Page 217 - CITS - Electrician - Trade Practical

ELECTRICIAN - CITS

EXERCISE 87 : Test burnt out DC machine for re- winding

Objectives

At the end of this exercise you shall be able to:
• test the armature for short in the coil with an external growler
• test the armature for open in the coil with an external growler.
Requirements

Tools/Instruments Materials
• Armature winding stand - 1 No • Soldering paste - 10 g
• Electric soldering iron 25W/240V - 1 No • Resin core solder 60:40 - 50 g
• Hack saw blade - 1 No
Equipment/Machines
• External growler 240V, 50HZ - 1 No
• DC armature - 1 No

Procedure

TASK 1 : Short circuit test

1 Place the armature on the yoke of the growler.
2 Switch ON the growler.
3 Hold the hacksaw blade over the top of the slot and along the length of the armature.
4 Rotate the armature slowly and observe the hacksaw blade vibration and growling noise.

5 Vibration of blade and growling noise indicate short in the coil.

TASK 2: Open circuit test
1 Connect the AC Milli- voltmeter /Ammeter (normally provided with growler) leads to the top two adjacent
segments keeping the growler switch ON.
2 Rotate the armature and continue testing all the adjacent commutator segments.
3 The low value of readings shows short in between the armature coils.

While rotating the armature the geometrical position of the test leads should not be changed for
subsequent testing.

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