Scratches and damage to the cable sheath surface are common during cable laying in the field. Minor damage only affects the sheath. How to repair cables while ensuring quality and short repair time has become a growing concern for cable consumers. Furthermore, on-site sheath repair technology and its quality are increasingly important to users due to their low cost and ease of implementation under harsh field conditions.
Cable repair work is often carried out under harsh conditions. It may be located in a power plant in its initial construction phase, a newly built railway in the field, on cable trays, or inside cable tunnels. Since cable sheath repair in the field is typically done using a plastic welding gun, which requires 220V AC power, and power is generally scarce in newly constructed field projects, or even if power is available, the randomness of the cable's location can make providing power difficult. Therefore, successful cable sheath repair requires both adequate personnel and a reliable power supply. Only by completing these two basic preparatory tasks can cable sheath repair work proceed smoothly.
To facilitate cable repair work, the construction unit should be equipped with a small field generator. Simultaneously, for convenient on-site repairs, the provided plastic welding guns must be of high quality. The nozzle heating area should be large, and the heating speed should be fast. Furthermore, cable damage during the laying process is random. While this work is relatively easy in general urban and plain areas, it is quite difficult in mountainous regions due to the complex terrain. Therefore, to reduce investment and quickly resolve problems, a crucial issue is ensuring sufficient personnel are available for cable laying and using standardized cable laying equipment to avoid and minimize sheath damage during the process.
On-site cable repair doesn't require highly advanced technology. Cable laying companies must ensure the cable's internal structure is undamaged before attempting repairs; otherwise, repairing the cable sheath is largely pointless. Timely repairs are crucial; otherwise, external moisture and humidity can penetrate, affecting the cable's lifespan. In the rainy season in southern China, failure to seal cable ends after installation can allow moisture to seep into the cable trench, resulting in 10-20 meters of cable breaking. Stripping the insulation reveals the conductor is completely blackened, leading to wasted cable. Therefore, after installation, thorough inspection, maintenance, and storage are essential to prevent shortened or terminated cable lifespan due to external factors before energization.
For on-site cable repair, sufficient tools and materials must be prepared. A plastic welding gun is essential, along with high-voltage insulating tape, waterproof tape, and sealing materials such as scraps from the plastic insulation and sheath. This is because cable insulation and sheath materials are mainly composed of cross-linked polyethylene, polyethylene, and polyvinyl chloride. Some materials are thermosetting, such as cross-linked polyethylene insulation, which cannot be repeatedly melted and reused. On-site repairs using raw materials require the use of high-voltage insulating tape and repair tapes provided by 3M. Other materials are thermoplastic and can be melted and reused at high temperatures, such as polyethylene and polyvinyl chloride. These materials can be obtained on-site by cutting strips of sheath material from the cable ends. This allows for repairs of low-voltage cable insulation and sheaths, and the repair quality can fully meet the requirements for normal cable performance. Another point to consider is the handling of sheath damage during the on-site laying of medium-voltage cables. This should not be done carelessly. Firstly, cables must be handled with care during laying. Secondly, the extent of internal insulation damage after external damage is sometimes unpredictable. I have personally conducted factory tests on cables with multiple sheath damages due to careless on-site installation, and found that the damaged areas exhibited excessive partial discharge and breakdown. Therefore, for medium-voltage power cables with sheath damage during on-site laying, it is best to cut the cable and make an intermediate joint or replace it entirely. Repairing the sheath at the damaged areas may pose potential safety hazards.
It has been proven that repairs to the insulation and sheath of low-voltage cables are only necessary when the cable damage is relatively minor, with only the insulation and sheath damaged while the rest of the cable structure remains intact. The requirements for medium- and high-voltage cables are even more stringent. In some current power transmission projects, to reduce the number of cable joints, long-length single-core cables are used. Due to the long laying distances, complex terrain, limited personnel, and lack of specialized cable laying equipment, the probability of cable sheath damage during construction is greatly increased. Some construction workers, after encountering such problems, simply wrap the cable with ordinary tape, a very irresponsible approach. They are completely unaware of the internal damage at the point of breakage, which could lead to insulation breakdown or other quality issues during on-site testing and subsequent operation.
