Design And Construction Of 25Amps Single Phase Automatic
Change Over
TABLE OF CONTENT
Title page
Approval page
Dedication
Acknowledgement
Abstract
Table of content
CHAPTER ONE
1.0
Introduction
1.1
General Description and application
1.2
Block Diagram representation
CHAPTER TWO
2.0 Theory Of Operation
2.1 The General Starter
2.2 The Change Over Switch
2.3 The General Turn Off Switch
2.4 The Power Supply
CHAPTER THREE
COMPONENT DESCRIPTION AND RATING
THE COMPONENT USED FOR THE PROJECT ARE LISTED
3.0
Definition And Analysis Of Component And Ratings
3.1
The Component Used For The Project
3.2
Power Transformers
3.3
Relays
3.4
Contactors
3.5
Battery
3.6
Switch
3.7
Capacitors
ii
3.8
Capacitor Ics
3.9
Logics Ics
3.10
Timer
3.11
Diodes
3.12
Indicator lamps
3.13
Circuit breaker
3.14
Wires jumpers and connectors
3.15
Transistors
3.16
Resistors
CHAPTER FOUR
4.0
Circuit Analysis
4.1
The Voltage Converters
4.2
The Comparators
4.3
The Logic Gates
4.4
The Generator Starter
4.5
The Change Over Switch
CHAPTER FIVE
iii
CONSTRUCTION AND ECONOMIC OF THE PROJECT
5.0
Construction Of The Casing
5.1
Economic Of The Project
5.2
Reliability
5.3
Maintainability
5.4
Project Evaluation
CHAPTER SIX
6.0
Testing
6.1
Trouble Shooting And Remedy
CHAPTER SEVEN
CONCLUSION
REFERENCES
CHAPTER ONE
iv
1.0
INTRODUCTION
As the quest for change over on public power supply and stand by generation
increase. Engineering have researches deep into the different methods of
achieving to both manual and automatic types.
It may not be taken seriously in some places where power supply is up to
90 constant or where intermittent outage causes no great damage. However,
place where they have business centers, industrial centers and even cold rooms
need to almost 100% supply. So in this case there is need to provide a standby
power supply in the event of power outage. The most important task is just to
provide a standby power supply by great attention is paid to the reliability of
the system. That is immediately and change over without fluctuations.
The first type of change over switch were purely manual operated. They
usually have three switch able position, main, off and generator. An arm is
provided from where the operator can have access to the switching. Here, the
effectiveness of the switching (i.e how fast it is effected each time power needs
to be changed) largely depends on the operator. The change over system will
be ineffective when the operator is not around.
v
The second generation of change over switches were made semiautomatic in which the mains power supply directly powers the contactors.
This arrangement is wired is such a way that if the mains power supply fails,
the contractors will all drop leaving the supply to the generator position. The
effectiveness of the system will now depend on the operator top start up the
generator on time.
The main problem suffered by the above mentioned two versions of the
change over switch is that the operator must have to be continuously on duty
for it to be very effective. They lent use full closed loop system to operate.
The present day technology has made it possible for the change over
switch to come in a number of designs switch using the closed loop system at
feed back control. Some of them use comparators, logic circuits and electronic
timers to achieve the task. Some even used simple micro processor chips to
function.
The design of this project is such that a combination of comparators
digitals switches (logic IC), electronics timers and electromagnetic switches are
used to achieve a very fast and effective change over in this case. This project
was entirely constructed and the thesis written by Nwalua Chukwukereze under
vi
the supervision of Engr. Ihedioha in partial fulfillment of the requirements for
the award of Higher National Diploma in Electrical Electronics Engineering.
The automatic change over switch makes use of protective relays and
contractors among other things which constantly monitor the power system to
ensure maximum continuity of the electrical service with minimum damage to
life and property. They are found mostly in domestic installations, hospital
threatres, conference halls, computer centres, data and research centres,
laboratories and industries that require three phase constant power supply. This
equipment however is used to protect some house holds appliances from
electrical faults which may arise due to voltage drop. It was designed and
constructed purposely to alleviate the suffering encountered by the consumers
following supply authority’s consistent failure to meet its obligations of
constant and uninterrupted power supply. A circuit breaker is in corporate as a
back up protection to improve the reliability of the system and to meet it’s
specification, although more back-up protection could have been incorporated
monitoring the supply but due to financial constraints, it has to be limited to
this operation. The schematic diagram of the automatic change over switch was
clearly explained as far as possible to be apprehended by any person within or
vii
outside the engineering field. It is my intention however to present the work to
Institute of Management and Technology (IMT) students in Engineering and to
the general public for consumption.
1.1 GENERAL DESCRIPTION AND APPLICATION
BRIEF DESCRIPTION: The change over switch is said to be automatic
because it employs full closed loop system. It has comparators that test both the
input and output conditions and then uses the information to switch the relays
to the appropriate positions.
There are three important switching position which are:
1) Switching of the contactors (i.e C/O)
2) Switching of the generator started if power fails
3) Switching off the generator as soon as power is restored
The system uses 3 comparators, one for each phase to test the voltage
conditions to a certain full voltage, low voltage or even power failure. When
the 3 phase voltage are okay between 190v and 230v not neutral, the voltage
from the converters to the input of comparators is higher than voltage reference
viii
at the non-inverting input. Hence, the output of the comparators will be below
(zero volts).
If there is low voltage (below 190v) in one or more of the phase voltages, the voltage at the inverting input will be less than
reference voltage at the non-inverting input this will produce a high output (+9v) from the comparator. One or more of this art the input of
the OR gate will cause the output of the OR gate to be high and after a delay time of about 30 seconds this voltage appears at the inputs of
the AND gate.
Now the inputs of the AND gate will depend on the position of the
enable switch. If it is switched off, the information from the comparators will
not pass the AND gate. But if it is switched on (i.e both inputs will now be
high) the information will be reflected at the output of the AND gate and it will
be used to achieve the 3 switches generator on/off and then change over switch.
Also if there is complete power failure in one or more phase, the
operation of the system will be the same as described above for low voltage.
For the switching actions, the information at the output of the AND gate
operates the 3 switches at the same time. It supplies voltage to the coil of
contactor “A” leaving the contacts on the normally close (NC) position ready
for generator supply. Also the generator starter and turn off receive
information, the turn off will switch on d.c supply to the high voltage coil
while the starter supplies starting pulses (through the multivibrator) to the kick
ix
starter. When the generator starts running, a signal is sent to the starter to
disable it.
Also the generator sends signals to the delay circuit and after some delay
time. It will switch on contactor “B” and the generator will start supplying. But
if the power is restored and the comparators okay the supply (i.e if it is above
190v) the OR gate output goes low and time delay, the C/O will be effected
again and the generator will be turned off by cutting off d.c supply to the high
voltage coil. The aim of the delay is to stoop any fluctuation in power which is
less than 15 seconds from reaching the control relays the power supply uses a
9v back.up battery with a 9v regulator. It is interesting to note that when supply
is restored, the system automatically returns the consumers to his original
power supply as the case may be.
1.2
BLOCK DIAGRAM REPRESENTATION
The block diagram representation of the automatic change over switch is the
one shown in figure 2.1 below, though for the previous years the details of the
Automatic C/O switch have never been shown in block form. Therefore, there
x
is need to show it in block form for proper understanding of the major
component parts of the system.
*** INSTRUCTIONS ***
Please Read The Below Instructions Carefully.
******************************
HOW TO ORDER THIS COMPLETE MATERIAL
If you want to order the complete materials (Chapter One
to Five, Including Abstract, References, Questionnaires, Proposal (where
applicable)) of the above mentioned topic, please visit
www.freeplace.org and click on “Order” (i.e.
www.freeplace.org/order)
******************************
HOW TO BECOME OUR PARTNER
To become our partner, visit www.freeplace.org and click on
partnership.
******************************
TERMS OF USE
This Material is for Academic Research Purposes only. On no
account should you copy this material word for word. Copying
this material “Word for Word” is against our “Terms of Use”.
That you ordered this material shows you have agreed Our
‘Terms of Use’.
xi
******************************
Better is not good enough, the best is yet to come!
Endeavour to be the best!!
xii