Conference Agenda

The current electrical evaluation of power cable is generally decoupled from the mechanical loading such that the results of electrical measurement cannot reflect the dielectric condition of power cable under operation [1-5]. The dielectric response of a 15 kV power cable has been investigated in this study, while mechanical compression is being introduced in transvers direction. The work reported is part of a U.S. DOE WETO Incubator program with submarine dynamic power cable (SDPC or SPC) for floating offshore wind transmission. The SDPCs are typically subjected to hostile mechanical and environmental loadings in operation, including tension/ bending related to self-weight, anchor impact, wave, current, floater-cable interaction, and so on. The SPDCs shall have a high level of structural integrity to ensure reliable power delivery. This is critical, especially considering SPC failures accounted for 80% of financial loss and insurance claims for offshore wind farms, and the cable failure attributed to cable design constituted near 15% of total failures [6,7]. The project is proposed to address the technical challenge with design and application of submarine power cable. The dielectric breakdown time of power cores was focused and experimentally studied. Particularly, the response of power core has been examined under monotonic and creep mechanical loadings when a high voltage is applied. It has been shown that the breakdown of power cores was dominated by the equivalent circumferential strain induced to the outer layer of power core. Besides the external factors such as mechanical load level and environmental temperature, the breakdown of power cores was also related to the metal shield and outer sleeve for the given power core. The recovery of electrical resistance after a cable specimen was taken off testing machine showed that the mechanical unloading had altered the dielectric status of the insulation layer substantially and further suggested the significance of studying the electrical response of power cables with the mechanical load applied concurrently.

References

1 Worzyk, T., 2009. Submarine power cables: design, installation, repair, environmental aspects. Springer

2 Marta, M., Mueller-Schuetze, S., Ottersberg, H., Isus, D., Johanning, L. and Thies, P.R., 2015. Development of dynamic submarine MV power cable design solutions for floating offshore renewable energy applications.

3 Gao, Q., Duan, M., Liu, X., Wang, Y., Jia, X., An, C. and Zhang, T., 2018. Damage assessment for submarine photoelectric composite cable under anchor impact. Applied Ocean Research, 73, pp.42-58.

4 IEC 63026-2019, Submarine power cables with extruded insulation and their accessories for rated voltages from 6 kV (Um = 7,2 kV) up to 60 kV (Um = 72,5 kV) –Test methods and requirements.

5 NDV-RP-F140, Electrical power cables in subsea applications, September 2019.

6 Gulski, E., Anders, G.J., Jongen, R.A., Parciak, J., Siemiński, J., Piesowicz, E., Paszkiewicz, S. and Irska, I., 2021. Discussion of electrical and thermal aspects of offshore wind farms’ power cables reliability. Renewable and Sustainable Energy Reviews, 151, p.111580

7 Strang-Moran, C., 2020. Subsea cable management: Failure trending for offshore wind. Wind Energy Science Discussions, pp.1-11

For the past 37 years, cable rejuvenation has been integral in the system resiliency programs of more than 300 utilities worldwide. During that time, more than 50 million meters of their aged underground medium and high-voltage cable has been rejuvenated through silicone injection. This technology extends the reliable service of aged cable by more than 40 years through a non-invasive process that restores dielectric strength and retards future water-tree growth. As a result, utilities have extended the reach of their capital budgets, improved their reliability indices, exceeded rehabilitation targets and reduced carbon emissions by over 660,000 metric tons of global warming potential. This presentation will highlight the methodologies and key findings from a comparative study on the life-cycle analysis (LCA) of cable rejuvenation and cable replacement. The work was conducted by an independent firm according to the life cycle inventory (LCI) and life cycle impact assessment (LCIA) standards established by the International Organization for Standardization (ISO) life cycle assessment standards ISO 14040 series. Through comparison of the global warming potential (GWP) for these two options, the data reveals a 99.9% savings in kilograms of CO2-eq when cable rejuvenation is selected to extend the life of power cables over replacement.

Investigations have revealed that crosslinked polyethylene (XLPE) cable joints are susceptible to moisture intrusion, leading to interfacial wetting and subsequent discharge, which ultimately contributes to widespread insulation breakdown accidents. Despite these observations, the exact mechanism behind moisture-induced insulation failure of composite interfaces in cable joints remains elusive, contributing to a dearth of effective diagnostic methods for assessing joint moisture levels. This paper focuses on the effects of moisture intrusion on the discharge failure process of cable joints under operating conditions. An accelerated moisture aging platform for cable joints is constructed in this study. The Partial Discharge (PD) measurement is performed at AC 10kV power cable joints. The partial discharge test results show that normal cable joints do not exhibit significant partial discharge phenomena during the early to mid-stages of moisture ingress. The maximum discharge amplitude suddenly increases in the late period of moisture ingress. Through the finite element simulation of the cable joint, it is found that when moisture approaches the conductor shielding within the interface, early-stage interface insulation discharge phenomena are initiated, which coincides with the result of the PD test. Anatomical examination reveals early-stage insulation degradation, characterized by non-conductive regions and dendritic carbonization development, ultimately leading to complete interface insulation failure. Based on the results, this paper summarizes four stages of partial discharge in moisture-affected cable joints, providing a theoretical basis for monitoring partial discharge in actual moisture-affected cable accessories.