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.

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 generalised 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.