THE DYNAMO. E. M. F. and output of the dynamo is usually regulated by varying the strength of the magnetizing current (produced by the dynamo or battery D) flowing in the coils of the field magnet by means of the hand regulator R. FIG. 63. B D WINDING FOR SEPARATELY EXCITED DYNAMO. NOTE-In the above illustration, as also Figs. 60, 61, 62, the external cir cuit is intended to represent a series of lamps in process of receiving the current. THE ARMATURE. The armature should always be considered as a cylindrical magnet having poles in opposite sides of its periphery, and the whole mass of the armature in what is known as the magnetic flux of the field. The armature is placed where it will be in the strongest magnetic flux and the iron core of the armature acts as a stepping stone between the poles of the field. It is because of this intermediate mass of iron that the flux is so strong. NOTE.-There are several ways of arranging the coils upon the armature, and the methods adopted may be classified as follows: :. Drum Armatures, in which the coils are wound longitudinally upon the surface of a cylinder or drum. Examples: the Siemens and Edison machines. 2. Ring Armatures, in which the coils are wound around a ring Ex amples: Gramme and Brush machines. THE ARMATURE. The types of armature in most extensive use at the present time are the following:: The Ring or Gramme Armature, in which the coils are arranged upon an iron ring. The Drum or Siemens Armature, in which the coils are arranged upon the surface of an iron cylinder or drum. Each of these forms of armature has its special advantages, and in a general way it may be said that whilst the ring armature is more suitable for generating small currents at high potentials, the drum is better adapted for producing moderate potentials and large currents. |