Spontaneous oscillations and modal resonance in Indian grid: A case study

Inter area oscillation in large grid is inherent to a large system. However, it is desirable that these oscillations are adequately damped for a secure and reliable transfer of power. Occurrence of Low Frequency oscillations in inter area range have been observed in the Indian grid after the synchronization of Southern grid with the rest of the Indian grid. These oscillations were generally triggered by unforeseen grid events such as unit tripping, load loss-changeover, line tripping etc. However, on one occasion, spontaneous oscillation and modal resonance was observed in the Indian system during normal operation. This paper presents the case study of that experience. The event was captured and analyzed with the help of synchrophasors units installed at various geographical locations across the grid. Possible remedial measures for further studies have also been suggested for improving the system security during such oscillation.