07-05-2011, 04:00 PM
Abstract
Most industrial and commercial processes are dependent on electrical power. In the event of power interruptions, the change-over from power supplied by a public utility to a generator is usually performed manually, often resulting in wasted time. Moreover, machine damage sometimes occurs because of human errors. These can cause significant financial losses. This paper presents the design and construction of an automatic phase change-over switch that switches electrical power supply from public supply to generator in the event of a power outage or insufficient voltage. The system uses an electronic control circuit involving integrated circuits, transistor and electromechanical devices.
Keywords: Relay, public supply voltage, generator, switching, electronic control circuit, transistor.
Introduction
Power instability in developing countries creates a need for automation of electrical power generation or alternative sources of power to back up the utility supply. This automation is required as the rate of power outage becomes predominantly high. Most industrial and commercial processes are dependent on power supply and if the processes of change-over are manual, serious time is not only wasted but also creates device or machine damage from human error during the change-over connections, which could bring massive losses.
The starting of the generator is done by a relay which switches the battery voltage to ignition coil of the generator while the main power relay switches the load to either public supply or generator. Fig 1 shows the general-ized block diagram of the system. The approach used in this work is the modular approach where the overall design was first broken into functional block diagrams, where each block in the diagram represents a section of the circuit that carries out a specific function. The functional block diagram of Fig. 1 also shows the interconnection between these blocks. Each section of the block is analyzed below.
A manual change-over switch consists of a manual change-over switch box, switch gear box and cut-out fuse or the connector fuse as described by Rocks and Mazur (1993). This change-over switch box separate the source between the generator and public supply, when there is power supply outage from public supply, someone has to go and change the line to generator. Thus when power supply is restored, someone has to put OFF the generator and then change the source line from generator to public supply.
In view of the above manual change-over switch system that involves manpower by using ones energy in starting the generator and switching over from public supply to generator and vice-versa when the supply is restored. The importance attached to cases of operation in hospitals and air ports in order to save life from generator as fast as possible makes it important for the design and construction of an automatic change-over switch which would solve the problem of manpower and the danger likely to be encountered changeover. The electronic control monitors the incoming public supply voltage and detects when the voltage drops below a level that electrical or electronics gadgets can function depending on the utility
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http://journal.au.edu/au_techno/2006/jul...o1_a10.pdf
