Question

The instantaneous voltage wave-form of a 3-\(\phi\) fully controlled rectifier with R-L load is more negative and less positive when the firing angle ‘α’ lies between

• A. 150$^\circ$ and 180$^\circ$
• B. 60$^\circ$ and 90$^\circ$
• C. 90$^\circ$ and 120$^\circ$
• D. 120$^\circ$ and 150$^\circ$

Hint:

In 3-\(\phi\) full converters with R-L loads, more negative voltage appears for higher firing angles beyond 120°.

Answer 1

The Correct Option is D

In a 3-phase fully controlled rectifier with an R-L load:
- As the firing angle \( \alpha \) increases, the average output voltage decreases.
- Beyond \( \alpha = 120^\circ \), the output voltage waveform starts including more negative portions due to delayed conduction.
- Between \( 120^\circ \) and \( 150^\circ \), the waveform becomes more negative and less positive.