Presentation on Dc Motor

1. DC MOTOR

2. Subhajit Bose(03)
Shuvankar Das(02)
Binoy Mourya(09)
Sushobhan Sarkar(06)
Prosenjit Debnath(35)

3. History of DC Motor
Michael Faraday (U.K.)

5. CONSTRUCTION

6. Working Principle of DC Motor

7. TYPES OF DC MOTORS
• DC motor are of 3 types they are…..
1. DC SHUNT MOTOR
2. DC SERIES MOTOR
3. DC COMPOUND MOTOR

8. 1. DC SHUNT MOTOR
Armature
• The parallel combination of two
windings is connected across a
common dc power supply.
• The resistance of shunt field
winding (Rsh) is always higher than
that is armature winding.
• This is because the number of turns
for the field winding is more than
that of armature winding.
• The cross-sectional area of the wire
used for field winding is smaller
than that of the wire used for
armature winding.

9. We know, 𝑇 ∝ ∅ 𝐼𝑎 N ∝ Eb/ ∅
And ∅ is constant here N ∝ (Vt-IaRa)
So , 𝑇 ∝ 𝐼𝑎

10. • The field winding is connected in
series with the armature.
• The current passing through the
series winding is same as the
armature current .
• Therefore the series field winding
has fewer turns of thick wire than
the shunt field winding.
• Also therefore the field winding will
posses a low resistance then the
armature winding.
2. DC SERIES MOTOR

11. We know, 𝑇 ∝ ∅ 𝐼𝑎 Again We know
For Dc series motor
Ia=If=I
So , 𝑇 ∝ 𝐼𝑎
𝐸𝑏=𝑁∅𝑍𝑃/𝐴60
N ∝ Eb/ ∅
So, N ∝ 1/ ∅
N ∝ 1/𝐼𝑎
𝑇 ∝ ∅ 𝐼𝑎
N ∝ 1/𝐼𝑎

12. DC
COMPOUND
MOTOR
LONG SHUNT
COMPOUND MOTOR
SHORT SHUNT
COMPOUND
MOTOR
CUMULATIVE
COMPOUND
MOTOR
DIFFERENTIAL
COMPOUND
MOTOR
3. DC COMPOUND MOTOR

13. I. LONG SHUNT COMPOUND MOTOR
• In this the series winding is
connected in series with the
armature winding and the
shunt winding is connected in
parallel with the armature
connection.

14. II. SHORT SHUNT COMPUND MOTOR
• In short shunt compound
motor the series winding is
connected in series to the
parallel combination of
armature and the shunt
winding
• This is done to get good
starting torque and constant
speed characteristics.

15. a) CUMULATIVE COMPOUND DC MOTORS
b) DIFFERENTIAL COMPOUND DC MOTORS
• If the two field windings i.e.
series and shunt are
wounded in such a way that
the fluxes produced by
them add or assist each
other
• If the two field winding i.e. series and shunt
are wounded in such a way that the fluxes
produced by them always try to oppose and
try to cancel each other.

16. We know the Back Emf, Eb = PØNZ/60A
(where, P = no. of poles, Ø = flux/pole, N = speed in rpm, Z = no.
of armature conductors, A = parallel paths)
Eb can also be given as, Eb = V- IaRa
thus, from the above equations N = Eb 60A/PØZ
but, for a DC motor A, P and Z are constants
Therefore, N ∝ K Eb/Ø (where, K=constant)
This shows the speed of a dc motor is directly proportional to the
back emf and inversely proportional to the flux per pole.

17. 1. Flux Control Method
2. Armature Control Method
To control the flux, a rheostat is
added in series with the field
winding, as shown in the circuit
diagram. Adding more resistance
in series with the field winding will
increase the speed as it decreases
the flux.
When the supply voltage V and the
armature resistance Ra are kept
constant, speed is directly
proportional to the armature current
Ia. Thus, if we add a resistance in
series with the armature, Ia decreases
and, hence, the speed also decreases.

18. 3. Voltage Control Method
a) Multiple voltage control:
In this method, the shunt field is connected to a fixed exciting voltage
and armature is supplied with different voltages. Voltage across
armature is changed with the help of a suitable switchgear.
b) Ward-Leonard System:
This system is used where very
sensitive speed control of motor is required
(e.g electric excavators, elevators etc.). The
arrangement of this system is as shown in
the figure at right.
M2 is the motor whose speed control is
required.
M1 may be any AC motor or DC motor with
constant speed.
G is a generator directly coupled to M1.

19. Speed Control Of Series Motor
1. Flux Control Method

20. 2. Variable Resistance In Series With Armature
By introducing a resistance in series with the armature, voltage across
the armature can be reduced. And, hence, speed reduces in proportion
with it.
3. Series-Parallel Control
This system is widely used in electric traction, where two or more
mechanically coupled series motors are employed. For low speeds, the
motors are connected in series, and for higher speeds the motors are
connected in parallel.
When in series, the motors have the same current passing
through them, although voltage across each motor is divided. When in
parallel, the voltage across each motor is same although the current
gets divided.

21. APPLICATIONS OF DC MOTORS
MOTORS.. APPLICATIONS…
D.C. SHUNT MOTOR
LATHES , FANS, PUMPS DISC AND BAND
SAW DRIVE REQUIRING MODERATE
TORQUES.
D.C. SERIES MOTOR ELECTRIC TRACTION, HIGH SPEED TOOLS
D.C. COMPOUND MOTOR
ROLLING MILLS AND OTHER LOADS
REQUIRING LARGE MOMENTARY TORQUES.

22. BIBLIOGRAPHY
www.google.com
en.wikipedia.org
Electrical Machines By
S. K. Bhattacharya