," ABB.

[11] P.Kunmar, Power System Stability and Control, McGraw-Hill.

[12] A. F. P.M. Anderson, Power System Control and Stability (Second Edition), IEEE Press,

2000.

[13] G. Shackshaft, "New Approach to the determination of synchronous machine parameters

from tests," PROC.IEE, 1974.

[14] B. Electric, "DECS-250 instruction manual," Basler Electric, 2013.

[15] I. S. B. IEEE Power Engineering Society. Energy Development and Power Generation

Committee, IEEE Recommended Practice for Excitation System Models for Power

System Stability Studies, IEEE, 2005.

[16] A. A. L.Guzzella, "Control of Diesel Engine," IEEE Control Systems, 1998.

[17] Woodward, "Governor Fundamental and Power Management Reference Manual,"

Woodward.

[18] W. F. Oy, "Installation Planning Instruction," Wartsila, 2014.

[19] I. E. M. Committee, "IEEE Guide for Test Procedures for Synchronous Machines," IEEE,

2009.

[20] "Electrical installations of ships and mobile and fixed offshore units," IEC, 1998.

[21] K. Valkeejarvi, "The ship's electrical network ,engine control and automation," Wartsila

Marine Technology.

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[22] "Power Plant Common Cause Failures," Dynamic Positioning Committee, 2012.

[23] P. Sen, Principles of electric machine and power electronics (Second Edition), John

Wiley&Son, 1998.

[24] J. J.Grainger, Power System Analysis, McGraw-Hill, 1994.

73

Appendix A Generator datasheet is given in Figure A.1.

Figure A.1 Generator datasheet

74

Appendix B

Regarding the excitation system faults, the simulation results of Fault 3, 4, 5, 6 and 7 are

shown in Figure B.1, B.2, B.3, B.4 and B.5.

Figure B.1 Fault3 (AVR increase to maximum), simulation results

75

Figure B.2 Fault4 (Exciter stator open circuit), simulation results

76

Figure B.3 Faul5 (Exciter stator short circuit), simulation results

77

Figure B.4 Fault6 (main generator rotor open circuit), simulation results

78

Figure B.5 Fault7 (main generator rotor short circuit), simulation results

79

Regarding the prime mover faults, the simulation results of Fault 10, 11 and 12 are shown in

Figure B.6, B.7 and B.8.

Figure B.6 Fault10 (diesel engine takes full load), simulation results

80

Figure B.7 Fault11 (diesel engine takes no load), simulation results

81

Figure B.8 Fault12 (diesel engine is blocked), simulation results

82

Appendix C

Regarding the excitation system faults, the deviation of Fault 3, 4, 5, 6 and 7 are shown in

Figure C.1, C.2, C.3, C.4 and C.5.

Figure C.1: Fault3 (AVR output increases to maximum), the deviation of parameters

83

Figure C.2: Fault4 (Exciter stator open circuit), the deviation of parameters

84

Figure C.3: Fault5 (Exciter stator short circuit), the deviation of parameters

85

Figure C.4: Fault6 (main generator rotor open circuit), the deviation of parameters

86

Figure C.5: Fault7 (main generator rotor short circuit), the deviation of parameters

87

Regarding the prime mover faults, the deviation of Fault 10, 11 and 12 are shown in Figure

C.6, C.7 and C.8.

Figure C.6: Fault10 (diesel engine takes full load), the deviation of parameters

88

Figure C.7: Fault11 (diesel engine takes no load), the deviation of parameters

89

Figure C.8: Fault12 (diesel engine is blocked), the deviation of parameters

90

Appendix D Generator 2 datasheet is given in Figure D.1.

Figure D.1 Generator 2 datasheet

91

Appendix E Generator 3 datasheet is given in Figure E.1.

Figure E.1 Generator 3 datasheet

common diesel generator protection of power systems in dp

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