Engineering Q&A
Describe with neat diagram phase sequence indicator.
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There are two types of phase sequence indicators and they are: 

(a) Rotating type (b) Static type. 


➢ Rotating type

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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). 

OR 

➢ 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.

image

➢ 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

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Rotating type phase sequence indicator:

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 three phase windings are energized by three phase supply. Which sweeps the stationary aluminum disc and produces eddy emf induced in the disc which circulates an eddy current in aluminum disc. A torque is produced with 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 to arrow head, the sequence of the supply is opposite to that marked on the terminals. 

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