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Low(ish) profile 'off the shelf' CBCT

Discussion in 'Electronic Components' started by Roger Hamlett, Jun 8, 2007.

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  1. Hi,
    I have an application, where I need to sense AC current imbalance between
    two lines. Perfect application for a CBCT. The wires themselves carry a
    reasonably high voltage (at moments, in excess of 3KV), so my 'prototype',
    has a Teflon block going through the transformer, with the two wires
    positioned in this (giving both good position stability, and insulation).
    Now, my problem is the size of the CBCT. There are readily available
    toroids, with hole sizes from perhaps 35mm and up. However I have a height
    limit over the board, which is making this unuseable. What I'd like to
    find, is something like a rectangular CBCT, with a central hole perhaps
    25mm wide, and a relatively low total height (not exceeding 50mm to the
    top of the winding), that is available 'off the shelf' (the run size is
    small, so doesn't warrant a custom transformer). Perhaps 500:1 ratio
    (though the circuit can be adjusted to handle a wide tolerance here), and
    peak current rating doesn't need to exceed 1A.
    I am in the UK, so a UK source would be preferred.
    Searches of the normal component manufacturers find lots of larger
    toroids, and a few rectangular designs, and a general Google search, gives
    lots of companies able to make custom units, but nothing visible 'off the
    So, has anyone any pointers to a supplier stocking items like this?.

    Many thanks in advance.
  2. Roger:

    Does your 'CBCT' relate to a standard Current Transformer?

    We have got some small CT's at work, I am working at home on a PCB today but can
    pop round lunchtime and see what size and spec they are.

  3. Sorry, 'CBCT', standard abbreviation, for 'core balance current
    transformer'. They differ slightly from the normal current transformers,
    being designed to give relatively high gains from the imbalance of current
    in two (or more) wires. Generally they give high outputs, for small
    imbalances, against a normal 'current transformer', which usually gives
    quite a low output current for a large input. :)
    They standard application, is the RCCB, which is normally based on these.

    Best Wishes
  4. OK, many thanks for the clarification. I think the ones we have are standard,
    but there are also some LEM/HEME types as well. I'll still have a dig through
    and report back.

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