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. 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.
1
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.
2
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.
3 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.
4
Figure 1.3 The configuration of DGMS
5 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
6 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.
푑휔 퐽 푟 = 푇 − 푇 (2.1) 푔 푑푡 푚푒푐ℎ 푒푙푒푐
퐽푔 is the moment of inertia of the generator.
휔푟 is the generator angular velocity.
푇푚푒푐ℎ is the mechanical torque from the diesel engine.
푇푒푙푒푐 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.
푒푑 푣푎 [푒푞] = 푃푠 [푣푏] (2.2) 푒0 푣푐
푖푑 푖푎 [푖푞] = 푃푠 [푖푏] (2.3) 푖0 푖푐
2휋 2휋 cos θ cos( θ − ) cos(θ + ) 푒 푒 3 푒 3 2 2휋 2휋 푃 = − sin θ − sin(θ − ) − sin(θ + ) (2.4) 푠 3 푒 푒 3 푒 3 1 1 1 [ 2 2 2 ]
푣푎, 푣푏, 푣푐 are the generator’s terminal voltage of phase a, b and c.
푖푎, 푖푏, 푖푐 are the generator stator current.
푒푑 is d axis stator voltage.
푒푞 is q axis stator voltage.
푒0 is 0 sequence stator voltage.
푖푑 is d axis stator current.
푖푞 is q axis stator current .
푖0 is 0 sequence stator voltage.
θ푒 is the angle between phase a and d axis.
7 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.
휓푑 = −(퐿푎푑 + 퐿푙)푖푑 + 퐿푎푑푖푓푑 + 퐿푎푑푖1푑 (2.5)
휓푞 = −(퐿푎푞 + 퐿푙)푖푞 + 퐿푎푞푖1푞 (2.6)
휓푓푑 = 퐿푓푑푖푓푑 + 퐿푎푑푖1푑 − 퐿푎푑푖푑 (2.7)
휓1푑 = 퐿푎푑푖푓푑 + 퐿1푑푖1푑 − 퐿푎푑푖푑 (2.8)
휓1푞 = 퐿1푞푖1푞 − 퐿푎푞푖푞 (2.9)
푖푓푑 is the rotor circuit current.
퐿푓푑 is the self-inductance of rotor circuit.
퐿1푑 is the self-inductance of d-axis damper winding.
퐿1푞 is the self-inductance of q-axis damper winding.
휓푑 is the d-axis stator flux linkage.
휓푞 is the q-axis stator flux linkage.
휓푓푑 is the rotor circuit flux linkage.
휓1푑 is the d-axis damper winding flux linkage.
휓1푞 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
1 푑휓푑 푒푑 = − 휓푞휔푟 − 푅푎푖푑 (2.10) 휔푏푎푠푒 푑푡
1 푑휓푞 푒푞 = + 휓푑휔푟 − 푅푎푖푞 (2.11) 휔푏푎푠푒 푑푡
1 푑휓푓푑 푒푓푑 = + 푅푓푑푖푓푑 (2.12) 휔푏푎푠푒 푑푡
1 푑휓1푑 푒1푑 = + 푅1푑푖1푑 = 0 (2.13) 휔푏푎푠푒 푑푡
1 푑휓1푞 푒1푞 = + 푅1푞푖1푞 = 0 (2.14) 휔푏푎푠푒 푑푡
휔푏푎푠푒 is nominal electrical angular speed.
8 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.
휓푎푑 = 휓푑 + 퐿푙푖푑 (2.15)
휓푎푞 = 휓푞 + 퐿푙푖푞 (2.16)
2 2 2 휓푎𝑖푟 = √휓푎푑 + 휓푎푑 (2.17)
휓푎푑 is d axis air gap flux linkage.
휓푎푞 is q axis air gap flux linkage.
휓푎𝑖푟 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.
퐾푠 = 푓(휓푎𝑖푟) (2.18)
If there is no saturation, Ks is a constant and equal to 1.
퐿푎푑 = 퐾푠 ∗ 퐿푎푑푢 (2.19)
퐿푎푞 = 퐾푠 ∗ 퐿푎푞푢 (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.
퐿푓푑푙 = 퐿푓푑 − 퐿푎푑 (2.21)
퐿1푑푙 = 퐿1푑 − 퐿푎푑 (2.22)
퐿1푞푙 = 퐿1푞 − 퐿푎푑 (2.23)
′ (퐿푑−퐿푙) 퐿푓푑푙 = 퐿푎푑 [ ′ ] (2.24) (퐿푑−퐿푑)
" (퐿푑−퐿푙) 퐿1푑푙 = 퐿푎푑퐿푓푑푙 " (2.25) [퐿푎푑퐿푓푑푙−퐿푓푑(퐿푑−퐿푙)]
" (퐿푎푞−퐿1푞푙) 퐿1푞푙 = 퐿푎푞 [ " ] (2.26) (퐿푞−퐿푞)
9
퐿푓푑푙 is the rotor circuit leakage inductance.
퐿1푑푙 is the d-axis leakage inductance.
퐿1푞푙 is the q-axis leakage inductance. ′ 퐿푑 is the d-axis transient inductance. " 퐿푑 is the d-axis sub transient inductance. " 퐿푎푞 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.
VOEL VT
VUEL
VRLMT/VTKA VRLMT
+
+ + + EFD VREF K ∑ ∑ Ka Ka ∏ KVHZ ∑ VHZ ∏ - -
0 0 0 FEX
VC VX=VESE(VE)
FEX=f(IN) +
∑ + ∑ KE
FEX=f(IN) +
IFD KD
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.
10 1.5
+ Q - VUEL ∑ Kg ∑ 1.5 + 0
QUEL_REF 0 Figure 2.3 Block diagram of under excitation limiter (UEL)
VREF
+ IEX - ∑ Kg ∑ -1 V VOEL + REF 0
IOEL_REF 0 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 - ∑ KVHZ ∏ VVHZ + 0
Corner VREF Frequency 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.
11 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.
Speed Set point Fuel Rack Position Governor Fuel flow limit Engine Output Torque Speed (Thermo dynamic) Emission control
(dP/dt control)
Diesel engine output power Turbocharger
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.
푇푚푒푐ℎ = 퐻퐿퐻푉푚푓휂푡ℎ푒푟푚푎푙 (2.27)
휂푡ℎ푒푟푚푎푙 = 0.4 (2.28)
푇푛표푚𝑖푛푎푙 푚푓_푚푎푥 = (2.29) 퐻퐿퐻푉∗휂푡ℎ푒푟푚푎푙
푚푓 푇푚푒푐ℎ = ∗ 푇푛표푚𝑖푛푎푙 (2.30) 푚푓_푚푎푥
퐻퐿퐻푉 is the lower fuel heating value (42700 kJ/kg).
휂푡ℎ푒푟푚푎푙 is thermal efficiency.
푚푓 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.
12 푣∗2휋 푚푓 = 푚̇ 푓 (2.31) 휔푒
푚̇ 푓 is the mass of fuel injected into one cylinder in one second. 푣 is 2, if the number of strokes of diesel engine is 4.
휔푒 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.
푚̇ 푎𝑖푟 = 푘푡푐휂푡푐휔푡푐 (2.32)
푚̇ 푎𝑖푟 is the mass of air into one cylinder in one second.
휂푡푐 is the efficiency of the turbocharger.
푘푡푐 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.
1 휔̇ 푡푐 = (푇푡푐(푃푚푒푐ℎ) − 푇푡푐_푓(휔푡푐)) (2.33) 퐽푡푐
퐽푡푐 is the inertia of the turbocharger
푇푡푐(푃푚푒푐ℎ) 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.
푇푡푐_푓(휔푡푐) 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.
PIDMAX
Speed
+ setpoint Governor Output ∑ Ka - - Speed sensor 0
Droop Diesel engine output power
Figure 2.7 Configuration of governor
13 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.
푚̇ λ = 푓 (2.34) 푚̇ 푎𝑖푟
λ is the ratio of fuel to air.
푚̇ 푓 is the mass of fuel injected into one cylinder in one second
푚̇ 푎𝑖푟 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
14 and required reactive power, the value of induction and resistance can be calculated as Equation 2.37, 2.38 and 2.39.
푣 = 푖푍 (2.35)
푍 = 푅 + 푋푗 (2.36)
푣2 푅 = 푛표푚 (2.37) 푃푠푒푡
푣2 푋 = 푛표푚 (2.38) 푄푠푒푡
푋 = 2휋푓푛표푚퐿 (2.39)
푣푛표푚 is the system nominal voltage
푓푛표푚 is the system nominal frequency
푃푠푒푡 is the active power set point under nominal voltage and frequency
푄푠푒푡 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.
푑푅 1 = (푃 − 푃푟푒푓) (2.40) 푑푡 휏load
푑퐿 1 = (푄 − 푄푟푒푓) (2.41) 푑푡 휏푙표푎푑
푍 = 푅 + 푋푗 (2.42)
푋 = 2휋푓퐿 (2.43)
푃푟푒푓 is the active power set point
푄푟푒푓 is the reactive power set point
휏푙표푎푑 is the time constant of constant power load
15 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.
Exciter A G E V 3~
V
Figure 2.8 Generator voltage step test configuration
16
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.
Terminal Voltage 8000.00 7000.00 6000.00 Matlab Result 5000.00 Measurement 4000.00 3000.00
2000.00 Terminal Voltage(V) Terminal 1000.00 0.00 0 5 10 15 Time(s) Figure 2.10 Terminal voltage comparison
17 Main Generator Rotor Voltage 60
50
40 Matlab Result 30 Measurement 20
10
MainGenerator Voltage(V) Rotor 0 0 2 4 6 8 10 12 14 -10 Time(s)
Figure 2.11 Main generator rotor voltage comparison
3 Exciter Stator Current
2.5
2 Matlab Result Measurement 1.5
1
0.5 Exciter Stator Current(A) Stator Exciter
0 -1 1 3 5 7 9 11 13 15
-0.5 Time(s) 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
18 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.
19 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].
DG set1 DG set2 DG set3
Diesel Engine Output Power
G G G Exciter Current 3~ 3~ 3~
Active Power Reactive Power
Net Frequency Net Voltage
dP/dt dP/dt dP/dt limit limit limit
Load Load Load
Figure 3.1: Three parallel diesel generators model configuration and measurement position.
20 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.
No load frequency – Full load frequency Droop% = ∗ 100 (3.1) No load frequency
Active Power Droop
60.5 0W; 60Hz 60
59.5
59
58.5
Frequency(Hz) 58 3,84MW; 57.5 57,6Hz 57 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 Diesel Engine Output Power (MW)
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.
no reactive power voltage−full reactive power voltage Droop% = ∗ 100 (3.2) no reactive power voltage
21 Reactive Power Droop 6.95 0Var; 6,93kV 6.9 6.85 6.8 6.75 6.7
LL Voltage(KV) LL 4,1MVar; 6,6kV 6.65 6.6 6.55 0 1 2 3 4 5 Reactive Power(MVar)
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.
22
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.
23 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.
Fault 1/2: 1.1 or 0.9 times the AVR Exciter AVR output before the fault Fault 3: Stator E Maximum output of AVR
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.
Fault4 Fault6 Exciter Current transducer AVR Fault 5 Fault 7
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.
24
Figure 3.7: Fault 1(AVR increases 10% its output) simulation results
25
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.
26 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.
27
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
28 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
29 boxes and derivative is remarked by purple boxes.
In the tables, 푄 means the actual reactive power. 푄푒푥푝 means the expected reactive power. 푉 means the actual generator voltage. 푉푒푥푝 means the expected generator voltage. 퐼푒푥 means the actual exciter current and 퐼푒푥_푒푥푝 means the expected exciter current.
푑푄 푑푉 푑퐼 푒푥 푑푡 푑푡 푑푡 Conditions 푄 푄 − 푄푒푥푝 푉 푉 − 푉푒푥푝 퐼푒푥 퐼푒푥 − 퐼푒푥_푒푥푝
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 Table 4.1 The performance of faulty generator during different kinds of situations
푑푄 푑푉 푑퐼 푒푥 푑푡 푑푡 푑푡 Conditions 푄 푄 − 푄푒푥푝 푉 푉 − 푉푒푥푝 퐼푒푥 퐼푒푥 − 퐼푒푥_푒푥푝
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 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.
30 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.
푄 푄 = 푛푒푡 (4.1) 푒푥푝 푛
31 푄푛푒푡 is the total reactive power online 푛 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.
푉푒푥푝 = 푉푠푒푡 − 푄푒푥푝 ∗ 푑푟표표푝% (4.2)
푉푠푒푡 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.
Exciter Generator Xd
Rex Rf Eex E
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 (퐼푒푥), exciter rotor internal voltage (퐸푒푥) and main generator rotor current (퐼푓) 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.
퐼푒푥 ∝ 퐸푒푥 ∝ 퐼푓 (4.3)
When we talk about the relationship between the main generator rotor current (퐼푓) and the main generator internal voltage (퐸), there is saturation between them. We can use linear line to replace the saturation curve in generator operation region. It means that 푋푑 is constant in certain operation region. The reason why 푋푑 is constant is that 푋푑 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 푋푑.
32 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 푋푑 under the rated terminal voltage. This value also can be found in the datasheet of generator. It is named as Saturated 푋푑.
The active power and reactive power of the synchronous generator can be calculated by Equation 4.4 and 4.5 [24].
|푉 ||퐸| 푃 = 푡 푠푖푛훿 (4.4) 푋푑
|푉푡| 푄 = (|퐸|푐표푠훿 − |푉푡|) (4.5) 푋푑 푃 is the active power of the generator.
푉푡 is the terminal voltage of the generator. 훿 is the phase angle between terminal voltage and internal voltage. 푄 is the reactive power of the generator.
At steady state, based on the reactive power droop and constant 푋푑, 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,
2 2 2 √(푋푑푄+푉푡 ) +(푃푋푑) 퐸 ≅ 퐼푓 ∗ 푋푑 = (4.6) Vt
푃 2 푄 푉푡 2 퐼푓 = √( ) + ( + ) (4.7) 푉푡 푉푡 푋푑
33
Equation 4.9 is obtained by using Equation 4.8 to replace 푉푡 in Equation 4.7. Now the relationship between main generator rotor current (퐼푓), active power (푃) and reactive power (푄) is known.
푉푡 = 1.05 − 0.05 ∗ 푄 (4.8)
푃 2 푄 1.05−0.05∗푄 2 퐼푓 ≈ √( ) + ( + ) (4.9) 1.05−0.05∗푄 1.05−0.05∗푄 푋푑
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 푋푑 as 1.1pu). The diagram is shown in Figure 4.3.
2.5
2
1.5 1.0pu P
0.8pu P
(pu) f I 1 0.6pu P 0.4pu P 0.5 0.2pu P
0 0 0.2 0.4 0.6 0.8 1 Q(pu)
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 (푃), main generator rotor current (퐼푓) has the linear relation with reactive power (푄). Therefore, based on Equation 4.3, we can conclude the relationship among active power (푃), reactive power (푄), and exciter current (퐼푒푥). It is shown in Equation 4.10.
퐼푒푥 = [푆푙표푝푒(푃푒푥푝) ∗ 푄푒푥푝 + 퐼푛푡푒푟푐푒푝푡(푃푒푥푝)] (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
34 added. The relationship between the frequency and exciter current is shown in Equation 4.11.
푉푡 ∝ 퐼푓 ∗ 푓 ∝ 퐼푒푥 ∗ 푓 (4.11) And the expected exciter current calculation changes from Equation 4.10 to 4.12.
퐼푒푥 = [푆푙표푝푒(푃푒푥푝) ∗ 푄푒푥푝 + 퐼푛푡푒푟푐푒푝푡(푃푒푥푝)] ∗ 퐶표푛푠푡푎푛푡 ∗ 푓 (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, 푃 means the actual active power. 푃푒푥푝 means the expected active power. 푓 means the actual generator frequency. 푓푒푥푝 means the expected generator frequency. 퐼푒푥 means the actual exciter current and 퐼푒푥_푒푥푝 means the expected exciter current.
푑푃 푑푓 푑퐼 푒푥 Conditions 푃 푑푡 푃 − 푃푒푥푝 푓 푑푡 푓 − 푓푒푥푝 퐼푒푥 푑푡 퐼푒푥 − 퐼푒푥_푒푥푝
>0 + ≈ 0 >0 - ≈/< 0 >0 + ≈ 0 Load step 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 >0 ++ >0 >0 + >0 >0 + >0 maximum Fault11: Diesel engine suddenly >/<0 -- <0 >0 -- <0 >/=0 -- <0 takes no load Fault12: Diesel engine has no >/<0 ++/-- >/<0 >0 - >/<0 >/=0 ++/-- >/<0 speed Table 4.3 The performance of faulty generator during different kinds of situations
35
푑푃 푑푓 푑퐼 푒푥 Conditions 푃 푑푡 푃 − 푃푒푥푝 푓 푑푡 푓 − 푓푒푥푝 퐼푒푥 푑푡 퐼푒푥 − 퐼푒푥_푒푥푝
>0 + ≈ 0 >0 - ≈/< 0 >0 + ≈ 0 Load step Fault8: Fuel rack increases 20% >/<0 - <0 >0 + >0 >/=0 - <0 Fault9: Fuel rack decreases >0 + >0 >0 - <0 >0 + >0 20% Fault10: Fuel rack increases to 0 -- <0 >0 + >0 >0 + >0 maximum Fault11: Diesel engine suddenly >0 ++ >0 >0 -- <0 >0 ++ >0 takes no load Fault12: Diesel engine has no >/<0 ++/ >/<0 >0 - >/<0 >/=0 ++/-- >/<0 -- speed 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 (푃) and frequency (푓) 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
(퐼푒푥) has the same behavior as active power (푃) 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.
36 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.
푃 푃 = 푛푒푡 (4.13) 푒푥푝 푛
푃푛푒푡 is the total active power online 푛 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.
푓푒푥푝 = 푓푠푒푡 − 푃푒푥푝 ∗ 푑푟표표푝% (4.14)
푓푠푒푡 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.
37 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.
P (Kw) P (kW)
Rated Power
Q (Kvar) ） Frequency (Hz
Terminal Voltage (V)
Q (Kvar)
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)
38 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
39
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
40
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
41 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.
42
Figure 4.8 Configuration of excitation system protection in CDG in protection system excitation of Configuration 4.8Figure
43
Figure 4.9 Configuration of prime mover protection in CDG in protection mover prime of Configuration 4.9Figure
44 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.
Figure 5.1 Configuration Configuration 5.1Figure
of CDG test setup test CDG of
45 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.
Setup Reactive Power Droop
405 0 kVar, 400V 400
395
390
385 36 kVar, 380V
380
375 Generator Generator Terminal Voltage (V) 0 5 10 15 20 25 30 35 40 Reactive Power(kVar)
Figure 5.2 Setup reactive power droop.
46 Generator 1 and 2 Active Power Droop
52.5 0 kW, 52 Hz 52
51.5
51
50.5
Frequency (Hz) 34 kW, 50 Hz 50
49.5 0 5 10 15 20 25 30 35 40
Active Power (kW)
Figure 5.3 Generator 1 and 2 active power droop
Generator 3 Active Power Droop
52.5 0 kW, 52 Hz 52
51.5
51
50.5
Frequency (Hz) 28.8 kW, 50 Hz 50
49.5 0 5 10 15 20 25 30 35
Active Power (kW)
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.
47 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
48 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
49 The motor load is shown in Figure 5.8
Figure 5.8 Motor load
50 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.
Rotor copper ring
Brush
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
51
Figure 5.10 Generator 2 terminal peak voltage comparison
Figure 5.11 Generator 2 exciter current comparison
52
Figure 5.12 Generator 2 rotor voltage comparison
Figure 5.13 Generator 3 terminal peak voltage comparison
53
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.
54
Reactive power droop : 5% Active power droop : 0% Active Reactive Measured exciter Simulated exciter Deviation(%) PF power(kW) power(kVar) current(A) current(A)
6.49 2.31 0.680 0.680 0.000 10.48 3.48 0.760 0.770 -1.316 0.95 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 6.54 3.22 0.705 0.710 -0.709 10.50 4.97 0.815 0.819 -0.491 0.9 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 6.55 3.76 0.724 0.729 -0.691 10.53 5.84 0.850 0.847 0.353 0.87 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
Reactive power droop : 5% Active power droop : 4% Active Reactive Measured exciter Simulated exciter Deviation(%) PF power(kW) power(kVar) current(A) current(A)
6.53 2.94 0.640 0.644 -0.625 10.51 4.72 0.758 0.761 -0.396 0.9 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 6.48 3.44 0.662 0.660 0.302 10.50 5.561 0.790 0.788 0.253 0.87 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 Table 5.2 Generator 2 exciter current comparison 2
55
Reactive power droop : 5% Active power droop : 0% Active Reactive Measured exciter Simulated exciter Deviation(%) PF power(kW) power(kVar) current(A) current(A)
6.62 3.78 0.640 0.650 -1.563 10.57 5.85 0.743 0.743 0.000 0.95 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 6.59 3.22 0.679 0.683 -0.589 10.57 4.97 0.793 0.794 -0.126 0.9 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 6.62 3.32 0.695 0.703 -1.151 10.58 3.46 0.824 0.826 -0.243 0.87 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 Table 5.3 Generator 3 exciter current comparison 1
Reactive power droop : 5% Active power droop : 4% Active Reactive Measured exciter Simulated exciter Deviation(%) PF power(kW) power(kVar) current(A) current(A)
6.50 2.93 0.620 0.624 -0.645 10.48 4.73 0.740 0.745 -0.676 0.9 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 6.50 3.45 0.630 0.642 -1.905 10.49 5.57 0.770 0.776 -0.779 0.87 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 Table 5.4 Generator 3 exciter current comparison 2
56 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 Reactive Power First Level 3kVar 3kVar System Deviation Detection Reactive Power Second 6kVar 6kVar Level Deviation Voltage First Level 1.5V 1.5V Deviation Voltage Second Level 2.8V 2.8V Deviation Exciter Current First Level 100mA 100mA Deviation Exciter Current Second 210mA 210mA Level Deviation Prime Active Power First Level 3.4kW 2.88kW Mover Deviation Detection Active Power Second Level 6.8kW 5.76kW Deviation Frequency First Deviation 0.2Hz 0.2Hz Frequency Second 0.45Hz 0.45Hz Deviation Dynamic Highest Active Power 30.6kW 25.9kW Window Boundary Lowest Active Power 0kW 0kW Boundary Highest Reactive Power 30.6kVar 30.6kVar Boundary Lowest Reactive Power -2kVar -2kVar
57 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.
58 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)
59
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)
60
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)
61 Figure 5.22, 5.23 and 5.24 show the behaviors of the setup and response of CDG when the 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)
62
Figure 5.24 Exciter current (the AVR set point of generator 3 increases 8V)
Figure 5.25, 5.26 and 5.27 show the behaviors of the setup and response of CDG when the AVR set point of generator 3 decreases 8V.
Figure 5.25 Reactive power (the AVR set point of generator 3 decreases 8V)
63 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.
64 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)
65 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)
66 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)
67 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.
68 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
69 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.
70 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.
71 [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.
72 Appendix A Generator datasheet is given in Figure A.1.
Figure A.1 Generator datasheet
73 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
74
Figure B.2 Fault4 (Exciter stator open circuit), simulation results
75
Figure B.3 Faul5 (Exciter stator short circuit), simulation results
76
Figure B.4 Fault6 (main generator rotor open circuit), simulation results
77
Figure B.5 Fault7 (main generator rotor short circuit), simulation results
78 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
79
Figure B.7 Fault11 (diesel engine takes no load), simulation results
80
Figure B.8 Fault12 (diesel engine is blocked), simulation results
81 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
82
Figure C.2: Fault4 (Exciter stator open circuit), the deviation of parameters
83
Figure C.3: Fault5 (Exciter stator short circuit), the deviation of parameters
84
Figure C.4: Fault6 (main generator rotor open circuit), the deviation of parameters
85
Figure C.5: Fault7 (main generator rotor short circuit), the deviation of parameters
86 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
87
Figure C.7: Fault11 (diesel engine takes no load), the deviation of parameters
88
Figure C.8: Fault12 (diesel engine is blocked), the deviation of parameters
89 Appendix D Generator 2 datasheet is given in Figure D.1.
Figure D.1 Generator 2 datasheet
90
Appendix E Generator 3 datasheet is given in Figure E.1.
Figure E.1 Generator 3 datasheet
91