Power Factor Calculator
Estimate power factor for your project with our free calculator. Get accurate material quantities, costs, and specifications.
Formula
PF = kW / kVA = cos(phi)
Power factor equals real power (kW) divided by apparent power (kVA), which is also the cosine of the phase angle between voltage and current. Reactive power (kVAR) equals kW times the tangent of the phase angle. To correct power factor, a capacitor bank rated at the difference between current kVAR and target kVAR is installed.
Worked Examples
Example 1: Factory Power Factor Correction
Problem: A factory draws 500 kW at 625 kVA. Calculate the power factor and capacitor size needed to reach 0.95 PF.
Solution: Power factor: 500 / 625 = 0.80\nPhase angle: acos(0.80) = 36.87 degrees\nReactive power: 500 x tan(36.87) = 375 kVAR\nTarget kVAR at 0.95: 500 x tan(acos(0.95)) = 164.3 kVAR\nCapacitor needed: 375 - 164.3 = 210.7 kVAR
Result: PF: 0.80 | Capacitor: 210.7 kVAR | New kVA: 526.3
Example 2: Motor Load Analysis
Problem: A 480V, 3-phase system has 200A current draw and 120 kW real power. Find the power factor.
Solution: Apparent power: 480 x 200 x 1.732 / 1000 = 166.3 kVA\nPower factor: 120 / 166.3 = 0.722\nReactive power: 120 x tan(acos(0.722)) = 115.1 kVAR\nThis is below the 0.9 penalty threshold.
Result: PF: 0.722 | kVA: 166.3 | kVAR: 115.1 | Penalty risk: Yes
Frequently Asked Questions
What is power factor?
Power factor is the ratio of real power (kW) to apparent power (kVA) in an AC electrical system. It ranges from 0 to 1, where 1.0 (unity) means all the power drawn is being used productively. A power factor of 0.8 means only 80% of the current drawn is doing useful work, while 20% is circulating as reactive power. Low power factor is caused by inductive loads like motors, transformers, and fluorescent lighting that require reactive power to maintain their magnetic fields. Poor power factor increases current draw, causes voltage drops, and results in utility penalties.
How do I improve power factor?
The most common method to improve power factor is installing capacitor banks that supply reactive power locally, reducing the reactive power drawn from the utility. Capacitors are sized in kVAR to offset the inductive kVAR of the load. Other methods include synchronous motors (which can generate leading reactive power), active power factor correction circuits in electronic equipment, and replacing lightly loaded motors with properly sized ones. Automatic power factor correction systems switch capacitor banks in and out based on real-time monitoring to maintain the target power factor as loads change throughout the day.
Why do utilities charge penalties for low power factor?
Utilities charge power factor penalties because low power factor forces them to generate, transmit, and distribute more current than necessary to deliver the same amount of useful power. This extra current causes increased losses in utility transformers and transmission lines, requires larger capacity infrastructure, and reduces the efficiency of the entire power grid. Most commercial and industrial utility tariffs require a minimum power factor of 0.85 to 0.95. Penalties can be calculated as a surcharge on the demand charge, a multiplier on the energy charge, or as an adjustment to billed demand.
What is the power triangle?
The power triangle is a right triangle that visually represents the relationship between real power (kW), reactive power (kVAR), and apparent power (kVA). Real power forms the horizontal base and represents useful work. Reactive power forms the vertical side and represents the power needed to sustain magnetic fields in inductive loads. Apparent power is the hypotenuse and represents the total power the supply must deliver. The angle between real and apparent power is the phase angle (phi), and the cosine of this angle is the power factor. The Pythagorean relationship gives: kVA squared equals kW squared plus kVAR squared.
What is a structural safety factor and why is it important?
A safety factor is the ratio of a structure's actual strength to the maximum expected load. Building codes typically require safety factors of 1.5 to 3.0 depending on the material and application. This accounts for material variations, unexpected loads, and degradation over time.
Is my data stored or sent to a server?
No. All calculations run entirely in your browser using JavaScript. No data you enter is ever transmitted to any server or stored anywhere. Your inputs remain completely private.