Table of Contents

Project Title...........................................................................................................................................3

Problem identification...........................................................................................................................3

Background information........................................................................................................................3

Aim and Objective................................................................................................................................3

1. Introduction.......................................................................................................................................4

Operation of a transfer switch...........................................................................................................5

Types.................................................................................................................................................6

Voltage Sensing.................................................................................................................................8

Switching...........................................................................................................................................9

Programming...................................................................................................................................12

Communication...............................................................................................................................13

2 Materials and Methods Used...........................................................................................................16

2.1 Mechanism of Operation of Electric Power Generators............................................................17

2.2 Standby Generators...................................................................................................................18

2.3 Transfer Switches.......................................................................................................................18

2.4 The Proposed Switching System................................................................................................19

3. Results and Discussion.....................................................................................................................25

4 Conclusions and Recommendations.................................................................................................27

4.1 Conclusions................................................................................................................................27

4.2 Recommendation......................................................................................................................28

References...........................................................................................................................................29

Acknowledgement

I have taken efforts in this project. However, it would not have been possible without the kind

support and help of many individuals and organizations. I would like to extend my sincere

thanks to all of them.

I am highly indebted to ICBT Campus & Mr. Manasir Munafdeen for their guidance and

constant supervision as well as for providing necessary information regarding the project &

also for their support in completing the project.

I would like to express my gratitude towards my parents & friends of ICBT Campus for their

kind co-operation and encouragement which help me in completion of this project.

I would like to express my special gratitude and thanks to industry persons for giving me

such attention and time.

My thanks and appreciations also go to my colleague in developing the project and people

who have willingly helped me out with their abilities.

Project Title

Automatic Transfer Switching System for a Standby Electric Generator

Problem identification

In the industry and hospitals power breaks is very harmful. In hospitals power break can

damage human life. In industry it can damage the productions.

Background information

This device mainly work with PIC Microcontrollers. This unit have three power inputs. When

one source is break it will switch to other power source automatically without dropping

current. A LCD shows what source is using now. If get any error automatically send SMS

using GSM.

Aim and Objective

Give a solution for that energy resources are simply inadequate. Most manufacturing

industries and firms have to contend with insecure and unreliable power supply coupled with

its attendant negative impacts on productivity and cost of production.

1. Introduction

Reliable and secure uninterruptible power supply is a sine qua non for virtually all industrial

operations. The reality, however, especially in most developing countries, is that energy

resources are simply inadequate. Most manufacturing industries and firms have to contend

with insecure and unreliable power supply coupled with its attendant negative impacts on

productivity and cost of production.

The quest for secure and reliable power supply remains a dream yet to be attained, especially

in most developing countries. This is as a result of population growth, industrialisation and

urbanisation (Aguinaga, 2008; Akparibo, 2011; Fuller, 2007; Kolo, 2007) and improper

planning by service providers and governments. Most manufacturing industries, firms and

institutions such as hospitals and healthcare facilities, financial institutions, data centres and

airports to mention but a few require constant power supply all year round. Power instability

generally retards development in public and private sectors of any economy (Kolo, 2007;

Anon., 2010; Chukwubuikem, 2012). Any instance of power failure could lead to prohibitive

consequences ranging from loss of huge amounts of money to life casualties (Aguinaga,

2008). The spate of frequent power outages without an effective back-up system is truly a

disincentive to investors in any developing economy like Ghana (Kolo, 2007).

Indeed, the ravages of power instability have equally necessitated automation of the

switching system between national grid energy system and standby generators used as

backup. In the last decade, different equipment and configurations have been used in order to

cope with this problem (Aguinaga, 2008). An automatic changeover system makes use of

sensors and transducers to realise the changeover in a shorter time while eliminating human

interference and its attendant errors (Chukwubuikem, 2012).

The main problems associated with a manual switching system are as follows: interrupted

power supply, device damage due to frequent commutations, possible causes of fire outbreak

due to switching sparks and frequent high maintenance cost due to changeover action and

wear and tear of mechanical parts. In this paper, we demonstrate how to surmount these

problems by the design of a Microcontroller-Based Automatic Transfer Switching System

(MBATSS). We have also performed a simulation to test the workability of the controller

using appropriate simulation software.

Operation of a transfer switch

As well as transferring the load to the backup generator, an ATS may also command the

backup generator to start, based on the voltage monitored on the primary supply. The transfer

switch isolates the backup generator from the electric utility when the generator is on and

providing temporary power. The control capability of a transfer switch may be manual only,

or a combination of automatic and manual. The switch transition mode (see below) of a

transfer switch may be Open Transition (OT) (the usual type), or Closed Transition (CT).

For example, in a home equipped with a backup generator and an ATS, when an electric

utility outage occurs, the ATS will tell the backup generator to start. Once the ATS sees that

the generator is ready to provide electric power, the ATS breaks the home's connection to the

electric utility and connects the generator to the home's main electrical panel. The generator

supplies power to the home's electric load, but is not connected to the electric utility lines. It

is necessary to isolate the generator from the distribution system to protect the generator from

overload in powering loads in the house and for safety, as utility workers expect the lines to

be dead.

When utility power returns for a minimum time, the transfer switch will transfer the house

back to utility power and command the generator to turn off, after another specified amount

of "cool down" time with no load on the generator.

A transfer switch can be set up to provide power only to critical circuits or to entire electrical

(sub)panels. Some transfer switches allow for load shedding or prioritization of optional

circuits, such as heating and cooling equipment. More complex emergency switchgear used

in large backup generator installations permits soft loading, allowing load to be smoothly

transferred from the utility to the synchronized generators, and back; such installations are

useful for reducing peak load demand from a utility.

Types

Open transition

An open transition transfer switch is also called a break-before-make transfer switch. A

break-before-make transfer switch breaks contact with one source of power before it makes

contact with another. It prevents backfeeding from an emergency generator back into the

utility line, for example. One example is an open transition automatic transfer switch (ATS).

During the split second of the power transfer the flow of electricity is interrupted. Another

example is a manual three position circuit breaker, with utility power on one side, the

generator on the other, and "off" in the middle, which requires the user to switch through the

full disconnect "off" position before making the next connection.

Closed transition

A closed transition transfer switch (CTTS) is also called a make-before-break transfer switch.

A typical emergency system uses open transition, so there is an inherent momentary

interruption of power to the load when it is transferred from one available source to another

(keeping in mind that the transfer may be occurring for reasons other than a total loss of

power). In most cases this outage is inconsequential, particularly if it is less than 1/6 of a

second.

There are some loads, however, that are affected by even the slightest loss of power. There

are also operational conditions where it may be desirable to transfer loads with zero

interruption of power when conditions permit. For these applications, closed transition

transfer switches can be provided. The switch will operate in a make-before-break mode

provided both sources are acceptable and synchronized. Typical parameters determining

synchronization are: voltage difference less than 5%, frequency difference less than 0.2 Hz,

and maximum phase angle between the sources of 5 electrical degrees. This means the engine

driving the generator supplying one of the sources generally must be controlled by an

isochronous governor.

It is generally required that the closed transition, or overlap time, be less than 100

milliseconds. If either source is not present or not acceptable (such as when normal power

fails) the switch must operate in a break-before-make mode (standard open transition

operation) to ensure no backfeeding occurs.

Closed transition transfer makes code-mandated monthly testing less objectionable because it

eliminates the interruption to critical loads which occurs during traditional open transition

transfer.

With closed transition transfer, the on-site engine generator set is momentarily connected in

parallel with the utility source. This requires getting approval from the local utility company.

Typical load switching applications for which closed transition transfer is desirable include

data processing and electronic loads, certain motor and transformer loads, load curtailment

systems, or anywhere load interruptions of even the shortest duration are objectionable. A

CTTS is not a substitute for a UPS (uninterruptible power supply); a UPS has a built-in stored

energy that provides power for a prescribed period of time in the event of a power failure. A

CTTS by itself simply assures there will be no momentary loss of power when the load is

transferred from one live power source to another.

Soft loading

A soft-loading transfer switch (SLTS) makes use of a CTTS, and is commonly used to

synchronize and operate onsite generation in parallel with utility power, and to transfer loads

between the two sources while minimizing voltage or frequency transients.

Static transfer switch (STS)

A static transfer switch uses power semiconductors such as Silicon-controlled

rectifiers (SCRs) to transfer a load between two sources. Because there are no mechanical

moving parts, the transfer can be completed rapidly, perhaps within a quarter-cycle of the

power frequency. Static transfer switches can be used where a reliable and independent

second source of power is available and it is necessary to protect the load from even a few

power frequency cycles interruption time, or from any surges or sags in the prime power

source.

Voltage Sensing

In this case to measure the voltage using a microcontroller that had an input range of 0 to 5

volts, and needed to measure voltages from 200V -280V.

To convert this large, alternating voltage range to something compatible with the micro, Most

do something along the lines of rectifying the AC voltage before feeding it into the micro.

While that may be fine for some, it creates ambiguity between low and high voltages. It need

something better. It would be great to have a circuit that multiplies the input voltage by a

constant, then adds half the supply voltage of the micro. It can do that with a op-amp.

If use op-amps before, this should look reasonably familiar – it is pretty much the standard

inverting amplifier. However, the key differences are that the non-inverting input is tied to

half of Vcc instead of ground, and the extra resistor pulling the inverting input up to Vcc –

this resistor should be exactly the same value as the other resistor called Ri.

The operation that this circuit performs is:

This can measure mains voltage with a range of 200 V to

280 V, and the microcontroller can accept voltages from 0 V to 5 V.

Switching

1. Relay

A relay is an electrically operated switch. Many relays use an electromagnet to mechanically

operate a switch, but other operating principles are also used, such as solid-state relays.

Relays are used where it is necessary to control a circuit by a low-power signal (with

complete electrical isolation between control and controlled circuits), or where several

circuits must be controlled by one signal. The first relays were used in long distance telegraph

circuits as amplifiers: they repeated the signal coming in from one circuit and re-transmitted

it on another circuit. Relays were used extensively in telephone exchanges and early

computers to perform logical operations.

A type of relay that can handle the high power required to directly control an electric motor

or other loads is called a contactor. Solid-state relays control power circuits with no moving

parts, instead using a semiconductor device to perform switching. Relays with calibrated

operating characteristics and sometimes multiple operating coils are used to protect electrical

circuits from overload or faults; in modern electric power systems these functions are

performed by digital instruments still called "protective relays".

Basic design and operation of relay

A simple electromagnetic relay consists of a coil of wire wrapped around a soft iron core, an

iron yoke which provides a low reluctance path for magnetic flux, a movable iron armature,

and one or more sets of contacts (there are two in the relay pictured). The armature is hinged

to the yoke and mechanically linked to one or more sets of moving contacts. It is held in

place by a spring so that when the relay is de-energized there is an air gap in the magnetic

circuit. In this condition, one of the two sets of contacts in the relay pictured is closed, and

the other set is open. Other relays may have more or fewer sets of contacts depending on their

function. The relay in the picture also has a wire connecting the armature to the yoke. This

ensures continuity of the circuit between the moving contacts on the armature, and the circuit

track on the printed circuit board (PCB) via the yoke, which is soldered to the PCB.

When an electric current is passed through the coil it generates a magnetic field that activates

the armature, and the consequent movement of the movable contact(s) either makes or breaks

(depending upon construction) a connection with a fixed contact. If the set of contacts was

closed when the relay was de-energized, then the movement opens the contacts and breaks

the connection, and vice versa if the contacts were open. When the current to the coil is

switched off, the armature is returned by a force, approximately half as strong as the

magnetic force, to its relaxed position. Usually this force is provided by a spring, but gravity

is also used commonly in industrial motor starters. Most relays are manufactured to operate

quickly. In a low-voltage application this reduces noise; in a high voltage or current

application it reduces arcing.

When the coil is energized with direct current, a diode is often placed across the coil to

dissipate the energy from the collapsing magnetic field at deactivation, which would

otherwise generate a voltage spike dangerous to semiconductor circuit components. Some

automotive relays include a diode inside the relay case. Alternatively, a contact protection

network consisting of a capacitor and resistor in series (snubber circuit) may absorb the

surge. If the coil is designed to be energized with alternating current (AC), a small copper

"shading ring" can be crimped to the end of the solenoid, creating a small out-of-phase

current which increases the minimum pull on the armature during the AC cycle.

2. Optocoupler

In electronics, optocoupler, or optical isolator, is a component that transfers electrical signals

between two isolated circuits by using light. Opto-isolators prevent high voltages from

affecting the system receiving the signal. Commercially available opto-isolators withstand

input-to-output voltages up to 10 kV and voltage transients with speeds up to 10 kV/μs.

A common type of opto-isolator consists of an LED and a phototransistor in the same opaque

package. Other types of source-sensor combinations include LED-photodiode, LED-LASCR,

and lamp-photoresistor pairs. Usually opto-isolators transfer digital (on-off) signals, but some

techniques allow them to be used with analog signals.

The value of optically coupling a solid state light emitter to a semiconductor detector for the

purpose of electrical isolation was recognized in 1963 by Akmenkalns,et al. Photoresistor-

based opto-isolators were introduced in 1968. They are the slowest, but also the most linear

isolators and still retain a niche market in audio and music industry. Commercialization of

LED technology in 1968–1970 caused a boom in optoelectronics, and by the end of the 1970s

the industry developed all principal types of opto-isolators. The majority of opto-isolators on

the market use bipolar silicon phototransistor sensors. They attain medium data transfer

speed, sufficient for applications like electroencephalography. The fastest opto-isolators use

PIN diodes in photoconductive mode.

Programming

PIC Microcontrollers

PIC for switching

Relay is used when we need to handle high voltages and currents through microcontroller

operated system. Relay coil's current requirement is usually more than 100mA (for small

relay about 100mA) and microcontroller cant supply this much of current to relay by it self.

So as shown in following schematic diagram, we have to use transistor to handle this current

requirement. Base pin of NPN transistor used here is connected to ground pin via resistor to

make sure that relay will stay off when microcontroller does not output +5V to transistors

base. This will make sure only logic 1 on microcontroller pin will activate relay. It is better to

use Darlington transistor to handle current requirement for relay, because darlington

transistor can handle more current than single transistor.

It is essential to connect a diode across relay coil in reverse bias to protect transistor form

back EMF created when relay is released from energized or ON state. If this diode is not

used, transistor and/or microcontroller which is driving relay may be damaged upon releasing

energized relay. The diode will short out the back EMF produced by coil when it turned OFF

from ON state.

Interfacing LCD with PIC Microcontroller

The 2x16 character LCD interface card with supports both modes 4-bit and 8-bit interface,

and also facility to adjust contrast through trim pot. In 8-bit interface 11 lines needed to

create 8-bit interface; 8 data bits (D0 – D7), three control lines, address bit (RS), read/write

bit (R/W) and control signal (E).

Communication

GSM

GSM is a standard developed by the European Telecommunications Standards Institute

(ETSI) to describe protocols for second generation (2G) digital cellular networks used by

mobile phones. It is the de facto global standard for mobile communications with over 90%

market share, and is available in over 219 countries and territories.

The GSM standard was developed as a replacement for first generation (1G) analog cellular

networks, and originally described a digital, circuit-switched network optimized for full

duplex voice telephony. This was expanded over time to include data communications, first

by circuit-switched transport, then packet data transport via GPRS (General Packet Radio

Services) and EDGE (Enhanced Data rates for GSM Evolution or EGPRS).

Radio frequency (RF)

Radio frequency (RF) is a rate of oscillation in the range of around 3 kHz to 300 GHz, which

corresponds to the frequency of radio waves, and the alternating currents which carry radio

signals. RF usually refers to electrical rather than mechanical oscillations; however,

mechanical RF systems do exist (see mechanical filter and RF MEMS).

Although radio frequency is a rate of oscillation, the term "radio frequency" or its

abbreviation "RF" are also used as a synonym for radio – i.e. to describe the use of wireless

communication, as opposed to communication via electric wires.

To receive radio signals an antenna must be used. However, since the antenna will pick up

thousands of radio signals at a time, a radio tuner is necessary to tune into a particular

frequency (or frequency range). This is typically done via a resonator – in its simplest form, a

circuit with a capacitor and an inductor form a tuned circuit. The resonator amplifies

oscillations within a particular frequency band, while reducing oscillations at other

frequencies outside the band. Another method to isolate a particular radio frequency is by

oversampling (which gets a wide range of frequencies) and picking out the frequencies of

interest, as done in software defined radio.

The distance over which radio communications is useful depends significantly on things other

than wavelength, such as transmitter power, receiver quality, type, size, and height of

antenna, mode of transmission, noise, and interfering signals. Ground waves, tropospheric

scatter and skywaves can all achieve greater ranges than line-of-sight propagation. The study

of radio propagation allows estimates of useful range to be made.

Frequency Wavelength Designation Abbreviation

3 – 30 Hz 105 – 104 km Extremely low frequency ELF

30 – 300 Hz 104 – 103 km Super low frequency SLF

300 – 3000 Hz 103 – 100 km Ultra low frequency ULF

3 – 30 kHz 100 – 10 km Very low frequency VLF

30 – 300 kHz 10 – 1 km Low frequency LF

300 kHz – 3 MHz 1 km – 100 m Medium frequency MF

3 – 30 MHz 100 – 10 m High frequency HF

30 – 300 MHz 10 – 1 m Very high frequency VHF

300 MHz – 3 GHz 1 m – 10 cm Ultra high frequency UHF

3 – 30 GHz 10 – 1 cm Super high frequency SHF

30 – 300 GHz 1 cm – 1 mm Extremely high frequency EHF

300 GHz - 3000 GHz 1 mm - 0.1 mm Tremendously high frequency THF

Wi-Fi

Wi-Fi is the name of a popular wireless networking technology that uses radio waves to

provide wireless high-speed Internet and network connections. A common misconception is

that the term Wi-Fi is short for "wireless fidelity," however this is not the case. Wi-Fi is

simply a trademarked phrase that means IEEE 802.11x.

Wi-Fi works with no physical wired connection between sender and receiver by using radio

frequency (RF) technology, a frequency within the electromagnetic spectrum associated with

radio wave propagation. When an RF current is supplied to an antenna, an electromagnetic

field is created that then is able to propagate through space.

The cornerstone of any wireless network is an access point (AP). The primary job of an

access point is to broadcast a wireless signal that computers can detect and "tune" into. In

order to connect to an access point and join a wireless network, computers and devices must

be equipped with wireless network adapters.

2 Materials and Methods Used

The materials and methods used to integrate the electric generator as an alternative power

source to the grid is very important in determining how secure and reliable the power supply

to load can be. The switching system could be manual, where a person switches the generator

set on when the grid supply is lost and switches the generator off when the grid power is

restored or alternatively, automatic switching, where the electric generator switches on and

off when the grid is restored (Chukwubuikem, 2012). outage because switching is effected on

the basis of energising and de-energising of the relay coils.

2.1 Mechanism of Operation of Electric Power Generators

Electric power generators could produce Direct Current (DC) or Alternating Current (AC).

AC power generators consist of armature windings placed in stator slots into which an AC

voltage is induced, and a rotor coupled to a prime mover. Mechanical rotation of the prime

mover cuts the magnetic flux produced in the stator field by an exciter. This induces an

alternating electromotive force in the stator windings. Any load connected to the stator

windings completes the external circuit and current flows through the load. Fig. 1 shows a

schematic diagram of a practical three-phase alternator.

Prime Mover Rotor 3-Phase Supply to Load Rf DC Exciter Alternator Slip BY R Stator

Fig. 1 A Practical Three-Phase Alternator

2.2 Standby Generators

Standby generators Anon. (2011) also known as backup or alternate generators, are secondary

sources of electric power usually kept at the premises of consumers to provide electrical

power in the event of failure of power supply from a power service provider. Standby

generators are installed at the consumer’s premises and run in parallel with the utility power

supply in order to augment the utility supply, when power is lost Anon. (2012a).

There are other electric generator switching automation systems using electromechanical

relays, contactors and timers which comes with some shortcomings, notably: poor sensing

ability to fluctuations due to the fact that relays do not function optimally at very low

voltages; and slow switching time in the event of mains power supply outage because

switching is effected on the basis of energising and de-energising of the relay coils.

2.3 Transfer Switches

Transfer switches, also known as changeover switches, are electrical devices designed to

power an electric load from multiple sources. They are mainly used with generator sets in

applications where the loads need, if not a fully continuous, at least a steady supply of electric

power (Aguinaga, 2008). Transfer switches could be manually or automatically operated. A

manual transfer switch box separates the utility supply from the standby generator. Whenever

there is power failure, changeover is done manually by humans and the same happens when

the public utility power is restored and this is usually accompanied with loud noise and

electrical sparks (Chukwubuikem, 2012). An Automatic Transfer Switch (ATS) is used with

standby systems. It includes a control circuit that senses mains voltage. When mains power is

interrupted, the control circuit starts up the generator set, disconnects the load from the utility

and connects it to the generator set. It then continues to monitor the mains status. When

mains power is restored, it commutes the load from the generator back to the utility within a

threshold time Anon. (2012a).

When the generator is disconnected, it goes through a cool-down process and then

automatically shuts down (Chukwubuikem, 2012). Fig. 2 shows a schematic diagram of a

typical transfer switch. Transfer switches could be installed between two generators, a

generator and a utility supply or between alternate utility providers Anon. (2012b).

Fig. 2 Schematic Diagram of a Typical Transfer Switch

2.4 The Proposed Switching System

In general, a switch control mechanism could be done electromechanically or solid state-

based. Both methods come with corresponding trade-offs ranging from efficiency to cost. The

methods of switching on standby generators can also be categorised mainly into two modes:

Open Transition (OT) mode and Closed Transition (CT) mode Anon. (2013a).

An ATS is an electrical device for transferring power sources to an electrical load. The switch

should have the ability to sense the loss or fluctuation of power from the main source and

based on that stimulus, initiate and execute the process of transfer of source to the load.

Normally, the sensing circuits are connected to the power sources through relays. Transfer

switching systems have been studied by numerous researchers with different applications

usually aimed at reducing component count and minimising power consumed by the control

circuitry (Aguinaga, 2008), (Kolo, 2007), (Chukwubuikem, 2012), Anon. (2013a). The ATS

is able to monitor all the sources consistently for over/under voltage and current conditions or

total loss of power and issue an appropriate command for the transfer of load to an alternate

power source.

This paper reports on the design of an efficient microcontroller-based ATS making use of

relays, voltage and current sensing circuitry, a display unit and an alarm unit in order to

reduce the circuit’s power consumption, operate fast, reduce component count and

considerably reduce cost. Fig. 3 and Fig. 4 show a block diagram of the overall system design

and the block diagram of the ATS respectively (Anderson, 2003).

The system hardware consists mainly of a Transfer Switch (TS) microcontroller serving as

the main controlling device to which all other devices are connected. The AC voltage sensing

circuits sense the status of the AC power from the mains and generator and communicate it to

the TS microcontroller

A Hall Effect current sensor feeds the load current to the TS controller. A source change

relay acts as switchgear to switch power sources between mains and generator to the load.

Fuel flow and starter relays are used to start the fuel flow pump and engine respectively. All

the relays are driven by a relay driver (ULN2003A). The TS microcontroller monitors the

charging state of a battery that supplies power to the entire control circuitry.

Voltage Sensing Circuits

Two AC voltage sensing circuits continuously monitor the state of the utility supply,

generator and communicate it to the TS microcontroller. The voltage sensor, as shown in the

circuit diagram in Fig. 5, is made up of a 240/3.4 V step down transformer, two resistors, a

diode and a capacitor. To ensure that 5 V TTL requirement of the microcontroller is not

violated, a voltage divider circuit, consisting of R1 and R2 is used to output about 5 V to the

controller. This is achieved by setting the ratio of R1 to R2 to be 10 is to 5. The values of R1

and R2 are deliberately selected in the kilo ohm range in order to limit the sink current to the

microcontroller. The diode and capacitor C1 are used to give a unidirectional DC to the

respective input pin of the microcontroller. An AC sensor (ACS712-05B-T); is used to

monitor the load for over- and under-current conditions.

The change breaker relay, OMIH-SH-105D, was selected to commute the power source from

utility to generator and vice versa. This is necessary in order to avoid both sources being

connected at the same time, otherwise the generator could “back feed” into the utility lines.

This is an unhealthy condition since personnel working on the line could be electrocuted.

This calculation is done for a typical company in Tarkwa.

Fig. 3 Block Diagram of the Overall System Design

Fig. 4 Block Diagram of Automatic Transfer Switch

Fig. 5 Schematic Diagram of AC Voltage Sensing Circuit

Schematic Diagram of the Hardware Design

The circuit diagram of the hardware design of the ATS is shown in Fig. 6. The

microcontroller receives its power from a MAX610 AC to DC converter through a 10 kΩ

resistor. Evenly spaced pulses coming from the oscillator enable harmonic and synchronous

operation of all circuits of the microcontroller. The oscillator module is usually configured to

use quartz crystal or ceramic resonator for frequency stabilisation.

Fig. 6 Circuit Diagram of Hardware Design of the Automatic Transfer Switch

Proteus Design Suit

The Proteus design suit is a professional printed circuit board (PCB) design software with

integrated shape based auto-router. It was used for the circuit simulation, schematic capture,

and the PCB design. It is developed by Labcenter Electronics Anon. (2013b). The method

adopted in this paper cover the system flow chart, programming the microcontroller and

simulation of the circuitry of the proposed design.

System Flow Chart

The flow chart for the firmware development is presented in Fig. 7

Fig.7 Flow Chart for Firmware Development

3. Results and Discussion

The results are based on the system flow chart developed, the corresponding hardware

programming and the simulation outcome. The programming of the hardware was done using

GCG Basic programming software. The proposed circuit was successfully simulated using

the proteus design suite software. This was done to ascertain the workability of the proposed

design. The results indicated that, the ATS responded appropriately to power outages, voltage

dips and swells, over and under-current conditions and restorations. A screen shot of the

simulated designed circuit is as shown in Fig. 8. The power source changeover was initialised

once the utility source became unavailable or experienced a voltage dip or swell or dangerous

a surge in current. Fig. 9 (a), (b), (c) and (d) respectively show the system responses

indicated.

Fig. 8 Screen Shot of Simulation of Designed Circuit

Fig. 9 System Response to Power Outages and Restorations: (a) Mains Supply Normal,

(b) Supply from Generator, (c) Voltage Surge on Mains and (d) Loss of Mains Supply

To ensure an almost seamless transfer of power supply, it is required that minimum time is

spent for the entire process of supply changeover. The generator, per the program run on the

controller, is expected to start within 10 seconds of utility power outage, and when rated

voltage is sensed by the generator AC sensor, the controller immediately pulses the

changeover relay to change the power source. Thus, on average, approximately 20 seconds is

expected to elapse during the interruption of power supply to the load.

4 Conclusions and Recommendations

4.1 Conclusions

This paper has presented the design of an efficient, cost effective and reliable

Microcontroller-Based Automatic Transfer Switching System (MATSS), which has the

ability to accurately monitor the power supply from the utility company and respond

appropriately upon a power outage by starting an on-site generator to supply power. Upon the

restoration of utility power, the system commutes the load back to utility and shuts down the

generator. Included in the design is an over-voltage/over-current protection unit. This enables

the system to automatically changeover when the voltage or current rises above its rating, to

protect equipment from damage. The cost of the MBATSS is approximately 330.87 USD to

construct and install. This new system thus offers considerable operational advantages and

cost saving over the manual system currently used by many companies in Ghana. The switch

transition mode used (open transition mode) eliminates the problem of standby power

generators “back-feeding” into the utility lines.

4.2 Recommendation

It is recommended that hospitals, financial institutions, internet service providers, mining and

allied companies , which require constant power supply should use the MBATSS.

References

Aguinaga, J. (2008), “Study of Transfer Switches”, Unpublished MSc Thesis Report, Helsinki

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