Short Circuit Strength of Power Transformers

Flip a coin.

Less insulation to fail with 168 turns.

And there was I thinking that fuses and overload breakers were there to protect the things. Silly me.

The best people to ask are the manufacturers.

As Crabtree has said the protection should operate before damage is done. A hypothetical question, do you ask out of interest or is it your homework?

Homework, CR4 has rules regarding this.

Worryingly this isn't a homework question, Vinod has said previously he works as a transformer designer.

CR4 Link

So, the point of the test is to discover which of these transformers survives an unprotected short circuit and which one catastrophically self-disassembles? Please make sure that all other CR4 readers are at least 1km away from it before carrying out the tests.

And how many years have you been designing transformers? In this thread, you don't seem to know where to place the transformer cooling fans and in this thread, you don't seem to know your suppliers and now your wondering which transformer will self destruct during a short circuit?

Are you even sure your a "designer" of transformers, because you sure sound like your still in school

I agree with PW Slack, "Please make sure that all other CR4 readers are at least 1km away from it before carrying out the tests."!!!!

And as Tony S stated,

GA's Tony and PW

At a first glance, lesser turn would have better capability against the short circuits - reason being if turns are less then the area of cross section of coil shall be more - resulting in bigger dia of coil - more area and better cooling.

Having said above mechanical strength depends upon number of factor including ratio of height to dia, coil supports and gap between adjacent coils etc.

I think you are quite right and very close to what I have thought all along .Your answer has given me confidence' Now to put it more specifically I had read that "all short circuit forces depend on Ampere Turns " In this case the Amperes are of short circuit current ie Turns multiplied by short circuit current in Amperes . Now short circuit current will depend on percentage impedance , since the impedance is the same in both cases then the short circuit forces will be less in the case of transformer with LESS TURNS Hence I THINK THAT THE TRANSFORMER WITH LESS TURNS WILL BE safer in short circuit test conducted at an accredited test house Do you think I am thinking on the right lines Please let me know your opinion about what I have written above regards Vinod

What makes you think that less impedance would be safer? Less impedance results in more current flow...therefore hotter wires and more likely catastrophic melt down and failure.

I see no answer from the OP to my question. A lot of people equate heat with resistance...in fact, it is an inverse relationship.

I think this person is still in school and facing questions that he either cut school or fell asleep during the lecture and didn't take notes on the subject

Instead of this thoughtless mind, or is it mindless thought, experiment why don't you contact an "accredited test house" and let them tell you what their experience is, then report back what they say.

I agree with powersolutionsFBD.

Let's say both transformer magnetic flux density will be the same then less turns larger iron column-better dynamic stability, but since will be more iron, iron losses will be a little more.

Lesser copper on the windings-lesser copper losses. My opinion: the total losses will be lesser if the number of turns is less.

Well more turns would supply more resistance which would result in lower amperage, and less heat. Thats just copper losses though. Impedance on a higher winding transformer would be higher, and result in less current. More iron in the core on a larger transformer would result in more hysteresis and eddy current losses. In a dead short, well........I would flip a coin and stand well back.

Option (A) is at advantage with a higher turn ratio and probably >= Option (B) impedance with some decimal points that can not be approximated.

Guys, my question has something to do with ampere turns and short circuit forces. I have read somewhere that short circuit forces are proportional to Ampere turns and this is what I want to understand. Please think on these lines and give me a sound and logical technical answer Thanks vinod

Why?

Your question has "something" to do with what you "have read somewhere".

Go back and read it again. Then perform the same searches/research we would to arrive at a, "sound and logical technical answer" to your question.

Or, flip a coin.

Pl do not waste our time. Think beyond what you have read such as; Is the reaction due to short circuit is between two transformers (two magnets) that you are talking of overall ampere turn, OR it is between adjacent turns and between limbs and you will get the answer? If it is between adjacent turn then number of turns do not matter.

Once again do some more of reading or visualize the situation yourself before posting your question. And if posted be clear with background in mind so that we do not waste our time unnecessarily.

Go with the one with more turns. Since they both have the same rating, the current carried is the same in both cases so the conductor can have the same cross sectional area, though you may want to increase it to account for the increased voltage drop through the longer length (this helps the following argument).

Assuming that the conductor is the same size in both cases, there is 7.15% more copper to heat up so it will be able to sink more heat which when coupled with a greater surface area immersed in the oil, increases the rate of heat rejection to the oil; both effects contribute to a greater thermal withstand capability.

Mechanically, more windings means that the forces will be spread out over a greater mass, which when coupled to a longer conductor length, yields a lower force per winding turn; therefore there will be less deforming force per unit of copper.

Another way to look at it; assuming that the style, winding factor, and diameter are the same, yields a taller coil, more surface area = better cooling, plus the deforming/hoop stresses are spread out over a greater area as well.

The above assumes that all other things are equal since it's possible to use different combinations of winding factors (disc, multilayer, sheet, parallel, interleaved, etc.) and core structures (core, shell, three or five limb) to design a special needs transformer that will prove this simplistic analysis wrong.