ACB trips when the control power transfer from UPS A to UPS B 3

[NickParker]

The control circuit is powered by two UPS units (UPS A and UPS B) with automatic transfer in case one fails. The motor feeder is supplied by an LV air circuit breaker (ACB), without a contactor. The ACB includes an undervoltage release (MN) and a shunt trip coil (MX).
Currently, when one of the UPS units fails, the ACB trips. However, I would like to prevent the ACB from tripping during the control power transfer between UPS A and UPS B. The control circuit diagram is attached for reference.
I would appreciate any suggestions!

 

[NickParker]

Another question is whether there will be any issues with the stop push button (local or remote). For instance, if I have implemented a time delay in the circuit during the transition period, when the operator presses the stop push button (either local or remote), do they need to push it down for longer than the time delay?

 

[che12345]

@ Mr NickParker (Electrical)(OP)7 Oct 24 09:38
'.. whether there will be any issues with the stop push button (local or remote)... if I have implemented a time delay in the circuit during the transition period, when the operator presses the stop push button (either local or remote), do they need to push it down for longer than the time delay?'
I have the following experience for your consideration.
1. Attention: stop push button (either local or remote) shall be wired to energize a separate "Opening coil", NOT by de-energizing the UV. The opening coil opens/trips the breaker INSTANTANEOUSLY, without any time delay. Note: the opening coil acts on the trip bar, which is independent of the UV.
2. BTW: All ACBs are designed with mechanical on/off push button. These on/off mechanical pb act directly and INSTANTANEOUSLY, independently of the closing, opening, UV or shunt.
Note: Breaker installed with UV but de-energized, the contacts shall NOT close but closing spring discharged; when the mechanical on pb is activated.
Che Kuan Yau (Singapore)

 

[waross]

Wire your emergency stop in the circuit between the capacitor or other time delay circuit and the UV coil.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[che12345]

'Wire your emergency stop in the circuit between the capacitor or other time delay circuit and the UV coil'.
I have different opinion.
Attention: this may defer between different OEMs, but the basic principle is usually the same.
1. The emergency stop , (if any) SHALL be wired directly to the "opening release" only. NOT between the cap or other time delay and the UV coil...
Note: 1. The opening release operates < 60 ms. It opens/trips the breaker INSTANTANEOUSLY.
2. This is "trip free" characteristic, i.e. it Shall trip/open the CB, even the on signal is present/persisted.
2. BTW: In case which requires very high safety in controlling CB opening remotely, the control and the opening release circuits SHALL be Duplicated. Note: Check, some CB design
have provision for a separate (another/second) opening release.
Che Kuan Yau (Singapore)