The Diseases Of Electrical Machinery

30 THE DISEASES OF commutator, to reconnect the winding with the ends of the sections reversed, as shown in Fig. 9. Nothing can be said against this method of connection. It is quite correct in itself; but still the machine will not generate any current unless either the direction of Fig. 9. Fig. 10. rotation of the machine is altered, or else the two ends of the magnet-winding are reversed. This case is not bad ; but it might happen, for example, that only one coil was incorrectly connected, as shown in Fig. 10. This coil will now generate a reversed electromotive- force and lower the voltage of the machine. Faults in the Magnets.—We now pass over to those faults in continuous-current machines which are principally caused by faults in the winding of the magnets. Here a wrong connection is by no means too rare. Everyone knows that in the case of a bi- polar machine, one pole should be a north-pole and the other a south-pole. Which of the poles should be north and which south depends upon the method of connection of the armature with the commutator, and upon the direction of rotation of the machine. Wrong Connection.—When, therefore, a con- tinuous-current machine does not give its voltage (at any rate when starting up for the first time), this fault is the most probable one, namely, that the two poles