Validation of a PD Monitoring System for Power Cables by Evaluating Joints with Defined Assembly Defects

In context of constantly growing high voltage cable networks in combination with volatile energy generation, the relevance of cable systems as part of modern power grids is increasing. Since cable connections can cover lengths of several kilometres an important question is how to implement equipment monitoring and asset management for such a distributed infrastructure. One aspect is the evaluation of the insulation condition of the equipment by partial discharge (PD) measurements. In contrast to detailed information offered by diagnostic PD measurements, monitoring systems usually provide a simplified dataset that can identify trends and changes under continuous operating conditions: Monitoring can detect PDs over time and hence, provides information about the deterioration of the insulation. To cover the entire cable asset, a distributed monitoring approach is favourable: E.g. monitoring devices installed at accessories, covering the accessory itself and the cable section between adjacent accessories. This contribution focuses on the validation of the capabilities of a HFCT based PD monitoring system installed at joints. Firstly, the design parameters of HFCTs and the influence of the environment (joint and cable) on the transfer impedance of an HFCT in the screen connection of a joint are discussed. Secondly, the localization information contained in the frequency spectrum of a PDs is evaluated and the significance of this information for monitoring applications is assessed. Finally, both the sensitivity and functionality of the developed monitoring system are validated by evaluating PD measurements of slip-on joints with defined assembly defects.