LAHORE, Aug 23: Power supply to four districts of the Punjab was disrupted for over four hours following tripping of a 220kv line circuit breaker at the 500KV grid station in Gatti which triggered a chain reaction in the system.

According to Wapda officials, the circuit breaker got damaged at 11.51am, which put pressure on other lines and caused breakdown. "Sudden load on the 500KV system triggered further crisis by sending the entire system out of order."

Electricity supply to Lahore, Faisalabad, Sahiwal and Sialkot was affected. The power supply to all four districts was restored by 3.30pm and the rest of the system made workable by 4.35pm.

Wapda has constituted an inquiry committee, headed by a general manager, to investigate the matter. A former member (power) said Wapda had been living dangerously for the last 10 years as far as the Gatti-Muzaffargarh transmission line was concerned.

"At present, there is only one 500KV line that has the entire load. Once it trips, there is no other line to fall back on. Consequently, very high transmission have been caused."

At one point, he said, a Wapda team estimated this loss at Rs7 billion a year. Despite these crippling losses, the authority had not been able to build another line during the last decade, he added.

He claimed that the contract for the line had been awarded thrice in the past, but it had been cancelled every time for reasons best known to the authority. Outages caused by the same line had twice resulted in countrywide blackouts, but the Wapda authorities had failed to respond to the situation.

In fact, it should been built by the time independent power producers (IPPs) came online in the late nineties. The authority had given the contract only a few days ago and it would take another two to three years when the line could be fully operational if nothing went wrong during this period.

Akram Arain, the chief of the Lahore Electricity Supply Company, said the outage of 500kv line at Gatti hit southern part of Lahore, as city got some power supply from the Ghazi Brotha Hydel Power Station through the Rawat Grid Station.

"The power supply system is a tricky one. An outage of one transmission line overloads other and causes tripping. Similarly, if one transformer is damaged, it affects others."

He said similar things happened at generation stations and a chain reaction started with one of them going out. He said: "All these things happen in fraction of a second and the entire system goes down. The case of Monday is not different."

He hoped that with the commissioning of a few more 220kv lines, which were being constructed between Daudkhel and Bannu, Muzaffargarh and Gatti, and Lahore-Rawat already online, the situation might improve a bit. But, he conceded that the entire transmission system needed an overhaul.

Meanwhile, the residents of Gulberg, Model Town, Faisal Town, the Mall and the Bhati Gate faced a great deal of difficulty during the breakdown. In some areas low voltage caused inconvenience to people.