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Category Energy & Power

Real Power (kW)

Equipment Profile (Auto-fill PF)

Power Factor (PF)

Apparent Power (kVA)-

Apparent Power (VA)-

S (kVA)

P (kW)

Q (kVAR)

ⓘ Generators are typically rated at 0.8 PF. A 0 kW load requires a generator of at least 0 kVA.

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About

Electrical sizing for backup systems requires distinguishing between real work capacity and the total electrical load drawn from the source. Equipment manufacturers rate engines in kilowatts (kW) representing mechanical power, while alternators and transformers are rated in volt-amperes (VA) or kilovolt-amperes (kVA) representing thermal capacity. Ignoring the Power Factor (PF) during this conversion leads to undersized UPS units and overloaded generators.

This tool bridges the gap by converting Real Power into Apparent Power. It accounts for the efficiency losses defined by the phase angle between voltage and current. Accurate conversion is critical in data centers and industrial settings where a 0.8 PF creates a 20% disparity between the power you pay for (utility meter) and the power your infrastructure must support.

Formulas

The relationship between Real Power (P), Apparent Power (S), and the Power Factor (PF) is governed by the Power Triangle geometry. To find Apparent Power in Volt-Amperes:

S_(VA) = P_(kW) × 1000PF

For results in Kilovolt-Amperes:

S_(kVA) = P_(kW)PF

Where PF is a decimal between 0 and 1, defined as:

PF = cos(φ)

Reference Data

Equipment Type	Typical Power Factor (PF)	Relation (S vs P)
Resistive Load (Heaters, Incandescent)	1.0	S = P
Modern Server PSU (Active PFC)	0.95 to 0.99	S ≈ P
Legacy UPS Systems	0.80	S > P
3-Phase Generators	0.80	Standard Rating
Induction Motors (Full Load)	0.85	S > P
Induction Motors (Unloaded)	0.35	S ≫ P
LED Drivers	0.90	Efficient
Welding Machines	0.50 to 0.70	High Reactive Load
Fluorescent Lighting (Magnetic Ballast)	0.40 to 0.60	Poor Efficiency
Rectifiers / VFDs	0.90	Variable

Frequently Asked Questions

Generators are limited by the thermal capacity of their windings (current), which correlates to kVA. Engines and motors are limited by mechanical work output, which correlates to kW. A 100 kVA generator can only produce 80 kW of real power if the load has a Power Factor of 0.8.

It means 100% electrical efficiency in terms of utilization. A PF of 1.0 (unity) implies that all drawn current does useful work. Lower PF values indicate that the system draws more current than is strictly necessary to perform the work, causing energy waste in distribution.

No. Real Power (kW) represents the "resistive" portion of the power triangle. Since the hypotenuse (kVA) is the vector sum of Real and Reactive power, kW can at most be equal to kVA (when PF is 1.0), but never higher.

For general estimation, use 0.8 for motors and legacy UPS systems, and 0.99 for modern computer power supplies. If you have a voltmeter and ammeter, you can calculate it by dividing Watts by the product of Volts and Amps.