What is RYB phase sequence
In a three phase alternator, three sets of coils are installed at a 120 degree angle. The three phase output voltage obtained from the three phase coil of this alternator is shown in Fig. A.
This three phase voltage creates three Waves with a difference of 120 degree electrical angle. When the voltage of the R Phase starts from zero at a positive time, the positive current increases and exactly 1/3 of the time the voltage of the Y Phase starts at the same time as the voltage of the B Phase.
The sequence in which these three phase arts have maximum and minimum values is called Phase Sequence. Which is shown in the picture in A.
What Is Importance of correct phase sequence
Correct Phase Sequence is very important for different types of three phase systems.
As the parallel operation of alternators requires Phase Sequence to connect their similar phases in parallel, the R Phase of an alternator will be connected to the R Phase of the other alternator, similarly Y and B are also connected to the Y and B of the other alternator respectively.
Similarly for three phase induction motors, phase sequence is also very important. Any two phase sequence can be interchanged and the direction of rotation of the three phase induction motor can be changed. Wrong Phase Sequence will rotate the machine drive in the wrong direction.
Phase sequence indicator
A Phase sequence indicator provides the correct phase-sequence in a three-phase system. The three phase sequence indicator has three RYB terminals connected to the three phase supply.
When supplied in the Indicator, the disk located in the Indicator starts rotating in the clockwise or anticlastic direction.
The direction of rotation of the disk is marked with the arrowhead above the indicator.
The phase sequence of the three-phase system can be changed by converting any of its two phases.