The Diseases Of Electrical Machinery

32 THE DISEASES OF The Order of the Poles in Multipolar Ma- chines.—In four-pole machines the poles that are opposite one another must be of the same name, so that a north-pole always shall follow a south-pole. Whatever be the number of poles, adjacent poles must always be of different polarity. A fault in this respect affects the working of the machine, the more the greater the number of wrongly connected poles, and the less the total number of poles. The results of wrongly connected poles are (i) too low armature voltage, (2) heavy sparking, (3) internal currents in the armature winding, resulting in heating. Fanit in the Magnet Winding.—A further fault may lie in a complete break in the field-magnet wind- ing, so that no current can flow in the coils, and then no voltage can be produced. In early machines one often found that, though the coils in themselves were properly wound, the ends of the wires were very care- lessly brought out Good mechanical ways of bring- ing out the ends of the winding were neglected until the last few years. The usual part to break is the beginning of the winding of a coil. Any break occur- ring at this point is most troublesome, since one must then usually unwind the whole coil to get at the broken part. Because of this, it is worth while to use for the commencement of a magnet coil a piece of thin flexible cable made of stranded copper wires, and to wind this several times round the coil before soldering it on to the wire with which the coil is to be wound. Above