| Abstract [eng] |
This Master’s Final Degree Project analyses the condition assessment of 110 kV XLPE cable insulation using complex diagnostic methods. The relevance of the project is determined by the fact that high-voltage cable lines are an important part of the electricity transmission infrastructure, while insulation defects may lead to long-term supply interruptions and significant operational losses. In practice, conventional testing methods are often suitable for detecting evident or already developed defects; however, early signs of insulation degradation are not always clearly identified. For this reason, the project mainly focuses on the applicability of the frequency domain spectroscopy (FDS) method for evaluating changes in the dielectric properties of XLPE insulation before clear partial discharge activity appears. The object of the project is the variation of dielectric response parameters of 110 kV XLPE cable insulation and their application in early insulation condition diagnostics. The aim of the project is to evaluate the applicability of the FDS method for detecting early degradation signs in 110 kV XLPE cable insulation. To achieve this aim, scientific literature and normative documents were analyzed, the main cable insulation diagnostic methods were described and compared, the theoretical basis of dielectric response methods was examined, suitable diagnostic equipment for laboratory testing was selected, and experimental investigations of XLPE cable insulation were carried out. In the experimental part of the project, XLPE-insulated cable samples were investigated. Three exposure scenarios were applied: moisture exposure, electrical stress caused by high voltage and load current, and thermal cycling. Dielectric response measurements were performed before and after each exposure using OMICRON DIRANA equipment. During the study, the frequency dependencies of the dielectric loss factor tg δ, power factor, active capacitance component C′ and loss capacitance component C″ were analyzed. In addition, an OMICRON FRANEO control measurement was used to assess whether the applied stresses caused structural or connection circuit changes that could affect the interpretation of FDS/PDC results. The results obtained showed that different types of stress affect XLPE insulation in different ways. In the moisture exposure test, a significant increase in tg δ, power factor and C″ was identified in the low-frequency range. During the electrical stress test, after the application of 100 kV AC voltage, an increase in dielectric losses was also observed in the low-frequency range, while after the load current exposure some parameters decreased or became more scattered. The thermal stress test showed that repeated temperature cycles mainly affect dielectric loss parameters in the low- and medium-frequency ranges. In all cases, the active capacitance component C′ remained relatively stable; therefore, the main changes were associated not with changes in cable geometry or structure, but with variations in the dielectric properties of the insulation. The results of the study confirmed that the FDS method, supplemented by PDC and FRANEO control measurements, can be applied as a complex method for early condition assessment of 110 kV XLPE cable insulation. This combination of methods enables changes in the dielectric properties of insulation to be detected, allows the response characteristics caused by different types of stress to be compared, and supports preventive diagnostic decisions before clear structural failure or partial discharge activity occurs. |
