ABSTRACT

This chapter discusses the direct current (d.c) machines; their construction form, principles of operation, operating characteristics and general applications. A machine may be a motor or a generator. As a motor it converts electrical power to mechanical power while as a generator it converts mechanical power to electrical power. The basic D.C. electrical machine consists of a single coil which is free to rotate within the magnetic field provided by a permanent magnet. Coils of wire are mounted in slots on a cylinder of magnetic material called the armature which is mounted on bearings and free to rotate. It is mounted in the magnetic field produced by field poles. The speed of a permanent magnet motor depends on the current through the armature coil and can be controlled by changing the armature current. With a constant D.C. supply, voltage is chopped by means of an electronic circuit so that the average value is varied, called as pulse width modulation (PWM).