Condition assessment of distribution PILC cables from electrical and chemical measurements

Electrical and chemical diagnostic techniques were used to measure the condition of distribution paper insulated lead covered (PILC) cables. Moisture content titration, using the Karl-Fischer method, was performed on small samples of paper tapes taken from several full-length field-aged PILC cables. The nondestructive electrical tests performed in the laboratory on the same cable samples were: the isothermal relaxation current (IRC), the LIpATEST leakage current test, the return voltage method (RVM), and dielectric spectroscopy. The electrical techniques ranked the cables consistently and it appears that the water content of the insulation is not the only factor influencing the dielectric losses and depolarization currents. In fact, the predictions made by the electrical tests do not agree at all with the moisture content measured by Karl-Fischer titration. It seems that moisture contents in paper-insulated systems deduced from dielectric or return voltage methods could be erroneous because several polarization. processes (other than water) may be present during the aging in service. More cables need to be tested to confirm these preliminary findings.