In three phase half wave rectifier, three diodes are connected to each of the three phase of secondary winding of the transformer. The three phases of secondary are connected in the form of star thus it is also called Star Connected Secondary.
The anode terminal of the diode is connected to the secondary winding of the transformer. And the three phases of the transformer is connected together at a common point called neutral. This neutral point provides the negative terminal to the load and is earthed.
Each diodes conducts for one third of the AC cycle and remaining two diodes will remains open circuit. The ouput DC voltage will be between the peak value of supply voltage and half of the supply voltage.
The ripple factor for 3 phase half wave rectifier is derived in the equations below.