Cross-linked cable is short for cross-linked polyethylene (XLPE) insulated cable. Cross-linked cables are suitable for transmission and distribution lines with power frequency AC voltage of 500KV and below.
At present, most of the high-voltage cables have been used for cross-linked polyethylene insulated cross-linked cables, which usually means that the insulation layer of the cable is made of cross-linked materials. The most commonly used material is cross-linked polyethylene (XLPE).
Processing engineering is the process of using polyethylene (PE) material with linear molecular structure through a specific processing method to form a cross-linked polyethylene with a body-shaped network split line structure. The long-term allowable working temperature is increased from 70°C to 90°C (or higher), and the short-circuit allowable temperature is mainly increased from 140°C to 250°C (or higher). While maintaining its original excellent electrical performance, it has greatly improved Actual performance.
At present, the process methods for producing cross-linked cables in the cable industry are divided into three categories:
The first type of peroxide chemical crosslinking includes saturated steam crosslinking, inert gas crosslinking, molten salt crosslinking, and silicone oil crosslinking;
The second type of silane chemical crosslinking;
The third type of radiation crosslinking.
1. Inert gas cross-linking: Dry chemical cross-linking adopts polyethylene insulating material added with peroxy compound cross-linking agent. After the conductor shielding layer, insulating layer, and insulating shielding layer are extruded through three layers, they are continuously and uniformly filled with high temperature , The sealed cross-linking tube of high-pressure nitrogen completes the cross-linking process. The heat transfer medium is nitrogen (inert gas), the cross-linked polyethylene has excellent electrical properties, and the production range can reach 500KV.
2. Silane chemical cross-linking: warm water cross-linking adopts polyethylene insulating material with silane cross-linking agent, and after extruding the foreign body shielding layer, insulating layer, and insulating shielding layer through the 1+2 extrusion method, the cooled and loaded plate The insulated core is immersed in 85-95℃ hot water for hydrolysis and cross-linking, because wet cross-linking will affect the water content in the insulating layer. Generally, the highest voltage level is only 10KV.
3.Irradiation cross-linking: Physical cross-linking uses modified polyethylene insulating material, and after the extrusion of the different shielding layer, insulating layer, and insulating shielding layer is completed by 1+2 extrusion, the cooled insulated core , The cross-linking process is completed evenly through the irradiation scanning window of the high-energy electron accelerator. No cross-linking agent is added to the radiation cross-linked cable material. During cross-linking, the high-energy electrons generated by the high-energy electron accelerator effectively penetrate the insulating layer, and the cross-linking reaction is generated through energy conversion, because the electrons have high energy. , And evenly pass through the insulating layer, so the formed cross-linked bond has high binding energy and good stability. The physical performance shown is that the heat resistance is better than the chemical cross-linked cable. However, it is mainly limited by the energy level of the accelerator (generally no more than 3. The effective penetration thickness of the OMev electron end is less than 10mm, considering the geometric factors, the voltage level of the production cable can only reach 10KV, and the advantage is below 6KV.
XLPE cable characteristics
The aging life of cable insulation material mainly depends on its thermal aging life. It is determined by the speed of thermal oxygen oxidation, thermal cracking, thermal oxidative cracking, polycondensation and other chemical reactions that occur in the insulating material under heat. Therefore, the insulating material The thermal aging life of the cable directly affects the service life of the cable. According to the chemical reaction kinetics derivation and the artificial accelerated thermal aging test (20-30 years), the long-term allowable working temperature of the irradiated cross-linked cable is:
1. If the power cable 0.6/1KV(LV Cable) is deduced according to the rated working temperature of 105 degrees, its thermal aging life exceeds 60 years.
If deduced according to the rated operating temperature of 90 degrees, its thermal aging life exceeds 100 years.
2. Overhead insulated cable 10KV 122 degrees
When overhead insulated cables are laid in the open air, the environmental and radiation resistance of insulating materials is more important. Irradiation cross-linked insulating materials have to undergo irradiation processing, and they have good radiation resistance. The radiation dose applied in the cross-linking production process leaves a large safety margin from the destruction dose. The radiation damage dose of polyethylene is 1000KGY, and the processing dose is about 200KGY. In addition to the improvement of the special formula, it is still cross-linked by radiation in a relatively wide range, so its performance will be affected by radiation during a long period of early use.
In cable production recently, the most commonly used insulating plastics are polyethylene and polyvinyl chloride. Among them, polyethylene materials have better electrical properties and better crosslinking properties. Therefore, a variety of industrial crosslinking production processes have been developed. Cross-linking and radial cross-linking In the process of production and laying, the insulation layer of the currently commonly used cross-linked cables has a higher hardness and strength (at room temperature), especially more difficult to peel off than PVC insulation. Because the spoke cross-linked cable has the best cross-linking performance and the highest degree of cross-linking, relatively speaking, the peel strength is also the highest. If the peeling of the cross-linked cable insulation layer is relatively easy (similar to polyvinyl chloride), it must be insufficient or no cross-linking. Under normal circumstances, the cross-linked cable produced by the warm water cross-linking process has more cases where the degree of cross-linking is not enough. The reason is that the degree of cross-linking of such products is relatively low, and the cross-linking process is not continuous and cannot be automatically controlled. Affected by human factors, under-crosslinking easily occurs.