Measurement of Dissipation Factor of Inner Layers of Insulation in Three-Core Belted Cables

Abstract

This paper presents a substantiation of an approach for direct measurements of dielectric dissipation factor of layers of insulation between the conductors of three-core power cables. Proposed approach is based on grounding of the inspecteddielectric layer through the sufficiently low electrical resistance. The results of carried out analysis, which was carried out taking into consideration the presence of numerous parasitic parameters of tested layer of insulation due to the capacitive coupling between the electrically conductive elements of three-core power cable, have shown that for the case of sufficiently low value of used resistor the value of phase shift between the waveforms of voltage drop on inspected layer of insulation and resistor, through which this layer of insulation is grounded, coincides with the value of phase shift between the sine waveforms of current and voltage for parallel equivalent scheme of tested layer of insulation with power losses. Because of the dependence of dielectric power loss angle on the value of phase shift between sine curves of current and voltage, the presented approach for the measurement of dielectric dissipation factor is based on such coincidence of values of phase shift. Depending on the value of applied resistor, the value of dissipation factor is calculated on the basis of measured value of phase shift between the voltage drop on the electrical resistor, through which tested layer of insulation is grounded, and either the waveform of voltage dropon the inspected layer of insulation, or the waveform of applied voltage. Factors that affect the accuracy of measurement are discussed, equivalent schemes of tested three core power cable for various ways of applying testing voltage are presented and theexample of practical implementation of presented approach for dissipation factor measurement is also given. Further development of presented approach for dissipation factor measurement is supposed to include the comparative analysis of the results of its practical implementation with the results obtained by applying previously developed techniques based on aggregate measurements.