This master’s thesis addresses the diagnostics of medium-voltage cable systems with extruded insulation using measurements of dielectric losses expressed by the dissipation factor tanδ. The method is an important tool for assessing the overall condition of cable insulation and for the early detection of degradation processes in electrical distribution networks.
The aim of the thesis is to present the theoretical background of tanδ measurements, describe field measurements performed with very low frequency (VLF) sinusoidal voltage in accordance with the IEEE 400.2 standard, and evaluate the influence of selected factors on the measured values based on actual field data. Particular emphasis is placed on monitoring changes in tanδ over time and on the possibility of predicting future degradation.
The thesis discusses the physical causes of dielectric losses and key diagnostic parameters. The practical part is based on an extensive set of field measurements carried out by Elektro Gorenjska using the VLF method. The results were analysed using cumulative distributions and compared with the reference criteria of the IEEE 400.2 standard (2024).
The results show that cable length, sheath integrity, and cable age influence the measured tanδ values. Cables with intact sheaths exhibit lower dielectric losses, while tanδ values generally increase with ageing. Repeated measurements demonstrate the possibility of linear prediction, confirming the applicability of the method for long-term condition monitoring and maintenance planning.
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