POWER CALCULATION

1) Turn off Caps Lock.

2) Arithmetic. Divide kW by pf.

KW/pf = KVA, not KVAR.

Derivation:

KVA = √(KW² + KVAR²)

KVA² = KW² + KVAR²

KVAR^{2 =} KVA² − KW²

KVAR = √(KVA² − KW²)

Since KVA = KW/pf, substitute in the preceding line to get the equation at the top.

Another way:

kVA = kW/PF

PF = √ (1-RF²) ; where RF = Reactive Factor

The same way, RF = √ (1-PF²)

KVAr = kVA X RF

Therfore:

kVAr = (kW/PF) • RF

Ain't that simpler?

Your approach will certainly work. Not knowing the training/experience of the poster, I was trying to limit the final formula to the two known values. Even so, substituting for RF in your formula gives

kVAr = (kW/PF) * √(1-PF²),

which is still simpler than my approach. It requires fewer calculation steps & reduce the possibility of a math error.

Thanks, SC!

One way to find required kvar when pf and kw is known is where:= Initial Power Factor Angle, = Final Power Factor Angle (desired pf) but this is not the only way to calculate capacitor bank required for correction of pf, other factor too has to considered such as capacitor voltage, Capacitor Reactance, THD to name a few.

Power factor is the ratio between KW and KVA.
There are two components of power factor, displacement power factor and distortion power factor.
Displacement power factor is caused by inductive or capacitive loads and is the cosine of the angle between the voltage and the current.
Distortion power factor is the result of electronic circuits on the supply that distort the current waveform. Switchmode supplies and VFDs are both sources of distortion power factor.

If you are sure that the quoted PF is displacement power factor only, then you can use triganometry to calculate the KVAR of the load. If you apply static correction to a motor, it is very important that you only correct 80% of the KVAR of that motor. see http://www.lmphotonics.com/pwrfact.htm

Best regards,
Mark Empson

http://www.LMPhotonics.com | http://www.LMPForum.com

Hello Guest,

Assuming your load is 200 kw @ 0.8 pf, and you need to make ithe pf 0.95,

Required kvar = 200 ( tan { cos inv (0.8)} - tan {cos inv (0.95)}).

Now you take it ahead from here...

Cheers.

PS : Avoid using CAPS as human eyes find them disorienting...!!