TABLE OF CONTENTS Rotating machines covers the whole spectrum of generators and motors of all types. They span the range from fractional horsepower motors to 1500-MVA generators with the family characteristic of a rotating shaft from which mechanical power is extracted or into which mechanical power is supplied. This chapter will examine some of the common characteristics of both generators and motors as they concern power electronics.
In these days, most prime movers for generators are rather nondescript turbines of one sort or another combustion, steam, or hydraulic, or even wind. The author was fortunate enough to have seen reciprocating steam engines powering generators. In a memorable field trip by the YMCA in Minneapolis to a local factory, the group saw a large Corliss steam engine in operation, replete with a polished brass flyball governor, a huge flywheel painted bright red, and a melange of awesome mechanical motions. It made a lasting impression on a ten-year old visitor.
DC motors and generators were the earliest entries in the transformation of industry from steam to electric power. This machine type consists of a stationary set of windings that provide a magnetic flux and a rotating set of armature windings that turn within this field. A commutator with brushes on the rotating windings maintains the torque in a constant direction with rotation. The torque produced is proportional to the flux, and the speed is inversely proportional to the flux. At constant field current, the speed is proportional to the armature voltage.
