Tripping coil inrush current

OMS:

Inrush current to shunt trips could easily be in the order of 100 x the duty VA rating if operating at 230V (for typical 25millisecond breaker operation)

Really 100x? That seems huge, but, since I've never measured it, I'm prepared to be advised! Just checking not a typo really

Whilst that peak isn't present over the full tripping cycle, it can be there long enough to seriously disturb the UPS


If you are going to do this with a UPS then the VA rating needs to be seriously larger than the total operating VA - you would probably be looking at an industrialised or ruggedized UPS with 12 pulse rectifier and a minimum of 300% overload capacity - something like the AEG Protect 8 series derated, to give you a 300% overload capability for say 5 seconds and a short circuit capability of 3 x design rating. (typically 3 phase in and 1 phase out at 230V  - smallest is around 10kVA rating)

Thanks for the recommendation OMS; definitely taken on board.

mapj1:

I presume the shunt trips and rewind motors are not the major load on the UPS, and that there is also some proper load as well  ?

The UPS is dedicated to a switchboard, so while there are standing loads such as protection relays and indicator lamps that affect - indeed are the main factor in - the standby time, when the protection operates it gets quite busy.

(after all 10kVA is quite a lot of shunt trip !) If there are not many it may be worth considering re configuring for a DC trip if they really are the dominant load.

Do you have part no.s  or data?

Perhaps I misled, sorry: The 10kVA isn't the shunt trip rating (!) but the order of UPS I was thinking I might need. (I was actually thinking 12-16kVA but perhaps even that's too small by the sound of it.

For example, the open shunt trips are (mostly) stated as 180VA 45ms; under the existing scheme it's possible that ten of them will operate simultaneously on a loss-of-mains event

There are other coils with different ratings but keeping it simple for the moment.

OMS:

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

I agree it's not how I would have done it! It's reassuring to see you're thinkng the same. But  the switchgear manufacturer sold the kit with a 230Vac option so I thought I might be missing a trick.

I will investigate swapping out though


Thanks both!

OMS:

Inrush current to shunt trips could easily be in the order of 100 x the duty VA rating if operating at 230V (for typical 25millisecond breaker operation)

Really 100x? That seems huge, but, since I've never measured it, I'm prepared to be advised! Just checking not a typo really

Whilst that peak isn't present over the full tripping cycle, it can be there long enough to seriously disturb the UPS


If you are going to do this with a UPS then the VA rating needs to be seriously larger than the total operating VA - you would probably be looking at an industrialised or ruggedized UPS with 12 pulse rectifier and a minimum of 300% overload capacity - something like the AEG Protect 8 series derated, to give you a 300% overload capability for say 5 seconds and a short circuit capability of 3 x design rating. (typically 3 phase in and 1 phase out at 230V  - smallest is around 10kVA rating)

Thanks for the recommendation OMS; definitely taken on board.

mapj1:

I presume the shunt trips and rewind motors are not the major load on the UPS, and that there is also some proper load as well  ?

The UPS is dedicated to a switchboard, so while there are standing loads such as protection relays and indicator lamps that affect - indeed are the main factor in - the standby time, when the protection operates it gets quite busy.

(after all 10kVA is quite a lot of shunt trip !) If there are not many it may be worth considering re configuring for a DC trip if they really are the dominant load.

Do you have part no.s  or data?

Perhaps I misled, sorry: The 10kVA isn't the shunt trip rating (!) but the order of UPS I was thinking I might need. (I was actually thinking 12-16kVA but perhaps even that's too small by the sound of it.

For example, the open shunt trips are (mostly) stated as 180VA 45ms; under the existing scheme it's possible that ten of them will operate simultaneously on a loss-of-mains event

There are other coils with different ratings but keeping it simple for the moment.

OMS:

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

I agree it's not how I would have done it! It's reassuring to see you're thinkng the same. But  the switchgear manufacturer sold the kit with a 230Vac option so I thought I might be missing a trick.

I will investigate swapping out though


Thanks both!