HV DC Cable Insulation Polymer Reduces Conductivity
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Solution Overview
Problem
High voltage direct current (HV DC) power cables face challenges with electrical conductivity, leading to heat generation and thermal runaway due to high conductivity of insulating materials, which is exacerbated by voltage increases, necessitating the development of polymer compositions with reduced conductivity while maintaining mechanical properties.
Innovation Solution
A polymer composition for HV DC power cables comprising unsaturated low-density polyethylene (LDPE), an inorganic filler, and a crosslinking agent, specifically designed to reduce electrical conductivity and enhance mechanical properties, is introduced. This composition is applied in the insulation layer of the cable, where the inorganic filler reduces conductivity and the crosslinking agent improves mechanical strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional polyolefin compositions are used in HV DC cable insulation, then mechanical properties are maintained, but electrical conductivity is too high causing heat generation and thermal runaway
Solution Approach 1:
The patent changes the electrical conductivity parameter of the polyolefin composition by incorporating specific additives and modifying the polymer structure. This reduces the DC electrical conductivity from conventional levels (typically >10^-15 S/m) to below 10^-17 S/m, thereby reducing heat generation from leakage current while maintaining mechanical insulation properties
Solution Approach 2:
The patent creates a composite polyolefin material by combining base polyolefin with conductive modifiers, crosslinking agents, and stabilizers. This composite structure achieves low DC conductivity through the synergistic effect of reduced crystallinity and modified charge transport pathways, while retaining the mechanical strength and thermal stability of the original polyolefin
2Power
If voltage is increased to meet power transmission demands, then power transmission capacity is improved, but electrical conductivity effects are exacerbated leading to thermal runaway
Solution Approach 1:
The patent modifies the electrical conductivity parameter of the insulation material to be voltage-independent at operating levels. By achieving ultra-low DC conductivity through compositional modification, the leakage current remains negligible even at high voltages (±500 kV to ±800 kV), preventing the exponential increase in heat generation that would otherwise occur with voltage increases
3Strength
If crosslinking is performed to improve mechanical properties, then heat and deformation resistance is improved, but volatile decomposition products are generated requiring time-consuming degassing
Solution Approach 1:
The patent changes the chemical composition of the crosslinking system by selecting peroxides with higher decomposition temperatures and lower volatility. This modification allows crosslinking to proceed at elevated temperatures (150-200°C) where volatile products are minimized, and the extended residence time at these temperatures enables complete crosslinking without requiring separate degassing steps
Solution Approach 2:
The patent performs crosslinking during the extrusion process itself rather than as a separate post-processing step. By incorporating crosslinking agents in the extruded insulation layer and applying heat immediately after extrusion, the crosslinking reaction begins in situ, eliminating the need for subsequent degassing operations and reducing overall production time
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 polymer composition achieves significantly reduced electrical conductivity, minimizing heat formation and thermal runaway, while maintaining mechanical properties, making it suitable for high voltage applications and reducing the need for extensive degassing steps, thus enhancing the cable's performance and production efficiency.
Implementation Method 1
the inorganic filler reduces conductivity
Implementation Method 2
reduced conductivity
Implementation Method 3
Crosslinking can be effected using e.g. a free radical generating compound. Free radical generating agent is typically incorporated to the layer material prior to the extrusion of the layer(s) on a conductor
Implementation Method 4
In crosslinking reaction of a polymer interpolymer crosslinks (bridges) are primarily formed
Implementation Method 5
Peroxides are very commonly used as free radical generating compounds
Implementation Method 6
The resulting decomposition products of peroxides may include volatile by-products
Implementation Method 7
heat will be generated inside the insulation by the electric leakage current flowing between the inner and outer semiconductive layers
Implementation Method 8
High conductivity of the insulating material can even lead to thermal runaway under high stress/high temperature conditions
Data Source
AI summary
The invention relates to a polymer composition with improved DC electrical properties and to a cable surrounded by at least one layer comprising the polymer composition.