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Thermal Effects of High-Frequency Voltage on Medium Voltage Cable Terminations

Field experiences have shown that transmission systems using voltage sourced converters (VSCs) with IGBT's can produce high frequency harmonic resonances in the VSC station environment. Modern cable terminations using non-geometric stress grading can be susceptible to degradation under these harmonics. In this study a setup was designed to test cable terminations under conditions representative of high frequency harmonic resonance in the field. Six different designs were experimentally analyzed for temperature increase under power frequency, high frequency, and combined voltage conditions. Further, analysis was carried out by circulating current, to test the additional effect of heating from load current. Results show a wide variation in local temperature gradients among termination designs. These differences can be attributed to variations in termination stress grading methods.