Degassing Crosslinked Power Cables Using High-Melting Point OBC
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Solution Overview
Problem
Peroxide-cured power cables retain decomposition by-products that affect performance, requiring degassing, but elevated temperatures for faster degassing risk damaging the cable core due to thermal expansion and softening of materials.
Innovation Solution
Incorporating a higher melting point olefin block copolymer in the semiconductive layer to enhance deformation resistance at elevated temperatures, allowing for higher temperature degassing without damaging the cable core, and using a peroxide crosslinking agent for crosslinking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If elevated temperature degassing is used to reduce degassing time, then productivity improves, but the cable core and semiconductive shield layer are damaged due to thermal expansion and softening
Solution Approach 1:
The patent changes the material parameter of the semiconductive shield layer by using a higher melting point polymer (polypropylene with melting point 160-170°C instead of conventional polymers). This parameter change allows the degassing temperature to be elevated to 100-150°C without causing softening or deformation of the shield layer, thus resolving the contradiction between degassing speed and cable integrity
Solution Approach 2:
The patent creates a composite semiconductive shield layer combining polypropylene base polymer with conductive fillers (carbon black or metal powder). This composite structure maintains the high melting point and dimensional stability of polypropylene while achieving the required electrical conductivity, enabling high-temperature degassing without damage
2Reliability
If elevated temperature degassing is used to remove decomposition by-products, then cable performance improves, but the semiconductive shield layer deforms causing flats and core damage
Solution Approach 1:
The patent changes the thermal parameter (melting point) of the shield layer material to polypropylene's higher melting point range (160-170°C). This parameter change provides a thermal buffer that prevents the shield layer from softening and deforming at degassing temperatures of 100-150°C, thus maintaining geometric integrity while achieving effective degassing
Solution Approach 2:
The patent applies beforehand cushioning by selecting a polymer with inherently higher thermal stability before the degassing process begins. The higher melting point polypropylene acts as a preventive measure that cushions the shield layer against thermal deformation during elevated temperature treatment, avoiding flats and core damage before they can occur
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 enables acceptably high deformation resistance, low volume resistivity, high scorch-resistance, and minimal impact on crosslinked polyethylene insulation, improving the degassing process and cable performance.
Implementation Method 1
The present invention uses a higher melting point olefin block copolymer for the semiconductive layer(s) to increase the deformation resistance at elevated temperatures
Implementation Method 2
The thermal expansion and softening of the materials from which the cable is constructed is known to damage the core
Data Source
AI summary
A power cable comprising: (A) a conductor, (B) an insulation layer, and (C) a semiconductor layer comprising in weight percent based on the weight of the semiconductor layer: (1) 49-98% of a crosslinked olefin block copolymer (OBC) having a density less than (<) 0.9 grams per cubic centimeter (g/cm3), a melt index greater than (>) 1, and comprising in weight percent based on the weight of the OBC: (a) 35-80% soft segment that comprises 5-50 mole percent (mol %) of units derived from a monomer comprising 3 to 30 carbon atoms; and (b) 20-65% hard segment that comprises 0.2-3.5 mol % of units derived from a monomer comprising 3 to 30 carbon atoms; (2) 2-51% conductive filler, the insulation layer and semiconductor layer in contact with one another, is degassed by a process comprising the step of exposing the cable to a temperature of at least 80° C. for a period of time of at least 24 hours.