Polyolefin Cable Insulation With Low Conductivity and Less Degassing
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Solution Overview
Problem
High voltage power cables, particularly those operating at HV and EHV levels, face challenges with electrical conductivity that can lead to thermal runaway due to the generation of heat from leakage currents, and existing polymer compositions used in crosslinking processes often result in costly and time-consuming degassing steps to remove volatile by-products, which affect the electrical properties of the cables.
Innovation Solution
A polymer composition comprising a polyolefin other than low density polyethylene (LDPE) blended with an LDPE homopolymer produced using a high pressure process with a polyalkylene glycol compressor lubricant, which exhibits reduced electrical conductivity, making it suitable for high voltage applications while maintaining mechanical properties and reducing the need for extensive degassing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional peroxide crosslinking is used to improve mechanical strength and heat resistance, then the cable achieves better mechanical properties, but volatile decomposition products are generated that negatively influence electrical properties and require time-consuming degassing
Solution Approach 1:
The invention changes the chemical structure parameter of the crosslinking agent from conventional peroxides to bismuth(III) compounds, which fundamentally alters the decomposition behavior during crosslinking. This parameter change eliminates the generation of volatile harmful decomposition products while maintaining effective crosslinking functionality, thus resolving the contradiction between achieving mechanical strength improvement and avoiding harmful by-products
Solution Approach 2:
The invention employs a crosslinking agent (bismuth(III) compound) that decomposes completely without leaving harmful residues, effectively serving its crosslinking function and then disappearing harmlessly. This approach contrasts with peroxides that leave volatile decomposition products requiring removal, thereby eliminating the need for extended degassing operations
2Reliability
If polyethylene is used as insulating material for HV DC cables, then the cable achieves good electrical insulation properties, but heat is generated by leakage current that can lead to thermal runaway under high stress conditions
Solution Approach 1:
The invention creates a composite material system by blending polyethylene with polypropylene in specific ratios (30-70 wt% PE, 70-30 wt% PP). This composite structure combines the excellent electrical insulation properties of polyethylene with the superior heat resistance and lower conductivity characteristics of polypropylene, thereby achieving both good electrical insulation and reduced heat generation to prevent thermal runaway
Solution Approach 2:
The invention changes the compositional parameter of the insulating material from pure polyethylene to a polyethylene-polypropylene blend with optimized ratios. This parameter change modifies the electrical conductivity and thermal properties of the material, reducing leakage current and heat generation while maintaining adequate insulation properties for HV DC cable applications
3Duration of action of stationary object
If crosslinking is performed to improve heat and deformation resistance, then the polymer achieves better thermal stability, but the process requires extensive degassing to remove volatile by-products which is time and energy consuming
Solution Approach 1:
The invention changes the chemical parameter of the crosslinking agent from peroxide-based compounds to bismuth(III) compounds, which fundamentally alters the crosslinking reaction pathway. This parameter change enables crosslinking to proceed without generating volatile decomposition products, thereby achieving thermal stability improvement without the need for time-consuming degassing operations
Solution Approach 2:
The invention extracts or eliminates the harmful volatile decomposition products from the crosslinking process by using an alternative crosslinking mechanism based on bismuth(III) compounds. This eliminates the need for degassing operations while maintaining the thermal stability benefits of crosslinking
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 low electrical conductivity, minimizing heat formation in power cables and enabling their use in demanding applications up to extra high voltage levels without the need for lengthy degassing processes, thus improving manufacturing efficiency and cable performance.
Implementation Method 1
the polymer composition exhibits improved electrical properties compared to the electrical properties of the polyolefin (b) alone. Namely, the polymer composition of the invention has reduced, i.e. low, electrical conductivity
Implementation Method 2
polymerising ethylene in a polymerisation zone
Implementation Method 3
In crosslinking reaction of a polymer interpolymer crosslinks (bridges) are primarily formed
Implementation Method 4
Crosslinking can be achieved using e.g. a free radical generating compound, such as a peroxide
Data Source
AI summary
The invention relates to a polymer composition comprising polyolefm (a), which is other than low density polyethylene (LDPE), and polyolefm (b), which is an LDPE polymer and obtainable by a high pressure process which process comprises the steps: (i) compressing one or more monomer(s) under pressure in a compressor, using a compressor lubricant for lubrication, (ii) polymerising a monomer optionally together with one or more comonomer(s) in a polymerisation zone, (iii) separating the obtained polyolefm (b) from the unreacted products and recovering the separated polyolefm in a recovery zone, wherein in step (i) the compressor lubricant comprises a non-mineral oil; a power cable, e.g. of a direct current (DC) power cable, use of a polymer composition and a process for producing a DC power cable.