CHAPER 5 POWER FLOW STUDY IN THE INTEGRATED GRID NETWORK

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1 91 CHAPER 5 POWER FLOW STUDY IN THE INTEGRATED GRID NETWORK CHAPTER CONTENTS: 5.1 INTRODUCTION 5.2 CONDUCTION OF VARIOUS POWER FLOW STUDIES ON THE MODEL 5.3 EXPERIMENTS CONDUCTED FOR VARIOUS POWER FLOW STUDIES 5.4 CHAPTER CONCLUSION 5.1 INTRODUCTION Power flow studies are important in planning and designing of the power system. The future expansion of power system as well as determining the best operation of existing system is also dependant of power flow studies of the system. In our designed system, the major information attained from a power flow study is the magnitude of the voltage at each bus and the real and reactive power flowing in each line. The designed prototype of power grid with SCADA software provides clear insight into the power flow mechanism of an interconnected grid network. It has facilities for measuring active parameters: V, I. mva, mw, mvar and Power Factor at each Generator, Transmission Line and load. The current that flows in different parts of a power system immediately after the occurrence of a fault differ from those flowing a few cycles later just before the circuit breakers trip to open the line on both sides of the fault. And those currents differ widely from the current which would flow under steady state conditions if the fault were not isolated from the rest of the system by the operation of circuit breakers. Selection of the circuit breaker depends upon the current flowing immediately after the fault occurs and the minimum current on which the breaker must break off.

2 CONDUCTION OF VARIOUS POWER FLOW STUDIES ON THE MODEL The main experiments that are conducted to examine proper power flow in the grid prototype are as follows: 1. Monitoring and Control of Voltage, Speed and Frequency through SCADA Automation 2. Synchronization amongst all the three generators 3. While achieving synchronization amongst all the three generators, checking the functionality of synchroscope and more importantly the functionality of protection system i.e. Reverse Power Relay (RPR) 4. The voltage changes of the generator bus bar on load fluctuation 5. Changes that occur in other two generators during fault in one generator (Regulation) 6. Changes that occur in other loads during fault in one generator (Load Shedding) 7. Changes that occur in transmission lines during fault in one generator. 8. Fault simulation to test status of Miniature Circuit Board (MCB) & Over Current Relay (OCR) 9. Observation and control of Active Power, Reactive Power and Power Factor in all the bus bars of generators, loads and transmission lines without the FACT device UPFC 10. Observation and control of Active Power, Reactive Power and Power Factor in all the bus bars of generators, loads and transmission lines with the FACT device UPFC (by varying its series and shunt transformer output)

3 EXPERIMENTS CONDUCTED FOR VARIOUS POWER FLOW STUDIES EXPERIMENT 1: This experiment comprises one generator, one 300 km transmission line, one 200 km transmission line and one load (Refer figure 5.1). Here the power flow study is made to examine the functionality of power transmission from generator to load via the transmission lines. Figure no. 5.1: Power flow from generator to load

4 94 In this experiment, there is a Generator. Transmission line is divided into two sections one of 300 km and the other of 200 km, and one Load. This is a three phase (RYB) system which represents the power flow. The experiment is conducted by operating the model manually as well as through SCADA. The generator voltage is kept at 100V. The generator current, power and other data are seen on MFM. The functionality of the related components mounted on the model is verified through this experiment. EXPERIMENT 2: This experiment is conducted with two generators, three transmission lines and two loads. Power flow is studied in using generators G1 & G2, loads L1 & L2, and transmission lines TL1 & TL2. Transmission line TL 3, which is a Tie Line, interconnects the two areas. In this power flow study the importance of direction of power flow and synchronization of the two generators were studied. Refer figure 5.2. Figure no. 5.2: The circuit of power system where two generators, two loads and three transmission line are interconnected

5 95 In this experiment the synchronization between two generators is achieved and process is studied, here a synchroscope is used for monitoring synchronization (Refer figure 5.3). The main factors which have to be controlled to achieve synchronizing state are: Frequency, Voltage and Phase Angle. These factors can be controlled by speed and excitation of motor generator and voltage regulation through voltage regulating VARIAC. This is necessary because exactly at that time the circuit breaker is switched on to join the tie line connected between the two generators. Without synchronization the two generators should not be connected to the bus bar as it may swing the alternator. There is Reverse Power Relay placed for protection to prevent power flow in reverse direction. Figure no. 5.3: Generator with Reverse Power Relay for its protection

6 96 Figure 5.2 shows the circuit that is tested using two generators, three transmission lines and two loads. At load bus 1 and load bus 2 are interconnected by a Tie Line to demonstrate the flow of power from bus 1 to bus 2. This is achieved by keeping the Voltage at load bus 1 higher than the load bus 2. The following information is obtained from the test. The power generated by the alternator 1 is 4 Ampere at 250 volts where as the load 1 was 3 Amperes, therefore the 1 Ampere power can be diverted through the Tie Line to the load bus 2 to supply the load 2 of 3 Ampere capacity, whereas the generator 2 contributed 2 Ampere. The process here is controlled manually as well as through computer command. Paralleling AC Generators in the Experiment: Most electrical power grids and distribution systems have more than one AC generator operating at one time. Normally, two or more generators are operated in parallel in order to supply the demand of power. Three conditions must be met prior to paralleling of (or synchronizing) AC generators: 1. Their terminal voltages must be equal. If the voltages of the two AC generators are not equal, one of the AC generators would act as a reactive load to the other AC generator. This causes high currents to be exchanged between the two machines, possibly causing generator or distribution system damage. 2. Their frequencies must be equal. A mismatch in frequencies of the two AC generators will cause the generator with the lower frequency to act as a load on the other generator a condition referred to as motoring. 3. Their output voltages must be in phase. A mismatch in the phases will develop opposing voltages. The worst case would be 180 out of phase, resulting in an opposing voltage between the two generators of twice the output voltage. This high voltage can cause damage to the generators and distribution system due to high currents. During paralleling operations, voltages of the two generators that are to be paralleled are indicated through the use of voltmeters. Frequency matching is accomplished through the use of output frequency meters.

7 97 Phase matching is accomplished through the use of a synchroscope. It is a device that senses the two frequencies and gives an indication of phase differences and a relative comparison of frequency differences. Along with various power flow studies, some fault studies are also done. Faults are simulated to test status of Miniature Circuit Board (MCB) & Over Current Relay (OCR). There is provision of applying and using Digital Numerical Distance Relay (DNDR). Experiments using DNDR can be performed by simulating different types of faults but are not performed in our work. DNDR will indicate the distance to fault. Different types of faults are studied that frequently occur in the transmission lines are: 1. Double Line Fault (Figure 5.4) 2. Triple line Fault (Figure 5.5) 3. Line to Ground Fault (Figure 5.6) 4. Double Line to Ground Fault (Figure 5.7) 5. Triple Line to Ground Fault (Figure 5.8) Figure 5.4: Double Fault Line Figure 5.5: Triple Line Fault

8 98 Figure no. 5.6: Line to Ground Fault Figure no. 5.7: Double Line to Ground Fault Figure no. 5.8: Triple Line to Ground Fault

9 CHAPTER CONCLUSION To study proper power flow and working of all the components installed on the model, a Power System Model is designed here which simulates 400 kv, 500 km High Voltage Transmission Line. The following experiments are performed using this model: 1. Simulating faults conditions in the two sections of the simulated transmission line. 2. Power flow in Interconnected Grid network. 3. Data Acquisition and Supervisory Control using the SCADA architecture provided on the model. Faults are simulated to test status of Miniature Circuit Board (MCB) & Over Current Relay (OCR). The experiments may be conducted on the Power System Model to study working of DNDR which will provide protection to the transmission line by tripping the circuit and indicating distances of different types of faults (L-G, L-L, LL-G, LLL, LLL-G) common in overhead transmission lines. In most of the cases, the lines are not provided with the arrangement of DNDR due to the cost factor. The SCADA automation is implemented on the model to understand the architecture and its performance on a grid network of power system. The software screen indicates the layout of facilities for data acquisition from the MFM and remote supervisory control command that is used to control operational function of the model. The SCADA architecture implemented on the power system model comprises Siemens PLC, relays, software and software program. The SCADA is tested on the model and is found to work smoothly and accurately. The precautions are taken for providing good earthing and using co-axial connecting leads.