Effect of Moisture on Frequency Domain Spectroscopy (FDS) for Oil-Impregnated-Paper Insulation

Oil and cellulose materials are widely used in transformers as the insulation and the moisture inside the oil-paper insulation is highly unfavourable, as the dielectric strength would be reduced and the aging would be accelerated. Monitoring the moisture in the insulation system accurately and efficiently is important for the transformer operation and maintenance. Frequency Domain Spectroscopy (FDS) can be used to monitor the moisture of the oil-paper insulation. In this research, FDS was applied to the oil-impregnated-paper samples with water content ranging from 0.69% to 6.43% of which the water content was controlled by water absorption method. Besides, the comparison work was made of FDS results between the samples prepared by water absorption method and drying method.