Design a Power System Simulator Model and Implement the Generator and Motor Controlling

Design a Power System Simulator Model and Implement the Generator and Motor Controlling G.U De Silva, G.B Alahendra, A.C.P Aluthgama, P.G.L Arachchi Supervised by: Prof. J Rohan Lucas, Eng. J. Karunanayake Department of Electrical Engineering, University of Moratuwa, Sri Lanka Abstract - The primary goal of the project is to design and build a Real Life Power System Model which is basically a model of a real life power Such a Power System model allows understanding the behavior of the power system or individual components under all conditions, whether abnormal or normal. Power system can become vulnerable in the face of possible system abnormalities such as control, protection, operational system failures, disturbances and human operation errors. Therefore, keeping the power supply stable and reliable is very critical issue for future power system design. This model will have the facility to simulate all types of normal/abnormal situations that occur in real life power system and users will have the facility to examine the effect of such conditions on a power system in a realistic manner. Keywords power system simulator model, fault, protection schemes I. INTRODUCTION A. Background of the project Most of the laboratory works on power system engineering area normally bring into play on individual components of the power system together with generators, transformers, lines, protective relays, etc. But it is not sufficient to understand the performance and operation of the many combinations of components in an integrated power system or in overall power Hence, To design and build a Power System Simulator Model was chosen as our Final Year Undergraduate Project in fulfillment of the required undergraduate electrical engineering course. B. Justification of the project The primary goal of the project is to design and build a Real Life Power System Model which is basically a scale down representation of a real power This is a hardware designed to mimic real systems and modern practice. Subsequently such a Power System Model allows understanding the behavior of the power system or individual components under all conditions, whether abnormal or normal. The model comprise of generators, generator transformers, transmission lines, grid substations, distribution lines, inductors, capacitors, circuit breakers, current transformers (CTs), potential transformers (PTs), protection relays, power system loads and metering facilities. To model the Real Life Power System Model, the design arrangement includes: A generator/transformer unit with automatic and manual voltage control, having an induction motor as a prime mover. Manual synchronizing facility with the grid or any other system Four transmission lines, a grid substation and a distribution system Variable resistive and inductive loads. An integrated protection system to detect and clear the faults at any point in the model power system Instrument transformers (CTs and PTs) to provide information to the protective and metering systems. Circuit breakers A fault creation facility for the application of any kind of faults on transmission lines. Metering facilities at various points in the system Facilities for remote operation of circuit breakers. C. Objectives of the project Currently, there are real life power system models commercially available with which wide range of experiments can be carried out to understand the power system behavior. Unique feature of such models is the opportunity those accord to observe the changes in general power system characteristics such as voltages, currents, power factors, real power, reactive power etc. at various points in the system due to changes effected at identified locations, which my simulate normal or abnormal conditions., thus enabling the students to clearly understand the power system behavior under normal/abnormal conditions. These abnormal conditions will include reactive/real power sharing, under different excitation levels or prime mover inputs or sudden changes in loads, various kinds of faults on being effected at various locations of the model power system Another important aspect of such a model is the opportunity students get to familiarize more closely with power system components like synchronous generators, transformers, protection relays, CTs and VTs and for learning how these components interact with to form the Hence such a model, which is in effect a small scale, integrated power system is an ideal piece of equipment for understanding the power system behavior and also to learn the operational/controlling aspects of a power Commercially available units are prohibitively expensive. However, the benefits students will gain in understanding power system behavior with the experiments that could be carried out with such a model are incomparable with those experiments that are normally being done with individual components in our laboratories. Hence the main objective of this project is to design and build a real life power system model at a lower cost equipped with almost all facilities that are normally incorporated in a commercially available unit,to provide the unique learning opportunity which only such a model can provide and also perhaps to offer as a means to industrial suppliers and utilities

for solving problems they confront in actual power system operation by performing tests simulating such This model also provides an opportunity to students for getting familiarized more closely with power system components like synchronous generators, transformers, protection relays, CTs and VTs and for learning how these components interact with to form the D. Special features of the model This scale down model of power system will cover all the general attributes of a real world power Generating system - 16KVA generator with manual/automatic voltage control. (Donated by Hayles Ltd.) - 8KW induction motor as a prime mover ( Available in the University) - VSD (Variable Speed Drive) - Manual synchronization facility Transmission Lines - With known values of resistance, capacitance and inductive impedances. Grid substation - 2x 1kVA transformers - Variable dynamic and static loads Power system operation - Reactive and real power sharing - Changes in excitation levels - Frequency changes when operating in the isolated mode. Fault creation - Three phase faults (L-L-L & L-L-L-G) - Phase faults (L-L, L-L-G, L-G) - Cross country faults Protection schemes - Generator protection - Transformer protection - Bus Bar protection - Transmission Line protection - Distance - Over-current & earth-fault - Differential Metering systems - Voltmeters, Ammeters, Ammeters, power factor meters, power (P & Q) at important locations - Test points to measure currents and voltages at all important locations. Power System Monitoring - Displaying system data - Alarms and indications Power System Controlling - Remote - Local E. Possible experiments demonstrate by the model A set of experiments can be demonstrated by the use of this Real Life Power System Model. These experiments are divided into following areas as follows. I. Fault studies The following are examples of studies that can be carried out on the Real Life Power System Model under this. Symmetrical Faults Unsymmetrical Faults Transient Stability Studies Stability Studies II. System protection This model contains a majority of power system protection applications. So following experiments can be set up and studied. Grading of Over-current Protection for Three Phase Faults High Set Instantaneous Settings Back Tripping Directional Control of Relay Tripping Distance Protection Three Zone Distance Protection Scheme Differential Protection Setting the Transformer Differential Protection Grid Transformer Differential Protection Busbar Protection Generator Protection II. PROJECT PROGRESS A. Outline Description of the Power System Design The proposed power system model mainly designed with an induction motor used as a prime mover, a 16kVA generator with an AVR, a 16kVA 400/110V generator transformer and four transmission lines. Excitation, metering and protection facilities are also provided in this model. So, current transformers (CTs), potential transformers (PTs), protection relays, meters and circuit breakers are also used. Figure I show the Single Line Diagram of the proposed Three phase Π transmission model is used for transmission lines with 100 km length. The transmission line parameters used for resistances, capacitances, and inductances are varied to get the required fault current that is sufficient to operate the protection relays. Various types of protection schemes are used in Line 1, 2 and 3 and those are described later in this paper and illustrated in Figure IV. B. Modeled the proposed system with PSCAD Figure II shows a simple model of our system which we used in PSCAD simulation. Here three phase fault to ground was simulated. A voltage source is used as the generator because of the difficulty in modeling the induction motor driven generator in the PSCAD. Voltage source data was fed according to the real generator data. Figure I - single line diagram of the proposed system

TABLE I BASE CALCULATION Typical Power System Power System Model Power Base 100 MVA 16 kva Voltage Base 132 kv 400 V 110 V Impedance Base 174.24 Ω 10 Ω 0.756 Ω Current Base 447.38 A 23.09 A 83.98 A Figure III shows simulation results for the three-phase fault to ground condition. C. Parameter Values of Components An understanding of the per unit values of the system components is essential to appreciate the theoretical significance of measurements made on the Power System Model. This can only be achieved on a proportional or per unit basis, where the actual value of the parameter is expressed as the ratio of that parameter to a chosen base value. System representation is achieved by having the same per unit values as the actual Actual values are obtained by multiplying per unit values by the appropriate base values. The base values of system voltage and apparent power chosen for the Power System Simulator Model are; Base voltages : 230 V (phase value) Base voltamps: 16 kva The derived base values for current and impedance are given below. For 400 V side; Base current = Base impedances = For 110 V side; Figure II - PSCAD simulation model of the proposed system [5] Base current = Base impedances = VA base = 16000 3 V LL base 3 400 (V base ) 2 V A base = (400) 2 1600 VA base = 16000 3 V LL base 3 110 (V base ) 2 V A base = (110) 2 1600 = 23.09 A = 10 Ω = 83.98 A = 0.756 Ω D. Fault Creation Circuit A fault creation circuit must be designed to create various types of faults on the power After creating faults, observed the characteristics of the voltages and currents produced from the fault conditions over duration of time. Then analyze whether currents and voltages will be sufficient to operate the protection relays. Finally the circuits must be able to withstand fault currents. Types of Faults which can be created through this circuit, Three phase faults (L-L-L & L-L-L-G) Phase faults (L-L, L-L-G & L-G) Cross country faults High impedance faults F. Protection Schemes and Relays[1] This section provides identification and a brief description of individual protection schemes and associated relays for each component of the Power System Model. Figure IV shows the schematic diagram of the power system model and that gives a clear idea about all the protection schemes used in our model. Protection for both generator and generator transformer can be provided by using a KBCH 130 relay. This offers 3 bias inputs per phase for the protection of a three winding power transformer or a two winding power transformer with 2 sets of CTs on one winding. Type KBCH relays offer biased differential current, restricted earth fault and over fluxing protections. Figure IV - schematic diagram Figure III - PSCAD simulation for 3 phase short circuit fault [5]

The OPTIMHO Full Scheme Distance Relay provides transmission line protection. The relay requires both CTs and VTs because it measures impedance and thereby, the distance to a fault on a line. KCGG140 model was selected as three phase over current and earth fault relay. G. Bus bar design In bus bar design first most suitable material has to be selected. By considering the parameters like High electrical conductivity, Good thermal conductivity, Strong in working conditions (to withstand stresses caused by fault currents), Low creep, Easy to join and resistance to corrosion, Copper bars were selected as the bus bar material. Generally bus bar ratings are determined only by the maximum desired working temperature for the material and its surroundings. Although in the past, working temperatures as high as 110 degrees centigrade were often chosen. But because of the importance in energy efficiency use of lower temperatures are enforced. For a particular temperature, the amount of heat generated in the bar by current flow is exactly equal to the amount of heat lost to the atmosphere. Therefore at working temperature, Heat Generated = Heat Lost to the atmosphere Copper Loss = Heat Lost by Convection and Radiation P copper = P convection + P radiation 2 I Where, θ Temperature rise above theambient v Vertical height of thesurface - Emissivity ρ l 7.66θ 1.25 5.7ε A v 0.25 T 2 Working temperature (K) T 2 Ambient temperature (K) T 4 2 I - Current l - Length ρ - Resistivity of the material A - Cross sectional area According to this equation bus bar dimensions can be calculated. H. Transmission line design R, L, Y Parameters of a typical 100km transmission line was selected as per unit values. R= 0.10185 pu X= 0.22945 pu Y= 0.04857 pu Base voltage = 110 V (Line - Line) Base VA = 16000 VA Base impedance = 110 2 /16000 = 0.756 Ω 4 1 T 10 8 According to the base and per unit values, actual values of transmission line components were calculated and table2 shows that values. III. IMPLEMENTATION OF GENERATOR AND MOTOR CONTROL A. Generator and motor coupling The induction motor drives a salient, four-pole generator through a flexible coupling. This coupler was selected according to the requirements of shaft diameters. The generator shaft is 5.9cm and motor shaft is 3.8cm. Hence the selected shaft coupler had to be lathed for proper fitting. This coupler is having a generally cylindrical configuration with an inner end and an outer end. When coupling the induction motor to the synchronous generator, there should be a proper alignment between these two. Because of that a bad alignment may cause vibrations and bearing damages. B. Prime mover (Induction motor) controlling Power system controlling is extremely important for a well designed power Basically governor shall look after the speed of a generator /turbine system and maintain the stability of the system during transients at all loads in a typical power In the case of power system simulator model, an induction motor is used as the prime mover to drive the synchronous generator. To accomplish the governing mechanism of the induction motor/generator unit in this model, variable speed drive (VSD) was selected. Hence this drive is operating as the speed-control unit of the model. Basic elements of this unit are shown in Figure V. There should be any speed sensing mechanism to provide the analog input to the VSD. Here a tacho generator was connected as the speed sensor to detect the shaft speed. This device is capable to produce a very precise voltage signal which is proportional to shaft speed. Tacho generators can also indicate the direction of rotation by the polarity of the output voltage. One of the more common voltage signal ranges used with taco generators is 0 to 10 volts. The analog voltage output signal from the tacho generator is then send to the variable speed drive (VSD). For this model, ACS550-01-015A8-4 type of drive was installed and this was selected according to the requirements of the induction motor power rating (7.5 kw). TABLE 2 ACTUAL VALUES OF TRANSMISSION LINE COMPONENTS Actual Value Actual Value Resistance (R) 0.077 Ω Resistance (R) 0.077 Ω Reactance (X) 0.1735 Ω Inductance (L) 0.06 mh Figure V speed control unit block diagram Admittance (Y) 0.0642 S Capacitance (C) 20.4 µf

It can be provided two analog inputs to the programmable control connection AI1 either a voltage signal (0 to 10 V) or a current signal (0 to 20 ma). [4] Hence by using a tacho generator, it can be simply provided a voltage signal (0 to 10 V) proportional to the shaft speed. This actual value provided by the taco generator is then compared with the set value (reference) in the VSD. If the input is differ from the reference, the supply power would be regulated in response to changes and that would tend to cause changes in frequency (speed) and maintain at the set-point of the motor and hence the generator. C. Synchronous Generator The synchronous generator for the power system simulator model was donated by Hayles (pvt) Ltd. The type of the generator is Mecc Alte Spa ECO 28SN/4, 4 pole brushless alternator. The casing is made of steel, the shields of cast iron, and the shaft of C45 steel and it has a keyed fan. It is self-regulating and incorporates a rotating inductor with damper cage winding and a fixed stator with skewed slots. The stator windings have a shortened pitch to reduce the harmonic content of the output waveform. All alternators feature both star with neutral (Y) and delta (Δ) connections. To reconnect from a star to delta connection (for ex. from 400V to 230V) there is a linking arrangement on the output terminal board. D. Generator terminal voltage controlling Another important aspect in the power system controlling is terminal voltage controlling of the synchronous generator which is shown in Figure VI. The generator terminal voltage varies due to the reactive power load variations of the For that purpose, an Automatic Voltage Regulator (AVR) is used in this model. Here, the AVR is linked with the main stator windings, as well as the exciter field windings to provide a closed loop control of the output voltage. Since the generator field coils are self excited, where some of the power output from the stator is used to power the field coils. In addition to being powered from the main stator, the AVR also drives a sample voltage from the output windings for voltage control purposes. In response to this sample output voltage, the AVR controls the power feed to the exciter field. Here, main exciter has a three phase rotor winding. So the output is rectified and delivering the DC field current directly to the generator. The generator controlling block diagram is shown in Figure VII. Figure VII generator AVR block diagram E. Generator Transformer Design The generator transformer is rated at 16 kva, 400/110 V at 50 Hz and has a phase connection of delta-star. The per unit impedance of the transformer is selected as 0.04 pu. The rated currents of each winding are illustrated in Table 3 IV. POSSIBLE EXPERIMENTS DEMONSTRATE BY THE MODEL A set of experiments can be demonstrated by the use of this Real Life Power System Model. These experiments are divided into following areas as follows. Fault studies The following are examples of studies that can be carried out on the Real Life Power System Model under this. - Symmetrical Faults - Unsymmetrical Faults - Transient Stability Studies - Stability Studies System protection This model contains a majority of power system protection applications. So following experiments can be set up and studied. - Grading of Over-current Protection for Three Phase Faults - Directional Control of Relay Tripping - Distance Protection and Differential Protection - Setting the Transformer Differential Protection - Grid Transformer Differential Protection - Bus bar Protection - Generator Protection TABLE 3 RATED CURRENT OF THE TRANSFORMER V line Rated Current Primary (Delta) 400V 23A Figure VI Generator terminal voltage controlling Secondary (Star) 110V 84A

Power System Operation The experimental studies in this section consider the operation of a system under steady state condition. It is mainly concentrated on three main areas of system operation: generation, transmission and distribution and utilization. Following experimental studies can be illustrated under this. - Synchronisation - Voltage Variation and Control - Load flow studies V. CONCLUSION The ultimate goal of the project is to design a power system model with all the general attributes available in a real world. After performing this, users will be able to familiarize with power system components, create normal/abnormal situations in the power system; analyze the system behavior. This model provides the hands-on experience to the user and methods of control of the real life power Upon successful implementation of this project will provide future opportunities for undergraduates, faculty members, engineers to study/demonstrate the power system behavior under abnormal/normal conditions and perhaps could be used to simulate the real life problems faced by industries to propose solutions to the same. ACKNOWLEDGMENT Sincere appreciation is expressed to Prof. J. R. Lucas and Engineer J. Karunanayaka, our project supervisors, who provided enlightening advice and guidance, and without personal interest and provision we could not have completed the design of the Real Life Power System Model. Eng. J. Karunanayaka must be really appreciated for the great support given by sharing his valuable experience with us in designing this model and also pointed out our weak points and questioned our progress throughout the project period. REFERENCES [1] GEC ALSTOM, Protective Relays Application Guide [2] B.M Weedy, B.J Corey, Electric Power Systems [3] Leonardo Energy, Bus bar design basics [4] ABB, ACS 550 User s Manual [5] PSCAD Version 4.2 software