I suppose the answer to the initial question "Why haven't transformers got smaller?" the TS is making a comparison with power semiconductors. Since the 1950s we've gone from germanium, to silicon, then thyrsistors, MOSFETs, IGBTs, Silicon Carbide and Gallium Nitride each increasing the amount of power that can be switched in a given volume, but in terms of magnetics materials, the best we've got in terms of flux density hasn't improved in 125 years. For reasons given by @WBahn mains transmission frequencies have also remained the same, so those two factors means that line-frequency transformers haven't got any smaller (apart from some small gains in the temperatures insulation will withstand). These limitation have been circumvented by using the advanced semiconductors to run the transformers at higher frequency as @Danko and @ronsimpson pointed out earlier.

 

And then me, badly informed reader, I ask why not 400 Hz for mains as well?

In addition to the other replies, the steel core losses increase very rapidly with operating frequency. A nice experiment if one has access to a 400Hz supply, is to connect an unloaded 50/60Hz transformer to it. Within a couple of minutes, the core will sizzle your fingers.
To operate at 400Hz, the steel core must be of a higher grade which is more expensive.

 

Yes, transformers get heavy and can be costly. However, a 400 Hz transformer verse a 50 ~ 60 Hz version is much lighter which is why aircraft systems use 400 Hz. Today look at SMPSs. They use a high frequency to function requiring lighter smaller transformers.

Ron

 

In addition to the other replies, the steel core losses increase very rapidly with operating frequency. A nice experiment if one has access to a 400Hz supply, is to connect an unloaded 50/60Hz transformer to it. Within a couple of minutes, the core will sizzle your fingers.
To operate at 400Hz, the steel core must be of a higher grade which is more expensive.

And thinner (which makes it more difficult to laminate)

 

The transformers in the high-frequency inverter type power supplies are quite small for the power they deliver. But the use several kilohertz voltages.
For all power transformers, the power limit is the saturation power of the magnetic material. That is because it is the magnetic field that transfers the power in a transformer.

 

oops

 

If you watched this movie, you could carry large buckets slowly or small buckets at high speeds.
When designing a transformer, the core can hold a certain amount of (Volts X Time) AT 60hz the time is large compared to a switching power supply running at 120,000hz.

 

IS there really no solution for this? Lots of smaller transformers are used in power supplies,

Generally Toroidal mains transformers are smaller than their EI counterpart, due to high implementation of retained field, rather that externally radiated.
IOW. more efficient.

 

Some steel laminations have better magnetic properties than others, and some shapes are a bit more efficient. AND indeed, toroid style transformers are more efficient but a bit more difficult to wind. AND mounting them can be more difficult than the more cubicly shaped transformers. So there are tradeoffs.
THAT is why switching mode power supplies are so popular. BUT where the only need is to change voltage, only a transformer will do.

 

Actually transformers have gotten smaller due to better cooling - however cost rules, and for common or garden types cheap = as big as they ever were. For cheap transformers the steel laminations are typically 0.35 - 0.5mm thick, which gives higher eddy current losses than say 0.15mm - by quite a bit. Also the best cold rolled grain oriented silicon electrical steels can operate up to 2.2 Tesla magnetic flux density, whereas the common stuff operates at 1.2 Tesla max - again for self heating reasons, so by using the best materials ( $$ ) we could almost halve transformer size & weight.

 

i don't understand why is that puny transformer considered "enormous"...
there are earrings that are larger than that. it can completely disappear in one hand. it is barely large enough to power decent transistor radio.
for comparison, there is tons of WAY larger specimen...

this is more like it:


and we don't want to talk about these:

 

Very good information about the core material in post #30! The losses in the steel core have been reduced and so the transformers have become smaller over the years. BUT those laws of physics have a tendancy to always prevail!

 

BUT those laws of physics have a tendancy to always prevail!

Tendency? I don't think they can be changed by executive order or even a constitutional amendment.

Although, once upon a time, a state legislature passed a bill that pi = 3.2 – who needs all those complicated digits?

In 1897, the Indiana General Assembly passed the infamous “pi bill,” which effectively treated pi as 3.2 rather than the true value.

 

I have found it rather easier to rewind Toroidal mains TFMRs There are a few youtube videos on it, it just requires making a simple spool similar to a weaving shuttle to wind the wire onto first. Many EI types have a lamination weld or other restrictions that makes it a little more difficult.
Also the turns/volt is quite a bit lower on Toroidal versions.

 

Tendency? I don't think they can be changed by executive order or even a constitutional amendment.

Although, once upon a time, a state legislature passed a bill that pi = 3.2 – who needs all those complicated digits?

In 1897, the Indiana General Assembly passed the infamous “pi bill,” which effectively treated pi as 3.2 rather than the true value.

Fortunately, that bill didn't make it out of the Indiana Senate.

While 3.2 is the most commonly cited value for by in that legislation, the bill was so poorly written that it actually implied several different values because it gave several different "constructions" for determining pi, including 3.2, 4, ~3.23. ~3.24, ~3.14, ~3.0. Interestingly, the one that comes close is only by pure coincidence. The construction provided is completely invalid.

Certainly not the only example of a legislature passing a bill that they clearly had no idea what they were voting on and probably hadn't bothered reading in the first place.

 

Certainly not the only example of a legislature passing a bill that they clearly had no idea what they were voting on and probably hadn't bothered reading in the first place.

Political theater we call it these days.....

 

Tendency? I don't think they can be changed by executive order or even a constitutional amendment.

Although, once upon a time, a state legislature passed a bill that pi = 3.2 – who needs all those complicated digits?

In 1897, the Indiana General Assembly passed the infamous “pi bill,” which effectively treated pi as 3.2 rather than the true value.

What I was hoping to get across is that not everybody that I have read in the past seems to understand the limitations, and so there is a request for help because something does not work as it was desired for it to work. It seems that I was a bit too subtle with that comment.

 

In 1897, the Indiana General Assembly passed the infamous “pi bill,” which effectively treated pi as 3.2 rather than the true value.

Indiana - true. Passed in the House, died in the Senate.

Alabama - urban legend: https://www.snopes.com/fact-check/alabamas-slice-of-pi/

Mississippi - not sure: https://www.snopes.com/fact-check/mississippi-fractions/

ak

 

I really see no value to telling what goofy rules different government bodies have produced.

Indiana - true. Passed in the House, died in the Senate.

Alabama - urban legend: https://www.snopes.com/fact-check/alabamas-slice-of-pi/

Mississippi - not sure: https://www.snopes.com/fact-check/mississippi-fractions/

WHAT I DO SEE is a a bit of ridicule about my statement: Very good information about the core material in post #30! The losses in the steel core have been reduced and so the transformers have become smaller over the years.

BUT those laws of physics have a tendancy to always prevail!

Evidently my slight effort at humor sidetracked the thread. My apology for that. I will try to avoid it here in the future.

 

Just rectify your mains supply, then switch it at a much higher frequency. Then you can use a smaller transformer. (Or persuade your power company to transmit it at a higher frequency)


Are you sure? Seems unlikely.

The items used to FILTER are NOT transformers. They are called CHOKES, or inductors.