Page 236 - CITS - Electrician - Trade Practical

ELECTRICIAN - CITS

EXERCISE 92 : Demonstrate Impregnations, Varnishing,

Baking & Assembling

Objectives

At the end of this exercise you shall be able to
• demonstrate varnishing of rewound three phase induction motor stator
• demonstrate assembling of rewound three phase induction motor.

Requirements

Tools/Instrument Tools/Instrument
• SEC cu wire - 400g. • Winding former
• Electric soldering iron 25W/240V - 1 No. Materials
• Hack saw blade - 1 No. • Soldering paste - 10g.
• Standard wire gauge
• Resin core solder 60:40 - 50g.

Procedure

TASK 1: Demonstrate varnishing of rewound three phase induction motor stator
1 Connect between coils, poles of the rewinding completed motor
2 Connect leads to terminal box and tie
3 Place the stator in baking oven at a temperature of approximately 250°F and preheated for approximately 1
hour to remove moisture from the windings and increases the perpetration of the varnish.
4 Dip the stator is then dipped in to a container of insulation varnish compatible with the type of wire used.
5 Loosen the varnish by thinner to penetrate the same in winding
6 Monitor the thickening of varnish and control thickness by thinner
7 Soak the winding in the varnish for approximately one-half hour or until all bubbling has ceased
8 Remove stator from the dip container and allow varnish to drip.
9 Place the stator on baking oven after varnish stopped for 8 hours or as recommended by the varnish
manufacturer
10 Scrap the inner surface of stator to remove the adhering varnish, and to maintain clear airgap
11 Use solventless polyester varnish /resin alternatively that can be applied to windings in less than 20 minutes.

12 The resin is then poured through the heated
windings while the stator is kept in a horizontal
position the resin is permitted to trickle through the
slots.
13 Heat the winding is by applying half the rated
voltage and sending current through winding.
14 Clean the motor parts by compressed air / blower
15 Test the winding by internal growler

TASK 2: Demonstrate assembling of rewound three phase induction motor.
1 Reassemble the motor in reverse of the dismantling sequence
2 Ttest the insulation resistance and winding resistances and record
3 Test the motor and run it for approximately 6 hours.

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