Jack knowledge about cable:knowledge of xlpe cable

Today, we continue to introduce cable knowledge . Have a blog introduces the history of power cables , in fact, a large part of the development of the cable insulation material development and progress ! Here we give a brief knowledge of XLPE cables !

XLPE cables usually refers to cable insulation layer using crosslinked material. The most commonly used material for the cross -linked polyethylene (XLPE). The crosslinking process is a linear molecular structure of polyethylene (PE) through a specific way of processing the material , to form cross- linked polyethylene cable of the mesh structure of the body . Making long-term allowable working temperature increased from 70 ℃ to 90 ℃ ( or higher ) , short allowable temperature increased from 140 ℃ to 250 ℃ ( or higher ) , while maintaining its original premise of excellent electrical performance , greatly improved actual performance.

Process approach

Currently XLPE cables and cable industry production process is divided into three categories: the first category peroxide crosslinking chemistry , including saturated vapor crosslinked crosslinking inert gas , molten salt crosslinked silicone crosslinking the country are using the first two kinds namely dry chemical crosslinking ; second category silane chemical crosslinking ; third category radiation crosslinking .

Inert gas

Adding peroxide crosslinking agents using the compound polyethylene insulation materials, completed by three co-extruded conductor shield – insulation – extruded insulation shield layer , continuous and uniform through full temperature, high pressure nitrogen seal crosslinked tube complete the crosslinking process. Heat transfer medium is nitrogen ( inert gas ) , cross-linked polyethylene excellent electrical properties, production range up to 500KV class .

Silane chemistry

Using silane coupling agent added polyethylene insulation, extruded through a 1 +2 manner allogeneic shield – insulation – extruded insulation shield layer will have a plate to cool insulated core immersed 85 – of crosslinked for 95 ℃ hot water , since the influence of the insulating layer is wet cross-linking of the water content. Generally only up to a maximum voltage level 10KV.
Irradiation crosslinked

After using the modified polyethylene insulation material is completed by an allogeneic shield +2 extrusion way – insulation – extruded insulation shield , the insulated core cooled , even by high-energy electron accelerator radiation according to the scan window to complete the cross-linking process . Radiation crosslinking cable compound without adding a crosslinking agent , when crosslinked by high-energy electron accelerator to produce high-energy electron beam effectively penetrate the insulation layer , resulting in cross-linking reaction by energy conversion , because the electron with high energy and uniformly through the insulating layer, the formation of crosslinks binding energy , good stability. Exhibit physical properties , heat resistance, superior chemical cross-linking cables. However, due to limitations accelerator energy level ( usually no more than 3.0Mev electron beam effectively penetrate the thickness of 10mm or less , by considering the geometric factor , producing cable voltage level can only reach 10KV, 6KV the following advantages .

Recognition

False identification XLPE cable breakdown methods:

In the course of using the system in a series resonant test voltage cable finished product and high partial discharge test, sometimes during the test due to various causes false sudden breakdown , how to identify the cable itself has a proper breakdown of the true , or other causes of false breakdown occurred cables , cable factory test for improving the efficiency of great significance.

Medium voltage XLPE power cables and high-voltage factory partial discharge test was conducted in a shielded room -by- disc , and then you can consider to replace the insulation core retest , if you replace wires, through the normal voltage test , should be able to determine whether the cable really happened breakdown. Or, re- boost, if the breakdown voltage showed a decreasing trend , you can also determine the cable breakdown really happened , if every breakdown voltage cables are on the same value , you should consider whether the cable ends occur breakdown , this time, partial discharge can be shielded room door door interlock switches , artificially closed, the shielded room door opened, boosting observe breakdown , breakdown soon be able to determine the position of the tip . If, after investigation, the cable ends no breakdown occurs , replace the multi- core insulated wire and cables , and even had qualified to do the exercises had been unloaded cable retest or re-examination , the breakdown voltage value remains the same , it should be recognized when the cable there has been a false breakdown , equipment should be checked , troubleshooting and then tested. But for some length of cross- examination of a large single medium voltage XLPE cables , but also to check whether it has exceeded the allowable load test equipment such cases, the testing process also appears detuning tripping , not the temerity to determine the occurrence of cable the breakdown.

There is a special need in this case also shows that sometimes the cable insulation internal short circuit, series resonance test system may not resonant boost, which also belongs to a special cable breakdown. Encountered this phenomenon, as long as the replacement of insulation good insulated core tests to confirm .