UPS Calcs

[hilltop]

I have an existing 3 phase 120/208V 20KV UPS

I need to calculate the total possible load that this unit may see.

Load testing is not accurate as loads very from day to day, month to month...I need to know actual if everything were running at the same time.

95% of the loads are lab equipment, single phase with voltage and Amps on name plate.
I have seen that the industry standard can be anywhere from 40% to 60% of nameplate amperage for actual running amperage.

I need some advice as to what I should use to calculate actual VA

Use VA of nameplate and subtract 40% to be safe???

 

[dbuckley]

The actual load versus nameplate varies enormously by equipment, computers typically state the power supply rating which may be several times the actual consumption, whereas an instrument with significant part of its load being heating will probably be right on the money.

Check out the menus on the UPS; it may tell you just what you want to know!

 

[__dan]

do the calculation backwards

do the calculation backwards

IMO, do the calculation backwards. Look at the UPS first, look at the kW rating, not the kVA rating, and look at if the manufacturer rates its kW suitable for loading at 100% continuous or not (80% continuous loading for kW).

The kW rating is power through the unit. The kVA rating is power through the unit plus an allowance for circulating reactive power. The reactive power may circulate just at the input or just at the output as it tries to balance it excess capacitive or inductive capacity with its mate elsewhere in the system. If the kVA circulates through the unit from input to output, you could exceed the kW rating.

Get a good number on actual kW rating for continuous loading of the UPS and then try to load it up safely to that rating. As stated, for computer power supplies, actual vs nameplate numbers are very different.

"Load testing is not accurate as loads very from day to day, month to month...I need to know actual if everything were running at the same time."

You are right on the money there. A large variation in equipment running and loading could be trouble. If your calculated attached loads exceed UPS capacity, I am thinking you may want a warning system, a load side digital power meter with alarm setpoints for excess loading. For the times when the guys try to run everything at the same time, realtime actual loading measurements and training for the guys to turn something off when they get a loading alarm. That may get you a little farther down the road to see when peak loading occurs and how often, do you have the actual demand for a larger UPS or can some type of load shedding complement your existing UPS capacity.

Loading up at the max rating will greatly reduce battery runtime, but you're probably more concerned with an orderly shutdown for power loss.