Objective:
To investigate the characteristics of wound rotor 3-phase induction motor.
Introduction:
In this lab we introduced about the Experiment wound/ slip 3-phase induction Motor or induction motor
at following features. Then there are following performance we did are given below ac motor has a lot of
application in today’s field of engineering and technology.in all small or medium sized motoring
applications induction motors come handy. Wound motors are used on the basis of their following types.
A wound rotor is the rotating part (rotor) used in the most common form of AC induction motor. It
consists of a cylinder of steel with aluminum or copper conductors embedded in its surface.
Theory:
Wound rotor motor:
A wound rotor has a 3-phase winding, similar to the stator winding. • The rotor winding terminals are
connected to three slip rings which turn with the rotor. The slip rings/brushes allow external resistors to
be connected in series with the winding. • The external resistors are mainly used during start-up under
normal running conditions the windings short circuited externally
Asynchronous Motor:
Stator winding is similar to that of a synchronous motor. It is wound for a specific number of poles. A
squirrel cage rotor or a wound rotor can be used. In squirrel cage rotor, the rotor bars are permanently
short-circuited with end rings. In wound rotor, windings are also permanently short-circuited, hence no
slip rings are required.
Synchronous Speed:
The rotational speed of the rotating magnetic field is called as synchronous speed.
where, f = frequency of the supply
P = number of poles
Slip:
Rotor tries to catch up the synchronous speed of the stator field, and hence it rotates. But in practice, rotor
never succeeds in catching up. If rotor catches up the stator speed, there wont be any relative speed
between the stator flux and the rotor, hence no induced rotor current and no torque production to maintain
the rotation. However, this won't stop the motor, the rotor will slow down due to lost of torque, the torque
will again be exerted due to relative speed. That is why the rotor rotates at speed which is always less the
synchronous speed.
The difference between the synchronous speed (Ns) and actual speed (N) of the rotor is called as slip.
Working Principle of An AC Motor:
We need to give double excitation to make a DC motor to rotate. In a DC motor, we give one supply to
the stator and another to the rotor through brush arrangement. But in induction motor, we give only one
supply, so it is really interesting to know how an induction motor works. It is very simple, from the name
itself we can understand that here, induction process is involved. Actually, when we give the supply to the
stator winding, a magnetic flux is produced in the stator due to the flow of current in the coil. The rotor
winding is arranged in such a way that each coil becomes short-circuited in the rotor itself.
The flux from the stator cuts the short-circuited coil in the rotor. As the rotor coils are short-circuited,
according to Faraday's law of electromagnetic induction, current will start flowing through the coil of
the rotor. When the current through the rotor coils flows, another flux gets generated in the rotor. Now
there are two fluxes, one is stator flux and another is rotor flux. The rotor flux will be lagging with respect
to the stator flux. Because of that, the rotor will feel a torque which will make the rotor to rotate in the
direction of rotating magnetic field. This is the working principle of an induction motor of either type –
single and three-phase.
Instruments:
Following instruments are required:
1) DC Generator.
2) Induction Motors.
3) Voltmeter.
4) Ammeter.
5) Wattmeter.
6) Trainer.
7) Wires.
8) Electrical Panel.
9) Load (Resistance).
Procedure:
In this experiment we discussed and perform the measurements of cage asynchronous motor and features.
1) This procedure is completed in following steps.
2) First of all, draw the circuit diagram on the rough paper according to the relative experiment.
3) Then check that the voltage on the module should be at zero.
4) Then put the wire knobs according to the circuit diagram.
5) After making the circuit on the module. So, switch on the module.
6) Now supply the voltage. the phase voltage not more 220v.stop the motor at first and then noted
the required parameter readings.
7) Note reading of the Voltmeter, ammeter and wattmeter.
8) Then perform this experiment at no load
9) Find out the no load speed and torque.
10) After that records some more value for each type put into the table.
Circuit Diagram:
Wound
rotor
Table:
Applied Voltage = V = 72V
Sr. Load IR IL Ig Torque P1 P2 PL RPM Efficiency
No.
(Ω) (A) (A) (A) (Nm) (W) (W) (W) 𝜼
1. 163 0.51 0.21 0.21 0.109 40 40 0.5 436 0.62
2. 200 0.49 0.20 0.20 0.006 38 38 0.4 596 0.52
3. 223 0.46 0.18 0.18 0.004 37 37 0.3 625 0.40
Conclusion:
In this lab our discussion is about the wound rotor or slip 3-phase induction motor at adjustable load
features. We are all understand and know well about the construction, principle and the all types of the
induction motor. After performing and doing the experiment we calculated the different values of the
required parameter. After performing the experiment, we resulted that when load is varying then rotor
current decrease which also increase in the RPM. Mechanical power is decreasing. We conclude that
wound induction motor has high starting torque, due to the resistance add in rotor. Wound induction
motor use where high starting torque require.
