Common faults in wire and cable lines include mechanical damage, insulation damage, insulation damp, insulation aging and deterioration, overvoltage, and cable overheating faults. When the above fault occurs in the line, the power supply of the faulty cable should be cut off, the fault point should be found, the fault should be checked and analyzed, and then repaired and tested.
The most direct cause of cable failure is the breakdown of insulation due to reduced insulation. There are mainly:
1. Overload operation. Long-term overload operation will cause the cable temperature to rise and the insulation to age, so as to break down the insulation and reduce the construction quality.
2. Electrical aspects: the construction process of the cable head fails to meet the requirements, the sealing performance of the cable head is poor, the moisture penetrates into the cable, and the insulation performance of the cable decreases; when the cable is laid, protective measures are not taken, the protective layer is damaged, and the insulation is reduced.
3. In terms of civil engineering, the drainage of the wells and trenches is not smooth, and the cables are soaked in water for a long time, which damages the insulation strength; the wells are too small, the bending radius of the cables is not enough, and they are damaged by external forces for a long time. It is mainly mechanical brutal construction in municipal construction, Gouging and cutting the cable.
4. Corrosion. The protective layer has been subjected to chemical corrosion or cable corrosion for a long time, resulting in the failure of the protective layer and the reduction of insulation.
5. The quality of the cable itself or the accessories of the cable head is poor, the sealing of the cable head is poor, the insulating glue is dissolved and cracked, and the resonance phenomenon that occurs in the station is the line disconnection fault, which causes the line interphase capacitance and ground capacitance to form resonance with the excitation inductance of the distribution transformer. loop, which excites ferromagnetic resonance.
Harm of resonance caused by disconnection fault
In severe cases of disconnection resonance, the superposition of high frequency and fundamental frequency resonance can make the overvoltage amplitude reach 2.5 times of the phase voltage, which may lead to the displacement of the neutral point of the system, the overvoltage of the windings and wires, and the insulation flash in severe cases. network, lightning arrester explosion, damage to electrical equipment. In some cases, the load transformer phase sequence may be reversed, and it may also transmit overvoltage to the low-voltage side of the transformer to cause harm.