CHAPTER SIX - D.C. Generators

Abstract

This chapter discusses the functioning of d.c. generators. Operation of a d.c. generator relies on the principle that when magnetic lines of force are cut by a conductor, a voltage is induced in the conductor. Size of induced voltage and resulting current are dependent on magnetic field strength, length of conductor, and speed of cutting. The direction of current flow is dictated by the relationship between magnetic field and direction of movement of the conductor. A simple generator can be constructed from a loop or coil of wire mounted on a spindle and arranged for rotation between opposite magnetic poles. The field-cutting action of the straight sides will cause current flow as the result of induced voltage. The voltages generated are in series and, therefore, add to give twice the voltage produced in one side. Direct current can be collected from the wire ends through the commutator that consists of two half-rings with brushes. A practical direct current generator has a large number of conductors that are caused to rotate in the magnetic field. The magnetic poles of a d.c. generator are magnetized iron cores with superimposed windings. The residual magnetism of the cores is essential to the initiation of current generation. When the generator is started, the rotating armature windings have current induced in them only because they cut through the weak fields produced by residual magnetism in the iron cores of the poles.