Polymer Composition for AC Power Cable Insulation

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Solution Overview

Problem

Polymer compositions used in power cables, particularly for high voltage applications, face challenges in maintaining low dielectric losses and electrical stability due to the presence of compressor lubricants like polyalkylene glycol, which can increase water uptake and lead to premature scorching, and existing solutions do not adequately address the complex electrical field distribution in DC cables.

Innovation Solution

A polymer composition for AC power cables comprising a polyolefin and a crosslinking agent, produced using a high pressure process with a mineral oil-based compressor lubricant, achieving a dielectric loss of tan δ (50 Hz) of 12.0×10−4 or less at 25 kV/mm and 130° C, which reduces dielectric losses and maintains electrical stability under high stress and temperature.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If polyalkylene glycol compressor lubricant is used in high pressure polymerization, then the compression process can be lubricated effectively, but the polymer composition exhibits increased water uptake and higher dielectric losses

Engineering Contradiction:

Improvecompression lubricationVSAvoiddielectric losses

Core Design Contradiction:

Ease of manufactureVSLoss of energy

Solution Approach 1:

The patent removes polyalkylene glycol lubricant from the system and replaces it with mineral oil-based lubricant. This extraction of the harmful component (polyalkylene glycol) eliminates the source of increased water uptake and dielectric losses while maintaining the necessary lubrication function in the compression process

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent changes the chemical composition parameter of the lubricant from polyalkylene glycol to mineral oil. This parameter change fundamentally alters the interaction with water and electrical properties, reducing dielectric losses and water uptake while maintaining lubrication effectiveness

Inventive Principle:

Principle #35Parameter changes

2Ease of manufacture

Engineering Contradiction:

Improvecompression lubricationVSAvoidthermal stability

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent extracts polyalkylene glycol lubricant from the system and replaces it with mineral oil-based lubricant, eliminating the premature scorching issue while maintaining necessary lubrication during compression

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent uses mineral oil as a simpler, more thermally stable lubricant alternative that does not promote premature crosslinking or scorching, effectively replacing the problematic polyalkylene glycol with a more reliable option

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Ease of manufacture

If conventional polymer compositions are used in DC cable applications, then the cable can be manufactured, but the space charge accumulation distorts the electric field and may lead to dielectric failure

Engineering Contradiction:

Improvecable productionVSAvoidelectrical stability

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent changes the chemical composition of the polymer from polyalkylene glycol-based to mineral oil-based, which fundamentally alters the electrical properties and reduces space charge accumulation, thereby improving electrical stability in DC cable applications

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent addresses the harmful effect of space charge accumulation by using mineral oil-based polymer composition that inherently reduces charge trapping, converting the potential failure mode into a reliable operation

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 exhibits unexpectedly low dielectric losses at high temperatures and stress, making it highly suitable for insulation layers in AC power cables, particularly for medium voltage, high voltage, and extra high voltage applications, while maintaining superior electrical properties.

Implementation Method 1

The tan δ and thus the dielectric losses (which are linearly proportional to the tan δ) shall be as low as possible for both technical and economical reasons

Methodology Applied

Scientific EffectDielectric loss:

Implementation Method 2

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

Methodology Applied

Scientific EffectSpace charge:

Data Source

PatentUS10950366B2Polymer composition and a power cable comprising the polymer composition

Publication Date: 2021.03.16 BOREALIS AG

AI summary

An alternating current (AC) power cable includes a conductor surrounded by at least an inner semiconductive layer including a first semiconductive composition, an insulation layer including a polymer composition, an outer semiconductive layer including a second semiconductive composition, and optionally a jacketing layer including a jacketing composition, in that order. The polymer composition of the insulation layer includes an unsaturated low density polyethylene (LDPE) copolymer of ethylene with one or more polyunsaturated comonomers and a crosslinking agent. The polymer composition of the insulation layer has a dielectric loss expressed as tan δ (50 Hz) of 12.0×10−4 or less, when measured at 25 kV/mm and 130° C. according to “Test for Tan δ measurements on 10 kV cables”.