CESC Special Protection Scheme — Grid Islanding (Kolkata)

In July 2012, a grid collapse blacked out over 600 million people across India — but Kolkata mostly stayed lit, because CESC's automatic islanding scheme cut the city loose from the collapsing grid.

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Kolkata's privately owned distribution utility, CESC (Calcutta Electric Supply Corporation, serving roughly 3.6 million consumers in and around the city), runs a Special Protection Scheme that automatically detaches its network from the wider regional grid — "islanding" — when it senses a severe external disturbance. The scheme proved itself on 31 July 2012, during the Northern/Eastern/North-Eastern grid collapse that cut power to over 600 million people, the largest blackout in history by population affected: while every other district of West Bengal went completely dark, according to the state's own chief minister at the time, CESC's islanded network kept Kolkata running (with a roughly 500-megawatt shortfall) and even continued to power the Kolkata Metro. The islanding logic runs on a SCADA/Distribution Management System that CESC's own technical disclosures date to "since the 1990s," alongside three other special protection schemes including under-frequency load shedding.