There are two types of phase sequence indicators and they are:
(a) Rotating type (b) Static type.
➢ Rotating type
1. It works on the principle of induction motors.
2. The arrow marked on the disc represents the direction of rotation.
3. If the phase sequence of supply is same as that of the terminals marked on the indicator the disc will rotate in the direction of rotation(RYB)
4. If the disc moves in the clockwise direction then chosen sequence is RYB and if the direction of rotation is in anticlockwise the sequence is reversed(RBY).
➢ Static type.
➢ Connect two lamps, lamp1 to R-phase, lamp2 to Y-phase and inductor to B-phase as shown in the below figure. Resistors are connected in series with the lamps for protecting the lamps from over currents and breakdown voltages.
➢ If the 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