The Tala project also suffered during the heavy monsoon rains in July end that had even cut of the Phuntsholing-Thimphu highway.
A landslide knocked out an Auxiliary Supply Transformer that supplies power to the butterfly valve chamber. This chamber can stop the flow of water to the generating units from the surge shaft using its gates.
The Druk Green Power Corporation MD Dasho Chhewang Rinzin said that once the control room got the signal that power supply was not going to the butterfly valve it had to shut down three of the six generating units to go and ascertain the problem.
In the process there was vibration which disturbed the alignment of the three generating units. One of the units came back on line easily while another took three days to align and the third unit took seven days to align.
This meant a total generation loss of 29 million units which equates to a loss of Nu 68 mn.
The MD said that excessive rainfall and floods during monsoons does not do the hydro projects any good as the projects are already operating at full capacity and excess rains only mean more silt and debris.
The MD said that the first half of the year from January to June 2016 saw the poorest generation compared to the previous eight years due to less river flow caused by uneven rainfall and no snowfall.
He said he hoped that the situation would improve with the monsoon expected to be better then average.