Military electronics

D

Dan Allen

Guest
Hiya,

How is it that military electronics, which have linear psu, can use an
input freq. from 40 to 400Hz??

I always thought the transformers were designed for one input
frequency.

I know the reason they have 400Hz, as it is what comes out from a
vehicle's alternator....but how do they make the transformer cover
that range, and keep the same rating / output voltage??

--
Dan
in UK
 
"Dan Allen" <dan@removethisbit.andthisbit.valvesunlimited.demon.co.uk> wrote
in message news:457h905671bspikp798ioghkalvlsvcv61@4ax.com...
Hiya,

How is it that military electronics, which have linear psu, can use an
input freq. from 40 to 400Hz??

I always thought the transformers were designed for one input
frequency.

I know the reason they have 400Hz, as it is what comes out from a
vehicle's alternator....but how do they make the transformer cover
that range, and keep the same rating / output voltage??

--
Dan
in UK
Click to expand...
A core material with sufficiently low losses allows a 40Hz transformer to
operate at 400Hz. Given the transformer equatio V=NBAw w=2*pi*f then B is
proportional to V/f. If f rises, flux density B is reduced. Therefore it is
sufficient to choose area A, flux swing B for Vinmax and fmin. Note:
4.44=2*pi/sqrt(2) for V as rms value (rms=peak/sqrt(2))

In theory you could run any 50Hz/60Hz xfmr at 400Hz. In practice you cant -
50Hz/60Hz transformers use the cheapest steel they can get away with, and
push it as hard as possible. Its high frequency losses are TERRIBLE, even
taking into account the reduction in B with increasing f - so much so that
it can be shown that transformers with more expensive core material (high
capital cost) are cheaper in the long run, due to the continuous loss in the
crappy 50/60Hz material.

cheers
Terry
 
On Wed, 5 May 2004 20:09:04 -0700, "Terry Given"
<the_domes@xtra.co.nz> wrote:

"Dan Allen" <dan@removethisbit.andthisbit.valvesunlimited.demon.co.uk> wrote
in message news:457h905671bspikp798ioghkalvlsvcv61@4ax.com...
Hiya,

How is it that military electronics, which have linear psu, can use an
input freq. from 40 to 400Hz??

I always thought the transformers were designed for one input
frequency.

I know the reason they have 400Hz, as it is what comes out from a
vehicle's alternator....but how do they make the transformer cover
that range, and keep the same rating / output voltage??

--
Dan
in UK

A core material with sufficiently low losses allows a 40Hz transformer to
operate at 400Hz. Given the transformer equatio V=NBAw w=2*pi*f then B is
proportional to V/f. If f rises, flux density B is reduced. Therefore it is
sufficient to choose area A, flux swing B for Vinmax and fmin. Note:
4.44=2*pi/sqrt(2) for V as rms value (rms=peak/sqrt(2))

In theory you could run any 50Hz/60Hz xfmr at 400Hz. In practice you cant -
50Hz/60Hz transformers use the cheapest steel they can get away with, and
push it as hard as possible. Its high frequency losses are TERRIBLE, even
taking into account the reduction in B with increasing f - so much so that
it can be shown that transformers with more expensive core material (high
capital cost) are cheaper in the long run, due to the continuous loss in the
crappy 50/60Hz material.
Click to expand...
I reckon rectumfry, filter and chop is the easiest way. Wheather the
militia men like or not maybe a different story
 
"Dan Allen" <dan@removethisbit.andthisbit.valvesunlimited.demon.co.uk> wrote
in message news:457h905671bspikp798ioghkalvlsvcv61@4ax.com...
Hiya,

How is it that military electronics, which have linear psu, can use an
input freq. from 40 to 400Hz??

I always thought the transformers were designed for one input
frequency.

I know the reason they have 400Hz, as it is what comes out from a
vehicle's alternator....but how do they make the transformer cover
that range, and keep the same rating / output voltage??
Click to expand...
I'm never seen hardware like this. The main specification for military
aircraft power is MIL-STD-704, and the two types of AC power it
specifies is single phase 115 VAC 60 HZ, and and single/three phase
115/200 VAC 400 HZ. There is an allowance in some cases for the
400 HZ to actually be 360 to 800 HZ.
 
On Wed, 5 May 2004 14:42:16 GMT, I was awakened by "Ken Finney"
<kenneth.c.finney@boeing.com> in sci.electronics.design who caused me
to spill hot coffee on my keyboard by writing the following:

"Dan Allen" <dan@removethisbit.andthisbit.valvesunlimited.demon.co.uk> wrote
in message news:457h905671bspikp798ioghkalvlsvcv61@4ax.com...
Hiya,

How is it that military electronics, which have linear psu, can use an
input freq. from 40 to 400Hz??

I always thought the transformers were designed for one input
frequency.

I know the reason they have 400Hz, as it is what comes out from a
vehicle's alternator....but how do they make the transformer cover
that range, and keep the same rating / output voltage??


I'm never seen hardware like this. The main specification for military
aircraft power is MIL-STD-704, and the two types of AC power it
specifies is single phase 115 VAC 60 HZ, and and single/three phase
115/200 VAC 400 HZ. There is an allowance in some cases for the
400 HZ to actually be 360 to 800 HZ.


I have a Valve Volt Meter CT343, about 1970, J.S (NATO) Number
Click to expand...
6625-99-943-6282. This is UK military

That's all I know about it. The input voltage is 100 - 250 1ph 40 -
400hz.

Same with the RF freq. meter I have, but the input voltage is fixed at
115v, and it is US Navy.

Maybe there are differnt US and UK spec, I don't know, but I've seen
quite a bit of UK kit, rated 1ph & 3ph 40-400hz


--
Dan in UK
 
Dan Allen wrote:
On Wed, 5 May 2004 14:42:16 GMT, I was awakened by "Ken Finney"
kenneth.c.finney@boeing.com> in sci.electronics.design who caused me
to spill hot coffee on my keyboard by writing the following:


"Dan Allen" <dan@removethisbit.andthisbit.valvesunlimited.demon.co.uk> wrote
in message news:457h905671bspikp798ioghkalvlsvcv61@4ax.com...

Hiya,

How is it that military electronics, which have linear psu, can use an
input freq. from 40 to 400Hz??

I always thought the transformers were designed for one input
frequency.

I know the reason they have 400Hz, as it is what comes out from a
vehicle's alternator....but how do they make the transformer cover
that range, and keep the same rating / output voltage??


I'm never seen hardware like this. The main specification for military
aircraft power is MIL-STD-704, and the two types of AC power it
specifies is single phase 115 VAC 60 HZ, and and single/three phase
115/200 VAC 400 HZ. There is an allowance in some cases for the
400 HZ to actually be 360 to 800 HZ.



I have a Valve Volt Meter CT343, about 1970, J.S (NATO) Number
6625-99-943-6282. This is UK military

That's all I know about it. The input voltage is 100 - 250 1ph 40 -
400hz.

Same with the RF freq. meter I have, but the input voltage is fixed at
115v, and it is US Navy.

Maybe there are differnt US and UK spec, I don't know, but I've seen
quite a bit of UK kit, rated 1ph & 3ph 40-400hz
Click to expand...
Probably because it's a fairly low-power device, so they can spend a few
extra $$ on the transformer in return for being able to plug it in anywhere.

I would be surprised with something that's wired into the aircraft and
has such a wide input range unless it's either small or uses a switching
supply.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
 
"Dan Allen" <dan@removethisbit.andthisbit.valvesunlimited.demon.co.uk> wrote
in message news:457h905671bspikp798ioghkalvlsvcv61@4ax.com...
Hiya,

How is it that military electronics, which have linear psu, can use an
input freq. from 40 to 400Hz??

I always thought the transformers were designed for one input
frequency.

I know the reason they have 400Hz, as it is what comes out from a
vehicle's alternator....but how do they make the transformer cover
that range, and keep the same rating / output voltage??
Click to expand...
It is common in military aircraft electrical systems.
 
"Dan Allen" <dan@removethisbit.andthisbit.valvesunlimited.demon.co.uk> wrote
in message news:ds2i90lafoe93dk9hdarm9bu579pb5ghm1@4ax.com...
On Wed, 5 May 2004 14:42:16 GMT, I was awakened by "Ken Finney"
kenneth.c.finney@boeing.com> in sci.electronics.design who caused me
to spill hot coffee on my keyboard by writing the following:


"Dan Allen" <dan@removethisbit.andthisbit.valvesunlimited.demon.co.uk
wrote
in message news:457h905671bspikp798ioghkalvlsvcv61@4ax.com...
Hiya,

How is it that military electronics, which have linear psu, can use an
input freq. from 40 to 400Hz??

I always thought the transformers were designed for one input
frequency.

I know the reason they have 400Hz, as it is what comes out from a
vehicle's alternator....but how do they make the transformer cover
that range, and keep the same rating / output voltage??


I'm never seen hardware like this. The main specification for military
aircraft power is MIL-STD-704, and the two types of AC power it
specifies is single phase 115 VAC 60 HZ, and and single/three phase
115/200 VAC 400 HZ. There is an allowance in some cases for the
400 HZ to actually be 360 to 800 HZ.


I have a Valve Volt Meter CT343, about 1970, J.S (NATO) Number
6625-99-943-6282. This is UK military

That's all I know about it. The input voltage is 100 - 250 1ph 40 -
400hz.

Same with the RF freq. meter I have, but the input voltage is fixed at
115v, and it is US Navy.

Maybe there are differnt US and UK spec, I don't know, but I've seen
quite a bit of UK kit, rated 1ph & 3ph 40-400hz
Click to expand...
Interesting. The main reason (a primary reason?) for the 400 Hz is so that
magnetics can be smaller and lighter on aircraft. Having magnetics that
can operate at 40 Hz sort of compromises the size and weight savings.

On another topic, I just finished reading a UK book on kit cars. I'm
astounded by the number of different words we have for the same
things (e.g. "valve" and "tube"). I knew about "spanners" and "the
bonnet", but the number of other words in this book astounded me.
Truly, we are a people divided by a common language.
 
On Wed, 5 May 2004 16:48:51 GMT, I was awakened by "Ken Finney"
<kenneth.c.finney@boeing.com> in sci.electronics.design who caused me
to spill hot coffee on my keyboard by writing the following:

Same with the RF freq. meter I have, but the input voltage is fixed at
115v, and it is US Navy.

Maybe there are differnt US and UK spec, I don't know, but I've seen
quite a bit of UK kit, rated 1ph & 3ph 40-400hz

Interesting. The main reason (a primary reason?) for the 400 Hz is so that
magnetics can be smaller and lighter on aircraft. Having magnetics that
can operate at 40 Hz sort of compromises the size and weight savings.

On another topic, I just finished reading a UK book on kit cars. I'm
astounded by the number of different words we have for the same
things (e.g. "valve" and "tube"). I knew about "spanners" and "the
bonnet", but the number of other words in this book astounded me.
Truly, we are a people divided by a common language.
Click to expand...
Another interesting thing I just found out. The US Navy Frequency
meter is rated 115v AC 50 to 1000Hz, Yes 1Khz!!!

That's what I though, higher mains freq. less iron, so the unit is
less overall weight - ideal for aircraft as eveyone says.

But as you've pointed out, if it works at 40Hz too, there is no weight
saving.

Think I'm going to see if I can find out more somewhere, very
intersting subject I just found:)

Thanks to those who have replied so far. All the equipment uses linear
power supplies, although all equipment is valve (tube) maybe that has
something to do with it....

I've found it intersting the differances between our words, and your
words, but meaning the same thing.

--
Dan
 
On Wed, 5 May 2004 20:09:04 -0700, I was awakened by "Terry Given"
<the_domes@xtra.co.nz> in sci.electronics.design who caused me to
spill hot coffee on my keyboard by writing the following:

"Dan Allen" <dan@removethisbit.andthisbit.valvesunlimited.demon.co.uk> wrote
in message news:457h905671bspikp798ioghkalvlsvcv61@4ax.com...
Hiya,

How is it that military electronics, which have linear psu, can use an
input freq. from 40 to 400Hz??

I always thought the transformers were designed for one input
frequency.

I know the reason they have 400Hz, as it is what comes out from a
vehicle's alternator....but how do they make the transformer cover
that range, and keep the same rating / output voltage??

--
Dan
in UK

A core material with sufficiently low losses allows a 40Hz transformer to
operate at 400Hz. Given the transformer equatio V=NBAw w=2*pi*f then B is
proportional to V/f. If f rises, flux density B is reduced. Therefore it is
sufficient to choose area A, flux swing B for Vinmax and fmin. Note:
4.44=2*pi/sqrt(2) for V as rms value (rms=peak/sqrt(2))

In theory you could run any 50Hz/60Hz xfmr at 400Hz. In practice you cant -
50Hz/60Hz transformers use the cheapest steel they can get away with, and
push it as hard as possible. Its high frequency losses are TERRIBLE, even
taking into account the reduction in B with increasing f - so much so that
it can be shown that transformers with more expensive core material (high
capital cost) are cheaper in the long run, due to the continuous loss in the
crappy 50/60Hz material.

Well I know SMPSU's rectifies the mains to DC, the switches it with
Click to expand...
transistors to a higher frquency, I think 400hz, for that reason, to
use less iron in the power transformers.

But I can't see how it would work in these linear supplies I have.

I know that's not what you said above, just me thinking 'out loud'

I must addmit the transformers do look higher quality than, el-cheapo
power trans from RS.

Cheers

--
Dan
 
"Dan Allen" <dan@removethisbit.andthisbit.valvesunlimited.demon.co.uk> wrote
in message news:457h905671bspikp798ioghkalvlsvcv61@4ax.com...
Hiya,

How is it that military electronics, which have linear psu, can use an
input freq. from 40 to 400Hz??

I always thought the transformers were designed for one input
frequency.

I know the reason they have 400Hz, as it is what comes out from a
vehicle's alternator....but how do they make the transformer cover
that range, and keep the same rating / output voltage??

--
Dan
in UK
Click to expand...
Dan,

I once measured the frequency response of a 60 Hertz transformer. It
actually had a bit less loss at 400 Hz than 60. Now this was one particular
transformer. I also tested a 60 Hz transformer in an audio circuit at 8
Ohms. Produced a somewhat mellow, but quite pleasing sound ( Comm receiver,
not HiFi). 40 Hz - don't know.

Tam
 
On Wed, 5 May 2004 18:00:57 UTC, Dan Allen
<dan@removethisbit.andthisbit.valvesunlimited.demon.co.uk> wrote:

A core material with sufficiently low losses allows a 40Hz transformer to
operate at 400Hz. Given the transformer equatio V=NBAw w=2*pi*f then B is
proportional to V/f. If f rises, flux density B is reduced. Therefore it is
sufficient to choose area A, flux swing B for Vinmax and fmin. Note:
4.44=2*pi/sqrt(2) for V as rms value (rms=peak/sqrt(2))

In theory you could run any 50Hz/60Hz xfmr at 400Hz. In practice you cant -
50Hz/60Hz transformers use the cheapest steel they can get away with, and
push it as hard as possible. Its high frequency losses are TERRIBLE, even
taking into account the reduction in B with increasing f - so much so that
it can be shown that transformers with more expensive core material (high
capital cost) are cheaper in the long run, due to the continuous loss in the
crappy 50/60Hz material.

Well I know SMPSU's rectifies the mains to DC, the switches it with
transistors to a higher frquency, I think 400hz, for that reason, to
use less iron in the power transformers.

But I can't see how it would work in these linear supplies I have.

I know that's not what you said above, just me thinking 'out loud'

I must addmit the transformers do look higher quality than, el-cheapo
power trans from RS.
Click to expand...
Terry's points are correct.

The losses in a transformer are usually considered as "iron" losses
and "copper" losses. The iron losses are dependent on hysteresis loss
in the core material and eddy current losses. "crappy" material is
likely to have a higher hysteresis loss. eddy current losses are
reduced by using thinner laminations. The minimum operating frequency
of a transformer depends on the total iron in the core (Terry's
point). So providing a low hysteresis material is used with thin
laminations transformers can easily be designed for a wider than usual
input frequency.

Remember that valve (tube for our US friends!) amplifiers used
transformers for the full audio range 20 Hz to 20 kHz.

The reason the military use 400 Hz is to reduce the wieght of the
transformer - very important in aircraft. A transfomrer designed to
work from 40 Hz to 400 Hz will have as much iron as a 40 Hz single
frequency transformer and laminations as thin as for a 400 Hz
transformer.

The linear regulator aspect is not an issue - all that the design
needs to do is to ensure that the ripple voltage at the lowest
frequency is small enough to prevent the regulator dropping out.

BTW SMPS usually operate at 20 kHz or higher - probably these days the
frequency is more like 500 kHz.

--
Jim Backus
jim <dot> backus <the circle thingy> jita <dot> demon <dot> co <dot>
uk
 
"Dan Allen" <dan@removethisbit.andthisbit.valvesunlimited.demon.co.uk> wrote
in message news:32ai90hhrpbnvb8kvh4hrulfkjurqrhngb@4ax.com...
On Wed, 5 May 2004 16:48:51 GMT, I was awakened by "Ken Finney"
kenneth.c.finney@boeing.com> in sci.electronics.design who caused me
to spill hot coffee on my keyboard by writing the following:


Same with the RF freq. meter I have, but the input voltage is fixed at
115v, and it is US Navy.

Maybe there are differnt US and UK spec, I don't know, but I've seen
quite a bit of UK kit, rated 1ph & 3ph 40-400hz

Interesting. The main reason (a primary reason?) for the 400 Hz is so
that
magnetics can be smaller and lighter on aircraft. Having magnetics that
can operate at 40 Hz sort of compromises the size and weight savings.

On another topic, I just finished reading a UK book on kit cars. I'm
astounded by the number of different words we have for the same
things (e.g. "valve" and "tube"). I knew about "spanners" and "the
bonnet", but the number of other words in this book astounded me.
Truly, we are a people divided by a common language.

Another interesting thing I just found out. The US Navy Frequency
meter is rated 115v AC 50 to 1000Hz, Yes 1Khz!!!
Click to expand...
You might be interested to know that some UK aircraft during WW2 used 1600Hz
to get the weight of equipment down.

A friend of mine also presented a paper to the UK MOD about 30 years ago,
proposing that the aircraft nominal 28V supply should be raised to
approximately 80V to save weight on the wiring. There would be a slight
increase in battery weight. The technical arguments for the changeover were
valid apart from the problems of actually implementing it.

That's what I though, higher mains freq. less iron, so the unit is
less overall weight - ideal for aircraft as eveyone says.

But as you've pointed out, if it works at 40Hz too, there is no weight
saving.

Think I'm going to see if I can find out more somewhere, very
intersting subject I just found:)

Thanks to those who have replied so far. All the equipment uses linear
power supplies, although all equipment is valve (tube) maybe that has
something to do with it....

I've found it intersting the differances between our words, and your
words, but meaning the same thing.

--
Dan
Click to expand...
 
"Graham Holloway" <eng@wps-electronics.demon.co.uk> wrote in
message news:c7cpe1$ajv$1$830fa7a5@news.demon.co.uk...
"Dan Allen"
dan@removethisbit.andthisbit.valvesunlimited.demon.co.uk
Click to expand...
wrote
in message
news:32ai90hhrpbnvb8kvh4hrulfkjurqrhngb@4ax.com...
On Wed, 5 May 2004 16:48:51 GMT, I was awakened by "Ken
Finney"
kenneth.c.finney@boeing.com> in sci.electronics.design
who caused me
to spill hot coffee on my keyboard by writing the
following:


Same with the RF freq. meter I have, but the input
voltage is fixed at
115v, and it is US Navy.

Maybe there are differnt US and UK spec, I don't
know, but I've seen
quite a bit of UK kit, rated 1ph & 3ph 40-400hz

Interesting. The main reason (a primary reason?) for
the 400 Hz is so
that
magnetics can be smaller and lighter on aircraft.
Having magnetics that
can operate at 40 Hz sort of compromises the size and
weight savings.

On another topic, I just finished reading a UK book on
kit cars. I'm
astounded by the number of different words we have for
the same
things (e.g. "valve" and "tube"). I knew about
"spanners" and "the
bonnet", but the number of other words in this book
astounded me.
Truly, we are a people divided by a common language.

Another interesting thing I just found out. The US Navy
Frequency
meter is rated 115v AC 50 to 1000Hz, Yes 1Khz!!!

You might be interested to know that some UK aircraft
during WW2 used 1600Hz
to get the weight of equipment down.

A friend of mine also presented a paper to the UK MOD
about 30 years ago,
proposing that the aircraft nominal 28V supply should be
raised to
approximately 80V to save weight on the wiring. There
would be a slight
increase in battery weight. The technical arguments for
the changeover were
valid apart from the problems of actually implementing it.
Click to expand...

The Bloodhound Ground to Air Guided missile (UK origin) had
an electronic system supplied with 1600hz (IIRC) power for
normal logic (Valves (tubes) etc) and 400hz 115volts 3
phase for gyros and other rotating things (antenna).
This power was generated in flight by a hydralic moter
altnator set.
But for ground testing in the workshop there was provided
1600hz supplies generated by an oscillator and a Valve power
amplifer capable of the required kilowatt or so. These were
Public Address amplifiers with the fixed input frequency.
This missile was developed in the 50s and only had a few
tranistors in circuits that failled development tests and
had to be redesigned late in the test phase.


--
John G

Wot's Your Real Problem?
 
"Jim Backus" <jhb@nospam.co.uk> wrote in message
news:TpquPuPd0tCd-pn2-qyV6UkYCpcBW@localhost...
On Wed, 5 May 2004 18:00:57 UTC, Dan Allen
dan@removethisbit.andthisbit.valvesunlimited.demon.co.uk> wrote:

A core material with sufficiently low losses allows a 40Hz transformer
to
operate at 400Hz. Given the transformer equatio V=NBAw w=2*pi*f then B
is
proportional to V/f. If f rises, flux density B is reduced. Therefore
it is
sufficient to choose area A, flux swing B for Vinmax and fmin. Note:
4.44=2*pi/sqrt(2) for V as rms value (rms=peak/sqrt(2))

In theory you could run any 50Hz/60Hz xfmr at 400Hz. In practice you
cant -
50Hz/60Hz transformers use the cheapest steel they can get away with,
and
push it as hard as possible. Its high frequency losses are TERRIBLE,
even
taking into account the reduction in B with increasing f - so much so
that
it can be shown that transformers with more expensive core material
(high
capital cost) are cheaper in the long run, due to the continuous loss
in the
crappy 50/60Hz material.

Well I know SMPSU's rectifies the mains to DC, the switches it with
transistors to a higher frquency, I think 400hz, for that reason, to
use less iron in the power transformers.

But I can't see how it would work in these linear supplies I have.

I know that's not what you said above, just me thinking 'out loud'

I must addmit the transformers do look higher quality than, el-cheapo
power trans from RS.


Terry's points are correct.

The losses in a transformer are usually considered as "iron" losses
and "copper" losses. The iron losses are dependent on hysteresis loss
in the core material and eddy current losses. "crappy" material is
likely to have a higher hysteresis loss. eddy current losses are
reduced by using thinner laminations. The minimum operating frequency
of a transformer depends on the total iron in the core (Terry's
point). So providing a low hysteresis material is used with thin
laminations transformers can easily be designed for a wider than usual
input frequency.

Remember that valve (tube for our US friends!) amplifiers used
transformers for the full audio range 20 Hz to 20 kHz.
Click to expand...
this makes the transformer design quite a bit trickier - "crappy" materials
wont work very well at all at 20kHz. I have used conventional iron-cored
chokes on the output of AC drives switching at 10kHz - this is a great way
to set them on fire, even 1A at 10kHz in a 50A 50Hz choke will COOK IT,
mostly due to core losses, which tend to go up as around f^2. Actually core
loss can be approximated by P = k*(B^m)*(f^n) where m = 1.6 or so, n = 2 or
so for steels. m,n can be found for a variety of materials eg ferrite (most
manufacturers give you this info). It is clear if m=1.6 and n=2 then as f
increases, although B goes down in proportion to f, k*(B^1.6)*(f^2) =
k2*(f^0.4)still goes up.

The reason the military use 400 Hz is to reduce the wieght of the
transformer - very important in aircraft. A transfomrer designed to
work from 40 Hz to 400 Hz will have as much iron as a 40 Hz single
frequency transformer and laminations as thin as for a 400 Hz
transformer.
Click to expand...
absolutely. It will, however, handle anything you can throw at it, ie is
grunt-proof - obviously an advantage for military equipment (else they
wouldnt have made it)

The linear regulator aspect is not an issue - all that the design
needs to do is to ensure that the ripple voltage at the lowest
frequency is small enough to prevent the regulator dropping out.

BTW SMPS usually operate at 20 kHz or higher - probably these days the
frequency is more like 500 kHz.
Click to expand...
yeah, not much point in only switching at 400Hz or so, unless the switches
are very slow, say SCR's.

--
Jim Backus
Click to expand...
Thanks Jim, nicely elucidated. Most of the 50Hz transformer manufacturers I
have spoken to in NZ dont even use grain-oriented silicon steel (this has
much lower hysteretic losses, as most of the domains within the material are
aligned by the manufacturing process. Ferromagnetics, Bozorth is a great
ref. if interested)- if you look at the flux path in an E core, it makes a
whole bunch of right-angle turns, which kind of defeats the purpose of grain
orientation. tape-wound toroidal cores do not suffer from this limitation,
and utilise grain oriented materials to very good effect. Metglass and other
such amorphous materials have such low hysteretic losses that they can be
used at smps frequencies - in which case the "lamination" or strip thickness
is on the order of 15um IIRC (cf 1mm lam's in an ordinary 50Hz xfmr) - mind
you, its so damn expensive you wouldnt want to use it....

Terry
 
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