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UPS Fault Level Calculation

Semaj

Does anyone know if there is a standardised way of calculating fault levels at the output of a large UPS like IEC60909 does for transformer and generator supplied faults?

I imagine things will change between manufacturers but a good rule of thumb would be very useful as it seems that no matter the installation, downstream of the UPS the breaker settings have been poorly thought out and my concern is that these downstream circuits will not actually acheive ADS due to the fault level being too low to trip the downstream breaker because the trip settings are too high.

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    I split the two scenarios up to try to make it clear that I wasn't claiming the UPS can't deliver infinite current but is limited to it's rated current.

    Up to that limit, if it acts as a constant voltage source then that would imply zero impedance contribution to the circuit

    But the moment you have a fault, the current is going to attempt to exceed the rated current and the voltage will start to collapse - a zero impedance doesn't account for that.

       - Andy.

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    I split the two scenarios up to try to make it clear that I wasn't claiming the UPS can't deliver infinite current but is limited to it's rated current.

    Up to that limit, if it acts as a constant voltage source then that would imply zero impedance contribution to the circuit

    But the moment you have a fault, the current is going to attempt to exceed the rated current and the voltage will start to collapse - a zero impedance doesn't account for that.

       - Andy.

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