HOW GOOD ARE ELECTRICAL DIAGNOSTIC TESTS TO PREDICT WATER TREES IN HV CABLES - AN EVALUATION USING OPTICAL MICROSCOPY

Motaheruddin Ahmed – Mohammad A. Al-Ohali – Mohammad A. Garwan
– Khaled Y. Soufi – Zakariya M. Hamouz

   DC Current, DC Conductivity and Partial Discharge tests were performed as diagnostic tools to indicate the presence of water trees in 15kV, 35kV and 69kV underground field-aged high voltage cable samples from the Eastern Province of Saudi Arabia. The insulation micro-sections of these cable samples were then observed under an optical microscope for visual detection of water trees. The DC Current and the DC Conductivity tests showed insulation deterioration in the 15kV, 35kV and the 69kV cable samples, with the possibility of existence of water trees in them. Optical microscopy confirmed the presence of water trees in the 35kV and 69kV cable samples, but not in the 15kV sample. The Partial Discharge test carried out on one 35kV cable sample of sufficient length also showed insulation deterioration. However, optical microscopy could not detect any water tree in this cable sample.

Keywords: DC current test, DC conductivity test, partial discharge test, optical microscopy

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