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How to use FEMM 4.2, need help.

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Patrick

Wed Aug 31 2011, 02:53AM

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

Following up on my previous related thread here:

i really need help figuring this out, Ive tried over the past 2 weeks to read the help file, but i just dont see how to get a useful result.

Im grateful to "2spoons" for his help, but i need a step-by-step click-by-click example on a file like this one, so i can see how its done.

]twocircles.zip[/file]

The larger outer circle would be the enviromental boundary, the left circle should be 14kv and right should be 0 volts, while the free space should be oil dielectric which is in the materials library. (in inches)

TY for any help.

EDIT: this pdf is helping, ill try again tomarrow morning. FEmm
]tutorial-electrostatic.pdf[/file]

Patrick

Thu Sept 01 2011, 04:38AM

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

Ive gotten this far, but still dont really see how this program works.

It looks like this.

but should look like this.

2Spoons

Thu Sept 01 2011, 05:59AM

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

FEMM discussion group on yahoo :

Patrick

Thu Sept 01 2011, 06:13AM

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

Im trying to do some analysis on the field distrubution on the HV resistors seen below.

1314857610 2431 FT123350 Fileld Analyisis1

--On the left, the long resistors are 20kV, 75Mohm, which had the blue silicone removed via sandpaper. This resistor is thus destroyed.

--On the right, the shorter resistors are 14kV, 125Mohm, MEK was used to removed the silicone which came off so easily this resistor is probably still useable.

*Notice the bottom 0.2 inches are different, and would have a different field distrubution, presumably.

Mattski

Thu Sept 01 2011, 06:46AM

Registered Member #1792 Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527

Looks like you've set the top right two line segments to 1V as well the two line segments they are facing. The "inner" two line segments should be 1V and the outer two should be 0V if you're following the tutorial. See below:

Patrick

Thu Sept 01 2011, 06:54AM

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

Mattski wrote ...

Looks like you've set the top right two line segments to 1V as well the two line segments they are facing. The "inner" two line segments should be 1V and the outer two should be 0V if you're following the tutorial. See below:

Ooops! your right.

Yay! (i changed the field from 0-1V to 0-1kV just to see what would happen)

TY, Mattski

jpsmith123

Thu Sept 01 2011, 02:34PM

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

Patrick I'm curious as to why you want to model these resistors? Is it just so you can learn how to do field simulations, or is there some other reason?

Patrick

Thu Sept 01 2011, 06:32PM

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

jpsmith123 wrote ...

Patrick I'm curious as to why you want to model these resistors? Is it just so you can learn how to do field simulations, or is there some other reason?

Reason: HV oscilloscope probes, high bandwidth.

Ive been thinking about Marco Denicolai's tesla coil + 600kV 10MhZ probe. Field analysis has proved to be important in desinging low capactance high bandwidth probes. (I think ive been following his work since 2000 or 2001 ?! WOW thats like about 10 years.)

At

he gives a good explanation of the field arrrangement and step response vs time.

My current thinking has me wanting to simulate grading plates for field control, on the top and bottom of the resistor string.

EDIT: Im going to presume that the funny greek symbol here (Epsilon sub X, and Epsilon sub Y), means dielectric constant or permitivity? I also assume some materials can show polarized field propagation? thus the different fields ?

Patrick

Fri Sept 02 2011, 04:51AM

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

Woooo Hoooo! Ive got it figured out!

Its about dam time.

Teal = 0 volts
Magenta = 14.5kV
Yellow = 7kV

A well linearized field seen above.

Much thanks to 2Spoons!

Mattski

Fri Sept 02 2011, 06:47AM

Registered Member #1792 Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527

wrote ...
EDIT: Im going to presume that the funny greek symbol here (Epsilon sub X, and Epsilon sub Y), means dielectric constant or permitivity? I also assume some materials can show polarized field propagation? thus the different fields ?

Yep, it's relative dielectric constant. Materials which are anisotropic (as opposed to isotropic) can have a material property such as dielectric constant which depends on the direction in which the field is applied. I'm not aware of common dielectrics which exhibit dielectric anisotropy though, generally you need to have a crystal for anisotropy.

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