Is there a such thing as Asymetric Current?

[Hameedulla-Ekhlas]

Asymmetrical and Symmetrical currents are nothing except fault currents which are balance and unbalance during any short circuit calculation.

You are right, it takes alot of calculation. I am using Etap power station 6.0 and Digsilent power factory Softwares for analysis of these faults.

I had already mentioned that it is nothing except faults but no one listened to me.

 

[mivey]

That is Germlish, a translation from German to English by a German translator. The term is NOT used in the USA.

The world is not that small. The tester could easily have been referring to an asymmetry between the current values and not fault current. If so, that would determine your answer. You would probably have to have attended his class to know for sure. Maybe he was German. We allow them to live here too, you know.

Here are some US and IEEE sources using the term "Asymmetric current" for other stuff:

"Asymmetric current?voltage characteristics of molecular junctions containing bipolar molecules"
Department of Chemistry and The James Frank Institute, The University of Chicago

"Polarization stabilization in vertical-cavity surface-emittinglasers through asymmetric current injection" Photonics Technology Letters, IEEE

"Asymmetric current-voltage characteristics in type-II superconductors" Center for Superconductivity Research, Department of Physics, University of Maryland, College Park, Maryland

"Collisionless magnetic reconnection in an asymmetric current sheet"
Department of Physics and Astronomy, University of California, Los Angeles, California, USA

"Driving toroidally asymmetric current through the tokamak scrape-off layer to suppress edge-localised modes" Lawrence Livermore National Laboratory ,Livermore, CA

"IMPROVED ASYMMETRIC CURRENT MODE DRIVER FOR DIFFERENTIAL TRANSMISSION LINES" Quantum Corporation , Milpitas, CA

"Identification of asymmetric current fluctuations in small systems" IEEE Proceedings of the 2006 International Conference on Nanoscience and Nanotechnology

"CHAOTIC MAGNETIC FIELDS DUE TO ASYMMETRIC CURRENT CONFIGURATIONS" Plasma Science & Fusion Center, Massachusetts Institute of Technology

"Controlled Polarisation Switching in VCSELs by means of Asymmetric Current Injection" One of the authors from University of Illinois

I am still waiting for your reference to the "asymetric current controls on a motor"!?

I gave you one. You did not like it. That's your problem. It is also referred to in some controls as the current assymetry setting.

 

[Cold Fusion]

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cf

 

[mivey]

I had already mentioned that it is nothing except faults but no one listened to me.

I heard you. But to say that is the only answer is wrong.

What you have failed to hear is that the person asking the question may have been referring to asymmetries between the current values. They would normally be called unbalances by most of us, but the wording made it look like that was what was being referenced.

You must recognize that not everyone uses the same terminology. Often times, if you are not familiar with the instructor and his quirks, it will cost you points on an exam.

 

[weressl]

The world is not that small. The tester could easily have been referring to an asymmetry between the current values and not fault current. If so, that would determine your answer. You would probably have to have attended his class to know for sure. Maybe he was German. We allow them to live here too, you know.

Here are some US and IEEE sources using the term "Asymmetric current" for other stuff:

"Asymmetric current?voltage characteristics of molecular junctions containing bipolar molecules"
Department of Chemistry and The James Frank Institute, The University of Chicago

"Polarization stabilization in vertical-cavity surface-emittinglasers through asymmetric current injection" Photonics Technology Letters, IEEE

"Asymmetric current-voltage characteristics in type-II superconductors" Center for Superconductivity Research, Department of Physics, University of Maryland, College Park, Maryland

"Collisionless magnetic reconnection in an asymmetric current sheet"
Department of Physics and Astronomy, University of California, Los Angeles, California, USA

"Driving toroidally asymmetric current through the tokamak scrape-off layer to suppress edge-localised modes" Lawrence Livermore National Laboratory ,Livermore, CA

"IMPROVED ASYMMETRIC CURRENT MODE DRIVER FOR DIFFERENTIAL TRANSMISSION LINES" Quantum Corporation , Milpitas, CA

"Identification of asymmetric current fluctuations in small systems" IEEE Proceedings of the 2006 International Conference on Nanoscience and Nanotechnology

"CHAOTIC MAGNETIC FIELDS DUE TO ASYMMETRIC CURRENT CONFIGURATIONS" Plasma Science & Fusion Center, Massachusetts Institute of Technology

"Controlled Polarisation Switching in VCSELs by means of Asymmetric Current Injection" One of the authors from University of Illinois


I gave you one. You did not like it. That's your problem. It is also referred to in some controls as the current assymetry setting.

It isn't a question what I like or not. What matters is what is the accepted vernacular in the electrical engineering field and in the US, not in Timbakthu. (Interestingly enough a guy from Khabul, Afghanistan seem to have a clearer understanding on the saubject.)

None of the above applies to the topic we discussing. I am surprised you were not citing examples of the asymetrical current flows in the Ganges.....

You have not given a single example in US motor protection context that applies the use of the word asymetric in the context of motor current.

 

[mivey]

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cf

I caught your post and it was true. There has to be a way to make it clearer. I just don't seem to be getting the point across.

 

[iwire]

Stupid question. The world asymetric is only used in context of fault.

Laszlo has spoken, I will now close the thread as all other answers are wrong. :grin:

 

[mivey]

...You have not given a single example in US motor protection context that applies the use of the word asymetric in the context of motor current.

What good would it do? You do not believe motors have asymmetry controls. Mind-boggling.

 

[weressl]

I caught your post and it was true. There has to be a way to make it clearer. I just don't seem to be getting the point across.

You getting the point allright, except it is just simply not valid. Either of you just supply any IEEE documentation when it refers to unbalanced currents in motors as asymetrical.

Enineering is not Alice's Wonderland where the world means what we want them to mean.

 

[mivey]

You getting the point allright, except it is just simply not valid. Either of you just supply any IEEE documentation when it refers to unbalanced currents in motors as asymetrical.

Enineering is not Alice's Wonderland where the world means what we want them to mean.

Who said the person giving the test was an engineer?

On a test, the world means what the person giving the test says it means.

 

[Hameedulla-Ekhlas]

Ok, very good friend never get serious, we are just learning and we never get complete.

I had given you IEEE Engineering reference as well as which is published in Newyork. I have given alot of explaination and this IEEE explains every thing about the asymmetric current. If you are not accepting it, please give a book reference with complete explaination like me. I will accept that as a engineer's answer.

If I be a professor and say something without a reference then I am nothing.

 

[weressl]

What good would it do? You do not believe motors have asymmetry controls. Mind-boggling.

Engineering is not a religion, it is not a question of belief.

I asked you for a concrete example.

 

[weressl]

Who said the person giving the test was an engineer?

Nobody, but the responbsibility is given to the IEEE to define the terms and their meaning in the field of electrical subjects. They are accepted as a de-facto creators of National Standards in the field.

On a test, the world means what the person giving the test says it means.

In Alice's Wonderland, yes. However the exam taker can take him to a US court and he will loose for unfairness. (Not to mention incompetency.)

 

[Cold Fusion]

...In Alice's Wonderland, yes. However the exam taker can take him to a US court and he will loose for unfairness. (Not to mention incompetency.)

Uhh, Toto, I don't think Eduardo is in Kansas any more.

Whoops wrong book.

cf

 

[mivey]

Ok, very good friend never get serious, we are just learning and we never get complete.

I had given you IEEE Engineering reference as well as which is published in Newyork. I have given alot of explaination and this IEEE explains every thing about the asymmetric current. If you are not accepting it, please give a book reference with complete explaination like me. I will accept that as a engineer's answer.

The question concerned a test question the OP saw. What I have been trying to explain is that the question could have been using terminology that is not directly out of a particular IEEE reference.

We can use reference material to debate the validity of the question, whether or not the question used correct terminology, whether the question adheres to industry standards, etc. But none of that will tell us the intention of the examiner.

Citing 1,127,364 engineering references will not prove what the examiner meant. I contend that it is a term that the examiner could have used (rightly or wrongly). It is a term I have shown that others use for things other than fault currents. That is just another possible answer to the examiner's question. It does not mean it is the only one. The question was poorly worded and leaves room for speculation.

Saying that asymmetric current is normally used in the context of fault analysis is correct. To quote an engineering standard, and say that that is definitive proof of the examiner's intent is wrong. To say no one ever uses the term outside the context of fault analysis is wrong. It should not take a reference source to see the truth in those statements as they are common sense.

If I be a professor and say something without a reference then I am nothing.

It could also mean the professor is an authority on the subject or that the information is common knowledge.

 

[mivey]

However the exam taker can take him to a US court and he will loose for unfairness. (Not to mention incompetency.)

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.

 

[mivey]

I had given you IEEE Engineering reference...please give a book reference with complete explanation like me. I will accept that as a engineer's answer.

From IEEE Std C37.96-IEEE Guide for AC Motor Protection

When a synchronous motor is running at rated load, and then one supply phase is lost, the motor will probably pull out-of-step and must be removed from service. However, if the motor is lightly loaded and continues running synchronously, there will be extra losses as a result of the asymmetry in line current, and destruction of the damper winding may result.

The asymmetry they are talking about is the asymmetry between the values of currents. Not the asymmetry about an axis. I am saying this is the type asymmetry that the question was referring to.

The fault current has asymmetry about the axis because of the DC component. But, it is not the only case where current can have asymmetry about the axis.

 

[mivey]

I asked you for a concrete example.

From IEEE Std C37.96-IEEE Guide for AC Motor Protection "...as a result of the asymmetry in line current..."

And with that bit of concrete, I will make one of these:
.....***
...*.RIP.*
.*.........*
*...Laszlo..*
*...........*
*.Hopelessly*
*...Wrong...*
*...........*
*...AGAIN...*
*...........*
*************

 

[mivey]

And just so you don't rise from the grave, perhaps a few nails in your coffin would be in order:
From a Rockwell Automation/Allen-Bradley (A Milwaukee based company) Motor Control:

Asymmetry (Phase Unbalance) and Phase Failure:
Asymmetrical phase voltages usually occur when the leads closest to the motor are too long. The resulting current asymmetry in the motor windings may then be 6-10 times the voltage asymmetry.
...
Programming, Setup, and Operation:
LCD Display = "ASYM…%"
Setting Range = 1-100
Description = "Current asymmetry in percent"

And from another one of their motor protection devices:

The motor protection relay shall offer the following metering functions:
...
Percent current imbalance or asymmetry (? 2% accuracy)
...
Percent voltage imbalance or asymmetry (? 2% accuracy)

and from their motor protection handbook:

Single-phasing and Line Unbalance (Asymmetry) Protection
It is standard for modern electronic relays to have at least single phase protection in addition to normal overload protection. It is best to disconnect a motor quickly with the loss of a phase, since in the majority of cases the motor would stall due to the reduced torque. This would unnecessarily heat the motor if only a thermal function was available. By early detection and trip, the waiting time until a restart can be kept to a minimum.

Another function is line unbalance or asymmetry protection. Formulas exist to calculate the extra losses fed into the rotor, which may be a good approximation of actual conditions. Currents at normal operating conditions can be in the order of 6 to 10 times the voltage unbalance. With an unbalance of as little as 3% the motor must be de-rated by approximately 10%. Motor manufacturers state that operation of the motor when the unbalance is greater than 5% is not recommended.

In addition, asymmetries do not normally just affect one motor, but the whole plant. If an unbalanced supply is a possible condition, then a central supervising relay should alert the attention of personnel to the fact that certain limit are exceeded and permitting them to take corrective measures before motor overheating becomes critical.

From maintenanceworld.com, an article posted from www.us.fluke.com in 2005 (also can be found in Fluke's 5-part Predictive Maintenance Series):

Voltage unbalance
In a three-phase system, significant differences in phase voltage indicate a problem with the system or a defect in a load. Voltage unbalance can cause three-phase motors and other three-phase loads to experience poor performance or premature failure because of mechanical stresses in motors due to lower-than-normal torque output, higher-than-normal current in motors and three-phase rectifiers, and unbalance current will flow in neutral conductors in three-phase wye systems.

Unbalance is tracked in percentages. The negative sequence voltage (Vneg) and zero sequence voltage (Vzero) together identify any voltage asymmetry between phases.

More from IEEE:
IEEE TRANSACTIONS ON ENERGY CONVERSION
"Dynamic Phasors in Modeling and Analysis of Unbalanced Polyphase AC Machines"

This paper describes a novel approach to dynamical modeling of asymmetries in electric machines and polyphase systems (e.g., the ones caused by unbalanced supply waveforms)

I'll throw one in from APQI (yeah, EU-Asia but they want a piece of you too):

A three-phase power system is called balanced or symmetrical if the three-phase voltages and currents have the same amplitude and are phase shifted by 120? with respect to each other. If either or both of these conditions are not met, the system is called unbalanced or asymmetrical.

Might as well let the UK take a swing:
From Newnes "Industrial Power Engineering and Applications Handbook"

System unbalance protection. As discussed earlier,an asymmetry in the supply voltage causes high I^2R losses in the stator, and eddy current losses in the rotor.

Thus, besides voltage unbalance it can also detect an inter-turn fault, which leads to a current unbalance. A small amount of unbalance is already detected by the thermal element of the overcurrent protection but a severe unbalance, such as during a single phasing, would require quicker protection and hence, this protection. The relay may be set for an I, of around 3% or so.

From "ELECTRICAL POWER EQUIPMENT MAINTENANCE AND TESTING" CRC Press, Florida

Voltage unbalance: In a three-phase system, significant differences in phase voltage indicate a problem with the system or a defect in a load. High voltage unbalance causes three-phase loads to draw excessive current and causes motors to deliver lower torque. Also, it causes motor overheating, for example, 3% unbalance in voltage causes a temperature rise of 25?C. The negative sequence voltage (Vneg) and zero sequence voltage (Vzero) are an indication of voltage asymmetry between phases. It is desirable to keep Vneg to be less than 2%. The negative sequence voltage and zero sequence voltage are also referred to as V2 and V0, respectively.

The Baldor (based in Arkansas) InteliLite NT Genset Controller manual states that it provides Current/Voltage asymmetry protection.

From one of ABB's motor protection relay manuals:

The phase unbalance unit monitors the current asymmetry of the network and protects the motor against heavy network unbalance or single-phasing.

 

[ohmhead]

Well iam just a simple construction electrician but heres some input .

Industrial ac motor 3 phase current issues !


AC motor may also draw current asymmetrically the asymmetric components

are much larger in energy efficient motors and the substantial asymmetric current during start up .


This kinda can be misinterpreted by a circuit breaker as a short circuit but its not a short circuit as a short circuit or fault between phases is not the same .

Lets make it simple with out all the calculations and formulas which only confuse us electricians people behind a desk only see design programs and design there is more to current in other conditions of a system also dc motors and equipment is yet another area of this .


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 ?