A concept,
Crosslinked cables usually refer to cables whose insulation is made of crosslinked materials. The most commonly used material is crosslinked polyethylene (XLPE). The crosslinking process is to make the linear molecular structure of polyethylene (PE) through a specific processing way to form the shape of the crosslinking polyethylene reticulated line structure. The long - term permissible working charge is increased from 700C to 900C(or higher), the short-circuit allowable temperature is increased from 1400C to 2500C(or higher), and the actual performance is greatly improved under the premise of maintaining its original excellent electrical performance.
Ii. Crosslinking process mode
At present, the process methods of cable production are divided into three categories: the first type of peroxide chemical crosslinking, including saturated vapor crosslinking, inert gas crosslinking, molten salt crosslinking, and silicon oil crosslinking. The second type, dry chemical crosslinking, is adopted in China. Chemical crosslinking of the second type silane; The third type of irradiation crosslinking.
Inert gas crosslinking -- dry chemical crosslinking
The polyethylene insulating material with peroxy compound crosslinking agent is used to extricate the conductor shielding layer -- insulation layer -- insulation shielding layer through three layers of co-extrusion, and then the crosslinking process is completed through the sealed crosslinking pipe filled with high temperature and high pressure nitrogen continuously and uniformly. The heat transfer medium is nitrogen (inert gas), crosslinked polyethylene has excellent electrical performance, and the production range can reach 500KV class.
Silane chemical crosslinking - Warm water crosslinking
The polyethylene insulating material with silane crosslinking agent was used to extrude the allogeneic shielding layer -- insulating layer -- insulating shielding layer by 1+2 extrusion method. Then the cooled insulated wire core was immersed in 85-950C hot water for hydrolytic crosslinking, because the moisture content in the insulating layer would be affected by wet crosslinking. Generally, the maximum voltage level is only 10KV.
Irradiation crosslinking -- physical crosslinking
The modified polyethylene insulating material was used to extrude the allogeneic shielding layer -- insulating layer -- insulating shielding layer by 1+2 extrusion method. After the extrusion, the cooled insulated wire core was uniformly processed through the irradiation scanning window of the high-energy electron accelerator to complete the crosslinking process. There is no crosslinking agent in the irradiated crosslinking cable material. During crosslinking, high-energy electron beam generated by high-energy electron accelerator effectively penetrates the insulation layer and generates crosslinking reaction through energy conversion. Because electrons have high energy and pass evenly through the insulation layer, the crosslinking bond formed has high energy and good stability. The thermal resistance is better than that of chemical crosslinked cable. However, due to the limitation of accelerator energy level (generally no more than 3.0Mev electron beam effective penetration thickness is less than 10mm, considering the geometric factor, the production cable voltage level can only reach 10KV, the advantage is less than 6KV.
Characteristics of irradiated crosslinked cables
Cable insulation aging life depends mainly on its thermal aging life, it is under the hot insulation materials in the thermal oxygen oxidation and thermal cracking of oxidation and thermal cracking, condensation and decided by the speed of chemical reaction, so the thermal aging of the insulating material life directly affects the service life of the cable, according to chemical reaction dynamics is derived and the artificial accelerated thermal aging test measured (20 to 30 years) irradiation crosslinking cable allowed working temperature for a long time for:
Power cable YJV0.6/1kV1160C
If derived at the rated operating temperature of 1050C, the thermal aging life is more than 60 years.
If derived from the rated operating temperature 900C, the thermal aging life is more than 100 years.
Overhead insulated cable JKLYJ10KV1220C
The environmental resistance and radiation resistance of the insulating material are more important when the insulated cable is laid in the open air. Irradiated crosslinked insulating materials pass through
Over-irradiation processing itself has a very good radiation resistance, and there is a large safety margin between the radiation dose applied in the crosslinking process and the damage dose. The radiation damage dose of polyethylene is 1000KGY, while the processing dose is about 200KGY. In addition to the improvement of special formula, it is still exposed to radiation cross-linking in a wide range, so its performance will be improved in the long early application process.
Iv. Performance comparison of commonly used plastic insulated cables:
At present, in cable production, the most commonly used insulation plastics are polyethylene and polyvinyl chloride, among which polyethylene material has better electrical properties and better crosslinking, so a variety of industrial crosslinking production processes, chemical crosslinking and irradiation crosslinking have been developed. In addition to the performance of the following table, in the process of production and laying, the commonly used crosslinked cable insulation layer is characterized by greater hardness and strength (at room temperature), especially more difficult than PVC insulation stripping. The irradiated crosslinking cable has the best cross-linking performance, the highest degree of cross-linking and the highest peeling strength. If it is easy to peel off the insulation layer of a crosslinked cable (similar to PVC), it must be that the crosslinking degree is insufficient or there is no crosslinking. In general, the crosslinking degree of the crosslinking cable produced by the warm water crosslinking process is often insufficient, because the crosslinking degree of this kind of cable is relatively low originally, and the crosslinking process is discontinuous and cannot be automatically controlled, which is greatly affected by human factors and prone to backlinking.