Brief introduction to process performance of crosslinked cable

Author：hlyb Add Time：2016-07-26 17:31:09

1、 Concept

Crosslinked cable usually means that the insulating layer of the cable adopts crosslinked material*** The commonly used material is cross-linked polyethylene (XLPE). The cross-linking process is to make the polyethylene (PE) material with linear molecular structure form cross-linked polyethylene with network branching structure through specific processing methods. The long-term allowable working mixed charge is increased from 700C to 900C (or higher), and the allowable short-circuit temperature is increased from 1400C to 2500C (or higher), which greatly improves the actual service performance on the premise of maintaining its original excellent electrical performance.

2、 Crosslinking process

At present, the process methods for producing crosslinked cables in the cable industry are divided into three categories: the first category is peroxide chemical crosslinking, including saturated vapor crosslinking

Inert gas crosslinking, molten salt crosslinking and silicone oil crosslinking are the second in China, namely dry chemical crosslinking; The second type is silane chemical crosslinking; The third type is irradiation crosslinking.

1. Inert gas crosslinking dry chemical crosslinking

The polyethylene insulating material with peroxide crosslinking agent is used to complete the conductor shielding layer - insulating layer - through three-layer co extrusion

After the extrusion of the insulating shielding layer, the crosslinking process is completed continuously and evenly through a sealed crosslinking tube filled with high temperature and high pressure nitrogen. The heat transfer medium is nitrogen (inert gas), cross-linked polyethylene has excellent electrical properties, and the production range can reach 500kV.

2. Silane chemical crosslinking warm water crosslinking

The polyethylene insulating material with silane crosslinking agent is used. After the extrusion of the allogeneic shielding layer - insulating layer - insulating shielding layer is completed by 1 + 2 extrusion, the cooled coiled insulating core is immersed in 85-950c hot water for hydrolytic crosslinking. Because the wet crosslinking will affect the water content in the insulating layer. Generally * * * high voltage level * * * up to 10kV.

3. Irradiation crosslinking - Physical Crosslinking

The modified polyethylene insulating material is used to complete the allogeneic shielding layer - insulating layer - insulating shielding layer by 1 + 2 extrusion

After extrusion, the cooled insulated core is evenly passed through the irradiation scanning window of the high-energy electron accelerator to complete the crosslinking process. No crosslinking agent is added to the irradiation crosslinking cable material. During crosslinking, the high-energy electron beam generated by the high-energy electron accelerator effectively penetrates the insulating layer and generates crosslinking reaction through energy conversion. Because the electrons have high energy and pass through the insulating layer evenly, the crosslinking bond formed has high binding energy and good stability. The physical performance is that the heat resistance is better than that of chemical crosslinked cable. However, due to the limitation of accelerator energy level (generally no more than 3.0mev), the effective penetration thickness of electron beam is less than 10mm. Considering the geometric factor, the voltage level * * * of production cable can reach 10kV, and the advantage is less than 6kV.

3、 Characteristics of irradiation crosslinked cable

The aging life of cable insulation material mainly depends on its thermal aging life, which is determined by the speed of thermal oxygen oxidation, thermal cracking, thermal oxidative cracking, polycondensation and other chemical reactions in the insulation material under thermal operation. Therefore, the thermal aging life of insulation material directly affects the service life of cable, According to the derivation of chemical reaction kinetics and the artificial accelerated thermal aging test, the long-term allowable working temperature of irradiated crosslinked cable (20-30 years) is:

1. Power cable YJV 0.6/1kv 1160c

If it is deduced according to the rated working temperature of 1050C, its thermal aging life exceeds 60 years.

If it is deduced according to the rated working temperature of 900C, its thermal aging life exceeds 100 years.

2. Overhead insulated cable jklyj 10kV 1220c

When overhead insulated cables are laid in the open air, the environmental and radiation resistance of insulating materials is more important. Irradiation crosslinked insulating materials shall be subject to

Over irradiation processing itself has good radiation resistance, and there is a great safety margin between the irradiation dose applied in the crosslinking production process and its damage dose. The radiation damage dose of polyethylene is 1000kgy, while the processing dose is about 200kgy. Combined with the improvement of special formula, it is still in the radiation crosslinking state in a wide range, so its performance will be improved after being irradiated in the long early use process.

4、 Performance comparison of common plastic insulated cables:

At present, polyethylene and polyvinyl chloride are commonly used in cable production, among which polyethylene material has better electrical properties and better crosslinkability. Therefore, a variety of industrial crosslinking production processes, chemical crosslinking and irradiation crosslinking, have been developed. In addition to the performance in the table below, during production and laying, At present, the insulation layer of the commonly used crosslinked cable shows high hardness and strength (at room temperature), especially more difficult to peel than PVC insulation. Due to the good crosslinking performance and high crosslinking degree of the radial crosslinked cable, the peel strength is relatively high. If the insulation layer of the crosslinked cable is easy to peel (similar to polyvinyl chloride), it must be that the crosslinking degree is not enough or there is no crosslinking. Generally, the crosslinking degree is not enough for the crosslinked cables produced by warm water crosslinking process. The reason is that the crosslinking degree of these products is relatively low, and the crosslinking process is discontinuous and can not be controlled automatically. It is greatly affected by human factors and is prone to under crosslinking.

Take 1 * 70 as an example to illustrate the characteristic comparison table of common plastic insulated cables

Project common PVC (polyvinyl chloride) chemical crosslinked polyethylene irradiation crosslinked polyethylene

200C volume resistivity 1 * 1013 1 * 1017 1 * 1017

Temperature resistance grade (0C) 70-150

Short time overload temperature (0C) 160 250 270

Ampacity (Times) 1.0 1.3 1.6

Aging condition 0C 7 days 1000C 7 days 1350c 7 days 1580C 7 days

Elongation under load (≤%) 175 100

Scratch and wear resistance test under load (Times) 20000 100000

The wear resistance is 5 times that of PVC, 10 times that of PVC and 5 times that of nylon

Oil and chemical corrosion resistance no change after immersion in gasoline for 7 days and no change after immersion in gasoline for 30 days

Dielectric constant 5.0 2.3 2.3

Oxygen index 28 20 37

Height of carbonization part of beam combustion ＜ 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%

Ozone resistance ozone concentration

Breaking time at 0.03% (H) 1000 1200

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Brief introduction to process performance of crosslinked cable