# Resistance of Armature Winding...

Aim:- Measurement of resistance of the armature winding, series field winding and shunt field winding of a DC machine.

NAME PLATE SPECIFICATIONS OF MACHINE:

BHP/KW = 75 HP

Voltage = 250V

Amperes = 15A

RPM = 1500 rpm.

Apparatus Required:-

 S. No. Name of Equipment Type Range Quantity 1. Ammeter MC 0-15A 1 2. Ammeter MC 0 – 20A 1 3. Voltmeter MC 0 – 30V 1 4. Voltmeter MC 0-300V 1 5. Rheostat Single tube 500ohms, 5A 1 6. Lamp load Resistive 250V, 1KW 1

Theory:- According to Ohm's law, the resistance 'R' of a winding is given by:

R = I/V

Where,

V = voltage drop across the winding

I= current through the winding

Circuit Diagram:-

PROCEDURE:

1. Measurement of armature resistance, series field resistance. Connections are made as shown in figure (a), the reading of various meters are recorded for different values of current flowing through the above winding. The variation in current is obtained with the help of lamp bank load. The readings are taken up to 125% of the rated current of the machine.

2. Measurement of shunt field resistance. Connections are made as shown in figure (b), the readings of various meters are noted down for various values of shunt field currents. The shunt field current is varied by a rheostat used a variable resistance.

Observation Table:-

(a) Armature Resistance:

 S. No. I (amp) V (volts) RA (ohms) 1. 2.4 4.6 1.92 2. 6 8.2 1.37 3. 8 9.4 1.175

Average RA = 1.44

(b) Series field Resistance:

 S. No. I (amp) V (volts) RY (ohms) 1. 6 1 0.17 2. 11.6 2.7 0.23 3. 16 3.6 0.225

Average RY = 0.625

(c) Shunt field Resistance:

 S. No. I (amp) V (volts) RZ (ohms) 1. 0.5 104 208 2. 0.75 152 202.67 3. 1 204 204

Average RZ = 204.89

Precaucation:-

1.     Make the connections properly.

2.     Note the readings of voltmeters and ammeters properly.

3.     Remove insulations from the connecting wire so as the current will flow properly