ABSTRACT
Induction machines are of robust construction and relatively low manufacturing cost. Induction machines are more economical than synchronous machines. For high power applications, this difference is less perceptible because those units are custom made. However, for medium and small sizes, the difference in price is dramatic, as much as 80%. For the same kVA rating, though, induction machines are larger than synchronous machines because their magnetizing current circulates through the stator winding. Induction generators connected to the grid need no voltage regulation, less constraints on the turbine speed control, and practically no maintenance. These advantages plus the fact that induction machines are readily available from several manufacturers, make them very competitive for just-in-time installation. The U.S. National Electrical Manufacturers Association (NEMA) has standardized the variations in torque-speed characteristics and frame sizes, assuring physical interchangeability between motors of competing manufacturers, thereby making them a commercial success and available for integral horsepower ratings with typical voltages ranging from 110 to 4160 V. As discussed in Chapter 2, the only perceived weaknesses of induction machines are lower efficiency — the rotor dissipates power — and the need for reactive power in the stator. This chapter will discuss the physical construction of various types of induction machines, emphasizing their features in generator mode.
