Power Factor Converter
Convert power factor between units instantly. Includes conversion tables, common equivalents, and calculation formulas.
Reviewed by Manoj Kumar, Mathematics Educator
Formula
PF = P / S | Q = sqrt(S^2 - P^2) | Phase = acos(PF) | Qc = P x (tan(old) - tan(new))
Power factor (PF) is the ratio of real power P (watts) to apparent power S (volt-amperes). Reactive power Q is found from the power triangle using the Pythagorean theorem. The phase angle is the arccosine of the power factor. For correction, the required capacitive reactive power Qc equals real power multiplied by the difference of tangents of the original and target phase angles.
Worked Examples
Example 1: Industrial Motor Power Factor
Problem:A motor draws 5 kW real power and 6.25 kVA apparent power. Calculate the power factor and reactive power.
Solution:PF = P / S = 5000 / 6250 = 0.80\nPhase angle = acos(0.80) = 36.87 degrees\nQ = sqrt(6250^2 - 5000^2) = sqrt(14,062,500) = 3750 VAR
Result:Power factor = 0.80, Reactive power = 3,750 VAR
Example 2: Power Factor Correction
Problem:Improve the motor above from PF 0.80 to PF 0.95 at 240V, 60Hz.
Solution:Qc = 5000 x (tan(36.87) - tan(18.19)) = 5000 x (0.75 - 0.3287) = 2106.5 VAR\nC = 2106.5 / (2 x 3.14159 x 60 x 240^2) = 96.8 uF
Result:Need 2,107 VAR correction, approximately 97 uF capacitor
Frequently Asked Questions
What is power factor and why does it matter?
Power factor is the ratio of real power (watts) to apparent power (volt-amperes) in an AC circuit. It ranges from 0 to 1, where 1.0 means all power is doing useful work. A low power factor means the circuit draws more current than needed, increasing energy losses and electricity costs. Utilities often charge penalties for power factors below 0.85 or 0.90. Motors, transformers, and fluorescent lighting are common causes of low power factor.
What is the difference between real, reactive, and apparent power?
Real power (P, measured in watts) performs actual work like heating, lighting, or running motors. Reactive power (Q, measured in volt-amperes reactive or VAR) oscillates between source and load in inductors and capacitors without doing useful work. Apparent power (S, measured in volt-amperes or VA) is the total power drawn from the supply, combining both real and reactive components. They form a power triangle where S squared equals P squared plus Q squared.
How can I improve a low power factor?
The most common method is installing power factor correction capacitors, which supply reactive power locally instead of drawing it from the utility. Capacitor banks can be fixed or automatic, switching stages as needed. Other methods include using synchronous condensers, replacing underloaded motors with properly sized ones, and using variable frequency drives. Improving power factor from 0.80 to 0.95 can reduce current draw by about 16 percent.
What is the phase angle in AC power?
The phase angle is the angular difference between the voltage and current waveforms in an AC circuit. In a purely resistive circuit, voltage and current are in phase (0 degrees) and the power factor is 1.0. Inductive loads (motors, transformers) cause current to lag voltage, creating a positive phase angle. Capacitive loads cause current to lead voltage. The power factor equals the cosine of the phase angle.
References
Reviewed by Manoj Kumar, Mathematics Educator · Editorial policy