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<br> <br> crosslinking processes described process is a linear molecular structure of the polyethylene (PE) material is processed by a specific manner, to form a cross-linked polyethylene mesh size sub-line structure. The long-term allowable operating temperature is increased from 70°C to 90°C (or higher), and the short-circuit allowable temperature is increased from 140°C to 250°C (or higher), greatly improving the premise of maintaining its excellent electrical performance. Actual use performance.
Method 2 breakdown false identification method to identify <br> <br> XLPE cable:
In the process of using the series resonance test system to perform partial discharge and high voltage test on medium-voltage cable finished products, false breakdown phenomenon may suddenly occur in the test process for various reasons. How to correctly identify whether the cable itself has a true breakdown or Other causes of false breakdown of the cable are significant for improving the efficiency of the cable factory test.
The partial discharge and high voltage test of medium-voltage cross-linked power cables are carried out in a shielded room on a disk-by-disc basis. In this case, re-examination of the insulated cores may be considered. If the core test is passed after the cores are replaced, the voltage test should be able to determine the cable. Breakdown really happened. Alternatively, if the breakdown voltage is gradually reduced, it can be determined that a true breakdown occurs in the cable. If the breakdown voltage of each cable is on the same value, consider whether the end of the cable has occurred. Breakdown, at this time, the partial discharge switch of the partial discharge shield room door can be artificially closed, the shield room door can be opened, the pressure can be increased, the breakdown phenomenon can be observed, and the end breakdown position can be determined very quickly. If there is no breakdown at the end of the cable after the investigation, replace the multiple insulated cores and cables, and even retest the cable that has passed qualified or no-load retest. The breakdown voltage always maintains the same value, and the cable should be confirmed. There was a false breakdown and the equipment should be inspected and tested before troubleshooting. However, for some large-length single-core medium-voltage cross-linked cables for cross-checking, it is also necessary to check whether they have exceeded the allowable load of the test equipment. In this case, the detuning tripping phenomenon will occur during the test, do not arbitrarily determine the cable Breakdown.
There also need a special case described here, the internal cable insulation may short circuit, the series resonant test system may not resonant step, which is a special cable breakdown. When this happens, it can be confirmed by simply replacing the insulated core with a good insulation test.
3 embodiment <br> <br> present process for producing a crosslinked cable and cable industry process divided into three categories: chemical crosslinking peroxides, including saturated vapor crosslinking,
Crosslinked inert gas, molten salt crosslinked, crosslinked silicone oil, are used in the second domestic i.e. dry chemical cross-linking; second silane chemical crosslinking; third category radiation crosslinking.
Inert gas is made of polyethylene insulation material with peroxide compound cross-linker added. After three layers of co-extrusion, the conductor shielding layer - insulation layer - after the insulation shield is extruded, continuously and uniformly through the seal filled with high temperature and high pressure nitrogen. The cross-linking tube completes the cross-linking process. The heat transfer medium is nitrogen (inert gas), cross-linked polyethylene has excellent electrical properties, and the production range can reach 500KV.
Silane chemistry adopts polyethylene insulation material added with silane cross-linking agent to complete the all-body shielding layer—insulation layer through extrusion of 1+2—after extrusion of the insulation shielding layer, the insulated wire core cooled and loaded is immersed. Hydrolysis cross-linking in 85-95°C hot water will affect the moisture content in the insulation due to wet cross-linking. The general highest voltage level is only 10KV.
The latest process method for the application of a chemically cross-linked, radiation-crosslinking functional masterbatch At present, the use of crosslinked functionalized parent particles of polyethylene cable allows the addition of a small amount of this functional masterbatch to particles of ordinary polyethylene cable. The cable can become a cross-linked cable.
There are three kinds of parent particles for the cross-linking function of the cable: chemical cross-linking function, electron beam irradiation cross-linking function, and ultraviolet light irradiation cross-linking function.
1. Cross-linking function mother particle for chemical cross-linked cable, Model: DH-125Y,
DH-125Y chemically cross-linked parent particles appear as colorless LLDPE plastic particles. Wire and cable factories only need to purchase common LLDPE polyethylene plastic particles on the market, such as LLDPE7042 and so on. Into 25 kg LLDPE7042 plastic particles, 1 kg of DH-125Y functional mother particles were added, and after being evenly turned by hand, the cable was directly put into the extruder of the cable and the cable was extruded to form a crosslinked wire and cable. This function of parent particles can produce cross-linked wire and cable up to 35KV.
2. Cross-linking function mother particle for electron beam irradiation cross-linked cable, Model: DH-125DF
The appearance of the DH-125DF electron beam irradiation crosslinking parent particles is colorless LLDPE plastic particles. 7042 plastic particles were added with 1 kg of DH-125DF functional masterbatch. After being evenly turned by hand, the cable was directly put into the extruder of the cable and the cable was extruded. The cross-linked wire and cable was made by electron beam irradiation. This function of parent particles can produce cross-linked wire and cable with long-term operating temperature of 125°C.
3. Cross-linking function mother particles for UV irradiation cross-linked cable, Model: DH-125ZF,
The appearance of the DH-125ZF ultraviolet radiation crosslinking parent particles is colorless LLDPE plastic particles. 7042 plastic particles are added with 1 kg of DH-125ZF functional mother particles. After being evenly turned by hand, the cable is directly put into the extruder of the cable and the cable is extruded. The cross-linked wire and cable is made by ultraviolet irradiation. The function of the parent particles can produce long-term working environment temperature of 125 °C cross-linked wire and cable.
advantage;
1, save money:
Reduce costs and cable manufacturer directly, than the market purchase came in chemistry, radiation cross-linked polyethylene cable special material particle cheap 1500 to 3,000 yuan / ton.
2, save time;
The purchase of chemical and radiation cross-linked polyethylene cable special material particles by the cable manufacturer requires a time period of around one week for inquiry, ordering, production, and transportation. When using the DH-125 functional mother particle, after the production plan is decided, the cable production can be directly performed after 5 minutes of preparation.
3, versatility,
Cable manufacturers can adjust their own varieties, soft hardness: DH-125 function of the mother particles, not only can be added to ordinary polyethylene PE particles, can also be added to ordinary cable particles do not have cross-linking, so that the original does not have to pay The performance of ordinary plastic cable particles becomes cross-linked plastic particles.
4 Irradiation cross-linking [1] The modified polyethylene insulation material is used to complete the foreign body shielding layer through the extrusion method of 1+2—insulation layer—after the insulation shielding layer is extruded, the insulated insulation core is cooled. The cross-linking process is completed uniformly through the irradiation scanning window of the high-energy electron accelerator. No cross-linking agent is added to the irradiated cross-linked cable material. During the cross-linking, the high-energy electron beam generated by the high-energy electron accelerator effectively penetrates the insulating layer, and a cross-linking reaction is generated through energy conversion because the electrons have high energy. , and evenly through the insulating layer, so the formation of cross-linking bonds with high energy, good stability. The physical properties exhibited are superior to those of chemically crosslinked cables in heat resistance. However, due to the accelerator energy level limit (generally not exceeding 3.0 MeV electron beam effective penetration thickness of 10mm or less, taking into account the geometric factor, the production cable voltage level can only reach 10KV, the advantage is below 6KV.
Detailed Description of Process 5 <br> <br> crosslinked wire and cable insulation having excellent electrical properties, good running performance and safety thermal overload mechanical properties, easy maintenance and installation operation and other advantages.
The cross-linking mechanism of the wire and cable insulation material is a physical or chemical method, so that the polymer insulating material is transformed from a linear molecular structure into a three-dimensional network structure, and the thermoplastic material is changed into a thermosetting insulating material, thereby improving the aging resistance of the insulating material. Mechanical and environmental resistance. The United States invented cross-linked insulated wire and cable from the 1950s and gradually applied it in the 1960s. In the past ten years, crosslinked insulation has been widely used in China. It has replaced oil-paper insulation and is gradually replacing PVC plastic insulation.
There are many kinds of cross-linked insulation, which are divided into two major categories from the cross-linking mechanism, namely physical cross-linking and chemical cross-linking.
1. Chemical cross-linking: chemical cross-linking is divided into two methods: high-temperature cross-linking and low-temperature cross-linking.
(1) High-temperature cross-linking, also known as peroxide cross-linking, generally uses organic peroxide as a cross-linking agent, and under the action of heat, it decomposes to generate active free radicals. These free radicals make the polymer carbon chain produce active sites. , And produce CC crosslinks, forming a three-dimensional network structure.
High-temperature cross-linking includes two forms of steam cross-linking and dry cross-linking. In the 1960s, most of the diplomatic cables used in the country were steam cross-linked. As the cross-linked steam increased the moisture content in the insulation, the insulation quality was not good. It has been completely eliminated; in the 1970s, dry cross-linking processes were commonly used abroad, and high-pressure vulcanizing pipes were used to rapidly cross-link the pipes.
(2) cross-linking, also known as low-temperature hot water or crosslinkable silane crosslinking, the crosslinked cable in hot water at 70-90 deg.] C, the insulating crosslinking agent - silane after water absorption, the linear structure of the mesh crosslinking reaction structure.
2, physical cross-linking: also known as irradiation cross-linked, divided into γ-ray cross-linking and electron beam cross-linking two methods.
(1) Because of the low dose rate of γ-ray cross-linking, the core wire of the cable cannot be penetrated during the irradiation process. Therefore, it is currently applied only in the cross-linking of heat-shrinkable materials, and γ- is generally not used in wire and cable production. Ray cross-linking.
(2) Electron beam cross-linking, using an electron accelerator in combination with a beam irradiation device, using a high-energy electron beam (generally between 1.0 and 3.0 MeV) to irradiate the insulating layer of the wire and cable, causing the polymer to generate free radicals , form CC crosslinks, generate a three-dimensional network structure.
6 performance comparison of commonly used insulated cable performance comparison:
At present, in the cable production, the most commonly used insulating plastics are polyethylene and polyvinyl chloride, among which the polyethylene material has better electrical properties and better cross-linking properties, and thus a variety of industrial cross-linked production processes have been developed, and the chemical Cross-linking and irradiation cross-linking. In addition to the performances shown in the following table, during the production and laying process, the insulating layers of the cross-linked cables commonly used today are characterized by greater hardness and strength (at room temperature), especially with respect to the peeling of PVC insulation. Since the cross-linked cable has the best cross-linking performance and the highest degree of cross-linking, the peel strength is relatively largest. If the peeling of the cross-linked cable insulation is relatively easy (similar to polyvinyl chloride), it must be that the degree of cross-linking is not enough or there is no cross-linking. Under normal circumstances, cross-linked cables produced by a warm water cross-linking process are often not sufficiently cross-linked due to the relatively low degree of cross-linking of such products and the fact that the cross-linking process is not continuous and cannot be controlled automatically. Human factors are highly influential and are prone to under-crossing.
7 Related Features Irradiation cross-linked cable characteristics:
The aging life of cable insulation depends mainly on its heat aging life, which is determined by the speed of chemical reactions such as thermal oxidation, thermal cracking, thermal oxidative cracking, polycondensation, etc., occurring within the insulating material under thermal conditions. The heat aging life has a direct effect on the service life of the cable. The long-term allowable working temperature of the irradiated cross-linked cable (20-30 years) measured by chemical reaction kinetic derivation and artificial accelerated thermal aging test is:
Power cable YJV0.6/1KV
If the rated working temperature is 105 degrees, the heat aging life is more than 60 years.
If the rated working temperature is 90 degrees, the heat aging life is more than 100 years.
Overhead insulated cables Overhead insulated cables are laid in open air. The insulation materials are more resistant to the environment and radiation resistance. Irradiation cross-linked insulating materials are subjected to irradiation processing, which in itself has a good ability to withstand radiation. The irradiation dose applied in the cross-linked production process leaves a great safety margin from its damaging dose. The radiation damage dose of polyethylene is 1000KGY, and the processing dose is about 200KGY. Combined with the special formula improvement, it is still radiation-crosslinked within a fairly wide range. Therefore, the radiation performance of the polyethylene in the long-term pre-use period will be somewhat improved. improve.
1. XLPE cable <br> <br> crosslinked cables are typically refers to use of the cable insulation layer crosslinked material. The most commonly used material is cross-linked polyethylene (XLPE).