Republic of Yemen Faculty of Engineering
Ministry of High Education Electrical of Engineering Department
Sana'a University Level 3
Load Characteristics of DC Shunt Motor
Done By\
Rabaa Muneer Saif Ebrahim
AC.NO\ 2020-037 Supervised By\
Eng-Tamer Al-Qadasi
Objective:
To connect and run the D.C. shunt motor and to obtain its loud
characteristics.
Connection Diagram:
Procedure:
1) Make the appropriate connections of the D.C. shunt wound motor
according to the circuit diagram.
2) Before operation connect the magnetic powder brake to the control
unit.
3) Set the control unit as follows:
- Speed range switch “min-1”:3000.
- Torque range switch “Nm”:1.
- Operation mode: MIN 1.
4) Put the motor into operation, and make it run to its normal speed.
5) Load the motor between no load operation and two times the
normal torque. Measure the torque T, the speed n, the armature
current Ia and the exciter current If under load.
6) Calculate the values of input power Pin, output power Po and
efficiency.
7) Using the measured and calculated values, draw the curves for the
D.C. shunt wound motor, i.e., n, Ia, 𝛈, Pin, Po=f(T).
Values:
T n Ia Iin Pin Pout 𝛈
0.1 2125 0.125 0.205 45.1 22.253 0.493
0.2 2060 0.24 0.32 70.4 43.145 0.613
0.3 2000 0.35 0.43 94.6 62.832 0.664
0.4 1980 0.45 0.53 116.6 82.938 0.711
0.5 1920 0.56 0.64 140.8 100.531 0.714
0.6 1850 0.68 0.76 167.2 116.239 0.695
Calculation:
𝐼𝑖𝑛 = 𝐼𝑎 + 𝐼𝑓 𝑤ℎ𝑒𝑟𝑒 𝐼𝑓 = 0.08 𝐴
𝑃𝑖𝑛 = 𝐼𝑖𝑛 𝑉𝑖𝑛 where 𝑉𝑖𝑛 = 220 𝑉
𝑇(2𝜋𝑛)
𝑃𝑜𝑢𝑡 = 𝑇𝜔 =
60
𝑃𝑜𝑢𝑡
𝜂= × 100%
𝑃𝑖𝑛
Relation between T & Ia & n
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
2125 2060 2000 1980 1920 1850
T Ia
Relation between Po &Pin & 𝜂
180
160
140
120
100
80
60
40
20
0
0.493 0.613 0.664 0.711 0.714 0.695
Pout Pin
Discussion:
1) Using the load characteristics describe the typical motor, speed,
torque behavior of the DC shunt motor.
The speed and torque can be controlled by varying the voltage and
current applied to the motor. The speed is proportional inversely to
the torque and current.
2) Describe the armature current curve.
The armature current is proportional inversely to the speed but it is
proportional directly to torque.
3) Describe the efficiency curve of the DC shunt motor.
The efficiency is proportional directly to output power and it
increases to a certain point but then decreases.
4) Why does the rotor speed of a DC shunt motor decrease only slightly
with increasing load?
Because the speed of the motor is determined by the relation
between armature current Ia and field current If and the field current
is constant.
5) How does the power delivered by a DC shunt wound motor change
with increasing load torque?
The power is determined by the speed and torque.
The power increases with increasing load torque up to a certain
point, then it starts to decrease as the load torque exceeds the
maximum torque that the motor can produce.
6) How can the nominal data of the motor be determined from the load
characteristics?
The nominal data can be determined by measuring performance
under different load conditions and analyzing to determine the rated
values.
Conclusion:
• The efficiency values are less than 1 because the values of input
power are greater than the values of output power.
• These motors are very easy to install and can work with speed
controllers, while not as initially potent, shunt DC motors do not
falter when providing their mechanical output, providing users
with consistency over raw output power.
• These motors have a low starting torque, so these motors cannot
be connected to a heavy load upon startup and must wait to be
used at the rated speed. They also slightly dip in speed when
heavily loaded, as no electric motor runs at ideal conditions, and
all experiences losses.
