Ultra-smooth semi-conductive shielding material for high-voltage direct-current cable

Abstract

The invention discloses an ultra-smooth semi-conductive shielding material for a high-voltage direct-current cable, wherein the ultra-smooth semi-conductive shielding material comprises 80-100 parts of polyethylene, 0-20 parts of an ethylene-vinyl acetate copolymer, 5-15 parts of superconductive carbon black, 1-2.5 parts of a cross-linking agent, and 0.1-0.5 part of an antioxygen. A semi-conductive shielding layer prepared from the ultra-smooth semi-conductive shielding material is capable of effectively outputting current and also has an ultra-smooth surface characteristic. The ultra-smooth semi-conductive shielding material has steady performance and can play roles of well uniformizing an electric field, preventing the partial discharge or insulation breakdown problem of the semi-conductive shielding layer resulted from serious electric-field concentration possibly caused by surface defects, inhibiting space charge accumulation in a cable insulation material, and reducing the conductivity of the cable insulation material.

Description

[0001] technical field [0002] The invention relates to a cable material, in particular to an ultra-smooth semi-conductive shielding material for a high-voltage direct current cable. Background technique [0003] With the continuous expansion of the power system, the continuous increase of transmission power, and the gradual increase of transmission distance, AC transmission encounters some technical difficulties. DC transmission is one of the directions to solve technical difficulties in power transmission. Compared with AC transmission, DC transmission has the advantages of high transmission efficiency, small line loss, convenient adjustment of current and change of power transmission direction, low investment cost, and the length is not limited by capacitive current. The advantages of short-circuit current between the power grid and corona radio interference are small. A number of studies have confirmed that the space charge in XLPE is the main cause of early insulation...

AI Technical Summary

Problems solved by technology

[0006] In the prior art semi-conductive shielding materials, in order to make the material have conductive properties, a large amount of carbon black needs to be added, but carbon black belongs to inorganic fillers, and has poor compatibility with organic base materials, and a large amount of added carbon black cannot be fully compatible with base materials. Moreover, when the semiconductive shielding material is extruded, in order to make the material have better compactness, a greater pressure is required. Under the action of extrusion pressure, a large amount of added carbon black is also easier to precipitate, which all lead to semiconductive shielding. Shield surface smoothness is poor

The existing technology generally uses polyethylene and / or ethylene-vinyl acetate copolymer (EVA) as the base material of the material. After adding a large amount of carbon black, the physical and mechanical properties of the material will deteriorate. The amount of EVA added is generally above 40%. To increase the mechanical and physical properties of the base material, such as increasing the tensile strength and elongation of the base material, reducing the viscosity of the base material, the compatibility between a large amount of EVA and polyethylene is also poor, which will also cause the surface of the semi-conductive shielding layer poor smoothness

[0007] If the semi-conductive shielding layer itself cannot ensure electrical smoothness (rough surface, even sharp protrusions), there are uneven pits or cracks, fractures, poor contact with insulation and other defects, it will be difficult to achieve a uniform electric field. It may even cause severe electric field concentration, leading to partial discharge or insulation breakdown, which is a major cause of space charge generation

[0008] Adding acetylene conductive carbon black or other common conductive carbon black to the semi-conductive shielding material in the prior art, the preparation and mixing have a great influence on the quality, and are sensitive to the strength of shear force and the length of mixing time. If the mixing time is not enough, The large particles of carbon black (usually between carbon black particles, due to the effect of cohesion, often aggregate into large particles), are not fully dispersed, which will affect the surface smoothness and mechanical and physical properties of future extrudates; if the mixing time is too long , due to the strong mechanical shear force will destroy the high structure of carbon black, reduce the chain state and affect the conductive performance; therefore, the performance of the semi-conductive shielding material is unstable