Power cables used before construction are mainly YJLV22 series cross-linked aluminum-core cables and YJV22 series cross-linked copper-core cables (10KV). Compared with overhead lines and old oil-filled cables, this type of cable has good insulation performance, high allowable working temperature (up to 90℃) and good mechanical strength. The mass application of the cable not only improves the reliability of power supply, but also beautifies the city cityscape and is worth promoting. However, in the long-term construction process, combined with a large number of feedback from the operating units, we found that the phenomenon of cable moisture into the water is becoming a potential hidden danger affecting the safe operation of the cable.

The solution of the cable moisture into the water

According to our current technical strength and existing equipment, it is very difficult to deal with water in the cable (such as the use of hot nitrogen gas pressure blowing dry). In practice, if the cable head is found to be waterlogged, we can only saw off the front end for a few meters to see if it is dry inside, and if not, continue to saw forward. But if the whole cable has been into the water, we can not do anything about it. Therefore, the cable into the water should mainly focus on prevention, through long-term practice we have concluded the following countermeasures.

(1) At present, we use 8.7/10 kV grade cable in the city network 6 kV system transformation The grade cable insulation thickness of 4.5 mm, while 6/10 kV grade cable insulation thickness of 3.4 mm. due to the increase in cable insulation thickness, reduce the field strength, can prevent the aging of the water tree, at the same time, due to the 6 kV neutral point small current grounding system in single-phase grounding, the cable to withstand 1.73 times the phase voltage, and as required to run for 2 hours, therefore, it is necessary to thicken the cable insulation layer.

(2) Since impurities and porosity in the insulation are the starting point for the occurrence of water trees, the quality of the cable is therefore essential to prevent the aging of water trees. When purchasing cables, it is necessary to choose manufacturers with excellent quality. We conduct strict tests on the samples sent by each manufacturer, and require each manufacturer to conduct bidding, from which high-quality and inexpensive products are selected.

(3) Ensure that the cable head is well sealed, and for the sawn cable ends, whether stacked or laid, they should be sealed up with plastic, using a special sealing sleeve for the cable to prevent moisture from penetrating.

(4) The cable head should be made in time after the cable is laid, and if it is really impossible to make it immediately due to the condition, the cable head will be sealed and wrapped and placed overhead.

(5) improve the technical quality of construction personnel, strengthen the management of the cable head production process, can effectively prevent the cable head in the production process into the water.

(6) In the cable direct burial laying we use PP-R new plastic pipe as casing, the tube corrosion resistance, smooth inner wall, good strength and toughness, thus can greatly reduce the occurrence of cable outer sheath breakage.

(7) Due to the limitations of the conditions, the local cable laying are in the form of direct burial or cable trench, we are located in the coastal area, the local saline land, coupled with poor drainage, resulting in the cable trench or cable well often have water. Therefore, in the early planning, it should be coordinated with the civil construction party in time to design cable ditches, culverts and cable wells to facilitate the drainage of cable ditches (wells). At the same time, pre-buried brackets in the cable trench to hold up the cable with brackets. In addition, for the current situation that there are many petrochemical enterprises within the jurisdiction of Shengli Oilfield, the nearby cable ditch must have perfect drainage facilities. In the design of the cable culvert, it should be as straight as possible to reduce the elbow, so that the cable can be laid easily;

(8) When the cable is laid, cable head production is completed. In the transfer of the operation management department before the formal commissioning of a DC voltage leakage test according to regulations, all qualified, before putting into operation. When the cable is found to have problems in operation, we need to strengthen the management staff to monitor the timely processing.