Calcutta, April 3: Foresight shown in the nineties saved Bengal today from a power breakdown whose domino effect could have wreaked havoc across the state.
The problem arose this afternoon when Jharkhand was forced to overdraw power from the eastern grid to tide it over a crisis triggered by the collapse of a thermal plant in Tenughat in the neighbouring state.
Once Jharkhand started to suck in more power, the frequency of power supply dipped, affecting the lines in Bengal.
The normal frequency is 50 cycles a second. Wide fluctuation in this rate can cripple transmitters.
If the dip in frequency is not controlled, it can set off a chain reaction that can cause permanent damage to equipment in sub-stations.
Such damage could have happened in Bengal today but for a cushion put in place in the nineties. The state power department, then under minister Sankar Sen, had installed a system called under frequency relays (UFRs) at key transmission points. UFRs ensure that sub-stations switch off on their own once the frequency drops below a certain level.
Learning lessons from two big grid collapses in the nineties, Bengal wanted to make sure that the transmission and distribution network is automatically isolated in the event of a contingency.
The effort paid dividends today. When the frequency dropped below 48.3 cycles a second because of Jharkhand's over-drawing, the UFRs activated themselves.
Following this, the substations at Malda, Satgachhia in Burdwan and Gokarna in Murshidabad, automatically tripped. Power outages did occur, but the impact was confined to the four areas.
The crisis was not over yet. Had the frequency plunged further, more UFRs would have been activated, setting off automatic shutdowns elsewhere.
Officials then stepped in. 'We immediately warned the Calcutta office of the Eastern Regional Load Despatch Centre (a representative body of the Power Grid Corporation that monitors grid discipline) and suggested that the 220-kv regional line from Santaldih to Chandil be switched off immediately to avert a disaster,' said M.K. Roy, member (commercial) of the state electricity board.
The line from Santaldih in Bengal to Chandil in Jharkhand was the one that carried power to the neighbouring state. After the line was switched off, the frequency started improving from around 3.30 pm.
'However, it took over an hour for the frequency to return to normal,' an official said.
As a result of the collapse of the state-owned Tenughat plant, the whole of Jharkhand, including capital Ranchi, reeled under power cuts.
Officials said the Santaldih-Chandil line was switched on around 5.30 pm after Jharkhand gave an assurance that it would not overdraw any more.
But Bengal districts reeled under two to three hours of power cuts this evening following the shutdown of two units at the National Thermal Power Corporation's Farakka plant on Saturday.
However, there was no shortfall in the CESC-served areas.