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Science Forum Index » Optics Forum » transferring electrical energy through metal wall
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| Mark Fergerson |
 Posted: Fri Oct 24, 2003 7:34 pm |
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<snip>
Quote: Thank you for your reply. There is some electrical device inside of
the pressure vessel, which has to be powered up. The device moves, so
wires do not work (well enough). It has to be a contactless method of
transmission of energy through metal wall. The pressure is, say,
several tens or hundreds atmospheres. The prototype vessel has no
pressure in it yet, as I am just trying out to develop the energy
transmission system. I even allowed a hole in the wall, just to see if
this makes the transmission of magnetic field any easier through it
(the hole could be covered by a non-magnetic metal later, in
principle). The first (unpressurised) prototype is made of aluminium,
but ultimately it has to be made of steel to withstand the pressure.
A thicker Al vessel could likely hold the pressure you
require, but might be too clumsy or expensive. But that's a
moot point because most any metal will turn magnetic flux
into power-eating eddy currents.
The powered device moves, you say. This is a problem no
matter how you eventually get power through the vessel wall.
Consider your original idea; the coil inside the vessel is
the secondary of a transformer and should not move relative
to the primary (the coil outside the vessel) in order to
keep power transfer predictable. This means the device will
be moving relative to the secondary, which means you'll need
some kind of flexible cabling or other method to get power
from the secondary to the device. If the device has too many
degrees of freedom for flexible cabling, you might consider
slip rings (assuming the device is supported in some form of
gimbal).
The vessel will have transparent observation ports so you
can tell what's going on inside, right? Have you considered
shining a bright light through another transparent port and
using photovoltaic cells inside the vessel to convert it to
current for the device? Given the poor conversion efficiency
of PV cells you'll need a lot more than a watt of light
input, and there will still remain the internal cabling
issue since the PV cells should remain stationary within the
vessel for the same reason as above.
Quote: It has not been decided yet what kind of steel will be used; here I
heard the suggestions that stainless steel is non-magnetic (and can be
low-conductive), and therefore will provide less absorption of
magnetic field (how much less ??). I have the knowledge of physics,
but I am not a specialist in electromagnetism; I do not know
practically such details as -- e.g. what is the difference between
ordinary steel and soft iron; what are the principles determining the
shape and the position of the "soft iron" poles ? I inserted ferrite
core into the solenoid only because I heard that ferrites amplify the
magnetic field by an order of three. But maybe ferrite core has no
place in the system...
There are many kinds of stainless steels; some are only
"surface stainless", which means their properties are
inconsistent through their thickness. Also, not all
stainless steels are non-magnetic. For that matter, no steel
is completely non-magnetic, all convert some fraction of an
impressed magnetic field to heat. Some research on your part
is indicated to find out which steels will work best
(actually "least badly" as you will end up trading
properties such as mechanical against magnetic).
"Soft iron" is both mechanically and magnetically soft;
the latter means that its magnetic domains rotate readily
when subjected to a field, with much less resistance than
"hard" alloys, even stainless steels. It also has more
permeability than many other alloys, which means it
concentrates (not "magnifies") magnetic flux similarly to
the way ferrites do, which means there'll be less stray flux
to generate wasteful eddy currents in the vessel wall. It's
also easier to work with than ferrites; it's less brittle,
and can easily be heat-treated to restore its magnetic
properties after mechanical working.
The basic principle of using soft iron or ferrite is
analogous to electrical wiring; electrically good conductors
like copper wire confine and direct current where you want
it, similarly does an easily permeable material confine and
"conduct" magnetic flux where you want it.
I mentioned soft iron to direct the flux to the device
before I knew it moved. If you are determined to use
magnetic fields, and can successfully imbed either iron or
ferrite in the wall of the vessel to make a core for your
transformer (while maintaining pressure integrity), you can
sidestep some of the above problems.
I mean something like this;
power input
(primary winding)
| |
__|______|___
outside | _/_/_/_/_ |<-- soft iron or ferrite core
_ _ ____| |_________| |___ _ _
_ _ ____| |_________| |___ _ _<-- vessel wall
| |_________| |
inside |___/_/_/_/___|
| |
| |
(secondary winding)
power to device
In the diagram, the vessel wall acts as a poor "magnetic
insulator" in a manner of speaking (a high-resistance
shorted turn, actually). The core would be made of sections
for easier assembly. You will still have the internal
cabling issue to the device, as well as mechanical supports
to figure out.
If the device didn't move, you'd simply leave out the
core section with the secondary winding and suspend the
device there; the core would then act as the "pole pieces" I
mentioned to direct the flux. A secondary winding fixed to
the device would convert the flux to usable current. If you
can restrict the motion of the device such that it sees
adequate flux at all times this might work, assuming the
magnetic properties of the rest of the device's structure
don't interfere too badly.
I don't intend to discourage you by pointing out all
these problems, but you must realize you presented a
particularly thorny question.
Mark L. Fergerson
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| Don Kelly |
| Posted: Sat Oct 25, 2003 5:23 pm |
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"Chuck" <trainman_7@msn.com> wrote in message
news:9b56f165.0310231606.1b8149b7@posting.google.com...
Quote: va1erian@mail.ru (va1erian@mail.ru) wrote in message
news:<487b31fd.0310220341.3eb1bb99@posting.google.com>...
Dear everyone,
Valerian, there is an approach which doesn't require you to drill a hole
through the vessel in order to transmit information into the interior of
the >vessel. The drawback is that it most likely requires more than 1 watt
of power. The
Quote: approach is the following: On the transmit side form two concentric
coils. The
first set is used to generate a large dc field in the metal so that
it becomes >magnetically saturated. This will reduce the permeability
to near free space >levels. When this occurs you will be able to use
the second set of coils to >transmit a ac field into your vessel.
--------
A problem with this is that when the metal is saturated, the second set of
coils will have no effect on the d(phi)/dt unless it overcomes the
saturation- at which point the permeability of the metal will not be near
that of free space.
--
Don Kelly
dhky@peeshaw.ca
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| Don Kelly |
| Posted: Sat Oct 25, 2003 7:08 pm |
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"Don Kelly" <dhky@peeshaw.ca> wrote in message
news:2CDmb.178272$9l5.83448@pd7tw2no...
Quote:
"Chuck" <trainman_7@msn.com> wrote in message
news:9b56f165.0310231606.1b8149b7@posting.google.com...
va1erian@mail.ru (va1erian@mail.ru) wrote in message
news:<487b31fd.0310220341.3eb1bb99@posting.google.com>...
Dear everyone,
Valerian, there is an approach which doesn't require you to drill a
hole
through the vessel in order to transmit information into the interior of
the >vessel. The drawback is that it most likely requires more than 1 watt
of power. The
approach is the following: On the transmit side form two concentric
coils. The
first set is used to generate a large dc field in the metal so that
it becomes >magnetically saturated. This will reduce the permeability
to near free space >levels. When this occurs you will be able to use
the second set of coils to >transmit a ac field into your vessel.
--------
A problem with this is that when the metal is saturated, the second set of
coils will have no effect on the d(phi)/dt unless it overcomes the
saturation- at which point the permeability of the metal will not be near
that of free space.
--
Don Kelly
dhky@peeshaw.ca
remove the urine to answer
Sorry- on second thought, I am wrong. However, in such a situation, the
"transformer" will have to be treated as an air coil unit as the DC
saturation will also affect any cores inside and outside the tank.
--
Don Kelly
dhky@peeshaw.ca
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| Philip Felton |
| Posted: Sun Oct 26, 2003 1:33 am |
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"va1erian@mail.ru" wrote:
Quote: Dear everyone,
I am doing a project to transfer electrical energy (about 1 W, pulsed)
through the metal wall (5-10 mm thick) of a pressurised vessel with an
efficiency 10%. I have considered the options to transfer acoustically
or optically, but the only suitable method turned out to be the
magnetic one. A primary coil on one side of the wall is fed with
pulsing/AC current, the resulting pulsing/AC magnetic field is
transferred through the metal wall, and the secondary coil on the
other side transforms the magnetic field into electrical current.
The only problem was that the steel wall absorbed all of the magnetic
field. I had to drill a hole in the wall of the physical model, so
that to allow the passage of the magnetic field. I inserted the
primary coil into the hole perpendicularly to the wall, and put the
secondary coil behind the wall with its axes parallel to the wall (for
certain reasons). Without the metal wall, the configuration of the
primary/secondary coil worked fine. But the introduction of the wall
into the system brought the voltage in the secondary coil close to
zero. It got me thinking -- I decided that even if the magnetic field
lines could get through the hole in the wall along the inserted coil
core, the lines had to return to the other magnetic pole of the
primary coil. And this was where the metal wall was the barrier to the
lines ! I thought that I would have to enlarge the hole and introduce
an air (magnetically easily penetratable) gap between the primary coil
and surrounding metal.
The question is, how large the hole has to be, so that to allow the
return passage of the magnetic field lines into the opposite pole of
the primary coil ? I thought I could use a simulation package to
analyse the distribution of magnetic lines, and thus I could find out
the effect of the size of the wall's hole on the efficacy of
transmission of magnetic energy through that hole. Can you recommend
me the simulation package which has a short and not-so-steep learning
curve ?
Your advice would be appreciated.
Regards,
Va1erian
A simple way to introduce electrical power into a pressure vessel is to
use a spark plug as an insulated feed-through, many different sizes and
designs. The insulator can be ground back to suit.
If the object you're transferring power to is moving you can use carbon
brushes.
Phil. |
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| Joseph.D.Warner |
| Posted: Mon Oct 27, 2003 11:17 pm |
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Child Taker wrote:
Quote: Mark Fergerson <nunya@biz.ness> wrote in message news:
snip
Thank you for your reply. There is some electrical device inside of
the pressure vessel, which has to be powered up. The device moves, so
wires do not work (well enough). It has to be a contactless method of
transmission of energy through metal wall. The pressure is, say,
several tens or hundreds atmospheres. The prototype vessel has no
pressure in it yet, as I am just trying out to develop the energy
transmission system. I even allowed a hole in the wall, just to see if
this makes the transmission of magnetic field any easier through it
(the hole could be covered by a non-magnetic metal later, in
principle).
<snip>
If that is what you need to do then using a ceramic-metal feedthrough
with the appropiate number of wires to bring the power to a device
inside the metal container and have that device wirelessly couple the
power to what every other instrument you have in the pressurized vessel.
Now you only have a few wires on the outside going to your power and
control circuitry.
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| va1erian@mail.ru |
| Posted: Mon Oct 27, 2003 11:18 pm |
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Mark, thank you for the scheme below. It is what I need. In the
prototype of the magnetic circuit, I glued up together the round
ferrite cores, and used a piece of 2 mm-thick steel just to try if the
energy transmission through the steel wall was reasonable. The output
of the secondary coil with the still wall in the magnetic circuit was
1/10 of the output of the secondary coil when the steel sheet was
removed from the magnetic circuit. I presume that the optimisation of
the magnetic circuit could provide an efficiency of transmission of at
least 50% or even more. I am thinking about using "soft iron" for
inductive core in the pressurised version of the apparatus, which will
allow to fix the iron cores into the steel wall and thus make the
vessel pressure-tight. I am thinking if I could use a magnetic field
modelling software package to analyze the magnetic circuit and to work
out the best circuit's configuration, the best magnetic parameters for
the soft iron cores and for steel etc. If you or someone could advice
me a suitable line of action (or software package), I would be
grateful.
Regards,
Va1erian
Quote: I mean something like this;
power input
(primary winding)
| |
__|______|___
outside | _/_/_/_/_ |<-- soft iron or ferrite core
_ _ ____| |_________| |___ _ _
_ _ ____| |_________| |___ _ _<-- vessel wall
| |_________| |
inside |___/_/_/_/___|
| |
| |
(secondary winding)
power to device
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| Steve Ivy |
| Posted: Tue Nov 04, 2003 3:26 am |
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Well it seems to me that the best answer is actually a compromise (or
a combination) of some of the other answers you have received so far.
1) Several people suggested high pressure feedthroughs (I agree)
2) You said that the parts receiving the energy inside the pressure
vessle must move (I take it they will rotate continuously?) and
therefore wires are not paractical (and for that matter I don't think
brushes are practical either since you will be operating the device in
a high pressure environment.)
so you feel that some sort of inductive coupling of the energy to the
moving parts is required. (Once again I agree)
So the answer is to put both your primary and your secondary on the
inside of the device and to power the primary via the high pressure
feed through and allow the secondary to move relative to the primary
to accomidate your necessary movement.
It sounds an awful lot like you are going to test a deepwater
submersible motor to me? Unless you are going to use a high pressure
gas?
This plan allows you to accomidate both the high pressure and still
have high electromagnetic conversion efficiency because you don't have
to resort to turning a bulkhead wall into a crappy transformer core.
Use a better and much more standard transformer/motor design instead.
Although this solution still avoids the basic problem of how to pass a
large amount of energy through a solid ferrous wall with resonable
efficiency and not drill holes?
That in it'self is an interesting question and I suggest that the
discussion continue on that problem.
Perhaps you could do it with with X-rays? I don't think so but I could
be wrong?
Thanks: Steve Ivy |
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