Chapter and disk drives, electric motors can be

Chapter 1

INTRODUCTION

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An electric motor converts electrical energy into mechanical
energy. The reverse of this would be the conversion of mechanical energy into
electrical energy and is done by an electric generator.

In normal motoring mode, most electric motors operate
through the interaction between an electric motor’s magnetic field and winding
currents to generate force within the motor. In certain applications, such as
in the transportation industry with traction motors, electric motors can
operate in both motoring and generating modes to
also produce electrical energy from mechanical energy.

Found in applications as diverse as industrial fans, blowers
and pumps, machine tools, household appliances, power tools, and disk drives,
electric motors can be powered by direct current (DC) sources, such as from
batteries, motor vehicles or rectifiers, or by alternating current (AC)
sources, such as from the power grid, inverters or generators. Small motors may
be found in electric watches. General-purpose motors with highly standardized
dimensions and characteristics provide convenient mechanical power for
industrial use. The largest of electric motors are used for ship propulsion,
pipeline compression and pumped-storage applications with ratings reaching 100
megawatts. Electric motors may be classified by electric power source type,
internal construction, application, type of motion output, and so on. However,
for a motor to work or achieve the purpose they are made to do whether in
industrial or workshop, they must be controlled. The direct, speed and torque
must be controlled by a controller.
A motor controller is a device or group of devices that serves to govern in
some predetermined manner the performance of an electric motor. A motor
controller might include a manual or automatic means for starting and stopping
the motor, selecting forward or reverse rotation, selecting and regulating the
speed, regulating or limiting the torque, and protecting against overloads and
faults.

Different starting methods are employed for starting
induction motors because Induction Motor draws more starting current during
starting. To prevent damage to the windings due to the high starting current
flow, we use different types of starters.
The simplest form of motor starter for the induction motor is the Forward
Reverse starter. The Forward Reverse Motor Starter consists of a
Circuit Breaker, Contactor and an Overload Relay for protection. Typically, the
contactor will be controlled by separate start and stop buttons, and an
auxiliary contact on the contactor is used, across the start button, as a hold
in contact.

 

1.1          
Overview

 

The device connects a motor to a
power source, such as in small appliances or power tools. The switch can be
manually operated or with a relay or contactor connected to some form of sensor
to automatically start and stop the motor. The switch has several positions to
select different connections of the motor. This allows reduced-voltage starting
of the motor, reversing control or selection of multiple speeds. Overload and
over current protection may be omitted in very small motor controllers, which
rely on the supplying circuit to have over current protection. Small motors may
have built-in overload devices to automatically open the circuit on overload.
Larger motors have a protective overload relay or temperature sensing relay
included in the controller and fuses or circuit breakers for over current
protection. An automatic motor controller may include limit switches or other
devices to protect the driven machinery.

 

1.2          
Project Idea

 

Electric motors can run in both forward and reverse
direction depending on the requirement of the application where it is to be
installed. For this type of application, a forward reverse motor controller is
applied to the control circuit of the electric motor to achieve this purpose.
The device required for the possibility of this operation is the magnetic contactor.

 

1.3          
Purpose of the project

 

The purpose of this project is to design a device for
starting and stopping the motor. It includes forward or reverse rotation of
motor, regulating the speed and limiting the torque. It will protect motor
against overloads and faults.

 

1.4          
Project Specifications

 

The project has simple
control circuitry. It is most economical
and cheapest starter. It is simple to establish, operate and maintain.

 

1.5          
Applications of the project

 

The forward reverse
method is usually applied to low voltage, medium voltage and light starting
torque motors.

The received
starting current is about 30 % of the starting current during direct on line
start and the starting torque is reduced to about 25 % of the torque. This
starting method only works when the application is light loaded during the
start.
If the motor is too heavily loaded, there will not be enough torque to
accelerate the motor up to speed before switching over to the delta position.

 

1.6          
Project Plan

 

Table 1 Project Plan

Tasks

Duration

Source Person

Literature Review

01 Week

Muhammad Sheraz, Shams-Ud-Din

Implementation of procedure

02 Week

Muhammad Sheraz, Shams-Ud-Din

Testing of project

03 Weeks

Muhammad Sheraz, Shams-Ud-Din

Final project and report submission

04 Week

Muhammad Sheraz, Shams-Ud-Din

 

Chapter 2

LITERATURE
REVIEW

1          
 

2          
 

2.1          
Background Theory

 

A starter turns an
electric motor or motor controlled equipment on or off, while providing
overload protection. Starters represent another evolution in motor control applications.

Contactors control
the electric current flowing towards the motor. Their function is to repeatedly
establish and interrupt an electrical power circuit.

Overload Protection
protects motors from drawing too much current, overheating, and from literally
burning out. 1

 

2.2          
Related Technologies

 

The related
technologies of starters are discussed below.

2.2.1      Direct On line     

It consists of
simple push button as the controller. When the start button is pressed, the
switch connecting the motor and the main supply is closed and the motor gets
the supply current. In case of over current, the stop button is pressed, and
the bypass auxiliary contact is opened.

2.2.2      Star Delta Starter

The 3 windings are
first connected in star connection and then after some time (decided by the
timer or other controller circuit) the windings are connected in delta
connection. In star connection, the current drawn is 0.58% of the normal
current and the phase voltage is reduced to 0.58%. Thus, the torque is reduced.

2.2.3      Auto Transformer starter

It consists of an
auto transformer (A Transformer with a single winding tapped at different
points to supply percentage of it primary voltage across secondary) in star
connection, which reduces the voltage applied to the motor terminals. It
consists of 3 tapped secondary coils connected to the three phases. In the
starting period the transformer allows application of lower voltages to the
three windings.

 

2.3          
Related projects

 

The projects
related to motor starters are discussed below

 

2.3.1      Motor start using Direct on Line
(DOL) starter

In this method, the
main heart of DOL starter is Relay Coil. Normally it gets one phase constant
from incoming supply voltage. When coil gets second phase relay coil energizes
and magnet of contactor produces electromagnetic field, due to this plunger,
contactor will move, and main contactor of starter closes and auxiliary changes
its position. NO will become NC and NC will become NO.

2.3.2      Motor start using Star- Delta
starter

In this method, the
three windings are first connected in star connection and then after some time
(decided by the timer or other controller circuit) the windings are connected
in delta connection.

2.3.3      Motor start using Auto
Transformer starter

In this method, the
starting current is limited by using a three-phase auto transformer to reduce
the initial stator voltage.

It is provided with
number of tapings. The starter is connected to one tapping to obtain the most
suitable starting voltage. The primary of the auto transformer is connected to
the supply line, and the motor is connected to the secondary of the auto
transformer.

 

2.4          
Limitations

 

It does not reduce the starting current of the motor.

High Starting Current:
Very High Starting Current (Typically 6 to 8 times the FLC of the motor).

Mechanically Harsh:
Thermal Stress on the motor, thereby reducing its life.

Voltage Dip:
There is a big voltage dip in the electrical installation because of high
in-rush current affecting other customers connected to the same lines.
Therefore, it is not suitable for higher size squirrel cage motors. 2

High starting Torque:
Unnecessary high starting torque, even when not required by the load, thereby
increased mechanical stress on the mechanical systems such as rotor shaft,
bearings, gearbox, coupling, chain drive, connected equipment, etc. leading to
premature failure and plant downtimes.

 

2.5          
Problem Statement

 

In some systems the
starting current of motor is required slow while in some systems starting
current is required fast, if current of the motor is not controlled according
to the requirement then the system may damage. So that is why motor current is
to be controlled as per the system requirements.

 

 

 

2.6          
Summary

 

The primary
function of forward reverse motor starter is to move the motor in forward and
reverse direction to which it is connected. These are specially designed
electromechanical switches like relays. The main difference between a relay and
a starter is that a starter contains overload protection for the motor. So, the
purpose of the starter is twofold, i.e., to switch the power automatically or
manually to a motor and at the same time protect the motor from overload or
faults.

Chapter
3

 

PROJECT DESIGN AND IMPLEMENTATION

 

3          
 

3.1          
Proposed Design Methodology

 

The forward and
reverse rotation of a motor can be caused by interchanging the connection of
any two of its three terminals. Contractors ‘F’ and ‘R’ are mechanically
interlocked. It means that if the contacts (1-2, 3-4, 5-6) of contractor R are
closed, contacts (1-2, 3-4, 5-6) of contractor F cannot be closed.

When the contacts
of contractor F are closed, L1 is connected to T1 through contact F (1-2), L2
is connected to T2 through contact F (3-4), and L3 is connected to T3 through
contact R (5-6). The motor M runs forward.

When the contacts
of contractor R are closed, L1 is connected to T3 through contact R (1-2), L2
is connected to T2 through contact R (3-4) and L3 is connected to T1 through
contact R (5-6). The motor M runs reverse.

Pressing the stop
push button de-energizes contactor F. This causes the contacts R (1-2, 3-4,
5-6) to open and stop the motor M from running forward. Contacts F (11-12)
close again maintaining contact F (13-14) open.

Pressing the
reverse push button energizes contactor R. Contactor R continually energizes
even if the reverse push button is released. Contacts R (11-12) open to prevent
contactor F to be energized. Contacts R (1-2, 3-4, 5-6) close to run motor M on
reverse direction.

Pressing the stop
push button again de-energizes contactor R. This causes the contacts R (1-2,
3-4, 5-6) to open and stops the motor from running reverse. Contact R (11-12)
close again maintaining contact R (13-14) open.

 

3.2          
Implementation Procedure

         

Figure 1 Block Diagram

 

Figure 2 Control Diagram

 

 

3.3          
Details about Hardware

         

Following components are used in project:

Circuit breaker

Contactors

Thermal overload relay

Push buttons

Indicator lights

Wires for connections

The chosen circuit
breaker is of 40 amperes. It protects the electrical circuit from damage caused
by excess current.

Two contactors are
used for forward and reverse rotation. They are used for switching of motor
switching circuits.

One thermal
overload relay is used after two contactors. It protects the motor against
overload.

In the end, a
three-phase motor is connected to relay.

 

 

 

3.4          
Details about Final Design

 

The complete
circuit is placed in a wooden box. The upper lid of box is made up of plastic
fiber.

Three phase
voltages were supplied to the final circuit and it was connected to induction
motor in delta connection. When forward push button was pressed, the motor
started to rotate clockwise. When reverse push button was pressed, direction
rotation of motor changes.

 

 

 

Figure 3 Hardware

 

3.5          
Summary

 

The connections of motor are
interchanged to make a forward reverse motor controller. Firstly, the push
button energizes the forward contactor to rotate motor in forward direction.
Then motor is stopped with help of stop push button. After that the other push
button energizes reverse contactor and motor rotates in reverse direction.
Chapter 4

 

TOOLS AND TECHNIQUES

 

4          
 

4.1          
Hardware Tools used

 

The tools used in
making of this project are push buttons, circuit breaker, contactors and
thermal overload relay.

4.1.1      Circuit Breaker

A circuit breaker
is an automatically operated electrical switch designed to protect an
electrical circuit from damage caused by excess current, typically resulting
from an overload or short circuit. The circuit breaker mainly consists of fixed
contacts and moving contacts. In normal “ON” condition of circuit
breaker, these two contacts are physically connected to each other due to
applied mechanical pressure on the moving contacts.

                                        

Figure 4 circuit breaker

 

4.1.2      Overload Relay

Thermal overload
relays are economic electromechanical protection devices for the main circuit.
They offer reliable protection for motors in the event of overload or phase
failure. The thermal overload relay can make up a compact starting solution
together with contactors

                                    .

Figure 5 overload relay

 

4.1.3      Contactor

A contactor is an electrically controlled switch
(relay) used for switching an electrical power circuit. A contactor is
typically controlled by a circuit which has a much lower power level than the
switched circuit, such as a 24-volt coil electromagnet controlling a 220-volt
motor switch. 3

                        

 Figure 6 contactor

 

 

 

 

 

 

 

 

4.1.4     
Push Button

A push button switch is a small, sealed mechanism
that completes an electric circuit when you press on it. When it’s on, a small
metal spring inside contacts two wires, allowing electricity to flow.  

                                        

Figure 7 push
button

                                                                                                                

 

 

4.2          
Summary

Four main
components are used in this project. Circuit breaker stops excessive current.
Contactors move motor in forward and reverse direction. Thermal overload relay
protects motor from damaging.

 

Chapter 5

PROJECT RESULTS
AND EVALUATION

All the results
were achieved. One push button was short circuited, it caused the whole circuit
to stop working. With instructor’s help the mistake was corrected and circuit
worked properly after that. Some modifications were made to final design. Two
indicators were added to show working of forward and reverse side. They worked
properly. The project was not very efficient, it has some limitations, but it
worked as the instructor wanted.

5          
 

5.1          
Presentation of the findings      

After making and modifying project at different stages the circuit was
able to run the motor in both forward and reverse direction.

5.1.1     
Hardware results

The first part of
project was circuit breaker. It worked properly and tripped when excess amount
of current was flown through its terminals.

In next part two
contactors were connected in parallel. When forward push button was pressed,
the current flew from forward contactor and motor started running in forward
direction. Because of interlocking current did not flow in reverse contactor.

Similarly, when
reverse push button was pressed, the reverse contactor worked accordingly and
started running the motor in reverse direction.

The last part of
the project contained overload relay. It was connected to keep the motor safe
in case of short circuit. When the push button caused short circuitry, motor
remained safe because of overload relay.

The whole project
was simple, and it worked fine.

 

5.2          
Discussion on the findings

 

The project was
compared with an already made controller. There were some limitations in this
design. It was rotating the motor in both directions.

The older
controller had star-delta starter connected to it. 4 It helped to run motor smoothly without any danger. The new
design was not that efficient.

This project
contained light indicators, which showed direction of rotation of motor.

 

5.2.1      Comparison with initial Project
Specifications

The project was
easy and simple. Its only purpose was to rotate the motor in forward as well as
in reverse direction.

This result was
achieved from the project as it was claimed in proposal.

 

 

           

5.2.2      Reasoning for short comings 

Some changings had
to make to the project because of unavailability of contactors of same values.

This took a lot of
time and a new hardware was designed for the changed design. At the end, all
results were same.

 

5.3          
Limitations of the working prototype

 

The final working
prototype had some limitations in it. To run a motor in both directions, it had
to run in forward direction first. Then motor is stopped with help of stop push
button. After that, it moved in reverse direction.

By pushing reverse
button while motor was moving in forward direction may cause short circuitry.
Similarly, pressing forward button while motor was moving in reverse direction
may cause short circuitry of project.

To start the motor,
delta motor connection was required. This connection was not added to the
project.

 

5.4          
Recommendations
and Future Work

 

A delta motor
connection should be made part of this project to start the motor smoothly.

Mechanical
interlocking should be made better for the safety of the circuit.

A timer can be
introduced to stop the motor automatically after running in both directions.

 

5.5          
Summary

 

In this chapter,
results of the project were discussed. All the parts of the project worked
properly. The project was compared with a standard working prototype. It had
limitations and short comings. The reasons of short comings were also given.

In the end, some
recommendations were given to make this project better for future use.

Chapter 6

 

CONCLUSION AND FUTURE WORK

 

The one main
problem was faced because of unavailability of required contactor. One
contactor worked for 180V and other was working for 220V. Because of this,
whole circuit was changed.

After working on
this project, it is concluded that this motor controller is very useful in
modern world. It can be used in lifts to move the lift in upward and downward
directions. It can be used in automatic doors to open and close them. It is
cheap and easy to make. It does not require modern techniques.

Its uses would
increase in future. It can be used in modern cranes as well, which require
movement in different directions.

 

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