An Adaptive Algorithm Based on Subharmonic and Time Domain Analysis to Prevent Mal Operation of Overcurrent Relay During Subsynchronous Resonance

Subsynchronous resonance (SSR) is a phenomenon in which electrical energy is exchanged between generators and transmission systems below power frequency. It happens due to interaction of a series compensated transmission line with a generator. It results in oscillation in the shaft and power swing. In addition, SSR causes increased magnitudes of voltage and current consequently occurrence of ferroresonance. It is obviously clear that protective relays are affected in such conditions. SSR can be damped by several methods; however, protective relays must be adaptive to prevent mal operation independently. In this paper, Manitoba Hydro electrical network with series capacitor is simulated by PSCAD/EMTDC. The impact of SSR and ferroresonance on operation of overcurrent relay is analyzed. An adaptive algorithm based on subharmonic measurement and ferroresonance analysis in time domain is proposed for overcurrent relay. The algorithm detects SSR and ferroresonance, and changes setting values of the relay to prevent mal operation. Furthermore, it distinguishes protection of the hydro generator against subharmonics, which interact with natural frequencies of the rotor. Finally, the algorithm is examined in SSR condition to certify the correct operation.