Generator load and motor-start sizing calculator

Preliminary estimate

Inputs

Load 1
Load 2
Load 3
Calculation note

The starting screen uses the largest entered starting kVA while other loads remain at running kVA.

Method

Running kVA = sum(running kW / running PF)

Starting kVA screen = running kVA - selected motor running kVA + selected motor starting kVA

Required kVA = max(running kVA, starting kVA screen) x (1 + margin percent / 100)

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Formula variables

  • Running kW is the expected steady load for each row.
  • Running PF converts each row from kW to kVA.
  • Starting kVA is the entered motor or equipment starting requirement.
  • Generator PF converts recommended kVA to a kW context value.

Assumptions

  • Running kVA is calculated from each load kW and running power factor.
  • Starting kVA screen uses the largest entered starting load while other loads remain at running kVA.
  • Margin is applied to both running and starting kVA before the larger requirement is selected.
  • Generator manufacturer sizing, transient response, voltage dip, fuel type, altitude, temperature, and standby-system rules are outside this screen.

Examples

600 V generator screen. A 39 kW load set with one 75 kVA starting load screens to about 116.51 kVA required after 15 percent margin, so the next standard value is 125 kVA.

Starting-load workflow. Use the largest realistic starting scenario first, then confirm voltage dip and transient response with generator manufacturer tools.