A metal-oxide varistor (MOV) is a common type of varistor. It consists of a ceramic mass of zinc oxide grains sandwiched between two metal plates. A varistor (variable resistor) is an electronic component that often incorporates them into the circuit to protect the circuit against excessive transient voltages in such a way that, when triggered, they move away from sensitive components by high voltages. Will isolate the current created. A varistor is also known as a voltage dependent resistor. The function of a varistor is to conduct significantly increased current when the voltage is excessive. Only non-ohmic (materials that do not obey Ohm's law) are usually called varistors.
A reverse leakage current appears at the diode junctions of each border when an external small voltage is applied across the electrodes. The current produced will also be very small. But, when a large voltage is applied across the electrodes, the diode border junction breaks down resulting in a combination of electron tunneling and avalanche breakdown. Thus the device is said to show a high level of non-linear voltage – current characteristics. From the characteristics, it should also be noted that the component will have a small amount of resistance at high voltage and high resistance at low voltage. The only problem with this component is that they cannot withstand a transient voltage higher than the rating. They wear out after a certain level. If so, they will need to be changed from time to time. When they absorb the transient voltage they dissipate it as heat. When this process is repeated for some time, the equipment starts to wear out due to excessive heat. They can be connected in parallel for increased energy-management capabilities. MOVs can also be connected in series to provide a higher voltage rating or to provide a voltage rating between standard increments.
Varistor is primarily used to perform as a line voltage surge suppressor. The device does not operate when the voltage is below the clamping voltage. But, if a high surge (light) higher in rate that a varistor can handle is passed through it, the component will not perform. The resulting current will be so high that it will damage the MOV.
The varistor's performance will slow down over time, even if small surges pass through it. The life of a MOV will be explained through the creator chart. The chart will have graphs and readings between current, time and the number of momentary pulses passing through the varistor. Another main factor affecting MOV performance is the energy rating. When the energy rating is increased, there will be an exponential change in the life of the varistor. Thus, there will be a change in the transient pulses that the device can manage. This increases the clamping voltage when each transient is broken. Performance can be increased by connecting more varistors in parallel. An increase in rating will also help the process. One of the best features of MOV is its response time. Spikes are shorted through the device within nanoseconds. But the response time may be affected by the increasing design method and the inductance of the component leads.