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Surge Protection

Discussion in 'General Electronics Discussion' started by shiekh, Oct 11, 2010.

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  1. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,412
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    Jan 21, 2010
    ...
    Don't worry. We won't hold it against you :D

    And I probably should add -- "Welcome to Electronics Point. I hope you enjoy yourself here".
     
  2. shiekh

    shiekh

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    Oct 11, 2010
    Still there is certainly a place for a harsh word now and again; it keeps us sharp... so I apologize if I stepped in clumsily, very bad form for a guest.

    I remain very much aware that the chances of my discovering something new are very close to zero indeed... so most all the time I will either tread old paths (the quarter wave approach) or walk barren lands (the idea of throwing the energy out as an EM 'transmission'); but for me it is a great way to learn, I only hope I am not wasting anyone else's time along the way.

    and thanks, I think I may well enjoy my stay, exactly because it is a little 'rugged' here.
     
    Last edited: Oct 12, 2010
  3. Militoy

    Militoy

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    Aug 24, 2010
    Many times the transient protection designed into a power supply or other piece of equipment is intended to protect the entire system - not just the equipment it's installed in. I wouldn't make my customers very happy if I "reflected" high voltage transients back into the system, blowing up other equipment on the same line. Much better to neutralize the transient in a controlled manner - dissipating it safely as heat exactly where I want to.

    BTW - Welcome to the forum. I wouldn't exactly call the banter here "rough" - engineers just tend to be sticklers for accuracy.
     
  4. shiekh

    shiekh

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    Oct 11, 2010
    Turning it to heat is great, but what if the surge has reached a point where it is not normally considered survivable? At that point your customers might already be out of the game, and desperate measures may be justified.

    Take an unterminated line (no equipment attached), the surge is going to bounce anyhow, and the customers are going to have to live with this. So (and this is a question) how is this mode of protection any different from the open line?

    And I would argue that the quarter wave insert does not turn the surge into heat, but reflects the bad frequencies back out... i.e. I am not really making a new suggestion; the same is probably true of the Baluns (thanks for the name). Just don't tell the other customers...

    Being a stickler for accuracy is a big deal in my opinion, without this the whole discussion wanders into the realm of delusion.
     
    Last edited: Oct 12, 2010
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    There will always be some point at which the measures you take will be insufficient. It's hard for some device to suddenly then say "Oh, lets do something different".

    Let's say you placed a fuse in series with an input so that if the current passing through your protection device was too high the fuse would blow, isolating the input until it was replaced. The only issue is that this does not protect you from an even larger overload that simply arcs across the now open fuse.

    You simply have to design for a certain maximum size hit, knowing that something bigger will always exist.
     
  6. shiekh

    shiekh

    77
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    Oct 11, 2010
    Absolutely, but if one design or appproach permits a higher maximum... then go with the 'stronger' design...

    If tossing the energy away is easier than dealing with depositing of that energy (as heat), maybe the first lets one deal with a higher maximum.

    Sure there will always be the direct hit that no approach is going to be able to deal with.



    On a differing note, one could in principle have a microprocessor control that would throw in MOVs for a mild pulse and throw in a reflector for higher pulses, so I guess in principle it is possible for a device to 'do something different', but I didn't have such an 'intelligent' responce in mind; one could even do this without a microprocessor.
     
    Last edited: Oct 12, 2010
  7. Militoy

    Militoy

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    Aug 24, 2010
    >>>>"...Turning it to heat is great, but what if the surge has reached a point where it is not normally considered survivable? At that point your customers might already be out of the game, and desperate measures may be justified.

    Take an unterminated line (no equipment attached), the surge is going to bounce anyhow, and the customers are going to have to live with this. So (and this is a question) how is this mode of protection any different from the open line?..."<<<<

    The idea of incorporating transient protection is to anticipate the types and frequency of transients that might be expected - and to never let them rise to the point where they can do damage. For instance - If I have placed an MDE MAX-260 TVS protector across the power input line of my equipment – any transient on the line will be clamped to below 345V peak within a few 10s of nanoseconds. An attenuated lightning strike would need to have over 288KW of peak energy – or 6500A for over 20uS - to overcome the protection. Granted – if a lightning streamer were to directly strike my input terminals – I would probably be in trouble. But the likelihood of this happening seems somewhat remote. I'm not sure I understand what you mean by an unsurvivable surge - unless you mean one that occurs on an unprotected or underprotected system. I can't think of too many kinds of surges that are worse than direct lightning effects - and we have to protect against those on a regular basis. Some of the testing of protected systems can get downright sporty.

    A transient on an unterminated line with "no equipment attached" won't harm anything - there's no customer equipment attached to be harmed. Transients on power lines and open antenna feeds, etc. will still ring down in a normal, exponential fashion - as losses in the insulation system bleed off and dissipate the energy. The feeder end of the power grid will always have some level of transient protection built in. The impedance of the power lines just prevent that protection from being of much help very far from the substation or distribution transformer.
     
  8. shiekh

    shiekh

    77
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    Oct 11, 2010
    But that is my exact point, my equipment will behave like an unterminated line, both will reflect, and both can affect other equipment on the same branch; but probably to a lesser extent than the original surge in that branch.
    Previously you were saying 'what about the other customers' and I am arguing I am as harmful as an unterminated line some place other on the same branch.

    288KW for over 20uS; that would pan out at over 6 Joules (not too much heat), but I am renowned at being bad at calculating.

    I fear I am starting to cause annoyance at this point.
     
    Last edited: Oct 12, 2010
  9. Militoy

    Militoy

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    Aug 24, 2010
    Actually, about 145 Joules, continuously. You combined two different conditions in the calculations - probably my fault, for lack of clarity. That part is capable of clamping 288,000 Watts at a .05% duty cycle. Plenty of clamping for lightning protection on most airborne or shipboard circuits. The only drawback of this TVS seems to be the price. In 100 piece quantities, I think they're getting around $65 each right now.

    So, I'm still not very clear as to your protection scheme. Can you give a simple description of your idea - so I can try a simulation with a standard IEC series of 2500V pulses?
     
  10. shiekh

    shiekh

    77
    1
    Oct 11, 2010
    Woo! 145W continuous... how do you keep it cool? That is one monster protector! makes my little TrippLite isobars look feeble...
    My idea? umm... now you got me!

    Popcorn anyone?
     
  11. Militoy

    Militoy

    180
    0
    Aug 24, 2010
    145 Joules isn't exactly the same as 145W of heat unless they were taking continuous strikes - but they are pretty hefty TVS devices for the level of protection they are designed for. They are robust enough, that after I introduced them into several military shipboard systems - DSCC assigned a National Stock Number to them.

    Nothing wrong BTW, with Tripp-Lite's products, for the market they serve. I don't know much about their Isobar line - but I set up a friend's remote desert cabin about 10 years ago with a combination wind / solar / battery system - and used Tripp-Lite inverters in the system. Kind of basic in design - but no repairs needed in 10 years of service says a lot for the reliability of their products.
     
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