three-phase center-tap full-wave rectifier
As shown in figure 1, a three phase full-wave rectifier requires a transformer with six secondary winding connected to give two separate three-phase supplies 1800 out of phase with each other.
The centre taps are connected by an interphase transformer which enables the two rectifier units to operate independently of each other. Obviously, each diode conducts for one third cycle. However, the addition of two outputs cancels the lowest frequency component of the ripple.
The output voltage has a mean value of 0.83 Vsm (less the diode voltage drop) and a ripple having a fundamental frequency six times the supply frequency.
Three-phase full-wave rectifier circuit is preferred for high powers because
(i) Each secondary carries current for one-third of a cycle;
(ii) Each primary carries current for two-third of a cycle;
Cu loss in the transformer winding is comparatively lower.