DEVELOPMENT OF QUADRILATERAL RELAY FOR EHV/UHV LINES

Abstract

The electrical power system should be designed and managed to deliver energy to the utilization points to with both reliability and economy. Transmission system is essential to route power from generation to load centers, which must have maximum in-service availability. The exposed nature of line makes them fault prone, and protection devices must trip to initiate isolation of any faulted circuit. Distance relays are used to detect and protect faults in transmission lines. Today, many manufacturers offer a choice of either mho or quadrilateral characteristics. The distance relays provide three zones of protection. Zone 3 is necessary as a backup for Zone 1 and Zone 2. In this report Quadrilateral characteristics compared with Mho characteristics shown that the correct choice and application of characteristic will improve the protection system dependability and security. The electric power system maintains a dynamic and delicate balance between generation and load in normal operation condition. A disturbance, such as a sudden change of load, a power system fault, or a trip of a large generation unit, may break the balance, cause the oscillations among the generator rotor angles and force the generators to adjust to a new operating condition. The oscillation will cause either stable and/or unstable power swings. However Zone 3 has a disadvantage that during a heavy load condition it may operates because the high load impedance moves into the zone. If Zone 3 mal-operates, it causes disconnection to transmission line consequently the adjacent lines may be over rated because the change of power flows. This may lead to cascading outage and power system instability.