Three-phase system Three-phase alternating current is produced in a generator with three separate windings. All values on the sinusoidal voltage are displaced 120° in relation to each other. Different units can be connected to a three-phase unit. A single phase unit can be connected between the phase and zero. Three-phase units can be connected in two ways, star (Y) or delta (Ä) connection. With the star connection a phase voltage lies between the outlets. With a delta connection a main voltage lies between the outlets.