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#66653 - 06/11/06 09:36 PM Over-voltage  
Fred  Offline
Member
Joined: Apr 2001
Posts: 449
Straughn, IN 47387
Had a neighbor call Friday afternoon. She said her power supply on her PC went bad and she called her computer guy out. He replaced the power supply and plugged the computer in and in 2 minutes it was smoked too. He replaced the power supply 2 more times with the same result before she called me. I checked voltage at her surge strip, which had a red indicator light showing "surge", and I was showing 142 volts. My first thought was open neutral so I proceed to the panel and find 142V on each line to ground and 284V between lines. We live out in the boonies about a mile apart. I call the line super at REMC and tell him what I have. He says that makes 4 in our township this week and sends a couple of guys out with a new tranny. We have had several thunder boomers last week so it must have been lightning. The tranny was only 10 years old and didn't show any outward signs of damage. I told the computer guy the next time he has a customer call with a power supply fried, check voltage before he replaces it and plugs it in. He could buy a good Fluke volt meter for what a power supply costs, or at least for what he charges for one.


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#66654 - 06/11/06 09:45 PM Re: Over-voltage  
Elviscat  Offline
Member
Joined: Aug 2005
Posts: 214
Seattle Washington USA
he replaced the power supply three times? after the first two go up in smoke in only a few minutes isn't that the sign to stop trying?


#66655 - 06/11/06 10:27 PM Re: Over-voltage  
hypress  Offline
Member
Joined: Jul 2004
Posts: 129
Charleston WV
What it sounds like to me is a turn to turn short in the primary of the pole transformers. Lightning storms will cause that.


#66656 - 06/11/06 11:34 PM Re: Over-voltage  
BigB  Offline
Member
Joined: Mar 2004
Posts: 719
Tucson, AZ USA
Reminds me of a call I had where the service neutral had opened. Fried the big screen tv, the guy brought in the bedroom tv, fried it too, then he hooked up a 3rd tv, you guessed it, fried that one too.


#66657 - 06/12/06 12:26 PM Re: Over-voltage  
Radar  Offline
Member
Joined: Apr 2004
Posts: 349
Los Angeles, CA
142V is a little tough on light bulbs too.

Isn't it a little strange that the problem shows up equally on both sides of the transformer's center point?


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#66658 - 06/12/06 01:06 PM Re: Over-voltage  
Texas_Ranger  Offline
Member
Joined: Dec 2001
Posts: 2,392
Vienna, Austria
Hmmm... problem on the HV side? _that_ would definitely cause a higher but balanced voltage!


#66659 - 06/12/06 03:50 PM Re: Over-voltage  
wa2ise  Offline
Member
Joined: Nov 2002
Posts: 782
Oradell NJ USA
As far as overvoltage from the POCO goes, about 15 years ago the entire town here had about 132/264V on one of the 3 phases. Took the POCO about a month to straighten it out. Seems the loads on the 3 phases was out of balance over the entire town.

Another time, when the big blackout in the Northeast in August a few years ago, I didn't lose power, but the line voltage oscillated from 90V to 140V every half minute for about an hour. I turned off all the air conditioners, fridge, freezer and the dehumidifier when that happened. The PC didn't mind it for several minutes and then I unplugged it as I didn't want to push my luck...


#66660 - 06/12/06 11:00 PM Re: Over-voltage  
WFO  Offline
Member
Joined: Sep 2005
Posts: 202
Cat Spring, TX
Since I work for a POCO, I feel like a little bit of a traitor, but if that happened on our system, we, as the POCO, would be liable for damages.
I suggest your friend look into this.


#66661 - 06/13/06 03:42 PM Re: Over-voltage  
RODALCO  Offline
Member
Joined: Dec 2005
Posts: 854
Titirangi, Akld, New Zealand
It look that it could be a tapchanger problem in the local substation.

If the AVR or tapchanger developed a fault the tapchanger keeps stepping up and may cause a high voltage on the 11 or 13.2 kV primary side of all transformers connected to a particular sub.

hence all the low voltages (115,230) will be on the high side.

How many taps does the primary side of US substation transformers have ?

In New Zealand there are 17 steps . from where tap 5 is the 33 kV point.


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