Analysis of cable line fault causes and countermeasures

Short-circuit fault: There are two-phase short-circuit and three-phase short-circuits, which are mostly caused by hidden dangers left in the manufacturing process.

Grounding fault: A certain core or several cores of the cable break down to the ground. The insulation resistance is lower than 10kΩ and the low resistance is grounded. 

Above 10kΩ is called high resistance grounding. Mainly due to cable corrosion, lead cracks, insulation dryness, joint processes, and materials.

Broken linear fault: a core or core of a cable is completely or not completely broken. Cables can be disconnected due to mechanical damage, terrain changes, or short circuits.

Hybrid failure: Two or more of the above faults.

External force damage: In the process of storage, transportation, laying, and operation of the cable, external force damage may occur, especially the directly buried cable that has been operated, which is easily damaged in the ground construction of other projects. Such accidents often account for 50% of cable accidents. 

In order to avoid such accidents, in addition to strengthening the quality of work in cable storage, transportation, laying, and other aspects, it is more important to strictly implement the ground-breaking system.

Corrosion of protective layer: Electrochemical corrosion of underground stray current or chemical corrosion of non-neutral soil invalidates the protective layer and loses the protection of insulation. 

The solution is to install the drainage equipment in the stray current dense area; when the local soil on the cable line contains the chemical substances that damage the cable lead pack, the cable should be installed in the tube and the neutral soil should be used as the cable liner. And the cover, but also asphalt on the cable.

Overvoltage, overload operation, improper selection of cable voltage, sudden high voltage intrusion, or long-term overload during operation may damage the insulation strength of the cable and break down the cable. 

This requires strengthening inspections and improving operating conditions to resolve them in a timely manner.

Outdoor terminal head soaking water: Due to poor construction, the insulating glue is not filled, causing the terminal head to be immersed in water and eventually explode. 

Therefore, it is necessary to strictly implement the construction process regulations, carefully check and accept; strengthen inspection and timely maintenance. 

The leakage of the terminal head destroys the sealing structure so that the impregnating agent at the end of the cable is lost, the thermal resistance is increased, the insulation is accelerated and aged, and the moisture is easily absorbed, resulting in a thermal breakdown. 

It is found that when the terminal head leaks oil, it should strengthen the inspection. In case of seriousness, it should be powered off and redone.