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 (VSRs) have been developed and introduced on the market. The rating of a VSR can be changed in steps: the maximum regulation range depends on the capability of the on-load tap changer used in combination with the regulation winding used for the shunt reactor. The maximum regulation range has increased over the years, from 50%, up to 80% at some voltage levels. VSRs are considered technically advanced products and are mainly supplied by larger global manufacturers.

Advantages
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 stabilise the voltage. Other important benefits are:
 * reduced voltage jumps resulting from switching in and out a traditional fixed shunt reactor
 * flexibility for future variation in load and generation patterns
 * improved interaction with other transmission equipment and systems such as coarse tuning of SVC equipment
 * limiting the footprint 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
 * mitigation of zero-miss phenomenon, while energisation of long power lines and cables