Semi-conductive strippable polyolefin shield material for high voltage DC (direct current) cables

Abstract

The invention provides a semi-conductive strippable polyolefin shield material for high voltage DC (direct current) cables. The shield material comprises the following components in parts by weight: 60-80 parts of LDPE (linear low density polyethylene), 20-40 parts of CPE (chlorinated polyethylene), 0.5-1.5 parts of BaTiO3, 8-15 parts of conductive potassium titanate whiskers, 0.2-0.6 part of stearic acid, 1-2.5 parts of a crosslinking agent, 0.3-0.8 part of a co-crosslinking agent, and 0.1-0.5 part of an antioxidant. The prepared semi-conductive polyolefin shield material has super smooth surface property, good physical properties and excellent comprehensive performance. The shield material can effectively derive the current, so as to well uniform the electric field, and further prevent the problems of the semi-conductive shield layer such as partial discharge or insulation breakdown caused by serious electric field concentration possibly due to surface defect. The ionized charge and injected charge are attracted into a deep drop, so as to prevent the charge from being accumulated in the partial area, and further prevent space charge accumulation in the cable insulation material and reduce the conductivity.

Description

technical field [0001] The invention relates to the field of cable materials, in particular to a semi-conductive strippable polyolefin shielding material for high-voltage DC cables. Background technique [0002] 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 insulati...

AI Technical Summary

Problems solved by technology

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) will not be fully dispersed, which will affect the surface smoothness and mechanical and physical properties of the extruded product in the future.

If the mixing time is too long, the high structure of carbon black will be destroyed due to strong mechanical shear force, and the chain state will be reduced to affect the electrical conductivity

Therefore, the performance of semi-conductive shielding materials is unstable

Secondly, when extruding the semi-conductive shielding material, 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 semi-conductive shielding. Poor surface smoothness of conductive shielding layer

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

Again, in order to make the material conductive, a large amount of carbon black needs to be added to the semi-conductive shielding material, but carbon black is an inorganic filler and has poor compatibility with the organic base material. A large amount of added carbon black cannot be fully compatible with the base material, and 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

In addition, the specific gravity of conductive carbon black is light, and its powder pollutes the environment during processing, and the dust is easy to inhale and harm the human body

Existing semi-conductive polyolefin shielding materials cannot suppress the accumulation of space charges, which limits their application in high-voltage DC cables