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This paper presents the characteristics of the contaminated underground cable joints tested by a very low frequency voltage source. The underground cable system used in the experiment was comprised of a 12/20(24) kV underground cable with a cross-section area of 240 mm2, and the length of 6 m. Four different case studies were simulated on the cable joint, i.e., a healthy heat shrink cable joint (case 1), a cable joint with an incision on XLPE surface(case 2), a cable joint contaminated with 20-micron iron powder on XLPE surface(case 3), and a cable joint contaminated with 20-micron copper powder on XLPE surface(case 4). The dielectric dissipation factor, also known as tan δ at very low frequency (0.1Hz) of such underground cable systems, was examined at 0.5 U 0 , 1 U 0 , and 1.5 U 0 , respectively. The very low frequency(VLF) test voltage was applied to the cable specimen, according to IEEE 400.2(2013). The test voltage was recorded and analyzed. It was found that the cable joint contaminated with 20-micron iron powder on XLPE surface had a maximum tan δ. The tan δ value decreased respectively for the cable joint with an incision on XLPE surface and the cable joint contaminated with 20-micron copper powder on XLPE surface. The healthy heat shrink cable joint showed the lowest tan δ. It was clearly shown that the contaminated cable joint caused higher very low frequency tan δ compared with the healthy cable joint.

The objective of this paper is to study the deterioration of impregnated kraft papers immersed in dielectric liquids under the chemical stress conditions by furan analysis according to ASTM D5837 and IEC 61198. Mineral oil and natural ester (FR3) were liquid used in this study. Kraft paper samples, 3 pieces per each case study, are prepared in rectangle shape with 25.4 ± 0.5 millimeters (1.00 ± 0.02 inches) wide and approximately 254 millimeters (10.0 inches) long according to the ASTM D828 standard. The paper and liquid insulation are heated to dehydrate at 80 °C for 12 hours with 200 mbar pressure, and then they are filled in 200 milliliter bottles and heated with 5 different temperatures being 60 °C, 80 °C, 100 °C, 120 °C and 140 °C respectively. In the case of 120 °C and 140 °C are only conducted with FR3 due to its thermal characteristics. After that, 98% concentration of acetic acid of 2 quantities, 0.04 and 0.08 milliliters, and oxygen (O2) at 1 psi for 1,200 ml, are used for the chemical aging process for 9 days of the test samples before being tested to find furanic compounds. According to the test result, it can be concluded that all 4 factors, temperature, acetic volume, oxygen and moisture, effect on generated furanic compounds of aging paper insulation.