Analysis of Liquid Dielectrics by Photometric Instruments

Abstract

The liquid dielectrics are used as an electrical insulation or as a medium for heat transfer in the power energy and high voltage devices such as transformers, HV cables or bushings. However dielectric degradations of these liquids are formed in time, most often caused by chemical pollution, thermal destruction or by the electric field influences. Especially electric strength and dissipation factor of insulating oil are affected by these negative influences. The result is the deterioration of devices isolation, which may cause the termination of devices life or even fire or explosion. To avoid loss of the device and further damage, the oil is periodically sampled from the device. The sample of oil is then analyzed, diagnosed and measured in the laboratory. Electrical parameters, mechanical and optical properties are the most common measured quantities. The optical analysis is usually very fast and reliable. There are many commercial analysis devices available on the market. However, none of them can measure all the parameters according to the standards with user settings. The design and realization of optical diagnostic equipment for analysis of liquid dielectrics according ISO 2049 and EN 60422 are the main contribution of this paper. Next monitored parameter is the spectral absorption and transparency of these liquids in the visible and UV spectrum. The proper function and accuracy of the measured methods will be verified in the Light laboratory and in the CVVOZEPower Laboratory in Brno University of Technology.