Power failure or 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 failure. 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, transfer of money between banks and lots more. This paper presents the design and construction of an automatic power changeover switch that switches power supply from public supply to generator once there is public power supply outage and it does this automatically. This is achieved by the use of integrated circuits that have timing abilities and relays to effect switching.
Keywords: Switching, relay, generator, motor, public power supply, transistor.
TABLE OF CONTENT
Table of content
1.1 General Description and application
1.2 Block Diagram representation
2.0 Theory Of Operation
3.1 Control Logic Unit
3.2 Motor Terminal
3.3 Output Load Terminal
3.4 Relay Switching Circuit
4.0 Performance Evaluation
As the quest for change over on public power supply and stand by generation increase. Engineering have researches deep into the different methods of achieving to both manual and automatic types.
It may not be taken seriously in some places where power supply is up to 90 constant or where intermittent outage causes no great damage. However, place where they have business centers, industrial centers and even cold rooms need to almost 100% supply. So in this case there is need to provide a standby power supply in the event of power outage. The most important task is just to provide a standby power supply by great attention is paid to the reliability of the system. That is immediately and change over without fluctuations.
The first type of change over switch were purely manual operated. They usually have three switch able position, main, off and generator. An arm is provided from where the operator can have access to the switching. Here, the effectiveness of the switching (i.e how fast it is effected each time power needs to be changed) largely depends on the operator. The change over system will be ineffective when the operator is not around.
The second generation of change over switches were made semi-automatic in which the mains power supply directly powers the contactors. This arrangement is wired is such a way that if the mains power supply fails, the contractors will all drop leaving the supply to the generator position. The effectiveness of the system will now depend on the operator top start up the generator on time.
The main problem suffered by the above mentioned two versions of the change over switch is that the operator must have to be continuously on duty for it to be very effective. They lent use full closed loop system to operate.
The present day technology has made it possible for the change over switch to come in a number of designs switch using the closed loop system at feed back control. Some of them use comparators, logic circuits and electronic timers to achieve the task. Some even used simple micro processor chips to function.
The design of this project is such that a combination of comparators digitals switches (logic IC), electronics timers and electromagnetic switches are used to achieve a very fast and effective change over in this case.
The automatic change over switch makes use of protective relays and contractors among other things which constantly monitor the power system to ensure maximum continuity of the electrical service with minimum damage to life and property. They are found mostly in domestic installations, hospital threatres, conference halls, computer centres, data and research centres, laboratories and industries that require three phase constant power supply. This equipment however is used to protect some house holds appliances from electrical faults which may arise due to voltage drop. It was designed and constructed purposely to alleviate the suffering encountered by the consumers following supply authority’s consistent failure to meet its obligations of constant and uninterrupted power supply. A circuit breaker is in corporate as a back up protection to improve the reliability of the system and to meet it’s specification, although more back-up protection could have been incorporated monitoring the supply but due to financial constraints, it has to be limited to this operation. The schematic diagram of the automatic change over switch was clearly explained as far as possible to be apprehended by any person within or outside the engineering field.
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