1.5.2
Armature
It is the rotating member of the
motor, consisting of a number of cop-
per conductors suitably placed and
connected so as to form a closed
winding. The armature consisting of
slots, teeth, winding and the core is
shown in figure 1.5. The rotating ar-
mature is subjected to an alternating
flux varying at frequency of 20 to 50
Hz, depending upon the number of
poles and speed (f= PN/120), which gives rise to eddy currents and hysteresis
losses in the armature core and teeth. The eddy-current loss is directly propor-
tional to the square of the thickness. Therefore the armature is built up of 0.4 to
0.5 mm thick magnetic steel laminations, insulated from one another by a thin
layer of class `H’ varnish. The punching are keyed to armature shaft. Longitudi-
nal ventilating ducts are provided in the core to improve the cooling.
Assembled hot in a press, the laminations are maintained by a cast steel
armature head at pinion end, and at other, by the cast steel armature sleeves
retained on the shaft by set ring and retaining ring at pinion end.
1.5.2.1
Armature Winding
It is composed of high conductivity electrolytic copper conductor, with 2/3-
tape kapton, bunch insulation being made by:
■
Glass mica silicon tape on the involute portion.
■
Nomex silicon mica wrapper in the slot portion.
The coils are maintained in the slots by moulded “Durestos” slot wedges or
laminated fibreglass slot wedges and by poly glass tape. The Choice of
armature winding is decided as following:
■
When the armature current is not high, a simple wave winding is preferred.
But for high armature current, number of parallel path should be more, as a
result lap winding is preferred because number of parallel path equals to
number of poles.
