Continuous Vacuum Monitoring in Vacuum Circuit Breakers

Vacuum presence monitoring is a routine maintenance procedure carried out on vacuum circuit breakers, in which the CB is isolated from the electrical network. The presence of the vacuum is verified by applying a voltage across the open contacts of the vacuum interrupters VI's higher than the breakdown voltage of such contacts in air. This procedure has a 50 years proven record and has found world wide acceptance. Today other methods are proposed to monitor the vacuum presence. These methods can be divided in 3 additional classes discriminated by the pressure range in which they are active. Each class has a clear advantage not shared by the others. Vacuum pressure monitors using high vacuum pressure gauges can give an early warning of an upcoming failure. Monitors using low vacuum pressure gauges detect the dielectric failure caused by vacuum loss as it comes. Monitors using barometric gauges clearly indicate the end of life of the VI. Today only these 3 systems can be used to monitor the pressure in a continuous way. The continuous vacuum monitor significantly decreases the probability to operate a VCB with a leaky VI, hence increasing the availability of the VI on the VCB for the network operator to 99.9999%. The continuous vacuum monitor based on low pressure vacuum gauges is considered an optimal engineering choice as it does not impact the design of the VI.