Symmetry of firing angles in a single-phase full-wave AC regulator In a single-phase full-wave AC voltage controller (regulator), are the firing angles in the positive and negative half-cycles kept equal for normal operation?

Introduction / Context:
AC regulators control the RMS value of the load voltage by delaying the firing of antiparallel SCRs in each half-cycle. To avoid DC components and ensure symmetrical waveforms, firing angles are typically chosen to be the same in both polarities.

Given Data / Assumptions:

• Single-phase full-wave regulator with two antiparallel thyristors.
• Goal is to control RMS voltage without introducing DC offset.
• Normal symmetrical firing strategy.

Concept / Approach:
If the firing angles differ between the positive and negative half-cycles, the average value of the load voltage becomes nonzero (introducing a DC component). This can saturate transformers, increase EMI, and stress devices. Hence, equal firing angles are maintained for symmetry and minimal DC offset.

Step-by-Step Solution:
Define α+ for the positive half-cycle and α− for the negative half-cycle.Set α+ = α− → symmetrical conduction windows → zero average (no DC component).Therefore, standard operation keeps equal firing angles in both half-cycles.

Verification / Alternative check:
Textbook waveforms for full-wave AC regulators show mirrored conduction intervals about the zero axis when α is the same in both halves.

Why Other Options Are Wrong:

• False or 90° difference: would deliberately introduce asymmetry and unwanted DC.
• Unity power factor or purely resistive caveats are unnecessary; symmetry is desired across many load types, though current waveforms vary with load.

Common Pitfalls:

• Assuming different α helps power factor; it generally harms waveform quality.

Final Answer:
True