Energy Processing and Smart Grid

CHAPTER 5INDUCTION MACHINES

5.1 INTRODUCTION

Induction machines are the most common form of electromechanical energy-conversion devices for industrial, commercial, and domestic appliances that operate at constant speed. The need for energy processing and conversion from electrical to mechanical energy to do mechanical work abounds in every sector of human endeavor. About one-third of the world's electricity consumption is used for running induction motors that drive pumps, fans, compressors, elevators, and machinery of various types to meet industrial, commercial, and domestic needs.

The AC induction motor is a common form of asynchronous motor whose operation depends on three electromagnetic phenomena:

1. Motor action. When an iron rod (or other magnetic material) is suspended in a magnetic field so that it is free to rotate, it will align itself with the field. If the magnetic field is moving or rotating, the iron rod will move with the moving field so as to maintain alignment.
2. Rotating field. A rotating magnetic field can be created from fixed-stator poles by driving each pole pair from a different phase of the AC supply.
3. Transformer action. The current in the rotor windings is induced from the current in the stator windings, avoiding the need for a direct connection from the power source to the rotating windings. Consequently, the induction motor can be considered an AC transformer with a rotating secondary winding.

5.2 CONSTRUCTION AND TYPES OF INDUCTION MOTORS

The ...