Using Option 4 of the IMC Program

SimPhase Induction Motor Calculations (IMC) program has 4 options.

Options 3 and 4 calculate the steady-state running conditions of an three-phase induction motor.

Option 3 corresponds to conventional motor calculations. The slip is known before the calculations (or it can be calculated because we know the speed).

With option 4 :

  • If the motor has no variable frequency drive (VFD) speed control : Steady-state conditions are calculated for your combination of terminal voltage and frequency. Both the motor speed and the motor slip can be unknown before the calculations.
  • If the motor has a variable frequency drive (VFD) speed control : The steady-state conditions are calculated for any value of motor speed you specify.

Option 4 uses the information about the mechanical load you defined for this motor.

Let’s do three simulations with option 4. Same three simulations with the same motor are done in this video

The same 25 HP, 460 Volts, 1500 RPM (50Hz) three-phase induction motor and the same mechanical load are used in all 3 simulations.

Simulation 1 : What are the running conditions of the motor if it is 80% loaded with the terminal voltage equal to 100% of its rated value ? The motor has no speed control. Both the slip and the speed are unknown before the calculations.

Because both the slip and the speed are unknown we cannot use conventional calculations. Option 4 can do the calculations for us.

Image 1 shows the running conditions calculated by option 4.

Image 1 Simulation 1 results

Simulation 2 : Same motor and same mechanical load. No speed control. Let’s assume that the load torque is proportional to the square of the speed (the load could be a water pump). What are the conditions of the motor if the terminal voltage amplitude falls to 90 % of its rated value ?

Image 2 has the results.

Image 2 Simulation 2 results

Simulation 3 : Same motor and same mechanical load. But now the motor has a variable frequency drive (VFD) speed control. What are the steady-state running conditions if the motor speed is set equal to 1000 rpm ?

Image 3 has the calculated conditions.

Image 3 Simulation 3 results

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