Power Cable Insulation Segmentation for Discharge Prevention
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Solution Overview
Problem
Medium voltage cables face issues with partial electrical discharges due to the lack of homogeneity and isotropy in polymer-mica mixtures used in insulating layers, leading to air bubbles and increased electric fields, which can be exacerbated by extreme conditions like fires or floods.
Innovation Solution
A power and telecommunications cable design featuring a central conductive element surrounded by multiple semiconductor and insulating layers, including a banded first insulating layer with a high percentage of fire-resistant inorganic filler, and a second extruded insulating layer, which attenuates electric fields and prevents partial discharges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an extruded mixture of polymer with mica is used in the insulating layer, then the cable provides electrical insulation, but the lack of homogeneity and isotropy causes air bubbles and localized electric discharges
Solution Approach 1:
The insulating layer is divided into multiple discrete insulating ribbons that are wrapped around the conductor in layers. Each ribbon is a separate component with uniform properties, eliminating the homogeneity issues of extruded mixtures. The ribbons are arranged in specific patterns (crossed, overlapping) to ensure complete coverage and uniform electric field distribution.
Solution Approach 2:
The insulating ribbons are made from composite materials containing mica particles dispersed in a polymer matrix. This composite structure provides both the electrical insulation properties and the fire resistance required, while the ribbon format ensures homogeneous material distribution without the mixing problems of extrusion processes.
2Ease of manufacture
If the insulating layer contains air bubbles due to non-homogeneous mixture, then the cable structure is simpler to manufacture, but localized electric discharges occur due to increased electric field at empty spaces
Solution Approach 1:
Instead of attempting to create a perfectly homogeneous extruded mixture, the solution segments the insulating layer into multiple discrete ribbons. This eliminates air bubbles by replacing the continuous extrusion process with a wrapping process where each ribbon is independently manufactured with uniform properties, then assembled into a complete insulating system.
Solution Approach 2:
The ribbon wrapping process allows for local optimization of the insulating structure. Each ribbon can be precisely positioned and overlapped with adjacent ribbons to ensure complete coverage of potential weak points. The semi-conductive layers are also applied locally at interfaces to address specific electric field concentration issues.
3Reliability
If the cable is designed with multiple insulating layers and semi-conductive layers, then partial electrical discharges are prevented, but the device complexity increases
Solution Approach 1:
The insulating system is segmented into multiple ribbons arranged in specific patterns, but these segments work together as an integrated system. The semi-conductive layers are applied at critical interfaces between ribbons and at the conductor surface, providing protection where it is most needed without requiring complex structures throughout the entire cable.
Solution Approach 2:
The insulating ribbons serve multiple functions simultaneously: they provide electrical insulation, fire resistance, and mechanical protection. The semi-conductive layers perform multiple roles by equalizing electric fields and preventing discharge at interfaces. This multi-functionality reduces the need for additional specialized components.
4Object-affected harmful factors
If the cable uses fire-resistant inorganic filler in the insulating layer, then fire resistance is improved, but the manufacturing precision and homogeneity are reduced
Solution Approach 1:
The insulating ribbons are manufactured as composite materials with fire-resistant inorganic filler (such as mica) dispersed in a polymer matrix. The ribbon format allows for controlled mixing and distribution of the filler during ribbon production, ensuring homogeneous material distribution within each ribbon while maintaining fire resistance. The discrete ribbon structure prevents the filler distribution problems that occur in large-scale extrusion processes.
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 effectively prevents partial electrical discharges and maintains operational continuity under extreme conditions by standardizing the electric field and providing fire resistance, ensuring insulation and operational integrity even when exposed to high heat or fire.
Implementation Method 1
The electrically insulating layer of the state of the art is thus subdivided into at least two independent electrically insulating layers, each comprised between two semiconductor layers
Implementation Method 2
the presence of the semi-conducting layers makes it possible to prevent the appearance of partial electrical discharges at the level of the interface between the latter and the electrically insulating layers
Data Source
Figure 1
AI summary
The power and/or telecommunication cable comprises: a central conducting element (2); an internal semiconductor layer (3) surrounding the central conducting element; a first electrically insulating layer (4) surrounding the internal semiconductor layer; a semi-conductive transition layer surrounding the first electrically insulating layer; a second electrically insulating layer (6) surrounding the transition layer; and an external semiconductor layer (7) surrounding the second electrically insulating layer. The first electrically insulating layer is composed of fire resistant materials. The power and/or telecommunication cable comprises: a central conducting element (2); an internal semiconductor layer (3) surrounding the central conducting element; a first electrically insulating layer (4) surrounding the internal semiconductor layer; a semi-conductive transition layer surrounding the first electrically insulating layer; a second electrically insulating layer (6) surrounding the transition layer; and an external semiconductor layer (7) surrounding the second electrically insulating layer. A material of the first electrically insulating layer has an electric permittivity higher than that of a material of the second electrically insulating layer. The first electrically insulating layer is composed of fire resistant materials. The cable further comprises: a second semi-conductive transition layer surrounding the second electrically insulating layer; a third electrically insulating layer surrounding the second semi-conductive transition layer; an external protective screen surrounding the external semiconductor layer; and a sheath surrounding the external protective screen.