Three-Phase Systems in Power Applications problems
- 1. In a △-connected source driving a △-connected load, the
Options- A. load voltage and line voltage are one-third the source voltage for a given phase
- B. load voltage and line voltage are two-thirds the source voltage for a given phase
- C. load voltage and line voltage cancel for a given phase
- D. load voltage, line voltage, and source phase voltage are all equal for a given phase Discuss
Correct Answer: load voltage, line voltage, and source phase voltage are all equal for a given phase
- 2. A constant load power means a uniform conversion of
Options- A. mechanical to electrical energy
- B. electrical to mechanical energy
- C. current to voltage
- D. voltage to current Discuss
Correct Answer: electrical to mechanical energy
- 3. A single-phase sinusoidal voltage of 120 V is connected to a 90 Ω load. Current in the circuit is
Options- A. 13.3 mA
- B. 133 mA
- C. 1.33 A
- D. 6.2 A Discuss
Correct Answer: 1.33 A
- 4. Compare the total copper cross sections in terms of current-carrying capacity for a single-phase and a three-phase 120 V system with effective load resistance of 15 Ω.
Options- A. single-phase 32 A; three-phase 16 A
- B. single-phase 16 A; three-phase 8 A
- C. single-phase 8 A; three-phase 4 A
- D. single-phase 16 A; three-phase 0 A Discuss
Correct Answer: single-phase 16 A; three-phase 8 A
- 5. In a Y-Y source/load configuration, the
Options- A. phase current, the line current, and the load current are all equal in each phase
- B. phase current, the line current, and the load current are 120° out of phase
- C. phase current and the line current are in phase, and both are 120° out of phase with the load current
- D. line current and the load current are in phase, and both are out of phase with the phase current Discuss
Correct Answer: phase current, the line current, and the load current are all equal in each phase
- 6. A three-phase generator is connected to three 90 Ω load resistors. Each coil generates 120 V ac. A common neutral line exists. How much current flows through the common neutral line?
Options- A. 0 A
- B. 1.33 A
- C. 3.99 A
- D. 2.66 A Discuss
Correct Answer: 0 A
- 7. A two-phase generator is connected to two 90 Ω load resistors. Each coil generates 120 V ac. A common neutral line exists. How much current flows through the common neutral line?
Options- A. 1.33 A
- B. 1.88 A
- C. 2.66 A
- D. 1.77 A Discuss
Correct Answer: 1.77 A
- 8. In a certain Y-Y system, the source phase currents each have a magnitude of 9 A. The magnitude of each load current for a balanced load condition is
Options- A. 3 A
- B. 6 A
- C. 9 A
- D. 27 A Discuss
Correct Answer: 9 A
- 9. In a three-phase system, the voltages are separated by
Options- A. 45°
- B. 90°
- C. 120°
- D. 180° Discuss
Correct Answer: 120°
- 10. In a Y-connected circuit, between each line voltage and the nearest phase voltage, there is a phase angle of
Options- A. 0°
- B. 30°
- C. 60°
- D. 120° Discuss
Correct Answer: 30°
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