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ELECTRICAL POWER
AC MOTOR & DC MOTOR
INTRODUCTION
 An electrical motor machine that converts electrical
energy to mechanical energy in the form of torque and
rotation.
 The motor is classifies into 2 types:-
Direct Current (DC) motor
2. Alternating Motor (AC) motor
1.
 A DC motor uses DC power supply or a battery as its
source of power.
 An AC motor is classifies into 2:1. a single phase motor which uses 240V AC power
supply,
2. a three phase motor which uses 415V AC power
supply.
INTRODUCTION
DC MOTOR
AC MOTOR
The unit of power for electrical motor is
watt (W).
Horsepower (HP) is also used to determine
the power of an electric motor.
DC MOTOR
a.
b.
c.
d.
Commutator
Frame
Field Pole
Ball Bearings
e. Shaft
i. Carbon Brush
f. Stator Winding j. Fan
g. Armature
h. Terminal Box
BASIC CONSTRUCTIONS
The basic construction of a DC motor comprises
the stator and the rotor.
STATOR
 has the field windings which produce the
magnetic field flux.
 fixed to the frame of the motor which is
stationary.
ROTOR
 located at the centre of the motor is attached to
the shaft.
 rotates in the electric motor.
BASIC CONSTRUCTION OF DC MOTOR
STATOR
ROTOR
MAIN COMPONENTS OF A DC MOTOR
1.
2.
3.
4.
Armature
Commutator
Field poles
Carbon Brush
 The armature and the commutator are mounted
onto the rotor
 The fields and the carbon brush are located in
the stator.
ARMATURE
 The part of the motor that rotates
 Receives the electrical energy
 Made up of :-
 the armature core - functions as an
electromagnet, producing the magnetic
field that will react with the stator to
force produce a rotation from the shaft.
 The armature windings - to
transform the armature core into an
electromagnet when current flows
through the windings and causing the
armature core to become an
electromagnet.
 The slots act a path for the armature
windings and divide the armature into
several segments.
COMMUTATOR
 A cylindrical shaped component
that mounted in the rotor.
 Made up of several segments
metal bars that are insulated
from one another.
 The number of segments
depends on the number of
armature windings.
 Allows the current from the
power supply to the armature
windings through the carbon
brush.
FIELDS POLES
 Produce a permanent magnetic field in the DC motor
 Small DC motors use the permanent magnets for the field
poles
 Bigger DC motors use electromagnet produce by field
 The windings that produce at the field poles are called field
windings.
CARBON BRUSH
 Shaped like a small cube acts as a connectors.
 The current from power supply flows through the
carbon brush via the commutator to the armature
windings.
 The carbon brush to feed current in and out of the
armature windings
PRINCIPLES OPERATION OF A DC MOTOR
 The rotation in a DC motor is due to the
interaction between magnetic fields (the
reaction between the field of the permanent
magnet and the field of the armature
magnet)
 The interaction between these two fields
produces a torque that causes the rotor to
rotate.
TORQUE GENERATION
 The strength of torque produced depends on the strength of the
magnetic field of the armature and the field poles.
 Figure (a) shows the magnetic flux that exists between the 2 field
poles.
 Figure (b) shows the direction of the flux in the armature through the
commutator.
 Figure (c) shows the interaction between magnetic flux and the field
poles magnetic flux. This interaction will produce torque.
• The direction of the torque is determined by the Fleming
Left Hand Rule.
thuMb
points to direction of
force (Movement)
First finger
Points to direction
of Field (N to S)
seCond finger
points to direction
of Current (+ to – )
Direction of
current flow
Direction of movement
(The conductor will move upwards or downwards
depending on the direction of the current)
BASIC DC MOTOR CIRCUIT
 DC motors are classified into three types:
1. Series motor
2. shunt motor and
3. Compound motor
 The classification is determined by the
connection between field winding and
armature winding and the supply.
SERIES MOTOR
 In a series motor, the field windings and the armature windings are




connected in series to the supply
The current that flows in the field windings will flow in the
armature windings.
When voltage is supplied, there is no back emf in the armature
which enables a high initial current to flow in the field windings and
the armature windings.
This condition generates a high initial torque.
Thus, the motor is suitable for operating systems with heavy loads
SHUNT MOTOR
 Uses a parallel connection for connecting the field windings
and the armature windings to the supply
 The parallel connection causes the current in the field
winding to be constant. The current in the armature winding
depends on the back emf.
 More suitable when constant speed is required without high
initial torque.
 Suitable for use in applications such as machine tools,
polishers and sprayers.
COMPOUND MOTOR
 The combinations of a series motor and a shunt motor.
 Has the field windings and the armature windings are connected in
series to the supply.
 One is connected in series to the armature windings and the power
supply. The other is connected in parallel to the supply.
 Has a good starting torque and at constant speed
 Usually used in heavy load machine. Such as in cutting and grinding.
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