AIM: Speed control of slip ring induction motor by rotor rheostatic control.

EQUIPMENTS:

1) Voltmeter (0-30) volts.

2) Ammeter (0-5) amp.

3) Tachometer

4) Connecting wires.

CIRCUIT DIAGRAM:

Fig.1 Speed control by rotor resistance method

RATINGS:

Induction motor ratings- Three phase, 5 HP, 1440 rpm, 7.5 Amp

THEORY:

The wound rotor consists of a slotted armature. Insulated conductors are put in the slots

and connected to form a three phase double layer distributed winding similar to the stator

winding. The rotor windings are connected in star. The open ends of the star circuit are

brought outside the rotor and connected to three insulated slip rings. The slip rings are

mounted on the shaft with brushes resting on them. The brushes are connected to three

variable resistors connected in star.The purpose of slip rings and the brushes is to provide

a means for connecting external resistance in the rotor circuit. The resistor enable the

variation of each motor phase resistance to serve two purposes:

a) To increase the starting torque and decrease the starting current from supply.

b) To control the speed of the motor.

PROCEDURE:

1) Make the connections as per circuit diagram.

2) Connect a rheostatic starter to the rotor circuit of the motor.

3) Connect a voltmeter across slip rings to measure the voltage.

4) Make the rotor rheostat to minimum position.

5) Measure the speed of motor for various values of rheostat.

OBSERVATION TABLE:

Sr

No.

Voltage across slip

rings (V)

Speed

(rpm)

%slip

(Ns-N1/Ns)

1

2

3

4

5

RESULT:

Voltage across slip

rings(V)% Slip

CONCLUSION:

Thus we studied the speed control of slip ring induction motor by rotor rheostatic control method.