In the long-term construction process, we found that the phenomenon that the cable is damp and influence has become a potential hidden danger affecting the safe operation of the cable.
The solution to the cable damp ingress
According to our current technical strength and existing equipment, it is very difficult to handle the inlet cable (such as using hot nitrogen pressure to dry). In actual operation, if the cable head is found to be in water, we can only saw off the front end for a few meters to see if it is dry inside. If it is not, continue to saw it forward. But if the entire cable has been flooded, we can't do anything about it. Therefore, cable water intake should be mainly based on prevention. Through long-term practice, we have summarized the following countermeasures:
(1) Because impurities, pores, etc. in the insulation are the starting point of the water tree, the quality of the cable is essential to prevent water tree aging.
(2) Ensure that the cable head is well sealed. For the cable ends that are sawed, whether it is stacked or laid, it should be sealed with plastic. It is best to use a special sealing sleeve for the cable to prevent moisture infiltration.
(3) After the wire is laid, it is necessary to make the cable head in time. If it is impossible to make it immediately due to the conditional restrictions, the cable head is sealed and placed in an overhead position.
(4) Improve the technical quality of construction workers and strengthen the management of the cable head manufacturing process, which can effectively prevent the cable head from entering the water during the production process. Practice has proved that once the cable enters the water, the earliest breakdown phenomenon is often the cable head, so the wire head is made well and can extend the overall life of the cable.
(5) When the cable is directly buried, PP-R new plastic pipe can be used as the casing. The pipe is corrosion-resistant, the inner wall is smooth, and the strength and toughness are good, so the damage of the outer sheath of the cable can be greatly reduced.
(6) In the early planning, the design of cable trenches, culverts and cable wells should be coordinated with the civil construction party in time to facilitate the drainage of cable trenches (wells). At the same time, the bracket is pre-buried in the cable trench, and the cable is supported by the bracket. When designing the cable culvert, it should be as straight as possible, reduce the elbow, and make the cable easy to lay;
(7) After the cable is laid and the cable head is completed, a DC withstand voltage leakage test shall be carried out according to the regulations before the transfer operation management department is officially put into operation. Only after passing the test, can it be put into operation.