A detailed description is made of a novel method of on-line vacuum monitoring for the vacuum circuit breaker (VCB). The vacuum interrupter is specially designed as an interrupter with inset double bellows. It makes good use of the balance between the ambient atmospheric pressure and the self-closing pressure inside the interrupter. Should leakage occur inside the interrupter

the self-closing pressure will change resulting in changes of the output data from the pressure components and the displacement sensor

which makes the VCB locally block and alarm while achieving the remote monitoring and alarming via the GPRS wireless network. The VCB with the inset double bellows and its on-line monitoring equipment have been applied in field operation and proved satisfactory in performance.