Question

Preparation (Pre-Lab) It is expected that the students have read and understood the textbook chapter and reviewed the lecture notes module corresponding to the AC Induction Machines. In particular, the students should be familiar with the theory and principle of rotating magnetic field, principle of operation of induction machines, procedures to determine the equivalent circuit parameters, and basic torque-speed characteristics. In addition, the students should review the material on motor control using the variable frequency 3-phase AC inverter. The Pre-Lab page should include the following:

- Prepare a list of equations for calculating the equivalent circuit parameters using the Blocked-Rotor and No-Load Tests.
- Write down the expression for the torque-speed characteristic at 60 Hz fixed frequency and constant voltage magnitude. Q. Juri Jatskevich 2020 1
- Assume an inductor (a magnetizing branch of the induction machine or a transformer) under sinusoidal AC excitation. Write down an expression for the magnitude of the flux in terms of voltage and frequency. Write a sentence to rationalize why the voltage and frequency should be adjusted together for the Variable Frequency Drive applications.

Answer 1

The magnitude of flux in an inductor or transformer can be expressed as (Voltage amplitude * Angular frequency * Inductance) / (2 * π). Adjusting voltage and frequency together in Variable Frequency Drive applications enables control of the speed and torque of the induction machine.

Step-by-step explanation:

The magnitude of the flux in an inductor or a transformer under sinusoidal AC excitation can be expressed as:

φ = (Voltage amplitude * Angular frequency * Inductance) / (2 * π)

The voltage and frequency should be adjusted together for Variable Frequency Drive (VFD) applications because the frequency affects the rotational speed and the voltage affects the torque. By adjusting both the voltage and frequency, the VFD can control the speed and torque of the induction machine.