Laboratory results from dielectric spectroscopy of field aged XLPE cables with respect to water trees

Abstract

This paper deals with the application of frequency domain dielectric spectroscopy for the detection of water trees in XLPE cables. During the research, dielectric spectroscopy measurements have been carried out on cable samples with and without water trees while it was attempted to preserve many of the uncertainties present in the field. The experiments support the applicability of a high voltage test developed primarily at KTH in Sweden, which utilizes the nonlinearity of the dissipation factor. Subsequently it was investigated whether this high voltage method also seems reliable at low voltages. It turned out that the fundamentals of the high voltage method were not directly applicable at low voltages as the nonlinearity of the permittivity is not noticeable at low voltages, at least compared to the deviations. Instead a novel method for interpreting the low frequency measurements is proposed though it needs further verification. Finally a theoretically possible modification of the measurement system is proposed, which deals with the problem of a limited current capability of the amplifier