Condition Assessment of Wind Farm Medium Voltage Cable Joints

Abstract

Rapid aging and failure in wind-farm collector systems has become an issue for grid owners. PD measurements of the cable systems can give good diagnostics, detect aging and pinpoint faults. Different PD measuring techniques are used today and the results will vary with applied voltage and frequency. This master thesis deals with preparation, electrothermal aging and characterization of XLPE cable joints. Dissection of the test objects was performed after aging and characterization. For characterization a variable frequency PD measurement setup has been built. The setup is defined by being able to detect PD with high accuracy in test objects at ± 17 kVpeak using Omicron MPD600 measuring equipment at variable frequencies between 10 mHz and 100 Hz. A PD-free low-pass RLC filter had to be used in the setup to reduce noise from the high-voltage source. The most important findings are that PD measurement results will vary significantly with regards to measuring technique. Aging may not be detected when measuring with too low frequency or voltage.