Analysis And Suppression Of Transient Over-Voltages In GIS

In our country a few Gas Insulated Substations (GIS) units have been in operation and large number of units are under various stages of installation. Although GIS have been in operation for several years, some of the problems need attention. These problems include, generation of over voltage during dis-connector operations, line to enclosure faults etc. These over voltages are caused in two ways, viz., due to switching operations of circuit breaker and line to enclosure faults. In the project work, very fast transient over voltages are generated due to switching operations have been analyzed and presented. Since the contact speed of dis-connector switches is low, re-striking occurs many times before the current interruption is completed. Each re-striking generates transient over voltage with different levels of magnitude. Since these transients have traveling wave behavior, they travel to the external systems through enclosures, bushings, cable joints etc., and cause damage to the outside equipment. They can lead to secondary break downs in GIS and may give rise to electromagnetic interference.It is important to develop a suitable simulation models for estimation of these voltages.