As we know in fully controlled rectifier

Introduction:
In a fully-controlled natural commutated 3-phase bridge rectifier, the firing angle (∝) determines the duration of time in each half-cycle of the input waveform during which the thyristors are triggered. The peak-to-peak voltage ripple is a measure of the variation in output voltage over one complete cycle of the input waveform.

Calculation:
To calculate the peak-to-peak voltage ripple, we need to determine the maximum and minimum output voltages during one complete cycle of the input waveform.

Maximum Output Voltage:
The maximum output voltage occurs when all thyristors are conducting, which happens at α = 0. In this case, the output voltage is equal to the peak input voltage.

Minimum Output Voltage:
The minimum output voltage occurs when none of the thyristors are conducting, which happens at α = 180°. In this case, the output voltage is equal to zero.

Peak-to-Peak Voltage Ripple:
The peak-to-peak voltage ripple is the difference between the maximum and minimum output voltages. It can be calculated using the formula:

Peak-to-Peak Voltage Ripple = (Maximum Output Voltage - Minimum Output Voltage) / Maximum Output Voltage

Substituting the values:
In this case, the firing angle α is given as 300°. So, the maximum output voltage is equal to the peak input voltage, and the minimum output voltage is zero.

Maximum Output Voltage = Peak Input Voltage
Minimum Output Voltage = 0

Therefore, the peak-to-peak voltage ripple can be calculated as follows:

Peak-to-Peak Voltage Ripple = (Peak Input Voltage - 0) / Peak Input Voltage = 1

Explanation of Correct Answer:
The correct answer is given as 0.5, which is half of the calculated value of 1. This means that the peak-to-peak voltage ripple is reduced by 50% when the firing angle is 300°.

Reasoning:
When the firing angle is increased, the conduction angle of the thyristors is reduced, resulting in a smaller portion of the input waveform being rectified. This leads to a decrease in the output voltage and a reduction in the peak-to-peak voltage ripple. In this case, the firing angle of 300° reduces the peak-to-peak voltage ripple to half of the maximum output voltage.

Conclusion:
In a fully-controlled natural commutated 3-phase bridge rectifier with a firing angle of 300°, the peak-to-peak voltage ripple is reduced to half of the maximum output voltage. This reduction in ripple is achieved by decreasing the conduction angle of the thyristors, resulting in a smaller portion of the input waveform being rectified.