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What are the concepts of Trikala system?|Three phase system ke concepts kya hain?

Hello friends In this article we will know what are the concepts of three phase system? What is Phase Sequence? What is double-subscript notation? How do you name a phase? And learn about various types of facts related to it.

Concepts of Trikala System | concepts of three phase system

In the analysis of the 3-phase system, we often encounter the following terms:



  1. phase sequence
  2. Phase Nomenclature
  3. double-subscript notation

phase sequence

The sequence in which the voltages in the triplet (or coil) reach their maximum positive value is called the phase sequence or phase sequence. This is determined by the direction of rotation of the alternator. Thus, Figure (iii) three coils A, B and C are generating voltage which are 120° displaced from each other.

Wave form for three phase A, B and C

Referring to the wave diagram in Figure (iii). It is easy to see that the voltage in coil A first attains maximum positive value, next in coil B and then in coil C hence the phase sequence is ABC. If the direction of rotation of the alternator is reversed, the sequence in which the three phases attain their maximum positive values ​​will be ABC.

Hence the phase sequence is now ABC i.e. the voltage in coil A first attains maximum positive value, next in coil C and then in coil C. Since the alternator can be turned in clockwise or anticlockwise direction, there can be only two possible phase sequences. Phase sequence is important in some applications. For example, 3-phase induction motors In a three phase induction motor, the phase sequence of the supply determines whether the motor turns clockwise or counterclockwise.

Phase Nomenclature

Three phase or windings may be numbered (1 , 2 , 3 ) or late termed ( A , B , C ). However, it is a common practice to name three phases or three natural colours. Red (R), Yellow (Y) and Blue (C) In that case, the phase sequence is RYB i.e. in phase R voltage First the maximum positive value is obtained, the next phase Y and then phase B. It may be noted that there are only two possible phage sequences. RYB and RBY Is.

By convention, the sequence RYB to positive and RBY is taken as negative. Throughout this book, unless otherwise stated, the phase sequence is referred to as R.YB is considered


double-subscript notation

The double-subscript notation is a very useful and can be found advantageous in the analysis of a 3-phase system. In this two letters are placed at the foot of the symbol for voltage or current. The two letters indicate the two points between which voltage (or current) exists and the sequence of letters indicates the relative polarity of the voltage (or current) during its positive half-cycle.

Thus VRY A voltage V between point R and Y indicates that point R is positive wrt. point y during its positive half-cycle and on the other hand, VYR means that the point is positive w.r.t. the point R during its positive half-cycle. Obviously,


VRY = – VYR

again IRY Indicates a current I between point R and Y and its direction is from R to Y during its positive half cycle. The advantage of the double-subscript notation lies in the fact that a formal description of the voltage or current in question is not necessary and the order of the subscripts fully describes the quantity.


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