There are 2 individual feeds of 120 VAC to the ABB DCS system. See image below.
The DCS power calculations are based on a 2N Redundancy; that is an individual Power Supply Module can supply the required current load to the DCS.
There is at least a 99% chance that you WILL NOT have any issues if you were to de-energize 1 of the 2 Power Supplies (either UPS or utility).
There is always a small risk that there could be an issue with the opposite Power Supply.
The Green Status LEDs on both Power Supplies seems to indicate that there are no issues.
When both Power Supplies are on, the load is shared between the 2 Power Supplies.
When only 1 Power Supply is on, there is no sharing of load; the 1 Power Supply has to handle it all.
When I installed the Power Supplies (and also during Plant Outages), I like to do a validation to make sure that each individual Power Supply can supply the load if the other fails.
When I’m doing these Power Supply Failure Tests during the Plant Outages, we do not have the “Full Load” on the DCS, but it is the closest test that I can do to make sure all is good.
I can also not account for any additional load that has been added since the Power Supply installation.
I would say that there is at least a 99% chance that you WILL NOT have any issues if you were to De-Energize 1 of the 2 Power Supplies.
There is always a small risk that there could be an issue with the opposite Power Supply.
The Green Status LEDs on both Power Supplies seems to indicate that there are no issues.
There is also a small risk that there could be an increased load on the Power System compared to when the system was tested after installation.
When both Power Supplies are on, the load is shared between the 2 Power Supplies.
When only 1 Power Supply is on, there is no sharing of load – the 1 Power Supply has to handle it all.
Ideally, power supply #1 would be assigned to UPS power and power supply #2 would be from utility grid. I would not put both the power supplies into the UPS or grid only… that would be putting all the eggs in one basket.