Classification of the causes of power cable faults
Underground power cable faults are complex and changeable. The causes of power cable faults can be roughly classified into the following categories.
Mechanical damage
Power cable faults caused by mechanical damage account for a large proportion of cable accidents. Some mechanical damages were very minor and did not cause malfunctions at that time. It was not until months or even years later that the damages developed into malfunctions. The main causes of mechanical damage to cables are:
(1) Damage during installation. The cable was accidentally damaged during installation. Excessive mechanical traction force damages the cable. Excessive bending damages the cable.
(2) Directly damaged by external force. Civil construction is carried out on or near the installed cable path, causing the cable to be directly damaged by external forces.
(3) The vibration or shock load of moving vehicles can also cause the lead (aluminum) sheath of underground cables to crack and be damaged.
(4) Damage caused by natural phenomena. If the inner insulating adhesive of the intermediate joint or terminal expands and cracks the casing or cable sheath; The outer sheath of the cable installed on the pipe opening or bracket is scratched; Excessive tensile force caused by land settlement can break the intermediate joint or conductor.
2. Insulation gets damp
Moisture in insulation can cause a decrease in the withstand voltage of power cables and lead to faults. The main reasons for cables getting damp are:
Water ingress is caused by the unsealed structure or improper installation of the joint box or terminal box.
(2) The cable is poorly manufactured, with small holes or cracks in the metal sheath.
(3) The metal sheath is punctured or corroded by external objects.
3. Insulation aging and deterioration
Insulation aging can cause a decrease in the cable's withstand voltage and lead to faults. The main reasons for cable aging are:
(1) The slag or air gaps inside the cable medium undergo dissociation and hydrolysis under the action of an electric field.
(2) Cable overload or poor ventilation in the cable trench causes local overheating.
(3) The insulation of oil-impregnated paper insulated cables is lost.
(4) Use of power cables beyond their service life.
4. Overvoltage
Overvoltage can cause electrical breakdown of the insulation layer of defective power cables, leading to cable faults. The main reasons are: atmospheric overvoltage (such as lightning strike); Internal overvoltage (such as operating overvoltage).
5. Poor design and manufacturing process
Poor design and manufacturing process of the cable head and the middle part can also cause cable faults. The main reason is: The design of the electric field distribution is not meticulous; Improper selection of materials; Poor craftsmanship and not made in accordance with the requirements of the regulations.
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