The document discusses the construction and working of DC motors. It describes the key components of a DC motor including the stator, rotor, yoke, poles, field windings, armature windings, commutator, and brushes. It also explains the different types of DC motors such as permanent magnet, separately excited, self-excited, shunt wound, series wound, and compound wound motors. Applications of different DC motor types are also summarized.

1. PRESENTED ON
DIRECT CURRENT
MOTOR
SUBMITTED TO
Mr. Rahul Garg
HOD (EE)
SUBMITTED BY
VIPUL KUMAR JANGIR
16EMTEE024

2. CONTENTS

3. INTRODUCTION OF DC MOTOR
• The DC machine are of two types namely DC Motors and DC
Generators.
• A motor is a machine that converts electrical energy into mechanical
energy.
• A generator is a machine that converts mechanical energy into
electrical energy.
• DC Motor is very similar to DC Generator in construction.

4. CONSTRUCTION OF DC MOTOR
• A DC Motor is a machine that converts electrical energy
into mechanical energy.
• A DC Motor is constructed with :-
1. STATOR
2. ROTOR
3. YOKE
4. POLES
5. FIELD WINDINGS
6. ARMATURE WINDINGS
7. COMMUTATOR
8. BRUSHES

5. STATOR AND ROTOR
• A rotating electric machine has two main parts, stator and rotor,
separated by the air gap.
1. The stator of the machines does not move and normally is the outer
frame of the machine.
2. The rotor is free to move and normally is the inner part of the
machine.
3. Both stator and rotor are made of ferromagnetic materials.

6. YOKE
• The magnetic frame or the yoke of DC motor made up of cast iron or
steel and forms an integral part of the stator or the static part of the
motor.
• Its main function is to form a protective covering over the sophisticated
inner parts of the motor and provide support to the armature.
• It also supports the field system by housing the magnetic poles and field
winding of the DC motor.

7. POLE CORES AND POLE SHOES
• The field magnets consists of pole cores and
pole shoes. The pole shoes serve two
purposes-
1. They spread out the flux in the air gap and
also, being of larger cross-section, reduce
the reluctance of the magnetic path.
2. They support the exciting coils.

8. POLE COILS OR FIELD WINDINGS
1. The field coils or pole coils, which
consists of copper wire or strip.
2. When current is passed through these
coils, they electromagnetise the poles
which produce the necessary flux that is
cut by revolving armature conductors.

9. COMMUTATOR
• The commutator of DC motor is a cylindrical
structure made up of copper segments stacked
together, but insulated from each other by mica.
• Its main function as far as the DC motor is
concerned is to commute or relay the supply
current from the mains to the armature winding
housed over a rotating structure through the
brushes of DC motor.

10. BRUSHES
• The brushes of DC motor are made with carbon or graphite
structures, making sliding contact over the rotating commutator.
• The brushes are used to relay the current from external circuit to
the rotating commutator form where it flows into the armature
winding.

11. MOTOR PRINCIPLE
DC motor working is based on the principle that
when a current carrying conductor is placed in a
magnetic field, the conductor experiences a
mechanical force.
The direction of this force is given by Fleming’s
left-hand rule and magnitude is given by;
F = BIL Newtons

12. BACK EMF
When the armature of a DC motor rotates under the influence of the driving
torque, the armature conductors move through the magnetic field and hence
emf is induced in them as in a generator.
The induced emf acts in opposite direction to the applied voltage V (Lenz’s
law) and is known as Back EMF or Counter EMF (Eb).
The equation to find out back emf in a DC motor is given below,
The back emf Eb(= PΦZN/60 A) is always less than the applied voltage V,
although this difference is small when the motor is running under normal
conditions.

13. TYPES OF DC MOTOR
• Permanent Magnet DC Motor (PMDC Motor)
• Separately Excited DC Motor
• Self Excited DC Motor
• Shunt Wound DC Motor
• Series Wound DC Motor
• Compound Wound DC Motor
• Short shunt DC Motor
• Long shunt DC Motor
• Differential Compound DC Motor

15. Separately Excited DC Motor
• As the name suggests, in case of
a separately excited DC motor
the supply is given separately to
the field and armature windings.

16. Permanent Magnet DC Motor
• The permanent magnet DC motor (also known as a
PMDC motor) consists of an armature winding as
in case of an usual motor, but does not necessarily
contain the field windings.
• The construction of these types of DC motor are
such that, radially magnetized permanent magnets
are mounted on the inner periphery of the stator
core to produce the field flux.

17. Self Excited DC Motor
In case of self excited DC motor, the field winding is connected either in
series or in parallel or partly in series, partly in parallel to the armature
winding. Based on this, self excited DC Motors can be classified as:
1. Shunt wound DC motor
2. Series wound DC motor
3. Compound wound DC motor

18. Shunt Wound DC Motor
In case of a shunt wound DC motor or more
specifically shunt wound self excited DC motor, the
field windings are exposed to the entire terminal
voltage as they are connected in parallel to the
armature winding as shown in the figure

19. Torque speed characteristic of a shunt wound
self excited DC motor
The shunt wound DC motor is a constant speed motor, as the speed does
not vary here with the variation of mechanical load on the output.

20. Series Wound DC Motor
In case of a series wound self excited DC motor or simply series wound DC
motor, the entire armature current flows through the field winding as its
connected in series to the armature winding.

21. Torque speed characteristic
In a series wound DC motor, the speed varies with load. And
operation wise this is its main difference from a shunt wound DC
motor.

22. Compound Wound DC Motor
The compound excitation characteristic in a DC motor can be
obtained by combining the operational characteristic of both the
shunt and series excited DC motor.

23. Cumulative Compound DC Motor
When the shunt field flux assists the main field flux, produced by the main
field connected in series to the armature winding then its called cumulative
compound DC motor.

24. Differential Compound DC Motor
In case of a differentially compounded self excited DC motor i.e. differential
compound DC motor, the arrangement of shunt and series winding is such
that the field flux produced by the shunt field winding diminishes the effect of
flux by the main series field winding.

25. The compounding characteristic of the self
excited DC motor
Both the cumulative compound and differential
compound DC motor can either be of short shunt or long
shunt type depending on the nature of arrangement.

26. Short Shunt DC Motor
If the shunt field winding is only parallel to the armature winding and not
the series field winding then its known as short shunt DC motor or more
specifically short shunt type compound wound DC motor.

27. Long Shunt DC Motor
If the shunt field winding is parallel to both the armature winding and the
series field winding then it’s known as long shunt type compounded wound
DC motor or simply long shunt DC motor.

28. Power Flow Diagram

29. Losses in a rotating DC machine
• Copper losses
1. Armature Cu loss
2. Field Cu loss
3. Loss due to brush contact resistance
• Iron Losses
1. Hysteresis loss
2. Eddy current loss
• Mechanical losses
1. Friction loss
2. Windage loss

30. Applications of DC Motors
The main applications of the three types of direct current motors are given
below.
1. Series Motors
The series DC motors are used where high starting torque is required, and
variations in speed are possible. For example – the series motors are used in
Traction system, Cranes, air compressors, Vaccum Cleaner, Sewing machine,
etc.

31. 2. Shunt Motors
The shunt motors are used where constant speed is required and starting
conditions are not severe. The various applications of DC shunt motor are in
Lathe Machines, Centrifugal Pumps, Fans, Blowers, Conveyors, Lifts, Weaving
Machine, Spinning machines, etc.

32. 3. Compound Motors
The compound motors are used where higher starting torque and
fairly constant speed is required. The examples of usage of
compound motors are in Presses, Shears, Conveyors, Elevators,
Rolling Mills, Heavy Planners, etc.
The small DC machines whose ratings are in fractional kilowatt are
mainly used as control device such in Techno generators for speed
sensing and in Servo motors for positioning and tracking.