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About

In alternating current (AC) electrical systems, power is not always equal to voltage multiplied by current. This discrepancy gives rise to two distinct measures: Apparent Power (measured in kVA, kilovolt-amperes) and Real Power (measured in kW, kilowatts).

The bridge between these two is the Power Factor (PF), a measure of efficiency ranging from 0 to 1. Generators and transformers are rated in kVA because they must handle the total current, but engines and motors consume Real Power (kW). Attempting to convert kVA to kW without knowing the Power Factor is impossible; a standard default is often 0.8 for diesel generators, while purely resistive loads (like heaters) have a PF of 1.0. This tool ensures accurate sizing by mandating the Power Factor input.

electrical engineering generators power factor kilowatts kva

Formulas

Real Power is a fraction of Apparent Power, determined by the phase angle difference between voltage and current.

P(kW) = S(kVA) × PF

Where:

  • P is Real Power (kW)
  • S is Apparent Power (kVA)
  • PF is Power Factor (dimensionless, 0 ≤ PF ≤ 1)

Reference Data

Equipment / Load TypeTypical Power Factor (PF)Efficiency Note
Resistive Load (Heaters, Toasters)1.0100% Real Power
Incandescent Lighting1.0100% Real Power
Standard Diesel Generator0.8Industry Standard Rating
Induction Motor (Full Load)0.85 - 0.90High Efficiency
Induction Motor (Unloaded)0.35 - 0.60Poor Efficiency
Welding Machines0.50 - 0.70Highly Inductive
Computer / IT Servers0.90 - 0.99Modern supplies have PFC
Fluorescent Lights (Magnetic Ballast)0.50 - 0.60Needs Capacitors
Arc Furnace0.70 - 0.80Heavy Industrial

Frequently Asked Questions

Generators are limited by the amount of current (Amps) their windings can carry, not just the mechanical power of the engine. Since kVA represents total current capacity regardless of efficiency, it is the safe rating for the alternator.
Mathematically, the Real Power (kW) becomes 0. This describes a purely reactive circuit (like a perfect capacitor or inductor) where energy oscillates back and forth but performs no "real" work.
No. Power Factor is the cosine of the phase angle and represents efficiency. A value greater than 1 implies creating energy, which violates physics. Valid range is 0 to 1.
Most portable and standby home generators are rated at a Power Factor of 1.0 or 0.8 depending on the manufacturer. Always check the nameplate.