A new method for measuring degradation level of insulating oil with temperature in microwave

Conventional methods for measuring a degradation level of transformer insulating oil have measured a carbon and moisture of the insulating oil. One of the disadvantages of using these methods is that it is necessary to stop the transformer operation. Both a carbon and moisture are generated by an abnormal discharge or a high temperature and cause a degradation of the insulating oil in a transformer. It is important to detect the degraded insulating oil because it let the transformer break down. That is, it needs to exchange the degraded insulating oil to new one through the fast detection at a proper time. We found that the dielectric constant of the new insulating oil is different from that of the degraded insulating oil. The measurement of the difference in them is helpful to easily detect the degraded insulating oil using a probe which can measure relative permittivity of a liquid. A transmission line, waveguide and a cavity are usually used to measure relative permittivity. The open-ended one port probe and the two-port probe using a transmission line are proper to measure liquids [1][2][3]. The proposed method is very useful to detect the degraded insulating oil compared to the conventional methods because we can measure the degradation level of the transformer insulating oil whenever we want without stopping the operation.