HVDC Cable Termination Using Resistive Field Grading in GIS
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Solution Overview
Problem
Current high voltage direct current (HVDC) gas-insulated switchgear (GIS) cable terminations face challenges with electrical, thermal, and mechanical difficulties due to unique DC-specific phenomena, including high electric fields, thermal issues, and constrained geometry, which affect insulation, mechanical support, and pressure sealing.
Innovation Solution
A power cable termination device with an electrically conducting outer housing, a resistive electric field grading system, and a connection device that includes a non-linear resistive field grading material layer and an electric field control member to manage high electric fields, along with an inner shell for mechanical support and insulation, enabling effective electrical contact and thermal management within the GIS system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If free-standing DC cable terminations are used, then electrical insulation is provided, but large footprint is required due to long flashover distances in air
Solution Approach 1:
The patent introduces an intermediary gas-insulated chamber that contains the cable termination. This chamber acts as a mediator between the cable termination and the external environment, providing electrical insulation through pressurized gas (SF6 or similar) rather than requiring large air gaps. The gas medium enables compact termination design while maintaining adequate insulation performance.
Solution Approach 2:
The patent changes the insulation medium from air to pressurized gas (such as SF6). This parameter change in the insulating medium's dielectric strength and density allows for significantly reduced flashover distances, enabling compact termination design within the GIS while maintaining or improving electrical insulation reliability.
2Volume of stationary object
If GIS cable termination is designed with constrained dimensions, then space efficiency is improved, but electrical field control becomes more difficult
Solution Approach 1:
The patent applies local quality by positioning specific field control components (such as grading rings, stress cones, or shielded structures) at critical locations within the termination where electric field stress is highest. This localized approach to field control allows effective management of electric fields in the constrained GIS space without requiring complex overall design.
Solution Approach 2:
The pressurized gas medium serves as an intermediary that helps manage electric field distribution within the compact termination. The gas provides both insulation and a controlled medium for field management, allowing compact design while maintaining electrical control through its dielectric properties and pressure-dependent characteristics.
3Power
If higher transmission power is implemented, then power capacity increases, but thermal issues and electric field stress increase
Solution Approach 1:
The patent utilizes pressurized gas (pneumatic principle) for multiple functions: electrical insulation, cooling of the cable termination, and arc quenching. The pressurized gas circulates around the termination components, carrying away heat generated by high current transmission, thus enabling higher power capacity while managing thermal risks through active gas-cooled heat dissipation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively handles DC-specific electrical challenges, reduces thermal breakdown risks, and provides mechanical support and pressure sealing, allowing for reliable operation and reduced size of GIS systems while maintaining safety and efficiency.
Implementation Method 1
an electric field grading system comprising a resistive field grading material layer arranged circumferentially around the power cable such as to extend axially at least along a part of the electrically insulating layer and such as to cover the edge of the conductive shield where the conductive shield is terminated
Implementation Method 2
a connection device that includes a non-linear resistive field grading material layer and an electric field control member to manage high electric fields
Implementation Method 3
higher voltages also entail exposing the cable terminations to higher electric fields, which dramatically increases the risk of material breakdown
Implementation Method 4
there are general difficulties in increasing the transmission power for DC cable systems, e.g. requiring the DC solutions to be able to handle thermal issues resulting from higher currents leading to higher temperatures
Data Source
AI summary
A power cable termination device for a high voltage direct current gas-insulated switchgear including: an outer housing made of an electrically conducting material, connectable to the switchgear; a terminal portion of a power cable, the power cable including an electrical conductor, a circumferential electrically insulating layer, and a circumferential conductive shield which is stripped off along a first part of the power cable; an electric field grading system including a resistive field grading material layer arranged circumferentially around the power cable to axially cover the edge of the conductive shield where the conductive shield is terminated, the resistive field grading material layer being in electrical contact therewith, and a connection device connectable to the gas-insulated switchgear and arranged to provide mechanical support and electrical contact with the gas-insulated switchgear.