I don't have any experience with star delta starters but on doing some research I concluded that 2 push buttons(NO and NC) are required to turn on or off the system. I have a pump which is star delta controlled, turns on when I push green NO button and turns off when I push red NC button. Now I want to control this via Arduino rather than manually pressing buttons. What I thought so far is to replace push buttons with relay(NO with NO and NC with NC respectively) and control those relays with Arduino. But I've seen many systems of star delta connection where motor turns on or off with just a normal on/off switch i.e. no separate push buttons. That will be more feasible to control via Arduino since only one relay is required. But I nowhere found a way to replace 2 push button circuit with normal on/off switch. Please help out.
You could maybe use a two pole relay if the starter doesn't mind the buttons being held
Or if one of the buttons has priority over the others you could hard-wire that button and just use the relay on the other.
Actually you need three(3) power contactors, and not a single relay for star/delta. But I suppose you have these contactors and timer unit in a box that is mounted on a pump itself.
Usually the star/delta schematics for the 1st contactor is as depicted. You have a start and stop button that are series wired with motor protection device and possibly an emergency stop. The strat button is self retained by using an auxiliary contact of the power contactor.
For use with your Arduino, you have to replace start/stop button combo with a relay, also yo have to remove the aux. contact from power contactor.