A new technique for condition monitoring of MV metalclad switchgear

Many failures in MV switchgear assemblies are caused by insulation failures and several methods have been developed to provide information about insulation condition. In-situ monitoring of medium voltage circuit breakers is, however, generally restricted to oil sampling and subsequent analysis. Other methods of assessing the condition of circuit breakers require that the circuit breaker should be de-energised and removed from service prior to examination. In this paper condition monitoring techniques that have been applied to circuit breakers are reviewed and a new technique is presented. The method makes use of current transformers to provide measurements of voltage waveforms across circuit breakers during operation. The effectiveness of the technique has been demonstrated on a limited range of equipment and switching conditions. The main advantage of the proposed system is that it can be applied to substations with only minor changes to the secondary wiring and condition of equipment can be evaluated without taking equipment from service. The system can be installed permanently in substations to give an history of the condition and service stresses on important circuit breakers or circuit breakers that are of particular interest