Technical part

The static frequency converter in the RHPP Bajina Bašta has the function of starting the 310 MW motor-generator machine in motor mode, synchronizing it to the 220 kV network.

Delivered equipment, assembled, tested and put into operation: two dry medium-voltage power transformers, SFP cabinet, medium-voltage plant, relay protection, medium-voltage disconnectors, cables and measuring transformers, modification of M/G control cabinet to RHPP and SCADA system.

Social and economic interest

With the help of this project, it is possible for the hydropower plant to work more efficiently because its aggregates will no longer be engaged and switched off for the needs of starting the pumping aggregates in the RHPP, but will be able to work continuously and produce green energy. In this way, around 5 GWh per year will be saved in production, making production more efficient. Also, another important aspect is that with the implementation of this solution, the working and exploitation life of aggregates that are used as power aggregates during synchronous start in flow-through hydropower plants will be extended by eight years, and the need for overhaul will be less. Compared to hydropower plants as we are already familiar with, RHPPs have the role of storing surplus energy, improving energy efficiency in production facilities, because every megawatt of savings, whether in money or energy, brings benefits.

Technical part

A new diesel electric device, with a 440 kVA capacity in Stand-by functioning mode, is intended for an emergency supply of the 0,4 kV 1st priority consumers, who shall be automatically switched on (connected) in case of a basic and backup power supply failure. Generator is connected to the section II of 0,4 kV, 50 Hz main distribution system, on the left bank. A diesel generator has an option of synchronisation, that is, a parallel functioning with a 0,4 kV network.

Diesel generator in Stand-by mode with a nominal power of 440 kVA is a stationary, closed type generator, and represents an emergency power supply source for the priority consumers.

Newly designed condition

For the purposes of backup electric power supply for the priority consumers, a diesel electric generator is designed, type „KOHLER-SDMO“, model: D440, closed type, in a soundproof enclosure. Room intended for a diesel generator facility is made of the solid material waterproof walls. This project also includes the necessary changes aiming to modernise the backup supply.

Geographic position

Hydroelectric Power Station „Zvornik is located on Drina river, in the western part of the Republic of Serbia, in an immediate vicinity of Mali Zvornik. HEPS „Zvornik“, as the furthest downstream location of Drina’s middle course, is a dam toe powerhouse with two mechanical buildings – one on the left, and other on the right bank, that together with a dam are damming the river Drina.

Climate

Climate of Drina’s drainage basin, where HEPS „Zvornik“ is located, is a typical continental climate with changes influenced by the mountains. Practically all the precipitation occurs during the winter months, i.e. from November to April. Frost occurs extraordinarily from November to March. Temperatures go from the lowest point of -30˚C, up to the maximal 40 ˚C.

Social and economic interest

A generator revitalisation increases reliability of the own consumption backup supply system of HEPS “Zvornik”, as well as the degree of safety and stability of power station’s backup supply, which leads to a higher reliability of the power station itself, within the Republic of Serbia’s energy system.

Technical information

As self-consumption power plants at the main and auxiliary power plants are vital for the operation of the entire power plant in order to prevent accidents, an additional source of independent power supply for self-consumption of “Đerdap 2 HEPP” was installed in the event that a power outage occurs. In case of an accident, the generator can power the entire plant for 72 hours.

Social and economic interest

Safer operation of the power plant, important for the stability of the electric power system and electricity generation.

Technical information

The existing G4 generator circuit breaker in Đerdap 1 HEPP was replaced, including the installation of a cabinet to house the auxiliary equipment of the circuit breaker. Due to the installation of a new generator circuit breaker, adjustments were made to the circuit breaker base and its fitting into the existing rail connection system on both the generator and transformer sides, since the new three-pole group of the installed generator circuit breaker, manufactured by ABB, type: HECS-130R, has different dimensions and structure from the old circuit breaker.

Social and economic interest

The largest hydroelectric power plant in the power system of Serbia.

Technical information

Generator stator overhaul works included repairing the hot spots on the stator sheet metals stacks and repairing the looseness of the stator sheet metal stacks. Firstly, the stator outer housing and shields were disassembled, then the generator rotor, hydrogen cooler and all other corresponding components to access the stator itself.

In order to repair hot spots and looseness of stator sheet metal stacks, full stator rewinding, inspection, cleaning and washing of the stator windings were carried out including all necessary tests before and after completion of the work, such as testing the stator winding insulation system parameter, bump test – stator sheet metal stack compaction test, and thermal imaging of stator sheet metal stacks by 1 T induction.

After complete electrical and mechanical assembly of the generator (rotor, bearings, covers, shields, coolers, lubrication and sealing components, flexible connections, brush mounts) and checking the generator gas part and cooling system tightness, as well as all necessary tests, a trial run was performed, respectively generator excitation, generator set first rotation and load synchronisation, including monitoring of generator heating up.

Reports on the executed overhaul works including all measurement and check lists, assessment of the equipment condition prior to and after the overhaul works, as well as recommendations for the next utilisation period were submitted to the user.

Social and economic interest

In addition to regular overhauls at Morava TPP, investment works were also executed for 125 MW generator set overhaul, where Elektromontaža performed stator overhaul.

The overhaul works contributed to the extension of the power plant’s service life, reliability and energy efficiency of the Block, while the operation of the power plant was made compliant with European environmental protection standards.

Technical information

In addition to the main generators in Vrla 1 HEPP, a home generator was installed, intended to be the source of power supply for self-consumption of all 4 power plants. The generators at Vlasinske HEPPs operate at power system loading. The source of the main supply for self-consumption on all Vlasinske Hydroelectric Power Plants is a 10 kV network, via transformers of 10/0.42 kV gear ratios and corresponding rated powers. The 10 kV network connects all 4 power plants and power supply is possible from 3 sources:

• Main power supply source – via one of two transformers with 35/10 kV gear ratio, 1000 kVA rated power and 110/35 kV transformer from 110 kV network in “Vrla 3” HEPP;
• Backup power supply source – via home generator in “Vrla 1” HEPP of 0.4 kV voltage, 750 kVA power, and a transformer with 10/0.4 kV gear ratio, 1000 kVA power;
• Safety power supply source – via 10 kV power line between “Vrla 1” HEPP and Valjevica and 10 kV switchgear in “Vrla 1” HEPP;

The home generator is a horizontal single-jet Pelton turbine that drives a 750 kVA three-phase synchronous generator. It is located in the left part of the powerhouse, viewed upstream, at an elevation of 869.00 meters above sea level.

Social and economic interest

The generator is intended to be the source of power supply for self-consumption of all 4 power plants – Vrla 1, 2, 3 and 4. By correct and reliable handling, the home generator may be utilized in the next 30 years. Fully automatic operation of the generator with remote control was also provided.

Technical information

Gaseous hydrogen is used in the technological process of generator cooling. In order to fill the generator with hydrogen and prepare it for operation, it is necessary to purge the generator with carbon dioxide. To ensure safety in this process, it was required to adapt the gas distribution installations consisting of:

• Carbon dioxide unit;
• Hydrogen unit;
• Gas distribution unit;
• Gas analyser panel;
• Hydrogen moisture separator;
• Air moisture separator;
• Expander – carbon dioxide heater.

Social and economic interest

The main objective of the adaptation was to ensure more reliable and safer operation of the gas distribution unit, i.e. to reduce the possibility of fire and explosion in the hydrogen unit by applying safety measures.

With this adaptation, the expansion of the technical gas unit provided two separate rooms, one designed to house hydrogen cylinder bundles and the other to house pressurized liquid carbon dioxide cylinders. A fire wall was constructed between the hydrogen unit and the carbon dioxide unit, with fire-resistance rating of 2 hours without openings, whereby the rooms housing the two units are completely physically separated.

Technical information

In terms of functionality, the 110 kV plant is comprised of the part housing the primary air-insulated switchgear and control gear, and a control building housing secondary equipment.

35 kV substation with 35/110 kV transformation and Košava WF complex are connected to 110 kV Košava Switchyard.

110 kV Košava Switchyard is part of the transmission system of Elektromreža Srbije. Pursuant to the EMS requirement, 110 kV Košava Switchyard shall be also capable of operating as an interconnecting plant, i.e. power transmission of one power line through 110 kV Košava Switchyard shall be possible.

The 110 kV plant, including gear, is built outdoors with safety distance for outdoor installation.

Two tubular busbar systems with seven bays are located in the 110 kV plant, and
in the first phase, five bays were equipped as follows:

1 Bay E01 – T01 transformer bay;
2 Bay E02 – line bay to Alibunar Substation;
3 Bay E03 – T02 transformer bay;
4 Bay E06 – coupler bay;
5 Bay E07 – line bay to Vršac 1 Substation.

Room for Bay E04 was left – spare 110 kV line bay, and for Bay E05 – transformer bay, for the third transformer T03, and these bays were not equipped within this project.

Social and economic interest

The construction of wind farms results in generation of electricity from renewable sources, i.e. from wind energy, which makes Serbia strategically positioned as a green energy producer.

Wind power is one of the clean ways to obtain electricity, which is why it is recognized in the world as an important factor for the future of our planet. Wind is a renewable energy source, which means that, unlike fossil fuels, for example, it will not be consumed, and it does not release combustion gases during electricity generation that would increase the greenhouse effect on our planet and thus aggravate global warming.