GATE 2024 EE – Question 28
A single-phase triac based AC voltage controller feeds a series RL load. The input AC supply is 230 V, 50 Hz. The values of R and L are 10 Ω and 18.37 mH, respectively. The minimum triggering angle of the triac to obtain controllable output voltage is
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Correct answer: (B) 30°
Explanation
The load impedance angle is $\varphi=\tan^{-1}\dfrac{\omega L}{R}$ with $\omega L=2\pi\times50\times18.37\times10^{-3}=5.77\ \Omega$, so $\varphi=\tan^{-1}(0.577)=30^\circ$. The output is controllable only for firing angles $\alpha\ge\varphi$, so the minimum is $30^\circ$.