In a three-phase circuit with VL = 400 V, IL = 20 A, and PF = 0.85, calculate real power.

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Prepare for the 3rd Year Electrical Trades Qualification (TQ) exam. Use flashcards and multiple choice questions to master the material. Each question comes with hints and explanations to help you succeed. Get set for your qualification!

Multiple Choice

In a three-phase circuit with VL = 400 V, IL = 20 A, and PF = 0.85, calculate real power.

Explanation:
Real power in a balanced three-phase system comes from the portion of the apparent power carried in phase alignment, captured by P = √3 × V_L × I_L × PF. Here the line voltage is 400 V, the line current is 20 A, and the power factor is 0.85, so the calculation is P = √3 × 400 × 20 × 0.85. Using √3 ≈ 1.732, this becomes P ≈ 1.732 × 400 × 20 × 0.85 = 11,777.6 W, about 11.8 kW. For context, the apparent power is S = √3 × 400 × 20 ≈ 13.856 kVA, and real power is S × PF ≈ 13.856 kVA × 0.85 ≈ 11.8 kW.

Real power in a balanced three-phase system comes from the portion of the apparent power carried in phase alignment, captured by P = √3 × V_L × I_L × PF. Here the line voltage is 400 V, the line current is 20 A, and the power factor is 0.85, so the calculation is P = √3 × 400 × 20 × 0.85.

Using √3 ≈ 1.732, this becomes P ≈ 1.732 × 400 × 20 × 0.85 = 11,777.6 W, about 11.8 kW.

For context, the apparent power is S = √3 × 400 × 20 ≈ 13.856 kVA, and real power is S × PF ≈ 13.856 kVA × 0.85 ≈ 11.8 kW.

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