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
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