Vacuum switch-disconnectors : 2. Compliance with insulation coordination

The behaviour under lightning is simulated numerically for vacuum switch-disconnectors (standard deviation StD of 16%) and gas switch-disconnectors (StD of 5%) in a critical case of a MV/LV distribution station connected to a single overhead line. Lightning activity is simulated in accordance with the guidelines of Insulation Coordination, IEC60071-2. The influence of protective measures by surge arresters is taken into account. If correct protection measures are taken, the time to failure exceeds 1000 years for both technologies. Without such protection the time to failure reduces to 100 years. The differences due to the technologies are minor (~30%) with an advantage for vacuum in the latter case and for gas in the former case. It is conclude that vacuum permits to realise reliable disconnector function in accordance with the performance criterion of insulation coordination and with the same level of reliability as SF₆.