LAHORE: A fact-finding committee has pointed out a fault in the switchyard of 747MW Guddu power plant that led to tripping of some other plants including the 1,200MW Haveli Bahadur Shah (Jhang), leaving whole of Punjab and Khyber Pakhtunkhawa and parts of Sindh and Balochistan without electricity for many hours on May 16.
The inquiry report on the major power breakdown was submitted to the then federal minister (Power Division) a couple of days before the end of the PML-N’s government by the committee. However, the government sealed it after deciding to not make it public, Dawn has learnt.
According to an official source in the Power Division, the committee while probing causes behind the breakdown reached a consensus that the fault originated from the switchyard of the Guddu-747 plant, sending it in island mode first and then tripping other plants of the state-owned generation companies (Gencos).
Fault in switchyard cascaded through the entire system in the North
“The fault caused deletion of as many as 2,800MW from the system within 30 seconds. Later its cascading affect travelled further and hit the recently inaugurated 1,200MW HBS plant after its frequency didn’t set, match or absorb the transmission and grid system frequency. Resultantly the frequency dipped to 45.5, playing havoc with the other plants and transmission and distribution lines that started tripping one by one,” the official, who requested anonymity, explained while discussing some findings of the report.
As the breakdown got worse, it also separated the North from South, leaving distribution companies with no option but to observe a massive forced loadshedding in a bid to reduce the load and avoid tripping of more plants. There was a general perception in the ministry that tripping of the 500kV/220kV double circuit Guddu-Muzaffargarh and DG Khan transmission lines caused the breakdown. The report also recommends strengthening the protection system in north to avoid such incidents in future.
On the other hand, public sector energy experts term the report as not based on facts as it has tried to defend the National Transmission and Despatch Company that is actually responsible for not upgrading its system that doesn’t provide adequate stability to the plants (especially the new ones) maintain their standard frequency ranged from 49.5-50.5. “That is why the HBS gas-fired plant went into the safe mode, which means that it continued to run, but didn’t generate power,” an expert, who desired anonymity told Dawn.
He said there were two type of frequencies — an adjusted frequency (49.5-50.5) provided to the plants by the grids’ system and the plant’s own frequency called Rate of Change in Frequency (RCF).
He said before blaming the HBS, one must see things deeply with background knowledge and study. He mentioned a power breakdown in the past that hit the integral parts of machines/turbines of the four sister plants (each ranging from 200-250MW), including one near Sheikhupura.
“When the breakdown occurred, the grid system didn’t give stability to the newly installed machines at these plants due to frequency mismatch. So the compressors of all these plants became out of order, leaving the plants idle for about six months,” he added.
For resolving the issue, experts at that time suggested taking extra safety/protection measure that could help machines going into island mode rather than tripping and damaging their own parts. He said new plants’ machines operate with 2,500-3,000 RPM while the old ones run on 1,000 RPM.
So the transmission system is an old one suiting aged plants and not the new ones. HBS too is a new plant with modern machines. Therefore, their behaviour will be different whenever they will not have the proper grids’ system stability to maintain the frequency.
“That is the reason behind taking the plant in safe mode and the government needs to have extra safety measures at HBS and all other new plants to avoid such incidents in future,” the official recommended.
Published in Dawn, June 5th, 2018