A Contactless Pirani Approach for Vacuum Monitoring in Vacuum Circuit Breakers

This article presents a method for determining the vacuum state in vacuum circuit breakers (VCBs) based on the Pirani approach. The method relies on exploiting eddy currents (ECs) over a low-cost sheet of iron (target) embedded inside the VCB, which is fixed to the shield of the VCB by a single welding point. This target and its assembly are compatible both with a low-cost manufacturing process and also with the specific fabrication and operating conditions of the VCB. ECs are used both for heating and for monitoring the temperature variation of the target during its cooling. A model based on two exponential kernels has been developed to identify the vacuum state from the cooling kinetics. An experimental setup has been developed to assess the potential performance of the method. The proposed approach is able to discriminate pressures below and above the reliable operating point in VCBs of 10−1 Pa.