Powering up: Determining where to tap stator windings
There are many applications where it is necessary for a low voltage, single-phase AC or DC power supply to be available for auxiliary equipment such as brakes, clutches, lamps, etc., used along with a three-phase motor. The single-phase voltage can be supplied by tapping the stator winding at the correct place. DC voltage can be produced by tapping the single-phase or three-phase voltage from the three-phase winding and rectifying it to DC. Determining where to tap the winding is fairly straightforward. A three-phase stator winding, when energized, will have a certain number of volts per turn. That is, if you know the number of turns in each phase, and you know the phase voltage, you can determine the volts per turn. Knowing the number of volts per turn, and the required voltage supply for the auxiliary equipment, you can calculate precisely where to tap the winding.