Armature winding and motor repair; practical information and data covering winding and reconnectig procedure for direct and alternating current ... and repair of motors and generators in indu

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1920 Excerpt: ... out" between the same points with an ordinary 110-volt lighting circuit test lamp. They are comparatively simple to locate and easy to repair by the use of insulating material used with the job. Short circuits of a few turns or a single coil become hot in a short time if the motor is run light on normal voltage. Their presence can be detected by feeling around the winding with the hand immediately after starting the machine and noting if any coils are much warmer than others. Short-circuit Detecting Device.--A device that can be used for detecting short circuits before the rotor is placed in the stator and without applying voltage to the winding itself, is shown in Fig. 158. It it somewhat similar to a large horseshoe magnet except that the iron part is built up of laminations. It may also be considered a core-type transformer having the primary coil only and having one side of the iron core missing. The coil is excited with alternating current of a suitable voltage and then the complete device is passed slowly around the bore of the-stator as shown in Figs. 159 and 160. The laminations of the stator core complete the magnetic circuit of the testing device and an alternating magnetic field flows in the stator core as shown by the dotted lines in Fig. 159. When moving the device around the stator bore, and it passes over a short-circuited turn or coil, such short-circuited turn or coil immediately acts as a short-circuited secondary coil on a transformer of which the exciting coil on the testing device is the primary. As in any short-circuited transformer an increased current flows both in the primary and in the secondary coil and can be detected by an ammeter in series with the device or by the heating which immediately takes place in the defective co...