Monitoring particle concentrations produced by arcing in SF6 circuit breakers using a chromatic modulation probe

An optical-fibre probe is described for monitoring the production and build-up of particulate material in high-voltage SF₆ circuit breakers, using the wavelength-dependent scattering of polychromatic light in conjunction with a chromatic modulation technique. It has been shown that the probe can be installed and routinely operated in a reliable manner within the tank of a 145 kV/40 kA circuit breaker during live arcing tests. Experimental results show that the severity and duration of arcing as well as the transient evolution of particle production and settling can be determined with the probe. As such, the results provide a means for tracking particulate conditions in a high-voltage circuit breaker with minimal intrusion into the circuit-breaker volume. It is concluded that the particulate mass per unit volume, formed by a single half cycle of arcing at the rated fault current, is only 0.1% of the total mass of SF₆ within the circuit breaker. The particulate material may remain in suspension within the circuit-breaker tank for approximately 30 minutes after the arcing event. The formation of a film of particles on the probe following settling may provide a means for determining the fault-current arcing history of an interrupter