Pacific Cable Shares Tips - How To Prevent Water From Entering The Cable

Water ingress of cables should be prevented in advance

Generally speaking, due to the strict electric field voltage test, the power cable cannot enter water during the production process, and the inside of the cable must be dry, so the water inlet cable cannot be shipped from the factory.

Once the cable enters the water, under the action of the electric field, water tree aging will occur, and eventually the cable will break. A water tree is an interstitial collection with diameters ranging from 0.1 meters to a few micrometers. The origin of the water tree is the impurities in the insulation. The pores and the uneven parts of the interface between the insulation and the inner and outer semiconducting layers. The development of water trees is generally more than 8 years. The higher the humidity, temperature and voltage, the more ions in the water, and the faster the development of water trees.

The water directly enters the low-voltage power cable, causing corrosion of metals such as steel strips and copper strips, and the insulation performance is reduced. When water passes through the insulating layer, it will cause cable breakdown, or even explode and hurt people.

1. During storage

Both ends of the newly purchased cylindrical cables are sealed with plastic glands, but after a period of use, the rest of the cables are wrapped in plastic paper and tied outside with ropes. Poor sealing performance. Over time, water vapor can seep into the cable.

2. When laying cables.

When the cable is laid, its cable head wrapped with plastic paper is sometimes immersed in water, allowing water to enter the cable; sometimes, the outer sheath is broken when pulling and passing through the tube.

3. After laying

After the laying is completed, the cable head is not made in time, so that the cable port is exposed to the air for a long time, or even immersed in water, so that a large amount of water vapor enters the cable.

4. When making the cable head.

Due to the intention of the production staff, the cable end sometimes slips into the cable well with accumulated water, which is due to the intention of the production staff.

5. When the cable is running.

During the operation of the cable, the accumulated water in the cable well will enter the cable along the gap, such as the breakdown of the intermediate joint.

Cable water treatment measures

After the cable is dried, it is very difficult to enter the water (such as drying with hot nitrogen pressure), and the corresponding equipment is generally not equipped. In actual operation, if the cable R6 enters water, generally only a few meters of the front end are sawed off. If the entire cable enters the water, it is not advisable. Therefore, to prevent water from entering the cable, attention should be paid to prevention and the following measures should be taken:

1. The cable head should be sealed.

The sawed-off cable ends should be sealed with plastic (special cable glands), whether they are stacked or laid, to prevent moisture from infiltrating.

2. Prompt production of cable heads: After laying the wires, the cable heads should be produced in time.

3. Purchase of cables.

Manufacturers with good quality must choose. The quality of the cable is very important to prevent the aging of the water tree, because impurities in the insulation, pores, etc. are the starting point of the water tree.

4. Strengthen the management of the cable head production process.

Once the cable enters the water, the cable end is usually the first to be broken down, so the wire end is well made and can prolong the overall life of the cable. For example, when cables are stripped of the semiconducting layer, they can scribe vertically on the semiconducting layer and strip the semiconducting like sugar cane. However, when scratching with a knife, if the scratch is too deep, it can damage the insulation and give the water tree a chance. Also, during the soldering process, the soldering tin will be melted directly with a blowtorch as the power source cannot be found. At this point, the flame can damage the copper shield and insulation. Therefore, to eliminate this phenomenon, the correct way is to configure the UPS, because the time required for welding is usually only 10 minutes and the power is only 500W.

5. Use of cold shrinkable cable head.

The cold-shrinkable silicone rubber cable fittings are simple and convenient to make, without the need for spray lamps and soldering tin. In addition, the silicone rubber cable accessories are elastic and stick closely to the cable, overcoming the shortcomings of heat shrinkable materials (heat shrinkable materials are not elastic, and a gap will appear between the cable and the cable body during the process of cable expansion and cold shrinkage, facilitate the development of water trees).

6. The cable branch box is used for long cables.

For example, for several long cables, each length is about 3 kilometers. For such cables, one or two cable branch boxes can be used in addition to the intermediate connectors. Once one section of the cable is flooded, they won't spread to other sections of the cable and are easy to find in sections in the event of a cable failure.

Use 8.7/10kV cables for 7.10kV systems.

The insulation thickness of this cable is 4.5mm, while the insulation thickness of the 6/10kV cable is 3.4mm. Due to the increase of the insulation thickness of the cable, the strength of the site is reduced, which can prevent the aging of the water tree. At the same time, the cable must be thickened. Because the L0kV neutral point small current grounding system is single-phase grounded, the cable must withstand 1.73 times of Phase voltage, and run as required for 2h.

8. PVC plastic for double-wall corrugated pipe.

This kind of pipe has the advantages of corrosion resistance, smooth inner wall, good strength and toughness, so when the cable is directly buried, the damage to the outer sheath of the cable can be greatly reduced.