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I am using Cadence-Orcade Lite. In it I have a circuit in which I want to note the behaviour of varistors (MOV, PSPICE models exist in Orcade for various varistors).

I am using LS40K680QP/EPC Model of a varistor and I want to depict the behavior of this device when transients in ac supply are applied.

I have connected an ac source in parallel with some load. When I simulate it, it doesn't have any effect on signal voltages even when the voltages are beyond its clipping voltage (or rated voltage from datasheet). It should clip voltages to the maximum operating voltage of varistor when supply voltage have transients in kilo volts.

I want to know, if there is some method to make this mov depict its actual behavior, or does it just not simulate real life?

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2 Answers 2

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I have connected an ac source in parallel with some load.

Most people, when they say transients, mean Voltage transients, so my guess is you've built this:

schematic

simulate this circuit – Schematic created using CircuitLab

It should clip voltages to the maximum operating voltage of varistor when supply voltage have transients in kilo volts.

Is wrong. Your voltage source is ideal. It will maintain the voltage, no matter what.

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  • \$\begingroup\$ Yes, exactly similar to this circuit. So it means the voltage appearing at R_Load will always be same as the voltage of the source. That means i can't simulate the real behavior of Varistor in Software. or is there any way?? \$\endgroup\$
    – BetaEngineer
    Commented Aug 16, 2018 at 11:40
  • \$\begingroup\$ You could model parasitic resistances of the voltage source, or add current limit circuitry. \$\endgroup\$
    – Zekhariah
    Commented Aug 16, 2018 at 13:29
  • \$\begingroup\$ Can you please explain "Parasitic Resistances or current limit circuitry"?? \$\endgroup\$
    – BetaEngineer
    Commented Aug 17, 2018 at 10:45
  • \$\begingroup\$ What @Zekhariah meant isn't usually called "parasitic resistance", but "source impedance", ie. a (typicaly small-valued) resistor in series with your voltage source. and "current limiting circuitry" means "circuitry that limits current". don't know how to explain that any better. \$\endgroup\$
    – Marcus Müller
    Commented Aug 17, 2018 at 10:49
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    \$\begingroup\$ To expand a little on @MarcusMüller's comment; many transients have limited energy and are sometimes better modelled with a charged RC network; much depends on just what type of transient you are trying to protect against. \$\endgroup\$
    – Peter Smith
    Commented Apr 14, 2020 at 10:17
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You will have to put in a source resistance in series to the excitation of the impulse voltage source and you will be able to simulate it. The MOV model will then be able to clamp the voltage and a voltage drop will appear over the source resistance.

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