Hydropower plant Boyana 100 years old
One of the oldest power plants in Bulgaria still operates today with its original equipment
On 12 January 2024, National Electricity Company celebrated the 100th anniversary of its oldest hydropower plant, Boyana Hydro Power Plant. The event was held in the presence of the Minister of Energy Rumen Radev, Deputy Minister of Energy Nikolay Nikolov, Chairman of the Board of Directors of Bulgarian Energy Holding prof. Vesselina Buchkova, veterans and employees of NEK.
"It's a pleasure to be here. It is a huge responsibility for the colleagues to keep the plant in functional condition and they deserve admiration for their excellent work," said the Minister of Energy Mr. Rumen Radev in his address. "The shift engineer's books that I have seen are amazing artefacts and remind us that to get somewhere, long before us, someone started, another developed the idea, another built on it. They were all professionals, they stood up for their ideas and ultimately succeeded."
The Executive Director of NEK Eng. Martin Georgiev greeted the guests at the event and emphasized the key role of the power plant for the Bulgarian capital city in historical terms. Commissioned on 13 December 1923, Boyana HPP contributed to the modern image of the city. A huge construction achievement at the time, the plant introduced leading European technologies and created economic and social benefits for society.
With its history of over 100 years, Boyana HPP is an example of the enthusiasm, consistency, and professionalism of the Bulgarian power engineers. The remarkable anniversary of the plant is not only a matter of pride for NEK, it is also a national pride.
Eng. Georgiev expressed his gratitude to the team of Boyana HPP for their efforts, professionalism and dedicated work and wished the plant to continue its operational life for many years and to be as trouble-free as ever.
At NEK, we are proud of the fact that the plant is still functioning flawlessly today with authentic hydro generators and equipment, while also contributing to the production of clean green electricity.
Additional information
Technical data
The plant is a diversion plant equipped with 2 Pelton type horizontal turbines of 1.24 MW capacity. The average annual production of the plant is 1,8 GWh. The primary energy source is the water intakes on the Boianska River.
History of Boyana HPP
Immediately after the Liberation of Bulgaria, the first investment projects began to contribute to the modernization of the country and to give it a European look. Electricity supply was an essential part of the development plan to create good living conditions in the country. With the election of Sofia as the capital of Bulgaria in 1879, the issue of electrification and the construction of an urban tram network in the city was put on the agenda.
The construction of Boyana HPP was originally planned as part of the city's electric lighting project. Consultations with investors and companies producing hydropower facilities had been launched. A construction site was selected and a procedure for the expropriation of the properties was launched.
The company "Ganz & Cie", which won the municipal tender in 1891, started the construction of Boyana HPP in 1892, but failed to complete it within the two-year deadline due to insufficient funds and the impossibility to reach the requested capacity. Additional measurements showed a river discharge four times lower than expected. The power plant was designed to capture the waters of Bojanska and Vladayska rivers, with a minimum capacity of 0,100 m3/s, a head of about 950 m and a capacity of 1 MW. Construction was halted in 1894 when the building and part of the penstock were completed, without starting the collecting canals and the compensating basin designed for 0.024 million m3. In 1895 the contract with the company was officially terminated.
The growing needs for electrification in the new century gave new impetus to the development of the project for the construction of Boyana HPP. Austrian engineers calculated that if a water intake was built at a greater height, the high pressure would compensate for the water flow. The construction of a water intake at the base of the Vitosha plateau, known to this day as the 'Stone Building', which is 989 m higher than the plant, was therefore started. The route covered 3,87 km of difficult steep terrain, which necessitated the construction of an overhead cableway. Construction of the penstock continued for a long time, with periods of interruption and renewal. The penstock is constructed underground, without exposed parts, consisting of two parallel seamless pipes with a diameter of 200 mm and a thickness of 32 mm.
In 1913 an order was placed with the Austrian company Voith for the manufacture of three water turbines and three centrifugal governors, as well as all the shut-off valves on the pressure structures. The project was originally to drive three generators with an output of 378 kW. The generators, as well as the main equipment for them, were ordered from the German electrical engineering company Siemens Schuckert. Their production was delayed. The first deliveries of the equipment, transported by barge on the Danube, began in 1916 at the height of the First World War. The transport was spotted by the Romanian side and destroyed with artillery from the shore, thinking that they were artillery pieces of the Austrian army. By the end of World War I, the Boyana Hydroelectric Project was again frozen. It was resumed immediately after the end of the war with an amendment to the order - instead of three generators with a capacity of 378 kW, two were ordered with Pelton-type turbines on a horizontal axis, with a total installed capacity of 1400 kW. In view of the capabilities of the construction and transport equipment available at the time, the installation and finishing works continued until 1923.
The generators and the hydraulic equipment were again transported by barges along the Danube to Vidin, and from there by trains to the Volujak station, then by ox carts to the site. For the cooling system of the bearings in the hydro units, a second water intake was built with a drop of 17 metres from the elevation of the plant. Thus, after several unsuccessful attempts to commission the facility, on 13 December 1923, Boyana Hydro Power Plant entered regular operation under the Metropolitan Directorate of Trams and Lighting of the Metropolitan Municipality. On the day of the opening, Tsar Boris III and the Mayor of Sofia Ivan Ploshtakov were present in person.
From the beginning of 1927 the power station provided power (voltage 7.3 kV and frequency 53 Hz) to the first Bulgarian rectifier station Pavlovo, which electrified the tram line Knyazhevo - Macedonia Square. The plant's auxiliary load was 110 V. As a gesture to the inhabitants of the village of Boyana, where the plant was built, free street lighting was installed in the settlement.
The two hydro units have a second set of larger diameter nozzles and needles that are installed each year prior to high water. At that stage, the power station had the status of a national site, with many people working four shifts a day for six hours each. The team consisted of a shift supervisor, two generator operators, two turbine operators, four oilers, four duty fitters and one telephonist. There are also cleaners, gardeners and general workers working in the power station area.
At that time, the power grid did not include other facilities and the plant operated on island. Due to the lack of automatic voltage regulators (AVRs) and any kind of automation, the shifts were very heavy, the generator operators stood continuously next to the rheostat wheel of the exciters. The plant area was guarded by the Bulgarian gendarmerie with a very tight security regime. After the commissioning in the 1930s of Simeonovo HPP, Mala Tsarkva HPP and Kurilo HPP, a common transmission network with a nominal voltage of 15 kV began to be built. For this purpose, a 2500 kV power transformer of Czech manufacture was purchased and a new overhead line was built. A new 15 kV busbar system was added. Two AVRs have been installed to facilitate the work of the operators. Gradually, the staff in the power plant began to decrease.
During the Second World War, during the bombing of Sofia, it was learned that the Allies had taken the Boyana Hydro Power Station as a strategic target. With this in mind, air defenses were deployed around the plant area to guard the airspace, and the building was repainted overnight in military camouflage colors. Workers and residents of the building are instructed to put tight curtains on the windows at night when an air raid alert is issued. Soldiers were stationed in former dormitories intended for workers involved in the construction of the plant. Boyana HPP survived all the bombing without any damage.
After the Second World War, new power plants with large capacity began to be built in Bulgaria. However, Boyana HPP remains of great importance for the power supply of the Boyana district. In 1957, a new transmission grid standard was introduced and the voltages were changed from 7 to 10 kV and from 15 kV to 20 kV. This necessitated the rewinding of the power transformer from 15 to 20 kV and the installation of a second transformer from 7 to 10 kV with the construction of a new 10 kV busbar system. In the late 1960s, additional automation and signalling was installed in the hydroelectric plant. In the 1970s, motor-driven gate valves were installed on the nozzles with automatic flow control depending on the water level in the upper reservoir.
