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i am talking about a 3 phase each 220V ac suply from a power generating company. my aim is to connect the three wires + earth into the input of my 3 phase selector, which in turn selects the highest voltage amongs the 3 voltages and suply the entire house with it. If there hapens to be any interruption in the active phase, it switches to another stable phase without power interuption in the house. I need Your help
What am I missing here or not seeing?
I would use three small step-down transformers to isolate each phase, say with 6-12VAC outputs. Rectify and filter the outputs to get a DC level from each transformer. Use three comparators (with sufficient hysteresis to tolerate normal voltage variations) between the three outputs (1 to 2, 1 to 3, and 2 to 3). Use logic gates on these signals to determine the phase with the highest voltage, which is then used to switch the house relays to the proper phase.
But doing that so that the house appliances won't notice is problematic considering the change of phase. Solid-state relays would give the fastest switching and minimize the transient.
Note: Make sure you have the relays interlocked so that not more than one can be energized at a time and that there is a slight delay from one turning on to the other turning off, unless you want to test the mains circuit breakers against a dead short.