transformer frequency dependency

[rob]

Hello all,
What determines the acceptable frequency for a given transformer?
I had believed that the higher voltages involved, you simply need to
use higher frequencies (ie the flyback transformer in a tv or
monitor).

But the power company routinely boosts 60Hz power up to several
thousand KV, and I am assuming they dont have to convert frequency of
the current to do it. What am I missing here? Thanks in advance...
Rob

 

[Dimitrij Klingbeil]

"rob" <ngneer314@yahoo.com> wrote in message
news:vjgv50dt97kocvv7glmfh82eqi7s9iuvcc@4ax.com...

Hello all,
What determines the acceptable frequency for a given transformer?
I had believed that the higher voltages involved, you simply need to
use higher frequencies (ie the flyback transformer in a tv or
monitor).

There are several factors, the core properties being an important one of
them. From a very simplified point of view, assuming that insulation
strength is sufficient, one could just take any transformer and run it at
higher voltages with higher frequencies. However there are practical limits
to this. A simple iron core has a way too high remanence to be operated
efficiently near to RF. That's what ferrite cores are for (flyback etc).

Of course, it is possible to build a flyback to operate at 60Hz, but that
one would be heavy. Besides, this would mean adding a big filter cap for a
clean DC because of the low frequency. Wint the hf flybacks, the plate
capacitance of the CRT is actually the only filtering needed.

But the power company routinely boosts 60Hz power up to several
thousand KV, and I am assuming they dont have to convert frequency of
the current to do it. What am I missing here? Thanks in advance...
Rob

Several thousand KV, that is several MV, is actually a little too much even
for interstate power lines, as far as I know. 1MV is in use, both AC (e.g.
Italy) and DC (e.g. China), it seems to be the upper limit for transmission
lines so far however.