Identification of Distance Relays Vulnerable to Power Swing in a Power System

Distance relays in a power system are prone to trip on power swing. A power swing blocking (PSB) function has to be provided with it to avoid the mal-operation. However, utility engineers are generally biased towards dependability. Therefore, zone 1 of a distance relay which provides primary protection. It is normally not supervised by such PSB function, but some times such tripping under severe power swing may trigger further cascade tripping in the system. Hence, utilities have to decide a policy for implementing the blocking function for various zones of the distance relay without compromising the dependability. The present paper offers an offline simulation based testing tool to identify distance relays vulnerable to power swing so that PSB function can be provided to only these relays selectively. The logic can be further extended to decide which zones to be prevented from tripping during power swing.