Thermoplastic Insulating Layer Crystallite Control
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Solution Overview
Problem
High voltage energy cables with thermoplastic insulating layers face issues with dielectric breakdown strength due to morphological defects like microvoids and microfractures, which are exacerbated by slow cooling rates during extrusion, leading to reduced dielectric strength.
Innovation Solution
Incorporating a nucleating agent, specifically aromatic sorbitol acetals, into the thermoplastic polymer material to reduce crystallite size and prevent morphological defects, while maintaining mechanical and thermopressure resistance properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thermoplastic insulating layer is used in high voltage cables, then the cable becomes recyclable and environmentally friendly, but the dielectric breakdown strength is reduced due to morphological defects
Solution Approach 1:
The patent changes the chemical composition parameters of the insulating layer by incorporating aromatic sorbitol acetals as nucleating agents (0.01-5% by weight) and specific antioxidants into the polypropylene matrix. This compositional modification alters the crystallization behavior and morphological structure of the thermoplastic material, enabling it to achieve both recyclability and enhanced dielectric breakdown strength suitable for high voltage applications
2Stress or pressure
If the insulating layer is made with thick cross-section for high voltage transmission, then the cable can transmit higher voltage, but slow cooling during extrusion causes large crystallites and morphological defects
Solution Approach 1:
The patent applies preliminary action by incorporating nucleating agents (aromatic sorbitol acetals) into the insulating layer material before extrusion. This pre-treatment ensures that during the subsequent cooling process of thick-walled insulating layers, crystallization begins at numerous nucleation sites, producing fine and uniform crystallites rather than large defective crystallites, thus maintaining manufacturing precision even in thick-section cables
Solution Approach 2:
The patent modifies the thermal and crystallization parameters of the insulating layer through additive incorporation. The aromatic sorbitol acetals and antioxidants change the crystallization kinetics, enabling controlled crystallite formation during cooling that produces uniform fine crystallites throughout the thick insulating wall, preventing morphological defects while maintaining high voltage transmission capability
3Strength
If nucleating agents are added to improve dielectric breakdown strength, then the electrical performance is enhanced, but the mechanical properties and thermopressure resistance may be affected
Solution Approach 1:
The patent creates a composite material system where aromatic sorbitol acetals (nucleating agents) and antioxidants are combined within the polypropylene insulating layer matrix. This composite approach allows the nucleating agents to enhance dielectric breakdown strength through controlled crystallization, while the antioxidants simultaneously protect the polymer matrix from degradation, maintaining mechanical property stability and thermopressure resistance despite the presence of additives
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 addition of nucleating agents significantly enhances dielectric breakdown strength by reducing the risk of morphological defects, improving the electrical performance of high voltage cables.
Implementation Method 1
Incorporating a nucleating agent, specifically aromatic sorbitol acetals, into the thermoplastic polymer material to reduce crystallite size and prevent morphological defects
Data Source
Figure 1
AI summary
A cable comprising at least one electrical conductor and at least one electrically insulating layer surrounding said electrical conductor, wherein the at least one electrically insulating layer comprises: (a) a thermoplastic polymer material selected from: at least one copolymer (i) of propylene with at least one olefin comonomer selected from ethylene and an a-olefin other than propylene, said copolymer having a melting point greater than or equal to 130°C and a melting enthalpy of from 20 J/g to 90 J/g; a blend of at least one copolymer (i) with at least one copolymer (ii) of ethylene with at least one a-olefin, said copolymer (ii) having a melting enthalpy of from 0 J/g to 120 J/g; a blend of at least one propylene homopolymer with at least one copolymer (i) or copolymer (ii); at least one of copolymer (i) and copolymer (ii) being a heterophasic copolymer; (b) at least one dielectric fluid intimately admixed with the thermoplastic polymer material; (c) at least one nucleating agent.