### 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**