After resolving the seepage issues on the cavern of the powerhouse, the only thing left on 17th December 2024 was running the two units, and here, project engineers and staff held their breath hoping that nothing would go wrong with them.
The launch went ahead, as planned, but after 13 days, both the generation units tripped and shut down on 30th December. The Bharat Heavy Electricals Limited (BHEL) engineer present at the site could work on and rectify one unit a few hours later.
However, he could not catch the flaw in the second unit, and so, the very next day a BHEL engineer flew in from Bangalore and worked on the issue and could get the unit up and running within 2 days of its shutdown.
The tripping of the units happened due to voltage fluctuation caused by an Excitation problem. The Excitation System regulates the power from the generators and allows it to be supplied to the power grid. The problem, in case of both the units, was caused by wrong wiring which was detected and rectified.
A senior official said that while both the units tripped, the shutdown was nowhere near serious as the previously problematic third unit of the 720 MW Mangdechu. In the Mangdechu project, an alien object was there in the unit.
To prevent any repeat of Mangdechu this time around, Bhutanese engineers were attached with BHEL engineers while installing the units to keep a close eye and be updated, and moreover, even a CCTV camera was placed right above the machine to see how it was being built and installed.
Meanwhile, to deal with the water seepage from the upstream wall in the powerhouse cavern near two units that were launched on 17th December 2024, some of the Control System machinery near the wall have been covered in protective plastic cover just in case, and the plan is to build a partition wall in between the seepage wall and the Control System.
The seepage is on the left side wall while entering the power house and the wall is around one meter from the machine.
The fear was that that if the water seepage continues and water enters, the control system then it will malfunction, leading to the overall malfunctioning of the units. However, senior officials assured that it will not be allowed to happen and rectification measures are already being put in place. Officials also say that some amount of seepage is expected in an underground powerhouse, and so drainage facilities are built in to carry away water.
The control system keeps an eye on things, like water levels, turbine speed, generator performance, and power output. It collects data from sensors placed around the hydropower plant. Based on the data, the control system can make adjustments. For example, if the water flow is too high or low, the control system will change the turbine speed to keep power production steady.
The Direct Current (DC) system, which powers the control panels, sensors and switches, is also facing a ground fault or leakage of electricity.
Ground faults occur when electricity escapes from its normal route and flows directly into the earth, which may lead to shocks and fire hazards if it happens at a place where electricity can spark or overheat.
It can cause shocks, fires, or damage to electrical equipment. The concerned officials are trying to trace and troubleshoot the ground fault without a concrete result, and are planning to insert aluminum cladding, and the equipment are expected to reach by next week.
However, despite the above issues the project so far has been a success compared to P I and it overcame many challenges to be completed.