Compact Product Suite for hydro power generation modernization in Bulgaria

Smooth integration of Vacha II station into the hydro power cascade while maximizing yield, and minimizing the need for human attention with remote operation


Due to excellent cooperation between the experts of ABB Bulgaria and NEK EAD, the Vacha II modernization project was completed successfully within a record term of 8 months.

A complex multitiered chain of power stations

The Vacha II hydro-electric power station is part of what the customer calls “the Dospat – Vacha Cascade”, a complex multitiered chain of power stations, the purpose of which is to extract a maximum of power from the natural resource the river system is while paying due attention to nature preservation.

Originally, the Vacha II station was commissioned in 1973 with two vertical Francis-turbine/generator sets, each with a generating capacity of 3.5 MW. The station is fed from the Krichim Dam through a pipeline it shares with another station in the cascade.

The project presented plenty of engineering challenges that stemmed from the overall mission: to integrate Vacha II smoothly into the cascade while maximizing yield, and minimizing the need for human attention. (One aspect of the latter requirement was that the station had to be operable remotely.)

The project included design, manufacture, delivery, installation, and commissioning of new excitation, medium-voltage switchgear, and control equipment for two hydroelectric power generators

Eight months later, ABB’s project team had the customer’s word that they had succeeded admirably.

“We have a broad palette of electrical and control equipment on offer and we are well stocked with local engineering, installation and support resources. Now, that simplifies life for our customers and enables us to provide next-door support for our installations for as long as our customers need it.”

Main facts

Industry Power
National Electric Company of Bulgaria (NEK EAD)
Country Bulgaria
Solutions Control System - Compact Product Suite consisting of:
  • AC 800M controllers
  • S800 I/O modules
  • Compact HMI
  • Operator workplaces

Excitation System - Unitrol F
Medium-voltage Switchgear - UniGear ZS1
Auxiliary Equipment - Low-voltage switchgear, ABB’s MNS Light, with withdrawable units

Good knowledge and experience, references and existing installed base of Advant OSC gave ABB an edge over competitors

Replacing relay-logic with computer-based control system

The relay-logic control system for the generating sets has been replaced with a new computer-based control system: ABB’s Compact 800 System. This system in turn consists of the following:
  • Two aggregate controllers, AC 800M plus accompanying S800 I/O, whose software implementation of the required controls has enabled a far more precise, sophisticated and smooth control of the generating sets than before. These controllers communicate with the relay protection equipment of the generators over Profibus DP field buses, eliminating the need for discrete wiring that would have necessitated far more cabling. Each aggregate controller has a color touch panel for local operation.
  • One station controller, also AC 800M + S800 I/O, for the handling of shared station functionality.
  • One operator workstation, Compact HMI, for visualization and human operation of the processes involved.

All controllers and the operator workstation are interconnected by an optical Ethernet communications network.

"Success doesn’t just happen. That’s something you have to work at on all levels and in all phases. That’s what we did also in the case of Vacha II and that’s why we were successful.”

Replacing electromechanical excitation system with static thyristor-based system

The existing electromechanical excitation systems have been replaced by new static thyristor-based systems: ABB’s Unitrol F. The electrical braking function has been implemented neatly in software across the Unitrol-embedded controllers and the aggregate controllers. New synchronization units have been installed, based on ABB Synchrotact 4, facilitating precise automatic and manual synchronization of the generators with the electric power grid.

New medium-voltage switchgear

New 6.3kV MV switchgear has been installed: ABB’s UniGear ZS1, with built-in digital protection as well as remote control and communication functionality. The switchgear has a small footprint, which enabled installation in the available space without alterations to the building.

New Auxiliary Equipment

New low-voltage switchgear, ABB’s MNS Light, with withdrawable units, has been installed to cater for the overall needs of the station, including supply and control of the aggregate governors. A dry MV transformer has also been installed.

All equipment installed is of the latest designs, offering faster synchronization, more accurate load balancing, and more sophisticated (including remote) control.

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