1. External force damage. Judging from the operational analysis in recent years, especially in Shanghai Pudong, where the economy is developing at a high speed, quite a number of cable faults are caused by mechanical damage.
2. Insulation is damp. This is also common and occurs generally at cable joints in direct buried or drained pipes. For example, if the cable joint is unqualified and the joint is made under humid climatic conditions, the joint will be filled with water or mixed with water vapor. After a long time, the water branch will form under the action of the electric field, which will gradually damage the insulation strength of the cable and cause malfunction.
3. Chemical corrosion. The cable is directly buried in an acid-base area, which often causes the cable armor, lead or outer sheath to be corroded. The protective layer is chemically corroded or electrolytically corroded for a long time, causing the protective layer to fail and the insulation to be lowered. Cable failure. Chemical: The corrosion of the cable in the unit is quite serious.
4. Long-term overload operation. Overload operation, due to the thermal effect of the current, the load current will inevitably lead to the heating of the conductor when passing through the cable. At the same time, the skin effect of the charge and the eddy current loss of the steel crucible and the loss of the insulating medium will also generate additional heat, thereby increasing the cable temperature.
5. The cable connector is faulty. Cable joints are the weakest link in cable lines, and cable joint failures caused by direct personnel failure (poor construction) often occur. During the process of making the cable joints, if the joints are not tightly pressed or insufficiently heated, the insulation of the cable heads will be reduced, causing an accident.
6, environment and temperature. The external environment and heat source where the cable is located can also cause excessive cable temperature, insulation breakdown, and even an explosion.
Common malfunctions
Common faults in cable lines are mechanical damage, insulation damage, insulation moisture, insulation aging deterioration, overvoltage, cable overheating faults, etc. When the above fault occurs on the line, the power supply of the faulty cable should be cut off, the fault point should be found, the fault should be inspected and analyzed, and then the repair and test should be carried out. The cut-out can be resumed after the fault is eliminated.
The most direct cause of cable failure is insulation breakdown and breakdown.
There are:
a, overload operation. Long-term overload operation will increase the cable temperature, insulation aging, resulting in breakdown of insulation, reducing construction quality.
b. Electrical aspects: the cable head construction process can not meet the requirements, the cable head sealing performance is poor, the moisture invades the cable inside, the cable insulation performance is degraded; when the cable is laid, the protective measures are not taken, the protective layer is destroyed, and the insulation is reduced.
c. In terms of civil works, the drainage of the wells and trenches is not smooth, the cables are soaked by water for a long time, and the insulation strength is damaged; the work well is too small, the bending radius of the cable is not enough, and the external force is destroyed by long-term extrusion. Mainly the mechanical barbaric construction in municipal construction. Digging and cutting cables.
d. Corrosion. The protective layer is subject to chemical corrosion or cable corrosion for a long time, resulting in failure of the protective layer and reduced insulation.
e, the cable itself or the cable head accessory is of poor quality, the cable head is poorly sealed, the insulating glue is dissolved, and the cracking occurs, resulting in the resonance phenomenon of the station. The line disconnection fault causes the line phase capacitance and the ground capacitance to resonate with the distribution transformer excitation inductance. The loop, thereby exciting the ferromagnetic resonance.