1.0 Introduction
Power instability in developing countries creates a need for automation of electrical power generation or alternative source 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 changeover are manual, serious time is not only wasted but also creates device or machine damage from human error during the changeover connections, and this could result in massive losses.
This project involves automatic changeover between main power supply and an auxiliary power supply, such as a generator. The project implements an automatic switching or starting of the power generator whenever the main power fails.
The basic operation of this project is to switch ON an auxiliary power supply (like a generator). This operation connects the power supply from the generator to the load after a predetermined time interval. This is intended to normalize the current from the generator. Switching is possible through the use of the relays which switch the battery voltage to ignition coil of the generator while the main power relay switches the load to either public supply or generator.
The system was designed to automatically change power supply back to the main supply moments after the A.C mains are restored and to switch OFF the generator. The device removes the stress of manually switching ON the generator when power failure occurs.
Whenever public supply is available, the relay 3 whose duty is to respond will immediately be energized and its two terminals C3 and B3 are connected together. Whenever the public supply is off from the transformer, the other two terminates C3 and A3 of the relay are connected together and the power circuit is then powered through the 12v battery.
The first important action to the circuit is the automatic resetting of both latches through Schmitt trigger and gate whenever there is public power supply. The gate allows Q and Q- of the latches to be at logical zero and one respectively. This is required for normal starting state. For the motor control latch Q is connected to transistor one through the base. The NPN device controls the relay. For Q at logical 1, transistor one is saturated and relay 1 is energized. Terminals C1 and B1 of the relay are connected together.
The operation allows electric current to flow through the motor / starter. It is noted that one of the motor terminals is already connected to 6v terminals i.e. positive side. The switching of the relay allows the other terminal to be grounded thereby completing the circuit of the electric motor.
The micro controller starts timing immediately, relay 3 supplies electric current to the logic control unit.
Relay 2 supplies power supply to the output load from two sources G and M. M represents public power supply and C1 represents supply from the generator.
Therefore the initial condition is the supply of power to the load through the normal A.C mains the control oscillator through its pin 3 sets the changeover latch for the Q output to change from logical zero to 1 for transistor two to be saturated in reversing the output condition of relay 2.
1.1 Methodology
The operational process is outlined below:
- The power circuit of the generator is not active where there is A.C mains supply.
- Its response to A.C mains supply power failure is by switching on the starting mechanism of the generator.
- There is a delay in the loading of the generator so as to attain stability for a while. After the said delay, the generator is loaded.
- Power supply from the generator is interchanged immediately the A.C mains is restored. After this the generator is switched OFF.
This material contains electrical diagrams, circuits, illustrations and more (Very detailed).
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