…  after three months of shutdown 

Hydropower: Dagachhu Hydropower Corporation Limited has rectified the fault in the tailrace tunnel (TRT) and begun generating power since last week.

The project was shut down since December 25 following a restriction in the flow of water from the TRT. With restriction in the flow of water, only 90 megawatt (MW) of power could be generated, of the designed 126MW.

Chief Executive Officer Thinley Dorji said the fault in the TRT was rectified by lowering the invert of the tunnel by 1.5 metres  from the junction where the water for the two generating units joined the 655m section of the tunnel.

“We completed the rectification without any problems,” he said.

However, power generation of the project is only 15MW currently.  The CEO explained that the low power generation was because of lower river inflow.

The present river inflow measured only 6 cumecs (cubic metre per seconds).

“The full capacity generation at 126MW is possible when the river discharge is at least 50 cumecs, and this is available for only for two months (60 days) during the monsoon,” he said. “With the rectification of the TRT completed, we do not foresee any problems in generating the full 126 MW when there is enough discharge in the river.”

With an anticipated loss of 42 MU (million unit) of electricity during the shutdown, the revenue loss is estimated to be about Nu 121 million (M).

The rectification of the tailrace tunnel was based on hydraulic simulation of the designed discharge through the tailrace tunnel. “We do not expect that there will be similar problems in future,” he added.

The CEO also said  that as soon as the problem was noted, all parties involved in the project, the management, consultants and the contractors  got together to work out and implement a solution.

Consultations were also held with experts beyond those involved in the project. “That enabled the project to quickly decide on the most suitable remedial measure, which was implemented in the most expeditious manner and with the minimum loss of generation and revenues.”

Civil Works Contractor carried out the rectification of the tunnel with no cost to the Dagachhu project.

In an earlier interview, the deputy CEO of the project, Sonam Wangdi said, they tried rectifying the problem without having to shut down the power plant by increasing aeration in the turbine pit-by drilling aeration hole. It did improve the flow and power generation increased to 108 MW.

However on the recommendation of Electro-Mechanical Contractor, the generation was limited to 100MW.

Dagachhu project is the first to be managed by a Bhutanese team. It is also the first public-private hydropower partnership. Druk Green Power Corporation holds a 59 percent equity, India’s Tata Power Company Ltd holds 26 percent and the National Pension and Provident Fund (NPPF) holds the remaining 15 percent.

The project has 25-year sales agreement with Tata Power trading company to supply it with 500,000unit hours of power annually. This is expected to generate Nu 15B or over USD 250M income in the next 25 years for the government.

Besides royalty energy, all the project’s power will be exported to India.

Nirmala Pokhrel, Tsirang