Cable Insulation Surface Roughness Reduction via Polished Blade Burnishing

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Solution Overview

Problem

Current methods for preparing insulation layer surfaces on high voltage cables fail to achieve the desired level of smoothness, leading to low DC breakdown strength and poor performance in both HVAC and HVDC applications due to rough surfaces.

Innovation Solution

A method involving a cutting tool with a polished blade that burnishes the insulation layer during cutting, followed by removal of the outer semiconducting layer and optionally part of the insulation layer, with surface roughness measurement and adjustment to achieve preselected reference values for Sa and Sdq parameters.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If conventional methods (sanding, glassing, peeling) are used to prepare the insulation layer surface, then the surface can be processed, but the surface roughness remains high which deteriorates DC breakdown strength and cable performance

Engineering Contradiction:

Improvesurface roughnessVSAvoidDC breakdown strength

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The cutting tool blade is pre-polished to achieve a surface roughness of Ra ≤ 0.4 μm before the cutting operation. This preliminary preparation of the tool ensures that when the tool contacts and burns the insulation layer surface during cutting, it transfers its smooth surface characteristics to the workpiece, thereby achieving low roughness on the insulation layer surface and improving DC breakdown strength.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The invention replaces conventional mechanical surface preparation methods (sanding, glassing) with a thermal field method. By controlling the temperature of the cutting tool blade to be higher than the insulation layer's glass transition temperature, the tool creates a thermal field that burns and smooths the insulation layer surface simultaneously during the cutting process, eliminating the need for separate mechanical finishing operations.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Manufacturing precision

If the cutting tool blade is polished to achieve low roughness, then the surface quality improves, but the device complexity and preparation time increase

Engineering Contradiction:

Improvesurface roughnessVSAvoidtool preparation complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The invention changes the temperature parameter of the cutting tool blade, maintaining it above the glass transition temperature of the insulation layer material. This parameter change allows the blade to have a dual function: cutting the outer semiconducting layer and simultaneously burning/smoothing the insulation layer surface. By controlling temperature rather than relying on complex mechanical polishing systems, the method achieves low surface roughness while simplifying the overall process.

Inventive Principle:

Principle #35Parameter changes

3Manufacturing precision

If the cutting tool operates at high temperature to burn the insulation layer, then surface smoothness improves, but energy consumption increases

Engineering Contradiction:

Improvesurface roughnessVSAvoidenergy consumption

Core Design Contradiction:

Manufacturing precisionVSUse of energy by moving object

Solution Approach 1:

The invention merges two separate operations into one: the cutting of the outer semiconducting layer and the smoothing of the insulation layer surface. By heating the cutting tool blade to a temperature above the insulation layer's glass transition temperature, the tool performs both functions simultaneously during a single pass, eliminating the need for separate heating and finishing operations, thereby reducing overall energy consumption.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The cutting tool blade is designed to perform multiple functions: cutting the outer semiconducting layer, heating/burning the insulation layer surface to achieve smoothness, and potentially removing material. This multi-functionality reduces the number of separate tools and operations needed, thereby reducing total energy consumption despite the high temperature requirement.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 method effectively minimizes surface roughness, improving the quality of cable transitions and jointing processes by ensuring the insulation layer surface meets specific roughness criteria, enhancing DC breakdown strength and overall performance.

Implementation Method 1

the side surface may be in contact with the insulating layer during cutting. Due to the contact between the insulation layer and the side surface during cutting, the side surface may burnish the obtained outer surface of the insulating layer during cutting

Methodology Applied

Scientific EffectBurnishing:

Data Source

PatentUS20230135919A1Method to minimize roughness on cable end insulation surfaces

Publication Date: 2023.05.04 NEXANS SA

AI summary

A method is provided for preparing an uncovered insulation layer surface of an end section of a cable. The uncovered insulation layer surface has an advantageous low roughness. A method is also provided for jointing two cables, and for preparing a termination assembly on a cable, a cable end, a joint, and a termination assembly.