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 R_A = 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 R_Y = 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 R_Z = 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