IEC Impedance and X/R Calculations

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%.

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.

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