TESTING OF DC MOTORS
BIRBHUM INSTITUTE OF ENGINEERING & TECHNOLOGY
PRITAM GHOSH
EE-08/14
3rd YEAR, 5th SEM
ELECTRICAL ENGINEERING
CONTENTS
WHY TESTING OF A DC MOTOR IS REQUIRED?
TYPES OF TESTING OF A DC MOTOR
DIRECT METHOD OF TESTING OF A DC MOTOR
SWINBURNE’S METHOD OF TESTING OF A DC MOTOR
REGENERATIVE OR HOPKINSON’S METHOD OF TESTING OF A DC MOTOR
CONCLUSION
REFERENCE
WHY TESTING OF A DC MOTOR IS REQUIRED?
Performance of the
machine
Losses & efficiency of
the machine
Quality of the materials
used
Modification in
manufacturing process
TYPES OF TESTING OF A DC MOTOR
DIRECT METHOD
INDIRECT METHOD OR SWINBURNE’S
METHOD
REGENERATIVE METHOD OR
HOPKINSON’S METHOD
DIRECT METHOD
Suitable for small D.C.
Machines
Brake test for D.C. Motors
Belt pulley arrangement
attached to spring
balances S1 & S2
Loads on pulley adjusted
by hand WHEELS H1 & H2
EFFICIENCY CALCULATION
Motor output power= ω*(S1 – S2)*r*9.81 watts
Motor input power= Vt * Il watts
Motor efficiency, ηm = [{ω*(S1 – S2)*r*9.81 }*100/(Vt * Il )]%
PRECAUTION
• THE BRAKE SHOULD BE
SUFFICIENTLY TIGHT FOR
A DC SERIES MOTOR
DISADVANTAGES
• Size of the motor is
restricted
• Spring balance readings
are not steady
SWINBURNE’S METHOD OF TESTING A DC MOTOR
• Most commonly used and simplest method of testing of shunt and
compound wound dc machines
• No load losses are measured separately
EFFICIENCY CALCULATION
Power absorbed by armature at no load= Vt *Ia0
Armature circuit loss = Ia02 *ra
No load rotational losses, W0 = (Vt *Ia0) – (Ia02 *ra )
Shunt field loss= Vt *If
Power input = Vt*IL
IL = I a + I f
Efficiency of the motor: ηm =1- [{W0 + (Ia02 *ra )+ (Vt *If )}/ (Vt*IL)]%
ADVANTAGES DISADVANTAGES
Iron loss is neglected
Required very less power We cannot be sure about the
satisfactory commutation on
loaded condition
Since constant losses are known, We can’t measure the
efficiency of Swinburne's test can temperature rise when the
be pre-determined at any load machine is loaded
In dc series motor, the
Swinburne’s test cannot be done
HOPKINSON’S METHOD OF TESTING A DC MOTOR
Two identical dc machines are
coupled, both mechanically &
electrically
One of these two machines is
operated as a generator to supply
the electrical power to the motor
and the other is operated as a
motor to drive the generator
Due to the drop in the generator
output voltage we need an extra
voltage source to supply the
proper input motor-generator set
EFFICIENCY CALCULATION
Input to motor armature= Vt*I1
Motor armature circuit loss= I12 *ra
Motor shunt field loss= Vt*If1
No-load rotational loss in two machines, W0= (Vt*I)- ra*(I12+I22)
No-load rotational loss in each machine=W0/2
Total motor loss, Wm = (W0/2)+(Vt*If1)+(I12 *ra)
Motor efficiency: ηm = [1-{Wm/Vt*(I1+If1)}]*100%
ADVANTAGES DISADVANTAGES
Very small power required Difficult to find two identical
machines
Both machines cannot be loaded
Temperature rise and commutation equally all the time
can be observed
It is not possible to get separate iron
losses for the two machines
Change in iron loss due to flux
distortion can be taken into account It is difficult to operate the machines
due to the advantage of its full load at rated speed because field currents
condition vary widely
CONCLUSION
Each process is necessary for testing of different kinds of dc
motors
Power required in Direct Method is much greater than that in
other two methods
No load rotational loss for a particular machine can be
determined separately only by Indirect Method
REFERENCE
Electrical Machinery, Dr. P. S. Bimbhra
Chapter: D.C. Machines(Page No. 495-501 )
http://www.electrical4u.com/hopkinsons-
test/
http://www.electrical4u.com/swinburnes-
test-of-dc-machine/
https://en.wikipedia.org/wiki/Electric_motor
