The Diseases Of Electrical Machinery

ELECTRICAL MACHINERY. 21 motor starts too quickly. This is to be especially noticed with those motors which are continually start- ing and stopping. Broken armature wires should, if possible, be soldered with silver solder. In urgent cases the two segments, between which the broken coil lies, may be short-circuited by driving in temporarily a small spike between the commutator segments at the lugs, or by dropping a small drop of solder between them. This is, however, only permissible when the commutator has a large number of segments, and at best it is only a temporary remedy. Bad Centering of the Armature.—While in the case of two-pole machines bad centering of the armature between the poles (so that it is nearer to one pole than the other) has no effect on the sparking, yet this can cause much trouble with multipolar machines. For example, most four-pole machines (except tramway motors and small motors) are con- nected so that in the armature winding there exist four parallel circuits. Incorrect centering will, in this case, cause the voltages in the four parallel circuits to be unequal. This generates a flow of internal balanc- ing currents, and causes uneven loading of the four different circuits, resulting in sparking; and, in certain cases, resulting also in a rapid and strong heating of the armature, even at times when the external circuit is open. In the case of those bipolar machines that have