Impact of Sub Synchronous Resonance on operation of protective relays and prevention method

Synchronous Resonance (SSR) is a phenomenon in which electrical energy is exchanged between generators and transmission systems below power frequency. It can be caused due to interaction of a series compensated transmission line with a generator; in addition, results in oscillation in the shaft and power swing. SSR causes increasing the magnitudes of voltage and current consequently occurrence of ferroresonance. It is obviously clear that protective relays are affected in such conditions. Although SSR is damped by FACTS devices protective relays must be adaptive to prevent mal operation independently. In this paper, Manitoba Hydro electrical network with series capacitors is simulated to investigate impact of SSR on operation of overcurrent relay. Ferroresonance occurs in most SSR conditions. Hence, in order to distinguish protection of hydro generator against sub harmonics, which interact with natural frequencies of the rotor; in addition, increasing reliability and security of protection a logical SSR detection algorithm based on sub harmonic measurement and ferroresonance analysis in time domain is proposed for overcurrent relay and examined in the network.