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July 1, 2018

Power plants’ shutdowns debilitate transmission system


July 1, 2018

LAHORE: Auto shutdowns of electricity generation plants are aggravating power woes as they further destabilise the transmission system, obstructing supply to the grid, a latest official report said.

The report on the system’s breakdown discussed the factors behind the recent successive power failures. It attributed the breakdown to tripping of re-gasified natural gas- (RLNG) based power plants during the critical phase.

The projects’ officials, however, denied the report’s findings.

The disconnect is usual due to built-in protection mechanism, they said.

Recently, the RLNG-based power plants abruptly closed power generation in the midst of transmission system’s recovery following a fault in Guddu power plant.

The failure of shunt reactor at Guddu plant yard and system initiated a partial system breakdown on 16 May amid power shortfall.

The report, however, said the system got stable due to operation of under frequency relays in the northern part, but then went into blackout due to early outage of recently-commissioned Haveli Bahadur Shah and Bhikki RLNG power plants in the centre region.

A senior official of the National Transmission and Despatch Company (NTDC) said RLNG-based power plants used to close their operation “in such an eventuality”.

The official, requesting anonymity, said the managements of the plants were asked to recalibrate auto-shutting system by making the parameters more flexible to avoid such a situation.

An energy ministry official said RLNG-based power projects were set up keeping in view their ability to produce power with much reliability and ease.

These modern plants quickly come online. “Unfortunately, the plants do not work in extreme situation.”

Officials said the managements of RLNG-based power plants are not paying heed to demands to recalibrate auto-shutdown features to cope up with the system fluctuations and without compromising on production.

A senior official, associated with a RLNG power plant, said there is no issue in recalibration, “but the findings (of the report) are incorrect”.

The official, on condition of anonymity, said all the power plants have built-in protection mechanism, and when the grid frequency fluctuates, the plant automatically disconnects from the grid and go into island mode.

The RLNG plants will continue to do so in the future for protection, he added.

“In fact, NTDC needs to fix its system otherwise this will continue to happen.”

The report said the massive failure of power network on May 21 occurred due to overloaded electricity transmission and distribution system, varying power generation and unbalanced power input from north, affecting power supply.

The failure started after outage of major 500/220 kilovolts of auto transformers at Rawat grid station.

This was followed by cascaded tripping as per protection schemes, saving sensitive power system equipment from damaging.

The report found that the tripping occurred when hydropower generation from Terbela and Mangla dams was low and Nandipur power plant was on a shutdown due to maintenance, which subsequently led to overloading of Rawat and resultant tripping.

Officials said system operator has been keeping the key installations in constant check to control the overloading and resultant tripping nationwide after the incident.

The report further said there was imbalanced power input from north and south during May.

Low hydropower generation in north was a problem as Mangla and Tarbela dams were generating almost half of their generating capacity due to low water flows.

Low hydropower supply caused overloading of grid stations and resulted in shortage of power supply to Islamabad, Gujranwala and Faisalabad power distribution companies.

Tripping of Port Qasim and Balloki power plants further aggravated the situation, reducing generation to 2,500 megawatts in peak summer.

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