Exp No.
7 SPEED CONTROL OF SLIPRING INDUCTION
MOTOR
AIM:
To perform the speed control test on slip ring induction motor by rotor resistance
control method. Plot the motor speed characteristics at different values of applied resistance
in slip ring of induction motor.
APPARATUS REQUIRED:
A PC with internet connection.
THEORY:
The slip ring or wound rotor motor is an induction machine where the rotor comprises
a set of coils that are terminated in slip rings. These are metal rings rigidly mounted on the
rotor, and combined with brushes (as used with commutators), provide continuous unswitched
connection to the rotor windings.
In t h e case of the wound-rotor induction motor, external impedances can be connected
to the brushes. The stator is the same as is used with a standard squirrel cage motor. By
changing the impedance connected to the rotor circuit, the speed/current and speed/torque
curves can be altered.(Slip rings are also often used in alternators as well as in synchro angular
data- transmission devices, among other applications.) The slip ring motor is used primarily to
start a high inertia load or a load that requires a very high starting torque across the full speed
range. By correctly selecting the resistors used in the secondary resistance or slip ring starter,
the motor is able to produce maximum torque at a relatively low supply current from zero speed
to full speed. This type of motor also offers controllable speed. Motor speed can be changed
because the torque curve of the motor is effectively modified by the amount of resistance
connected to the rotor circuit. Increasing the value of resistance will move the speed of
maximum torque down. If the resistance connected to the rotor is increased beyond the point
where the maximum torque occurs at zero speed, the torque will be further reduced. When used
with a load that has a torque curve that increases with speed, the motor will operate at the speed
where the torque developed by the motor is equal to the load torque.
PROCEDURE:
STEP 1: Make connections as per the instructions given below. If the wire is wrongly
connected, Click on node number to detach the wire.
Si. No. Current (A) Power (W) Speed (RPM)
5
STEP 2: Click on "Check" button for checking the connections.
If connection is correct, an alert appears. Click ok. Now, go to step 4.
If connection is wrong, an alert appears. Click ok. Now, go to step 3.
STEP 3: Check the connection and either detach the incorrect wire connection or Click on
Reset button and start from step 1.
STEP 4: Switch on the MCB.
STEP 5: Click on the autotransformer knob.
STEP 6: Slide the knob of the Rheostat to change the resistance.
STEP 7: Click on "Add to table" button to insert the readings in the table.
STEP 8: Follow the procedure from step 6 to step 7, till you have the 6 readings in the table.
STEP 9: After taking minimum 6 readings, Click on the "Graph" button.
STEP 10: Click on "Print" button to print the full connections with graph and table.
Viva Questions
1. How speed is controlled in slip ring induction motor?
Speed Control by Rotor Rheostat Control With the same rheostat added to the rotor circuit, it is
possible to regulate the speed of slip ring motors. The resistance is engaged maximum during
starting and slowly cut-off to increase the speed of the motor.
2. What are the different methods of speed control of slip ring induction motor?
The slip rotor induction motor speed can be varied by varying the rotor circuit resistance or rheostat,
The rotor resistance can be changed by using a diode bridge rectifier and chopper. Speed can also
be varied by varying the duty cycle of the gate pulses given to chopper.
3. Why slip rings are used?
Slip rings are a mechanical device that allow the transmission of electrical power and signals from
a fixed point to a rotating device and are used to simplify the operation of a system or improve its
mechanical performance.
4. What are the types of slip ring?
Types Of Slip Rings. Capsule slip rings, through hole slip rings, high-speed slip rings, collector
rings, disc electric conduction slip rings, wireless slip rings, high-frequency electric conduction
slip rings, capacitive slip rings, and so on are all available on the market today.
5. Which material is used in slip ring?
A slip ring comprises a metal ring and brush contact, which is made up of graphite and usually runs
on the outer diameter of the metal ring. The brushes can be made of phosphor bronze as well, but
graphite is cheaper.
Video Link: https://www.youtube.com/watch?v=lNtGR4zOt1w
RESULT:
Thus the Speed control of three phase slip ring induction motor is obtained.
