A high accurate sensor research and its application for VCBs' internal pressure on-line condition monitor

To improve the intelligence and reliability of the vacuum circuit breakers in power gird, a high accurate smart system was designed for On-line condition monitor of vacuum interrupters inner pressure. Through the study of dielectric theory and exploration of the inherent laws of shield potential with different pressure in VIs, it shows that with the deterioration of internal pressure the AC component on shield potential increase while the pressure stays lower than 0.1Pa and the DC component appears when the pressure increases to 0.1Pa. The structure, size and installation location of the sensor were designed with reasonable calculation to detect the weak changing signal. To meet the requirements of sampling signal characteristics, digital filter was developed to eliminate noise interference, the processed signal shows good smoothness and linearity after filtered. Fast Fourier transform (FFT) method is adopted to extract the amplitude of AC component on the shield potential, and fitting the empirical formula is derived based on the offline curve of AC component increment and inner pressure of VIs. Applying the previous theoretical studies to actual 10kV VCB on-line condition monitoring system design, focus was placed on the AC component of shield potential in the monitor devices. The feasibility of the sensor and transformation algorithm was proved in the end of this research.