Semiconductive Shield Composition for HV Cable Smoothness
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Solution Overview
Problem
High voltage and extra high voltage power cables face issues with protrusions and weld lines in semiconducting shield layers, which lead to electrical stress concentration and reduced cable life, necessitating a composition that ensures smoothness and avoids these defects.
Innovation Solution
A composition comprising a nonpolar ethylene-based polymer, a polar polymer of ethylene and an unsaturated alkyl ester, acetylene carbon black, and a curing agent, with a phase-separated structure and specific weight ratios, is used to create a semiconductive shield layer that minimizes weld lines and protrusions, ensuring smooth interfaces and improved electrical resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a semiconducting shield layer is used in MV/HV/EHV cable construction, then electrical resistance control and partial discharge elimination are improved, but weld lines and protrusions occur during co-extrusion causing electrical stress concentration
Solution Approach 1:
The patent changes the molecular weight parameters of the polymers used in the semiconducting shield composition. Specifically, it employs a first polymer with weight average molecular weight of 50,000-200,000 and a second polymer with weight average molecular weight of 200,000-1,000,000. This parameter change in molecular weight distribution improves melt flow characteristics during co-extrusion, reducing weld line formation and protrusions while maintaining the required electrical resistance properties of the semiconducting shield layer.
Solution Approach 2:
The patent creates a composite semiconducting shield composition by combining two different polymers with distinct molecular weight ranges. The first polymer (lower molecular weight) provides good processability and melt flow, while the second polymer (higher molecular weight) ensures mechanical strength and electrical performance. This composite approach allows the composition to achieve both smooth interface during co-extrusion and reliable electrical performance in HV/EHV cables.
2Manufacturing precision
If acetylene carbon black is used in the semiconducting shield formulation, then surface smoothness is improved, but manufacturing complexity increases
Solution Approach 1:
The patent specifies precise parameters for acetylene carbon black inclusion in the composition, controlling its quantity and distribution within the polymer matrix. By carefully controlling the carbon black loading level and its dispersion state, the formulation achieves smooth extruded surfaces that eliminate protrusions while maintaining manageable manufacturing processes. The parameter control ensures consistent electrical and mechanical properties without excessive formulation complexity.
3Ease of manufacture
If triple extrusion system is used to form semiconductive layers, then cable construction is achieved, but weld lines form at the interface of two semiconducting shield melts
Solution Approach 1:
The patent modifies the rheological parameters of the semiconducting shield composition by using polymers with specific molecular weight ranges and ratios. This parameter change optimizes the melt flow index and viscosity characteristics, allowing the two semiconducting shield melts to fuse together during co-extrusion without forming weld lines. The controlled molecular weight distribution ensures proper interdiffusion of polymer chains at the interface, eliminating weld line defects while maintaining the triple extrusion cable construction capability.
Solution Approach 2:
The patent applies local quality control by ensuring that the semiconducting shield composition has specific properties at the interface region where the two melts meet. The molecular weight distribution and polymer composition are designed to promote localized chain entanglement and fusion at the weld interface, creating a homogeneous transition zone that eliminates protrusions and weld line defects while maintaining the overall cable construction integrity.
Data Source
Figure 1
AI summary
Semiconductive shield layers for power cable constructions are made from a composition comprising: (A) A nonpolar, ethylene-based polymer having a density of greater than (>) 0.90 g/cc and a melt index of >20 g/10 min at 190℃/2.16 Kg; (B) A polar polymer consisting of ethylene and an unsaturated alkyl ester having 4 to 20 carbon atoms; (C) Acetylene carbon black; and (D) A curing agent; with the provisos that (1) the composition has a phase separated structure, and (2) the weight ratio of nonpolar polymer to polar polymer is from 0.25 to 4.