Page 227 - CITS - Electrician - Trade Practical

ELECTRICIAN - CITS

7 Measure the insulation resistance every hour during the heating period to note a fall in IR value and recovery
by end period.
8 Cool down armature to approximately 60-degree Celsius.
9 Select the varnishing method as dipping or pouring with spoon based on the size of armature.
10 Dip the rotor vertically with commutator segments upside to a container of insulation varnish compatible with
the type of wire used.
11 Loosen the varnish by thinner to penetrate the same in winding
12 monitor the thickening of varnish and control thickness by thinner
13 Soak the winding in the varnish for approximately one-half hour or until all bubbling has ceased.
14 remove armature from the dip container and allow varnish to drip.

TASK 3: Bake the rewound armature
1 place the armature on baking oven after varnish for 8 hours or as recommended by the varnish manufacturer
2 measure the insulation resistance of armature and cool to about 60-degree Celsius.
3 Repeat steps from 11-16 for second impregnation.
4 scrap the surface of armature to remove the adhering varnish, and to maintain clear airgap
5 use solventless polyester varnish /resin alternatively that can be applied to windings in less time.
6 check the armature for balance in a dynamic balancing machine / static balancing machine. The rotated
armature will stop at different position, if balanced. Apply small seal non-conducting paste to balance and
retest.
7 Assemble armature to the rotor and test run it with load.

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CITS : Power - Electrician & Wireman - Exercise 89