electricity - traditional transformer design improvement

The traditional tranformers suffer a lot of losses in various forms, some of them are as follows : 1. Flux leakage 2. Eddy currents 3. Hysteresis

Figure :

But as we are taught induction we come across the attached figure of two inductors placed coaxially various times. My point is that if we would actually place inductors in this way, we would have the following benefits :

Note : taking inner coil as primary

1. NO NEED OF CORE : As the flux of inner coil passes from outer on its own, no core is needed for transferring flux from primary to secondary


2. NO FLUX LEAKAGE : As entire flux of inner inductor passes from outer, no flux is leaked.


3. NO EDDY CURRENTS: As no core is used no eddy currents are generated.


4. NO HYSTERESIS : Similarly due to absense of core, no loss due to hysteresis is encountered.

So what really is the problem in creating transformers in such a way to reduce losses much more than the current status ?

All relevant opinions and comments appreciated

My original post : http://thinklo.blogspot.in/2013/10/improving-transformers.html

Answer

Well a problem with your concept is that an "air core" transformer can produce only a limited magnetic flux density; limited by the amount of current you can run through it.

If your transformer is for power conversion/transmission, your scheme would be extremely inefficient at power line frequencies. It can be shown that the efficiency is maximized when the "copper losses" are equal to the "iron losses" or "core losses if you prefer.

Since, your transformer has no iron core, there are very low to near zero core losses, but the copper losses (wire resistance) is very high.

With an "iron" core, you can get magnetic fields of 10-15,000 Gauss (is that 1-1.5 Tesla), because of the high permeability, so you can use fewer turns of thicker wire, so less resistance, and copper losses, but more core losses, eddy currents, hysteresis losses etc.

The design of efficient and cost effective transformers, is a very complex discipline.

Sometimes it can get slightly insane. Problem with iron cores, is that they saturate somewhere in the 15-20,000 Gauss region, so if you want to go higher in flux density than that, you have to get rid of the iron. Someone did that once on an electromagnet for an accelerator. They used just two turns of wire, each a foot in diameter (the wire, not the coil). They put 800 Volts across those two turns and it drew 6 million Amps; but gave them twice the field they could get with iron. Guys name was Marcus Oliphant, in Australia. They called his machine (which worked) the white Oliphant.