Page 191 - Electrician - TT (Volume 2)

ELECTRICIAN - CITS ELECTRICIAN - CITS

Fig 6

Testing of windings

Objectives: At the end of this lesson you shall be able to:
• test the rewound motor for continuity and measure the coil resistance
• test the coils of the winding for short circuit using internal growler or voltmeter or ohmmeter
• test the winding for ground and insulation resistance
• test the winding for correct magnetic polarity using a magnetic compass or screwdriver or a search coil
• test the 3-phase winding for equal value of phase currents
• test the newly wound motor under no-load.

After the motor is rewound the following tests are carried out in the windings.
1 Continuity test/resistance test.

2 Short circuit test/growler test.
3 Insulation resistance test.
4 Polarity test.
5 Unbalanced current test - for 3-phase winding.

6 No-load test.
Continuity test/resistance test : This test is done to check up the continuity of each winding. If there is any open
in the winding, it is to be rectified.

The usual cause of an open circuit in a winding is loose connection or break in the winding wire. The open circuit
may be located by connecting one lead of the test lamp to one end of the winding and touching the other lead to
the end of each coil end in sequence in the same phase.

Refering to Fig 1, if the lamp does not glow at point 3 but glows at point 2 then the third coil is faulty. If the lamp
glows at 2 and 3 but not at 4 then the fourth coil is faulty. By repeating this process the coil which has the open
circuit, can be identified.
Similarly, the other winding can also be tested for open circuit.
The resistance of each coil may be measured by a low range ohmmeter. The resistance of each coil must be the
same. The high value of resistance or infinity value indicates open in the windings.

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CITS : Power - Electrician & Wireman - Lesson 86-92 CITS : Power - Electrician & Wireman - Lesson 86-92