The peroxide chemical cross-linking method is that the peroxide is decomposed by heat to form a free radical with high chemical activity, the free radical captures the hydrogen atom in the polyethylene molecule, and the polyethylene that loses the hydrogen atom becomes a macromolecular free radical, a macromolecular free radical. They react with each other to form carbon-carbon cross-linking to obtain cross linked polyethylene structure.
By modifying the material and improving the purity of the material, the electrical resistance and breakdown strength of the cross-linked polyethylene insulating material can be enhanced.
Cross-linked polyethylene insulation material ages under the action of heat and oxygen, reducing the service life of the cable. The charge transport regulation ability and breakdown field strength of insulating dielectrics can be improved by adding nanopolymers.
The electrical resistance of cross-linked polyethylene insulating materials can be improved by adding voltage stabilizers.
However, due to the poor compatibility between the voltage stabilizer and the polymer, the small molecules of the voltage stabilizer are easily migrated and precipitated from the macromolecules of the advanced polymer compounding, resulting in a significant decrease in the working life and electrical resistance of the cable insulation layer.
A university proposed a preparation method of cross-linked polyethylene insulation material for cables containing high electrical resistance compounding agent. The chelated ring aromatic ketone grafted cross-linked polyethylene insulating material prepared by this method has an AC breakdown field strength of 118kV/mm and a DC breakdown field strength of 440kV/mm at room temperature.
The material was tested for electrical tree initiation voltage using a needle-plate electrode structure, and the voltage was 4.5kV at 90°C. The AC breakdown field strength of the XLPE insulating material without adding voltage stabilizer at room temperature is 112kV/mm, the DC breakdown field strength is 410kV/mm, and the average electrical tree initiation voltage at 90℃ is 4.0kV.
For the cross-linked polyethylene insulating material with the addition of voltage stabilizer, but the voltage stabilizer is not graftable and does not contain a six-membered chelate ring structure, the AC breakdown field strength at room temperature is 109kV/mm, and the DC breakdown field is 109kV/mm. The intensity is 424kV/mm, and the electric tree initiation voltage is 2.8kV at 90℃.
It can be seen that the use of a voltage stabilizer containing a six-membered chelated ring structure composed of hydroxyl, carbonyl and benzene rings can form a uniform and dense electronic interaction space in the polymer. In the service temperature range of the cable insulation layer, the resistance to electrical tree and the breakdown strength are significantly improved.
The transmission mode of high-voltage power system is divided into high-voltage alternating current and high-voltage direct current. The high-voltage direct current transmission system has the characteristics of low line cost, small line active power loss, fast adjustment speed, stable and reliable operation, etc., and has become the development focus of high-voltage and ultra-high-voltage power transmission.
Since the DC breakdown strength and space charge suppression performance of the existing cross-linked polyethylene insulating materials cannot meet the requirements, a company has prepared a cross-linkable polyolefin composition with a DC breakdown strength of 410kV/mm and a gel content of 410kV/mm. It is 82.5% (w), the room temperature distortion rate of space charge is 3.3%, and its DC breakdown strength is excellent, which can suppress the injection and accumulation of space charge. When used for high-voltage insulated cables or ultra-high-voltage insulated cables, it can significantly improve the long-term running stability of the cables and prolong the service life of the cables.
The clean production process of cross-linked polyethylene insulation material from professional polymer compound manufacturer is carried out by melting polyethylene and antioxidant under high temperature conditions, and then absorbing it after filtering through a filter screen.
Due to uneven temperature and long residence time of materials, coke will be produced, resulting in short production cycle, frequent replacement of high-mesh filters, and the quantity and size of impurities in insulating materials cannot be effectively controlled.