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
