AC Voltage Controllers MCQ [Free PDF] – 4 Objective Questions with Answers

Unlike an inverter, an AC voltage controller does not change AC to a new frequency; it controls the portion of each source cycle applied to the load. With phase control, delaying the firing angle reduces RMS output. Key relation: For a resistive single-phase phase-controlled load, Vrms depends on firing angle α; frequency at the load remains the source frequency.

Exam focus: AC controller → same frequency, variable RMS voltage. Common trap: Confusing an AC voltage controller with a frequency converter/inverter.

AC voltage controllers vary the rms AC voltage supplied to a load without changing the supply frequency. A classic application is resistive electric heating, where delivered power is smoothly controlled by phase-angle or integral-cycle control.

In an N-stage sequence controller, the supply voltage is divided across the staged secondary arrangement; each secondary is designed for a fraction of the total controlled voltage. The keyed relation is Vs/n per stage.

The load current is I = P/(V·pf) = 2000/(230×0.8) ≈ 10.87 A. With a safety factor of 2, the required SCR rms current rating is about 21.74 A.