Application of XLPE cable in urban network

Actively develop the ABC cable distribution network to meet the needs of load growth and urban construction (improvement of the city appearance and reduction of land occupation). In recent years, with the extensive use of cables in urban network construction and transformation, cable failures have gradually increased.

It is an important task for electric power workers to discuss the problems that should be paid attention to in the use of cables in urban networks.

1. Analysis of common cable faults The most direct cause of cable faults is breakdown due to insulation degradation.

Analyze the causes of cable failures in recent years, mainly include:

(1) Overload operation. Long-term overload operation will cause the temperature of the power cable to rise and the insulation aging, which will lead to insulation breakdown.

(2) Construction quality. Electrical aspect: the construction process of the cable head fails to meet the requirements, the sealing of the cable head is poor, moisture invades the inside of the cable, and the insulation performance of the cable is reduced; protective measures are not taken when the cable is laid, the protective layer is damaged, and the insulation is reduced. In terms of civil engineering: poor drainage of pipe trenches in industrial wells, long-term soaking of cables in water, impairing the insulation strength; too small industrial wells, insufficient cable bending radius, and long-term extrusion.

(3) Damage by external force. Mainly, it was the brutal construction of machinery in municipal construction, digging wounds and cutting cables.

(4) Corrosion. The protective layer suffers from chemical corrosion or electric corrosion for a long time, which causes the protective layer to fail and the insulation decreases.

(5) The quality of the cable itself or the cable head accessories is poor, and the insulating glue dissolves and cracks, resulting in insulation degradation and accidents.

2. Response measures

(1) The design model should have a proper margin. On-site operating experience shows that for the important load cables that are continuously produced, a proper margin should be left in the design and selection. Although the investment is slightly larger, it can ultimately reduce cable failures and extend cable life.

(2) Laying methods should be adapted to local conditions. Different laying methods should be adopted for different areas. Commonly used laying methods are: direct buried laying, pipe laying, trench laying, laying in tunnels, etc. In urban areas and rainy and humid areas, direct burial should not be used; cable tunnels or cable wells should be used in areas where the number of cables is relatively concentrated; when trenches are not suitable, pipe laying methods can be used.

3) Choose good quality cables and cable head accessories. The quality of the cable is very important to prevent the deterioration of water branches. When choosing a cable, you should have a certain understanding of the production process and management of the cable, so that you can buy a good quality cable and lay the foundation for reducing failures. The quality problems of the cable head accessories will dissolve and crack the cable head insulation, causing the cable to be damp, the insulation drop, and cause accidents; in recent years, we have begun to adopt cold shrinkage on the cable heads and middle heads on both sides of the main cable (especially outdoors) Head craft. Because the processing and installation are more convenient, and it is easy to store and not easy to deform, the construction quality is less affected by human factors, so it is gradually promoted.

Cable quality defects and troubleshooting methods

The degree of crosslinking (hot extension) is unqualified
If the degree of cross-linking does not meet the standard, the thermal-mechanical properties of the cable are unqualified and cannot meet the requirement of 90°C working temperature.
The reasons for the unqualified cross-linking degree are the unqualified formula and the improper proportion of the compounding agent. The formula should be adjusted to solve it; the second is the improper vulcanization process, such as low air pressure, fast line speed, high cooling water level and other factors.
The solution is to first find out what is the reason, which may be one or several reasons at the same time, and eliminate the reasons.
Unqualified structure and appearance
(1) The thinnest point of the insulating layer thickness is lower than the minimum value specified in the standard, or the average thickness is lower than the nominal value. The reasons for the unqualified insulation thickness are the fast line speed, the small amount of glue from the extruder, and the improper mold selection.
The solution is to reduce the linear speed or increase the speed of the extruder and adjust the size of the die.

(2) Eccentricity
The reason for the eccentricity is that the mold is not adjusted or the suspension control has changed after the recruitment is adjusted.
The solution is to control the drape as stable as possible during driving.
Bamboo-shaped
The reason for the appearance of the bamboo-shaped outside of the cable is electrical and mechanical systems that cause the traction speed to be unstable, and the second is that the core is too small, or the conductor outer diameter is uneven.
The troubleshooting method is to check the mechanical and electrical system and eliminate the fault. Properly adjust the size of the core, control the outer diameter of the suburbs and counties as uniform as possible, and the stranded wire that exceeds the process regulations can be used.
Surface scratches
(1) The cable touches the upper or lower wall or foreign matter in the vulcanizing tube. Therefore, it is required to adjust the degree of suspension, try to make the wire core move in the middle of the cross-linked tube, and clean up in time if foreign matter is found.
(2) There is burnt on the outer edge of the mold sleeve. The solution is to adjust the temperature of the mold sleeve when starting the car to prevent overheating. Once it is found to be burnt, it should be stopped immediately to remove it, or it will not get better by itself.

Impurities
Most of the impurities in insulating materials and semi-insulating materials are brought in during mixing and during the feeding process of the extruder. Strict attention should be paid to the cleanliness of materials during operation to prevent the mixing of external impurities. Another kind of impurity is scorch, which affects the performance and service life of the cable. Therefore, the temperature is strictly controlled during mixing and extrusion to prevent the occurrence of scorching.
bubble
There may be two reasons for bubbles generated in the insulation, one is caused during extrusion. The solution is to select appropriate molds. There are bubbles in the shielding layer. The main reason is that there is water in the material. It should be dried before extrusion. The second is insufficient cooling. At this time, the following will appear. A circle of bubbles will appear on the circumference equidistant from the core.
The elimination method is to strengthen cooling, raise the water level and lower the temperature of the cooling water.
Unqualified ABC cable performance

(1) Unqualified free discharge and dielectric loss
The causes of dissociation discharge and dielectric loss unqualified are complex, and they are shielded from the outside. Whether the insulation contains bubbles and impurities is closely related to the performance of the raw materials. The elimination method is to keep the raw materials clean and strictly follow the production process.
(2) Cable insulation breakdown
The main cause of cable insulation breakdown is the mixing of insulating materials and external damage. Due to strict avoidance of external damage, the mixing of impurities should be avoided as much as possible. The semi-finished products are strictly managed to prevent stumbling.
(3) Cushion breakdown
The main reason for the cushion layer breakdown is the steel with burrs, curling, and puncture the cushion. The method of elimination is the use of different quality requirements for the unqualified steel belt. The cushion shall be made of plastic tape with higher hardness, and ensure The thickness of the cushion.If you want to buy cables, you can learn about our Huaxing cables