Pressure Measurement and Characteristic Analysis on a 252-kV Puffer-Type SF Circuit Breaker

The transient pressure process in an interrupter, which determines the gas blasting characteristic of an SF 6 circuit breaker (CB), is of interest to designers and developers. In this investigation, piezoresistive pressure transducers and thermally and electrically insulating tubes, which damped the reflection of the pressure waves, were employed to measure the transient gas pressure in a 252-kV puffer-type SF 6 CB during no-load operation and fault current interrupting. The pressures of the puffer cylinder, throat, upstream, and downstream of the nozzle have been measured. The insulating tube can protect the pressure transducer from the high voltage and high temperature present during fault current interrupting. It is found that the reflection of the pressure wave inside the insulating tube will cause serious high-frequency oscillations, which superimpose upon the actual pressure waveforms during fault current interrupting. Filling the insulating tube completely with small polytetrafluorethylene (PTFE) particles can effectively damp the reflections and greatly suppress the oscillations. The pressure characteristics of the interrupter under 20-50 kA rms current have been analyzed through the method established in this investigation.