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Metal Oxide Varistors (MOV) Definition, utility and working

In electronics, a Metal Oxide Varistor (MOV) is a voltage-dependent resistor. In this specific resistor, metallic oxide plays the role of the resistance material. Many MOVs use zinc oxide (ZnO), which has typically undergone a production process similar to ceramic fabrication. In this article, you will learn more about metal oxide varistors, their utility, working and frequently asked questions related to these varistors.

Table of Contents

What is the meaning of metal oxide varistor

A Metal Oxide Varistor, often known as a MOV, is a kind of resistor that is voltage-dependent. The role of the resistance material is fulfilled by metallic oxide within this specific resistor. MOVs often make use of zinc oxide (ZnO), which has traditionally been subjected to a manufacturing process that is analogous to that of ceramic fabrication. A ZnO-based voltage dependent resistor (VDR) usually has a comparatively small diameter and short length, so that it can easily fit within the outline of a conductor, which is normally found in electrical equipment and systems.

What is the meaning of metal oxide varistor
The meaning of metal oxide varistor

What are the advantages and disadvantages of MOV

Varistors made of metal oxide have a lot of useful applications and advantages. Varistors made of metal oxide, for instance, are more compact despite their exceptionally high level of stability and durability. The high temperature does not prevent it from functioning normally. In addition, in contrast to carbon composition resistors, metal oxide varistors are far less expensive and generate almost no audible noise.

The Metal Oxide Varistor found in transient voltage surge suppressor TVSS does not offer reliable safety for sensitive electronics. In particular, there is no protection against prolonged over voltages, which can damage the protected device and any attached machinery. For instance, the varistor could overheat and fail due to a semiconductor flaw in the protected system, allowing the overload current to flow unchecked into the protected circuit.

Why is Metal Oxide Varistor applied

A Metal Oxide Varistor, or MOV for short, is used as a safety measure in AC-fed power supply circuits. The variable resistance it offers serves as a buffer to protect the circuit from spikes in voltage. Because of its small stature, a MOV is well-suited for uses where space is at a premium. MOVs are utilized in these contexts to safeguard high-priced components including power supply, displays, and other electronics. Whenever the current through the MOV is greater than its rated capacity, a powerful electromotive force (EMF) is produced, which in turn triggers an avalanche of electrons across the MOV’s internal structure. The MOV opens as a result of the avalanche, diverting the current surge to ground and sparing the rest of the circuit from destruction.

Where are MOV used

In most electronic circuits, metal oxide varistors are utilised primarily for the purpose of providing protection against power surges, extremely brief spike noise, and inductive surges. These are especially important in the protection of sensitive, high voltage devices such as microprocessors and solid state drives. Varistors have high energy capacity, but they discharge that energy over a relatively long period of time (compared to a diode), therefore they are useful in applications such as protection of an inductive load such as transformers or motors.

How do metal oxide varistors work

Metal oxide varistor refers to an electrical component that helps shield electronic devices and other electrical apparatus from voltage spikes. Its resistance will automatically alter in a manner that is determined by the voltage. After the voltage across the varistor has increased to a certain point, the resistance will begin to drop. This characteristic is absolutely necessary for protecting circuits from potentially harmful voltage spikes. MOVs are commonly used to provide this protection in many current surge protectors.

How do metal oxide varistors work
How do metal oxide varistors work

How do you make a Metal Oxide Varistor

Metal oxide varistors are made by mixing zinc oxide (ZnO) with other metal oxides during manufacture. High-temperature crushing and sintering creates a polycrystalline structure between the highly conductive ZnO grains, with very robust boundaries. Having reached this level, the previous one’s work has culminated in this structure.

How do you identify a metal oxide varistor

One can see that the symbol for a varistor in a circuit is quite similar to the sign for a thermistor. This is something that may be noted. It is made up of the basic symbol for a resistor, which is a rectangle with a diagonal line going across it. This makes up the entirety of the symbol. In addition to that, it consists of a little portion that is attached in a parallel fashion to the main body of the resistor symbol. The fact that the variator does not follow a linear pattern is demonstrated by this fact.

How does a metal oxide varistor failure

Long-duration over voltages, such as those that arise from shutting off a reactive load, or the thermal runaway of a MOV that is tied to the ac mains, are two possible reasons for the failure of metal oxide varistors. Another possibility is that the failure was caused by a combination of both of these factors. If an MOV is used in steady-state conditions with a voltage that is higher than the voltage rating that the MOV was intended for, there is a significant possibility that the MOV will fail open circuit.

What is the metal oxide varistor symbol

The following are examples of the two different common symbols for varistor:
IEEE standard symbol for varistor

IEEE standard symbol

IEC standard symbol for varistor

IEC standard symbol

Conclusion

We are hopeful that you have equipped yourself with the knowledge of metal oxide varistors. Because of its characteristics, the metal oxide varistor is an excellent candidate for use in surge protectors for electrical systems. To elaborate on its advantages in surge protection, we may say that since the metal oxide varistor is one of the best electronic devices to protect electrical systems, it is imperative that you as future engineers should be able to recognize their good points.

FAQ

MOVs, or metal oxide varistors, are surge suppressor devices that are non-linear and bidirectional. During a surge or other kind of transient event, they are frequently used in a wide variety of applications for the purpose of regulating the voltage. This is a common objective for their employment.

The voltage rating of the MOV, which is also referred to as the "varistor voltage," is determined by measuring the voltage that is present across a varistor while 1 mA of current is flowing through it. Conducting behaviour begins at this point on the varistor's voltage scale, which corresponds to the beginning of the device's I-V characteristic curve. This point also marks the maximum value of the device.

A young physicist by the name of Michio Matsuoka and his colleagues at the Matsushita Electric Co. in Osaka, Japan, came up with the idea for a varistor that was based on zinc oxide in July of 1967.

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