100 KVA UPS Power Factor

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Snowjob

Snowjob

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Why do 100KVA UPS spec sheets quote input power factor as .98 and output power factor as .8?

Is there something I am missing here?
 
I think I answered my own question

I think I answered my own question

The UPS is almost a pure resistive load from the input power perspective and can accomodate normal real world power factor (.8) at the output.
 
A VFD does the same thing. The switching power supply charges the UPS DC bus in unity with voltage(although it isn't a pretty sine wave) so you have close to unity power factor. The output power factor of the UPS depends on what is plugged into it. It can accommodate a load with .8 power factor at it's full nameplate power rating. If the supplied load has a lower power factor then .8 the UPS can't be fully loaded. Generators are this way. They rate generators in KW(real) at a given PF.
 
UPS calculation

UPS calculation

I am modelling the UPS for EDSA. Is this calculation below correct?

100KVA UPS spec sheets quote input power factor as .98 and output power factor as .8.

The UPS is almost a pure resistive load from the input power perspective and can accomodate normal real world power factor (.8) at the output.

A 100kVA UPS rating implies the output power is 100KVA at 80 KW and 60 KVAR (.8 PF).

However how do you calculate the input draw? Assuming AC-AC efficiency of say 90% and PF of 99% (approximate as 1.00)

a) The 100KVA becomes 100 KW at the input because of the almost unity PF draw.

b) 100 KW/ .90 = 111 KW draw at the input 0 KVAR

am I right?
 
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I would be more inclined to think that the ups could supply 80% of the input, than I would be inclined to think that you could supply it with 111% of what it is rated at.
 
Snowjob said:
The UPS is almost a pure resistive load from the input power perspective and can accomodate normal real world power factor (.8) at the output.
Click to expand...
If you put a scopemeter on the ups input and monitored the current I would bet money you wouldn't think it looks like a resistive load. It would look look pretty nasty, which is why harmonics can come into play.

Snowjob said:
A 100kVA UPS rating implies the output power is 100KVA at 80 KW and 60 KVAR (.8 PF).

However how do you calculate the input draw? Assuming AC-AC efficiency of say 90% and PF of 99% (approximate as 1.00)

a) The 100KVA becomes 100 KW at the input because of the almost unity PF draw.
Click to expand...

Why would you assume KVA = KW ?

Snowjob said:
b) 100 KW/ .90 = 111 KW draw at the input 0 KVAR

am I right?
Click to expand...

I'm not sure where you come up with a & b, but assuming you have 100KVA, 80KW and 60KVAR, your power is 80KW. If you assume your .9 efficiency then your 80KW / .9 = 88KW reflected on the line side.
 
StephenSDH said:
Why would you assume KVA = KW ?
.
Click to expand...
I took the 100 KVA figure on the output where PF is .8.

I tried to back calculate what this would require on the Input
On the input PF approx = .99 or 1.00 so I translated (perhaps mistakenly) the 100 KVA into a 100 KW draw at the input. Am I wrong for doing this?
 
Snowjob said:
Why do 100KVA UPS spec sheets quote input power factor as .98 and output power factor as .8?

Is there something I am missing here?
Click to expand...
They are two different things.
An output power factor of 0.8 limits output power to 80 kW.
The input pf depends on the input circuit topology. A 0.98 pf infers an active front end - the bit that converts ac to dc. Unless the manufacturer is being a bit loose on defining pf as just displacement rather than total.
 
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