5 April 2017

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.


three-phase-half-wave-rectifier.png














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 RL – 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 RL – 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 RL – 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.


waveform-of-the-three-phase-half-wave-rectifier-waveform


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