IEC Impedance and X/R Calculations

Option Descriptions

Model

Motor Type

Impedance and X/R Calculations

Individual

Induction without AFD

1) Calculate the MW per pole-pair by dividing MW by pole-pairs.

  • MW is the rated output MW for the motor.
    • Metric: MW = rated kW for motor / 1000.
    • U.S: MW = HP * 0.746 / 1000.
  • Pole-pairs = system frequency * 60 / motor sync RPM (from the Specifications tab.)

2) Calculate the X/R ratio of the motor.

  • If the motor kV is greater than 1.0 and the MW per pole-pair is greater than or equal to 1.0, then X/R is 10.0.
  • If the motor kV is greater than 1.0 and the MW per pole-pair is less than 1.0, then X/R is 6.667.
  • If the motor kV is less than or equal to 1.0, the X/R ratio is based on the ANSI calculations.

Impedance is 16.7%.

Group

Induction without AFD

Impedance and X/R are calculated as follows:

  • If motor kV less than or equal to 1.0, then impedance is 20% and the X/R ratio is 2.381.
  • If the motor kV is greater than 1.0 and MW per pole-pair is greater than or equal to 1.0, then impedance is 16.7% the X/R ratio is 10.0.
  • If the motor kV is greater than 1.0 and the MW per pole pair is less than 1.0, the X/R ratio is 6.667.

Individual or Group

Induction with AFD

DC with AFD

Impedance is 16.7% and the X/R ratio is 10.

Individual or Group

Synchronous

Synchronous Condenser

Uses the ANSI default calculations for impedance and the X/R ratio.

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