Company: Henan Lubao Special Cable Co., Ltd.
Contact: Manager Su
Address: No. 13 Workshop B, Tiantan Venture Park, Huling Industrial Gathering District, Jiyuan City, Henan Province
What should I do if the cable gets water? Cable water hazard
After the cable enters the water, under the action of the electric field, the water tree aging phenomenon will occur, which will cause the cable to break down.
Water trees are collections of water-filled voids with a diameter of 0.1m to a few microns.
The existence of impurities, pores in the insulation, and the local high electric field formed by the unevenness of the interface between the insulation and the inner and outer semiconductive layers are the starting points for the occurrence of water trees.
The development process of water tree is generally more than 8 years. The higher the humidity, temperature and voltage, the more ions contained in the water, the faster the water tree develops.
Water in the cable
1. When buying the newly-built tube cable, both ends are sealed with plastic sealing sleeves, but after a period of use, the rest is wrapped with plastic paper and tied with a rope outside. The sealing is not good. Water vapor will penetrate the cable.
2. When the cable is laid, when the cable is laid, the cable head wrapped with plastic paper is sometimes immersed in water to allow the water to enter the cable; when pulling and pipe running, sometimes the outer sheath ruptures.
3. After laying, the cable head is not produced in time, so that the unsealed 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 the cable head is made During the production of the cable head (including the terminal head and the intermediate connector), the cable end sometimes slips into the cable well with water due to the intention of the producer.
5. When the cable is running, during the cable running, if there is a breakdown of the intermediate connector, the water accumulated in the cable well will enter the cable along the gap; at the construction site, the cable will be damaged or broken by external forces, and water will also enter the cable. Henan wire and cable .
It is very difficult to dry the cable after it enters the water (such as pressure drying with hot nitrogen), and generally there is no corresponding equipment.
In actual operation, if the cable R6 enters the water, we just saw off the front end for a few meters. If the entire cable has entered the water, we are not advisable.
Therefore, the prevention of cable water ingress should be based on prevention, and the following measures should be adopted:
1. The cable head should be sealed. The cable ends that are sawed off, whether stacked or laid, should be sealed with plastic (using a cable-specific sealing sleeve) to prevent moisture from penetrating.
2. Make the cable head in time after wiring.
3. When purchasing a cable, you must choose a manufacturer of excellent quality. Impurities, pores, etc. in the insulation are the starting point of water tree occurrence, so the quality of the cable is very important to prevent water tree aging. Henan wire and cable.
4. Strengthen the management of the production process of the cable head. Once the cable enters the water, it is often the cable head that has early breakdown. Therefore, the cable head is made well, which can extend the overall life of the cable. For example, when the cable is peeling off the semiconductor layer, we draw a few vertical lines on the semiconductor layer, and then peel off the semiconductor like sugarcane peeling. However, if you use a knife to draw too deeply, it will hurt the insulation layer and bring opportunities to the water tree. In addition, when soldering, because the power cannot be found, the torch will be used to melt the solder. At this time, the flame will damage the copper shielding layer and the insulating layer. Therefore, this phenomenon must be avoided. The correct method can be configured by UPS because the solder The time required is generally only 10 minutes, and the power is only 500W.
5, using cold-shrinkable cable head 3M company's cold-shrinkable silicone rubber cable accessories, simple and convenient production, no torch, no soldering. And the silicone rubber cable accessories are elastic and tightly attached to the cable, which overcomes the shortcomings of heat shrinkable materials (heat shrinkable materials have no elasticity, and during the process of thermal expansion and contraction of the cable, there will be a gap with the cable body. Provided convenience for the development of water trees). At present, the intermediate connectors of all the main cables of our office use 3M's cold-shrinkable cable accessories.
6. Long cables use cable branch boxes. Several long cables from our office are about 3km in length. For such cables, in addition to the intermediate connector, we also use one or two cable branch boxes. Once one of the cables enters After water, it will not spread to other sections of the cable, and it is easy to find in sections when the cable fails.
7. In the 10kV system, 8.7 / 10kV grade cables are used. The insulation thickness of this grade of cable is 4.5mm, while the insulation thickness of 6 / 10kV grade cables is 3.4mm. As the insulation thickness of the cable increases, the field strength is reduced, and the aging of the water tree can be prevented. At the same time, when the 10kV neutral point low-current grounding system is single-phase grounded, the cable must withstand 1.73 times the phase voltage and operate as required. 2h, so it is necessary to thicken the cable insulation. Henan wire and cable.
8. Use PVC plastic double-wall corrugated pipe. The pipe is corrosion-resistant, the inner wall is smooth, and the strength and toughness are good. Therefore, when the cable is directly buried, the outer sheath of the cable can be greatly reduced.
9. Design of cable trench (pipe) and cable well Due to the limitation of conditions, our cables are laid in the form of direct buried or cable trench, and most of them are buried directly. Our area belongs to rainy coastal areas. The length of cable trench or cable well is medium. There is standing water in the year. Because the depth of the cable trench or cable well will exceed the depth of the sewer, drainage is difficult. Therefore, when planning, coordination should be made to facilitate drainage of the cable trench (well). If it is impossible to prevent water from accumulating in the cable well, the intermediate joint in the cable well shall be supported by a bracket. In addition, our area is a heavy chemical industry area. There are many chemical companies in the area. During inspections, we found that some of the wires in the cable trenches near the chemical plant have been seriously deformed. Therefore, the cable trenches near the chemical plant must have Perfect drainage facilities. In addition, when designing the cable pipe, try to be as straight as possible, reduce the elbow, and make the cable easy to lay. At the same time, when the cable well is manufactured, we divide it into a large cable well and a small cable well. The large cable well can be used to pull cables and coils. To make intermediate joints, and in the middle of the road, etc., where it is not convenient to make a wire well, but there must be corners, we changed to a small cable well, which is only used to place the steering pulley when laying cables.
10. Test of the cable After the cable head is manufactured. Do a high-voltage DC leakage test before commissioning. After that, we will only perform pre-tests on the outgoing cables of the substation, and do not test other cables. Because once the outgoing cable of the substation fails, the short-circuit current will cause a great impact on the equipment of the substation, so if there is a problem with the wire, it is necessary to strengthen the operation management and timely replace it. We believe that the post-processing of cable failure is the same trouble as the cable that is found after the cable test: finding the point of failure, or even replacing the cable. The disadvantages of the former are: the impact of unplanned power failure and short-circuit current is that the life of the cable can be extended without testing (some cable tests are not ideal, but they can still run for a long time, and the cable impact will increase after the DC test). May wear), the fault point is relatively obvious, easy to find. The advantages and disadvantages of the latter are exactly the opposite of the former. Therefore, for cable users who do not test, we focus on the reliability of their power supply. For example, 10kV switching stations that supply power to users use dual power supplies to implement dispatch automation. Once one incoming cable fails, immediately switch to another Powered by cable. In fact, in the new "Precautionary Test Rules for Power Equipment", it is no longer required to perform a DC withstand voltage test on a cross-linked cable at a certain time, and only the insulation resistance is measured, which can further simplify the preventive test of the cable.