Voltage Transformer Protection Based on Distinguishing Ferroresinance from Permanent Faults

Ferroresonance is highly probable in voltage transformers connected to ungrounded power systems.It is important to damp transient oscillations after ferroresonance occurrence in order to improve accuracy of measurements as well as protecting voltage transformer. One of the most effective methods to suppressferroresonance oscillations is connecting a damping resistor at open delta connection in three phase systems. However, when a permanent fault happens, zero sequence currents damage the resistor severely.This paper offered a new algorithm to distinguish ferroresonance conditions from permanent faults andisolate the damping resistor when a permanent fault condition is detected. Simulation results certify the accuracy and practicality of the proposed method.

Keywords:

Ferroresonance , Permanent Fault , Voltage Transformer , Damping Resistor