A single phase 240 V, 1 kW heater is connected across single phase 240 V, 50 Hz supply through an SCR. For firing angle delay of 90˚, calculate the power absorbed in the heater element.

• A. 300 W
• B. 275 W
• C. 225 W
• D. 250 W

Answer: (D)

Resistance of heater, R = V²/P
R = 57.6 ohm

RMS value of voltage through controlled SCR = (Vm/2π)*(1 + cosα)
= 120 V

Power absorb by heater = Vrms²/R
= 120²/57.6
= 250 W