Home > News > Working of Metal Oxide Varistor (MOV)

News

Working of Metal Oxide Varistor (MOV)
2014-08-18 16:06:29

Working of Metal Oxide Varistor (MOV)

Working of Metal Oxide Varistor (MOV)

The resistance of the Metal Oxide Varistor (MOV) is very high. First, let us consider the component to have an open-circuit as shown in figure . The component starts conducting as soon as the voltage across it reaches the threshold voltage. When it exceeds the threshold voltage, the resistance in the MOV makes a huge drop and reaches zero. This is shown in the figure 1(b). As the device has very small impedance at this time due to the heavy voltage across it, all the current will pass through the metal oxide varistor itself. The component has to be connected in parallel to the load. The maximum voltage that will pass through the load will be the sum of the voltage that appears across the wiring and disconnect given for the device. The clamp voltage across the MOV will also be added. After the transient voltage passes through the component, the Metal Oxide Varistor (MOV) will again wait for the next transient voltage. This is shown in the figure 1(c).

MOV Performance

The varistor is mainly used to perform as a line voltage surge suppressor. The device does not conduct when the voltage across it is below the clamping voltage. But, if a high surge (lighting) that is 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 Metal Oxide Varistor (MOV).

The performance of the varistor will slow down with time even if small surges pass through it. The life of a MOV will be explained through the manufacturers chart. The chart will have graphs and readings between the current, time and also the number of transient pulses that passes through the varistor.

Another main reason that affects the performance of a Metal Oxide Varistor(MOV) is the energy rating. When there is an increase in the energy rating, 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 breaks down.

The performance can be increased by connecting more varistors in parallel. An increase in rating will also help in the process.

One of the best features of the Metal Oxide Varistor (MOV) is its response time. The spikes are shorted through the device within nanoseconds. But the response time can be affected by the mounting design method and inductance of component leads.

 


  [Return Home] [Print] [Go Back]   Next