Represents the combined voltage-and-current capacity of the electrical system without converting it to useful real power.
MFG POWER · ENGINEERING & SPECIFICATION
kW vs kVA
Understand what each rating means, how power factor changes the relationship, and why two generators with the same kVA can still be different buying decisions.
The formula is simple. The buying decision is not. A useful comparison starts with the rating basis, power factor, duty and real load.
01 / WHAT THE RATINGS MEAN
kVA IS APPARENT POWER. kW IS REAL POWER.
For generator buying, both numbers matter because the alternator and engine are not being described in exactly the same way.
Represents the portion of electrical power that can perform useful work at the stated power factor.
Describes the relationship between real power and apparent power. It is part of the comparison basis, not a decorative number.
02 / WHY 0.8 PF APPEARS SO OFTEN
0.8 POWER FACTOR IS A COMMON GENERATOR RATING BASIS — NOT A UNIVERSAL LOAD CONDITION.
A generator nameplate may use 0.8 PF as its rating convention, while the actual connected load behaves differently.
Generator ratingOften expressed with an assumed 0.8 lagging power factor for the rated kVA/kW relationship.
Actual loadMay operate at a different power factor depending on motors, UPS, VFDs, lighting, rectifiers and other equipment.
Buyer riskUsing one assumed PF for every load can make sizing and quotation comparison misleading.
03 / THE SIMPLE MATH
THE EQUATION CHANGES WITH THE POWER FACTOR.
AT PF 1.0
100 kVA = 100 kW
Unity power factor means all apparent power is converted to real power.
AT PF 0.8
100 kVA = 80 kW
This is the common generator example most buyers recognize.
AT PF 0.7
100 kVA = 70 kW
The same kVA now corresponds to less real power.
Buying rule: never compare kVA and kW without checking the stated power factor and rating basis.
04 / LOAD TYPE
THE LOAD CAN CHANGE THE ELECTRICAL BEHAVIOR.
Power factor is not the only issue. Starting current, harmonics and transient behavior also affect generator selection.
MotorsStarting current can be much higher than running current, and PF changes with operating condition.
UPS / rectifiersNonlinear current can increase harmonic and alternator demands even when headline kW looks acceptable.
VFD loadsDrive characteristics, harmonic content and motor starting method affect the generator response.
Heating / resistiveUsually closer to unity power factor and simpler from a kW/kVA conversion perspective.
05 / ENGINE vs ALTERNATOR
ONE RATING INVOLVES TWO DIFFERENT LIMITS.
A genset has a mechanical prime mover and an electrical alternator. A complete comparison checks whether both are appropriately matched.
The engine must provide enough mechanical power for the required real electrical output after system losses.
The alternator must carry the required current and manage voltage regulation, temperature rise and load characteristics.
A generator set should be evaluated as a matched system under the intended duty and site condition.
06 / BUYER COMPARISON
DO NOT LET “100 kVA” END THE TECHNICAL REVIEW.
CheckWhy it matters
Rated kVA / kWConfirms the headline relationship.
Power factor basisDefines how kVA was converted to kW.
Prime / standby dutyChanges the allowable generator rating.
Ambient / altitudeCan reduce engine and alternator capability.
Engine modelDetermines real mechanical capability and transient response.
Alternator modelDetermines current, regulation, excitation and thermal capability.
Load typeMotors and nonlinear loads can change sizing needs.
Test basisConfirms whether the quoted rating was actually verified under load.
07 / COMMON MISTAKES
WHERE kW / kVA COMPARISONS GO WRONG.
01Assuming 1 kVA = 1 kW
That is only true at power factor 1.0.
02Using 0.8 PF for every actual load
The genset rating convention and the actual site load are not the same thing.
03Ignoring duty rating
A standby rating and a prime rating should not be treated as equivalent.
04Ignoring motor starting
Running kW alone may not show the transient requirement.
05Ignoring derating
High temperature and altitude can reduce usable output.
06Comparing only nameplate numbers
Engine, alternator and test basis still need to be checked.
MFG BUYER VIEW
THE NUMBER IS ONLY USEFUL WHEN THE CONDITIONS BEHIND IT ARE CLEAR.
For procurement, kW and kVA should be treated as part of a rating system rather than as isolated numbers. The useful question is not only “what is the rating?” but also “under what power factor, duty and site condition?”
MFG POWER compares the rating basis together with the engine, alternator, load type and test condition before treating two offers as equivalent.
NOT SURE WHETHER TWO GENERATOR QUOTATIONS ARE REALLY EQUIVALENT?
CHECK THE RATING BASIS BEFORE YOU COMPARE THE PRICE.
Send the quotation, datasheet or load requirement. MFG POWER can help identify whether the kW/kVA, duty, power factor and component basis are actually comparable.
Review my generator rating