ObjectiveMcq
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In a three-phase system, the order in which the ____________ attain their maximum positive value is called Phase Sequence.
Correct Answer: B — Voltages
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.