UPS Response to Transformer Magnetizing Inrush

[ish1284]

I have a 1000kW UPS going on to feed a number of PDU (power distribution unit) transformers and trying to set the feeder breakers to the UPS as well as the UPS output breakers. How do modern UPS's typically handle the magnetizing inrush of transformers? Will it typically let through all of the inrush current such that it will be seen on both the feeder breaker and the output breaker in its entirety? Or is there typically a current limit that will not let through the inrush in its entirety?

Thanks in advance!

 

[Jraef]

I have a 1000kW UPS going on to feed a number of PDU (power distribution unit) transformers and trying to set the feeder breakers to the UPS as well as the UPS output breakers. How do modern UPS's typically handle the magnetizing inrush of transformers? Will it typically let through all of the inrush current such that it will be seen on both the feeder breaker and the output breaker in its entirety? Or is there typically a current limit that will not let through the inrush in its entirety?

Thanks in advance!

There are several different types of UPS configuration, no one answer can apply to all. It's really a question for the supplier of the particular UPS you are working with.

 

[ghostbuster]

In the past,we have seen some UPS systems momentarily transfer to bypass to handle the inrush and then switch back to normal operating mode (Note: doing this transfer usually creates a voltage transient 100 to 200 volts that the all the UPS sensitive loads "see". Most UPS suppliers will usually try to downplay this scenario )

 

[ron]

1MW UPS is almost surely modern. That word means that it could be double conversion operating in ECO mode (bypass) until a pq issue arises (means it can see downstream inrush through to the input), line interactive (similar to the double conversion in ECO mode), or rotary (which is similar to line interactive). The only one that wouldn't pass it through to the input would be a double conversion unit that doesn't have ECO mode and is purposefully selected to accommodate downstream inrush without going to bypass as was mentioned.

Set the CB settings to accommodate the inrush the best you can and not end up with super high arc flash incident energy.

 

[publicgood]

It is not recommended to energize downstream transformers on UPS inverter. Most typically, the design should include UV trip for all downstream transformer primary breakers. Many UPSs come "up" online by default; thus, the reason for the trip. The operator would then place the UPS in maintenance bypass to energize the transformers before going online.

Having said that, we are all assuming you are talking about a transformer-less static online double conversion UPS. Please clarify.