Intelligent optical fibre monitoring of oil-filled circuit breakers

Intelligent monitoring encompasses the extraction of information from data sets, which are only partially complete because of practical constraints on the deployment of measurement techniques. An experimental technique is described for monitoring a number of conditions within oil-filled circuit breakers from a single measurement method and using an optimised number of optical fibre sensing channels. The technique is based upon detecting changes in the optical intensity of light transmitted through the circuit breaker medium, using optical fibre delivery and capture at a number of different axial and radial locations within the circuit breaker chamber. It has been used during development testing at a short circuit test station for two oils with very similar physical characteristics but different kinematic viscosity as the arc extinguishing media. Results are presented which examine the dependence of the contact travel time upon arc duration and oil type. Quantitative information is given concerning the optical recovery time of the oil as a function of arc duration and axial location within the circuit breaker. The technique also detects the occurrence of fresh oil injection into the contact gap and enables the duration of its occurrence to be determined