Radiometric measurement of circuit breaker interpole switching times

Monitoring the switching times of circuit breakers is important in the condition assessment of the operating mechanism. Although methods exist for this, they are not applicable to existing plant without retrofitting. Recent research shows that arcing produces impulsive radio frequency radiation. Using direct digital sampling of the antenna signals, impulses from operating circuit breakers may be recorded. From timing analysis of the received impulses, the interpole switching time of the circuit breaker can be measured. Results of this method are shown for a field trial on a 132 kV SF6 circuit breaker attached to a capacitor bank. The relationship between the opening and closing impulses is discussed. This method of timing measurement can be applied to energised plant. Measurement of the interpole switching times is completely non-invasive, whereas the overall switching time requires a clamp CT fitted on the CB wiring.