EEE363 (Exp 2) Study of The Torque Speed Relationship of DC Shunt

Department of Electrical and Computer Engineering
North South University
EEE 363 – Electrical Machines

Experiment No: 02
Study of the Torque Speed Relationship of DC Shunt Motor
Name of the experiment:

Study of the Torque Speed relationship of DC Shunt Motor.
Objective:
• To study the torque vs Speed characteristics of a shunt wound DC motor.
•To calculate the efficiency of the shunt wound DC motor.
Theory:
The speed of any DC motor depends mainly upon its armature voltage and the strength of the
magnetic field. In a shunt motor, the field winding, as well as the armature winding, is connected
in parallel (shunt) directly to the DC supply lines. If the DC line voltage is constant, then the
armature voltage and the field strength will be constant. It is, therefore, apparent that the shunt
motor should run at are reasonably constant speed.
The speed does tend to drop with an increasing load on the motor. This drop in speed is mainly
due to the resistance of the armature winding. Shunt motors with low armature winding
resistance run at nearly constant speeds.
Just like most energy conversion devices, the DC shunt motor is not 100% efficient. In other
words, all of the electric power which is supplied to the motor is not converted into mechanical
power. The power difference between the input and output is dissipated in the form of heat, and
constitutes what are known as the “losses" of the machine. These losses increase with load, with
the result that the motor gets hot as it delivers mechanical power.
In this Experiment you will investigate the efficiency of a DC shunt motor.
Equipment required:
1. DC motor/generator module.
2. Power supply module.
3. DC voltmeter/ammeter module.
4. Electrodynamometer module.
Procedure:
CAUTION
High voltages are present in this Experiment! Do not make any connections with the power on!
The power should be turned off after completing each individual measurement!
1. Using your Power Supply, DC Motor/Generator, DC Voltmeter/Ammeter and

Electrodynamometer, connect the circuit shown in Figure
2. Set the shunt field rheostat control knob at its full cw position (for maximum shunt field
excitation). Make sure the brushes are in their neutral position.
3. Set the dynamometer control knob at its full ccw position (to provide a minimum starting load
for the DC motor).
4. Turn on the power supply. Adjust the variable output voltage to 240 V dc as indicated by the
meter. Note the direction of rotation; if it is not clockwise, turn off the power supply and
interchange the shunt field connections.
5 a) Adjust the shunt field rheostat for a no-load motor speed of 240 r/min as indicated on your
hand tachometer. (Make sure that the voltmeter, connected across the input of your circuit,
indicates exactly 240 V dc).
Note: Do not change the field rheostat adjustment for the remainder of the experiment.
b) Measure the line current, as indicated by the ammeter, for a motor speed of 240 r/min. Record
this value in Table
Data Table1:
Note: For an exact torque of 0 Nm, uncouple the motor from the dynamometer.
E(volts) I(amp) Speed(r/min) TORQUE(N.m)
0.3
0.6
0.9
1.2
6 a) Apply a load to your DC motor by varying the dynamometer control knob until the scale
marked on the stator housing indicates 0.3 N-m. (Readjust the power supply, if necessary, to
maintain exactly 240 V dc).
b) Measure the line current and motor speed. Record these values in Table1.
c) Repeat for each of the torque values listed in the Table, while maintaining a constant 240 V dc
input.
d) Return the voltage to zero and turn off the power supply.
7 a) Plot the recorded motor speed values from Table 4-1 on the graph of Figure 4-2.
b) Draw a smooth curve through your plotted points.
c) The completed graph represents the speed vs torque characteristics of a typical DC shunt-
wound motor. Similar graphs for series wound and compound wound DC motors will be
constructed in the following two Experiments. The speed vs torque characteristics for each type
of motor will then be compared and evaluated.
8. Calculate the speed vs torque regulation (ful load = 1.2 N-m) using the equation:
(𝑛𝑜 𝑙𝑜𝑎𝑑 𝑠𝑝𝑒𝑒𝑑 ) − (ƒ𝑢𝑙𝑙 𝑙𝑜𝑎𝑑 𝑠𝑝𝑒𝑒𝑑)
𝑅𝑒𝑔𝑢𝑙𝑎𝑡i𝑜𝑛 = 𝑥 100%
(ƒ𝑢𝑙𝑙 𝑙𝑜𝑎𝑑 𝑠𝑝𝑒𝑒𝑑)
Speed regulation = %
Questions:
1. Calculate the mechanical output power by the shunt-wound DC motor when the torque is 1.2
N-m. Use the equation:
2 * 3.1416 * 𝑁 * 𝑇
𝑃𝑜𝑢𝑡 =
60
Where, Pout = Mechanical Output Power in watts (W)
N = Speed in revolutions per minute (r/min)
T = Torque in Newton-meter (N·m)
Pout = (W)
2. What is the input power (in watts) of the motor in Question 1?
Input power = W
3. Knowing the input and output power in watts, calculate the efficiency of the motor in
Question1.
Efficiency = (power output/power input) x 100%
Efficiency = _%
4. What are the losses (in watts of the motor in Question 1)?
Losses = W
5. List where some of these losses occur.
6. Would the losses decrease if a cooling fan is mounted on the motor shaft?
Explain. -
[] Yes [] No
7. Give two reasons why losses are undesirable.
8. which type of DC motor acts almost as a constant speed motor and why?

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Department of Electrical and Computer Engineering

North South University

EEE 363 – Electrical Machines

Name of the experiment:

•To calculate the efficiency of the shunt wound DC motor.

In this Experiment you will investigate the efficiency of a DC shunt motor.

1. Using your Power Supply, DC Motor/Generator, DC Voltmeter/Ammeter and

b) Draw a smooth curve through your plotted points.

Where, Pout = Mechanical Output Power in watts (W)

N = Speed in revolutions per minute (r/min)

T = Torque in Newton-meter (N·m)

2. What is the input power (in watts) of the motor in Question 1?

Efficiency = (power output/power input) x 100%

5. List where some of these losses occur.

7. Give two reasons why losses are undesirable.

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