Bulgaria’s state-owned utility Natsionalna Elektricheska Kompania EAD (NEK EAD) has signed a memorandum of understanding with Toshiba International Europe Ltd., the UK subsidiary of Japan’s Toshiba Corp., to restart operations at the Chaira pumped-storage hydropower plant.

The facility is the largest of its kind in Southeastern Europe and is located in the Rhodope Mountains near the town of Devin. It was commissioned in stages between 1995 and 2010. The plant is equipped with four reversible Francis pump-turbines, each rated at 216 MW in generating mode and 197 MW in pumping mode.

Units 1 and 2 entered service in 1995, making Chaira the largest pumped-storage facility in Southeastern Europe at the time. Units 3 and 4 were subsequently commissioned in 1999, completing the four-unit configuration.

“The Chaira pumped-storage hydropower plant (PSHPP), the largest in the country, has an installed capacity of 864 MW across four units. However, due to aging infrastructure, some units are currently out of operation, underscoring the urgent need for comprehensive restoration and optimized plant-wide operation,” Toshiba said in a statement.

The plant was idled in March 2022 following a serious turbine accident during post-rehabilitation testing of Unit 4. Bulgaria’s Ministry of Energy stated that the root cause was material fatigue combined with the original turbine design and cavitation effects.

“Toshiba has already been commissioned to carry out repair work on Unit 1 and will also conduct studies and provide technical support for the plant as a whole, including operational and maintenance support for Units 2, 3 and 4, as well as recommendations to enhance the reliability and efficiency of key equipment such as pumped-storage turbines and generators,” the company added.

Toshiba supplied the pumped-storage turbine and generator for Unit 1 of the Chaira plant in 1994. Its involvement later expanded to all four units. It also provided four generators with a combined rating of 940 MVA.

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