Description
ABSTRACT
This project work is on the design and construction of automatic phase selector for 3-phase power supply. It provides a means of switching from one phase of AC mains to another in the case of failure in the existing phase; This project has been improved on the existing types of electromechanical device that has being in use over the years.
Hence this has been achieved by the use of operational amplifier, timing circuit and high current relay switches and it is powered by 12V dc power supply.
The aim of this work is to design and construct an Auto Phase Selector introduces an automatic solution to overcome power fluctuation/phase interruption by selecting next most healthy available phase to feed the equipment without any notice of power outage.
CHAPTER ONE
- INTRODUCTION
In Nigeria today the problems of power outage across phases is so rampant thus leading to some sensitive equipment and appliances being redundant, this could sometimes be the cause of one phase going out with respect to the other.
It may surprise one to note that in an attempt to solve this problems, so many unskilled electricity consumers has in recent past resorted to some crude means of swapping between phases to obtain power. So many souls have been lost in this act. This is an undesirable condition to consumers and the need now arises to design a device that can automatically select among the phases and make power supply available at the consumer’s terminal.
However, this can only be possible if one have a three phase met or and there is supply from any of the service line or the entire line, this project known as a three phase automatic phase selector has been constructed with a view of solving the problems stated above. The design and construction was based on the principle of Electro magneto-Dynamism and alignment as demonstrated in the contactor arrangement.
Among other components are the timers miniature-circuit breakers the contactors and indicator bulbs, the ease with which the device is operated is well elaborated to ensure simplicity effort were made to present a stop by step operation of the project. As much as there is no project without limitation and applications, we have as well dedicated a section of this paper to look into it.
In order to ease the effort of technicians in restoring the devices should there be any malfunction associated.
Faults and how they are cleared is presented, however, there are no user serviceable parts in the device therefore all maintenance should be referred to a qualified electrical personnel.
In this system, If any one or two phases in a 3-phase supply interrupted/goes low and you want equipment to work on normal voltages then this circuit will give solution. This system is designed to monitor the presence of supply to the three phases and to display condition of each phase on an LCD.
1.2 OBJECTIVE OF THE PROJECT
The objective of this work is to provide uninterruptable power supply for single phase loads even in the failure of one or two phases in a three phase system.
1.3 SIGNIFICANCE OF THE PROJECT
Industries require three phases power to run their machinery. Some of them require continuous \ uninterrupted power to maintain their data. Auto phase selector unit for those equipment whose supply is single phase. The single phase supply is selected automatically from three phases supply.
Auto Phase Selector introduces an automatic solution to overcome power fluctuation \ phase interruption by selecting next most healthy available phase to feed the equipment.
1.4 STATEMENT OF THE PROBLEMS
In every home, office or industries, automatic phase selector plays a vital role, that is, It provides a means of switching from one phase of AC mains to another in the case of failure in the existing phase; This project has been improved on the existing types of electromechanical device that has being in use over the years.
In the course of designing this project, different kinds of problem was notice such as:
- Difficulty in troubleshooting with circuit without the circuit diagram
- Difficulty in connecting the output without the three phases short-circuiting, until a multiplexing circuit was gotten.
- Difficult in wiring because of the strong wiring the project required.
1.5 SCOPE AND LIMITATION OF THE STUDY
This work covers only a three phase automatic phase selector which can only be used for providing a means of switching from one phase of AC mains to another in the case of failure in the existing phase.
| A Microcontroller based system will continuously monitor the incoming phase and accordingly display the details on an alphanumeric LCD also it will display the output phase. |
| Technical Specification |
| 1. It monitors all three phases and pass one of them.
2. It displays all available phases on LCD 3. One LCD and Keypad with three keys are provided for input from user. 4. If a phase ® is disconnected. New phase (S/T) will select at once and remain connected. |
1.6 APPLICATION OF THE PROJECT
Applications of this project are as below:
- Small and Medium Scale Industries
- Residential Apartments.
CHAPTER FIVE
5.0 SUMMARY
Phase selector provides a means of switching from one phase of AC mains to another in the case of failure in the existing phase; it also changeover to generator if there is failure in all the three phases of the AC mains.
In three-phase applications, if low voltage is available in any one or two phases, and you want your equipment to work on normal voltage, this circuit will solve your problem. However, a proper-rating fuse needs to be used in the input lines (R, Y and B) of each phase. The circuit provides correct voltage in the same power supply lines through relays from the other phase where correct voltage is available.
The distribution line supplying your home may be single phase and have only two wires strung between the poles (we will use the overhead power lines as examples because they can be easily seen). However, the distribution line may be made up of 4 lines. What are the others? The other lines carry the currents from two other electrical circuits, making a total of three circuits or phases. The reason why there are only 4 lines is because the 3 phases have a common neutral line (i.e. 3 active lines and 1 common neutral line).
Because the magnitude and direction of the electricity flowing in each of the phases is slightly displaced in time from the electricity flowing in the other phases, the current flowing in the common neutral will be the sum of the neutral currents from the 3 phases. The resultant current in the common neutral is smaller in a 3 phase system than in systems with other numbers of phases. This ability to use a common neutral of relatively small capacity has large economic advantages and is the main reason why 3 phases are used.
3 phase electricity has another advantage. We mentioned above that, in Canada, the voltage between the active and neutral in the single phase, low voltage supply to our homes is 220 volts and that this phase is only one of the phases in the 3 phase system. The voltage between the phases of a 220/220V 3 phase system is 240 volts (in Canada). A 240 volt, 3 phase supply is able to deliver more energy than a 120 volt, single phase supply. 3 phase supplies are normally restricted to large electrical loads, such as large electric motors. Commercial buildings are often wired for three phase power. Air conditioners for instance are run on the three phase power while single phase power is typically used for most electrical, electronic and lighting equipment.
A single phase supply must have a neutral, whereas a 3 phase supply does not require a neutral. More complicated reasons deal with fixing the voltage of the single phase supply relative to the ground (because domestic appliances have their metal enclosures connected to ground) and for fault protection purposes. 3 phase, medium voltage, distribution systems and high voltage transmission systems therefore use one wire for each phase and no neutral.
5.2 CONCLUSION
The mains supply in Nigeria fluctuates widely due to overloading, ageing and improper distribution of loads among the three phases of the consumers’ substation transformer.
Appliances such as video cassette player, television as well as those containing compressors like air conditioners, refrigerators, etc could be damaged due to this variation and fluctuation in voltage mains.
The automatic three-phase selector is an electronic circuit that is capable of detecting voltage levels by means of a controller that does some level of comparison before initializing a logic combinational circuit that does some logic combination before initializing an electronic relay switch action. The relay is energize only when the mains voltage is within an accepted predetermined limit, outside of which relay remains dormant .voltage levels below the desired range is ignored. This device is designed to work with a 3-phase input signal. The device functions in the form of an automatic electronic switch, switching between three potentials, with the aim of supplying the highest potential to the load.
5.3 RECOMMENDATION
Carrying-out this work by final year student is a right thing and at the right time.
This work was built with quality wiring and contains many connections, I recommend that if failure occur, it should be troubleshoot by a qualify personnel along with the circuits diagram.
This project was built for Educational purposes. If one want to use it for industrial or home applications, I recommend that a hook should be attached to the casing that would allow fixing the system on the wall.
