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LAHORE: The second unit of Tarbela 4th Extension Hydropower Project resumed its operation on Friday after engineers removed the fault with its draft tube gates.

Last week, the first unit of the project was put back into power generation after the engineers lifted the draft tube gates that were stuck when silt was piled up because of unprecedented slide of water levels to the dead level and issues with valves on the penstock.

According to an official, the project is required to undergo testing for another 570 days of defect liability period (DLP) with total responsibility of the contractor for its repair, maintenance and replacement. “Tarbela produces more than 3,400MW energy through its 14 units commissioned on its first three tunnels. The project of three units of 470MW each was planned in 2012-13 on 4th tunnel called Tarbela 4th Extension to add 1,410MW to the national grid. A coordinated construction schedule was planned to make full use of flood season of 2018. The first unit was inaugurated on March 10, 2018,” explained a source.

He said that taking full consideration of hydrological data of the last 10 years, the wet commissioning of the first unit was carried out between Feb 20 and March 10. Wet commissioning is about uninterrupted tests, including mechanical speed, balancing of generator and load rejections. Fortunately, there were sufficient water levels and during wet commissioning, the unit remained at different loads till maximum load of 303MW as per water head.

Unprecedented changes in hydrological behaviour, climate change and huge deposits of silt in Tarbela led to lower water levels. Later, the unit was completely flushed, cleaned and shut down on March 11. However, sequel to water levels raise in June, the unit restarted and ran optimally without any trouble, producing 173 million units till July 5.

The official said that following another unprecedented slide of water below the dead level, the unit was again shut down.

He said the movement of pivot of silt delta and a crack in one of the valves (purely a technical issue) led to jamming of draft tube gates. The project is now under testing and the defect liability period. Valves have been replaced. Both the stuck gates had been raised without compromising technical regimes, he added.

A press release issued by a spokesperson for Wapda says that first and second units are adding 300MW and 470MW to the national grid.

“The third unit of the project is also complete and expected to start power generation by the end of this month,” it adds.

Published in Dawn, September 15th, 2018