1.0 INTRODUCTION
The poor state of power supply in developing countries, calls for alternatives sources of power generation and automation of electrical power generation to back up the utility supply. Over time, automation of electrical power supply has become so vital as the rate of power outage is predominantly high .
As a result of this power outage developing countries like Nigeria, experience slow development processes in both the public and private sectors of their economy. Investors from foreign lands do not feel secure to come and set up business or industries - in spite of the large market made available in such populated nations, because of frequent power failures experienced. In addition, delicate processes and operations such as surgery cases in hospitals, transfer of money between banks, data and information transfer at data centers, require constant power supply in order to prevent the loss of life or data resources which could be very expensive to business operations.
Therefore, it is for these reasons that automatic change over were developed.
Initially, these switches were designed for manual operations, but with an
increase in the technological advancement of electrical power control and automation that, Automatic change over control were created.
It eliminates the element of manpower interaction in starting a generator and changing power supply from one source to another.
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 microcontroller chips to function.
The design of this project is such that a combination of comparators digitals switches (logic IC), electronics timers and electromagnetic switches, contactors and circuit breakers are used to achieve a very fast and effective change over in this case.
The automatic change over switch makes use of 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.
1.1 GENERAL DESCRIPTION AND APPLICATION
BRIEF DESCRIPTION: An automatic changeover is used with standby systems. It includes a control circuit that senses mains voltage. When utility power is interrupted, the control circuit starts up the generator set, disconnects your house from the utility and connects it to the generator set. It then continues to monitor mains status. When it's restored, it commutates your household wiring from the generator back to the utility. When the generator is disconnected, it goes into a cool-down process and then automatically shuts down.
There are three important switching positions which are:
1) Switching of the contactors
2) Switching of the generator started if power fails
3) Switching off the generator as soon as power is restored
The automatic changeover switch monitors the supply of voltage from a single phase line and a generator supply, it then base its control operation on the availability or unavailability of power supply from either sources. It consists of a series of relays contactors and protective devices that help form the control circuit.
The automatic changeover switch system can be divided into there main functional blocks namely; the relay switching block, timer relay block, and the contactor switching block.
The relay switching block comprises the voltage monitoring relay that monitors the supply voltage level and the certain pins of the microcontroller that act as sensor relays. The delay timer multifunctional relays of the utility and that of the generator sections provide some delays before energizing the contactors which in turn provide power supply to the connected load.
1.1 BLOCK DIAGRAM REPRESENTATION
The block diagram representation of the automatic change over switch is the one shown
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