NEW DELHI/CHANDIGARH, Jan 2 — The all-important northern power grid, which supplies power in the entire north-western region, tripped twice at 4: 45 and 10: 19 this morning, respectively, resulting in disruption in power supply for over eight hours which stopped hundreds of passenger and goods trains in their tracks; hit flights in and out of the Delhi airport; affected business activity and industrial production besides water supply based on tubewells.

The tripping plunged the states of Punjab, Haryana, Himachal Pradesh, Delhi, Uttar Pradesh, large parts of Rajasthan and the Union Territory of Chandigarh into darkness at 4.45 a.m. According to sources in the power sector the fault had occurred at a 400 KV grid thermal power plant maintained by the UP State Electricity Board at Pankhi, Kanpur. The fault was identified at bus bar from where power is distributed, sources informed The Tribune.

Even VVIP areas in the national capital, including the Prime Minister’s residence, Rashtrapati Bhavan, and North and South Blocks, housing important Central Government offices, went without electricity for about 20 minutes as the Northern Grid failure triggered a shutdown of all the four power stations in the city at Rajghat, Indraprastha Estate, Badarpur and Dadri. Supply in the VVIP areas was restored only after the Delhi Vidyut Board (DVB) with the help of Power Grid Corporation of India (PGCI) diverted power supply from gas turbines.

The Prime Minister’s residence and the Rashtrapati Bhavan have back-up systems to meet such eventuality.

Sources said a sudden fault at Pankhi resulted in loss of hundreds of mega watts of power which runs through the grid. This led to a sudden decline in frequency of cycles required to maintain the grid. This loss of power had a cascading affect and the system collapsed, explained an engineer.

According to Union Power Ministry sources, the tripping occurred due to `under-frequency’ in the Pankhi plant due to intense cold wave triggered by rain. This kind of tripping occurs in thermal plants during winters primarily due to cold conditions which fails to meet the heating requirements for normal power generation and transmission. Sources said such breakdowns could occur in the near future too as the technology currently in use in thermal power plants does not have in-built protective mechanism to neutralise the negative impact of the cold spell.

Normally the grid has a self-protecting system of under frequency relays (UFR) which automatically shut down portions of the power supply to any given area as and when the frequency drops below the desired level. But this is effective only is case of gradual decline in frequency due to say an overdrawal but is not designed to handle situations like the one today.

Even engineers struggled to restore normalcy, the Union Power Minister, Mr Suresh Prabhu, said that a thorough probe would be conducted to fix responsibility for the sudden failure of the northern grid. “We have appointed a committee under the chairmanship of Mr R.N. Srivastava, Chairman of the Central Electricity Authority (CEA), to enquire into the breakdown of the grid,” Mr Prabhu told newspersons here. CEA has been asked to submit the report within a week entailing the reasons for the failure, suggest preventive measures and ways to restore the breakdown in the shortest possible time (in case of reoccurrence), he said.

Mr Prabhu claimed that 60 to 70 per cent of power generation was restored by 1700 hrs, adding that off-peak demand of 12,000 MW of the Northern Region is likely to be restored by 10 tonight.

Meanwhile, Power Grid Corporation of India Director (Operations) Bhanu Bhushan told The Tribune that restoration of normal power supply would take some time. “We are still in a critical stage’’ but engineers were at work for restarting the generation.

As it happens electricity fault always travels backwards resulting in the collapse of the grid and shutting down of power generating turbines at Bhakra Nangal, Pong and Dehar, Ranjit Sagar, Chamera, Ropar and Panipat Thermal power plants besides other hydel and thermal projects. Engineers at the Bhakra Beas Management Board (BBMB) — the biggest supplier of power to the grid — re-activated its Ganguwal hydel works at the outset to supply power to the thermal stations which take about 3 to 4 hours to provide peak power supply.

On the other hand, the grid was restored and was nearing full load capacity when it collapsed for the second time around 10: 19 a.m. This was probably due to sudden overloading resulting in drawal from various quarters, said sources.

Disruption in power supply brought more than hundreds of trains running in up and down directions to a grinding halt. Thousands of passengers on board the trains had to wait inside the bogies for several hours with minimal facilities. Later the railways managed to berth a few of the long distance trains at stations using diesel locomotives. Important long distance trains were running late between four and seven hours. Some of the prestigious trains like the Shatabdis were running late by three to four hours.