What Is the Principle of a Surge Arrester?

The principle of surge arrester: when lightning overvoltage along the overhead lines into the substation or other buildings, will occur when the flashover, and even the insulation of electrical equipment through. Therefore, if the power inlet of electrical equipment is connected in parallel with a protection device that surge arrester, when the overvoltage value reaches the specified action voltage, the arrester immediately act, flow through the charge, limit the overvoltage amplitude, to protect the equipment insulation; voltage value is normal, the arrester and quickly restore the original state, to ensure that the system normal power supply.

Surge arrester requirements

1. Normal operation does not discharge, over-voltage discharge correct action.

2. After the discharge to have self-recovery function.

Surge arrester related parameters

1. Continuous operation voltage: that is, the permitted long-term working voltage. It should be equal to or greater than the highest phase voltage of the system.

2. Rated voltage (kV): that is, the maximum allowable short-time frequency voltage (arc extinguishing voltage). Surge arrester can act in this frequency voltage discharge and extinguish the arc, but not in this voltage long-term operation. It is the arrester characteristics and structure of the basic parameters, but also the basis for the design.

3. Frequency withstand volt-second characteristics: indicates that the zinc oxide arrester in the specified conditions, the ability to withstand overvoltage.

4. Nominal discharge current (kA): used to divide the arrester level of discharge current peak.

The surge arrester protection is based on three premises:

1. Olt-second characteristics and the volt-second characteristics of the protected insulation have a good match

2. To ensure that its residual voltage is lower than the impact electrical strength of the protected insulation

3. The protected insulation must be within the protection distance of the arrester

The arrester which uses zinc oxide semiconductor as a resistor material, such type of arrester is known as a metal oxide surge arrester or ZnO Diverter. This arrester provides protection against all types of AC and DC over voltages. It is mainly used for overvoltage protection at all voltage levels in a power system. 

The metal oxide surge arrester has the following merits:

1. It eliminates the risk of spark over and also the risk of shock to the system when the gaps break down.

2. It eliminates the need of voltage grading system.

3. At the normal operating condition, the leakage current in the ZnO is very low as compared to other diverters.

4. There is no power follow current in ZnO diverter.

5. It has high energy absorbing capability.

6. ZnO diverters possess high stability during and after prolonged discharge.

7. In ZnO diverter, it is possible to control the dynamic overvoltages in addition to switching surges. This results in economic insulation coordination.