Aging and failure of wires and cables
Analysis of the aging and failure causes of wires and cables
Causes of aging
1. External force damage. Judging from the operation analysis in recent years, especially in cities with rapid economic development, a considerable number of cable failures are caused by mechanical damage.
2. The insulation is damp. This situation is also very common, and generally occurs at the cable joints in direct burial or piping. For example: unqualified cable joints and joints made in humid weather conditions will cause the joints to enter water or mix with water vapor. For a long time, water branches are formed under the action of electric field, which gradually damages the insulation strength of the cable and causes failure.
3. Chemical corrosion. The cable is buried directly in the acid-base area, which will often cause the cable armor, lead skin or outer sheath to be corroded. The protective layer suffers from chemical corrosion or electrolytic corrosion for a long time, which causes the protective layer to fail, the insulation is reduced, and the cable malfunctions. The corrosion of the cables in the chemical unit is quite serious
4. Long-term overload operation. Overload operation, due to the thermal effect of the current, the conductor will inevitably heat up when the overload current passes through the cable. At the same time, the skin effect of the charge, the eddy current loss of the steel armor, and the insulation loss will also generate additional heat, which will increase the temperature of the cable.
5. The cable connector is faulty. Cable joints are the weakest link in the cable line, and cable joint failures caused by direct faults (poor construction) by personnel often occur. In the process of making cable joints, if there are reasons such as insufficient joint crimping, insufficient heating, etc., the insulation of the cable head will be reduced, which will cause an accident.
6. Environment and temperature. The external environment and heat source of the cable can also cause the cable to overheat, insulation breakdown, and even explosion and fire.
The most direct cause of cable failure is breakdown due to insulation degradation.
There are:
A. Overload operation. Long-term overload operation will increase the temperature of the cable and age the insulation, which will cause insulation breakdown and reduce construction quality.
B. Electrical aspects: The construction process of the cable head fails to meet the requirements, the sealing of the cable head is poor, moisture penetrates into the cable, and the insulation performance of the cable decreases; Failure to take protective measures when laying the cable, the protective layer was damaged and the insulation was reduced.
C. Civil engineering issues include: The drainage of the well pipe trench is not smooth, and the cable is soaked in water for a long time, which damages the insulation strength; The working well is too small, the cable bending radius is not enough, and it is damaged by the external force for a long time. Mainly the brutal construction of machinery in municipal construction, digging wounds and digging cables.
D. Corrosion problem. The protective layer has been subjected to chemical corrosion or cable corrosion for a long time, causing the protective layer to fail and the insulation to decrease.
E. The cable itself or the cable head accessories are of poor quality, the cable head is poorly sealed, and the insulating glue is dissolved and cracked. The resonance phenomenon that causes the station to appear is the line disconnection fault, so that the line-to-phase capacitance and the ground capacitance and the distribution transformer's excitation inductance form a resonant circuit, thereby exciting the ferromagnetic resonance.
Causes of aging
1. External force damage. Judging from the operation analysis in recent years, especially in cities with rapid economic development, a considerable number of cable failures are caused by mechanical damage.
2. The insulation is damp. This situation is also very common, and generally occurs at the cable joints in direct burial or piping. For example: unqualified cable joints and joints made in humid weather conditions will cause the joints to enter water or mix with water vapor. For a long time, water branches are formed under the action of electric field, which gradually damages the insulation strength of the cable and causes failure.
3. Chemical corrosion. The cable is buried directly in the acid-base area, which will often cause the cable armor, lead skin or outer sheath to be corroded. The protective layer suffers from chemical corrosion or electrolytic corrosion for a long time, which causes the protective layer to fail, the insulation is reduced, and the cable malfunctions. The corrosion of the cables in the chemical unit is quite serious
4. Long-term overload operation. Overload operation, due to the thermal effect of the current, the conductor will inevitably heat up when the overload current passes through the cable. At the same time, the skin effect of the charge, the eddy current loss of the steel armor, and the insulation loss will also generate additional heat, which will increase the temperature of the cable.
5. The cable connector is faulty. Cable joints are the weakest link in the cable line, and cable joint failures caused by direct faults (poor construction) by personnel often occur. In the process of making cable joints, if there are reasons such as insufficient joint crimping, insufficient heating, etc., the insulation of the cable head will be reduced, which will cause an accident.
6. Environment and temperature. The external environment and heat source of the cable can also cause the cable to overheat, insulation breakdown, and even explosion and fire.
Common faults of cables
Common faults of cable lines include mechanical damage, insulation damage, insulation damp, insulation aging deterioration, overvoltage, cable overheating faults, etc. When the above-mentioned fault occurs in the line, the power supply of the faulty cable should be cut off, the fault point should be found, and the fault should be checked and analyzed. Then repair and test, and power supply can be restored after the fault is eliminated.The most direct cause of cable failure is breakdown due to insulation degradation.
There are:
A. Overload operation. Long-term overload operation will increase the temperature of the cable and age the insulation, which will cause insulation breakdown and reduce construction quality.
B. Electrical aspects: The construction process of the cable head fails to meet the requirements, the sealing of the cable head is poor, moisture penetrates into the cable, and the insulation performance of the cable decreases; Failure to take protective measures when laying the cable, the protective layer was damaged and the insulation was reduced.
C. Civil engineering issues include: The drainage of the well pipe trench is not smooth, and the cable is soaked in water for a long time, which damages the insulation strength; The working well is too small, the cable bending radius is not enough, and it is damaged by the external force for a long time. Mainly the brutal construction of machinery in municipal construction, digging wounds and digging cables.
D. Corrosion problem. The protective layer has been subjected to chemical corrosion or cable corrosion for a long time, causing the protective layer to fail and the insulation to decrease.
E. The cable itself or the cable head accessories are of poor quality, the cable head is poorly sealed, and the insulating glue is dissolved and cracked. The resonance phenomenon that causes the station to appear is the line disconnection fault, so that the line-to-phase capacitance and the ground capacitance and the distribution transformer's excitation inductance form a resonant circuit, thereby exciting the ferromagnetic resonance.
