Impact of vacuum switch-disconnectors on reliability of MV distribution networks

Using vacuum technology in 100% of distribution switchgears will increase the number of vacuum interrupters in the network by a factor of 20. Here a statistical analysis is used to evaluate the consequences of a complete substitution of Gas Insulated Switchgear (GIS) by vacuum insultaed Switchgears on the reliability of a cable network. Frequency of insulation failures is similar to this due to the vacuum switchgear already used in main distribution. The Average System Interruption Duration is impacted by only 0.03 minutes; to be compared to 0.17 minutes due to insulation failure in the main substation and 20 minutes due to cable failure. With respect to security of operation it is found that the major part of the insulation failures leads to earth fault currents readily interrupted by upstream protection without physical degradation of the equipment. It is concluded that a complete substitution in MV distribution networks by vacuum switch-disconnectors has a negligible impact on reliability and safety.