the epileptic power supply in Nigeria and other developing countries today, a
high demand of an alternative service is required. A single phase automatic
change over switch from the public mains supply to the auxiliary supplies
(single phase ac generator) and vice-versa has been developed. The design was
realized using major components like a step down transformer (220V-12V dc),
atmega8 microcontroller, rectifiers, voltage regulators, 555 timers,
relays, circuit breaker and others like
resistors, diodes, and capacitors. The device automatically switches from
public mains to an auxiliary whenever there is an outage in the public mains.
This device also detects the public main power supply when available and
switches from auxiliary power supply to the mains with a delay period of 4
seconds in starting and switching off the generator. The device has been
constructed successfully, and it demonstrated a tendency to automatically
switch from mains to the auxiliary source and vice-versa without human interception.
TABLE OF CONTENTS
1.1 Background of study
1.5 Scope and Limitation of the Study
quality issues- Definitions
of power quality issues
2.3.1 Typical harmonic generating loads
184.108.40.206 DC motor drive
220.127.116.11 Induction motor drive
2.3.2 Study of
typical nonlinear loads
18.104.22.168.2 Single phase half controlled converter
22.214.171.124 Single phase voltage regulator using
126.96.36.199 Lighting loads
188.8.131.52 Chopper fed DC drive
quality improvement techniques
element passive filters
and digital controllers
3.1 Block Diagram of
Automatic Changeover Switch
CONCLUSION AND RECOMMENDATION
1.1 Background of study
The need for
continuous power supply and its reliability has increased rapidly over the
years, especially in all those areas where uninterrupted power supply is a
must. Modern systems are power dependent. Their complexity has increased as
continuous information and communications are needed to control automated
process, be in industries, commercial complexes, hospitals, hotels or even
modern residences. The need, as such, for independent standby power system has
therefore increased manifold. The power distribution, control, monitoring and
protection of standby power systems need to be integrated. Standby generator
systems, for example are required to serve:-
supplied by UPS systems. The period of non-availability of power, before the
standby supply takes over, is bridged by battery banks. Typical loads are
computers, hospital equipment, microprocessor controlled industrial machines
mostly involve standby generator systems which supply power to lighting
systems, air conditioning, elevators etc in Airports, Hotels and commercial
also use standby generator systems mostly in process industries as they relate
to high restarting times or high down times. Automatic transfer from mains
supply to standby supply is vital for all the above kinds of loads.
In the event
of power failure, the standby power is usually expected to take over
automatically. Electrical starting equipment, battery bank and diesel generator
are required for the automatic operation. The automatic transfer is achieved
mostly by automatic mains failure systems. The process of on-load transfer has
to be monitored and controlled for a smooth Changeover and within safety limits
of all elements of the system. This is achieved by an Automatic Changeover
switches find a wide application wherever the reliability of electrical supply
from the utilities is low and they are used in lighting/motor circuits wherever
continuity of supply is necessary, for switching to an alternative source from
mains supply and vice versa. They are switch disconnectors with independent
manual operation capable of making, carrying and breaking currents under normal
circuit conditions which may include operating overload conditions and also
carrying currents under specified abnormal circuit conditions such as those of
short circuit for a specified time.
changeover switch (also known as automatic transfer switch ATS) is an integral
part of a power generation process, allowing smooth and immediate transfer of
electric current between multiple sources and load. When the generator is in
operation, the transfer switch prevents any feedback current to the load. It
also ensures that the different power sources are synchronized before the load
is transferred to them. The transfer switch senses when there is interruption
if the mains supply remains absent. Fluctuations and voltage drop below a
particular level within a specified time in the mains supply will also cause
the automatic transfer switch to transfer the load to the generator. The
starting of the generator is done by a relay which switches the battery voltage
to the ignition coil of the generator. In about a few seconds when the
generator is producing full power, the transfer switch disconnects the load
from the mains supply and connects it to the generator supply, restoring
electricity to the load. The transfer switch continues to monitor the mains
supply and when it is restored, it switches the load from the generator back to
the mains supply. Once the generator is disconnected, it goes through a cool
down routine and shuts down automatically.
outage in general does not promote development to public and private sector.
The investors do not feel secure to come into a country with constant or
frequent power outage. These limit the development of industries. In addition
there are processes that cannot be interrupted because of their importance, for
instance surgery operation in hospitals, bank transactions and lots more. An
automatic change over switch can be entertained to allow smooth and fairly
uninterrupted supply of electricity for operation and services that require no
discontinuity in electricity supply. This is achieved by the use of integrated
circuits that have timing abilities and relays to effect switching.
supply instability in developing countries creates a need for automation of
electrical power generation or alternative sources to back up the utility
supply. This automation becomes predominantly high. Most industries and
commercial processes are partly dependent on generators and public power
supply. The public mains supply remains epileptic especially in tropical
African countries where Nigeria forms a part. Therefore, if the processes of
power changeover between these two power supplying sources are manual, human
error during change over connections may occur; leading to machine damage,
electric shock electrocution as well as increased down time consequently
introducing massive losses.
plays a major role in economic development of a nation, and this forms the
basis of this study, with interests in human, infrastructural and economic
development. In most developing and
undeveloped 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 of power supply to
meet up with the energy demands.
all the existing types of changeover switch, the most populous changeover is
the manual change over which consists of a manual change over switch box,
switch gear and cut-out fuse or the connector fuse. Ahmed et. al., 2006
stipulates that, this change over switch box separates the source between the
generator and public supply, as the contact is manually switched from mains
terminal to the generator terminal and vice versa. Many challenges are
experienced in this manual changeover as it requires lots of human activities
in its operation. Electric shock can occur during the switching due to electric
wire contact with the device metal casing as a result of crack in the ceramic
insulator in the switch. This has led to several deaths and damage to
electrical appliances. Nwaforet. al., 2012 also stipulates one of the
disadvantages as wear and tear of some mechanical parts due to frequent
movement from one source to the other.
changeover switch is another type of changeover switch, which involves the use
of electrochemical type relays, contactors, voltage monitoring relays and delay
timer relays as main components of the device. The device is cheap and the
construction is easy, but associated with noise in switching of relays, leading
to wear and tear, loss of reliability, and thereby making the device to be
prone to failures.
electronic change over switch has proven to be a better device compared to both
the manual and electrical changeover switch as it gives no noise, eliminates
wear and tear, reduces damages to lives, and maintains high quality of service
as it provide quick response for the interchanging of power to the load
automatically from the main supply to the generator and vice versa. The
electronic changeover device employed in this research work changes over
immediately when the public mains is out. However, the generator starter/off
has a periodic delay to start/off the generator. This requires the generator to
have a kick starter and off facility, and a battery in good condition. This
paper presents the construction of a single phase power changeover switch that
switches power supply from public mains supply to an auxiliary source (ac
generator) and vice versa.
The main aim
of this study is to design and construction of an automatic changeover switch
that will switch load from the mains power supply (PHCN supply) to a back-up
power supply (generator) with simplicity.
Due to inconsistent
supply of power, there is a growing need for an alternative source of power
supply. This has led to heavy capital investment in a bid to curb power failure
and ensure regular power supply for our industries, hospitals and homes. The
problem of power failure can be checkmated with the use of standby generating
Engineering author Tony Rudk Inn said in his book titled "Upgraded signal
source with improved performance and reliability" that the cost and
depreciation 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 firms 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 hospitals undergoing a surgical
operation and the power supply suddenly goes off, the patient might lose his
life due to power outage.
if the President of the country is making a nationwide broadcast and all of a
sudden there is power failure in the transmitting station, it would be viewed
as an attempt to sabotage the government ruling and some people must go for it.
Sequel to the
rate at which more sophisticated electrical/electronic gadgets are being
procured an installed in our homes, hospital 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 phase selector circuit which
switches on the load from National Electric Power Authority (NEPA) to a generator
when power comes back. Also when there is a phase failure in any of the NEPA
phase carrying the load, the change-over switch will be changed to alternative
1.5 SCOPE AND LIMITATION OF THE STUDY
change over switch is aimed to achieve the following automatic actions.
To start the
back to PHCN
To change the
To change to
alternative phase in case of phase failure.
change over unit can be operated in single or three phase-system. The automatic
change over switch has the following advantages.
minimizes damage to lives/equipment since it has its own monitoring system and
its switching requires no human contact with the switch, thus eliminating human
reduces its change-over timing to the minimum due to its fast response to power
maintains high quality of service through its fast and prompt response
avoids and reduces fuel consumption since the generator is switch off
immediately PHCN supply is restored.
size and capacity of the Unit will depend upon the load for which it will be
used. The Unit is also portable, easy, convenient and safe to install.
electrical engineering, a switch is an electrical component that can break an
electrical circuit, interrupting the current or diverting it from one conductor
to another. In the design, I used the switches S1 S2, S3. Switch S1 is to
prevent the generator from starting in case PHCN restores power, Switch S2 is
to prevent the auxiliary contact from energizing the relay that connects the
starter; Switch S3 is to start the generator manually.
cable is defined as an insulated conductor, single or stranded which makes an
overall mechanical protection. Cables have two major parts, the conductor and
the insulator. The conductor is that part of the cable which allows current to
flow through it, while the insulator is the outer covering which serves as a
protection to the conductor and does not allow current to flow through it.
Cables are channels through which current are being transferred in various
are devices that can resist the flow of electrical current. They are
bi-directional components. Resistors are made of metal, carbon or ceramic. They
are of two types namely fixed type and variable types.
resistors, colour coding is used to identify their values which are measured in
a unit Ohms with the symbol (Ω). The schematic diagram of resistors is shown
are electronics components that store electrical changes/energy by
electrostatic stress in a dialectric. Capacitors basically consist of two
conducting surface separated by a layer of an insulating medium lied
dielectric. The dielectric may be air, vacuum, per, mica, ceramic plastic
electrolyte. Each of these materials has the values called dielectric constant.
are two terminal semi-conductors that allow current to flow in one direction.
The terminals are anode and cathode. When connecting positive terminal of the
source (EMF) to the positive terminal of the diode and negative of the source
to the negative of the diode, it is said to be in forward biased mode and it
will conduct. But when connecting positive terminal of the source to the
negative terminal of the diode and negative of the source to the positive
terminal of the diode, it is said to be in reverse biased mode and it will not
is a static electrical machine through which power from one part of the circuit
(primary side) is transferred to the other part (secondary side) of the circuit
by means of electromagnetic induction. It input and output current/ voltage
differs depending on the windings.
are made up of P-type and N-type semi-conductor materials. It is being formed
into two junctions. PN junction and NP junction separated by either N or P semi—conductor
in between the junctions. This results in a three terminal electrode of
emitter, collector and base.
is a five layer bi-directional device which can be triggered into conduction by
both positive and negative triggering pulse at it gate. It is used to control
AC power to a load by switching ON and OFF during positive and negative half
cycles of the input AC power.
PROJECT REPORT ORGANIZATION
project report is presented in five chapters to appropriately illustrate the steps
involved in its implementation.
One introduces the project overview, objectives and its significance. Chapter
Two is basically the literature review and some theories relevant to the
Three x–rays the methodology and analysis while
Four elaborates on the implementation, testing and result.
Finally, Chapter Five
is about the summary of the entire theories and recommendation.
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