The Diseases Of Electrical Machinery

ELECTRIC AL MACHINERY. 5 ture the two sides of a winding are not at an angle of i8o° to one another (fig. i), but are wound with a shortened pitch, so that the angle which the two sides Fig. i. Fig. 2. of a coil build one with another is only a little larger than the angle subtended by the pole piece (fig. 2). With this type of armature the brushes must not be placed in the middle between two poles, but must be moved a considerable distance doser to one pole tip. It is therefore necessary, since the type of winding can but rarely be seen from the finished armature, to place the brushes according to the mark which is placed by the maker on the brush gear of almost every machine Most modern machines are provided with one mark only. This is because the same position is correct for both no load and full load. It is usually necessary, at any rate for motors, to specify that this should be the case. Machines of earlier date, however, were pro- vided with two marks—one for no load and the other for full load. It should be noticed that for dynamos the brush-holder must be shifted in the direction of rotation with increased load to give them a forward lead, while for motors the brushes must be moved in the opposite direction, giving them a backward lead.