Principle of protection gap arrester

The simplest and most economical arrester is the protective gap, consisting of a pair of angular electrodes and an air gap between them, as shown in Figure 1. The gap further includes a main gap and an auxiliary gap, and the auxiliary gap is to prevent the main gap from being short-circuited by an external object (such as a bird, a branch, etc.) to cause a malfunction. The shape of the electrode is favorable for arc extinguishing. When the voltage is applied by the overvoltage, the distance between the lower end of the gap is small, and the arc is generated first to generate an arc. The high temperature of the arc causes the temperature of the surrounding air to increase sharply, and the hot air flow rises and self-electricity. Under the action of the power, the arc is elongated upward and the arc resistance is increased. When the arc is stretched to a certain length, the energy supplied by the power source is difficult to maintain its combustion, and the arc is extinguished. The arc-breaking ability of the protection gap is poor, and only the capacitive current arc of the small-current grounding system when the single-phase grounding is small can be extinguished. If the power frequency flowing through the protective gap is large, the gap arc cannot be extinguished by itself, which will cause The circuit breaker trips. Although it limits the overvoltage and protects the equipment, it will trip the circuit breaker and affect the power supply to the user. This is the main disadvantage of the protection gap. For this reason, the protection gap and the automatic reclosing are often used together. The protection gap has poor arc-extinguishing ability, the gap is in the air and the electric field between the poles is very uneven. The discharge characteristics are greatly affected by atmospheric conditions, the discharge dispersion is large, the volt-second characteristic is steep, and it is difficult to match the insulation characteristics of the protected equipment. Will form a chop, so the application is less, generally used in places that will not cause serious consequences, such as low-voltage distribution network.

Figure 1 Protection gap

1-main gap; 2-auxiliary gap; 3-insulator

The guard gap is the simplest type of arrester. The commonly used protection gap is shown in Figure 2 and is called the horn gap. It is made up of a series of main gaps and auxiliary gaps. The role of the auxiliary gap is to prevent the main gap from being short-circuited by the foreign object. The two electrodes of the main gap are formed in an angular shape in order to make the power frequency arc easily elongate and self-extinguish under the action of its own electric power and hot air flow.

Figure 2 horn protection gap structure

1-insulator; 2-main gap; 3-auxiliary gap

The advantage of the protective gap is that the structure is simple and the cost is low. However, since the discharge gap is exposed to the air, the discharge characteristics are greatly affected by the environment, the discharge dispersion is large, the volt-second characteristic curve is steep, it is not easy to be insulated with the equipment, the arc-extinguishing ability is poor, and the ability to cut off the power-frequency freewheel is poor; Chopping occurs during discharge, which is harmful to equipment with coils. Therefore, the protection gap is mainly used for less important protection in distribution lines below 10kV. A structural data reference table for the guard gap.

Table protection gap structure data