The Diseases Of Electrical Machinery

28 THE DISEASES OF In order to explain this fault, we will represent the State of affairs diagrammatically in the following way : r~ Figs. 4-7. In all these figures the dotted lines represent the points where a short-circuit is present. In Figs. 4-7, we see a commutator diagrammatically represented with all its segments and the armature winding (twelve segments—one segment represented twice over). In one coil there is a short-circuit. We then see from Fig. 4 that this coil will take no part in the work of the machine, since it constitutes, in itself, a closed Circuit. Since in this coil, however (if the machine is separately excited, or is run as a motor), an E.M.F. will be generated, and since the coil is short-circuited, a very heavy current will result, and this coil will be- come heated. In Fig. 5 we have represented two adjacent seg- ments joined together. This will obviously have the same result as the above. The coil which is connected to the two segments is short-circuited, and therefore, when rotated in a magnetic field, a strong current will be induced in it. If the two faults do not occur in one coil but in two separated coils or commutator segments (this last can occur only through the two segments being in con-