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Thread: Locating near OHL

  1. #1
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    Default Locating near OHL

    G'day All,


    Surveyor here, who has been roped into doing some locating. I could use a little advise from the professionals. I've done a little bit of this over the years, with a RD400, and have access to an RD4000 at the moment.

    Got a project where the client wants us to locate some pipes which are between 3 400Kv ovehead lines. From what little I know about EM fields, the pipes will already have an inductive signal induced by the field from the 400Kv lines. What I would like to know is whether the detector will be overwhelmed by that same field? Some of these pipes are only 10-15m from the powerline.

    Will using the RD4000 Tx on a specific frequency help me get past this, or is this just an area where locating with this sort of equipment just will not work?

    Any advise would be great!

    Thanks.

  2. #2
    Senior Member Dave72's Avatar
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    Default Re: Locating near OHL

    I dont think the problem would be the power lines, because you can use other frequencies in the 4000, like 8khz etc. Trying to locate in 'power mode' might be a little tricky.
    You do mention "pipes", as in more than one.
    Is there a way to isolate the pipes electrically ? If they're working pipes,probably not.. they would all be connected via framing and etc (and for safety, Id think).. so if you clip onto some part of pipe #1, the signal would go down all the pipes together. Depending on the separation of the pipes, that might be ok anyhow, just locate in peak, not null.
    Dont forget also.. that if your peak and null dont agree , then the depth reading is not accurate. If the pipes do a bend, then the peak will be off one way and the null will be off the other way (I always forget, which way.. inside or outside.. its in the user guide anyhow..).

    If that's all sand there.. would be sweet to try out a ground-penetrating radar (GPR) unit.
    Good luck.
    (May you live in interesting times)

  3. #3
    Member Utilitrack's Avatar
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    Default Re: Locating near OHL

    1) Use the lowest frequency on your 4000- 8khz? 2) direct connect if possible if test stand is nearby- assuming that your pipleines are coated steel.
    3) Beware ore of the counterpoise (ground grids of your electrical transmission structures, your independent ground stake should driven as far away as possible -use a 50'-100' coil of wire to get out of the ROW to ground if possible- you will still probably bleed over to the ground grid.

    Good luck!!!

  4. #4
    Senior Member headcipher's Avatar
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    Default Re: Locating near OHL

    Quote Originally Posted by Playing In The Sandpit View Post
    G'day All,


    Surveyor here, who has been roped into doing some locating. I could use a little advise from the professionals. I've done a little bit of this over the years, with a RD400, and have access to an RD4000 at the moment.

    Got a project where the client wants us to locate some pipes which are between 3 400Kv ovehead lines. From what little I know about EM fields, the pipes will already have an inductive signal induced by the field from the 400Kv lines. What I would like to know is whether the detector will be overwhelmed by that same field? Some of these pipes are only 10-15m from the powerline.

    Will using the RD4000 Tx on a specific frequency help me get past this, or is this just an area where locating with this sort of equipment just will not work?

    Any advise would be great!

    Thanks.
    Shouldn't have much in the way of problems locating below high voltage.

    You should though wear gloves and be careful hooking up conductively.

    We've had locators shocked by hooking up to facilities without gloves below our overhead lines. A charge built up inductively, it will follow ground through you if you aren't careful.

  5. #5
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    Default Re: Locating near OHL

    Guys,

    Thanks a lot to each of you for the advice and suggestions. I'll give it a try tomorrow.

    Dave72: GPR was my inital thought, but it's pretty much impossible to rent them in this part of the world. Would be a perfect job for it in the sand.

    Thanks & Regards
    Doug.

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