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1 PAPER CODE: STUIJT20160004 Vol 1 Issue 3 -April, 2017 PUBLISHED BY: WWW.STU.EDU.GH

STU INTERNATIONAL JOURNAL OF TECHNOLOGY (STUIJT) Vol 1 Issue 3 -April, 2017 (ISSN 2508-0997, Online) PUBLISHED BY; WWW.STU.EDU.GH

AUTOMATIC PHASE SELECTOR FOR MULTISOURCE POWER SUPPLY

Alexander Kyereh1, & Gyimah Kopri2.

1Lecturer, Electrical/Electronic Dep’t, Sunyani Technical University

2Sunyani Technical University

Abstract

The ability to supply reliable power to consumer loads is a major aim of the utility company. In

Ghana and other developing countries, most institutions like hospitals and banks need not to be

denied electrical energy for even a short period of time. This has, therefore, called for an

investment in alternative means of providing electricity such as solar energy. But since solar energy

has cheap running cost, it is important to combine it with other forms of power supply to provide

high reliability and economy. Based on technological advancement, various theories have been

implemented to design different kinds of means to attain automatic means of healthy phase

selection in times of fault. In this paper, a real-time automatic phase selector was designed using

logic gates and power electronic devices. A prototype of the design was constructed and tested at

the lab for the purpose of evaluation and assessment. Results proved that, the selection was

successful in terms of speed among the three phase combination. Miniaturization of digital circuits

and scalability of other electronic circuits are, therefore, recommended to improve upon such

designs and development.

Keywords: Phase selector, logic gate, solar energy, multisource, miniaturization.

Introduction

One primary concern of every electrical power utility is the provision of uninterrupted power

supply in an effective and efficient manner. More importantly all electrical systems are built upon

the three important factors viz. reliability, safety and economy. Safety and reliability is ensured by

making use of automation and switching load to efficient phase conforms economy (Gupta, 2015).

It is therefore, required to supply a high level of quality power to specific devices to supplement

this goal as certain critical loads demand an uninterrupted supply with a minimum case of

disruption. In addition, there are processes that need not be interrupted because of their importance,

such as surgery operation in hospitals, transfer of money between banks and lots more (Ezirim,

2015).



The advent of renewable power supplies is one of the alternative catalysts to eradicate the problem

of power failure in the national grid. Some of the emerging types of renewable power supplies that

are embraced in the country include solar and wind turbines. By addressing these concerns, the

power engineer is therefore, required to provide the best engineering standards and regulations to

deliver a better distributing scheme and maintaining the power system to a good reliable state in

this area of concern. With applications where the national grid is supplemented by two alternative

buck-up supplies such as solar and generator set, careful selection of an economic source is required

to be connected constantly to the load to provide high level of reliability. Moreover, the

transmission power of double-circuit transmission lines is large, so it is an important problem to

avoid the cut-off of both lines when inter-line fault happens which gains wide attention in

engineering application (Deng, 2012).

The need for electronic phase selector is therefore, an area of importance to be employed in such a

situation to address this particular issue for such critical loads. In this paper, a high speed electronic

circuit is presented to take care of selection between three alternative sources of power.

Statement of the problem

As a primary requirement, special electrical appliances and devices such as surgical equipment and

banking systems need not to be denied of constant quality power supply. The existing power supply

scheme to this type of loads is based on a fixed source of supply which proves to be less reliable in

times of power failure as the electrical engineering field has gone a great revolution. In the fixed

connection scheme, the load is entitled to only a single source of supply and in times of power

failure, a lot of time is wasted in putting things right for the continuity of power flow and has

always been the worry on such critical systems. This has, therefore, called for the need for an

automated system of controlling the selection of both economic and reliable sources at a time by

implementing fully electronic systems.

The general objective of this paper was to design a fully automatic electronic system in combination

of power electronic technology that could be used to select the most economic and reliable source

for a single phase electrical load from one of the three different sources by studying the approaches

of phase selector design, identifying means of implementing a digital phase selector using logic



gates in combination with power electronic devices, and providing means of prioritizing a selected

source that is the most reliable and cost effective to be connected to the load.

Related literature review

Over the years, many approaches have been adopted in configuring changeover/phase selector

systems. Some of these systems are discussed below:

a) Manually controlled Change-over

The manual changeover or selector switch system still remains the oldest changeover switch box

used by majority of electricity consumers. Manual changeover switch box separates the source

between a generator and public supply. Whenever there is power failure, change-over is done

manually by an individual and the same happens when the public power is restored. This is usually

accompanied by a loud noise and electrical sparks.

Limitations of manual Change-over system

There are several limitations associated with the manual change-over system. Christian (2012)

reported the following limitations:

i. Manual change-over is time wasting whenever there is

power failure.

ii. It is strenuous to operate because a lot of energy is required.

iii. It causes device process or product damage. iv. It has

the potential to cause fire outbreak.

v. It is usually accompanied by a lot of noise which may sometimes be psychologically

destabilizing.

vi. Maintenance is more frequent because the change-over action causes tear and wear.

b) Sequential Logic-Controlled Change-over (SLC)

In sequential logic control power selection, sequential digital circuits are used to effect the detection

and control of the supplied power. Sequential logic control approach involves only an automatic



violation of the public power source in the event of power failure, but the generator activation to

supply alternative power is done manually. In effect the sequential logic control is more efficient

than the manual control (Christian, 2012).

Disadvantages of Sequential Logic Control System

i. The main possible clock rate is determined by the slowest logic path in the circuit,

otherwise known as the critical path. Every logical calculation, from the simplest to the

most complex must be complete in one clock cycle, so logic paths that complete their

calculations quickly are idle much of the time, waiting for the next clock pulse.

ii. The clock signal must be distributed to every flip-flop in the circuit. As the clock is usually

a high frequency signal, this distribution consumes a relatively large amount of power and

dissipates much heat. Even the flip-flop that is doing nothing consumes a

small amount of power, thereby, generating waste heat in the chip (Christian, 2012).

c) Microprocessor-Based Control

The microprocessor-based control operates through a central processing unit programmed in a

software-implemented format and stored in memory; Random Access Memory (RAM) and/or

Read Only Memory (ROM) subsequently used to effect controls in real time.

There are two aspects of microprocessor control namely; Microcontroller-Based Controls and

Computer-Based Controls (Christian, 2012).

Microcontroller Based Controls

In microcontroller-based controls, microcomputers are employed with the resulting systems

described as embedded. It gets information like data status from sensors and then issues control

commands to actuators. One distinguishing feature of the embedded system from other real-time

system is that they are only executing task relative to a fixed and well-defined work load. They do

not provide any development environment; they are low-level programmed (Christian, 2012).

Computer-Based Controls

The computer-based control operates through a computer system employed in a multi-

machinedistributed computing environment. Other features, known as real-time software,

extensions are provided for programming languages and protocols, enabling such systems to be



programmed and checked. These systems are programmed to override the operating system

mechanism to control directly the hardware. They are high level language programmed.

This project, however, is designed and implemented as a microprocessor-based controlled system

specifically using the microcontroller as its basic component. It is a dedicated embedded system.

Dowuona (2008) found out that emergency power systems were used as early as World War II on

naval ships. In combat, a ship may lose the function of its steam engines which powers the steam-

driven turbines for the generator. In such situations, one more diesel engine is used to drive backup

generators. Early changeover switches relied on manual operation: two switches would be placed

horizontally in line and the “ON” position facing each other, with a rod placed in between them. In

order to operate the changeover switch, one source must be turned OFF, the rod moved to the other

side and the other turned on.

Oduobuk et al (2014) reported that, the automatic phase changer was made from several electronic

components which include; operational amplifiers, diodes, resistors, capacitors, Zener diodes,

transformers, relays and fuses. Results obtained during the test showed that whenever the system

senses a higher voltage across at least one of the three inputs, it then engages the load.

The system was designed to handle light load and not big loads. This is because of the use of 12

Volts/ 6A relay switch in the system. Such loads include; television sets, radio sets, standing fans

and small lighting points. Also, system reliability, compatibility, and durability in this work were

not considered.

Furthermore, the main aim of this project was to present the real idea of an automatic phase switch

for 220 V to 240 V alternating current. Although, there are many designs and prototype systems

that can perform almost similar functions like, single phase change-over switches, two phase

automatic transfer switch and three phase automatic change-over switch, this prototype is about an

automatic phase switchover (phase selector) which is designed for only three phase AC input power

to single phase output applications. The system is basically designed to select between the three

phases at reasonable speed, and also address phase imbalances with respect to loads. This means

automatic switching between the three phases and output. only single phase.



Joseph (2014) designed an RF remote control based phase selector system. The system was

designed with few semi-conductors and electro-mechanical devices. The semiconductor devices

include 555 integrated circuit, 4017 decade counter integrated circuit, transistors and diodes while

electromechanical switches used were relays and contactors coupled with other electronic devices.

Results showed that the system starts switching sequentially from one output stage (Phase) to

another whenever it senses an RF signal of 300 MHz from a VG40T remote control transmitter.

The main drawback of this system is the restricted transmission medium around a band of 300

MHz.

Omar (2002) indicated that, a single-pole autoreclosures were first reviewed in the project. It was

concluded that the benefits of using single-pole autoreclosure, stem from the economic and stability

considerations that preclude the use of three-phase autoreclosure. Besides, to minimize system

insecurity and instability, reliable phase selection of the faulted phase is very important in order to

avoid unnecessary three-phase tripping or alternatively tripping of the incorrect phase. Also, the

selection process was demanded to be accomplished in minimal time before breaker opening.

Traditional phase selectors were reviewed in accordance to be based on power frequency

measurements and, therefore, suffer from some deficiencies in performance due to remote-end

infeed, fault resistance, mutual coupling from adjacent lines, and their limited accuracy for high-

impedance faults. Other authors used neural networks with their ability to map complex and highly

nonlinear input-output patterns to provide accurate phase selection as well as using the fault-

generated noise with the neutral networks.

In this paper, wavelet transforms with their ability to focus on short transients and highfrequency

components can provide an effective solution to the accurate phase-selection problem. The paper

presents a novel technique for phase selection using wavelet transforms. The technique is basically

different from different conventional algorithms in that it uses the sharp transitions generated under

arcing faults. A 400-kV power system was simulated using the EMTP and the generated data were

used to test the performance of the technique. The paper concludes by presenting results based on

the extensive simulation study.



The realization of phase selection by Dowuona (2008) has had a remarkable improvement ever

since. This is due to technological advancement in the electrical and computer engineering field.

As directed towards the aim of maintaining electrical power reliability different models have been

released to achieve this aim.

The manually controlled phase selection, sequential logic control and microprocessor based phase

selections are the main bases for further algorithm to achieve the selection purpose. After a close

study of the merits and demerits of various approaches, relevant studies were reviewed to figure

out the gaps of development with respect to current research in the area of the study. The use of

discrete electronic components by Oduobuk et al (2014) to achieve the phase selection still left

behind the focus on speed and accuracy though the idea of phase selection was realized. Besides,

the system was limited to light loads according to the relay types employed in the design process.

Stepping ahead in technology was the remote control based phase selector system by Oduobuk et

al (2014). This was to enhance security and speed by employing several digital devices as well as

relays which also suffer electromagnetic losses due to the use of these relays.

The further narrowing down of the study and design criteria had an encounter with the neural

networks approach based on wavelet transform. The optimization of this had been noted to work

around the sensing part but still leaves the gap of tackling the processing aspect. This helped to

conclude the study with a new system design as explained in the next section.

Design methods

This section elaborates on the design approach adopted to come out with the system based on both

software and hardware implementations. The study, analysis and evaluation of several theories to

formulate a conceptual framework. Both functional and technical requirements are sandwiched to

design a novel system to meet market demand and to serve as a basis for future replication and

modification of all kinds. Logic selection is an area of major concern in the process of the design.

Hence, other theories and principles were incorporated to aid the flexibility and durability of the

design. An analytical exercise was performed on various sections of the implementation like power

supply, selection algorithm and process; and finally used as a key means of evaluation for the

successful selection of the optimal method for the design.



The choice of the transistor-transistor logics (TTL) for the processing phase is based on its ability

to provide effective and efficient digital synthesis for the design with low cost. The system was

first simulated on the Proteus ISIS environment for high level mathematical modelling to help in

the Boolean formulation and the minimization based on Boolean algebra and Karnough map. A

highlight on the block diagram is provided alongside with the individual skid interconnections to

produce an entirety.

Block diagram

The overall system consists of the following individual modules; phase sensor, control, driver, triac,

and the load section. Here, the phase sensor picks information from the lines. It is a unit consisting

of three separate sensor modules to function for each line of the three supplies (ie. Solar, Grid, and

gen set). The sensor is made to detect voltage presence and absence without dealing with the aspect

of overvoltage or under voltage. The three output of the sensor are then fed into the control block

for further process. In the control block, the logic control system depends on the internal logic

circuitry to take decision for the actuation purposes at the output to achieve the selection purpose.

Commands are then issued based on the sensor information received to the driving circuit in three

different lines. At most a single line is actuated to drive the load. The driver is a circuit that has the

ability to buffer high current from low current device to drive the individual actuators at the triac

block. Electrical current from the driver then selects a single phase to be connected to the load

through a thyristor (mainly triac). This is demonstrated in Figure. 1.



Fig. 1. Block diagram of the design.

Source: Field study.

Power supply unit

The power supply unit is a regulated DC power supply which takes its source from a DC battery.

The battery is made of two 12V batteries connected in parallel. It is regulated at 12V and 5V to

supply individual DC components in the control circuit and associated circuits. The three 0.01uF

capacitors C1, C2 and C3 are connected to further filter the supply from any pulses. Based on the

drive circuit and the actuator circuit, the LM7812 regulator is used to regulate the supply to 12V to

be fed to them. On the other hand, the control unit is made up of 5V devices and hence the

LM7805 regulator is used to supply 5V to it. The 100Ω and the LED connected to serve as an

indicator circuit.



Fig. 2. Schematic diagram of the power supply unit.


Sensor

The sensor is a combination of electronic components to interface with the three different phases

from the solar, grid and gen-set and connect it to the corresponding D.C component to be fed to

the control block for processing as synthesis. It consist of IN4007 p-n junction diode, 15k-1w

resistor, 10uf capacitor, 9.1V Zener diode, 1k(1/4w) resistor, 10k resistor, a 5v D.C supply and

opto-coupler. As shown in fig. 3. The p-n junction diode is connected in series with the A.C source

which provides a half wave rectification. The rms voltage output is given by:

𝑉(𝑅𝑀𝑆) 𝑑𝑡…………….. (1)

𝜋

𝑉𝑚𝑠𝑖𝑛𝜃𝑑𝜃

𝜋 𝜋

𝑉𝑜𝑙𝑡

The 10uf capacitor is used to provide a filtering purpose to reduce the pulsating level of the output

D.C component. 15k (1w) resistor and the 9.1v zener diodes are put in the circuit to provide a

voltage divider. In this configuration, the output voltage at point A is regulated as 9.1V. Current

sinking by the opto-coupler is further protected by using the 1k (1/4w) resistor in series. To detect



voltage presence at point E, current must flow through the internal diode of the opto-coupler which

in effect biases the photo transistor to allow current to flow from the 5V supply to ground.

Fig. 3. Schematic diagram of the sensor unit.


Hence point E is 5V when the system is circulating current (ie the voltage across the 10k resistor

becomes 5V), and vice versa. In the course of testing, the voltage detection at point E could not

differentiate between no-voltage and low voltage or normal voltage and overvoltage. Output of the

sensor unit at point E is fed to the control block.

Control block

The control block consists of logic gates to issue the selection algorithm table. Table 1 shows the

truth table of the design. Solar, grid, and gen-set show the input status from the sensor block, and

solar_1, gride_1, and gen-set_1 show the phases that are to be selected to be connected to the load.



Table 1: Truth table of the design.

Solar Grid Gen-set Solar_1 Grid_1 Gen-set_1

0 0 0 0 0 0

0 0 1 0 0 1

0 1 0 0 1 0

0 1 1 0 1 0

1 0 0 1 0 0

1 0 1 1 0 0

1 1 0 1 0 0

1 1 1 1 0 0


As indicated by the truth table, when all inputs are off, the output connections are all disabled. With

solar and grid OFF and only gen-set ON, the gen-set is connected and solar and grid disabled.

Similarly, when solar is OFF, and grid is ON, the grid is selected without caring about the gen-set

status. Finally, the solar is treated as a high priority such that when the solar is on, it is automatically

connected without caring about the grid and the gen-set lines. Analytically, the truth table is used

to design the Boolean equivalence for gate selection which is given as follows:



Let Solar = R

Grid = Y

Gen-set = B

For GEN-SET

B1 = R. Y. B…………………………………………………(2)

Fig. 4. Schematic diagram of the prime implicant for GEN-SET LINE.


For GRID

Y1 = RYB + RYB … … … … … … … . . … … … … … … … … … . . (2)

Y1 = R (YB + YB)

Y1 = RY(B + B)

But B + B = 1

Y1 = RY(1) = RY

Fig. 5. Schematic diagram of the prime implicant of GRID-LINE.




For SOLAR

𝑅1 = 𝑅𝑌𝐵 + 𝑅𝑌𝐵 + 𝑅𝑌𝐵 + 𝑅𝑌𝐵 … … … … … … . … … … … … . . (3)

𝑅1 = 𝑅(𝑌𝐵 + 𝑌𝐵 + 𝑌𝐵 + 𝑌𝐵)

But 𝑌𝐵 + 𝑌𝐵 = 1

𝑅1 = 𝑅(𝑌𝐵 + 𝑌𝐵)

Also, 𝑌𝐵 + 𝑌𝐵 = 1

𝑅1 = 𝑅

R

Fig. 6. Schematic diagram of the prime implicant of SOLAR LINE.

Source: field study.

In all, two NAND gates, three AND gates and three NOT gates are used to come out with the

design. The gates are 5V devices which are supplied through the VDD pins with a GND pins as

their ground. The output of this network then generates the output to select at most one line to be

connected to the load. Three outputs are supplied to a driver circuit.

Buffer Unit

Also known as the driver, the buffer unit serves as the interface between the control block and the

high voltage through the triacs which activates the output load circuit. The ULN2003A is used in

this particular work. It is a high-voltage, high-current Darlington transistor array. It consists of



seven NPN Darlington pairs that feature high-voltage outputs with commoncathode flyback diodes

for switching inductive loads.

Triac

The individual triacs are connected to the three outputs of the source. On the other hand the three

logics solar_1, grid_1, and gen-set_1, are connected to M1 of the triac. The other two phases also

work in similar manner to ensure the constant power to be connected to the load. The load is an

A.C appliance which needs an uninterrupted supply.

Component selection

Component testing and selection is the art and science of predicting the functional behavior of an

electronic unit in a specific design through experimental process. This involves isolated testing of

individual components of their relevant electrical, mechanical and environmental properties to

ensure reliability and effectiveness for the target circuit. An error made in component selection can

therefore cause serious damage up to an extent of thrashing and disqualifying the entire design and

the product.

In this exercise, we drew a line of compromise and a comparison between the cost and academic

requirement to make the choices. Mechanical parameters were also used to indicate the physical

form, mounting style, size and weight of the components. These features decide how the

component connects with others in the circuit board. The list below shows a summary of the

mechanical properties that were considered in the selection process:

• Mounting style

• Number of terminals or pins

• Package dimensions

• Package style (rectangular or circular)

• Pin style (solder ball or gull win)

• Seated height

• Weight

• Terminal spacing



Finally, consideration is given to environmental parameters related to components’ behavior and

rating with respect to the different environmental conditions. The list below shows some of the

environmental properties considered.

• Derating temperature

• Material composition

• Moisture sensitivity

• Radiation effect

Presentation of results, testing and discussion

Based on the method used in designing this piece of work, it became necessary for it to be tested

and evaluated according to engineering characteristics. The outcome of the circuit was therefore,

simulated using Proteus ISIS software before the hardware construction. With the three inputs (R,

Y and B) connected to the system, the solar line is always selected irrespective of the conditions of

the other phases. The next priority is the grid line which is selected when solar line is off. The gen-

set line being the last priority takes on when the solar and grid lines are off. Table 2 shows the final

truth table of the results obtained

Table 2. Truth table of the results obtained.

R Y B CONNECTION TO

LOAD

OFF OFF OFF NONE

OFF OFF ON B

OFF ON OFF Y

OFF ON ON Y

ON OFF OFF R

ON OFF ON R

ON ON OFF R

ON ON ON R




The main challenge faced in finalizing the design was related to user requirements and functional

requirements. On the user point of view, flexibility of the system must be attained. Therefore the

installation of the system settings (ie. user preference) during the installation phase was exempted

and there was no means of providing display to show what happens in the system on an LCD.

Priority settings on phases for desired operation of the system were made on the design phase to

make the system rigid on the user’s point of view. In addition, economic requirements were also

considered to produce much affordable product to the market in the future. This was made by

utilizing simple electronic components which can withstand more workload at a time.

From the system point of view, constraints such as speed and accuracy were demanded. Integrated

circuits (ICs) with microcontroller functionality and Diode Transistor logic (DTL) circuits were

considered during the design process but the choice of transistor-transistor logics (TTL) for this

design proved to be the best of all choices. The TTL is a simple electronic IC which provides much

functionality with low power consumption rate.

Conclusion

This study shows a remarkable implementation of an intelligent phase selecting system to

supplement the reliability of power supply to critical loads which need uninterrupted power supply.

As an academic material, a lot of principles and theories have been invested in the design of this

system to accomplish the task at hand. The study was organized based on the ability to incorporate

both hardware and software technologies to design a TTL logic gate based phase selector at both

efficient and effective manner. This was made possible by using a collection of electronic

components and organized into a portable unit based on the Boolean functions implemented on the

gate level. With the help of simulation software a final delivery of the system was realized. Finally,

the system was organized in a hardware model to be tested and evaluated in the lab for further

evaluations, analysis, and other studies by future researchers and technicians.

Recommendations



The full realization of the circuit and packaging was made simple and large in size to expose

it to better understanding and critics during its presentation. It is, therefore, recommended that:

• Special kits should be designed by technicians to support such an objective to facilitate the

adventure of such technical projects

• Miniaturization of digital circuits and scalability of other electronic circuits have been one

of the principal motivational keys to improve upon such designs and development. The

packaging and the efficiency of this piece of work were left with little concern, hence,

future researchers as well as technicians should undertake such work in a more advanced

pattern

• Electronic shifter circuits to provide voltage transformation is another important area of

study for future works. In such implementation, passive components can be used to realize

this idea which may not deliver the desired efficiency when considered on the basis of

speed and accuracy. An interface to the external grid circuit for sensing purpose is,

therefore, left as another key area for further research.

References

Christian, M. (2012) Smart Phase Change-over system with AT89C52 Microcontroller IOSR

Journal of Electrical and Electronics Engineering (IOSRJEEE) ISSN: 2278-1676 Volume

1, Issue 3. PP 31-34.

Deng, X., Yin, X., Zhang, Z. Kong, X. & Qiu, C. (22010). A Novel Fault Phase Selector for

Double-Circuit Transmission Lines TELKOMNIKA, Vol.10, No.7, November 2012, pp.

1730-1738.

Ezirim U. I., Oweziem, U. B., Obinwa, C. C. & Ekwueme, S. O. (2015). Design of an

Automatic Power Phase Selector, International Journal of Engineering and Innovative

Technology (IJEIT) Volume 5, Issue 2.

Gupta, A. K., Singh, C., Singh, G. & Kumar, A. (2015). Automatic Cost Effective Phase Selector



International Journal of Advanced Research in Electrical, Electronics and

Instrumentation Engineering (An ISO 3297: 2007 Certified Organization) Vol. 4, Issue 5,

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Joseph, O. E., Ntiense, I. S. & Nkra, O. P.(2014). Development of RF Remote Control Based

Phase Selector System”, IOSR Journal of Engineering (IOSRJEN) ISSN (e): 2250-3021,

ISSN (p): 2278-8719 Vol. 04, Issue 06.||V4|| PP 23-34.

Oduobuk, E. J., Ettah, E. B. & Ekpenyong, E. E. (2014). Design and Implementation of

Automatic Three Phase Changer Using LM324 Quad Integrated Circuit” International

Journal of Engineering and Technology Research Vol. 2, No. 4, pp. 1 – 15.

Omar A. S. Y., (2002) New Algorithm to Phase Selection Based on Wavelet Transforms IEEE

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