Kuensel | Dechen Dolkar | September 18, 2024
Barely a month after successfully testing and commissioning of the first two generating units of the 1020 MW Punatsangchhu-II Hydroelectric Project, water seepages have been detected from the crown of the powerhouse cavern in the machine hall, causing a temporary suspension of testing and commissioning activities.
The initial reservoir filling began on February 21, 2024, after the completion of civil works for key components of the project. This was followed by the filling of the water conductor system, which includes the desilting chambers, headrace tunnel, surge shaft, pressure shaft, and tailrace tunnel.
On August 15, 2024, a key milestone was achieved with the mechanical spinning of the first two generating units.
However, reports of a major leakage from the turbine stirred concerns.
The Ministry of Energy and Natural Resources (MoENR) and the Chairman’s office for Hydropower projects stated that while there was no turbine leakage, water seepage from the powerhouse cavern had been detected.
This issue has disrupted wet testing for the first two units and slowed the assembly and installation of electro-mechanical equipment for the remaining units.
An MoENR official said that the seepage issue was taken up with the designers and consultants, Central Water Commission and Water and Power Consultancy Service Limited, who recommended immediate remedial measures such as installing a false ceiling and provision of temporary channels to manage the seepage.
The technical group met on September 5, 2024, and recommended immediate remedial measures, which include immediate installation of false ceilings in the powerhouse cavern and service bay and dewatering of the water-conducting system.
The project management team has begun lowering the dam water level to empty the headrace tunnel, surge shaft, and pressure shaft. This process is expected to take over a month, with a similar time frame required for re-filling the water conductor system.
The official mentioned that the installation of electro-mechanical equipment is expected to resume after false ceilings are installed, which is expected to take about three months.
“The timeline for resuming the commissioning of the generating units will depend on the treatment measures recommended after inspecting the emptied water conductor system,” he added.
For the long-term solution, the technical group has determined that the water-conducting system (headrace tunnel, surge shaft and pressure shaft) has to be emptied to locate the source of the seepages and implement appropriate measures to address the seepages at the source.
The project has initiated advanced planning to address these issues, including consultations with designers, consultants, and contractors, including identifying vendors and sourcing equipment and materials, to expedite the necessary repairs.
The official said that seepage issues are not uncommon in hydropower projects, especially during the initial stages of reservoir filling and system activation. “These issues typically subside over time,” he said.
“The behaviour of the powerhouse cavern is being monitored through data collected regularly from instruments, and this data is being interpreted by scientists from premier rock mechanics institutes like National Institute of Rock and Mechanics and the designers,” the official said. “So far, no signs of distress in the powerhouse cavern have been observed.” When asked if the timeline pressure from the government was a factor contributing to the water seepage, the official clarified that there was no timeline pressure from either government, and no compromises were made in the quality of the work executed. “However, due to the seepage in the machine hall, the commissioning of the units is being delayed,” the official said.
DZ 
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