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TransFormer Surge Arrestors

Discussion in 'Electrical Engineering' started by J.B. Wood, Nov 20, 2013.

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  1. J.B. Wood

    J.B. Wood Guest

    Hello, everyone. In July 2012, in the aftermath of the derecho storm
    that clobbered the Washington, DC metro area many pole-mounted medium
    voltage power distribution transformers had to be replaced for various
    reasons. In my area of Arlington County I noticed that the replacements
    don't have the customary surge arrester that is usually bolted to the
    side of the transformer case. For the record the MV system in my
    neighborhood is of type 34.5/19.9 kV.

    Again, I'm referring to the arrestor, not the fuse/cutout combination
    that connects the transformer primary side to the feeder. Is this a
    cost-cutting measure? Thanks for your time and comment. Sincerely,
  2. Don Kelly

    Don Kelly Guest

    You may find that the surge arrestor is not necessarily mounted on the
    transformer but is a separate unit near it (typically looks like an
    insulator between the fuse and the transformer but there will be a lead
    to ground (probably to the ground on the transformer).
  3. J.B. Wood

    J.B. Wood Guest

    Thanks for the informative reply, Don. I looked again and all I can
    observe between the transformer HV (primary) terminal and the MV feeder
    is the usual series combination of a manual-reset cutout and a fuse.
    Also, the replacement transformers, unlike those they replaced, have a
    (plastic?) shroud that covers about half the length of the transformer's
    HV terminal insulator.

    The surge arrester's principal function is to protect against lightning
    strikes (or perhaps induced potential from unusual sunspot/auroral
    activity) so I suppose it could be left out without undue risk for power
    outages and equipment damage. Or perhaps the replacement units are more
    robust and don't require an arrester. Sincerely,
  4. Don Kelly

    Don Kelly Guest

    The setup can vary from utility to utility- Here only an arrester and a
    fuse are used-no cutout. The fuses are in tubes and, if I recall
    correctly the fuse holder acts as a cutout. Some appear to have the
    arrestor and fuse on a common mount. An underground MV cable has fuse
    and arrester on the pole where the cable goes down.
  5. If I recall correctly, that is where the old transformers made their center
    tap to ground bond. Modern transformers usually have those on the lower part
    of one of their sides. As with the new, there is a bus bar that worms its way
    up the guts to the "neutral".
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