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Calculating Field Intensity at Edges of Cap Plates.

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Patrick

Tue Jul 19 2011, 06:04AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Im having trouble calculating field intensity (V per m) wether or not im going to have problems in oil given 14 kV on a copper foil 0.004 inches thick, along with 0.008 inches Mylar. Intensity of field is uniform between plates, but at the edges of the foil the field is more complicated.

Can anyone reccommend a field simulator/solver? and how to use it. (Im not good with integral calculus by the way.)

2Spoons

Tue Jul 19 2011, 06:16AM

Registered Member #2939 Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615

FEMM4.2 is a free 2D fea solver for magnetics, electrostatics, current flow and thermal.

Patrick

Tue Jul 19 2011, 06:19AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Pic of plates...[DXF file]

Ok, yellow plates are copper foil 0.004 inches thick, mylar is 0.0045 inches and ther are 2, so 0.008 or 0.009 total D, the potential is 14kV for a lifetime, and 20kV occasional surges. vacuum oil with all air displaced, i worry about sharp edges closely spaced causing corona or breakdown even under oil.

Screen Cap: from FEMM4.2,

Field intensity....

I have to admit this program is pretty cool, i need to figure out how E-field types work and how to load my geometry
and V locations though.

EDIT: this program is hard to figure out, i cant see how to get surfaces to a defined V, though i have my DXF loaded, so thats good.

EDIT: it keeps saying: "Materials have not been defined for all block labels, cannot anaylze the problem" damit

Patrick

Tue Jul 19 2011, 06:49PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

I cant figure this program out, need help please.

jpsmith123

Tue Jul 19 2011, 09:25PM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843

If I get a chance later I'll try to simulate it for you.

Patrick

Tue Jul 19 2011, 09:31PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

jpsmith123 wrote ...

If I get a chance later I'll try to simulate it for you.

TY, set the plates for 0 volts and 14,000 volts, and set the gap for transformer oil, which is in the material library.... hope this is enough info...

cant post a DXF though fourum wont allow it.
DXF in zip...
]dxffile.zip[/file]

jpsmith123

Tue Jul 19 2011, 10:00PM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843

In my never ending quest for a better field simulator (I'm still looking for something that can simulate switched charged conductors), I happened to see that Infolytica has an evaluation version of their ElecNet simulator that can be downloaded (I think you have to give them an email address or something). Unfortunately it's limited to 2D problems, whereas the full program will also do 3D.

If you look around, you might be able to find the full version somewhere as well.

So far I haven't done much with it myself, so I can't help you set up any problems yet.

Patrick

Tue Jul 19 2011, 10:18PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

can you simulate DXF files i give you?

I worry about the oil breaking down. i need a coaxial cap, 10pF at 14kV, ive increased the gap to 0.055" of oil, but the plates are only 0.004 inches thick...

tell me any other info you need, this is a pressing problem for me.

2Spoons

Tue Jul 19 2011, 10:46PM

Registered Member #2939 Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615

I've created a FEMM file for you. It is necessary to create an outer boundary for the problem, I like to use a big circle with the default boundary conditions which have the field gradient normal to the boundary = 0. If you make this outer boundary big enough it doesn't really affect the result in the areas of interest. I've added block labels for transformer oil and air. I know it seems odd to make the plates out of air, but it doesn't actually make any difference as the conductor is defined by the plate boundary. If you select one of the plate boundaries (it will go red) then open the properties box you will see I have added a "conductor" property to each line on the plate boundary. Conductors are defined in the 'properties' menu - I've defined one as zero volts and one as 14000 volts. Conductors are merely equipotential surfaces as far as electrostatics is concerned.

Now go play with your new toys !
]cplates.zip[/file]

2Spoons

Tue Jul 19 2011, 10:52PM

Registered Member #2939 Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615

Ran the sim - peak E field is ~2e9 volts/m. Did I get your units wrong in the dxf? I used mm. Switched to inches and got a field peak of 9e7 V/m.

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