Breakdown Light Emission Spectrum of Mineral Oil Including a Water Droplet Observed with a Spectroscope and Optical Sensors Attached with a Colour Filter

Abstract

It is well known that breakdown (BD) and partial discharge (PD) inception voltages in mineral oil could be decreased as which water content increased. The authors have investigated influences of water content in the mineral oil on the PD and BD properties, together with the movement and deformation of a water droplet leading to BD by a high-speed video camera. In this study, the author investigated light emission properties of the mineral oil at BD observed by the high-speed video camera and a spectroscope with taking influences of the water droplet into consideration. The BD took place intermittently many times at once in the same path that was formed along with the enlarging water droplet. At this time, changes of the light emission color in the BD path was clearly observed, which seemed to correspond to optical wavelengths (colors) of line spectra of hydrogen; Hα, Hβ and Hγ, as well as band spectra of molecules related to C and CH system. In order to confirm these spectra, the authors observed the wavelengths with the spectroscope during the BDs. Also, the authors constructed a new optical measurement system with photo-multiplier tubes (PMTs) that were attached with a color filter to enable to selectively measure the time-change of the spectrum intensity. These results are expected to become a basic data and would be applied to the condition monitoring of oil-insulated high voltage apparatus such as power transformers and bushings.