Views: 0 Author: Site Editor Publish Time: 2019-09-07 Origin: Site
1.Lightning protection
Lightning strikes can cause atmospheric overvoltages. Most of them are inductive overvoltages. The overvoltage generated by the lightning strike on the transmission line is called the direct lightning overvoltage, and its voltage value is particularly high, which is extremely harmful due to 102~104V. Therefore, for outdoor power systems and electrical equipment, measures must be taken to prevent overvoltage.
The use of ZnO varistor arresters is very effective in eliminating atmospheric overvoltages. It is generally connected in parallel with electrical equipment. If the electrical equipment requires a low residual voltage, multi-level protection can be used.
2. Circuit protection
In practical applications, various electronic circuits and electrical equipment are often affected by operating overvoltages. The so-called operating overvoltage is the suppression of overvoltage generated when the electromagnetic energy is rapidly converted and the electrical energy is rapidly transmitted when the operating state of the circuit suddenly changes. In order to prevent such overvoltage, high-energy ZnO varistor can be used to protect various large-scale power supply equipment, large electromagnets and large-sized motors. For automotive circuits, communication lines and many civil electrical circuits, low-voltage ZnO varistors or other types can be used. The low voltage varistor is protected.
3. Switch protection
When a circuit with an inductive load is suddenly disconnected, its overvoltage can exceed several times the supply voltage. Overvoltage can cause arcing and spark discharge between contacts, which can damage contacts such as contactors, relays, and electromagnetic clutches, and shorten the service life of the device. The varistor has a shunt at high voltages and can therefore be used to protect the contacts by preventing spark discharges at the moment the contacts are opened.
4. Device protection
In order to prevent the semiconductor device from being burnt due to overvoltage for some reason, it is often protected by a varistor. The figure below shows the application circuit of the varistor protection transistor. The damage of the overvoltage to the transistor can be effectively suppressed between the collector and the emitter of the transistor or the primary shunt varistor of the transformer. At normal voltages, the varistor is in a high-impedance state with minimal leakage current. When subjected to an overvoltage, the varistor quickly changes to a low resistance state, and the overvoltage energy is absorbed by the varistor in the form of a discharge current. After the surge voltage is passed, when the circuit or component is subjected to a normal voltage, the varistor returns to a high resistance state.
