Alternator Output Calculator
Calculate alternator output power, current and derating for temperature and power factor.
About Alternator Output Calculator
Generators are rated in kVA at a reference temperature and altitude. Both hot ambient conditions and thin air at altitude reduce cooling capacity, so the usable rating falls before power factor is even considered. A 100 kVA set in a hot plant room may deliver only 76 kW, which is why generator sizing so often disappoints on commissioning.
Formula
Alternator Output
Available kW = nameplate kVA × (1 − derating) × power factor
- derating
- Reduction for ambient temperature and altitude, which limit cooling
Worked example
With the default values below, Alternator Output Calculator returns Available Real Power of 76.000. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Nameplate ratingminimum 0 kVA
- 100 kVA
- Load power factoraccepts 0.01–1
- 0.8
- Line voltageminimum 1 V
- 400 V
- Derating for ambient temperatureaccepts 0–100 %
- 5 %
- Derating for altitudeaccepts 0–100 %
- 0 %
Results
- Available Real Power
- 76.000 kW
- Derated Apparent Power
- 95.000 kVA
- Full-Load Line Current
- 137.12 A
- Total Derating Applied
- 5.00%
- Reactive Capability
- 57.000 kVAR
Step by step
- 1Values used
- 2Alternator Output
- 3Available Real Power= 76.000 kW
- 4Derated Apparent Power= 95.000 kVA
- 5Full-Load Line Current= 137.12 A
- 6Total Derating Applied= 5.00
- 7Reactive Capability= 57.000 kVAR
Assumptions and limits
- The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax or compounding frequency into account.
- Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Alternator Output calculated?
Available kW = nameplate kVA × (1 − derating) × power factor Generators are rated in kVA at a reference temperature and altitude. Both hot ambient conditions and thin air at altitude reduce cooling capacity, so the usable rating falls before power factor is even considered.
Why does Alternator Output matter?
A 100 kVA set in a hot plant room may deliver only 76 kW, which is why generator sizing so often disappoints on commissioning.
What values do I need to enter?
This calculator takes 5 inputs: Nameplate rating, Load power factor, Line voltage, Derating for ambient temperature, Derating for altitude. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.