The Static Var Compensator (SVC) built by Siemens Power Transmission and Distribution (PTD; Erlangen, Germany) in Radsted on the island of Lolland, on behalf of the largest Danish consumer-owned power company, SEAS-NVE, went into operation in summer 2007.

The main reason to integrate the compensator in the network was voltage fluctuations caused by the 165.5-MW Nysted offshore wind park connected to the offshore platform, also operated by SEAS-NVE, which affected the voltage quality in the 132-kV transmission network. The Siemens system provides the reactive power needed for this, improves the voltage quality and increases the system stability of the weak transmission grid in the south of Denmark. It will also help minimize any impact on the transmission system in the future that results from further wind farms planned in this region.

The main element of the Danish turnkey project is the SVC for the 132-kV transmission system in the Radsted high-voltage switchgear station. This also includes the expansion of the existing 132-kV outdoor switchgear station for linking the SVC to the power grid. Siemens developed an advanced solution for Radsted that met the requirements of the power company, while complying with the high standards for noise abatement.

The SVC system operates in a 12-pulse configuration consisting of a thyristor-controlled reactor (TCR) and one filter in each of the two secondary circuits of the high-voltage transformer. The 12-pulse configuration has the advantage that the odd-order harmonics, which are generated by each of the TCR branches, mutually compensate each other. This configuration helps the system fulfill the strict requirements in terms of maximum occurrence of undesired harmonics at the system connection point.

To meet the rigid audible noise requirements that apply in the vicinity of the system, the SVC has been enclosed completely inside a building for the first time and has been equipped with special noise-deadening materials and components.

SVC is a part of the flexible alternating current transmission systems (FACTS) technology. FACTS can control the parameters that determine the operation of the power grid and define the quality of transmission. These parameters include transmission impedances, currents, voltages and phase angles between the different network nodes. A distinction is made in reactive power compensation between parallel and series compensation. Series compensators connect capacitors into the high-voltage transmission line. This fixed or variable reactive impedance reduces the transmission angle so that greater active power can be transmitted without jeopardizing system stability.

In the case of parallel compensation, a variable reactive power source feeds into a selected network point by a transformer. The reactive power needed in each case is generated there to keep the voltage at a constant level. The system voltage can be exposed to undesired fluctuations due to load shutoff or power system faults, such as short circuits, which need to be controlled quickly. As in the Radsted substation, this function is performed by a SVC within its power range, which is designed to match the particular network.