Is there a such thing as Asymetric Current?

[mivey]

...So Mivey has a point its not just a short circuit condition as a based fact .


This is from Werninck Electric motor they kinda know motors comments ?

You have chosen wisely. :grin:

Unfortunately for some of the posters, they kind of forgot (or have not learned) that the idea of using symmetrical components to analyze unsymmetrical systems is not limited to fault analysis. The idea is that you can take a system with asymmetries and break it into different component symmetrical systems to make the math much easier (positive, negative, and zero sequence components).

This idea was developing in the late 1800's. Fortescue put the pieces of the puzzle together in his famous work of 1918 where he tied in the zero sequence component. Work in the 1920's by Wagner & Evans helped to document its use in fault analysis and was published in their classic book in 1933.

The idea of a balanced circuit being called symmetrical and unbalanced circuits being called unsymmetrical or asymmetrical and vice-versa is not limited to the world of fault analysis. Trying to say the words "asymmetric" or "asymmetry" or any derivatives of words like "symmetric" are restricted to fault analysis is just plain silly. That is just as silly as saying the method of symmetrical components is restricted to fault anaylsis.

 

[ohmhead]

Well Mivey i been around electrical work for many years iam not good with formulas never went to school for engineering but i read alot and it interest me i just have to know how things work.

I found out years ago that there is always someone smarted then the next and we all have different areas of special interest i ask questions to see if i can find the answer that i do not know and hopefull the one teaching me does .

This field were in has so many different areas i think one person can take a life time to get just a part of what we would like to understand .

This is a good forum the NEC code questions are top rate and i like the theory questions by being a electrician for over 40 years ive now can enjoy the part i missed and did not have the chance to learn .

 

[K8MHZ]

Mivey,

Is standing wave ratio an expression of symmetry? In other words, would a standing wave ratio of 1:1 indicate symmetry versus a standing wave ratio of say 9:1 would indicate asymmetry?

If so, then we could consider a balun a device that changes electrical symmetry.

Or am I stretching this a bit?

 

[mivey]

Mivey,

Is standing wave ratio an expression of symmetry? In other words, would a standing wave ratio of 1:1 indicate symmetry versus a standing wave ratio of say 9:1 would indicate asymmetry?

If so, then we could consider a balun a device that changes electrical symmetry.

Or am I stretching this a bit?

I would have to think about it some, but my first thought in the general case would be no. You could have the same discontinuities or terminations in all three phases and the lines would be symmetric. So maybe symmetric in one respect and asymmetric from the termination standpoint.

So, on the other hand, if we were just talking about the non-unity caused by the terminations, you could say that there is an asymmetry between the impedance of the line and the impedance of the termination.

Sorry for thinking out loud, but I guess you could look at a balun as changing the symmetry between the line and termination impedances.

 

[hurk27]

Mivey,

Is standing wave ratio an expression of symmetry? In other words, would a standing wave ratio of 1:1 indicate symmetry versus a standing wave ratio of say 9:1 would indicate asymmetry?

If so, then we could consider a balun a device that changes electrical symmetry.

Or am I stretching this a bit?

SWR is more akin to impedance of a circuit then it is symmetry of the given signal,

SWR is a function of the absorption of a given radiator of the energy supplied by the transmitter at a given frequency and transmission line, If the line and radiator is at resonate then the SWR should show a 1:1 match, which is a perfect match between a given transmitter and radiator and the line impedance, which is unheard of in the real world. A 9:1 SWR would just mean that 90% of the transmitter power is reflected back to the transmitter causing a build up of voltage/current in the transmitter.

Baluns are nothing more then a transformer to change the impedance of the transmission line, they would no more add too or take away the symmetry of a given signal.

Symmetry/antisymmetry would be more akin to distortion like Harmonic or frequency, over driving a transmitter with modulation is one such case.

 

[mivey]

SWR is more akin to impedance of a circuit then it is symmetry of the given signal,

SWR is a function of the absorption of a given radiator of the energy supplied by the transmitter at a given frequency and transmission line, If the line and radiator is at resonate then the SWR should show a 1:1 match, which is a perfect match between a given transmitter and radiator and the line impedance, which is unheard of in the real world. A 9:1 SWR would just mean that 90% of the transmitter power is reflected back to the transmitter causing a build up of voltage/current in the transmitter.

Baluns are nothing more then a transformer to change the impedance of the transmission line, they would no more add too or take away the symmetry of a given signal.

Symmetry/antisymmetry would be more akin to distortion like Harmonic or frequency, over driving a transmitter with modulation is one such case.

Impedances can also be described as symmetrical and unsymmetrical, so symmetry/asymmetry also applies to impedances, not just waveforms.

 

[weressl]

Not if everyone was given the same info. I had many "unfair" professors. That's life. I got over it.

In what world do you think a student can take a professor to court and prove him incompetent? That is truly a wonderland.

That is what is academic appeal does.

Of course it is an entirely different battlefield and bringing it up here is comical.

 

[weressl]

But the question seemed to be asking about the effect of an asymmetric current in a motor, not the motor's contribution to a fault. The phrase asymmetric current does not have to mean fault current.

IMO, they wanted to know the effect of asymmetric currents on the motor. These currents can be caused by asymmetric voltages and the effect is an increase in the winding temperature.

Unbalanced is the accepted technical vernacular, not asymetric, for what you attempt to describe.

Again; the question was stupid from the technical and scientific viewpoint. If that was a journeyman exam, they would not be expected to know about asymetrical fault currents. The asymetrical fault current does not appear at the motor in case of fault unless the fault is within the motor. It's effect is immaterial to the motor.

 

[mivey]

Unbalanced is the accepted technical vernacular, not asymetric, for what you attempt to describe.

I have already said that the term unbalanced is more common.

We can only guess as to why the examiner would use asymmetric to describe unbalanced currents. Perhaps he was not from around here. Perhaps he was used to motor protection from specific manufacturers that use the term asymmetric for unbalanced voltages and currents. Perhaps that is just his preference.

But whatever the reason, the student should be aware that they may see this type usage again on another question or when working with motor protection devices from certain manufacturers. They must understand the context of the usage and not just assume "asymmetric" must mean fault current.

Again; the question was stupid from the technical and scientific viewpoint. If that was a journeyman exam, they would not be expected to know about asymetrical fault currents. The asymetrical fault current does not appear at the motor in case of fault unless the fault is within the motor. It's effect is immaterial to the motor.

With the knowledge that they probably would not be asking about asymmetric fault current, and that they were asking about the effect of the current in the motor, and now that you know the term asymmetric is used for unbalanced currents as well, you should see where a reasonable person can conclude that the question could be asking about unbalanced currents and not asymmetric fault currents.