Different Moisture Contents of Pressboard Effect on Electrical and Chemical Characteristics of Liquid Insulation

This paper represents electrical and chemical characteristics of mineral oil samples obtained from the test cell containing the pressboards with different moisture contents immersed in the mineral oil. The pressboards with the dimension of 100×100 mm and the thickness of 12.8 mm were used in the experiment. The pressboards were divided into two groups. The first group contained the moisture content of 3 % while the second group contained the moisture content of 7%. Then, four pressboards of each group were inserted between plane to plane electrodes contained in the test cell by which one electrode was energized by 12 kV AC; another electrode was grounded. Three identical mineral oil samples were taken from the test cells after the pressboards and mineral oil had experienced by electric field stress for 5, 10, and 15 days respectively to investigate on the changing of electrical and chemical properties of the mineral oil. The tests were performed with each oil sample on the topics of breakdown voltage, power factor, moisture content, acid number, interfacial tension and dissolved gas analysis. From the experiments, the electrical and chemical characteristics of the mineral oil with the pressboards containing different moisture contents were clearly different.