Emergency Generator Sizing

Three checks, the largest wins: the running load (PG1), the voltage dip when the largest motor starts (PG2), and the engine's instantaneous load while it starts (PG3).

Screening

Loads kW is shaft output for motors, input for other loads

Starting	LR / limit	Start PF



—	—	—
—	—	—

Generator

Subtransient Xd″ (%)Xd″ presetAllowable dip ΔV (%)Engine overload KRated PF

Example values. No public table gives Xd″ by rating; use the manufacturer's data sheet once a unit is chosen. Fire pumps are also checked against a 15% dip.

Result

List the loads on the generator, mark motors with their starting method, and size.

RokBench is a screening tool intended to assist qualified engineers. It does not constitute engineering services, does not produce sealed or certified deliverables, and does not replace applicable codes, standards, manufacturer documentation, or the judgment of a licensed professional responsible for the design. Verify all results independently before use. Report a problem with this result.