Every year into the rainy season, especially in the fall of this year, especially the rain, cable part of the forgotten head after the most common problem is the cable water. After the cable water, the role of the electric field, the occurrence of water tree aging phenomenon, and finally lead to cable breakdown. The water tree is a collection of voids with a diameter of 0.1 m to several microns filled with water. The local high electric field formed by the presence of impurities, pores and insulation in the nonuniformity of the bonding surface of the inner and outer semiconducting layers is the starting point of the water tree. Water tree development process is generally more than 8 years, humidity, temperature, the higher the voltage, the more water contained in the water, the faster the development of water trees.
Reason for water intake
Custody: the new to buy into the cable, the two are sealed with plastic seal, but with a period of time, the rest of the plastic paper wrapped with a rope outside the bar, the seal is not good, the day long, water vapor It will penetrate the cable.
When laying the cable: When the cable is laid, the cable head wrapped in plastic paper is sometimes immersed in the water, so that the water enters the cable; in the case of traction and piercing, the outer sheath rupture sometimes occurs.
After laying: not in time for the production of cable head, so that the cable port is not sealed long-term exposure to the air, and even immersed in water, so that a large number of water vapor into the cable.
When the cable head is made: When the cable head is made (including the terminal head and the middle connector), the cable end is sometimes slid into the cable wells with water due to the effect of the production staff
When the cable is running: the cable is running, such as breakdown of the middle connector, the water in the cable well will enter the cable along the gap. In the construction site, the external force causes the cable to break or breakdown.
Drying of the cable after the water is very difficult (such as with hot nitrogen pressure blowing), generally do not configure the corresponding equipment. In practice, if the cable, such as water, just saw the front of a few meters, such as the entire cable has been water, it can not be desirable. Therefore, the cable water to prevent, should be the main prevention, using the following measures:
The cable head should be sealed. Saw the cable end, whether it is stacked or laying, are sealed with plastic (with a cable-specific seal), to prevent moisture infiltration.
Cable laying after the timely production of the cable head.
Strengthen the management of cable head production process. Once the cable into the water, the earliest breakdown phenomenon is often the cable head, so the wire head made well, you can extend the overall life of the cable. Such as the cable in the stripping of the semiconductor layer, in the semiconductor layer on a few vertical lines, and then peeled like a sugar cane like a semiconductor. But in the knife plan, if the plan is too deep, it will hurt the insulation layer, the water tree to bring opportunities.
Using cold shrink cable head. 3M's cold shrink silicone rubber cable accessories, making simple and convenient, no torch, no solder. And silicone rubber cable accessories are flexible, tightly attached to the cable, to overcome the shortcomings of the thermal material (heat shrink material is not flexible, in the process of thermal expansion and contraction of the cable, there will be gaps between the cable body, which For the development of water trees to provide a convenient).
10kV system using 8.7 / 10kV grade cable. The thickness of the cable insulation thickness of 4.5mm, and 6 / 10kV grade cable insulation thickness of 3.4mm. As the cable insulation thickness increases, reducing the field strength, to prevent the aging of the water tree, at the same time, because lokV neutral small current grounding system in the single-phase ground, the cable to withstand 1.73 times the phase voltage, To run for 2h, it is necessary to thicken the cable insulation.
PVC plastic double wall corrugated pipe. The tube corrosion resistance, smooth wall, good strength and toughness, and thus laying in the cable buried, can greatly reduce the cable sheath damage.
Design of cable trough (pipe) and cable well. Due to the conditions, cable laying are used in the form of buried or cable trench, and to direct burial, such as coastal rainy areas, cable trenches or cable wells in the water for many years. As the depth of the cable trench or cable well will exceed the depth of the sewer, drainage is difficult, so the planning should be coordinated to facilitate the cable trench (well) drainage. If you can not do the cable wells are not water, the cable should be the middle of the middle of the bracket with a stand.
In addition, in the cable laying design, as far as possible, to reduce the elbow, so that the cable is easy to lay; at the same time, in the cable production, divided into large cable wells and small cable wells, large cable wells can be used to traction cable, Do the middle of the road, and in the road which is not easy to do wire wells, but must have a corner of the place, change to do a small cable wells, the cable wells are only used to lay the cable when the steering pulley.