Variable shunt reactor
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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[citation needed] 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[by whom?] as technically advanced products and are mainly supplied by larger global manufacturers such as ABB and Siemens.