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Disc rotation In Phase Sequence Indicator is determined by
The supply voltage
An arrow
The turns ratio
The load current
An arrow
In an induction motor-type phase sequence indicator, the direction of rotation of the aluminum disc indicates the phase sequence of the three-phase supply. An arrow marked on the instrument casing or dial plate shows the standard sequence (usually RYB or clockwise), allowing the operator to verify whether the disc rotates in the correct direction.
In an induction motor-type phase sequence indicator, the direction of rotation of the aluminum disc indicates the phase sequence of the three-phase supply. An arrow marked on the instrument casing or dial plate shows the standard sequence (usually RYB or clockwise), allowing the operator to verify whether the disc rotates in the correct direction.
╧ЙsтАЛ=P120fтАЛ тАФ Synchronous speed of the rotating magnetic field
TтИЭV2sin╬╕ тАФ Torque produced in the rotating aluminum disc
The phase sequence indicator works on the principle of a 3-phase induction motor. When connected to a 3-phase supply, a rotating magnetic field (RMF) is produced by the coils, inducing eddy currents in the aluminum disc. The interaction between the RMF and eddy currents generates a torque that rotates the disc. If the supply sequence matches the standard sequence, the disc rotates in the direction indicated by the arrow.
Induction-type phase sequence indicators operate based on a rotating magnetic field similar to a 3-phase induction motor.
A marked arrow on the dial indicates the standard phase sequence (usually clockwise for RYB).
Static-type phase sequence indicators use two lamps and an inductor/capacitor instead of a rotating disc.
Simple, rugged, and reliable mechanical construction.
Provides a direct visual indication of the rotational direction of phase sequence.
Contains moving parts that are subject to mechanical wear and tear over time.
Requires minimum voltage to produce sufficient torque to rotate the disc.
Determining phase sequence before paralleling 3-phase transformers or alternators.
Ensuring correct direction of rotation for 3-phase induction motors before commissioning.
Option A (Supply voltage) determines the magnitude of torque, not the reference sequence marker.
Option C (Turns ratio) applies to transformers, not phase sequence indicators.
Option D (Load current) is incorrect because sequence indicators are voltage-operated devices.
B is correct тАФ An arrow provided on the dial or housing indicates the standard reference direction for disc rotation in a phase sequence indicator.
Always verify phase sequence prior to paralleling 3-phase alternators or transformers to prevent severe short-circuit currents due to out-of-phase connection.