Technical Analysis of 220 kV High-Voltage Cable Construction in Winter

1.Work Environment Requirements and Safeguard Measures

Based on technical requirements for cable equipment storage, laying, transportation, laying, transposition, testing, and cable terminations, the project owner and construction units have conducted extensive trials and implemented protective measures regarding ambient temperature, humidity, bending radius, traction control, and route optimization. These measures ensure high-voltage cable quality and on-site safety under harsh winter conditions.

2.1 Ambient Temperature Requirements and Safeguard Measures

The working environment humidity for cable laying must be maintained at 70% or below, with temperatures at or above 5°C. When laying cables in trenches, the temperature should not fall below 0°C, and a dust-free environment is preferred. To ensure compliance with cable laying temperature requirements, the construction unit has implemented the following measures, as shown in Figures 1, 2, and 3.

First, to ensure the safe and reliable installation of Ningxia's first 220 kV high-voltage cable, technical personnel from the cable manufacturer are required to provide full-process guidance and supervision of cable conditions. This ensures that critical stages—including storage, handling, laying, shelving, termination fabrication, and cable testing—meet relevant environmental and technical requirements.

Second, to ensure effective thermal insulation at cable storage locations, insulation sheds are erected according to plan and wrapped externally with cotton material. The outer cotton fabric is buried 10–20 cm underground. Inside the shed, electric heaters and hot air blowers provide continuous heating to maintain the outdoor cable storage temperature above the required minimum.

Third, cables are preheated for 24 hours prior to laying. After transferring cables from storage to the terminal pole, a 6m × 6m insulation shed is immediately erected. Electric heaters and hot blowers are used inside the shed for continuous heating. After 24 hours of preheating, manufacturer technicians assess whether the temperature meets the required conditions for cable laying.

Fourth, continuous thermal insulation and dust protection are maintained throughout the laying process. Plastic tarpaulins are laid along the entire cable route. The area around direct-buried cable channels is regularly sprayed with water to maintain a dust-free environment. Exposed cables are wrapped with insulating cotton cloth, quilts, and tarpaulins, while electric heaters are used inside trenches. Openings at manholes and trench ends are sealed to ensure the cable laying temperature remains within required specifications.

2.2 Cable Laying Requirements and Safeguard Measures

After the ambient temperature for cable laying meets the relevant technical requirements, the cable bending radius should be at least 120°, and the cable must not be damaged during the laying process. When mechanically pulling the cable, the maximum traction strength should preferably comply with specified values.

According to cable laying technical requirements, first ensure reliable communication. Dedicated personnel shall be assigned to supervise key locations, including inside and outside the station, each manhole entrance, and corners within trenches, under the unified command of the site supervisor to ensure safe and reliable cable installation. Second, in cable tunnels and maintenance passageways, pull ropes are deployed manually. A steel mesh sleeve is installed to replace the pulling head, and an anti-twist device is added between the cable pulling end and the traction rope. The maximum allowable traction strength during mechanical cable laying should preferably conform to the values specified in the table below.

To ensure the maximum cable traction force complies with the above requirements, four conveyors and two capstans are deployed along the cable route. The conveyors are positioned 70 m, 140 m, 210 m, and 280 m from the terminal tower, respectively, while the capstans are located 240 m and 362 m from the terminal tower, as shown in Figures 4, 5, and 6.

Finally, hoisting pulleys are suspended at the entry and exit points of the pull rope to prevent damage to the cable and rope when entering or exiting the cable tunnel. Along the straight sections of the tunnel, one straight-line ground pulley is placed every 2–2.5 meters, and one corner ground pulley is installed at each turning point. If excessive force is encountered at a corner, a hoisting pulley may be used instead to facilitate turning. Pulley placement may be adjusted appropriately along the route based on actual field conditions.

2.3 Cable Testing Requirements and Safeguard Measures

Testing must be stopped if the environmental humidity exceeds 80%. When wind speed at the test site reaches Force 4 (8 m/s), aerial test wiring work must be halted immediately.

According to relevant technical requirements for cable testing, weather conditions must first be monitored in a timely manner, with on-site wind speed measured using an anemometer. Secondly, prior to conducting cable tests, the entire reel of cable must be dried or wiped to ensure the test site meets all required technical conditions. Figure 7 shows personnel performing external insulation testing on the cable.