Phase Sequence  

•  There are three voltages having same magnitude and frequency dis-         placed by an angle of 120° electrical.

 

•  The emfs induced in the three coils or phases attain their positive maximum value in the order of a 1 a 2 , b 1 b 2 , and c 1 c 2 ; therefore, the phase sequence is a, b, and c.

 

•  The order in which the voltages (or emfs) in the three phases attain their 

         maximum positive value is called the Phase Sequence.  

 

 Important Points-

 

•  The direction of rotation of three-phase induction motors depends upon the   phase sequence of three-phase supply.  

 

•  To reverse the direction of rotation, the phase sequence of the supply       given to the motor has to be changed.

 

• The parallel operation of three-phase alternators and transformers is only possible if phase sequence is known.