Three-Phase Systems in Power Applications Quiz

Objective Questions (MCQs) on Three-Phase Systems in Power Applications


Q.1 In a three-phase system, the voltages are separated by
A. 45°
B. 90°
C. 120°
D. 180°
Answer: Option C

Q.2 In a three-phase system, when the loads are perfectly balanced, the neutral current is
A. zero
B. one-third of maximum
C. two-thirds of maximum
D. at maximum
Answer: Option A

Q.3 In a certain three-wire Y-connected generator, the phase voltages are 2 kV. The magnitudes of the line voltages are
A. 2,000 V
B. 6,000 V
C. 666 V
D. 3,464 V
Answer: Option D

Q.4 In a -connected source feeding a Y-connected load,
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
Answer: Option A

Q.5 In a Y-Y source/load configuration, the
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
Answer: Option A

Q.6 In a Y-connected circuit, the magnitude of each line current is
A.one-third the phase current
B.three times the corresponding phase current
C.equal to the corresponding phase current
D. zero
Answer: Option C

Q.7 A constant load power means a uniform conversion of
A. mechanical to electrical energy
B. electrical to mechanical energy
C. current to voltage
D. voltage to current
Answer: Option B

Q.8 A two-phase generator is connected to two 90 load resistors. Each coil generates 120 V ac. A common neutral line exists. How much current flows through the common neutral line?
A. 1.33 A
B. 1.88 A
C. 2.66 A
D. 1.77 A
Answer: Option D

Q.9 A single-phase sinusoidal voltage of 120 V is connected to a 90 load. Current in the circuit is
A. 13.3 mA
B. 133 mA
C. 1.33 A
D. 6.2 A
Answer: Option C

Q.10 A three-phase generator is connected to three 90 load resistors. Each coil generates 120 V ac. A common neutral line exists. How much current flows through the common neutral line?
A. 0 A
B. 1.33 A
C. 3.99 A
D. 2.66 A
Answer: Option A

Q.11 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 .
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
Answer: Option B

Q.12 If in a Y-connected ac generator, each phase voltage has a magnitude of 90 VRMS, what is the magnitude of each line voltage?
A. 0 V
B. 90 V
C. 156 V
D. 180 V
Answer: Option C

Q.13 Polyphase generators produce simultaneous multiple sinusoidal voltages that are separated by
A. certain constant phase angles
B. certain constant frequencies
C. certain constant voltages
D. certain constant currents
Answer: Option A

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