Specifications

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Dynamic balancing : Dynamic balancing machines are available to balance the armature or
rotating the arts of electrical machines. The armatures are fixed on those machines and rotated
at the rated seed. A pointer or an indicator shows the position on the armature and the weight to
be added. The balancing machines available are either with the mechanical balancing or with
the stroboscopic balancing.
6.3 TESTING OF ARMATURE: After an armature is wound and the leads are connected to the
commutator, a test should be conducted. From this test, defects may be revealed, which might
have occurred during winding.
The common defects in armature windings are grounding, shorts in the coils, open in the
coil and reversal in the coil connection. These defects can be located by different test procedures.
Armature winding resistance test : Resistance of the armature coils measured by using a
low range ohmmeter and preferably with the Kelvin bridge. Resistance between consecutive
segments in the case of simplex la winding (for wave and multiplex windings at a distance of
commutator itch Yc) is measured.
Fig. 6.13 shows a simple arrangement to measure the resistance between the successive
commutator segments. As shown in this Figure, a cotton tape with a counterweight is passed
around the commutator to hold the connecting leads to the segments.
Fig. 6.13
Measurement of resistance is done in all the coils by changing the position of the connecting
leads to successive commutator segments. The resistance measured should be the same in
all coils. Lower resistance shows short in turns, while a higher resistance shows higher numbers
of turn or open in the coil.