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

# Re: [femm] Current transformer ...

- To: femm@yahoogroups.com
- Subject: Re: [femm] Current transformer ...
- From: David Meeker <dmeeker@foster-miller.com>
- Date: Tue, 08 May 2001 15:59:28 -0400
- Organization: Foster-Miller, Inc.
- References: <3AF66A63.26680.FD8AB3B@localhost>

jrcamacho@ufu.br wrote:

> Dear femm friends,
> I am doing an analysis on femm of a six current transformers
> connected to a generator neutral, due lack on information I would
> like to know magnetic properties of two materials used in these
> transformers.
> First: What magnetic material is generically used in the core? M36-
> Steel?

I often use 0.014 inch thick M19 laminations as sort of a "generic" but quality steel. This type of steel is described as:
"at the top of the scale for desirable core-loss properties. Very good permeability at low and intermediate inductions. The list of applications includes high-efficiency rotating equipment, relays, and dry-type transformers. Especially applicable when highest possible energy efficiency is desired or when efficiency increase is to be obtained without change of shape, size, or weight of motor."

> Second: The magnetic property of Epoxy? The information on
> "sigma" is needed for this material.

For the purposes of a magnetics finite element analysis, it is probably OK to assume that the epoxy has a permeability of 1 and an electrical conductivity of 0. However, there are special-purpose types of epoxy that are intentionally doped to make them electrically conductive for the purpose of electrostatic shielding, or filled with powdered iron to make solid ferromagnetic cores that aren't subject to eddy current losses (see here for example). However, I'd guess that your in your case, the epoxy is just used to pot your transformer, rather than for some other special purpose.

> Third: What is the range of current density generically used in the
> secondary of these transformers?

The current density at which you can operate has a strong dependence on thermal considerations (how much heat you can reject). That being said, however, you often see bulk current densities (i.e. averaged over the entire cross-section of occupied by the coil consisting of the wire, insulation, and the space between wires) in electric machines of between 1 and 5 MA(rms)/m^2, with something like 2 MA(rms)/m^2 being fairly typical. It is probably realistic to assume about a 0.5 fill factor (fraction of the bulk coil cross-section actually occupied by copper) for a "typical" transformer winding--a carefully made bobbin-wound coil is like 0.65-0.7

> Any clues will be welcome.

David Meeker

    begin:vcard
    n:Meeker;David
    tel;fax:781-890-3489
    tel;work:781-684-4070
    x-mozilla-html:TRUE
    url:http://members.aol.com/dcm3c
    org:Foster-Miller, Inc.;Electrical and Electronic Systems Group
    version:2.1
    email;internet:dmeeker@foster-miller.com
    title:Senior Engineer
    adr;quoted-printable:;;350 Second Avenue=0D=0A;Waltham;MA;02451-1196;USA
    fn:David Meeker, Ph.D.
    end:vcard

- References:
  - Current transformer ...
    - From: jrcamacho@ufu.br

- Prev by Date: Superconductor model
- Next by Date: Re: [femm] Superconductor model
- Previous by thread: Current transformer ...
- Next by thread: help: split-phase motors
- Index(es):
  - Date
  - Thread