Electrician Red Seal · Question
A three-phase 550 V, 60 Hz induction motor is drawing 15 A per phase at full load. If the motor's nameplate indicates a power factor of 0.85 lagging and an efficiency of 90%, what is the approximate mechanical output power of the motor in horsepower?
Input power (P_in) = sqrt(3) * V_L * I_L * PF = sqrt(3) * 550 V * 15 A * 0.85 = 12,233 W. Output power (P_out) = P_in * Efficiency = 12,233 W * 0.90 = 11,009.7
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Question: A three-phase 550 V, 60 Hz induction motor is drawing 15 A per phase at full load. If the motor's nameplate indicates a power factor of 0.85 lagging and an efficiency of 90%, what is the approximate mechanical output power of the motor in horsepower?
Answer options:
- 10.5 hp
- 12.4 hp ✅ 14.7 hp
- 16.9 hp
Correct answer: 14.7 hp
Explanation: Input power (P_in) = sqrt(3) * V_L * I_L * PF = sqrt(3) * 550 V * 15 A * 0.85 = 12,233 W. Output power (P_out) = P_in * Efficiency = 12,233 W * 0.90 = 11,009.7 W. Converting to horsepower: P_out (hp) = 11,009.7 W / 746 W/hp = 14.76 hp. So, 14.7 hp is the closest answer.
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