Effect of temperature on sensitivity of diagnostic tests on oil-impregnated paper insulation

In today's economic climate, it is important for utilities to know the condition, by means of suitable diagnostic tests, of the oil impregnated paper used as the primary insulation in equipment such as transformers, switchgear, bushings, cables and their accessories. The results of several diagnostic tests on aged and unaged bushings are described in this paper. The test techniques include tan delta and loss current waveforms at 60 Hz, dielectric spectroscopy from 0.1 to 100 Hz, and recovery voltage. The results show that some of the techniques were able to detect significant changes in aged bushings, particularly at high temperatures. Further work is, however, recommended to improve our understanding of the changes in parameters such as loss current waveform, low frequency tan delta, and recovery voltage.