Classification of electric motors

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Classification of Electric Motors
In the previous topic” Electrical Motors Basic Components “, I explained the construction and basic
components of the main motor types of motors; AC and DC motors.
Today, I will explain the different types in electric motors world as follows.
Main Types of Motor
Electric motors are broadly classified into two categories as follows:
1. AC Motors.
2. DC Motors.
Within those two main categories there are subdivisions as shown in the below image.
Motor Types
Notes: Recently, with the development of economical and reliable power electronic components, there
are numerous ways to design a motor and the classifications of these motors have become less rigorous
and many other types of motor have appeared. Our classification of motors will be comprehensive as can
as possible.
First: DC motors
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DC motors
DC power systems are not very common in the contemporary engineering practice. However, DC motors
have been used in industrial applications for years Coupled with a DC drive, DC motors provide very
precise control DC motors can be used with conveyors, elevators, extruders, marine applications,
material handling, paper, plastics, rubber, steel, and textile applications, automobile, aircraft, and
portable electronics, in speed control applications.
Advantages of DC motors:
1. It is easy to control their speed in a wide range; their torque-speed characteristic has, historically,
been easier to tailor than that of all AC motor categories. This is why most traction and servo
motors have been DC machines. For example, motors for driving rail vehicles were, until recently,
exclusively DC machines.
2. Their reduced overall dimensions permit a considerable space saving which let the manufacturer of
the machines or of plants not to be conditioned by the exaggerated dimensions of circular
motors.
Disadvantages of DC motors
1. Since they need brushes to connect the rotor winding. Brush wear occurs, and it increases
dramatically in low-pressure environment. So they cannot be used in artificial hearts. If used on
aircraft, the brushes would need replacement after one hour of operation.
2. Sparks from the brushes may cause explosion if the environment contains explosive materials.
3. RF noise from the brushes may interfere with nearby TV sets, or electronic devices, Etc.
4. DC motors are also expensive relative to AC motors.
Thus all application of DC motors have employed a mechanical switch or commutator to turn the
terminal current, which is constant or DC, into alternating current in the armature of the machine.
Therefore, DC machines are also called commutating machines.
Types of DC motors:
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The DC motors are divided mainly to:
1. Brush DC motors (BDC).
2. Brushless DC motors (BLDC).
1. A Brush DC motors
Types of DC motors
Brush DC motors
A brushed DC motor (BDC) is an internally commutated electric motor designed to be run from a direct
current power source.
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Applications:
Brushed DC motors are widely used in applications ranging from toys to push-button adjustable car
seats.
Advantages:
Brushed DC (BDC) motors are inexpensive, easy to drive, and are readily available in all sizes and shapes
Construction:
Brushed DC motor Construction
All BDC motors are made of the same basic components: a stator, rotor, brushes and a commutator.
1- Stator
The stator generates a stationary magnetic field that surrounds the rotor. This field is generated by
either permanent magnets or electromagnetic windings.
2- Rotor
Rotor (Armature)
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The rotor, also called the armature, is made up of one or more windings. When these windings are
energized they produce a magnetic field. The magnetic poles of this rotor field will be attracted to the
opposite poles generated by the stator, causing the rotor to turn. As the motor turns, the windings are
constantly being energized in a different sequence so that the magnetic poles generated by the rotor do
not overrun the poles generated in the stator. This switching of the field in the rotor windings is called
commutation.
3- Brushes and Commutator
Commutator Example
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Segments and Brushes
Unlike other electric motor types (i.e., brushless DC, AC induction), BDC motors do not require a
controller to switch current in the motor windings. Instead, the commutation of the windings of a BDC
motor is done mechanically. A segmented copper sleeve, called a commutator, resides on the axle of a
BDC motor. As the motor turns, carbon brushes (ride on the side of the commutator to provide supply
voltage to the motor) slide over the commutator, coming in contact with different segments of the
commutator. The segments are attached to different rotor windings, therefore, a dynamic magnetic
field is generated inside the motor when a voltage is applied across the brushes of the motor. It is
important to note that the brushes and commutator are the parts of a BDC motor that are most prone
to wear because they are sliding past each other.
How the Commutator Works:
How the Commutator Works
As the rotor turns, the commutator terminals also turn and continuously reverse polarity of the current
it gets from the stationary brushes attached to the battery.
Types of BDC motors:

Types of DC motors
The different types of BDC motors are distinguished by the construction of the stator or the way the
electromagnetic windings are connected to the power source. These types are:
1. Permanent Magnet.
2. Shunt-Wound.
3. Series-Wound.
4. Compound-Wound.
5. Separately excited DC motor.
6. Universal Motor.
7. Servo Motors.
A- Permanent Magnet

Permanent Magnet Motor
A permanent magnet DC (PMDC) motor is a motor whose poles are made out of permanent magnets to
produce the stator field.
Advantages:
1. Since no external field circuit is needed, there are no field circuit copper losses.
2. Since no field windings are needed, these motors can be considerable smaller.
3. Widely used in low power application.
4. Field winding is replaced by a permanent magnet (simple construction and less space).
5. No requirement on external excitation.
Disadvantages:
1. Since permanent magnets produces weaker flux densities then externally supported shunt fields,
such motors have lower induced torque.
2. There is always a risk of demagnetization from extensive heating or from armature reaction
effects (Some PMDC motors have windings built into them to prevent this from happening).
B- Shunt-Wound

Shunt-Wound Motor
Shunt-wound Brushed DC (SHWDC) motors have the field coil in parallel (shunt) with the armature.
The speed is practically constant independent of the load and therefore suitable for commercial
applications with a low starting load, such as centrifugal pump, machine tools, blowers fans,
reciprocating pumps, etc.
Advantages:
1. The current in the field coil and the armature are independent of one another. as a result, these
motors have excellent speed control.
2. Loss of magnetism is not an issue in SHWDC motors so they are generally more robust than PMDC
motors.
3. Speed can be controlled by either inserting a resistance in series with the armature (decreasing
speed) or by inserting resistance in the field current (increasing speed).
Disadvantages:
1. Shunt-wound Brushed DC (SHWDC) motors have drawbacks in reversing applications, however,
because winding direction relative to the shunt winding must be reversed when armature voltage is
reversed. Here, reversing contactors must be used.
C- Series-Wound
Series-Wound Motor
Series-wound Brushed DC (SWDC) motors have the field coil in series with the armature. These motors
are ideally suited for high-torque applications such as traction vehicles (cranes and hoists, electric trains,
conveyors, elevators, electric cars) because the current in both the stator and armature increases under
load.
Advantages:
1. The torque is proportional to I2 so it gives the highest torque per current ratio over all other dc
motors.

Disadvantages:
1. A drawback to SWDC motors is that they do not have precise speed control like PMDC and SHWDC
motors have.
2. Speed is restricted to 5000 RPM.
3. It must be avoided to run a series motor with no load because the motor will accelerate
uncontrollably.
D- Compound-Wound
Compound-Wound Motor
Compound Wound (CWDC) motors are a combination of shunt-wound and series-wound motors.
CWDC motors employ both a series and a shunt field. The performance of a CWDC motor is a
combination of SWDC and SHWDC motors. CWDC motors have higher torque than a SHWDC motor while
offering better speed control than SWDC motor.
It is used in Applications such as Rolling mills, sudden temporary loads, heavy machine tools, punches,
etc.
Advantages:
1. This motor has a good starting torque and a stable speed.
Disadvantages:
1. The no-load speed is controllable unlike in series motors.
E- Separately excited DC motor
Separately excited DC motor
In a separately excited DC motor the field coils are supplied from an independent source, such as a
motor-generator and the field current is unaffected by changes in the armature current. The separately

excited DC motor was sometimes used in DC traction motors to facilitate control of wheel slip.
F- Universal Motor
Universal Motor
The universal motor is a rotating electrical machine similar to DC series motor, designed to operate
either from AD or DC source. The stator & rotor windings of the motor are connected in series through
the rotor commutator. The series motor is designed to move large loads with high torque in applications
such as crane motor or lift hoist.
G- Servo Motors

Servo Motors
Servo Motors are mechanical devices that can be instructed to move the output shaft attached to a
servo wheel or arm to a specified position. Servo Motors are designed for applications involving position
control, velocity control and torque control.
Servo Motors Components
A servo motor mainly consists of a DC motor, gear system, a position sensor which is mostly a
potentiometer, and control electronics.

Servo Motors Applications
In the next Topic, I will explain the Brushless DC Motor (BDLC) & AC Motors Types. So, please keep
following.
Note: these topics about Motors in this course EE-1: Beginner's electrical design course is an introduction
only for beginners to know general basic information about Motors and Pumps as a type of Power loads.
But in other levels of our electrical design courses, we will show and explain in detail the Motor and
Pumps Loads calculations.
You might also like:
Classification of
Electric Motors -
Part Four
Classification of
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Part Two
Classification of
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Classification of
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Electrical Motors
Basic Components
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13 comments:
Yasa November 15, 2012 at 8:29 PM
thanks for detailed info!!!
Baldor Single Phase motors
Reply
Abdelrahman Saleh December 31, 2012 at 12:26 AM
PLZ, we want data about nameplate :))
Reply
Abdelrahman Saleh December 31, 2012 at 12:27 AM
What's the main disadvantage of induction motors ??.
Reply
Ali Hassan December 31, 2012 at 3:07 PM
to Abdelrahman Saleh:
I will post an article about how to read the motor nameplate data in the new course " motor advanced
course". just keep following

Reply
Ali Hassan December 31, 2012 at 3:08 PM
to Abdelrahman Saleh:
the main disadvantage of induction motors are:
- Not easy to have variable speed control.
- Requires a variable-frequency power-electronic drive for optimal speed control.
- Most of them run with a lagging power factor.
Reply
tarek_abukhadra January 16, 2013 at 2:11 PM
عمل رائع ومجھود یستحق الشكر
Reply
shakeel ahmed May 24, 2013 at 8:27 PM
where is ac motor part ?
Reply
Replies
Reply
Ali Hassan June 3, 2013 at 11:30 AM
Please visit the Motor course's main page at :
http://www.electrical-knowhow.com/2012/11/course-motor-1-introduction-to.html
you will find all the articles regarding AC motors
Ferdous ibn kader July 12, 2013 at 10:10 AM
well organized lecture sheet!!! really awesome article.
www.mrosupply.com
Reply
hans raj July 28, 2013 at 6:19 AM
Nice page thnks sir i like it
Reply
hans raj July 28, 2013 at 6:20 AM
Nice page thnks sir i like it
Reply
haritha perera October 22, 2013 at 9:09 AM
wooooooooooow thankzzzzzzzzzzzzzz i think it is good for everyone
Reply
Replies
Reply
Hussein Usman November 20, 2013 at 3:21 AM
tnx

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