1.
In a three-phase system, the order in which the ____________ attain their maximum positive value is called Phase Sequence.
A
Power
B
Voltages
C
Resistance
D
Current
View Answer
Correct Answer: B — Voltages
Explanation:
The correct answer is B: Voltages.
Phase sequence in a three-phase system refers to the order in which the voltages of the three phases attain their maximum positive value.
Working Principle:
- In a three-phase system, the three phases are designated as R, Y, and B (or A, B, C).
- The voltages are sinusoidal and mutually displaced by 120 degrees.
- In a positive (standard) sequence, voltages peak in the order R → Y → B.
- Reversing the sequence (e.g., R → B → Y) changes the direction of motor rotation.
Importance of Phase Sequence:
- Motor Rotation: Phase sequence directly determines the direction of rotation of three-phase motors. An incorrect sequence causes reverse rotation, potentially damaging equipment.
- Power Distribution: Correct phase sequence is essential for proper operation of all equipment connected to a three-phase supply.
- Synchronization: Critical when synchronizing multiple generators or motors in a system.