The Diseases Of Electrical Machinery

ELECTRTCAL MACHINERY. 25 may serve. If heavier currents are on hånd from some supply system, an incandescent lamp or, better, a volt- meter may be used. The following is then the process for finding the position of the short-circuit. The machine is discon- nected completely from the leads. The main leads and the shunt leads are therefore removed from the terminal board. The brushes are lifted off, and the customary connection on the terminal board between one pole of the armature and the field winding is removed. One wire from the galvanoscope is pressed upon the frame, that is on the iron, taking care that the end of the wire really makes a metallic contact, the other is applied to— 1. Each of the brush spindles. 2. The field terminals. 3. The commutator. If in any one of these cases the galvanoscope needle is markedly deflected, then there is a short- circuit in the part under test. If a beil is being used, the ringing of the bel! indicates that there is a short- circuit. The fault can sometimes be repaired by carefully examining the machine ; for example, in the first case, where the insulation between the spindle and the rocker is defective, or in the second, where one of the field terminals has become connected to the iron. A break in the armature cannot often be repaired on the spot; repair in the factory is usually necessary.