1. Irradiation cross-linked cable XLPE cable concept
Cross-linked cable usually refers to the insulation layer of the cable using cross-linked materials. The most commonly used material is cross-linked polyethylene wire (XLPE cable). The cross-linking process is to form a cross-linked polyethylene with a body mesh structure through a specific processing method. The long-term allowable working temperature is increased from 700C to 900C (or higher), and the short-circuit allowable temperature is increased from 1400C to 2500C (or higher). On the premise of maintaining its original excellent electrical properties, the actual use performance is greatly improved.
2. Irradiation cross-linked cable XLPE cable cross-linking process
At present, the cable industry produces cross-linked cables in three processes: the first type is peroxide chemical cross-linking, including saturated vapor cross-linking, inert gas cross-linking, molten salt cross-linking, silicone oil cross-linking, and the second type, i.e. dry chemical cross-linking, is used in China; the second type is silane chemical cross-linking; the third type is irradiation cross-linking.
1. Inert gas crosslinking – dry chemical crosslinking
Use polyethylene insulation material with peroxide crosslinking agent, complete the conductor shielding layer – insulation layer –
After the extrusion of the insulation shielding layer, continuously and evenly pass through a sealed crosslinking tube filled with high-temperature, high-pressure nitrogen to complete the crosslinking process. The heat transfer medium is nitrogen (inert gas), the crosslinked polyethylene has excellent electrical properties, and the production range can reach 500KV.
2. Silane chemical crosslinking – warm water crosslinking
Use polyethylene insulation material with silane crosslinking agent, complete the extrusion of the heterogeneous shielding layer – insulation layer – insulation shielding layer through 1+2 extrusion, and then immerse the cooled and mounted insulation core in 85-950C hot water for hydrolysis and crosslinking, because wet crosslinking will affect the water content in the insulation layer. Generally, the highest voltage level is only 10KV.
3. Irradiation cross-linking – physical cross-linking
Use modified polyethylene insulation material, complete the extrusion of the heterogeneous shielding layer – insulation layer – insulation shielding layer through 1+2 extrusion method
After extrusion, the cooled insulation core is evenly passed through the irradiation scanning window of the high-energy electron accelerator to complete the cross-linking process. No cross-linking agent is added to the irradiation cross-linked cable material. During cross-linking, the high-energy electron beam generated by the high-energy electron accelerator effectively penetrates the insulation layer and produces a cross-linking reaction through energy conversion. Because the electrons carry high energy and evenly pass through the insulation layer, the cross-linking bond formed has high binding energy and good stability. The physical properties shown are that the heat resistance is better than that of chemical cross-linked cables. However, due to the limitation of accelerator energy level (generally not more than 3.0Mev, the effective penetration thickness of electron beam is less than 10mm, and considering geometric factors, the voltage level of the produced cable can only reach 10KV, and the advantage is below 6KV.
3. Characteristics of XLPE cable of irradiated cross-linked cable
The aging life of cable insulation material mainly depends on its thermal aging life, which is determined by the speed of chemical reactions such as thermal oxidation, thermal cracking, thermal oxidation cracking, and polycondensation in the insulation material under thermal work. Therefore, the thermal aging life of the insulation material directly affects the service life of the cable. According to the deduction of chemical reaction kinetics and artificial accelerated thermal aging test (20-30 years), the long-term allowable operating temperature of irradiated cross-linked cable is:
1. Power cable YJV 0.6/1KV 1160C
If deduced according to the rated operating temperature of 1050C, its thermal aging life exceeds 60 years.
If deduced according to the rated operating temperature of 900C, its thermal aging life exceeds 100 years.
2. Overhead insulated cable JKLYJ 10KV 1220C Overhead insulated cables are laid in the open air, so the environmental resistance and radiation resistance of the insulating materials are more important. Irradiation cross-linked insulating materials must undergo irradiation processing, which has good radiation resistance. The radiation dose applied during the cross-linking production process has a large safety margin from its destructive dose. The radiation destructive dose of polyethylene is 1000KGY, while the processing dose is about 200KGY. In addition, with the improvement of special formula, it is still in the radiation cross-linked state within a fairly wide range, so its performance will be improved during the long initial use process.
IV. Medium-voltage cross-linked polyethylene insulated power cable in the national standard for wires and cables
Medium-voltage cross-linked polyethylene insulated power cable (voltage level: 6/6KV-26/35KV; implementation standard: GB/T12706.2-2002)
Medium voltage cross-linked polyethylene cable adopts a fully dry chemical cross-linking method to change the polyethylene molecule from a linear molecular structure to a spatial mesh structure, so that the thermoplastic polyethylene is converted into a thermosetting cross-linked polyethylene, so that its mechanical properties, thermal aging properties and environmental stress capacity are greatly improved, and it has excellent electrical properties. It has the characteristics of high normal operating temperature, simple structure, small outer diameter, light weight, easy use, and no restrictions on laying height. It is suitable for power frequency rated voltage 1-35KV distribution system.
YJV62, YJLV62 cross-linked polyethylene insulated double non-magnetic metal belt armored PVC sheathed power cable.
YJV63, YJLV63 cross-linked polyethylene insulated double non-magnetic metal belt armored polyethylene sheathed power cable.
YJV63, YJLV63 cross-linked polyethylene insulated double non-magnetic metal belt armored polyethylene sheathed power cable.
Other models are similar to irradiation cross-linking (only the voltage is different)
YJV, YJLV, YJY, and YJLY are suitable for indoor laying. They can withstand certain laying traction, but cannot withstand mechanical external forces. Single-core cables are not allowed to be laid in magnetic pipes.
YJV22, YJLV22, YJV23, and YJLV23 are laid indoors, in tunnels, and cable trenches, and can withstand certain mechanical external forces, but cannot withstand excessive tension.
YJV22, YJLV22, YJV23, and YJLV23 are laid indoors, in tunnels, and cable trenches, and can withstand certain mechanical external forces, but cannot withstand excessive tension.
YJV32, YJLV32, YJV33, and YJLV33 are suitable for high-drop areas and can withstand certain mechanical external forces and considerable tension.
YJV62, YJLV62, YJV63, and YJLV63 are single-core cables used in AC circuits and should be armored with non-magnetic materials.
YJV62, YJLV62, YJV63, and YJLV63 are single-core cables used in AC circuits and should be armored with non-magnetic materials.
V. Performance comparison of irradiated cross-linked cables XLPE cables and commonly used plastic insulated cables (PVC cables):
Currently, the most commonly used insulating plastics in cable production are polyethylene and polyvinyl chloride, among which polyethylene materials have better electrical properties and better cross-linking properties, so a variety of industrial cross-linking production processes have been developed, including chemical cross-linking and irradiation cross-linking. In addition to the performance in the table below, during the production and laying process, the insulation layer of the commonly used cross-linked cables currently exhibits greater hardness and strength (at room temperature), especially more difficult to strip than polyvinyl chloride insulation. Since the cross-linking performance of the radiation cross-linked cable is the best and the degree of cross-linking is the highest, the peeling strength is relatively the largest. If the cross-linked cable insulation layer is easier to strip (similar to polyvinyl chloride), it must be that the degree of cross-linking is insufficient or there is no cross-linking. Generally speaking, cross-linked cables produced by warm water cross-linking process often have insufficient cross-linking degree. The reason is that the cross-linking degree of this type of product is relatively low, and the cross-linking process is non-continuous and cannot be automatically controlled. It is greatly affected by human factors and is prone to insufficient cross-linking.
Taking 1*70 as an example, the comparison table of common plastic insulated cable characteristics is as follows
Items Ordinary PVC (polyvinyl chloride) and chemical cross-linked polyethylene Irradiated cross-linked polyethylene Comparison
200C volume resistivity 1*1013 1*1017 1*1017
Temperature resistance level (0C) 70 90 90-150
Short-term overload temperature (0C) 160 250 270
Current carrying capacity (times) 1.0 1.3 1.6
Aging conditions 0C 7 days 1000C 7 days 1350C 7 days 1580C 7 days
Elongation under load (≤%) 175 100
Scratch resistance test under load (times) 20000 20000 100000
Abrasion resistance 5 times that of PVC 10 times that of PVC, 5 times that of nylon
Oil resistance and chemical corrosion resistance No change after 7 days of immersion in gasoline No change after 30 days of immersion in gasoline
Dielectric constant 5.0 2.3 2.3
Oxygen index 28 20 37
Bundle combustion carbonization part height ＜2.5 ＜1 ＜0.3
Light aging resistance KJ ＜230 ＜300 ＜400
Tensile strength N/cm2 12.5 at 700C 12.5 at 900C 23.1 at 900C
Elongation at break 125% at 700C 200% at 900C 240% at 900C
Ozone resistance Ozone concentration
Break time at 0.03% (hours) 1000 1000 1200
VI. XLPE Cable/XLPO Cable Model Characteristics and Application
Irradiated Crosslinked Polyolefin Cable Materials (XLPE/XLPO)
RYD series XLPE/XLPO materials are compounded from polyolefin resin, elastomer resin and flame retardant. Based on advanced alloying technology, the product has excellent comprehensive properties, such as high strength, high flexibility, high temperature resistance, oil resistance, wear resistance, etc., and is widely used in insulation and sheathing of various heat-resistant cables.
