[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

# Re: how do I model a torroidal transformer ?

- To: femm mailing list <femm@yahoogroups.com>
- Subject: Re: how do I model a torroidal transformer ?
- From: David Meeker <dmeeker@ieee.org>
- Date: Thu, 28 Aug 2003 12:33:21 -0400
- User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.4; MultiZilla v1.4.0.4A) Gecko/20030624

Keith Gregory wrote: All, I would use the current block for as quick model but points if I wanted to model individual turns - there could be a lot though! Anyway, I would think that a stored energy approach would give inductance with any method of representing the winding. It would be interesting to find out if anyone's got the time. I'm not sure how good inductances would be though because for a normal toroid the end winding is about the same size as the bits that are being modelled. Keith. Well, you have to be a bit careful in models with point currents. In theory, a coil composed of point currents has an infinite inductance. As you get closer and closer to the point, the field gets higher and higher. Ampere's loop law says that B=mu*i/(2*Pi*r) where r is the distance away from the point, mu is the permeability, and i is the point current. So, if you were integrating energy out to some particular radius, R, away from the wire, you'd be integrating B^2/(2 mu)*2*Pi*r from r=0 to R. Expanding this out a bit, one is integrating mu*i^2/(4*Pi*r). The 1/r type of integral doesn't converge if one of the limits of integration is zero. What this means to finite element results is that you will get reasonable flux density predictions with point currents if you aren't in close proximity to the points (e.g. at points inside the toroid); however, the stored energy (and therefore inductance) that you'd evaluate with point currents is highly dependent on mesh density. For example, I've attached a model that's sort of like a coax cable--a point current in the center of a 1 cm radius circular region with A=0 defined at the boundary. For an increasing mesh size, the stored energy per meter is: 0.1 cm mesh == 3.903e-07 J 0.05 == 4.833e-7 0.025 == 5.354e-7 0.0125 == 6.128e-7 0.00625 == 6.740e-7 0.003125 == 7.391e-7 Dave. -- David Meeker email: dmeeker@ieee.org www: http://femm.berlios.de/dmeeker

Attachment: `zip00051.zip`
Description: Zip compressed data

- Prev by Date: Re: [femm] how do I model a torroidal transformer ?
- Next by Date: Lua language
- Previous by thread: Re: [femm] how do I model a torroidal transformer ?
- Next by thread: B-H curve of neodymium magnet
- Index(es):
  - Date
  - Thread