Speed control of a d.c shunt motor SAIF ALDIN ALI MADIN سيف الدين علي ماضي S96aif@gmail.com The object of the experiment is to study the effect of load the speed of a shunt motor and to examine the different application on method of speed control.

1. SAIF AL-DIN ALI MADI
Department of Mechanical Engineering/ College of Engineering/ University of Baghdad
1
[Electricity Laboratory II]
University of Baghdad
Name: - Saif Al-din Ali -B-

2. SAIF AL-DIN ALI MADI
Department of Mechanical Engineering/ College of Engineering/ University of Baghdad
2
TABLE OF CONTENTS
Experiment Name................................................................I
Experiment Aim..............................................................II
Theory............................................................................III
Procedure........................................................................V
Data and processes........................................................VI
DISCUSSION……………….................................................VII

3. SAIF AL-DIN ALI MADI
Department of Mechanical Engineering/ College of Engineering/ University of Baghdad
3
1. Experiment Name: speed control of a D.C shunt motor
2. Experiment Aim: The object of the experiment is to study the
effect of load the speed of a shunt motor and to examine the
different application on method of speed control.
3. Theory:
When a motor operates a center elector motive force E is induced
in the armature as a result of conductors rotating and cutting the
flux and lines
Ec=Vt-Ia Ra (1)
Where
Vt = applied terrestrial voltage
la = armature current,
Ra = armature resistance
Ec is proportional to the speed of the armatures and the flux of the
field,
Ec=KØN (2)
K=a constant dependent an armature winding.
Ø= flux per pole
N = armature speed
Combining eq. (1) and (2) above gives:
𝑁 =
𝐕𝐭 − 𝐈𝐚 𝐑𝐚
𝐊Ø
As seen from eq. (3) the speed can be controlled in three Ways;
1. By changing the field strength through the variation of the field
current.
2. By increasing the armature resistance through insertion an
additional resistance in series with the armature.
3. By varying the applied terminal voltage.

4. SAIF AL-DIN ALI MADI
Department of Mechanical Engineering/ College of Engineering/ University of Baghdad
4
4. Procedure:
Take the name plate data of the generator used in the experiment
 Run (1): (speed chara of shunt motor)
1. Connect the circuit diagram shown in fig (1) Switch on the d.c supply
and start the motor with the help of starter; Adjust the field current of
motor to give rated speed at no load.
2. Load the motor to 100% of rated value in 6 steps and record all
readings, Keeping the terminal voltage and field current constant.
.
 Run (2): (changing of field flux)
Adjust the field current to give a no - Load speed of 110% of rate Value and
repeat run (1) item (2)
 Run (3): (Adding resistance to Ra).
1. Insert aproper rheostat (the max, allowable current of this rheostat must
be 120% of the rated armature current) in series with the motor armature
circurit, With this rhcostat equal to zero, adjust the no - load speed to the
rated value as in run (1) item (1)
2. Load the motor to rated value ariniature current, then adjust the rlieostat
in the armature circuit until the speed drops to 30% of rated value with
rated armature current
3. Keeping the rheostat setting and field current constitut, red rice the
Ladd current of generator to zero in about 6 steps and record all readings

5. SAIF AL-DIN ALI MADI
Department of Mechanical Engineering/ College of Engineering/ University of Baghdad
5
5. Data and processes:
RUN1
NO Ia (A) N If V
1 1 1350 0.3 218
2 2 1325 0.3 218
3 3 1320 0.3 218
4 4 1300 0.3 218
5 5.4 1275 0.3 218
6 6.8 1260 0.3 218
RUN2
1 1 1450 0.25 218
2 2.6 1400 0.25 218
3 3.4 1400 0.25 218
4 4.2 1380 0.25 218
5 5.2 1360 0.25 218
6 6.2 1350 0.25 218
RUN3
1 5.4 1250 0.25 195
2 4.4 1275 0.25 195
3 3.6 1320 0.25 202
4 2.8 1350 0.25 208
5 1.8 1460 0.25 210

6. SAIF AL-DIN ALI MADI
Department of Mechanical Engineering/ College of Engineering/ University of Baghdad
6
6. DISCUSSION:
1. Draw three charts, each one the speed - load chara. N = f (Ia). From
results obtained from runs (1), (2) and (3).
1250
1260
1270
1280
1290
1300
1310
1320
1330
1340
1350
1360
0 1 2 3 4 5 6 7 8
Nr.P.m
Ia (A)
RUN 1
1340
1360
1380
1400
1420
1440
1460
0 1 2 3 4 5 6 7
Nr.P.m
Ia (A)
RUN 2

7. SAIF AL-DIN ALI MADI
Department of Mechanical Engineering/ College of Engineering/ University of Baghdad
7
1200
1250
1300
1350
1400
1450
1500
0 1 2 3 4 5 6
Nr.P.m
Ia (A)
RUN 3
1200
1250
1300
1350
1400
1450
1500
0 1 2 3 4 5 6 7 8
Nr.P.m
Ia (A)
RUN 3 RUN 1 RUN 2

8. SAIF AL-DIN ALI MADI
Department of Mechanical Engineering/ College of Engineering/ University of Baghdad
8
2. In the above experiment, while starting the motor, what will
happen if the armature circuit resistance is maximum?
𝑁 =
𝐕𝐭 − 𝐈𝐚 𝐑𝐚
𝐊Ø
𝐑𝐚 = 𝑀𝐴𝑋
𝐑𝐚 Reverse relationship with speed
𝑁 ≈ 0
3. If the armature current and field current of shunt motor are both
reversed, does the motor direction get reversed?
The field and armature windings carry same current as they remain
connected in series. Now, if field winding is reversed without touching
armature winding, then torque generated will be negative and hence the
motor will rotate in reverse direction. If both armature and field are
reversed then motor will continue to rotate in same direction as
Torque = køIa=k If Ia
Where k, k’ are constant. Ø is the net flux due to field current If=Ia, armature
current. If both windings are reversed, then both If and Ia will be equal and
negative and hence there product which is proportional to torque will be
positive. If any one of the field or armature current is reversed then, Torque
will be negative or opposite. This view us based on the assumption that the
motor is operating under normal required condition and of course on loaded
condition.

9. SAIF AL-DIN ALI MADI
Department of Mechanical Engineering/ College of Engineering/ University of Baghdad
9
4. What precautions concern,
A. the field circuit
B. The armature current must be taken when operating the shunt
motor
The starting current must be at a low value because this may harm the
motor and cause a high starting rotation which is dangerous. This
precaution was achieved by starting the motor with maximum armature
resistance so that the starting current is low
The two functions of the armature rheostat were one, to ensure a low
starting armature current and two, to vary the armature current which
is proportional to the speed of the motor
A shunt motor, connected with an external resistance in series with its
armature, is switched on. External resistance is needed to have a safe
starting current.
A shunt motor, connected without an external resistance in series with
its armature, is switched on. It can be dangerous to the apparatus and
may break
5. How does the saturation in the machine affect the speed of shunt
motor?
Most DC Motors are operated in the knee region to prevent any
fluctuation in speed during voltage sag/swells and other minor
disturbances. This is because speed is inversely proportional to the field
flux. Now, if you are performing any experiment pertaining to Speed
Control, care should be taken that the field should not be saturated
otherwise chances are that the speed will always remain constant (due
to saturation which makes the field constant) even if you vary current to
the field to vary the field.

10. SAIF AL-DIN ALI MADI
Department of Mechanical Engineering/ College of Engineering/ University of Baghdad
10
6. How will the load current affect the speed except it's effected on I R,
drop?
It’s called speed regulation of a DC motor, which is the capability
a DC motor shows to recover the speed under variable load.
In general the speed of a shunt DC motor is directly proportional to
the armature voltage and inversely proportional with the field
current, disregarding inherent losses.
Ideally, for constant armature voltage and field current, the motor
speed should be constant, despite of the armature current. The
armature current is proportional to the rotorical torque (the load
attached to its shaft).
However, when the load increases, the speed tends to fall
accordingly, leading to a decrease of the emf. As a result, the
armature drains more current from the power supply to balance the
increase in torque, hence keeping the speed tightly attached to the
armature voltage.
Due to the inherent ohmic and magnetic losses, viscous friction
and other losses, the speed recovering falls below 100%. A typical
graph representing the speed regulation is depicted as follows:
In practical terms, the speed regulation of a DC motor can be as good
as 90%.
If a tight speed regulation is a requirement, a complex feedback loop
must be implemented to control the armature current accordingly, in
order to compensate for the inherent losses.

11. SAIF AL-DIN ALI MADI
Department of Mechanical Engineering/ College of Engineering/ University of Baghdad
11
7. Discuss the three method of speed control from results obtained,
which method is feasible and for what purposes that they used?
1. ran1. We observe the voltages and the current of the coil
constant and the value of 0.3 and the current (Ia) and we hope to
get high speeds
 Connect the circuit diagram shown in fig (1) Switch on the d.c supply and
start the motor with the help of starter; Adjust the field current of motor to
give rated speed at no load.
 Load the motor to 100% of rated value in 6 steps and record all readings,
Keeping the terminal voltage and field current constant.
2. Run 2. For current 1 speed is higher than the first run1.
The speed is reversed with the Ia current and the coil
current is reduced by. 0.05
 Adjust the field current to give a no - Load speed of 110% of rate Value
and repeat run (1) item (2)
3. Run 3. Notice the change of v due to the entry of Ra in the
case. Speed has also had a significant impact. If we
compare the number 1 to the number 5, we notice a
decrease in speed due to pregnancy
 Insert aproper rheostat (the max, allowable current of this rheostat must be
120% of the rated armature current) in series with the motor armature
circurit, With this rhcostat equal to zero, adjust the no - load speed to the
rated value as in run (1) item (1)
 Load the motor to rated value ariniature current, then adjust the rlieostat in
the armature circuit until the speed drops to 30% of rated value with rated
armature current
 Keeping the rheostat setting and field current constitut, red rice the Ladd
current of generator to zero in about 6 steps and record all readings

12. SAIF AL-DIN ALI MADI
Department of Mechanical Engineering/ College of Engineering/ University of Baghdad
12