Islanding scheme for power transmission utilities

Mostly power utilities are connected with national grid at multiple grid interconnection points. Any unattended major disturbance in the national grid, may lead to tripping of inter-/intra-regional transmission lines and loss of generating units. These trippings/loss of generating units further results in load/generation mismatch in the national grid and finally leads to grid failure event. In order to minimize the occurrence of complete grid blackouts in India, regional protection committees are advising the power utilities to install a local defense mechanism to isolate their power network during grid disturbances. Defense mechanism will isolate the local network from the national grid well before grid collapse point to cater essential electric demand in local network with the help of local generation. As per the guideline issued from the regional power committee, an under frequency islanding schemes needs to be designed. The islanding schemes presented in this article works on the principle of load shedding corresponding to different rates of change of frequency and flat under frequency response. The designed protection scheme is implemented and its dynamic performance is assessed in the Delhi Transmission utility. The rate of change of the frequency will be sensed at load dispatch center and predefined load shedding takes place in online mode at 33/66 kV feeder to maintain the load generation balance in the islands(s) within the acceptable stability limits.