Generator Parameter Calculator

Turn generator nameplate and manufacturer data into the parameters used for power system studies. Calculate full load amps, per-unit resistance, X/R ratios, and DC time constant.

What are generator parameters used for?

Generator parameters can be used to model generator characteristics on a time-current characteristic (TCC) plot and to calculate the generator's fault contribution for arc flash and equipment duty studies. Typical TCC elements:

Full load amps
Overload curve
Short-circuit withstand capability point
Short-circuit decrement curve

Generator Parameter Calculator

Enter the available generator manufacturer's published/nameplate data in boxes 1 and 2 to calculate the values to the right.

1. Generator rating

kVA, kW & power factor

Select Calculate for one value to be calculated from the other two. Leave all three unchecked to enter every value manually.

Rated kVA Calculate

Rated kW Calculate

Power factor (0 < PF ≤ 1) Calculate

Rated 3-phase L-L voltage (V)

Frequency (Hz)

Connection

2. Impedance and reactance

Reactance base (kVA) Same as rated kVABase kVA of the below reactance values.

Ra (Stator resistance)

Ra already given in puChanging units clears the entry.

X″d — subtransient (pu)

X′d — transient (pu)

Xd — synchronous (pu)

X₂ — negative sequence (pu)

X₀ — zero sequence (pu)

3. Additional manufacturer data

Optional inputs for reference only. No impact to calcuated values to the right.

Td″ — subtransient time (ms)Direct-axis short-circuit time constant.

Td′ — transient time (ms)Direct-axis short-circuit time constant.

Referenced ambient (°C)

Allowable temperature rise (°C)

Example based on: CAT 3.0 MW generator data sheet.

Formulas and calculation basis

Full load amps: FLA = rated kVA × 1,000 / (√3 × V_LL)
Rating conversions: kW = kVA × PF
kVA = kW / PF
PF = kW / kVA
Base impedance: Zbase = V_LL² / (base kVA × 1,000)
Per-unit stator resistance: For a Wye line-to-line entry: Ra (Ω/phase) = Ra (Ω L-L) / 2
Ra (pu) = Ra (Ω/phase) / Zbase
When Ra is entered in pu, it is used directly.
X/R ratios: x/r (subtransient) = X″d (pu) / Ra (pu)
x/r (neg sequence) = X₂ (pu) / Ra (pu)
x/r (zero sequence) = X₀ (pu) / Ra (pu)
DC time constant: Tdc (ms) = X″d (pu) / (2π × f × Ra (pu)) × 1,000

V_LL is rated line-to-line voltage in volts, f is frequency in hertz. The base kVA is three-phase apparent power. Resistance and reactance must be on the same base. Changing the base kVA does not convert the entered reactances, use the published manufacturer's data.

X′d, Xd, Td″, and Td′ can be used to approximate the generator decrement. The Tdc result above describes DC decay using x/r (subtransient). This page calculates parameters, not overload or decrement curves, withstand limits, incident energy, or equipment duty.

Manufacturer data sheets specify the rating and voltage bases for per-unit reactances . See the CAT 3.0 MW generator data sheet used for the calculator example. Its 9.0E-4 Ω stator resistance is entered as 0.0009 Ω/phase for the SERIES STAR connection.

Evaluate your generator source contributions

Power System Calcs provides short circuit studies, protective device coordination studies, and arc flash studies for commercial, industrial, and mission-critical facilities.

Request a quote