Typical Faults and Causes of Overhead Lines and Cable Lines？

Common Faults in Overhead Lines

1. Conductor Short Circuits and Damage
   Causes of conductor short circuits and damage:
   • a. Small spacing between conductors or uneven alignment of three-phase conductors, prone to inter-phase collisions and short circuits due to strong winds, which may also burn the conductors.
   • b. Falling tree branches, internal metal objects, or accidental contact by cranes during operation can cause conductor short circuits and damage.
   • c. Long-term corrosion by harmful substances in the surrounding environment reduces the effective cross-sectional area of the conductor. If the damage is not severe, patch repair may be considered.
2. Overheating of Conductor Joints
   Causes of overheating at conductor joints:
   • a. The load current exceeds the allowable value for the conductor cross-section.
   • b. Poor construction quality of conductor joints.
   • c. Long-term exposure to wind and rain leads to severe oxidation and corrosion, increasing contact resistance at joints and causing heat generation.
     Measures: Reduce the load, monitor operation, and schedule maintenance based on the situation.

Common Faults in Cable Lines

1. Water Ingress in Plastic Cables
   Water intrusion into plastic cables easily causes insulation aging, especially when the conductor temperature is high, accelerating moisture-induced degradation. Therefore, water intrusion is strictly prohibited during transportation, storage, laying, and operation of plastic cables.
2. Overload Operation of Cables
   The safety of cable operation is closely related to its current-carrying capacity. Overloading increases fault rates and shortens service life. Damage caused by overloading mainly includes:
   • a. Damage to conductor connections;
   • b. Accelerated aging of cable insulation;
   • c. Swelling or even cracking of the sheath (e.g., fatigue, cracking, and swelling of sheaths in cables with poor manufacturing quality or installation conditions under long-term overload);
   • d. Swelling and cracking of cable terminals due to expansion of asphalt insulation glue.
3. Damage from External Forces
   Approximately 50% of cable accidents are caused by external mechanical damage (e.g., poor municipal management, improper construction). Precautions include:
   • Avoiding mechanical damage during cable transportation, hoisting, and building penetration.
   • Alerting construction workers to take protective measures when working near cable routes.
4. Contamination of Cable Terminal Bushings
   Solutions: Regularly clean the bushings (preferably during power outages); apply pollution-resistant coatings or increase the creepage level of bushings in severely polluted areas.
5. Water Ingress and Explosion of Outdoor Terminals
   Caused by improper construction or maintenance, to condensation in the terminal, moisture penetration of insulation, and subsequent explosion.
6. Explosion of Cable Intermediate Joints
   Mostly due to overloading (expansion of insulation glue in the joint box causing shell cracking) or poor conductor connections (overheating of joints to explosion).
7. Inspection Points for Outdoor Cable Terminals
   • a. Check for cracks in terminal bushings and heating of grounding wire clamps;
   • b. Inspect the insulation glue inside the terminal for softening, overflow, shortage, or surface moisture;
   • c. Check for oil leakage at all sealed parts of the terminal;
   • d. Ensure the grounding wire is in good condition.