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Planned Upgrade Set the Stage for Indian Blackout

Upgrading an extrahigh-voltage AC line created a weak link

3 min read
People in a dark building at night.
Photo: Adnan Abidi/Reuters

7 August 2012—Both blackouts in India last week originated with disturbances on the same transmission line, according to the National Load Despatch Centre (NLDC) [PDF], which is responsible for monitoring the national grid and managing interregional links. Prior to both grid failures, the line that connects Agra, in the northern regional grid, to Bina, part of the western grid 400 kilometers farther south, faced power flow well beyond its normal operating limits.

According to a preliminary notice that the NLDC released on 1 August, the 400-kilovolt circuit was carrying up to 1000 megawatts of power. In India, the transmission utility usually tries to keep power flow below “surge impedance loading” [PDF], a level at which the voltage at the sending and receiving end of the line is exactly the same because reactive power is neither produced nor absorbed. The 1000 MW of power flow was well above surge impedance loading for the section, which the NLDC calculated to be 691 MW. 

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