Comparison of moisture contents in PILC cables measured by chemical titration and determined from electrical and dielectric measurements

Abstract

Moisture content titration, using the Karl-Fischer method, was performed on small samples of paper tapes taken from thirteen MI-length field-aged distribution Paper Insulated Lead Covered (PILC) cables. It has often k e n suggested in the literature that the moisture content of paper-oil systems could be estimated from some electrical and dielectric measurements, especially from return voltage and from dielectric spectroscopy measurements. We performed these measurements on field-aged PILC cables. We have also performed other non-destnrctive electrical tests: the isothermal relaxation current (IRC) and the LIpATEST leakage current test. In addition, AC breakdown measurements were also performed on the same samples. The electrical techniques ranked the cable's condition 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 of moisture content made by the electrical tests did not agree at all with the moisture content measured by Karl-Fischer titration. The presence of acids due to thermal aging andor pd activity is another parameter affecting the electical life of the examined PILC cables, especially by generating polar compounds.These results strongly indicate that moisture contents in any paper-oil system determined from indirect electrical measurements can be misleading and give incorrect estimation of the real moisture content. It seems much more likely that eledcal and dielectric measurements are sensitive to all polar products, not only water, especially in aged insulation.

Dielectrometry Measurements of Moisture Diffusion and Temperature Dynamics in Oil Impregnated Paper Insulated Electric Power Cables

“…But the significance has been questioned elsewhere. Bucholz et al have concluded that "the main degradation process of the examined PILC cables does not seem to be associated to moisture in paper but rather to the aging of oil [15]. "…”

“…The isothermal relaxation current (IRC) test measures the relaxation current after the application of a DC voltage [8,15]. The leakage current test (LIpaTEST TM ) measures the leakage current during the application of a DC voltage and relates it to the cable capacitance and the length of the cable [8,15].…”

“…The leakage current test (LIpaTEST TM ) measures the leakage current during the application of a DC voltage and relates it to the cable capacitance and the length of the cable [8,15]. The return voltage method (RVM) has been used to determine the polarization spectra and insulation condition of oil-paper transformers [20], and PILC cables [15].…”

“…The Karl Fischer method is used for the purposes of determining moisture content in solid and liquid samples [1,15]. It is discussed in Section 7.3.…”