Switching transient levels relevant to medium voltage switchgear and associated instrumentation

Relevant transients in medium voltage switchgear installations are rather due to circuit breaker operations, in contrast to the high voltage situation where the most severe transients are produced by disconnector actions in gas insulated substations. So far the behaviour of those transients is influenced and determined by the actual load conditions of the switchgear as well as by the parameters of the connected power cables. An extensive set of switching transient measurements on several types of switchgear, air- as well as gas-insulated ones, are presented. Important parameters such as transient rise time or relevant frequency of the transient oscillating behaviour could theoretically be derived. The coupling of the transients on primary circuit elements to the secondary components of the switchgear installations was also investigated. Coupling behaviour of both the conventional instrument transformers as well as of the non-conventional ones, the so-called `sensors´ which are going to replace the conventional instrument transformers in future installations, was taken into account