The insulation of HVDC extruded cable system joints. Part 1: Review of materials, design and testing procedures

Abstract

This position paper by the DEIS HVDC Cable Systems Technical Committee provides a review of existing diagnostic electrical and dielectric techniques for testing the insulation of polymeric extruded HVDC cable joints in the present Part 1. Here, the state of the art on the insulation of HVDC extruded cable system joints is covered with reference to types, design and testing techniques. This helps to identify routine tests as the first target for the onset of new testing procedures, AC-PD measurements as the readily-available measurement from manufacturers' practices for quality control of the insulation of accessories during routine tests and VHF/UHF wireless sensors as the best tool for performing such measurements on joints in the noisy factory environment. Thereby, a novel protocol for the measurement of partial discharges using AC voltages and VHF/UHF sensors, for quality control during routine tests on such joints, is derived in the next Part 2. This protocol is the main novelty of this investigation.

Electric Field Distribution in HVDC Cable Joint in Non-Stationary Conditions

“…Accessories may represent a weak point in HVDC cable links, especially when moving to ever-higher voltages where the feedback on in-service behaviour is lacking [1,2]. Compared to bulk cables in which many research works are conducted, both experimentally and in modelling, for assessing insulation endurance, anticipating field distribution in accessories is more difficult to tackle.…”

“…As stated previously, accessories represent weak points of the transmission system. Cable joints are mainly of two types for cables with extruded insulation [1], generally composed of cross-linked polyethylene (XLPE). The 'factory' joints apply mainly to submarine cables, and are processed at the time of extrusion, for example for jointing two cables of several tens of km each, for the purpose of production lines maintenance.…”

“…It is recognized that the dielectric/dielectric interface represents a threat for the accessory reliability and the tangential field can be a driving mode for failure [1,[8][9][10]. Whereas the behaviour of the radial field distribution in a bilayer dielectric can be reasonably anticipated based on the conductivity behaviour, the tangential component is more difficult to tackle, especially the respective role of geometry and thermal stress.…”

“…The tangential and radial electric fields are computed in these transient electrical and thermal conditions. To evaluate how far the nature of material imparts the field distribution, the case of a joint fully composed of XLPE, as could be the case for factory joints [1], is considered. We also modelled the association of silicone rubber (SiR) with XLPE.…”

A New Approach to Partial Discharge Detection Under DC Voltage: Application to Different Materials

“…To overcome these main problems related to the PD measurements under DC stress, some authors have proposed new techniques mainly based on a DC voltage with superimposed periodic waveforms or ripples [12]- [16]. Furthermore, some IEC standards and recommendations of IEEE and CIGRÈ have proposed test methods for HVDC extruded cables and accessories adopting PD measurement techniques suitable for AC [17]- [20]. This solution could give good results in terms of research of defects generated during the fabrication process.…”