Physics going on in a transformer

I think the suggestion made by Mike that the magnetic field strength is constant is slightly misleading, I am sure not deliberately but it leads from another phenomenen which is usually not mentioned in textbooks. I will attempt to explain it. Imagine you have a toroidial core, with a winding spaced from another on the opposite side of the toroid. Imagine the energy flow between the windings, the magnetic field in the core carries this energy from one side to the other. Loading MUST increase this magnetic field energy transfer, and it does, and causes increased losses. But this may be imagined in the second winding reducing the magnetic field in the same way as the primary winding increases it. However magnetic circuits do not work quite like that, and that is why practical transformers have the secondary winding wound on top of the primary winding, but still with a complete magnetic circuit (the core in a loop). Magnetism in this toroidial confguration has "resistance" and loss, but if the same piece of magnetic material has both the primary gain and secondary loss in the same place it is very efficient. One still needs the core to work, but the whole arrangement and "magnetic circuit" is not quite as often described. There are many things about magnetism (and electricity) which we do not fully understand, whatever you read in "text books", these are usually just restatements of that which is written elsewhere. The important thing is to keep an open mind and think about the problem, it may well not be quite as others describe. but consider things like energy flow above. The idea that a coupled winding reduces the magnetid field is somewhat counter intuitive, but if you think about it inductors of all kinds have slightly strange energy flows, think about "back EMF" in energy terms and it is obvious that the magnetic field energy must go somewhere when the magnetising current stops!


David CEng etc.

I think the suggestion made by Mike that the magnetic field strength is constant is slightly misleading, I am sure not deliberately but it leads from another phenomenen which is usually not mentioned in textbooks. I will attempt to explain it. Imagine you have a toroidial core, with a winding spaced from another on the opposite side of the toroid. Imagine the energy flow between the windings, the magnetic field in the core carries this energy from one side to the other. Loading MUST increase this magnetic field energy transfer, and it does, and causes increased losses. But this may be imagined in the second winding reducing the magnetic field in the same way as the primary winding increases it. However magnetic circuits do not work quite like that, and that is why practical transformers have the secondary winding wound on top of the primary winding, but still with a complete magnetic circuit (the core in a loop). Magnetism in this toroidial confguration has "resistance" and loss, but if the same piece of magnetic material has both the primary gain and secondary loss in the same place it is very efficient. One still needs the core to work, but the whole arrangement and "magnetic circuit" is not quite as often described. There are many things about magnetism (and electricity) which we do not fully understand, whatever you read in "text books", these are usually just restatements of that which is written elsewhere. The important thing is to keep an open mind and think about the problem, it may well not be quite as others describe. but consider things like energy flow above. The idea that a coupled winding reduces the magnetid field is somewhat counter intuitive, but if you think about it inductors of all kinds have slightly strange energy flows, think about "back EMF" in energy terms and it is obvious that the magnetic field energy must go somewhere when the magnetising current stops!


David CEng etc.