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Thread: capacitors?

  1. #1

    Question capacitors?

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    Morinig gentlemen, I was trying find some info on some capacitor accidents or near misses. We have some lineman that don't think or unaware of the dangers of capacitors in a trouble or regular linework situation. If anyone has had any insights or stories I would appreciate all. Thanks. flashman.

  2. #2

    Default

    What does OSHA say

    1910.269(w)(1)
    "Capacitors." The following additional requirements apply to work on capacitors and on lines connected to capacitors.

    Note: See paragraphs (m) and (n) of this section for requirements pertaining to the deenergizing and grounding of capacitor installations.

    1910.269(w)(1)(i)
    Before employees work on capacitors, the capacitors shall be disconnected from energized sources and, after a wait of at least 5 minutes from the time of disconnection, short-circuited.

    1910.269(w)(1)(ii)
    Before the units are handled, each unit in series-parallel capacitor banks shall be short-circuited between all terminals and the capacitor case or its rack. If the cases of capacitors are on ungrounded substation racks, the racks shall be bonded to ground.

    1910.269(w)(1)(iii)
    Any line to which capacitors are connected shall be short-circuited before it is considered deenergized.

    http://www.usace.army.mil/publicatio...684/chap13.pdf
    Last edited by CPOPE; 01-12-2007 at 08:42 PM.

  3. #3

    Default

    Use a load break tool to open them up

  4. #4
    dbrown20 Guest

    Default Capacitors

    Flashman, come to think of it they did have a pretty bad one in the AEP system back in the summer. Serviceman closed in a capacitor from a small service bucket with one of those short extendo sticks and the capacitor blew up and severely burned him. I think he has made a full recovery by now but we saw a picture of his bucket and it was pretty badly burned also. If you're in the AEP system you probably read of this. It happened in Texas.

    Saw a guy get the crap knocked out of him once by a capacitor that wasn't discharged.

    I don't recall if the former was from a fixed bank or not. dbrown20

  5. #5

    Default

    we consider compasitors the mostdangerous piece of equiptment we have ,,they not only store volts but also amps

  6. #6

    Default

    Quote Originally Posted by scammy View Post
    we consider compasitors the mostdangerous piece of equiptment we have ,,they not only store volts but also amps
    Or to be more technical. They store a "charge". The voltage will depend entirely on the charge in them. The amps bit is their devastating ability to dump their entire charge in one blinding bang with much more force than a source with higher impedance like a line.

    Worse still is the fact that their construction is basically a coil of alternate layers of insulator and conductor, often with an electrolyte or oil in between. The large conductor area, thin insulation and the enclosed nature means that a common failure mode is an internal short with violently explosive results. Not so great if you just closed it in.

    Most caps have some form of discharge system fitted in the form of a suitably rated resistor to trickle discharge them when not powered, but these are not reliable and often fail. You should always assume that a capacitor is charged and use a suitable high impedance device to shunt it and discharge the stored energy in a controlled manner.

    Incidentally, the charge on a cap on an AC application will be directly connected to the exact point it is disconnected. If you pulled one of it's leads at the mains zero crossing point (where the sine wave changes polarity) then the charge on the capacitor could be zero. If however you pulled it at the peak then it could be fully charged. The chances of you pulling it at zero charge, particularly fast enough to avoid an arc is almost zero.

    If however the cap is in parallel with a functional transformers primary, then that should discharge the cap.
    Portable defibrillators were first invented to save the lives of linemen. Where's yours?

    www.bigclive.com

  7. #7
    Join Date
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    Default your right

    dbrown, you got it right. I don't know about up there but we are now required to test them before closing in on them. If there even slightly out of range we are required to at least pull the jumpers and tag it as bad. And then we are required to contact dispatch and have them log it in the abnormal database. That was the problem in Abilene this particular cap tested bad at some point but not taken out of service for some reason. When the service man went to close his seasonal banks he did not know this one was bad. So now we test before we close, we close them from the ground if possible and we don't do it without a qualified observer. Sure make you respect them.

  8. #8

    Default thanks

    thanks clive you are correct with the word (charge),,,cap bank or capasitors alone should be respected and aproached with open eyes,, did see the results of one that had exploded,,,way more powerfull than a grenade,,compares more to a claymore mine

  9. #9
    dbrown20 Guest

    Default Bad Capacitors

    Quote Originally Posted by wstxpwr View Post
    dbrown, you got it right. I don't know about up there but we are now required to test them before closing in on them. If there even slightly out of range we are required to at least pull the jumpers and tag it as bad. And then we are required to contact dispatch and have them log it in the abnormal database. That was the problem in Abilene this particular cap tested bad at some point but not taken out of service for some reason. When the service man went to close his seasonal banks he did not know this one was bad. So now we test before we close, we close them from the ground if possible and we don't do it without a qualified observer. Sure make you respect them.
    Those with a blown fuse are always left for the line crews to test where I work. The service people never try them. If they are not within normal range then we change them if there's one handy or disconnect them. If there several in the bank then it may be evened up and then closed in and the bad one replaced later. dbrown20

  10. #10
    NU Limey Guest

    Default capacitors

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    Cap. maintainence is a big pain. When working on them you have to make sure after you deenergize they are shorted out, we usually use a piece of wire in a shot gun grounding the bushing to a ground for about 10 sec. There are testers on the market to check them, depending on your line voltage and kvar. We don`t have too many issues at 5 and 12kv. When we get to 34.5, that a different ballgame, we have alot of 1800 and 2400 kvar banks. A while ago our company retrofitted these and others with oil switches. After burning up a couple loadbreak tool trying to open cutouts, things got a re-look. Load break tools alone are not designed for bigger banks. There are various that have to be looked at first, proximity to other cap banks, conductor size,etc. Most of our oil switched banks are timed controlled from the ground to allow the person to get out of harms way in case something wrong. last year I watched an oil switch launch after the fuse was thrown in and the switch was in the open position. We all give these things alot of respect and never turn your back on them!!

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