Seven states in the northern region, including Punjab, faced a blackout from 2.30am to 9.30am on Monday following a disturbance in the northern grid, which caters to 28% of the country's population.
Essential services were largely disrupted and life thrown out of gear as railways, airport, hospital emergency, water supply services were affected by the outage.
It was the worst blackout in north India in the last 11 years. The grid had failed earlier in 2001-02.
Officials said that the northern grid failed due to some technical snag at Agra which led to power disruption. Overdrawing of power by UP and Haryana was cited as the main reason.
"What we feared has happened. The grid was under severe stain as many states, particularly UP and Haryana, were overdrawing more power to meet their requirements due to poor monsoon," said an official, adding that states were overdrawing power despite several warning.
Norhern grid caters to all seven northern region states of Delhi, UP, Haryana, Punjab, Himachal, Jammu and Kashmir and Uttarakhand and UT Chandigarh.
The failure led to chaos in the entire region as all power stations were shut, as power distribution in all states is interconnected through the grid.
At the time of the filing of the report, Punjab had managed to restore only 40% electricity supply. "We are working on starting power generation at all plants and hopefully they will be operational by 10pm," said GS Chabra, director, generation, PSPCL.
Bhakra Beas Management Board (BBMB), which is main hydro unit of the entire region, was the first unit that resumed operations and helped thermal units to start operation. Restart of a thermal unit requires power.
"After two hours, we were able to supply power to major thermal plants," said a BBMB official, adding that that Sunday night was horrible as technical snag did not allow supply of power to Punjab-based power plants to restart.
"As there was some supply problem from BBMB, Punjab units were restarted at 9.30am onwards and subsequently all projects will be functioning in the next eight hours," said Chabra.
Train services were also disrupted in Punjab, Haryana and Chandigarh, leaving a large number of passengers stranded. Officials said over 200 train schedules were disrupted on account of the power failure.
Railways authorities later detached diesel-run engines from goods train to attach them to passenger trains to run them.
"After resumption of supply, Punjab first connected railway and hospital lines at 9.40am onwards. Then we restored supply to water supplies and later to domestic sector," said AK Verma,director, distribution. Next, he said, power to industry would be restored.