Switching overvoltages caused by shunt reactor switching and mitigation methods

In high voltage grids with a high amount of underground cables, the voltage limits might be exceeded due to the rising demand of reactive power. A common compensation method is the installation of shunt reactors, which are connected at the tertiary side of transformers or directly at the high voltage busbar. This article discusses the main influence factors of transient overvoltages during switching of these shunt reactors and analyses their effects on the equipment by transient simulations. Furthermore, the essential criteria and challenges for the design of circuit breakers and components regarding transients are shown. For safe operation, the transient stress must be below the maximum limits of all equipment and therefore different mitigation methods are introduced. In the end, a commonly used mitigation method, a so-called RC-Snubber, is designed for the tertiary side of transformers in a practical application.