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Tripping coil inrush current

Jam
Hi all,


I have been asked to re-specify a UPS for an existing switchboard with 230Vac shunt tripping coils and spring motors. The installation was designed and built by others but not commissioned so I can't assume that the existing UPS is up to the job in all realistic scenarios. While we can stagger the motor operations, my concern is that, in island mode, the inrush current to the tripping coils will exceed the overload capacity of the UPS and cause the inverter to panic and shut down before the tripping operation is reliably complete.


Does anyone here know whether a 7-10x inrush assumption is reasonable on this scale (200-700 VA)? Coil operation is fast - 2 to 4 cycles, although presumably it's energised for a bit longer while everything clears - so might this already be considered in the device datasheet?


Alternatively, do small(ish = 10-20kVA) UPSs not react quickly enough to short overloads? After all, it's kind of like a downstream fault being cleared by an external device.


(I would normally use a DC battery supply and the IEEE-485 method for sizing, if it's on any relevance)


Thanks,


Jam
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    You could also think about using a 1:1 Ferroresonant Transformer on the output of the UPS.  You might be able to get the inrush current that the UPS sees down with this. I have seen these used successfully for riding through voltage dips and although this is the reverse I think the same magnetic energy storage mechanism will help to cut the instantaneous load on the UPS.  I suspect you would need to rig up a test as calculation / modelling would require lots of data which you prob don't have and be beyond most software.  You might need to try a seriously overrated unit to get the effect you need.

    Let us know if you go this route.


    Peter
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  • 0
    You could also think about using a 1:1 Ferroresonant Transformer on the output of the UPS.  You might be able to get the inrush current that the UPS sees down with this. I have seen these used successfully for riding through voltage dips and although this is the reverse I think the same magnetic energy storage mechanism will help to cut the instantaneous load on the UPS.  I suspect you would need to rig up a test as calculation / modelling would require lots of data which you prob don't have and be beyond most software.  You might need to try a seriously overrated unit to get the effect you need.

    Let us know if you go this route.


    Peter
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