BALANCED SYSTEM AND UNBALANCED SYSTEM
A set of three sinusoidal voltages (or current) that are equal in magnitude but having a progressive phase differences of 120 degree constitute a balanced three phase voltage system. The three phase quantities are otherwise said to be unbalanced.
Phase sequence is the order or sequence in which the current or voltages in different phases attain their maximum values one after the other.
PHASE SEQUENCE OF 3 PHASE SUPPLY IS ESSENTIAL FOR: The direction of rotation of 3 phase induction motor depends upon the phase sequence of 3-phase supply, to reverse the direction of rotation; the phase sequence of the supply given to the motor has to be changed.
The parallel operation of 3-phase alternator and transformer is only possible if phase sequence is known.
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