Low temperature and moisture effects on oil-paper insulation dielectric response in frequency Domain

Results of Frequency Domain Spectroscopy measurements are known to be largely influenced by environmental conditions, such as the temperature. From fields and laboratory investigations this technique was found to be highly operating conditions (external and internal factors) dependant. Because field measurements, (generally performed after de-energizing the equipment), last hours after de-energizing the transformer, the ambient temperature may affect the results. Especially in cold regions of the world, extreme care are required to interpret the results when performing tests at relatively low surrounding temperatures. A better understanding and analysis of the dielectric test results are therefore only possible with a clear understanding of the physical behaviour of the insulation system in response to the ambient conditions. The purpose of this contribution is to report the effects of low temperature on the dielectric response of oil impregnated paper insulation in frequency domain. Moisture content inside the solid insulation acted as parameter.