A notable feature of induction motors, including polyphase motors, is their very simple construction, which illustrates two dismantled 3-phase induction motors. Their being relatively inexpensive and needing little maintenance as well as their being operable directly from the 3-phase mains supply without needing intermediate circuitry has led to the widespread use of induction motors. In this chapter, the operation, performance and applications of 3-phase and single-phase mains-energised induction motors are discussed. In addition, a fundamental consideration is given to the rules concerning rotating and alternating fields, to their generation in polyphase windings and to their function in induction motors.

Millions of shaded-pole induction motors are made every year, with power ratings from a fraction of a watt to about 150 W. Applications are generally in small electrical appliances that require only a few watts of power, e.g. for driving heater fans or slide projector fans. In the household appliance market shaded-pole motors are used in washing machines as discharge pump motors and in cookers as fan motors in large quantities. In ironing machines, these motors are used with reduction gearing for driving the rollers. The direct drive to the drum of a washing machine for spinning has become a classical application for larger twoor four-pole shaded-pole motors with power ratings from 60 to 150 W. The motor is also used in vending machines for driving the fans and in combination with gearing and linkages for selecting and delivering the goods. The construction of the shaded-pole motor is simple, particularly with respect to the windings. Large quantity production and extensive automation results in a favourable price per unit, and the shaded-pole motor often offers the most cost-effective solution to a drive problem. Their disadvantages compared with, say, capacitor start and run motors should be considered, however namely their low efficiency and very often their unfavourable torque-speed characteristics.

Universal motors are commutator machines. They may be driven from AC or DC mains. Their speed of rotation is limited only by the mechanical strength of the rotor and the bearings and the useful brush lifetime. Universal motors driven from single-phase AC mains run at speeds from 3000 rev/min to 25 000 rev/min and have powers up to 1200W. The less expensive induction motors are limited in speed by their operating principles and the mains frequency. In the following pages the construction, operation, performance and application possibilities of the universal motor are discussed.

Controllable electrical drives are now almost without exception driven electronically. The continuing development of new components, as well as the steady reduction in the cost of electronics, gives the development engineer many possibilities for optimising his drive designs.

There are several types of stepper motor currently available, with permanent magnet or soft-iron rotors, and there are hybrids. Permanent magnet stepper motors have found the widest application because they have good dynamic and static characteristics and a relatively high efficiency. Also, they have a static holding torque when not energised, which the soft-iron rotor motor does not have. A further advantage is that they have good damping. Therefore the following discussion is limited to stepper motors with permanent magnets and to hybrid motors. The characteristic property of the stepper motor is the step-by-step turning of the motor shaft. One complete turn of the shaft is made up from an exactly specified number of steps, which is determined by the motor design. This property meets the requirement for operating directly from digital signals. The stepper motor can thus be the bridge between digital information and incremental mechanical displacement. If a stepper motor drive is to be secure and interference-free, certain fundamental points must be taken into account.

An electric motor, with its magnetically generated parasitic torques, magnetostriction, radial forces of attraction, rotor imbalance and turbulent air flow, is a source of noise and vibration which is transferred via its mountings and couplings to its surroundings. Reduction of vibration transfer and noise propagation in a drive is seen as a figure of merit. It is therefore necessary as a part of quality assessment and control to measure noise and vibration. The following discussion will therefore concentrate on the definition of sound field quantities, oscillation measurement, noise measurement, vibration excitation and propagation, and also vibration and noise reduction.