Power System Protection Manual - Klipsch School …

1 Power System Protection Manual Note: This Manual is in the formative stage. Not all the experiments have been covered here though they are operational in the laboratory. When the full Manual is ready, we will make it available here. Electrical Engineering Department, Birla Vishvakarma Mahavidyalaya (BVM) Engineering College, Vallabh Vidyanagar, Gujarat, India Pin:388120. Experiment No-1 Radial Feeder Protection Theoretical Background: Whole of the Power System can be subdivided in to number of radial feeders fed from one end. Generally such radial feeders are protected by over current and earth fault relays used as primary relays for 11 kV and 66 kV lines.

2 For lines of voltage rating beyond 66 kV, distance Protection is applied as a primary Protection whereas over current and earth fault relays are used as back up relays. A simplified radial feeder network without transformers (in actual practice transformers do exist at substations) is shown in single line diagram of fig. below. SoSoR1urceFuseToLoadR2R3 STransmissionLineSection ISection IISection IIIABCDR1urceFuseToLoadR2R3 STransmissionLineSection ISection IISection IIIABCD Fig. A Typical Radial Transmission Line If the fault occurs in distribution network, fuse should isolate the faulty section.

3 Should the fuse fail, relay R3 shall give back-up Protection . Relays R1, R2, and R3 act as primary relays for faults in section I, section I, and section III respectively. If fault in section III is not cleared by relaying scheme at relaying point R3, relay R2 will act as a back-up. Similarly back-up Protection is provided by relay R1 for faults in section II. A,B, C and D are substations in fig. Generally Inverse time overcurrent relays with Definite Minimum Time feature (IDMT relays) are used in practice. There are many types of such relays available in relay-market, viz.

4 Normal inverse relays, very inverse relays and extremely inverse relays. The characteristics of these relays are shown in fig. The other types of o/c relays are 3 second relay and second relay. This means the time of operation of the relay is either 3 or second at Plug Setting Multiplier (PSM) equal to 10. Long time inverse relays are used for o/c cum overload application. Voltage restrains o/c relays have their own application. Very inverse relays are less prone to the ratio ZS/ZL. Extremely inverse relays are yet better.

5 Very inverse relays are faster in operation for close-in faults yet maintaining the discrimination with fuse and other relays. Extremely inverse relays are more meritorious 1in this aspect too. Instantaneous o/c relays are not immune to ZS/ZL ratio. Definite time o/c relays are 100 % immune to this ratio. Very inverse relays can be used with an additional advantage while protecting a machine or a transformer as they match with the heating characteristic of equipment better than their normal inverse equivalent.

6 Extremely inverse relays can best co-ordinate with the fuse characteristic. The aim of this experiment is to reveal these facts experimentally. Fig. Normal, Very and Extremely Inverse Characteristics aboratory Simulations:L a live model of a radial feeder fed from one end can be Referring to circuit of Fig. Main AC Circuit in the Experiment. AVR1R2R3230 V, 50 Hz1-phase, ac supplyC1-1C2-1C3-110/510/510/59 9 MCB550 (Load)18 (Fault resistance)S1S2S3 AVR1R2R3230 V, 50 Hz1-phase, ac supplyC1-1C2-1C3-110/510/510/59 9 MCB550 (Load)18 (Fault resistance)S1S2S3 Section -ISection -IISection -IIIS ection -ISection -IISection -III 2 This is only a single phase version of a radial feeder.

7 Transmission lines are simulated by Fig. Control Circuit in the Experiment. 9 ohms resistors as we are studying only the steady state behavior of the relays and the network. Circuit breakers are simulated by contactors. Distributor is protected by a Amp Semaphore indicators on the panel show the status of the contactor(whether ON or OFF). Visual neon lamp indictors are also used. Faults in different sections can be created by switches S1, S2 and S3. Fault limiting resistance of 18 ohms is used for practical purposes only, as otherwise the source would get shorted for a fault at start of the first section.

8 For fault in distributor, Ohmic value of load rheostats can be decreased. MCB simulates fuses or MCCB. In actual practice secondary rated current (1 Amp or 5 Amp) and relay rating should be same. Here secondary rating is 5 Amp and relay rating is 1 Amp. This is contradicting the practice for for practical purpose. 1111 DCDC SupplySupply(a) C1PB-1PB-2C1-2A1-1C2PB-1PB-2C2-2A2-1C3PB -1PB-2C3-2A3-1A1R1-1A1-2PB-3A2R2-1A2-2PB -3T2A3R3-1A3-2PB-3T30 V L1L2L3C1PB-1PB-2C1-2A1-1C2PB-1PB-2C2-2A2 -1C3PB-1PB-2C3-2A3-1A1R1-1A1-2PB-3A2R2-1 A2-2PB-3T2A3R3-1A3-2PB-3T30 V L1L2L3 (b) A1-3A2-3A3-3 Buzzerbulb110 VDC SupplyC1-3C2-3C3-3S-1S-2S-3S-1, S-2, S-3 are semaphore indicatorsA1-3A2-3A3-3 Buzzerbulb110 VDC SupplyC1-3C2-3C3-3S-1S-2S-3S-1, S-2, S-3 are semaphore indicators 3 Referring to control circuit of figure (a) ad (b)

9 , any section can be manually charged Fig. Control Circuit in the Experiment. bservations and calculations:nor made off using start (PB1) and stop (PB2) push buttons, which are spring loaded. On occurrence of fault, the corresponding section relay will operate and the concerned auxiliary relay A1, A2 or A3 will energize giving signal to the concerned contactor and making it off. This will also activate the buzzer and bulb which can be reset using Accept pushbutton PB3. Back up can be shown by using switches T1 and T2 on the panel.

10 Time of operation of relays can be measured by a time interval counter connected as shown in fig. (c). S1S1S1A1-4A1-4A1-4 (c) S2S3To timer Start terminalsA2-4A3-4To timer Stop terminalsS2S3To timer Start terminalsS2S3To timer Start terminalsA2-4A3-4To timer Stop terminalsA2-4A3-4To timer Stop terminals O extreme faults in sections I, II and III by adjusting the Fault Location Fault Current (A) 1. Measure the fault currents forcorresponding rheostat in minimum (zero resistance) and maximum (full resistance) positions and using the corresponding fault-switch S1, S2, or S3 (refer fig.)