OVER VOLTAGE PROTECTION BY VARISTORS


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A varistor protects the electrical and electronic device from overvoltage transients it is a two terminal semiconductor device and its resistance is depended on its input voltage it is a passive two-terminal semiconductor device. Varistor provides overvoltage protection by the voltage clamping
The word varistor is formed by the word VARI-able resi-STOR varistor can change its resistance value automatically with the change in voltage across it
Varistor plays an important role in protecting the electronic circuits from switching spikes and the overvoltage transients
Varistors will be connected in circuits across mains supply and it will be the phase to neutral and phase to phase for the AC operation and for the Dc voltage it will be positive to negative

METAL OXIDE VARISTOR

Construction of a varistor
It is created by using crystals of silicon carbide or metal oxide which will be then pressed into a ceramic material
The electrical character of the device is depended on the temperature provided and the atmospheric conditions too for having better electrical contacts the contacts are metalized with silver and copper
Metal oxide varistor is a voltage-dependent resistor and the resistance material is a metallic oxide. MOV’s are the most type of voltage clamping device it conducts during specific voltage and it will stop conduction when the voltage falls below a threshold level

OPERATION AND CHARACTERISTICS OF VARISTOR

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In here we can see that the resistance is not proportional to the voltage. Voltage is low when resistance across it is high if low voltage is applied to the device there will be high resistance and very low current flows and if the voltage increases then the current increases

ADVANTAGES

• Excellent overvoltage protection
• Bidirectionality could be achieved because it doesn’t show the polar effect