PHASE SEQUENCY INDICATOR.

Phase sequence meter is used for detecting the sequence of the supply in three-phase electric circuits. Since the direction of rotation of three phase electric motors can be changed by changing the phase sequence of supply. And also the correct operation of measuring instruments like 3 phase energy meterand automatic control of devices also depend on the phase sequence.

It works on the principle of induction motors. The principle of rotating type phase sequence indicator is similar to that of a three phase motor. Consider the working of a motor for a better understanding of these indicators. For three phase motors, we require three phase power supply, whereas this three phase power must be supplied in a particular sequence. Let us assume that the three phase supply given to the motor has a phase sequence of RYB, then the motor will rotate in clockwise direction – and, if the phase sequence of supply is reversed, then the motor will rotate in counter clockwise direction. This may cause severe problems to the load and entire system.