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Thread: Danger! High resistance!

  1. #1 Danger! High resistance! 
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    A few months ago I carried out the high voltage experiment I told you guys I was planning. I did learn allot about the properties and safety behind HV, but never reached my main goal, which involved the use of a 100 megaohm resistor. I noticed that without a resistor connected, and using the earth itself as a form of resistor for the + and - ends, with 10 inches of cardboard on top of rubber and plastic as suspenders would suffice to keep the electricity from running though the sleeving into the ground before its destination. Though when i hooked up the resistor, either the electricity would flow through the shielding through the ground isolation pillars and into the ground, or it would actually arc across the surface of the resistor rather than go through it. Essentially when faced with such a high resistance, the voltage would prefer to go anywhere else no matter what the barrier. This reminded me of something I saw on a website that said, "Danger, high resistance!". I though it was just a joke, but it seems that there are dangers in using very high resistance resistors with high voltage (and of course the resistor was well rated to take the voltage and current, in fact up to 75Kv). I need the power to go through the resistor though.......so, how can I do this? I though of using small glass sheets, or even teflon blocks for ground isolation, but what about the resistor? It is an Ohmite Mox96021.


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  3. #2  
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    A 100 megohm resistor is actually a pretty good insulator. If the high voltage arcs across the resistor it may be for the same reason you could get arcing across an insulator; i.e., there may be moisture and dirt on the surface.


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  4. #3  
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    So you think oil, water or dirt could be causing it? I thought the same thing, but doubted that that would be enough....

    Mmmm....time to clean it, I guess. Will bleach suffice? or will that make it worse if any residue is left?
    Of all the wonders in the universe, none is likely more fascinating and complicated than human nature.

    "Two things are infinite: the universe and human stupidity; and I'm not sure about the universe."

    "Great spirits have always found violent opposition from mediocrities. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices but honestly and courageously uses his intelligence"

    -Einstein

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  5. #4  
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    Quote Originally Posted by Cold Fusion
    So you think oil, water or dirt could be causing it? I thought the same thing, but doubted that that would be enough....

    Mmmm....time to clean it, I guess. Will bleach suffice? or will that make it worse if any residue is left?
    I'd probably just use soapy water and dry it off. The salt from your hands would be the worst problem. Maybe handle it with gloves.
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  6. #5  
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    Ha, I have touched it relentlessly since I got it (showing it to people "hey! check out this 100 MEGAOHM RESISTOR!!11!1!!").

    I will try that and see what happens.
    Of all the wonders in the universe, none is likely more fascinating and complicated than human nature.

    "Two things are infinite: the universe and human stupidity; and I'm not sure about the universe."

    "Great spirits have always found violent opposition from mediocrities. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices but honestly and courageously uses his intelligence"

    -Einstein

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    Use your computing strength for science!
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  7. #6  
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    Not sure I agree with Harold on this one, arcing is actually a result of the ionisation of gas (ie in this case air), it suggests you are using a voltage which is in excess of the rating of the resister. If the body of the resistor was contaminated then the electricity would flow through the contamination which in itself would not form any arcing in normal circumstances. what is the length of the resistive portion of the resister and how much voltage are you applying?
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  8. #7  
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    Many outages of transmission lines due to insulator surface pollution have been experienced, especially in converter stations [1]. Under adverse environmental conditions, some pollution is deposited on the insulator surface. A wet conducting path is formed when moisture is present due to dew deposition of light rain and a leakage current begins to flow on the insulator surface. The surface layer is heated which causes an increase in the conductivity and the leakage current. The heating results in local drying of the surface layer, and so-called “dry bands” occur. Partial arcs occur across the dry bands on the insulators. The partial discharges increase with a number of streamer discharges and glows occurring across those dry bands having the highest potential gradient. These discharges also cause audible noise. Finally, the partial streamer discharges (partial flashovers) are “connected” in series, and a complete flashover occurs.
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  9. #8  
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    I think your two contacts are too close to each other.

    The higher the voltage, the greater the potential between the two terminal thus causing arching.

    The arching could even happen between the terminals of the resistor if the voltage is high.

    Try completely insulating(air tight) the terminals with glass or ceramic material.
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  10. #9  
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    I am using 10K volts. It is rated for up to 75K volts. It is around 4 inches long, I believe to prevent direct arcing. What I have observed is the electricity running up the outer insulation to a particular point on the end of the resistor. I assume that it then travels across the surface and comes out the other end. I know It is not going through the resistor since my transformers internal circuit breaker blows every time I try (I have blown it over 200 times trying to make this work. I guess its pretty resilient).
    Of all the wonders in the universe, none is likely more fascinating and complicated than human nature.

    "Two things are infinite: the universe and human stupidity; and I'm not sure about the universe."

    "Great spirits have always found violent opposition from mediocrities. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices but honestly and courageously uses his intelligence"

    -Einstein

    http://boinc.berkeley.edu/download.php

    Use your computing strength for science!
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