Construction Of Automatic Phase Changer

CHAPTER FOUR
WORKING
In three –phase application, if low voltage s available in any one or two phases , and you want your equaipment to work on normal voltage, this circuie will solve your problem. However, a proper – rating fuse needs to be used in the input lines {R,Y and B} of each phase. The circuit provides correct voltage in the same power supply lines through relays from the other phase where correct voltage is available. Using it you can operate all your  equipment even when correct voltage is available on a single phase in the building.
    The circuit is built around a transformer , comparator translator  and relay. Three identical sets of this circuit, one each for three phases, are used. Let us now consider the working of the circuit connecting red cable {call it R phases}
    The main power supply phase R is stepped down by transformer X1 to deliver 12V 300Ma , which is rectified by diode 01 and filtered by comparator C1 to produce the operating voltage for the operational amplifier {I C1}
    The voltage at inventing pin2 of operational amplifier {IC1} is taken from the voltage  divider circuit of resistor R1 and present resistor VR1.VR1 is used to set the reference voltage according to the requirement. The reference voltage at non – inventing pin3 is fixed to 5.1V through zener diode  ZD1. Till the supply voltage available in phase R is in the range of 200v- 230v, the voltage at inventing pin2 of IC1 remains high, i.e, more than reference voltage of 5.1v, and its output pin 6 also remains high. As result, transistor T1 does not conduct, relay RL1 remains de- energized and phrases supplies  power to load L7 via normally closed {N/C} contact of relay RL1.
    As soon as phase- R voltage goes below 20v, the voltage at inventing pin 2 of IC1 goes below reference voltage of 5. 1v, and its output goes low. As a result, transistor T1 conducts and relay RL1 energizes and load L1 is disconnected from phase R and connected  to v through relay  RL2.
     Similarly, the auto phase- change of the reaming two phases, Viz phase v2 and phase B can be able to take – on the load when transferred from other phases. While wiring, assembly and installation of the circuit, make sure that you
{1} use good – quality, multi-stand insulated copper wire suitable for your current requirement
{2} use good – quality relay with proper contact and current rating
{3} mount the transformer {s} and relays on a suitable cabinet
{4} use a tab block {TB} for incoming/ outgoing connections from mains
PERFORMANCE EVALUATION
Table 1. Variation of d.c voltage against input public