Answer:
0°
Step-by-step explanation:
The maximum voltage across the load of a single-phase AC voltage regulator occurs when the firing angle is 0 degrees or when the thyristor is triggered at the beginning of the positive half-cycle of the input AC voltage.
At this point, the thyristor conducts for the entire half-cycle, allowing the maximum voltage to be delivered to the load. As the firing angle is increased, the conduction angle of the thyristor decreases, resulting in a lower average output voltage.
Therefore, the maximum voltage across the load of a single-phase AC voltage regulator occurs when the thyristor is triggered at the beginning of the positive half-cycle of the input AC voltage, which corresponds to a firing angle of 0 degrees.