Asymmetric Shield Grounding for Power Cable Fault Current Release
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Solution Overview
Problem
Conventional power cable systems face challenges in ensuring safety and preventing communication failures when installed over long distances, as providing a parallel ground wire is difficult due to the need for large drill diameters and low positional accuracy in horizontal directional drilling, leading to issues with fault current release and magnetic field cancellation.
Innovation Solution
A power cable system with a conductor, insulator, inner shield layer, inner corrosion-proof layer, outer shield layer, and outer corrosion-proof layer, where only the inner shield layer is directly grounded at one end and only the outer shield layer is directly grounded at the other end, allowing fault currents to flow safely to earth ground and cancel magnetic fields without the need for a parallel ground wire.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a parallel ground wire (ECC) is provided along the power cable to ensure safety and fault current release, then reliability is improved, but device complexity and installation difficulty increase due to the need for large drill diameters and precise positional accuracy in horizontal directional drilling
Solution Approach 1:
The patent merges the ground wire function with the existing shield layers (inner and outer shield layers) of the power cable. Instead of adding a separate parallel ground wire, the shield layers themselves are configured to provide grounding paths, thereby eliminating the need for additional drilling and installation complexity while maintaining safety and fault current release capabilities
Solution Approach 2:
The shield layers are designed to serve multiple functions: electrical shielding, fault current path, and grounding function. By making the shield layers multi-functional, the patent eliminates the need for a separate ground wire (ECC), thereby reducing installation complexity while maintaining reliability
2Reliability
If both inner and outer shield layers are directly grounded at both ends to ensure fault current release, then reliability is improved, but energy loss increases due to circulating currents and overheating
Solution Approach 1:
The patent applies different grounding configurations to different shield layers at different locations: the inner shield layer is directly grounded at one end, while the outer shield layer is directly grounded at the other end. This localized differentiation allows fault current release while preventing circulating currents that would cause energy loss and overheating
Solution Approach 2:
The asymmetric grounding configuration (inner shield grounded at one end, outer shield grounded at the other end) breaks the symmetry that would otherwise create circulating current paths. This asymmetric arrangement allows fault current to flow to ground while preventing the formation of closed loops that cause energy loss
3Reliability
If a parallel ground wire is provided to cancel magnetic fields and prevent communication failures, then reliability is improved, but manufacturing precision requirements increase due to the need for accurate positional alignment
Solution Approach 1:
The magnetic field cancellation function is merged with the existing shield layers that are already positioned around the power cable conductors. Since the shield layers are inherently positioned close to the conductors during cable manufacturing, no additional positional accuracy is required for magnetic field cancellation, thereby eliminating the need for precise drilling and installation
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
This configuration ensures safe fault current release and prevents communication failures by allowing fault currents to flow through the inner and outer shield layers, maintaining transmission capacity without overheating, even when installed over long distances.
Implementation Method 1
an inner shield layer; an inner corrosion-proof layer; an outer shield layer; and an outer corrosion-proof layer
Implementation Method 2
only the inner shield layer among the inner shield layer and the outer shield layer is directly grounded at one end of the power cable in an axial direction, and wherein only the outer shield layer among the inner shield layer and the outer shield layer is directly grounded at the other end of the power cable in the axial direction
Implementation Method 3
allowing fault currents to flow through the inner and outer shield layers, maintaining transmission capacity without overheating, even when installed over long distances
Data Source
AI summary
A power cable includes a conductor; an insulator; an inner shield layer; an inner corrosion-proof layer; an outer shield layer; and an outer corrosion-proof layer, provided from center toward outside, wherein only the inner shield layer among the inner shield layer and the outer shield layer is directly grounded at one end of the power cable in an axial direction, and wherein only the outer shield layer among the inner shield layer and the outer shield layer is directly grounded at the other end of the power cable in the axial direction.