UPS Sizing

[nightfox1925]

I am sizing a suitable UPS with a given continuous load and an inrush value in both RMS and Peak Values.

The Transient Loading condition of a UPS is:

Transient KVA = ( Cont. Load KVA + Inrush KVA)*1.5

where: 1.5 = 150% UPS overload capability
Inrush kVA = Inrush kVA of the largest load
Cont. Load kVA = continuous kVA of the rest of the
load.

My question is, am I going to utilize the measured Inrush Peak or the Inrush RMS?

 

[EmergencyPowered]

Most UPS loads are a fixed value, with small variations over time. Use the steady state load and pick the common size which gives you the headroom for future growth using roughly 125-150% of actual load.
Common sizes nowadays are 75KVA, 125KVA, 225KVA, etc.
If affordable, go with N+1 redundancy and run units in parallel for most reliability and ease of maintenance.

If load is 100KVA, get a single 125KVA of even better two running in parallel.

 

[EmergencyPowered]

I forgot to mention: UPS loads are normally powered up in BYPASS so that inrush is not carried by the
rectifier/inverter. If all is well, load should rarely have to be restarted.

 

[nightfox1925]

A good point mentioned is that the UPS loads are normally started in the BYPASS mode.

Do you have any vendor reference or standard clause reference that states this kind of operation. I would appreciate it much.

 

[EmergencyPowered]

No references.....but if you really need SERIOUS inrush ability consider ROTARY UPS's such as those from PILLER, Inc