The discharge time constant of a varistor refers to the time required for the resistance value of the varistor to recover from a low resistance state to a high resistance state after the circuit is disconnected. This time constant is related to the material properties and structural design of the varistor.
Factors affecting the discharge time constant are as follows:
- Material composition: The material composition of the varistor affects its discharge characteristics. The discharge time constant of zinc oxide (ZnO) varistors is generally shorter.
- Structural design: The structural design of the varistor, such as the shape and position of the electrodes, also affects the discharge time constant.
- Operating voltage: The discharge time constant of the varistor will be shorter at higher operating voltages.
- Operating temperature: Increases in temperature will accelerate the discharge speed of the varistor and reduce the discharge time constant.
- Aging condition: After long-term use, the varistor will age and the discharge time constant will gradually increase.
The discharge time constant of the varistor can be measured via the following methods:
- Disconnection method: A certain voltage is applied to both ends of the varistor to make it enter a low resistance state, and then the circuit is suddenly disconnected, and the resistance value is measured over time to obtain the discharge time constant.
- Short circuit method: A certain voltage is applied to both ends of the varistor to make it enter a low resistance state, and then a short circuit is suddenly created, and the current is measured over time to obtain the discharge time constant.
Usually the discharge time constant of the varistor is between 1-100 milliseconds, depending on the material and structural design. Reasonable control of the discharge time constant helps to improve the protection performance and service life of the varistor.