Phase Sequence Indicator:
There are two types of phase sequence indicators:
(a) Rotating type phase sequence indicator
(b) Static type phase sequence indicator
(a) Rotating Type Phase Sequence Indicator:
It consists of three coils mounted 1200 apart in space. The three ends of coils are brought out and connected to three terminals marked R-Y-B as shown in figure. The coils are star connected and are excited by supply whose sequence is to be determined. An aluminum disc is mounted on the top of coils. The coils produce rotating magnetic field, when they are energized by three phase supply. The rotating magnetic field sweeps the stationary aluminum disc and produces eddy currents in the aluminum disc. A torque is produced by the interaction of eddy currents with the field. The disc revolves because of the torque and the direction of rotation depends upon the phase sequence of the supply. An arrow indicates the direction of rotation of the disc. If the direction of the rotations is same as that indicated by arrow head, the phase sequence of the supply is same as the marked on the terminals of the instrument. However, if the disc revolves opposite to the direction indicated by arrow, the sequence of the supply is opposite to that marked on the terminals.
(2) Static Type Phase Sequence Indicator:
It consists of two lamps and one inductor. Connect two lamps, lamp1 to R-phase, lamp2 to Y-phase and inductor to B-phase as shown in the figure. Resistors are connected in series with the lamps for protecting the lamps from over currents and breakdown voltages. If the phase sequence of supply is RYB, then the lamp 2 will glow brighter than lamp 1; if the sequence of the supply is reversed or altered, then the lamp 1 will glow brighter than the lamp 2.