Hysteresis

[Burnerbob]

I was taught that this is the constant contraction and expansion of coils in motors and transformers, and it eventually leads to failure of them.
The example that was taught to me was using "rubber-bands" and adding and removing a metal weight. Each time the rubber band expands from the weight added and contracts when the weight is removed, eventually causing the rubber band to break.
I want to be sure I give the correct information when teaching. :smile:

 

[ray cyr]

I was taught that hysteresis is the phenomenon that causes heat inside of a transformer or the coils of a motor. This is from the friction of the molecules inside the conductors constantly aligning and re-aligning as the magnetic flux flops from north to south and back causing the molecules to flop with it.

 

[gar]

080824-1517 est

Burnerbob:

I was taught that this is the constant contraction and expansion of coils in motors and transformers, and it eventually leads to failure of them.

This I will classify as incorrect.

Look at these internet references:
http://en.wikipedia.org/wiki/Hysteresis good
http://www.lassp.cornell.edu/sethna/hysteresis/WhatIsHysteresis.html also good
http://dictionary.reference.com/browse/hysteresis not so good
http://dictionary.reference.com/search?q=magnetic hysteresis not so good

I really did not understand the rubber band discussion.

.

 

[steved]

I don't think that's quite correct. Hysteresis refers to a property of a system that depends on the prior history of the system. See the Wikipedia article on hysteresis for more information. There are various types of hysteresis. Magnetic hysteresis is what causes the heating of transformers.

The failure of coils due to repeated thermal expansion and contraction is probably due to metal fatigue.

 

[cadpoint]

a few hot Links

a few hot Links

hysteresis
Merrian -websters here (one in the same as below)

Main Entry: hys?ter?e?sis
Pronunciation: \ˌhis-tə-ˈrē-səs\ Function: noun Inflected Form(s):
plural hys?ter?e?ses \-ˌsēz\ Etymology:
New Latin, from Greek hysterēsis shortcoming, from hysterein to be late, fall short, from hysteros later — more at out Date: 1881 : a retardation of an effect when the forces acting upon a body are changed (as if from viscosity or internal friction); especially : a lagging in the values of resulting magnetization in a magnetic material (as iron) due to a changing magnetizing force
— hys?ter?et?ic \-ˈre-tik\ adjective

Another one: (from Here, same as below)
3 definitions found

From The Collaborative International Dictionary of English v.0.48 [gcide]:

Hysteresis \Hys'te*re"sis\, noun [NL., fr. Gr. ? to be behind, to lag.] (Physics) A lagging or retardation of the effect, when the forces acting upon a body are changed, as if from velocity or internal friction; a temporary resistance to change from a condition previously induced, observed in magnetism, thermoelectricity, etc., on reversal of polarity.

From WordNet (r) 2.0 [wn]:

hysteresis

noun: the lagging of an effect behind its cause; especially the phenomenon in which the magnetic induction of a ferromagnetic material lags behind the changing magnetic field

"DEFINE" is: Thisdictionarywasderivedfrom the Webster's RevisedUnabridgedDictionaryVersionpublished 1913 by the C. & G. MerriamCo. Springfield, Mass. Under the direction of NoahPorter, D.D., LL.D.


I don't like Wiki or answer.com their cleaned up version of "wiki"

 

[Burnerbob]

I don't think that's quite correct. Hysteresis refers to a property of a system that depends on the prior history of the system. See the Wikipedia article on hysteresis for more information. There are various types of hysteresis. Magnetic hysteresis is what causes the heating of transformers.

The failure of coils due to repeated thermal expansion and contraction is probably due to metal fatigue.

It mentions the rubber-band theroy, but says nothing about failure, just mentions "Hokes Law".
I did some research and in the book "Electric Motor Repair" from the IEE, it states that Hysteresis and Eddy Currents cause a loss of power. ???????

 

[zog]

I was taught that this is the constant contraction and expansion of coils in motors and transformers, and it eventually leads to failure of them.
The example that was taught to me was using "rubber-bands" and adding and removing a metal weight. Each time the rubber band expands from the weight added and contracts when the weight is removed, eventually causing the rubber band to break.
I want to be sure I give the correct information when teaching. :smile:

If you are teaching about hystersis in a transformer you will want to explainn a B/H curve and some different examples of different materials B/H curve charteristics. From there you can explain hystersis and losses.

 

[Burnerbob]

If you are teaching about hystersis in a transformer you will want to explainn a B/H curve and some different examples of different materials B/H curve charteristics. From there you can explain hystersis and losses.

Can you recommend a good book with details. I believe in backing up everything, as one of the biggest problems I have encountered training so-called seasoned technicians is they are very weak in fundamentals. Thanks to you and everyone else.

 

[winnie]

1) Hysteresis as applied to electric motors and transformers generally means magnetic hysteresis of the core. The core material acts just a bit like a permanent magnet, holding on to a bit of the magnetism caused by the current flowing through the coils. Since the current through the coils is constantly changing, bit of permanent magnetic nature is somewhat fighting the changing magnetic field. The effort to 're-magnetize' this permanent magnetism is one of the loss terms in a motor, and results in lower efficiency and more heat.

As Steve notes, hysteresis is a general term applied to numerous systems; its just that magnetic hysteresis is a pretty dominant feature in an electric motor.

As happens, when you change the magnetization of a piece of metal, you _do_ change its size very slightly. Because of this, the _mechanical_ pressure of a motor housing on the motor core can change the efficiency slightly. I don't know the details.

Whenever something moves, it can cause something to rub and cause failure. I have a dim recollection of a story of an underground distribution cable that would move slightly when load changes caused temperature changes; this motion caused an insulation failure where the cable passed through an opening somewhere.

I don't _know_, but my gut feelings are:
1) Movement caused by the magnetic AC cycle is not going to be a big issue.
2) Movement caused by temperature changes caused by load changes might be enough to be the straw that breaks the camels back.
3) Other defects will be a much more significant issue with equipment life.

-Jon

 

[gar]

080824-1951 EST

Burnerbob:

I think the first two references I gave you above provide a relatively good definition of the word hysteresis related to electrical ferromagnetic materials and mechanical materials.

In the elastic range of good materials it is generally assumed that d = K * f where d is displacement, K is a constant, and f is the applied force. When you look closely at a material you will find that even after stress relieving that there still may be a very small difference of the zero reading of d after a force has been applied and relaxed. Thus, that equation is not quite correct. My son is machining the mechanical structures for force load cells for a customer. Initially one might assume that 7075 (aircraft aluminum alloy -- high strength) might be a better transducer material than 6061 (a less high strength more common alloy). Turns out this is not the case and the 7075 has more hysteresis than the 6061 based on that customer's tests.

steved gave you a nice simple explanation (definition).

Hysteresis refers to a property of a system that depends on the prior history of the system.

Following are two reference books, but I do not think they will help you. This will very much depend upon your background.

"Electric and Magnetic Fields", Stephen S. Attwood, 1949, John Wiley & Sons, Chapter 13, Ferromagnetism.

"Alternating-Current Machinery", Bailey and Gault, 1951, McGraw-Hill Book Co., various places -- in particular maybe Chapter 1, Transformers, p 6 - 11, p 16 - 22, and look up hysteresis in the index.

.

 

[Burnerbob]

080824-1951 EST

Burnerbob:

I think the first two references I gave you above provide a relatively good definition of the word hysteresis related to electrical ferromagnetic materials and mechanical materials.

In the elastic range of good materials it is generally assumed that d = K * f where d is displacement, K is a constant, and f is the applied force. When you look closely at a material you will find that even after stress relieving that there still may be a very small difference of the zero reading of d after a force has been applied and relaxed. Thus, that equation is not quite correct. My son is machining the mechanical structures for force load cells for a customer. Initially one might assume that 7075 (aircraft aluminum alloy -- high strength) might be a better transducer material than 6061 (a less high strength more common alloy). Turns out this is not the case and the 7075 has more hysteresis than the 6061 based on that customer's tests.

steved gave you a nice simple explanation (definition).


Following are two reference books, but I do not think they will help you. This will very much depend upon your background.

"Electric and Magnetic Fields", Stephen S. Attwood, 1949, John Wiley & Sons, Chapter 13, Ferromagnetism.

"Alternating-Current Machinery", Bailey and Gault, 1951, McGraw-Hill Book Co., various places -- in particular maybe Chapter 1, Transformers, p 6 - 11, p 16 - 22, and look up hysteresis in the index.

.

Thank you. My Background is Commercial Refrigeration and Oil Burners, however I always strive to learn as much as I can as I teach the aforementioned trades.
An instructor is only as good as the material he presents and I like to be sure it is presented properly. Evidently the person who taught the "Motor" class I took 25 years ago needed a class himself. :smile:

 

[gar]

080825-0633 EST

Burnerbob:

The books I referenced are not first year engineering books and assume considerable electrical background knowledge, and math background in college algebra, calculus, and differential equations.

However, you can ignore some of the math and maybe still get some feeling for what happens in a ferromagnetic circuit. There are some very different magnetization curves for different materials shown in Attwood's book.

With a measurement at any one frequency and excitation level it is not possible to know the distribution of core loss between eddy-current and hysteresis. Bailey and Gault describe a procedure to estimate the allocation of these losses.

Besides core losses in a transformer you have I^2*R losses (loss in the resistance of the wire) in the windings. These losses come from two sources -- the current to supply the core losses and the load current.

You will probably find many newer books that cover this material. Go to a local engineering university and find out what books are used in the classroom in this subject area and then to their library to find the books. At least for public universities their libraries should be open to residents.

.

 

[zog]

Can you recommend a good book with details. I believe in backing up everything, as one of the biggest problems I have encountered training so-called seasoned technicians is they are very weak in fundamentals. Thanks to you and everyone else.

The Practical Transformer Design Handbook by Eric Lowdon