Phase Rotation-CW/CCW

[eeguy]

Can someone please explain the concept of phase rotation. Is it simply the order that the phases peak in? For instance is an ABC phase rotation the case where phase A leads phase B by 120 degrees, and B leads C by 120 degrees? If so, why are the terms clockwise and counter clockwise sometimes used with phase rotation? For instance, whats the difference between ABC clockwise and ABC counter clockwise? Lastly, is there a standard phase rotation for a 3 phase utility? How about a 3 phase generator?

 

[electricpete]

Can someone please explain the concept of phase rotation. Is it simply the order that the phases peak in?
YES.

For instance is an ABC phase rotation the case where phase A leads phase B by 120 degrees, and B leads C by 120 degrees?
YES.

If so, why are the terms clockwise and counter clockwise sometimes used with phase rotation? For instance, whats the difference between ABC clockwise and ABC counter clockwise?
I can think of a few reasons why we use these terms - not sure which is really the right answer.
#1 - In a 3-phase ac motor, the direction of rotation of the stator field can be reversed by swapping any two leads which equates to changing the phase rotation.
#2 - When we express voltages mathematically as phasors,
this really corresponds to rotating vectorS in the positions which would be seen if a strobe flashed at syncronous frequency. But we also need to assume a direction of rotation of the phasor (I believe clockwise is the convention). i.e. if we have phasors Va = 1<0, Vb=1<240, Vc=1<120, this is equivalent to Va leading Vb only if we assume clockwise rotation of the phasor. The same phasor voltages would correspond to Vb leading Va if we assumed counterclockwise rotation of the phasors.

Lastly, is there a standard phase rotation for a 3 phase utility? How about a 3 phase generator?
Each utility has it's own standard nomenclature. I worked in T&D dept of a utility formed from merger of two smaller utility. There was a lot of confusion on the terminology. In practice during construction activities like installation of a mobile transformer, they would calculate expected phase postions, but always check the phase rotation with a meter as a final double check before paralleling sources.

 

[jbartos]

Suggestions marked ///\\\:
Can someone please explain the concept of phase rotation.
///It is better to refer to the phase rotation as to phase sequence since there are phase sequence meters, relays, etc. The phase &quot;rotation&quot; is often used in context with rotating machinery where the rotation is actually involved.\\Is it simply the order that the phases peak in?
///Yes. It is simply the sequence in which the phase waveforms peak.\\ For instance is an ABC phase rotation the case where phase A leads phase B by 120 degrees, and B leads C by 120 degrees?
///Yes, it may be since the &quot;leads&quot; is relative. It depends how it is defined.\\If so, why are the terms clockwise and counter clockwise sometimes used with phase rotation?
///Terms clockwise (CW) and counterclockwise (CCW) are often used with the rotating machinery since this is very convenient designation. Almost, everyone knows what is CW and CCW. However, one may more properly use the phase sequence.\\For instance, whats the difference between ABC clockwise and ABC counter clockwise?
///This is an improperly posed question, since practically ABC may be related to clockwise (or CCW) and correspondingly ACB is then CCW (or CW). Therefore, the relativity is there and must be dealt with.\\ Lastly, is there a standard phase rotation for a 3 phase utility?
///It depends to which industry standards the utility adheres to, if any.\\ How about a 3 phase generator?
///The rotation of 3-phase generator is dependent on the prime mover direction of rotation in most cases. However, it may have specified its unique direction too.
Visit

http://www.flex-core.com/pdf-files/142-257-lit.pdf

http://www.rotoups.com/products/roto-powercon1.shtml

http://www.sew.com.tw/pro-list.htm#6

etc. for more info.\\

 

[corona]

From:Corona

There is more than one concept related to phase rotation, depending on two different main concepts.

1. Mathematical Concepts
2. Physical Concepts

Your are right when you view ABC as simply the order in which the phases rotate.
This is a physical concept.

Although ABC rotation an CW and CCW are similar notions, they are different.

When conducting a mathematical vector analysis of a power systems, generators, and motors or other 3-phase system component an arbitrary starting point, for the analysis is selected. The starting point is either CW or CCW and is carried constant throughout the calculations. Historically, the CC selection was used but modern analysts are using a CCW selection. This is a mathematical concept.

Another physical concept ional view is that of a three phase motor, originally to run CW,
on a wired ABC phase rotation, and then rewired to run CCW, on ACB rotation, by changing the phase conductors to the motor.

I don’t have any information on the utility standards.

I hope that this has been helpful to you.

 

[electricpete]

minor correction to my response - in item #2 - change CW to CCW everywhere and change CCW to CW (dislexia strikes agian ;-)

 

[stevenal]

I found it interesting after completing my studies and entering the field, to see a phase rotation meter. A correct phase rotation, that is ABC, or a CCW revolving set of phasors mathematically; would spin the dial CW.

 

[jbartos]

Suggestions:
1. What about the &quot;phase rotations&quot; at linear motors? Does not one follow the phase sequence, if there is no actual physical rotation?
2. To the previous posting: What if there are more phases, e.g. 15 phase motor? Was the phase rotation meter up to 15 phases?