Variable shunt reactor

Variable Shunt Reactors are used in high voltage energy transmission systems to stabilize the voltage during load variations. A traditional shunt reactor has a fixed rating and is either connected to the power line all the time or switched in and out depending on the load. Recently Variable Shunt Reactors (VSR) have been developed and introduced on the market. The rating of a VSR can be changed in steps, The maximum regulation range typically is a factor of two, e.g. from 100-200 Mvar. The regulation speed is normally in the order seconds per step and around a minute from max to min rating. VSRs are today available for voltages up to 550 kV. The largest three-phase VSRs in operation have a rating of 120-200 Mvar at 420 kV and single-phase variable shunt reactors banks rated 200-285 Mvar at 420 kV have been installed in Italy.

The variability brings several benefits compared to a traditional fixed shunt reactors. The VSR can continuously compensate reactive power as the load varies and thereby securing voltage stability. Other important benefits are:

reduced voltage jumps resulting from switching in and out of traditional fixed reactors
flexibility for future (today unknown) load and generation patterns
improved interaction with other transmission equipment and/or systems such as coarse tuning of SVC equipment
limiting the foot print of a substation if parallel fixed shunt reactors can be replaced with one VSR
a VSR can be used as a flexible spare unit and be moved to other locations in the power grid if needed

VSRs are considered as technically advanced products and are mainly supplied by larger global manufacturers such as ABB and Siemens.

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