Phase shift

[roy167]

In an ABC balanced phase sequence, the phasors can be written as A angle 0; B angle 240, C angle 120. 

Another way to represent is A angle 0; B angle -120 , C angle -240 ( this makes more sense to me, B lags A by 120, C lags B by 120)

Is there a standard that is being used? you can have correct answer for more than one angle. 

Any  resource that clarifies this confusion? If the angle is negative, can you always add +360 and get your angle in positive if the answer choices are in positive?  

 

[a4u2fear]

I have never seen it described like you have it.

Most references (think counter clock wise):

ABC positive is A<0, B<-120, C<120 (A leads B, B leads C, C leads A)

ABC negative is A<0, B<120, C<-120 (C leads B, B leads A, A leads C)

 

[roy167]

I'm learning more on this, from what I gather so far. 

You can have ABC or ACB phase sequence or positive sequence. Counter clockwise rotation. 

You can have ABC or ACB phase sequence  or negative sequence. Clockwise rotation. 

So there is no ACB or BAC in positive and or negative sequence. Only sequences available are ABC and ACB, the direction of the rotation determines whether it is positive or negative sequence. 

Earlier I thought ABC was positive sequence and ACB was negative sequence. 

Can someone confirm this understanding is correct?   

 

[a4u2fear]

you are confusing yourself, and maybe others.

a three phase system only has two possible sequences, abc and cba (abc in reverse)

as i've stated above, ABC positive (abc) and ABC negative (cba) are typically the only ways these are spoken about.

in all of the problems i've done, i've only seen it stated ABC positive or ABC negative.  If you are given the phases with angles then it is meaningless anyway to think about the terminology.

 

[roy167]

you are confusing yourself, and maybe others.

a three phase system only has two possible sequences, abc and cba (abc in reverse)

as i've stated above, ABC positive (abc) and ABC negative (cba) are typically the only ways these are spoken about.

in all of the problems i've done, i've only seen it stated ABC positive or ABC negative.  If you are given the phases with angles then it is meaningless anyway to think about the terminology.

Yes, I correct myself. There are only two phase sequences ( ABC being positive sequence) and ACB being negative sequence (rotating CCW).The above was the understanding at the time I wrote, later on digging more I came to the same conclusion as you mentioned. Thanks

 

[roy167]

One more question, power factor can be calculated by number of different ways. One of the way is Cosine (voltage angle - current angle), 

What I am confused about is  should you take line voltage and line current or phase voltage and phase current angles? Does it matter?  Assume that you don't know anything else other than the above four quantities and it is 3 phase balanced wye/delta source load problem.