Common fault types and characteristics of overhead transmission lines

Overhead transmission lines are the main components of the power system and transmission network. They undertake most of the industrial and domestic transmission tasks, and are also the most vulnerable parts of the power system. The common faults are classified according to their nature. They are mainly classified into transient faults and permanent faults. The transient faults mainly include flashover caused by lightning overvoltage and short circuit caused by birds. The permanent faults are mostly due to the climate or the equipment itself. Caused by other reasons, such as ice and snow weather or line aging, etc., transient overvoltage breakdown of transmission line insulation devices, equipment installation, storms, earthquakes, etc. caused by permanent short circuit of transmission lines. According to its specific classification, it can be divided into horizontal and vertical faults. The horizontal faults are mainly single-phase, two-phase and three-phase short-circuit. Vertical faults mainly have one-phase and two-phase disconnection problems. These faults can easily cause the transmission line to trip. If there is an accident, it is necessary to find out the cause of the failure in the first time of the failure, solve the problem in a targeted manner, or take precautionary measures against a certain failure in advance.

1. Characteristics of bird damage

Birds often land on overhead transmission lines for rest, but they are also harmful to transmission lines. The hazards mainly come from flashovers caused by nesting, flying and bird droppings. The materials of the nests built by birds on the transmission lines are mostly branches. The branches have little effect on the lines in dry weather. Once they encounter rainy weather, the nests are easily blown onto the wires or insulators, which is easy to cause overhead. If the transmission line is short-circuited to the ground, serious accidents such as burning the ground wire may occur; and objects such as branches that are squatting during the flight of the bird may also fall onto the transmission line once they fall on the insulator equalizing ring or tower. When there is a gap between the insulation of the wire, it is easy to form a line fault, and when the bird droppings fall on the cross-arm of the tower, the insulation of the line insulator will be caused, and it will be easy to produce flash when encountering wet weather or foggy weather. Network accident.

2. Tripping caused by lightning strikes

Lightning weather hitting overhead transmission lines is very easy to form an overvoltage inside the line. This overvoltage is also called external overvoltage because it originates from the outside of the power system. It is usually divided into induction and direct lightning overvoltage. It is easy to cause flashover and tripping inside the line. The lightning flashover discharge is mainly caused by tripping. It will form obvious discharge marks on the surface of the insulator of the transmission line. Generally, after the insulator is affected by lightning and discharge, it will When the iron piece melts, the surface of the porcelain material will be burned off, and the original material of the glass material will directly form a network crack. Lightning strikes may cause permanent faults in the transmission line. Such faults are usually caused by the complete disconnection of the porcelain insulator of the transmission line, the break of the lightning rod or the disconnection of the grounding line during the lightning strike. It may also return to the insulation property after the switch is overlapped. The main reason for this phenomenon is that the air insulation is usually able to automatically restore the insulation. After the air insulation is broken down, it can recover itself and re-form the insulating air gap.

3. Characteristics of ice faults on transmission lines

The line icing is mainly caused by the bad snow or storm weather, as well as the influence of temperature and humidity. Under this phenomenon, the air changes greatly, and it is easy to attach the ice layer on the surface of the line, and the ice layer will gradually decrease with the temperature. Thickening, once the ice layer is formed, it will cause excessive load on the transmission line and ice flashing of the insulator, which will cause the deformation of the tower, the damage of the tower or the insulator and the flashover. The load is mainly caused by the weight of the line and the ice coating. Weight and wind generation. In certain cases, the transmission line will produce a large amplitude and frequency diagnosis, that is, galloping, which will have a direct impact on the safe and reliable operation of the transmission line.

4. Characteristics of insulator flashover

Generally speaking, the insulators of transmission lines need to be safely transmitted even when the internal and external overvoltages and long-term voltages are running. However, long-term operation will cause contamination on the surface. These pollutions are easy to weather in fog, rain and melting snow. In the middle, the pollution resistance of the insulator itself is lowered, causing the transmission line to form a dirty flashover fault during the delivery voltage. Contamination flashover accidents are generally prone to occur in wet weather, such as light rain, sleet, etc. In the rain or heavy rain, rain will wash away the dirt on the surface of the line, and the phenomenon of flashover will be less, and due to autumn. With less rain in winter and easy to form wet weather such as fog, flashover accidents usually occur in the late fall and winter.