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  1. #1

    Default Stray/unfound voltage

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    A customer owned 2500 KVA 277/480 padmount went bad yesterday. Our transformer/apparatus repair shop foreman went out to high pot it and their secondaries to help the customer determine the problem and cause. A lineman deendergized and isolated our primary from the transformer and parked the deenergized and grounded elbows onto parking stands. The TX windings tested bad on A phase and then they were in the process of disconnecting the secondaries from the transformer when both the transformer shop foreman and a customer electrician were both hit with voltage from B phase secondaries in the padmount. Once again they checked for voltage using a digital voltmeter and found no voltage. The customers main breakers were all open, the primary was isloated from the transformer and grounded, all known feeds were either open or open and grounded.

    The transformer shop foreman says he has been hit with 120 and even 277 ac before and this was not what he felt when he got hit this time, he said it was more like a big electric fence charger or something. The customers electrician nearly got hung up on it.

    They checked and rechecked only to find nothing and even checked their voltmeter on a known voltage to ensure it was working properly. After changing out the transformer we checked for voltage again this time both for ac and dc voltage only to find nothing. No one was zapped again and no voltage source was found..........strange indeed.

    After much talk and thought we came up with a few ideas, maybe someone else has ran across this.

    This transformer is feeding a job site that is building a new biomass powerplant (100 MW i believe). It is far from being done however. One idea is with all the battery powered JLG and scissor lifts perhaps one of the chargers is bad and when began acting like a DC to AC inverter and backfeeding the secondary. This would mean that not only the charger went bad but that a main breaker was bad as well. Possible I guess but it would be crazy. Plus why didnt the voltmeter "see" the voltage? Just a crazy situation it would seem.

    We changed the TX and reenergized it and the secondary with no other problems, I hate to chalk this up to unknown so any ideas would be appreciated.
    This country is being destroyed by those who could not have created it. In order to return the days of this country being the proverbial shining city on the hill for all of the world to see, we must first return to the ways that enabled the light to first shine.

  2. #2
    Join Date
    Oct 2006
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    South East Texas
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    3,278

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    Ummmmmmmmmmm could it have been a capacitive charge in the secondary, that once discharged went away?

  3. #3

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    Dont really know........the two people who got bit by it was not at the same time and they said it was not just a pop and done, the one guy it grabbed and he couldn't get off of it for a second, anytime i have been hit by a capacitive charge (URD on a reel trailer) it was a pop and its done sort of thing. Could have been though I guess if it was a big enough capacitive charge. There were a large number of secondary cables and that 2500 KVA sure has a lot of windings, but why only on B phase secondary?


    Good idea Poot.
    This country is being destroyed by those who could not have created it. In order to return the days of this country being the proverbial shining city on the hill for all of the world to see, we must first return to the ways that enabled the light to first shine.

  4. #4

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    It does sound like it was a capacitive charge. Possibly caused by the hi-pot tester. It wouldn't show up on a meter set to AC since the charge would be DC, and it would keep delivering shocks until the charge had been reduced to the level where the voltage wan't high enough to shock.
    Portable defibrillators were first invented to save the lives of linemen. Where's yours?

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  5. #5
    Join Date
    Aug 2002
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    Northern Michigan
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    I assume they couldn't recreate it? Maybe they didn'ttry, not sure I would. But it would be interesting to go there again in a week and see if you could recreate it.
    Note to self, just because it pops into my head doesn't mean it should come out of my mouth.

  6. #6

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    That is one unusual story,you said the main breaker was open,so I assume it wasnt a switch handle.I once had something happen that was kind of similar....it was while working on a large bank feeding a large building,the electricans said all the load was off and the switch was opened....but when we opened up the disconnects we created a fire that burned the bond wire off at the pole,I think that was due to capacitors on the customers side and a faulty switch.....that was long ago ,but it was a good fire.

  7. #7

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    Quote Originally Posted by Pootnaigle View Post
    Ummmmmmmmmmm could it have been a capacitive charge in the secondary, that once discharged went away?
    That's all I could think of Poot. Has to be that.
    But, Why would such a capactiance charge have ben held in the first place?????

  8. #8

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    I agree with Big Clive.

  9. #9
    Join Date
    Oct 2006
    Location
    South East Texas
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    3,278

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    Ummmmmmmmmm I am jus thinkin out loud here but ummmmmmm a voltmeter is really a resistor that measures the voltage drop and so wouldnt the charge be drained right through the VM? Ummmmm this is a question not an answer.

  10. #10

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    We once had some strange un-known amperage,strangely enough it was on the same circuit and same area that the bank feeding the building was.Seems like the trouble board was getting an amp reading on the first section of the circuit,when we didnt see anything feeding off of it in the field,this was happening during some overhead switching.....there are those times when you see the so called un-knowns.....but rarely do you see it happening again.

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