CONSTRUCTION AND DESIGN OF AUTOMATIC CHANGEOVER SWITCH
INTRODUCTION
1.1
BACKGROUND OF STUDY
The project is designed for power supply applications. It involves
automatic changeover between the main power supply and an auxiliary power
supply, such as a generator. The circuit of the project consists of logical
control unit and relay switches. The basic operation of the project is to switch
ON an auxiliary power supply (like a generator). This operation connects the
power supply from the generator to the load after a predetermined time
interval. Switching is possible through the use of the relays. The system was
designed to automatically change power supply back to the main supply moments
after the A.C. mains are restored and to switch OFF the generator. The device
removes the stress of manually switching ON the generator when power failure
occurs. The operation allows electric current to flow through the
motor/starter. It is noted that one of the motors terminals is already
connected to 12V+ terminals. The switching of the relay allows the other
terminal to be grounded thereby completing the circuit of the electric motor.(Hammed and Mohammed, 2006).
Power supply instability in developing countries creates a need
for automation of electrical power generation or alternative sources of power
to back up the utility supply. This automation becomes necessary as the rate of
power outage becomes predominantly high. Most industries and commercial
processes are partly dependent on generators and public power supply which is
epileptic especially in tropical Africould countries where Nigeria forms a
part.
However, if the starting of the generator is automatically done by a relay
which switches the battery voltage to ignition coil of the generator while the
main power relay switches the load to either public supply or generator, the
down time would greatly be reduce thereby maintaining the tempo of production
in such industries. The approach used in this work is the modular approach
where the overall design is first broken into functional blocks. Each of these
blocks carries out a specific function in the entire system by the
interconnections between the block (Kolo, 2007).
Electricity (energy), which plays a major role in economic
development of a nation, forms the basis of this study, with interests in
human, infrastructural and economic development. In most developing and
underdeveloped parts of the world, the supply of electricity for industrial,
commercial and domestic use is highly unstable. This gives rise to the frequent
use of alternative sources of power supply to meet up with the energy demands.
The introduction of these alternative sources of supply brings forth the
challenge of switching smoothly and timely between the mains supply and the
alternative sources whenever there is a failure on the mains source. There is
also the need to reduce drudgery from switching between the two sources on the
human side. Solving these challenges forms the focus of this work. The
Automatic Change-over switch, automatically switches over to the alternative
source of power supply (generator) when there is a power outage. It equally
switches over to the mains supply when power is restored and turns off the
generator automatically. Therefore automatic power change-over switch is a
device that links the load and mains supply or the alternative supply together.
This enables the use of either the mains supply or an alternative source when
there is outage on the mains source. This could either come in with three phase
or single phase. This device maintains constant power supply
to the load by automatically activating the generator when there is need.
(Boylestad and Nashelsky, 2012).
1.2
AIMS AND OBJECTIVES
Due to inconsistent supply of
power, there is a growing need for an alternative source of power supply. The analysis of this project cannot go without enumerating
the goals meant to be achieved in the pursuit of this work. This include:
1. To
develop a simple low-cost device aimed at easing constant power outage faced by
industry, hospitals,
schools and homes.
2. To minimize power
interruption.
An
Engineering Author, “Tony Rudkin” said in his book titled “Upgraded Signal Source
with Improved Performance and Reliability” that the cost and depredation
associated with breakdown vary from one application to the other, and in some
cases, the user has little choice but to ensure that a stand-by unit is
available to take over on event of failure of primary system.
If some of
these big firm do not make provisions for stand-by power source, frustration
could set in which may lead to the closure of business and thus throwing
workers into unemployment. Also in the case of hospital, undergoing a surgical
operation and power supply suddenly go off, the patient might loose his or her
life due to the power outage.
In his book,
Tony Rudkin also said that the depredation caused by such reduce efficiency of
the organization and leads to a great deal of frustration. Sequel to the rate
at which more sophisticated electrical/electronics gadgets are being procured
and installed in our homes, hospitals and business premises, there is a
justifiable need for a faster and more reliable change over system in an event
of power outage.
In view of these considerations, this
project is aimed at designing and constructing a workable automatic change over
switch with a phase failure detecting circuit also known as “Automatic Mains
Failure” which switches on the head from power Holding Company (PHCN) to a generator when power fails and
from generator to PHCN when power comes back.
1.3
SCOPE
AND LIMITATION
The automatic changeover switch, the
switch aimed at achieving the following automatic actions;
a)
To
change power over to generator
b)
To
change back to PHCN
The automatic change over unit could be operated in single or
three phase system. The automatic changeover switch has the following
advantages;
a)
It
minimizes damages to lives/equipment since it has its own monitoring system and
its switching requires no human contact with the switch, thus eliminating human
error.
b)
It
reduces its change over timing to the minimum due to its fast response to power
outage.
c)
It
maintains high quality of service through its fast and prompt response.
Moreover, the size and captivity of the unit would depend
upon the load for which it would be used. The unit is also portable, easy,
convenient and safe to install. Figure 1.0 shows the working principle of
automatic changeover switch
Figure 1.0: Block diagram showing the
working principle of automatic changeover switch