DC Power Cable Insulation Composition for Space Charge Control
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Solution Overview
Problem
There is a need for power cables with improved electrical properties, particularly for direct current (DC) applications, as existing materials face challenges with space charge buildup and electrical conductivity, which can lead to dielectric failure and thermal runaway, and compressor lubricants used in high-pressure polymerization processes can affect the polymer's electrical properties.
Innovation Solution
A power cable design featuring a conductor surrounded by semiconductive and insulation layers, where the insulation layer comprises a low-density polyethylene (LDPE) copolymer with specific comonomers and a compressor lubricant containing mineral oil, resulting in reduced electrical conductivity and improved electrical properties, and the use of crosslinking agents like peroxides to enhance the cable's performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional compressor lubricants (e.g., polyalkylene glycol) are used in high-pressure polymerization, then the polymerization process can be maintained, but the electrical properties of the resulting polymer deteriorate due to space charge buildup and increased electrical conductivity
Solution Approach 1:
The patent changes the chemical composition parameter of the compressor lubricant from conventional polyalkylene glycol to a specific mineral oil (meeting white mineral oil standards) with controlled composition and properties. This parameter change results in polymer with significantly reduced space charge buildup and improved electrical conductivity for DC cable applications
Solution Approach 2:
The patent converts the typically harmful effect of lubricant contamination during polymerization into a beneficial outcome. The mineral oil lubricant, which would normally be considered an impurity, actually improves the electrical properties of the polymer by reducing space charge accumulation and enhancing DC electrical conductivity performance
2Reliability
If mineral oil-based compressor lubricant is used in high-pressure polymerization, then electrical conductivity is improved and space charge issues are reduced, but the polymer composition becomes more complex with lubricant traces
Solution Approach 1:
The patent converts the typically harmful effect of lubricant contamination during polymerization into a beneficial outcome. The mineral oil lubricant, which would normally be considered an impurity, actually improves the electrical properties of the polymer by reducing space charge accumulation and enhancing DC electrical conductivity performance
Solution Approach 2:
The patent specifies precise compositional parameters for the mineral oil lubricant (meeting white mineral oil standards in European Directive 2002/72/EC) and controls the lubricant concentration in the final polymer to be up to 0.4 wt%, transforming a potential composition stability issue into a controlled and beneficial parameter
3Temperature
If high electrical conductivity of insulating material is used, then heat dissipation is improved, but thermal runaway risk increases under high stress conditions
Solution Approach 1:
The patent optimizes the DC electrical conductivity parameter of the insulating material to a specific range that balances heat dissipation and thermal stability requirements, preventing both excessive heat accumulation and thermal runaway under high stress conditions
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 cable achieves significantly reduced electrical conductivity and improved electrical properties, effectively addressing space charge issues and thermal runaway, while the mineral oil-based lubricant minimizes adverse effects on the polymer, resulting in enhanced reliability for high-voltage DC power cables.
Implementation Method 1
The electric field in a DC cable is much more complex and depends on the conduction, trapping and build-up of electric charges, so called space charges, inside the insulation. Space charges inside the insulation will distort the electric field and may lead to points of very high electric stress
Implementation Method 2
The DC electrical conductivity is an important material property e.g. for insulating materials for HV DC cables. The strong temperature and electric field dependence of this property will influence the electric field distribution via space charge build-up
Implementation Method 3
HP process is typically operated at high pressures up to 4000 bar. In known HP reactor systems the starting monomer(s) need to be compressed (pressurised) before introduced to the actual high pressure polymerisation reactor
Implementation Method 4
polymerising a monomer optionally together with one or more comonomer(s) in a polymerisation zone
Implementation Method 5
the use of crosslinking agents like peroxides to enhance the cable's performance
Data Source
Figure 1
AI summary
The invention relates to a cable comprising a semiconductive layer and an insulation layer with improved DC electrical properties.