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Thread: Induced heating in HV busduct fastening bolt.

  1. #1

    Induced heating in HV busduct fastening bolt.

    I thought I would share this infrared image and digital photo that I took last week at a power station in central Queensland. the image is of a fastening bolt on flange connecting to a generator terminal box. This flange was on the C phase outgoing side and as you can see the metal is hot and dis-coloured. I have come across a lot of different examples of induced heating but this one is quite different. The other fastening bolts on the flange are not hot at all.
    I have considered that the bolt and nut may be loose after I left the site however this will not be checked until the shutdown later this month. I have also considered that it may be an earthing problem.

    My question is has anyone come across this particular example where one bolt/nut only is hot. If so what was the eventual outcome/problem and how was it rectified by the electrical maintenance team?

    Many Thanks Mike Henneker
    Attached Files Attached Files

  2. #2
    Mike that's an awesome image and certainly one of the higher temperature examples i've seen of induction heating. Yes, i have seen it quite localised, and while i don't have a detailed understanding of Faraday's laws, i would say this is the focal point of the eddy currents. Presumably another high current carry conductor is directly adjacent to this bolt? Whether the bolt was loose or not it shouldn't matter as this is not a part of the electrical circuit (part of the bolted structure), therefore high resistance connection would not be an issue.

    Rectification usually invovles interrupting/dispersing the electromagnetic fields or use of non ferrous components. Many examples i have found have been due to incorrect groupings of conductings as they pass through or via metal structures. This can be simply corrected by either removing the metal or regrouping the conductors. In this instance, and without a "broader" image of the scene and location of equipment it would be hard to say.
    Brenton Ward
    Level III Infraspection Institute Certified Thermographer
    Level II Airborne Ultrasound

  3. #3
    Quote Originally Posted by Brenton View Post
    Mike that's an awesome image and certainly one of the higher temperature examples i've seen of induction heating. Yes, i have seen it quite localised, and while i don't have a detailed understanding of Faraday's laws, i would say this is the focal point of the eddy currents. Presumably another high current carry conductor is directly adjacent to this bolt? Whether the bolt was loose or not it shouldn't matter as this is not a part of the electrical circuit (part of the bolted structure), therefore high resistance connection would not be an issue.

    Rectification usually invovles interrupting/dispersing the electromagnetic fields or use of non ferrous components. Many examples i have found have been due to incorrect groupings of conductings as they pass through or via metal structures. This can be simply corrected by either removing the metal or regrouping the conductors. In this instance, and without a "broader" image of the scene and location of equipment it would be hard to say.
    Brenton, thanks for your feedback. The unusual thing about this heating is that there is not another high carrying conductor in close proximity. This is an isophase bus duct setup (single conductors enclosed in a separate earthed housing from generator to transformer) and is separated from the other conductors. I have done some research and there is a possibility that there are circulating earth faults inside the duct . The other bus duct flange fastening bolts on the other phases are OK. I will continue to search to find an answer as it would be great to find a cause. Not being onsite when they check or do the rectifications is always difficult....I think the electrical engineers struggle with this as well..

  4. #4
    Reposted images

    Name:  infrared-induction-1.jpg
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Size:  16.7 KBName:  infrared-induction-2.jpg
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Size:  12.3 KB
    Brenton Ward
    Level III Infraspection Institute Certified Thermographer
    Level II Airborne Ultrasound

  5. #5
    Name:  infrared-induction-3.jpg
Views: 518
Size:  72.6 KB
    A more common example!
    Brenton Ward
    Level III Infraspection Institute Certified Thermographer
    Level II Airborne Ultrasound

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