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GENERATOR SIZING GUIDE

How to choose the right diesel generator size

Correct generator sizing protects reliability, fuel efficiency and power quality. The connected kW is only the starting point: motor starting, power factor, load steps, phase, harmonics and operating duty can all change the required generator capacity.

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kW
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kVA
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PRP / LTP
Select the correct duty

IN THIS GUIDE

01Convert the site load from kW to kVA02Allow for motors and starting current03Include site and future requirements

01

Convert the site load from kW to kVA

Generators are commonly rated in kVA while electrical equipment may be listed in kW. For a simple balanced load, kVA equals kW divided by power factor. A 100 kW load at 0.8 power factor is therefore 125 kVA before starting currents, load steps or engineering margin are considered.

02

Allow for motors and starting current

Motors, pumps, compressors and refrigeration equipment can draw several times their running current while starting. Direct-on-line starts usually create a larger demand than star-delta, soft-start or variable-speed arrangements. The largest starting event and sequence should be checked against generator voltage-dip performance.

  • List each load in kW, kVA or amps
  • Identify single-phase and three-phase equipment
  • Record the largest motor and its starting method
  • Separate essential loads from loads that can remain off
  • Confirm whether the duty is standby or prime

03

Include site and future requirements

Altitude, ambient temperature, non-linear loads, uneven phase loading and planned expansion can affect the final selection. Avoid adding an arbitrary percentage without understanding the load: too small risks unstable power, while excessive oversizing can increase cost and lead to poor diesel-engine loading.

BUYER QUESTIONS

generator sizing guide FAQs.

Clear starting points for specifying a dependable Ferbo power solution.

How do I calculate generator kVA from kW?

Divide kW by the expected power factor. At a power factor of 0.8, 80 kW equals 100 kVA. Starting loads and other project factors must then be assessed separately.

Should I size from the prime or standby rating?

Use the rating that matches the intended duty. Select from prime power for regular operation and from standby power for emergency operation within the manufacturer's stated limits.

Is a larger generator always better?

No. An undersized generator can struggle with load steps, but a substantially oversized diesel generator can operate too lightly. The best selection matches both the running and starting load profile.

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