Question

Assume a directional relay that calculates and compares zero sequence current (lo, operate quantity), with zero sequence voltage (-3Vo, polarizing quantity). The relay operates with maximum torque when lo lags -3 Vo (negative 3 Vo) by 65 degrees, which indicates a forward fault: (12 points) Calculate the polarizing and operating quantities from the following phase quantities VB N-1152-118° kv Ve N=119 1170 kV .A 23202-36° A Assume the VT ratio is 1400/1, and the CT ratio is 400/1. The relay characteristic requires the following Polarizing: 13Vol > 2V secondary zing: 3Vo> 2V secondary .Operating:lo0.5A secondary [NOTE: The quantities are lo, not 3lo, and 3Vo, not Vo) Using phasors and the characteristic of this zero sequence directional relay, determine whether the element will indicate a forward fault (operate decision) or a reverse fault (non-operate decision) Phasor diagram must show the reference phasor, maximum torque line, and operate and non- operate zones. Clearly label all phasors.

Answer 1