Three-Phase Systems in Power Applications problems
- 1. If in a Y-connected ac generator, each phase voltage has a magnitude of 90 VRMS, what is the magnitude of each line voltage?
Options- A. 0 V
- B. 90 V
- C. 156 V
- D. 180 V Discuss
Correct Answer: 156 V
- 2. A three-phase △-connected generator is driving a balanced load such that each phase current is 12 A in magnitude. When I ?a = 12 ∠30° A, what are the polar expressions for the other phase currents?
Options- A. I ?b = 12 ∠150° A, I ?c = 12∠?90° A
- B. I ?b = 12∠120° A, I ?c = 12∠30° A
- C. I ?b = 12∠30° A, I ?c = 12∠120° A
- D. I ?b = 12∠90° A, I ?c = 12∠90° A Discuss
Correct Answer: I ?b = 12 ∠150° A, I ?c = 12∠?90° A
- 3. In a △-connected generator, all of the phase voltages are
Options- A. zero
- B. equal in magnitude
- C. one-third of total
- D. one-sixth of total Discuss
Correct Answer: equal in magnitude
- 4. In a certain three-wire Y-connected generator, the phase voltages are 2 kV. The magnitudes of the line voltages are
Options- A. 2,000 V
- B. 6,000 V
- C. 666 V
- D. 3,464 V Discuss
Correct Answer: 3,464 V
- 5. The most common type of ac motor is the
Options- A. single-phase induction motor
- B. two-phase induction motor
- C. three-phase induction motor
- D. two-phase squirrel-cage motor Discuss
Correct Answer: three-phase induction motor
- 6. In a three-phase system, when the loads are perfectly balanced, the neutral current is
Options- A. zero
- B. one-third of maximum
- C. two-thirds of maximum
- D. at maximum Discuss
Correct Answer: zero
- 7. In a △-connected source feeding a Y-connected load,
Options- A. each phase voltage equals the difference of the corresponding load voltages
- B. each phase voltage equals the corresponding load voltage
- C. each phase voltage is one-third the corresponding load voltage
- D. each phase voltage is 60° out of phase with the corresponding load voltage Discuss
Correct Answer: each phase voltage equals the difference of the corresponding load voltages
- 8. In a balanced three-phase load, each phase has
Options- A. an equal amount of power
- B. one-third of total power
- C. two-thirds of total power
- D. a power consumption equal to
IL
Discuss
Correct Answer: an equal amount of power
- 9. In a Y-connected circuit, the magnitude of each line current is
Options- A. one-third the phase current
- B. three times the corresponding phase current
- C. equal to the corresponding phase current
- D. zero Discuss
Correct Answer: equal to the corresponding phase current
- 10. Polyphase generators produce simultaneous multiple sinusoidal voltages that are separated by
Options- A. certain constant phase angles
- B. certain constant frequencies
- C. certain constant voltages
- D. certain constant currents Discuss
Correct Answer: certain constant phase angles
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