Components commonly used in SPD
SPD Components commonly used in SPD 2020-08-24 Components commonly used in SPD 199

Let us understand 3 components commonly used in SPD.


Transient voltage suppressors:They are based on avalanche diodes and zener diodes. Diodes are made of semiconductors usually silicon, at a junction between n and p doped regions. TVS devices provide protection with combination of forward bias and reverse bias breakdown conduction.

MOV (Metal Oxide varistor) : Varistors are usually made of ceramic of zinc oxide grains in a matrix of other oxides. The grains form diodes with surrounding matrix, creating a complex array of parallel and anti-parallel diodes. At higher voltages, the individual diodes begin to conduct and the resistance of the varistor drops dramatically.

Gas Discharge Tubes: They are usually formed with ceramic body filled with gas mixture containing neon and argon and two or more electrodes. When voltage across the electrodes exceeds a specified value an arc occurs within the tube which provides low current path.


Following table mentions difference between these components.


Type

Speed

Accuracy

Current capability

Lowest crowbar trigger voltage

Wearout

Gas Discharge Tube (GDT)

Slow

Fair

High

75 V

Will fail after numerous stresses depending on severity.

Transient Voltage Suppressor (TVS)

Fast

Good

Low

NA

NO

Metal Oxide Varistor (MOV)

Fair

Poor

Medium

NA

Yes


Components commonly used in SPD

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