Overvoltage Protection

Metrosil acts as an “electric safety valve”.

Protecting insulation and equipment from the effects of overvoltages.

What is a Varistor?

A varistor is an electronic component that varies its electrical resistance according to the applied voltage, hence the name ‘varistor’. Also referred to as a voltage-dependent resistor or a non-linear resistor, it is used to provide overvoltage protection to electrical circuits. Overvoltage protection is possible due to the non-linear, non-ohmic current-voltage characteristics of a varistor. Should a voltage unexpectedly exceed a predetermined value, the varistor becomes a short circuit, taking the excessive voltage away from the area it is protecting.

Our strong heritage in electrical insulation means that “Metrosil” is often used as a generic term for a varistor.

Graphs Illustrating Voltage Spikes With and Without Metrosil Protection
Scenery Depicting Power Generation, Transmission and Distribution Network

Electrical Safety Valve

When an inductive DC current is suddenly broken, there is a transient rise in voltage across the inductance, which can be up to 10-20 times the supply voltage and can damage insulation or circuit components. The source of this overvoltage is the energy that is stored in the magnetic field of the inductance at the moment of switching off. It is therefore essential to provide some means for this energy to dissipate itself harmlessly. The non-linear properties of Metrosil varistors provide an “electrical safety valve” to protect insulation and equipment against such overvoltages. If a circuit is broken, the current diverts through the Metrosil and rapidly decays to zero. The voltage then reduces accordingly to allow this current to pass. Our technical experts design varistor assemblies to exact specifications, ensuring that maximum voltages are never exceeded.

Typical Applications

Metrosil non-linear resistors can be supplied for all AC and DC voltages – for use with almost any inductive device. Our varistors are typically used for current and voltage transformer protection, protecting power networks worldwide. However, they are also utilised within contactors; clutch and brake coils; relay coils and solenoids; electromagnets; fields of motor generators and alternators; and custom high energy applications. Where there is a need for high energy, there is a need for Metrosil. To find out if Metrosil is suitable for your application, please contact us.

Metrosil 8000 Series Varistor Assembly at an Angle

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