Routine Test for Measurement of D.C. Resistance of Winding

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Routine Test for Measurement of D.C. Resistance of Winding

Q. Explain routine test for measurement of D.C. resistance of winding.

Routine test :

The resistance of each winding is measured by passing direct current and temperature of the winding is recorded. Care must be taken to reduce self – inductive effects. The arrangement is shown in  the Figure B. The ammeter, voltmeter and variable resistance are connected as shown.

Routine Test for Measurement of D.C. Resistance of Winding
Figure A
Routine Test for Measurement of D.C. Resistance of Winding
Figure B
Routine Test for Measurement of D.C. Resistance of Winding
Figure C

The value of measured resistance changes due to increase in temperature. For copper conductors therefore, the resistance at required temperature is found as follows : 

R2 / R1 = t2 +  234.5 / t1 + 234.5

Where,

t2=Temperature (°C) of the winding at the end of test 234.5

t1 =Temperature (°C) of the winding (cold) at the beginning of test

R1= Resistance of the winding at the end of test /

R2= Initial resistance of winding (cold)

If very accurate results are required then Kelvin’s bridge or Whetstone’s bridge method is employed.

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