Transformer Core

Yes.

Two minutes. I wonder if that's quick enough?

If ignorance is bliss, we have a bunch of insanely happy beggars out there.

What is a transmitter? Underwear adverts. What next?

"What is a transmitter? Underwear adverts. What next?"

is farther to Chicago or by bus iz awate yer repli

There. More fodder for the cannon

Fortunately, I missed that one. ^_Loons!!!

Come on! The lingerie thread was quite fun, and I played it straight--for a while, until a certain pun blew it outta here. (Admin = prudes. Also too quick to to blow off "homework," some of which isn't. I would also like the over-unity nonsense to stay alive longer, all the better to whack it. Truncating such threads fails to give sufficient rope to the flakes. Better to be hanged by satire rather than censorship, I say.)

And how, exactly, does a higher-than-design current flow through a conductor? Isn't this what the circuit's protective device is supposed to prevent?

when the magnetic flux flows through Iron - once it crosses the limit, the ferromagnetic material saturates. At this point its permeability equals the permeability of air and hence all the extra flux simply redistributes through air.

I am not aware that this may cause any permanent damage to the core.

Unless there is DC present, the core will not saturate before damage occurs.Some transformers are used for this saturation feature, but seldom seen anymore.

"Unless there is DC present, the core will not saturate before damage occurs "

This is testimony that transformer designers usually understand their craft. However, reduce the core cross section of any transformer core and it will saturate without DC present.

There r over flux relays meant specially fr protection against these type of conditions.

You should empty the crumbs out of your keyboard. Some of the letters are not coming through when you type.

perhaps he's missing a finger

It all depends on how much you want to overflux-

- There are effects , a few potentially damaging but for that we need to know

a) % overfluxing

b) reason of overfluxing

c) Equipment you are overfluxing

If we are I am convinced that you are permitted to overflux then we I will answer. It has quite a bit of smell of homework.

Else - it has potentially damaging effect. Put overflux protection device (after all if it doesn't have then why this device is there at all)

If home work - think what may happen when the core saturates- or even before, as the flux density rises what damaging potentials increase.

at 80 degrees Celsius, magnets lose their magnetic ability. Increased heat slowly ruins the transformer. Some magnets may be permanently destroyed. Over-fluxing will cause heat.

Put the dots together now...

Overvoltage is a side effect of increased magnetic flux. There is great electro-mechanical stress placed on the transformer. This is usually a problem with older transformers and in-rush current.

Magnets in a transformer? What is to be attracted?

every electric current has an accompanying magnetic field. This is how a transformer interacts with electrons in the iron core. (oversimplified) I should have state magnetic fields and not magnets in the answer. Higher states of flux create heat. One respondent mentioned that it dissipated into the air and he was right. The transformer's heat sinks.

Another derivation of Fudd's first law of opposition, "If you push something hard enough, it will fall over."

Firesign Theater, "I think we're all bozos on this bus."

You better go with a over dimensioned than under dimensioned core material. Whether E with I cover, square core or Ring ferrite core, once saturation has reached you have reached your maximal (undistorted signal) power ratio. What happens next? Your primary sees a more resistive load (a lot lower ohms value ), uses more energy- heats up / your secondary outputs more towards like a square signal - and heats up too You can bet your copper insulation burns - if not the insulation (paper material) between the layers and the core-. Possible damage can be enormous, from blowing a fuse to burning down your house. With the risk of a non relevant quote of the funny guys: some transformers have a core modification for current restriction (non electronic High Voltage neon sign transformers) I hope this helps

Dear everybody! Electric alternating current with e.g. 50 Hz (AC, DC is not usable in transformers) induces eddy current (also as foucoult current known) in all iron materials. As higher the current, the more is the temperature as the result of losses in the iron plates etc. If the current will be increased, the temp will rise so high, that the copper wiring will melt.
If you use high fequency, the core will melt before the copper wiring (coil). This phenomen is based on eddy current. The copper coil lasts longer, because the the HF current is only on the surface of cable/wire and therefore the heat in the core is much less then in the iron.

That is only one, small effect. There are more.

Dear Guest! What do you mean with only "one"?? If there are more you are thinking about, state them, its interesting for all readers!
The effect I wrote about isn´t so small; the industry uses often high frequency induction melting pots for very clean melts. Just visit the "Museum of Science" in London, there is a miniature melting device using HF exhibited, very informative.

If temperature rises, the isolation of the copper windings will fail at about 200 - 250_degree Celcius and you get a short circuit.

At these temperatures, the iron core is still undamaged.

The energy impact of a short circuit is much bigger then eddy currents....

And this is absolutely true. Guest should remove AC out of the brackets in his first reply too - you read AC wrong - this is a what happens - and is a GA

? Guest should remove AC out of the brackets in his first reply

Eddy, magnetostiction, hysterisis are the first few of them. ...

1. We are talking here about overfluxing and not exactly induction heater or melting? It will be a bit difficult to generate enough eddy at the normal line frequencies to melt the metal. Typically these work in 10s to 100s of KHz at least the ones we have.

2. These are typically not overfluxed - the overflux will saturate the core and the rest of the flux will bypass through air and hence not much of eddy will be created either.

3. Usual electro-mechanical machines are a bit protected agaist eddies- laminations, varnishing, silicon steel,... so these are not same as induction heaters.

However the overfluxing will first increase the iron losses. These losses will have immediate effect of heating up the core. This along with the amplified magnetostiction will damage the varnish/resin insulation between laminates and that will have secondary effect of increasing the eddies. Since now though the flux linkages are same, the effective resistance has gone down.

And the increase in magnetizing current will also increase the copper losses as mentoned in several posts earlier.

I mentioned post 15, first line. Comment of oe1shs. My mistake, sorry.

magnetostiction is another and has a potential to be extremely distructive if the pieces fall in place (but since this is homework of OP I didn't want to spell out all)

In fact just try the net on effect of overfluxing or some similar query, you may get some interesting information.

Eddy, magnetostiction, hysterisis are the first few of them. But no, as someone has mentioned, there is no property loss, a ferromagnetic material doesn't become paramagnetic or some other, that is ruled out. And as far as I know even μ doesn't change.

Each transformer coupled class A amplifier deals with DC through the transformer and is made for that purpose.

It depends on the type of core material. Cores tend to be more rugged than windings, however, operating steel cores in saturation generates heat, mechanical vibration, and will eventually damage the core. It also generates considerable acoustic noise.

Steel is definitely no optimal core material. It is commonly known that Iron, low or no carbon - Fe - has less Foucault effects - To even lower this effect thin plates of soft Iron are used to"cut" these down. The ferrite structure is a composed iron dust core for the same reasons

"Steel is definitely no optimal core material".

Although I agree with your statement from a technical point of view, steel is often the optimal choice when cost is a factor.

All the generators or motors, at least those we make - cores are steel- of course not normal- CRGO Si Steel but still they are steel. Ferrite cores are not practicable here (and the basic advantage of these are negated by the ruggedness of the steel)

The same goes for transformers too. Thanks for clarification. Technology advances.

When there is a problem that exposes the transformer to shot cct current, the flux density and mutual inductance are affected as they are greatly reduced. This will cause severe heating of the transformer coils/laminations and if the heating is in excess, it will destroy the insulation of the lamination and cause the the entire magnetic laminated cct to become one solid metal. In this condition, the eddy current path in severely increased, the transformer can never recover from over heating and no quality rewinding can improve it.

The only way out to revamp the transformer is to remove the magnetic cct for re insulation of the lamination.

Also some rewinder engage in the un fare practices of burning electric motors to enable them remove the stator wires. Such motor will never be usefully and will continue to drain limited resources, as over heating will continue un abated.

Dickson

I thought "soft" iron, with minimal or no alloying elements such as go into steel, was the material of choice. I'm not sure about this, though.

I think that is still the best option. CRGO Si steel however seems to work too. I guess it is mainly done for production reasons. The soft plate iron doesn't cut too well and is more difficult to stamp with calipers. Also don't get too nervous with sending DC trough a transformer, when designed for it. For almost a century end stages in transformer coupled audio and servo amplifiers had their DC set-point (the old tube anode) through one of the coils. It is still used now with some class A amplifiers with semiconductors.

In other words, a laminated SI steel core can hold 1500 times better magnetic flux than air. However, two kinds of losses are caused by the movement of magnetic flux in a transformer steel core. Another was called "EC Loss," and the other was called "Hysteresis Loss"

Transformer losses are produced by the electrical current flowing in the coils and the magnetic field alternating in the core. The losses associated with the coils are called the load losses, while the losses produced in the core are called no-load losses.

"What Are Load Losses?

Load losses vary according to the loading on the transformer. They include heat losses and eddy currents in the primary and secondary conductors of the transformer.

Heat losses, or I 2R losses, in the winding materials contribute the largest part of the load losses. They are created by resistance of the conductor to the flow of current or electrons. The electron motion causes the conductor molecules to move and produce friction and heat. The energy generated by this motion can be calculated using the formula:

Watts = (volts)(amperes) or VI.

According to Ohm's law, V=RI, or the voltage drop across a resistor equals the amount of resistance in the resistor, R, multiplied by the current, I, flowing in the resistor. Hence, heat losses equal (I)(RI) or I 2R.

Transformer designers cannot change I, or the current portion of the I 2R losses, which are determined by the load requirements. They can only change the resistance or R part of the I 2R by using a material that has a low resistance per cross-sectional area without adding significantly to the cost of the transformer. Most transformer designers have found copper the best conductor considering the weight, size, cost and resistance of the conductor. Designers can also reduce the resistance of the conductor by increasing the cross-sectional area of the conductor.

What Are No-load Losses?

No-load losses are caused by the magnetizing current needed to energize the core of the transformer, and do not vary according to the loading on the transformer. They are constant and occur 24 hours a day, 365 days a year, regardless of the load, hence the term no-load losses. They can be categorized into five components: hysteresis losses in the core laminations, eddy current losses in the core laminations, I 2R losses due to no-load current, stray eddy current losses in core clamps, bolts and other core components, and dielectric losses. Hysteresis losses and eddy current losses contribute over 99% of the no-load losses, while stray eddy current, dielectric losses, and I 2R losses due to no-load current are small and consequently often neglected. Thinner lamination of the core steel reduces eddy current losses.

The biggest contributor to no-load losses is hysteresis losses. Hysteresis losses come from the molecules in the core laminations resisting being magnetized and demagnetized by the alternating magnetic field. This resistance by the molecules causes friction that results in heat. The Greek word, hysteresis, means "to lag" and refers to the fact that the magnetic flux lags behind the magnetic force. Choice of size and type of core material reduces hysteresis losses."

https://www.copper.org/environment/sustainable-energy/transformers/education/trans_losses.html