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Phase sequence commonly refers to the three phases of a power system symbolically represented as red, yellow and blue. One of them is considered a base and the next phase is known to have120 degree angle shift i.e. if blue is considered to be at0 degree then yellow and blue will be120 &240 degrees of angle shifted in time domain respectively.
Phase sequence is important in case the three phase connection is provided to an induction motor as i.e. interchanging any two phases will reverse its direction of rotation that may lead to undesired situation during operation.
There are3 Phase sequences in Power Generation,Transmission & Distribution all across the Globe as given below :-
1) Zero Phase Sequence
2) Positive Phase Sequence
3) Negative phase Sequence.
In a balance3 Phase System, when Ia + Ib + Ic = Zero ( Neutral ) & Ia = Ib = Ic,
Now3 Ia =0/N.
Normally at50 Hz,3 Phases are as R (0 Degree ) Y(120 Degree) B(240 Degree)
Positive Phase Seq. Flow from R to Y, Y to B & B to R.
At3rd Harmonics,150 Hz,3 Phases are R (0 X3 =0 Deg) Y(120X3=0 Deg) B(240X3=0 Deg)
That means R,Y,B are in Same Phase.
Now at5th Harmonics,at250 Hz R (0X5=0 Degree) Y (120X5=240 Deg) B(240X5=120Deg)
That means now Rotation got reversed/Negative.
Accordingly at9th Harmonics Zero-Phase Sequence, at11th Negative-Phase Sequence,13th Posative Phase Sequence,15th Zero-Phase Seq,17th Negative-Phase Sequence.
Note:-
In normal Practice Positive Phase Sequence at50 Hz is healthy Phase Sequence for all Electrical Systems across the World.
Negative Phase Sequence is not Desirable ( Tripping15 % in HV Generation,T&D , maximum30 % for LT),as because of Heating effect of all Electrical accessories is the result of it.
To cope with Zero Phase Sequence proper grounding through Resistance or Grounding_trafo(Having Calculated Loading Resistor) is universally adopted.....
Finally Negative Phase Sequence & Zero Phase Sequence WORSE-UNWANTED Phase Sequence.
it is the set for recognise the same phase example red whit red yelow with yelowand also blue
