Three Phase Systems In Power Applications(Electrical Engineering ) Questions and answers for exam Preparation

Question 1. In a Y-connected source feeding a ∆-connected load,

Each phase of the load has one-third of the full line voltage across it
Each phase of the load has two-thirds of the full line voltage across it
Each phase of the load has the full line voltage across it
Each phase of the load has a voltage across it equal to $$\sqrt 3 $$

Explanation:-

Answer: Option C. -> Each phase of the load has the full line voltage across it

Question 2. The stator is the rotating assembly in a generator or motor.

True
False

Explanation:-

Answer: Option B. -> False

Question 3. In a Y-connected circuit, between each line voltage and the nearest phase voltage, there is a phase angle of

0°
30°
60°
120°

Explanation:-

Answer: Option B. -> 30°

Question 4. An alternator is an electromechanical ac generator.

True
False

Explanation:-

Answer: Option B. -> False

Question 5. 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.

Single-phase 32 A; three-phase 16 A
Single-phase 16 A; three-phase 8 A
Single-phase 8 A; three-phase 4 A
Single-phase 16 A; three-phase 0 A

Explanation:-

Answer: Option B. -> Single-phase 16 A; three-phase 8 A

Question 6. In a ∆-connected source driving a ∆-connected load, the

Load voltage and line voltage are one-third the source voltage for a given phase
Load voltage and line voltage are two-thirds the source voltage for a given phase
Load voltage and line voltage cancel for a given phase
Load voltage, line voltage, and source phase voltage are all equal for a given phase

Explanation:-

Answer: Option D. -> Load voltage, line voltage, and source phase voltage are all equal for a given phase

Question 7. In a Y-Y source/load configuration, the

Phase current, the line current and the load current are all equal in each phase
Phase current, the line current and the load current are 120° out of phase
Phase current and the line current are in phase and both are 120° out of phase with the load current
Line current and the load current are in phase and both are out of phase with the phase current

Explanation:-

Answer: Option A. -> Phase current, the line current and the load current are all equal in each phase

Question 8. The most common type of ac motor is the

Single-phase induction motor
Two-phase induction motor
Three-phase induction motor
Two-phase squirrel-cage motor

Explanation:-

Answer: Option C. -> Three-phase induction motor

Question 9. In a ∆-connected generator, all of the phase voltages are

Zero
Equal in magnitude
One-third of total
One-sixth of total

Explanation:-

Answer: Option B. -> Equal in magnitude

Question 10. In a three-phase system, when the loads are perfectly balanced, the neutral current is

Zero
One-third of maximum
Two-thirds of maximum
At maximum

Explanation:-

Answer: Option A. -> Zero