Working of Three Phase Half Wave Uncontrolled Rectifier

• Figure A shows a three phase half wave uncontrolled rectifier circuit using delta – star transformer. 
• The anode of the diode D1, D2 and D3 are connected to the secondary winding of the transformer with R phase, Y phase and B phase respectively. 
• The cathode of the three diodes is connected to the neutral point of the secondary winding. 
• The resistive load is connected between neutral point and common cathode point of the diodes.

Working

• The three phase supply voltage waveform is shown in the figure B. 
• The diode can block negative voltage and it conducts when phase voltage is maximum of the three phases. 
• The effect of the transformer winding reactance is neglected. The working of three phase uncontrolled rectifier is given below.

Point a 

• The voltage of phase R becomes zero . 
• The voltage of phase B becomes positive with respect to phase Y resulting diode D3 conducts. 
• The load current flows through phase B – diode D3 – load resistance R_L – n.

Point b 

• The voltage of phase Y becomes negative . 
• The voltage of phase R becomes positive with respect to phase B resulting diode D1 conducts. 
• The load current flows through phase R – diode D1 – load resistance R_L – n.

Point c

• The voltage of phase B becomes negative . 
• The voltage of phase Y becomes positive with respect to phase R resulting diode D2 conducts. 
• The load current flows through phase Y – diode D2 – load resistance R_L – n.
• There are three diodes and each diode conducts in a proper sequence of D3 – D2 – D1 – D3 and so on. 
• The conduction angle for each diode is 120 degree.

                                            

THREE PHASE HALF WAVE UNCONTROLLED RECTIFIER.PDF

THREE PHASE HALF WAVE UNCONTROLLED RECTIFIERS WAVEFORMS.PDF

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