Effects of physical-chemical properties of oil on the dielectric response of transformer oil samples and transformer insulation

The paper presents original results of an experimental research project carried out at the Milan Vidmar Electric Power Research Institute of Ljubljana. The purpose of the project was to investigate the dielectric behavior of transformer oil samples of different qualities. They were chosen so as to allow for assessment of effects of moisture, ageing degree, furans content and oil type on their dielectric behavior. Testing was made at a room temperature in the standard IEC test cell. The dielectric response was measured and recorded by means of polarization spectrum measurement in the time domain (the return voltage measurement). The paper also reports and comments on testing results as obtained by RVM for oil samples taken from transformers in service and on results of polarization spectrum measurements made for the same transformers.