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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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  • Former Community Member
    0 Former Community Member
    I read it as the tripping relays and the motor recharge mechanisms are the only load on the UPS


    I'm surprised a little that the motor mechs aren't recharging from the available mains or generator supply  - probably not that much point in opening and closing CB's on a dead system (and if you had to, then hand pumping the spring reserve is always an option)


    From there swapping the shunts to DC and providing a modest battery charger switch trip and close unit would make maybe more sense


    Regards


    OMS
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  • Former Community Member
    0 Former Community Member
    I read it as the tripping relays and the motor recharge mechanisms are the only load on the UPS


    I'm surprised a little that the motor mechs aren't recharging from the available mains or generator supply  - probably not that much point in opening and closing CB's on a dead system (and if you had to, then hand pumping the spring reserve is always an option)


    From there swapping the shunts to DC and providing a modest battery charger switch trip and close unit would make maybe more sense


    Regards


    OMS
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