With two power-generating units shut in Chukha Hydropower Plant (CHP) and Mangdechhu Hydroelectric Project Authority, the country is losing about Nu 25.22 million revenue every day.
One of the four generating units of the 336 megawatt (MW) CHP was down since August 27.
Managing director of DGPC, Dasho Chhewang Rinzin, said that the stator has been taken out onto the service bay. The rotor poles have been removed. “This has enabled a detailed analysis of the consequential damage due to the field connection bar coming loose.”
He said that from the assessment, some 10 percent of the stator punchings will also need to be replaced in addition to the stator bars and the rotor field coils. The rotor earth fault has also been located.
“The management and maintenance teams at Chukha supported by the other units are working round the clock to ensure that the unit can be brought back into operation before the next monsoon,” Dasho Chhewang Rinzin said.
The managing director said that the CHP made a quick assessment of the restoration works required and it was established that it would not be possible to bring the unit back into operation within the tail-end period of the monsoon that was remaining. “It was decided that it would be best to consult the original equipment manufacturer, M/s Bharat Heavy Electrical Ltd (BHEL), to ensure that the generating unit was properly restored before the onset of the next monsoon,” Dasho Chhewang Rinzin said.
He said that the DGPC has also consulted other experts to assess the extent of the damage and how best the unit could be restored.
Dasho Chhewang Rinzin also said that the CHP is presently preparing to award the work for the restoration of the unit considering two very important aspects. Firstly, the unit has to be restored before the next monsoon. Secondly, it is being proposed to make a few small changes in the design and engineering of the field connection bar to ensure that such incidences, although rare, do not occur in the future. “These design changes, if felt necessary, may get be replicated in the other generating units and at the other power plants also,” he said.
He said that it is very crucial for DGPC and the Mangdechhu management to fix such problems at the earliest and bring the generating units back on-line. “The monsoons are fast receding and while that provides some respite, the timeline is to restore the generating unit of CHP latest by April 2020.”
One generating unit at CHP experienced a severe rotor earth fault on August 23, 2016. The rotor earth fault could not be located and was later determined to be dynamic in nature. To isolate and to help locate the fault, a field connection bar was disconnected between the slip ring and the rotor rim.
While on the mechanical run, it appears that the field connection bar came loose with consequential damage to the stator bars and the rotor poles. “The incident is still being analysed to determine the root cause,” Dasho Chhewang Rinzin said. “It was fortunate that the damages were limited to the stator bars and rotor poles due to the quick actions taken by the officers on duty to bring the unit to a quick stop.”
Dasho Chhewang Rinzin also clarified that one of the Chukha’s generating unit broke down on August 26 and not from the second week of August as reported earlier.
Mangdechhu Hydropower Plant
The third generating unit of 720MW MHPA in Trongsa is also temporarily suspended since September 28.
Dasho Chhewang Rinzin said he cannot speak on behalf of MHPA as it is under another management. “However, there has been a number of initial problems that were encountered during testing and commissioning. New projects normally face such problems.”
He said that while three generating units are operating at the moment, a problem that has cropped up with the fourth unit is being rectified. “River inflows are decreasing and it is understood that the project management, the electro-mechanical equipment manufacturer (BHEL) and the operation and maintenance team are working closely together to rectify any problems there might be with the generating units.”
The joint managing director of MHPA, Chencho Tshering, said that the maintenance should be carried out for each unit as per the operation manual guideline after running it for more than 500 hours.
“The machine unit 3 is stopped for technical inspections of runner and simultaneously the repair of pneumatic brakes in unit three is carried out for one push-button operation,” he said.
The water volume currently is depleted to 90 cubic metres and each unit requires 29.5 cubic metres per second with 10 percent E-Flow in Mangdechhu basin.
Implication in revenue
Dasho Chhewang Rinzin said that there are always revenue losses when a generating unit gives problems during the peak monsoon season. “At rated +10 percent, a generating unit at Chukha hydropower plant would generate over 2.2 million units that translates to Nu 5.65 million in revenues on a daily basis.
In case of Mangdechhu, Dasho Chhewang Rinzin said a generating unit would generate some 4.75 million units that translates to Nu 19.57M in revenues on a daily basis. “But such break-downs sometimes happen even under best of conditions. Under such circumstances or even otherwise, operation and maintenance teams work round the clock to restore the units as soon as possible to minimize such losses,” he said.
The power from Chukha is exported at Nu 2.55 per unit while MHPA tariff is fixed at Nu 4.12 per unit.
Additional reporting by Nim Dorji in Trongsa.