transformer frequency dependency

[rob]

Hello all,
In my experience it seems that when you try to produce higher
voltages with a transformer (like the flyback xformer in a tv) you
must excite it with a very high frequency. If you put 60Hz for example
into a flyback, you wouldn't get as your output voltage the input
times the turns ratio, and the primary would just draw tremendous
current and get real hot.

But I know that for the power distribution grid used by the utilities,
power is routinely stepped up and down to several thousand Kv, and
they are running at only 60 Hz.

So i take it that the "higher voltage, higher frequency needed" theory
of mine isn't correct. What formula or factor defines what frequency a
transformer needs to function? Whats the lowest limit of frequency you
can run a transformer at?

Thanks in advance...
Rob

 

[John Popelish]

rob wrote:

Hello all,
In my experience it seems that when you try to produce higher
voltages with a transformer (like the flyback xformer in a tv) you
must excite it with a very high frequency. If you put 60Hz for example
into a flyback, you wouldn't get as your output voltage the input
times the turns ratio, and the primary would just draw tremendous
current and get real hot.

But I know that for the power distribution grid used by the utilities,
power is routinely stepped up and down to several thousand Kv, and
they are running at only 60 Hz.

So i take it that the "higher voltage, higher frequency needed" theory
of mine isn't correct. What formula or factor defines what frequency a
transformer needs to function? Whats the lowest limit of frequency you
can run a transformer at?

Thanks in advance...
Rob

There are more factors than just voltage. Size and power level are
also involved in the efficiency calculation. A high frequency
transformer made with a ferrite core may be the best compromise for a
100 watt 10,000 voltage transformer, but is a very poor choice for a 1
megawatt 10,000 volt transformer.

Laminated silicon steel has a lot higher flux capability and is more
efficient if the frequency is low. Raising the frequency of an iron
core transformer to produce more volts per turn to shorten the
windings applies more voltage around each lamination, increasing the
eddy current losses more than it decreases the per cycle hysterisis
losses that you would have if the higher frequency was used to lower
the peak flux.

--
John Popelish

 

[Active8]

On Tue, 23 Mar 2004 04:46:18 GMT, rob wrote:

Hello all,
In my experience it seems that when you try to produce higher
voltages with a transformer (like the flyback xformer in a tv) you
must excite it with a very high frequency. If you put 60Hz for example
into a flyback, you wouldn't get as your output voltage the input
times the turns ratio, and the primary would just draw tremendous
current and get real hot.

But I know that for the power distribution grid used by the utilities,
power is routinely stepped up and down to several thousand Kv, and
they are running at only 60 Hz.

They're a lot bigger, too, aren't they?

So i take it that the "higher voltage, higher frequency needed" theory
of mine isn't correct. What formula or factor defines what frequency a
transformer needs to function? Whats the lowest limit of frequency you
can run a transformer at?

It's depends on the core.

Google on "Producing Wound Components"

--
Best Regards,
Mike

 

[Robert Baer]

rob wrote:

Hello all,
In my experience it seems that when you try to produce higher
voltages with a transformer (like the flyback xformer in a tv) you
must excite it with a very high frequency. If you put 60Hz for example
into a flyback, you wouldn't get as your output voltage the input
times the turns ratio, and the primary would just draw tremendous
current and get real hot.

But I know that for the power distribution grid used by the utilities,
power is routinely stepped up and down to several thousand Kv, and
they are running at only 60 Hz.

So i take it that the "higher voltage, higher frequency needed" theory
of mine isn't correct. What formula or factor defines what frequency a
transformer needs to function? Whats the lowest limit of frequency you
can run a transformer at?

Thanks in advance...
Rob

In some parts of the world, power transformers were run a low as 25
cycles per second.
I believe that most, if not all of those 1920's-1940's systems have
been replaced with more efficent and smaller transformersrunning at 50Hz
or so.

 

[Ban]

Robert Baer wrote:

rob wrote:

Hello all,
In my experience it seems that when you try to produce higher
voltages with a transformer (like the flyback xformer in a tv) you
must excite it with a very high frequency. If you put 60Hz for
example into a flyback, you wouldn't get as your output voltage the
input times the turns ratio, and the primary would just draw
tremendous current and get real hot.

But I know that for the power distribution grid used by the
utilities, power is routinely stepped up and down to several
thousand Kv, and they are running at only 60 Hz.

So i take it that the "higher voltage, higher frequency needed"
theory of mine isn't correct. What formula or factor defines what
frequency a transformer needs to function? Whats the lowest limit of
frequency you can run a transformer at?

Thanks in advance...
Rob

In some parts of the world, power transformers were run a low as 25
cycles per second.
I believe that most, if not all of those 1920's-1940's systems have
been replaced with more efficent and smaller transformersrunning at
50Hz or so.

We are running the trains in Europe with 16 2/3Hz still now. Even if the
transformers are more bulky, efficiency is equal to higher frequency and the
big advantage is you will need only 1/3 of the feed-points, because the
distance where power can be delivered is much higher. The inductivity of the
lines will turn the phase between voltage and current, so there is a maximum
distance until the angle is 90° and no real power can be transmitted.
--
ciao Ban
Bordighera, Italy

 

[Winfield Hill]

Ban wrote...

We are running the trains in Europe with 16 2/3Hz still now.

Hmm, that's exactly 1/3 of 50Hz, what's the reason for that?

Thanks,
- Win

whill_at_picovolt-dot-com

 

[Ban]

Winfield Hill wrote:

Ban wrote...

We are running the trains in Europe with 16 2/3Hz still now.

Hmm, that's exactly 1/3 of 50Hz, what's the reason for that?

Thanks,
- Win

whill_at_picovolt-dot-com

The reason was that the same turbine could simultaneously generate a 3phase
50Hz or a single phase 16 2/3Hz, an integer ratio between the two different
frequencies is needed.
The main reason for the low frequency is reduced brush-fire of the motor
when turning at low speeds. Here is a German site with a few pictures from
the start of the train electrification 1911.
http://www.elektrische-bahnen.de/history/eb_1623de.htm#20er
--
ciao Ban
Bordighera, Italy

 

[Ken Smith]

In article <c3p0pe0117i@drn.newsguy.com>,
Winfield Hill <Winfield_member@newsguy.com> wrote:

Ban wrote...

We are running the trains in Europe with 16 2/3Hz still now.

Hmm, that's exactly 1/3 of 50Hz, what's the reason for that?

They did it just to cause trouble for the German magnetic observatories
and their geophysical industry. The whole of planet earth hums at a
mixture of 50 and 60Hz. These don't cause trouble if you sample at a 10Hz
rate. The only major exceptions are the 16Hz trains and the ~47Hz power
system in China.

--
--
kensmith@rahul.net forging knowledge

 

[Tim Shoppa]

Winfield Hill <Winfield_member@newsguy.com> wrote in message news:<c3p0pe0117i@drn.newsguy.com>...

Ban wrote...

We are running the trains in Europe with 16 2/3Hz still now.

Hmm, that's exactly 1/3 of 50Hz, what's the reason for that?

Historically: Rotary converters. No gearing necessary, just use a
different number of poles on input vs output.

I doubt that any are in use today in Europe (they've been museum
pieces for traction power in the US for decades now), but after a standard
gets set it often lives for several generations of technology.

Tim.

 

[Tony Williams]

In article <c3p0pe0117i@drn.newsguy.com>,
Winfield Hill <Winfield_member@newsguy.com> wrote:

Ban wrote...
We are running the trains in Europe with 16 2/3Hz still now.

Hmm, that's exactly 1/3 of 50Hz, what's the reason for that?

To get the low frequency AC supply for traction they
would have used rotary frequency converters. F-in
would be 50Hz, and the integer ratio of pole-pairs
means that F-out can't be anything other than an integer
division of the input frequency... /2, /3, or /4,etc.

Traction motors were often brushed series-wound commutator
motors, like dc motors but running on an AC supply. The
need for a very low frequency supply comes from an obscure
sum in that application (which I forget the details of)
but which basically says that a good power factor can only
be obtained with a high ratio of shaft-speed to the supply
frequency. The shaft-speed of an old traction motor would
be relatively low, limited by bearing and gearbox technology.

The modern version of that is my B&D electric drill which
is also a series-wound commutator motor, but running on 50Hz,
and with a corresponding very high shaft-speed, of around
20000 rpm.

--
Tony Williams.

 

[Robert Baer]

Ban wrote:

Robert Baer wrote:
rob wrote:

Hello all,
In my experience it seems that when you try to produce higher
voltages with a transformer (like the flyback xformer in a tv) you
must excite it with a very high frequency. If you put 60Hz for
example into a flyback, you wouldn't get as your output voltage the
input times the turns ratio, and the primary would just draw
tremendous current and get real hot.

But I know that for the power distribution grid used by the
utilities, power is routinely stepped up and down to several
thousand Kv, and they are running at only 60 Hz.

So i take it that the "higher voltage, higher frequency needed"
theory of mine isn't correct. What formula or factor defines what
frequency a transformer needs to function? Whats the lowest limit of
frequency you can run a transformer at?

Thanks in advance...
Rob

In some parts of the world, power transformers were run a low as 25
cycles per second.
I believe that most, if not all of those 1920's-1940's systems have
been replaced with more efficent and smaller transformersrunning at
50Hz or so.

We are running the trains in Europe with 16 2/3Hz still now. Even if the
transformers are more bulky, efficiency is equal to higher frequency and the
big advantage is you will need only 1/3 of the feed-points, because the
distance where power can be delivered is much higher. The inductivity of the
lines will turn the phase between voltage and current, so there is a maximum
distance until the angle is 90° and no real power can be transmitted.
--
ciao Ban
Bordighera, Italy

Thanks for the heads-up; was not aware of any power below 25cps (not
counting DC).