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Circuit and electromagnetism basics

For a balanced three-phase load with a line voltage of 200 V, a line current of 10 A and a power factor of 0.8, which is closest to the load's active power (total of all three phases)?

  1. AAbout 1.6 kW
  2. BAbout 4.8 kW
  3. CAbout 2.8 kW
Show answer and explanation

Answer: C. About 2.8 kW

The active power of a balanced three-phase load is P = √3 × VL × IL × cos φ, whether it is Y- or delta-connected: √3 × 200 V × 10 A × 0.8 ≈ 2771 W ≈ 2.8 kW. Viewed as a Y connection, the phase voltage is 200/√3 ≈ 115.5 V and the phase current is 10 A, so each phase takes 115.5 × 10 × 0.8 ≈ 924 W, and three times that is the total.

  • A. About 1.6 kW uses the single-phase formula V × I × cos φ.
  • B. About 4.8 kW computes one phase using the line voltage and then multiplies by three.
  • C. Correct. √3 × 200 × 10 × 0.8 ≈ 2.8 kW.
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