Crosslinked Polyolefin Insulation for HV DC Cables
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Solution Overview
Problem
Current power cable insulation materials for high voltage and extra high voltage applications, particularly in DC systems, face challenges with high electrical conductivity leading to thermal runaway and require costly degassing steps to remove volatile by-products from crosslinking processes, which are time and energy consuming.
Innovation Solution
A crosslinked polymer composition comprising a polyolefin, peroxide, and sulfur-containing phenolic antioxidant with specific properties, including a melt flow rate of less than 1.7 g/10min, reduced peroxide by-products, and low 2,4-Diphenyl-4-methyl-1-pentene content, which is crosslinked using a radical reaction, resulting in reduced electrical conductivity and improved mechanical properties without the need for extensive degassing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional crosslinking with peroxide is used to improve mechanical strength and heat resistance, then the polymer composition achieves sufficient crosslinking degree, but volatile decomposition products are generated that negatively influence electrical properties and require costly degassing steps
Solution Approach 1:
The patent changes the chemical structure parameter of the peroxide from conventional types to a cyclic peroxide with specific molecular characteristics. This parameter change reduces the formation of volatile decomposition products while maintaining the crosslinking effectiveness needed for mechanical strength and heat resistance.
Solution Approach 2:
The patent converts the potentially harmful volatile decomposition products into minimal or negligible amounts by selecting a specific cyclic peroxide structure. The decomposition products that do form are non-volatile and do not negatively influence electrical properties, effectively turning a harmful effect into a benign one.
2Reliability
If degassing step is implemented to remove volatile by-products, then electrical properties of the cable are improved, but the production process becomes time and energy consuming
Solution Approach 1:
The patent extracts or eliminates the source of volatile decomposition products by selecting a specific cyclic peroxide structure that does not produce volatile by-products during crosslinking. This removes the need for the degassing step entirely, saving time and energy while maintaining electrical properties.
3Reliability
If high conductivity insulation material is used, then electrical field influence is reduced, but thermal runaway occurs under high stress conditions due to heat generation from leakage current
Solution Approach 1:
The patent changes the electrical conductivity parameter of the insulation material to an optimized range. The crosslinked polymer composition achieves a balance where conductivity is low enough to prevent thermal runaway from leakage current heating, yet sufficient to maintain electrical field stability and prevent excessive electric field influence.
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 solution achieves significantly lower electrical conductivity, minimizing heat formation in power cables and allowing for a more efficient cable production process by eliminating the need for lengthy degassing steps, while maintaining mechanical strength and thermal stability.
Implementation Method 1
Crosslinking can be achieved using e.g. a free radical generating compound, such as a peroxide. Free radical generating agent is typically incorporated to the layer material prior to, or during, the extrusion of the layer(s) on a conductor.
Implementation Method 2
The polymer composition comprises a polyolefin, peroxide and sulphur containing phenolic antioxidant... reduced peroxide by-products
Data Source
AI summary
The present invention relates to a crosslinked polymer composition, which is obtained by crosslinking a polymer composition, which polymer composition has a melt flow rate (MFR) of less than 1.7 and comprises a polyolefm, peroxide and sulphur containing antioxidant, characterised by that the crosslinked polymer composition has an Oxidation Induction Time, determined according to ASTM-D3895, ISO/CD 11357 and EN 728 using a Differential Scanning Calorimeter (DSC), which Oxidation Induction Time corresponds to Z minutes, and comprises an amount of peroxide by-products which corresponds to W ppm determined according to BTM2222 using HPLC, wherein Z1 ≤ Z ≤ Z2, W1 ≤ W ≤ W2, and W≤ p - 270 * Z, wherein Z1 is 0, Z2 is 60, W1 is 0 and W2 is 9500, and p is 18500; and use thereof, a power cable insulation and a power cable, useful in high voltage (HV) and extra high voltage (EHV) cable applications direct current (DC) applications.