Increase of Production efficiency

Repair of 170 MVA transformer, Koman HPP

Scope

Repair and return into operation of the 170 MVA standby power transformer, 242/13,8 KV, No 319043 in Koman HPP, damaged in 2013 during operation in Unit no.4. The repair was performed in order to normalize the availability of reserve Units in Koman HPP. The lack of the standby power transformer in Koman HPP reduces the availability of reserve Units in case of eventual damage of any of the Units transformers, currently in operation, causing a risk of financial losses due to the lack of energy generation during the favourable hydro period.
The repair and availability of this transformer has enabled the return of the availability of Units in Koman HPP, thus normalizing the situation.

Main activities

The project for the on site repair of the 170 MVA standby power transformer in Koman HPP consists of:
• Dismantling, opening and ejection of the active parts (nucleus and windings)
• Dismantling of the phase A windings, damaged during the failure
• Replacement of phase A set of windings with new windings, specially manufactured for this transformer type
• Replacement of solid insulations made of paper gaskets at the windings of three phases
• Cleaning of the terminal tank and replacement of all the sealing gaskets
• Replacement of damaged and depreciated accessors
• Assembling the active rehabilitated part in the tank
• On site transformer drying and drying with hot oil circulation
• Replacement of utilised oil of the transformer with new oil
• Electric tests for every phase, including the final phase
• Sand blasting and painting of all the metal parts (tank, breather, coolers and other accessors).

Expectations

All the works for the on site repair of the 170 MVA transformer were performed with quality. The final tests and the 72-hour load test are successfully performed. The investment was completed within the terms established under the contract.
The transformer was returned into operating conditions and is ready for normal operation according to the
dispatcher regime plan.

The transformer is expected to operate normally and to pass the 1 year technical guarantee established in the contract. During the technical guarantee period, all the controls and tests will be conducted to verify the isolation level and other technical parameters