Although substantial studies have been performed on overhead line and cable, there is far fewer studies on the potential risk posed to interfaces within cable joints for high voltage (HV) cable systems. There are significant cost and time associated with any cable repair, with the situation likely to worsen with an increasing number of cable installations and an ageing fleet of cable assets. The availability of a ‘Universal Joint’ would enable a package to be made available for a speedy cable repair solution that can promptly re-establish service in the event of a cable fault, this emergency return to service solution would greatly improve resilience of a fast-changing electricity infrastructure.
Benefits
As HV cable assets age there is increased outage risks and impacts to network resilience. It is predicted that 50% of our 275kV and 400kV cables will be subject to constraints in the future. Developing a universal repair approach that will reduce the cable repair time substantially will enable resilience for a net zero network and also reduce constraints. Currently less than 30 400kV jointers in the UK are certified and possess the skills to complete these type of cable repairs. A significant number of this workforce will disappear due to retirement. This universal approach will streamline the training process and further support network resilience. In addition, a £125k per annum saving on cable spares will be realised if this product is implemented.
Learnings
Outcomes
UoM
A range of inorganic particle-filled silicone insulation materials for high-voltage applications was developed. The selected material demonstrated a 10–15% improvement in dielectric strength compared to conventional silicone. Furthermore, the experimentally obtained 10% probability of dielectric breakdown was up to 30% higher, indicating improved consistency and reliability of the filled material, which should lead to a more robust material in practice.
Alongside this, analysis of the thickness-dependent dielectric performance suggests that the enhanced material could reduce insulation thickness, thereby reducing the connector size and easing transport and installation. This needs to be investigated further to determine the potential insulation thickness reduction. Alternatively, it could support operation under higher voltage stresses than conventional silicone materials of comparable size.
The material production process was successfully scaled from laboratory batches of <0.1 kg to 30 kg batches using commercially scalable methods in collaboration with an industrial processing partner, demonstrating readiness for commercial manufacture.
Pfisterer
Elaboration of a joint design with good opportunities to fulfil the requirements and benefits for the intended application.
Lessons Learnt
UoM
UoM carried out a structured material screening approach, which enabled rapid identification of promising filler technologies for enhancing the performance of silicone-based insulation systems. Filler morphology and particle size were found to have a significant influence on dielectric performance, highlighting the importance of optimising filler characteristics rather than solely focusing on filler chemistry. Enhanced dielectric strength can be achieved whilst simultaneously improving mechanical and thermal properties, demonstrating the potential for multifunctional material systems in future high-voltage connector applications. Dielectric strength testing at specimen thicknesses up to 4 mm provided valuable insight into performance at dimensions closer to those required for practical high-voltage equipment, helping to bridge the gap between laboratory studies and industrial implementation. Early consideration of manufacturability is critical when developing advanced material systems. The successful transfer of the selected formulation to a commercial mixing process demonstrated that promising laboratory-scale materials can be produced using industrially relevant manufacturing techniques.
Pfisterer
A general solution for a dry pluggable joint feasible for all voltage classes has been elaborated. This concept could allow different future applications i.e. a dry pluggable joint could, for example, be beneficial for temporary cable links to support re-routing during construction works. In addition, experience from lower voltage classes shows that pluggable joints can enable specific grid configurations in special cases. A key advantage is the “universal” character, allowing connection of a wide range of cable cross-sections, which is one of the main motivations behind the iCARE project. In addition to the main insulation, the joint housing concept is a crucial aspect besides voltage withstand capability, a cable joint must also fulfil mechanical and sealing functions. Depending on the application (e.g. direct burial or installation in air, such as in a tunnel), it needs to meet a range of specific requirements. For this reason, the joint housing is a critical component and must be carefully considered. In this case, we are dealing with a relatively large housing produced in low volumes. This requires balancing several aspects, including weight, sealing performance, mechanical strength, manufacturing feasibility, and minimizing on-site installation effort. A basic concept has already been developed; however, further work is required to refine the design in detail.
