FEDERAL UNIVERSITY OF TECHNOLOGY AKURE
NAME: ILUBANWO OLUKOREDE BABATUNDE
DEPARTMENT: INDUSTRIAL AND PRODUCTION ENGINEERING
MATRIC NUMBER: IPE/19/1432
COURSE: ELECTRICAL AND ELECTRONICS ENGINEERING
MACHINE 2(EEE 308)
TITLE: PRE PRACTICAL ASSIGNMENT
LECTURER: DR. OGUNBOYO PATRICK TAIWO
PRE-PRAC QUESTIONS
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8.
What is meant by induction motors?
Where are induction motors used?
What is the working principle of induction motors?
Why is starter used in induction motors?
What are the advantages and disadvantages of induction motors.
What are the parts of induction motors?
List the types of single phase induction motor
List the type of 3 phase induction motor.
1. What is meant by induction motors?
Induction motors are electric motors that use alternating current (AC), propelled by a
magnetic field that rotates. They are made up of a rotor, a stator and coils that convert
electrical energy into mechanical energy using electromagnetic induction. AC induction motors
are highly efficient and flexible, and relatively simple in design, which allows them to match the
load demand for almost any electrical application.
A stator is an outer, non-moving chamber in which the rotor spins. It is formed by a ring of
electromagnets designed as a cylinder to produce a rotating magnetic field. Copper wire wound
throughout the cylinder’s interior creates magnetic poles, with one pole of each magnet facing
towards the center. When alternating current flows through these wire coils, they form a pair
of alternating poles. The alternating poles create an alternating magnetic field that rotates with
unified strength.
A rotor also consists of a group of electromagnets arranged around a cylinder, and it is
housed inside the stator. The magnet fields activated within the rotor are attracted to the
magnetic field produced by the stator. Hence why the magnetic field induced in the stator
induces a magnetic field in the rotor.
Induction motors are referred to as ‘asynchronous motors’ because they operate at a speed
less than their synchronous speed.
2. Where are induction motors used?

HVAC Systems (Heating, Ventilation, and Air Conditioning): In HVAC systems,
induction motors operate fans, blowers, and air handlers. They play a critical role in
maintaining comfortable temperatures and air quality in residential, commercial,
and industrial buildings.

Home Appliances: Many household appliances utilize induction motors. Washing
machines, refrigerators, dishwashers, and food processors rely on these motors to
drive various rotating components and ensure the proper functioning of these
appliances.

Automotive Industry: Induction motors are gaining prominence in the automotive
sector, especially in electric and hybrid vehicles. They are used for propulsion,
contributing to efficient and quiet operation.

Water Treatment: Water treatment plants use induction motors to power pumps,
blowers, and mixers in processes such as water supply, wastewater treatment, and
desalination.

Renewable Energy: Induction motors are employed in various renewable energy
systems. For example, they are used in wind turbines to convert the kinetic energy
of the wind into electrical energy. They also find applications in hydroelectric power
plants.

Mining: Induction motors are used in mining equipment, such as crushers,
conveyors, and hoists, to facilitate the extraction and transportation of minerals and
ores.
. AC induction motors are efficient and flexible, which allows them to match the load
demand for almost any type of electrical application.
Induction motors are used in a wide variety of applications across numerous industries due
to their efficiency, reliability, and cost-effectiveness.
3. What is the working principle of induction motors?
The motor which works on the principle of electromagnetic induction is known as the
induction motor. The electromagnetic induction is the phenomenon in which the electromotive
force induces across the electrical conductor when it is placed in a rotating magnetic field.
When the three phase supply is given to the stator, the rotating magnetic field produced on it.
The polarities of the magnetic field vary by concerning the positive and negative half cycle of
the supply. The change in polarities makes the magnetic field rotates. The conductors of the
rotor are stationary. This stationary conductor cut the rotating magnetic field of the stator, and
because of the electromagnetic induction, the EMF induces in the rotor. This EMF is known as
the rotor induced EMF, and it is because of the electromagnetic induction phenomenon.
The conductors of the rotor are short-circuited either by the end rings or by the help of the
external resistance. The relative motion between the rotating magnetic field and the rotor
conductor induces the current in the rotor conductors. As the current flows through the
conductor, the flux induces on it. The direction of rotor flux is same as that of the rotor current.
Now we have two fluxes one because of the rotor and another because of the stator. These
fluxes interact each other. On one end of the conductor the fluxes cancel each other, and on
the other end, the density of the flux is very high. Thus, the high-density flux tries to push the
conductor of rotor towards the low-density flux region. This phenomenon induces the torque
on the conductor, and this torque is known as the electromagnetic torque. The direction of
electromagnetic torque and rotating magnetic field is same. Thus, the rotor starts rotating in
the same direction as that of the rotating magnetic field. The speed of the rotor is always less
than the rotating magnetic field or synchronous speed. The rotor tries to the run at the speed
of the rotor, but it always slips away. Thus, the motor never runs at the speed of the rotating
magnetic field, and this is the reason because of which the induction motor is also known as the
asynchronous motor.
4. Why is starter used in induction motors?
For single phase supply no starter is required while starter is required for 3 phase motors
because 3 phase motors takes very high current when motor is switched on (due to induction
effect). This high current may reach up to 5-7 times than that of full load current of the motor
and this high current reduces the supply
voltage to motor temporarily which causes voltage fluctuation in the line and fluctuation in
voltage affects the operation of other equipment. So, it is important to reduce initial high
current of the motor & that is done by starter. Induction motors use starters to supply the first
burst of electrical energy required to get the motor up and running. This is why starters are
employed:
Overcoming Initial Resistance:
An induction motor requires an initial burst of electrical current to start since the stationary
rotor has a high resistance. It is referred to as "locked rotor current."
Preventing Overload:
In the absence of a starter, the initial surge of current may be excessive and overload the
electrical system. Voltage drops may result from this, which may harm the motor as well as any
attached equipment.
Reducing Mechanical Stress:
Getting a motor started while it is fully loaded might result in mechanical stress and wear
on the motor's parts. This stress can be decreased by using a starter, which enables a regulated
and steady increase in current.
Increasing Efficiency:
Star-delta starting and auto transformer starting are two ways you can use with a starter.
These techniques lessen the initial current and voltage spike, which may result in motor running
that is more effective.
Increasing Motor Life:
The motor's lifespan can be increased by minimizing the stress and strain experienced
during startup, which will result in cheaper maintenance and replacement expenses.
Compliance with Regulations:
To ensure safe and effective motor operation, several industries or regions have
regulations in place that demand the usage of starters.
Assuring Consistent Performance:
In applications where accuracy and dependability are crucial, starters offer a controlled and
consistent starting approach.
In conclusion, starters are used with induction motors to provide a controlled and smooth
start, safeguarding the motor and the electrical system. They support effective and dependable
motor operation by lowering mechanical stress and managing the early surge of current.
5. What are the advantages and disadvantages of induction motors.
Advantages of Induction Motors:
Reliability: Induction motors are known for their high reliability. They have fewer moving
parts compared to some other motor types, reducing the likelihood of mechanical failure.
Low Maintenance: Due to their simplicity and robust design, induction motors require
minimal maintenance. They don't have brushes or commutators that need regular replacement.
Longevity: When properly maintained, induction motors can have a long service life,
making them a cost-effective choice in the long run.
Efficiency: Induction motors are generally efficient, especially when operating at or near
their rated load. This efficiency contributes to energy savings.
Robustness: They can operate in a wide range of environmental conditions, including high
temperatures and dusty environments, without significant performance degradation.
Cost-Effective: Induction motors are often cost-effective, making them a popular choice for
various applications, particularly when standard performance is sufficient.
Wide Range of Sizes: They are available in a wide range of sizes and power ratings, making
them suitable for both small and large applications.
Disadvantages of Induction Motors:
Limited Speed Control: Induction motors have a fixed synchronous speed determined by the
frequency of the power supply. They are not suitable for applications requiring precise speed
control over a wide range.
Lower Starting Torque: Induction motors may have limited starting torque, which can be a
drawback for applications with high-inertia loads or when a high starting torque is required.
Complex Control for Variable Speed: Achieving variable speed control with induction motors
requires additional equipment such as variable frequency drives (VFDs), which can increase
system complexity and cost.
Lower Efficiency at Low Loads: Induction motors can be less efficient when operating at low
loads, which may result in wasted energy in applications with variable loads.
Inefficiency at Low Power Factor: Induction motors can operate at low power factors, which can
result in increased energy costs and affect the quality of electrical supply in industrial settings.
Maintenance for Large Motors: While smaller induction motors are low maintenance, larger
motors can be more complex and require periodic maintenance, which can be costly.
Acoustic Noise: Induction motors can generate noise, which may be a concern in applications
where quiet operation is required.
Starting Current: The inrush current during startup can be relatively high, potentially causing
voltage dips in the electrical supply and affecting other connected equipment.
6. What are the parts of induction motors?
`
Here are the main components of an induction motor:

Stator: The stator is the stationary part of the motor and is composed of a core made
of laminated steel sheets. It contains insulated windings that receive the alternating
current (AC) supply. When energized, these windings create a rotating magnetic field.

Rotor: The rotor is the rotating part of the motor. It can be of two types:
Squirrel Cage Rotor: This is the most common type. It consists of laminated steel
core with conductive bars (like a squirrel cage) shorted at both ends. The rotor's design
allows it to react to the rotating magnetic field and start moving.
Wound Rotor: This type has windings similar to the stator on its rotor. The rotor
windings can be connected externally to resistors or other external circuitry. This
allows for some control over the motor's performance characteristics.

Bearings: Induction motors typically have two bearings that support the rotor. These
bearings allow the rotor to rotate smoothly within the stator.

Shaft: The shaft connects the rotor to the external load or machinery that the motor is
driving. It needs to be strong and properly aligned to ensure smooth operation.

End Bells or End Shields: These are protective covers at either end of the motor. They
provide structural support and protect the interior components from dust, moisture,
and other contaminants.

Air Gap: This is the space between the stator and rotor where the magnetic interaction
occurs. The size and uniformity of the air gap are critical for proper motor
performance.

Ventilation Openings: These are openings in the motor housing that allow for cooling
air to circulate around the motor, dissipating heat generated during operation.

Terminal Box: This is a compartment where the electrical connections are made,
allowing the motor to be connected to an external power supply.

Cooling Fan: In some motors, a fan is attached to the rotor shaft. It helps in drawing air
through the ventilation openings, aiding in the cooling process.

Core and Laminations: The stator core is made up of thin, insulated steel sheets
(laminations) that are stacked and bonded together. This construction reduces energy
losses due to eddy currents.

Thermal Protection (Optional): Some motors may have thermal protection devices like
thermistors or thermal switches to prevent overheating.
7. List the types of single phase induction motor

Split-Phase Induction Motor:
This is the most common type for household applications. It has two windings: a
start winding and a run winding. The start winding has higher resistance and lower
inductance to create a phase shift, which gives the motor a starting torque.

Capacitor Start Induction Motor:
This motor includes a start capacitor in addition to the start winding. The capacitor
provides an extra phase shift, which increases starting torque. Once the motor reaches
a certain speed, a centrifugal switch disconnects the start winding and capacitor.

Capacitor Start-Capacitor Run Induction Motor:
This motor has both a start capacitor and a run capacitor. The start capacitor
provides high starting torque, and the run capacitor continues to improve efficiency
and performance as the motor operates

Shaded-Pole Induction Motor:
Shaded-pole motors have a single winding with part of it surrounded by a copper
ring. This ring creates a time lag in the magnetic field, causing the motor to start and
rotate.
8. List the type of 3 phase induction motor.
Three-phase induction motors come in a variety of designs, each intended for a
particular use. Here are the main categories:

Induction motor with a squirrel-cage rotor:
The most prevalent kind of three-phase induction motor is this one. Its name
comes from the shape of the rotor, which is similar to a squirrel cage. Because the
rotor bars are shorted at both ends, they can operate effectively.
 Induction motor with wound rotor:
This type's rotor windings resemble those of the stator's. The external resistors or
other control mechanisms are linked to the rotor winding. As a result, the performance
parameters of the motor can be somewhat controlled.
 Double Cage Rotor Induction Motor:
Two sets of rotor bars are positioned concentrically in a motor known as a double
cage rotor induction. The inner set has stronger resistance and lower reactance,
making it better suited for running circumstances, while the outer set has lower
resistance and higher reactance, offering high starting torque.
 Slip Ring Rotor Induction Motor:
Like wound rotor motors, slip rings and brushes are used to make external
electrical connections to the rotor windings. Speed and torque may be controlled more
precisely with slip ring motors.
 Motor with Synchronous Speed Induction:
This motor has the capacity to operate without slip at synchronous speed (the
speed of the spinning magnetic field). It is accomplished by modifying the magnetic
field of the rotor using additional circuits.
 Single Phase Induction Motor with Auxiliary Winding:
Despite being typically single-phase motors, they can be categorized as a form of
three-phase motor when initiating auxiliary windings.
 Generators by induction:
Induction generators function in a manner similar to motors even though they are
not officially a "type" of motor. They are employed in various renewable energy
systems, such as specific kinds of wind turbines, to produce electrical power.