Power Factor Calculator – Real, Apparent & Reactive Power
Calculate power factor and electrical power values for AC circuits
How to Use
- Enter any two values: real power (W), apparent power (VA), power factor, or phase angle
- Leave the values you want to calculate empty
- Click calculate to see all power values and power factor rating
- Power factor = Real Power / Apparent Power = cos(φ)
What is Power Factor?
Power factor is a dimensionless number between 0 and 1 that represents the ratio of real power (active power) to apparent power in an AC electrical system. It indicates how efficiently electrical power is being converted into useful work.
A power factor of 1 (or 100%) means all the power is being effectively used for work. A lower power factor indicates that some power is wasted as reactive power, which doesn't perform useful work but still flows through the electrical system.
Power Factor Formulas
Key formulas for power factor calculations:
- Power Factor: PF = P / S = cos(φ)
- Real Power: P = S × PF = S × cos(φ)
- Apparent Power: S = P / PF
- Reactive Power: Q = √(S² - P²) = S × sin(φ)
- Phase Angle: φ = arccos(PF)
Where P is real power (watts), S is apparent power (volt-amperes), Q is reactive power (volt-amperes reactive), and φ is the phase angle.
Types of Power
| Power Type | Symbol | Unit | Description |
|---|---|---|---|
| Real Power | P | Watts (W) | Power that performs useful work |
| Apparent Power | S | Volt-Amperes (VA) | Total power supplied by source |
| Reactive Power | Q | VAR | Power that flows back and forth |
Power Factor Ratings
- Excellent (≥0.95): Very efficient power usage, minimal reactive power
- Good (0.85-0.94): Acceptable efficiency for most applications
- Fair (0.70-0.84): Moderate efficiency, consider power factor correction
- Poor (<0.70): Inefficient power usage, correction highly recommended
Why Power Factor Matters
Maintaining a high power factor is important for several reasons:
- Reduces energy costs and utility penalties
- Decreases losses in electrical distribution systems
- Reduces voltage drops in long cable runs
- Increases capacity of electrical systems
- Extends equipment life by reducing heat and stress
- Improves voltage regulation and power quality
- Reduces carbon footprint by using less total power
Power Factor Correction
Low power factor can be improved using:
- Capacitor banks: Most common method for inductive loads
- Synchronous motors: Can generate or absorb reactive power
- Active power factor correction: Electronic circuits that adjust in real-time
- Phase advancers: For improving power factor of induction motors
Frequently Asked Questions
- What causes low power factor?
- Low power factor is typically caused by inductive loads such as motors, transformers, fluorescent lighting, and welding equipment. These devices draw reactive power to create magnetic fields, which reduces the overall power factor.
- What is a good power factor?
- A power factor of 0.95 or higher is considered excellent. Most utilities require industrial customers to maintain a power factor of at least 0.90 to avoid penalties. Residential power factors typically range from 0.85 to 0.95.
- How does power factor affect my electricity bill?
- Many utility companies charge penalties for low power factor, especially for commercial and industrial customers. Poor power factor means you're drawing more current to do the same work, which increases losses and strain on the electrical system.
- What is the relationship between power factor and phase angle?
- Power factor equals the cosine of the phase angle (PF = cos φ). When voltage and current are perfectly in phase (φ = 0°), power factor is 1. As the phase angle increases, power factor decreases. At 90° phase difference, power factor is 0.
- Can power factor be greater than 1?
- In ideal conditions, power factor ranges from 0 to 1. However, in systems with leading power factor (capacitive loads), it's still expressed as a value between 0 and 1, sometimes noted as 'leading' to distinguish it from 'lagging' (inductive) power factor.