Based on our current technological capabilities and existing equipment, we need to treat incoming waterpower cableIt is very difficult (such as using hot nitrogen to pressurize and blow dry). In practical operation, if water enters the cable head, we can only saw off the front few meters and check if it is dry inside. If not, we can continue to saw forward. But if the entire cable has been flooded, we are powerless. Therefore, the prevention of cable water ingress should be the main focus. Through long-term practice, we have summarized the following countermeasures:

1) At present, we are using 8.7/10kV grade cables in the renovation of the 6kV urban network. The insulation thickness of this grade of cable is 4.5mm, while the insulation thickness of the 6/10kV grade cable is 3.4mm. Due to the increase in cable insulation thickness, the field strength is reduced, which can prevent the aging of water trees. At the same time, since the 6kV neutral point low current grounding system needs to withstand 1.73 times the phase voltage when grounded single-phase and operate for 2 hours as required, it is necessary to thicken the cable insulation layer.

2) Due to impurities and pores in insulation being the starting point of water treeing, the quality of cables is crucial in preventing water treeing aging. When purchasing cables, it is necessary to choose manufacturers with excellent quality. We conduct strict tests on the samples submitted by each manufacturer for inspection and require them to bid to select high-quality and cost-effective products.

3) Ensure good sealing of cable heads. For sawn cable ends, whether stacked or laid, they should be sealed with plastic. It is recommended to use cable specific sealing sleeves to prevent moisture from entering.

4) After laying the wires, the cable heads should be made in a timely manner. If it is not possible to make them immediately due to limited conditions, the cable heads should be sealed and placed overhead.

5) Improving the technical quality of construction personnel and strengthening the management of cable head production technology can effectively prevent water from entering the cable head during the production process. Practice has proven that once a cable is submerged in water, the cable head is often the first to experience breakdown. Therefore, a well made wire head can extend the overall lifespan of the cable. When peeling off the semiconductor layer of a cable, we first need to make a circular cut on the semiconductor layer according to the specified size, then make several vertical cuts, and then strip off the semiconductor one by one along the cut. When using a knife to cut, the force must be controlled appropriately. If the cut is too shallow, it is difficult to remove the semiconductor layer. If the cut is too deep, it will damage the insulation layer and bring opportunities for the formation of water trees. When encountering cables with semiconductors that cannot be peeled off, the semiconductor layer must be scraped off with glass sheets. This requires construction personnel to be careful and meticulous, not only cleaning the semiconductor layer, but also avoiding damage to the main insulation as much as possible. Finally, the surface of the main insulation must be polished smooth. In addition, when making heat shrink heads and soldering them, some construction workers often use a blowtorch to melt the solder directly to save time. At this time, the flame can damage the copper shielding layer and insulation layer. Therefore, it is important to prevent such phenomena from occurring during on-site production. When heat shrinkable materials are heated and hardened, they no longer have elasticity, which is determined by their material properties. In long-term operation, due to thermal expansion and contraction, small gaps will gradually form at the cable joints, leading to water vapor infiltration. In view of this, our company has basically eliminated heat shrink heads and widely used silicone rubber cold shrink cable accessories produced by 3M Company. Compared with heat shrink heads, 3M cold shrink heads have a simple and convenient manufacturing process, without the need for hot work or soldering. And silicone rubber cold shrink material has stable performance, elasticity, and can be tightly attached to cables without cracking after long-term use, effectively overcoming the disadvantages of heat shrink materials.

6) When laying cables directly, we use PP-R new plastic pipes as sleeves. This pipe is corrosion-resistant, has a smooth inner wall, and has good strength and toughness, which can greatly reduce the occurrence of cable outer sheath damage.

7) Due to limitations in conditions, local cable laying adopts direct burial or cable trench forms. We are located in a coastal area, which is mostly saline alkali land. In addition, poor drainage often causes water accumulation in cable trenches or cable wells. Therefore, in the early planning stage, it is necessary to coordinate the design of cable trenches, culverts, and cable wells with the civil construction party in a timely manner to facilitate the drainage of cable trenches (wells). At the same time, pre embed brackets in the cable trench to support the cables. In addition, in response to the numerous petrochemical enterprises within the jurisdiction of Shengli Oilfield, nearby cable trenches must have complete drainage facilities. When designing cable culverts, it is important to keep them as straight as possible and minimize bends to facilitate cable laying;

8) After the cable laying is completed and the cable head is made Before being handed over to the operation management department for formal operation, a DC withstand voltage leakage test must be conducted according to regulations. Only after everything is qualified can it be put into operation. When problems are found with the cables during operation, management personnel should strengthen monitoring and handle them in a timely manner. Once a cable malfunction occurs, it will be very troublesome to handle. It is necessary to locate the fault point, or even replace the entire cable. The system will be affected by short-circuit currents, causing unplanned power outages, and so on. Therefore, preventive testing before acceptance is essential. Of course, the DC withstand voltage test is a destructive test that may have some impact on the lifespan of the cable. Sometimes the cable test data is not ideal, but the cable can smoothly transmit power and run for a long time. Therefore, in the new "Preventive Test Regulations for Power Equipment", it is no longer mandatory to conduct DC withstand voltage tests on cross-linked cables at certain intervals, only measuring insulation resistance, which can simplify the preventive test of cables. Accidents are not uncommon. When such accidents occur, the insulation of the cable is severely damaged, which can also cause water to enter the cable.