Power Factor Calculator
Calculate power factor, reactive power, and correction capacitor for AC circuits
Formula
P = S × PF, Q = S × sin(φ), C = (Q₁ - Q₂) / (2πf × V²)
Reference: IEC 60038 standard voltages
How It Works
Power factor is the ratio of real power (watts) to apparent power (volt-amperes) in an AC electrical system, representing the efficiency of electrical energy utilization. In alternating current circuits, power factor ranges from 0 to 1, with 1 being ideal and indicating perfect synchronization between voltage and current waveforms. A low power factor means more reactive power is being consumed, which increases energy losses and reduces system efficiency. Power factor correction involves adding capacitive or inductive elements to minimize the phase angle between voltage and current, thereby improving overall electrical system performance and reducing utility demand charges.
Worked Example
Consider an industrial motor drawing 50 kW with an initial power factor of 0.65. The apparent power would be 76.92 kVA (50 kW ÷ 0.65). By calculating the required correction capacitance using vector calculations, we can determine the precise capacitor needed to raise the power factor to 0.95. Assuming 480V, 60Hz supply, the correction capacitor would be approximately 45 μF. This correction reduces reactive power consumption, decreases line current, and potentially generates significant energy cost savings for the facility.
Practical Tips
- ✓Always measure true RMS values for accurate power factor computation
- ✓Use temperature-compensated capacitors for stable performance
- ✓Regularly monitor and maintain power factor correction equipment
- ✓Consider harmonic filters for complex electrical systems
Common Mistakes
- ✗Incorrectly measuring power factor without considering phase angle
- ✗Using oversized or undersized correction capacitors
- ✗Neglecting harmonic distortion effects on power factor calculation
Frequently Asked Questions
What is an acceptable power factor?
Generally, a power factor above 0.90 is considered good. Most utilities encourage maintaining power factor between 0.95 and 1.0 to optimize energy efficiency.
How often should power factor correction be checked?
Recommended annual inspections are typical, with quarterly checks for critical industrial installations experiencing significant load variations.
Can power factor correction save money?
Yes, improving power factor can reduce utility bills by decreasing reactive power charges and potentially lowering peak demand costs.
Are capacitive or inductive corrections used?
Capacitive correction is most common, used to counteract inductive loads like motors and transformers by supplying leading reactive power.
What happens if power factor correction is incorrect?
Improper correction can lead to resonance, equipment damage, and potentially increased energy consumption instead of reduction.
Shop Components
Affiliate links — we may earn a commission at no cost to you.
Related Calculators
General
Capacitor Energy
Calculate energy stored, charge, and current in capacitors for power supply design
Power
LDO Thermal
Calculate LDO regulator power dissipation, junction temperature, thermal margin, and minimum dropout voltage for thermal design validation.
Power
Buck Converter
Design a synchronous buck (step-down) converter: calculate duty cycle, inductor value, output capacitor, input capacitor, and theoretical efficiency.
Power
Voltage Divider
Calculate voltage divider output voltage, current, Thévenin impedance, and power dissipation from Vin, R1, and R2. Ideal for bias networks and level shifting.
Power
LED Resistor
Calculate the correct current limiting resistor for an LED. Shows exact value, nearest E24 standard, actual current, and power dissipation.
Power
Battery Life
Estimate battery runtime for IoT and portable devices given average current draw, duty cycle, self-discharge rate, and depth-of-discharge cutoff. Suitable for LiPo, alkaline, NiMH, and coin-cell batteries.