Explain the operation of three phase half wave controlled rectifier with circuit diagram and also sketch its input and output waveform

Ans:

Circuit diagram:

 

Operation: 

• The 3-phase input supply is applied through the star connected supply transformer as shown in the figure. The common neutral point of the supply is connected to one end of the load while the other end of the load connected to the common cathode point 

•  When the SCR T1 is triggered at ωt=(∏/6 + α)=(30° + α) , the phase voltage Van appears across the load when T1 conducts. The load current flows through the supply phase winding 'AN' through SCR T1 as long as T1 conducts. 

•  When SCR T2 is triggered at ωt=(5∏/6α), T1 becomes reverse biased and turns-off. The load current flows through the SCR and through the supply phase winding 'B-N' . When T2 conducts the phase voltage vbn appears across the load until the SCR T3 is triggered. 

•  When the SCR T3 is triggered at ωt = (3∏/2 + α)=(270°+α) , T2 is reversed biased and hence T2 turns-off. The phase voltage Vcn appears across the load when T3 conducts. 

•  When T1 is triggered again at the beginning of the next input cycle the SCR T3 turns off as it is reverse biased naturally as soon as T1 is triggered.

Input & output waveforms: