"Momina Klisura" HPP on its 50th anniversary: After the rehabilitation, it works at full capacity, with new equipment and with greater flexibility

Marinela Arabadzhieva

The rehabilitation of the Momina Klisura HPP is important not only for the plant. It is important for the country as a whole, as hydroelectric plants (HPPs) are a main pillar of the country's energy system. This was stated by the executive director of the National Electric Company (NEC), Martin Georgiev, at the official opening of the modernized plant. This is happening on a day when the Momina Klisura HPP turns 50 years since its commissioning. Successful completion of rehabilitation is key. NEC is the largest producer of electricity from renewable energy sources in Bulgaria, and we are aware of the sustainable management of this sector, as it is important for the decarbonization of the country, Georgiev pointed out.

"The modernization of the plant will contribute to the reliable operation of Bulgaria's electricity system in the coming decades," Deputy Minister of Energy Krasimir Nenov said. He also emphasized the role of the Momina Klisura HPP in the decarbonization of our country. The Deputy Minister of Energy described the project as a "great example" of cooperation with a reliable partner such as the European Bank for Reconstruction and Development (EBRD) and, in particular, the International Fund "Kozloduy" (IFK) managed by the institution.

The Belmeken-Sestrimo-Momina Klisura cascade includes the Belmeken Pumped Storage Hydroelectric Power Plant (PSHPP), the Sestrimo Hydroelectric Power Plant (HPP), the Momina Klisura Hydroelectric Plant, the Belmeken Dam, the Stankovi baraki day leveler and the Momina Klisura day leveler. It is located on the northeastern slopes of the Rila mountain and extends from 1920 m above sea level at the Belmeken dam up to 251 m above sea level at the Momina Klisura hydroelectric power station. The total installed capacity of the cascade is 735 MW in generator mode and 104 MW in pump mode.

"Momina Klisura" HPP, part of the cascade, is located about 100 km southeast of Sofia. The plant is a derivation plant with an installed capacity of 120 MW and is the third last step of the "Belmeken-Sestrimo-Momina Klisura" hydropower cascade. The average annual electricity production is 136 GWh. It was put into operation in 1973 and this year marks its 50th anniversary.

The scope of rehabilitation of Momina Klisura HPP includes design, manufacture, supply, installation, technical adjustment, testing and commissioning of equipment such as new ball valves, hydraulic cylinders for guide apparatus and synchronous turbine dischargers, turbine equipment, pumps for technical waters, new turbine regulators, excitation systems and control and monitoring systems for the entire plant with new operator stations.

"The rehabilitation of the plant was carried out in two stages. The first stage covered one hydro unit while the other was operating. After the rehabilitation and successful tests, it was put into regulatory operation," explained the head of the Momina Klisura HPP, Angel Bogdanov, clarifying that the plant did not stop working.

"During the rehabilitation period, it operated with a power reduced by half - with 60 MW, while now it is already at full power of 120 MW," he added. According to Bogdanov, after the new equipment was put into operation, the plant works much faster and more efficiently.

"The new systems are more flexible and in four and a half minutes the hydro unit goes into parallel with the electricity system and can produce. Before rehabilitation, it took 10-12 minutes. So, considering the commissioning process, there is a possibility of islanding regulation, which is extremely beneficial to the power system. Before the modernization, we did not have this possibility. Now we have one," he added.

According to Bogdanov, with the new equipment, the life of the Momina Klisura HPP is extended by at least 20 years.

The modernization of the plant is part of the project for the rehabilitation of facilities of the hydropower system, co-financed with grants from the EBRD-administered "International Fund to Support the Decommissioning of Units of the Kozloduy NPP" (KIDSF) and the company's own funds.

The overall modernization of the "Belmeken-Sestrimo-Momina gorge" cascade is worth 19 million euros and is being implemented in stages. The modernization of the "Momina Klisura" HPP alone is of the order of 5 million 700 thousand euros. Financing is from own funds and from the Kozloduy International Fund.

The companies working in the field of hydropower equipment are not many, it became clear from the explanations of the representative of the rehabilitation consortium KONČAR KET - ČKD BLANSKO – RUDIS, Runic. He emphasized that considering the solar capacity in Europe, the hydropower capacity is far less. According to Runich, in a recent conversation with the EC, the hydropower circles requested a change in the energy policy and the allocation of more funds to the sector, given its great importance for decarbonization. "The Momina Klisura HPP rehabilitation project contributes to this initiative," he pointed out, emphasizing its importance for the KONČAR KET - ČKD BLANSKO - RUDIS consortium itself.

The Momina Klisura HPP team was honored with a plaque, which the Executive Director of NEK Martin Georgiev presented to the manager Angel Bogdanov.