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# hysteresis losses in enclosures

- To: femm@egroups.com
- Subject: hysteresis losses in enclosures
- From: erik_t_viking@my-deja.com
- Date: Wed, 25 Oct 2000 08:55:05 -0000
- User-agent: eGroups-EW/0.82

    Hello All,

    First of all, I'm new to this newsgroup and also to FEA and FEMM in
    particular. Having studied in Germany, I'll do my best to translate
    what little I know of electromagnetics into English.

    I'm trying to model hysteresis and eddy current losses we are
    experiencing in certain parts of enclosures of high-voltage
    switchgear our company is developing.

    The enclosures are oval, with half-circles (46 cm diameter) on each
    end, connected by parallel straight walls of 90 cm length. Thickness
    is 1 cm. Height varies between 80 and 150 cm for various design
    options. In this are, equally spaced with 45 cm, the three round
    aluminium conductors (diameter 10 cm) for phases R,S and T. Current
    is 4000 Amps (rms) at 50 Hz.
    The enclosure is filled with insulating gas (mu rel. = 1), the
    outside is plain air.

    Trying to reduce cost, the enclosures are made of low-grade steel
    known as Fe37, which has similar properties as the Steel M-36 from
    the Materials Library of FEMM. (mu rel. approx. 1600, sigma = 9.5
    MS/m)
    Experimental measurements of heat production result in 300-600 W/m2
    on the high-stressed left and right sides.
    However, results from FEMM show a maximum |B| of 0.15 T, reducing
    rapidly towards the outside. According to the hysteris curves I have,
    this should result in far less than 100 W/m2 hysteresis losses. Eddy
    current losses are then also neglegible.

    I'm using the following (planar) geometry:
    _______
    / \
    | O O O |
    \_______/ \_Fe37, 1 cm thickness

    R S T

    R: I=5657 + j0 Amps
    S: I=-2828 - j4898 Amps
    T: I=-2828 + j4898 Amps

    And now my questions, related to FEMM:

    1. Why is the electrical conductivity of ALL steels in FEMM set to 0?
    I'm using 9.5 MS/m as a normal value, about 1/3 of the 34.4 MS/m of
    Al.

    2. Can I model various phase-shifted currents by setting the real and
    imaginary parts of the current density? I'm using 0.72 MA/m2
    (resulting in a total peak value of 4000xsrt(2) Amps for the given
    conductors).

    3. What boundary conditions to specify for this kind of problems?

    4. Along the inner surface of the enclosure, I've specified a mesh of
    0.02 cm. Is this fine enough given the skin dept of slightly less
    than 1 mm? More nodes seems to crash this machine :-(

    5. Does anyone know a steel with a relative permeability of around
    1600 with 'worse' hysteresis properties as the M-36 steel?

    6. If |H| and |B| are known, then how do I estimate the resulting
    heat losess for this situation. I only have detailed curves for
    laminated transformer steels for |B| > 1 T, which of course are
    softer ferrites.

    I would appreciate the comments or experiences of anybody who has
    ever used FEMM for AC current magnetic fields.

    Thanks in advance,

    Erik Evertz
    VA TECH ELIN HOLEC HIGH VOLTAGE BV
    R&D Dep.
    Amersfoort,The Netherlands

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