Technical Committee finds BHEL at fault in failure of 3rd unit in Mangdechu

The Monsoon season is at its peak but the third unit of the Mangdechu project is still not operational as it undergoes extensive repairs after a major failure and fire in 21st September 2020.

The team at the site is rushing to put the unit online by 31st July but it may take until the first week of August if not till mid-August. Even than the unit will have caused a loss of Nu 1.2 bn plus to the government revenue for 2021. This can jump to nu 1.8 bn in losses if it takes till September.

In 2020 the same unit after going down from 23rd May 2020 to 27th June 2020 had caused a loss of Nu 1.3 bn.

So far BHEL has blamed the Operation and Maintenance (O&M) staff for the faults while Bhutanese officials blamed BHEL’s manufacturing defects for the failure.

An independent technical committee constituted by the Mangdechu Project has found that BHEL is responsible for the failure of the third unit in question.

The remarkable thing about the four-member Technical Committee is that of its four members, it has three members from India in the form of Power Systems CEO from India, a former Director Technical from the National Hydropower Corporation of India, a senior former MD of various projects in India and only one member from Bhutan in the former MoEA Secretary Dasho Yeshi Wangdi.

The Technical Committee categorically says that there is no lapse on the part of the O&M staff of MHPA.

The report says that the committee observed that the O&M staff of MHPA always informed the Original Equipment Manufacturer (OEM), which is a polite term for BHEL, for their support and intervention during every incidence of faults since the machine was under the defect liability period, but the positive response from OEM was not forthcoming.

It says there are inherent defects of insulation of the windings and poor workmanship during the erection and assembly stage which caused the defects leading to oil spillage and carbon and soot deposits.

The erection was done by BHEL staff.

The report says that BHEL is responsible for the non functioning of the SOE recorder or Sequence of Events Recorder till August 2020. This basically means the failure of the system that provides a complete picture of the electrical network. It can also include playback of a previously recorded monitored data, calculated system parameters, sequence of events, and message log. This means this system could have recorded the faults that occurred till then.

It says the fault of 21st September 2020 is attributable to the inherent defects in the insulation and the windings of the generator. The windings are the wires that are wrapped around the machine and the insulation prevents the electric charge from going elsewhere. It also prevents any fire.

It also says that the extensive damages to the stator windings have happened due to the delay in the opening of the FB. It says BHEL’s design of unit protection scheme did not provide any redundancy to execute fail safe trip command to FB.

This essentially means that once things started to go down the system should have tripped faster but it took time to trip which exposed the machine to more damage.

The report says the Rotor earth fault relay connection scheme requires to be reviewed. This system essentially sends a tripping command when there is a fault.

Communication is being drawn up to send the findings to BHEL in India and to discuss the issue and the way forward.

The report will be presented to the MHPA Board. One option will be to explore the potential of the insurance companies paying for the unit.

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