Ferroresonance in Southern Regional Grid of India- Grid Operator’s Perspective

In electricity networks where Back to Back (BTB) HVDC systems are connected to EHV AC lines having Fixed Series Compensators (FSCs), ferroresonance has been observed during post fault disturbances in the grid. This causes an undamped exchange of energy between FSC and the saturating magnetic circuits of the converter transformers in BTB HVDC system. This may also result in higher voltages and currents causing detrimental effects on power quality and sustained oscillations. Ferroresonance condition imposes threat to grid causing tripping of EHV lines, adversely affecting the reliability of the power system. In this paper, investigation on real cases of Ferroresonance observed in Southern Regional Grid of India in a BTB HVDC system at Gazuwaka have been discussed. Further, ferroresonace detection methods and techniques for mitigation of the effects of Ferroresonance have been discussed.