ABSTRACT
The
Project Design and construction of a transfomerless over voltage and under
voltage switching circuits deals with low level and high level voltage inputs.
It is designed and constructed to protect electrical equipment against
excessive low voltage, which may result in malfunctioning, and excessive high
voltage which may cause damage to the equipment.
The circuit has
the advantage in that it is transformerless, hence, making the whole circuit
very compact and cost effective. Because most electrical equipment function
properly between voltages of 180V and 240V, this project is designed to operate
within this range.
However, a delay
is incorporated to handle the case of intermittent and electric surge. This
helps to prevent the equipment from erratic switching.
TABLE OF CONTENTS
Pages
Title page
Certification
Dedication
Acknowledgement
Abstract
Table of Content
CHAPTER ONE
1.1
Significance of the Project
1.2
Important Terms
1.3
Generalized Block Diagram
CHAPTER TWO
2.0
OP-AMOS and Comparator
2.1
Transistors
2.2
Relays and Electromechanical Devices
2.3
Other Passive components
CHAPTER THREE
3.1
Circuit Description
3.2
Operation Principle
3.3
Supply (Dropper, Rectification/Smoothing, Regulation)
3.4
Window comparator
3.5
Differential Amplifier
3.6
Designing the Window
3.7
Switching (Delay, Transistor Switching Relay)
3.8
Output
3.9
Circuit Diagram
CHAPTER FOUR
4.0
Testing
4.1
Implementation
4.2
Construction
4.3
Problems Encountered
CHAPTER FIVE
5.1 Maintenance
and Troubleshooting
CHAPTER SIX
6.3 References
CHAPTER ONE
1.0 INTRODUCTION
This
project is titled OVER VOLTAGE AND UNDER VOLTAGE SWITCHING CIRCUIT of specification (frequency 50Hz Norminal
operating limit of this cut – out are
180v – 240v). This circuit is an
electronics and safety device that is used to protect electronic equipment from
line voltage fluctuations by switching
off the supply when the line voltage goes to high or falls too low. The
supply to the equipment is restored automatically when the line voltage returns
to its normal value.
Transformerless
high/low voltage protector uses a capacitive reactance method of voltage
divider to drop a main voltage to lower value for rectification as its supply
section. The rectified and stabilized d.c is used to supply a comparator
circuit (connected as a window
comparator) which compares the proportion of the range of the input voltage to
two reference of the comparator circuit which in turns delivers on output to a
switching circuit. The switching circuit, comprises of a transistor circuit and
a relay. The contacts of the relay controls the power circuit which is used to
power equipments connected to the circuit. In brief, it is the condition of the
output of the comparator that determines when the equipment connected to it
will switch ON or OFF.
Having
acquired the basic knowledge of electronics. It is found necessary to bring the
exercise together to design and construct an electronic device that can sense
whether the line voltage is too-high or too-low and then disconnect the supply
to the load, providing a good amount of protection to electronics gadgets or
electrical appliances.
To
achieve this we employed the use of a number of preset variable resistors to
increase or reduce the voltage drops of the circuiting. The use of transistor
as a switch is also included in the design which regulates various input to the
relay which now activates the load circuit when the voltage is considered
suitable for the safe operation of the connected load. The operation amplifier
in the circuit is used as a comparator. The relay and transistor (switching
circuit) are used to cut-off supply to the load/appliances when the voltage is above
the specification of this project.
1.1
SIGNIFICANCE OF THE PROJECT
The
regulated output voltage from this cut-out safety device is used to operate
electronic and electrical devices like refrigerators, photocopiers, sanding
fans, radio, television, electric grinder and so on, from excess or low supply
voltage.
1.2
IMPORTANT TERMS
The
following terms are associated with
power supply
(i)
Range: The maximum and minimum limits of
the output voltage of the power supply between 180v and 240v.
(ii)
Efficiency: The ratio of output power to input
power expressed as a percentage.
Efficiency = VoIL x
100%
VacIac
Where Vo is the output voltage in volt
IL is the load current in Ampere
Iac is the
input current from the main in Ampere Vac is the input voltage from
the mains in volt.
(iii)
Load regulation: The maximum change in output
voltage due to a change in load current from no load to full load.
% voltage regulation
= No load voltage – Full load voltage X
100%
No load voltage
1.3 GENERALIZED
BLOCK DIAGRAM
The project is divided into blocks as
shown below.
Fig
1 Block diagram of Transformerless high/low voltage protector,
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