Construction Of Automatic Phase Changer

BLACK DIAGRAM OF AN AUTOMATIC CHANGER
The comparator/voltage sensor compare two voltages and give an output which tell if they are equal or uneaqual the comparator stage in this system is used to sense when the public supply voltage has dropped below certain level. The input public supply voltage is converted to D.C in the power supply stage and regulated to 12v and 5v for the power supply needed in the circuit. The unregulated voltage varies as a public supply input varies in this case 160V is the limit which the system changes over from public supply or generator the sensor stage monitors the unregulated voltage dropped across R1 and R2 as shown in fig 2 below the voltage feeds an input on ICI which compares.
This input with affixes reference across VR1. the drop across R1 at 160V AC is set as the reference any voltage drop below this send a low to the input of the d flip flop to switch the transistor I switch off the relay is reenergized and the contacts change over two relay are connected in parallel  RLA1 is a 1OA relay which switches the battery
12v to the ignitions coil (or starter coil) of the generator and switches it off once public supply is black the second relay relay  RLA2 is a 30a relay that select generator or public supply output to load as shown in fig 4.
The generator output is normally closed. Hence once de-energized the generator output is fed to load and once energized (by the presence of public supply) the relay (normally open contact connect public supply output to load) the introduction of 7474- segment logic device is to ensure prefect switching and eliminate fluctuation which is synonymous with voltage comparators as explained by fizzler (1991). This could be very devastating as the relays would be switching erratically. The switching stage switches the relay contact on and off in the presence and absence of the public supply voltage the output change-over power is determined by the relay contact ratings.