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Old 09-18-2013, 08:01 PM   #1
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Might have been discussed before if so I apologize.

Why don't power companys install diodes on the secondaries of there transformers to prevent people from backfeeding them with generators when a power outage happens? I know many lineman have been killed or hurt because of this and while im sure it would be costly I dont understand why they havent done this already?

A bit off the wall but just curious if it could happen. If a trans is back fed its putting hi volt back on the transmission line. If another trans is a block downstream on the same line couldnt that trans become live and (while im sure limited by the amp output of generator) power that house also?

Had a boring day today and figured these would be good to discuss.
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Old 09-18-2013, 08:10 PM   #2
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It cost money.. Honestly.. I have been hammed by a gen starting back feeding POCO lines off the same transformer. I don't know what happened the poor bas$turd down the street...2007 ice storm in Oklahoma city. all I can say is Check..double check.. PPE up. or ground it.
What I want to know.. your bugging into a dead POCO line..and the POCO throws it in..and I ground it to the ground rod..How hurt will I be? or will I know it by the sound of the wire ? any Lineman know? because I have my hands on it.. and face near it.
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Old 09-18-2013, 08:12 PM   #3
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How would a diode work?

The service is AC, the polarity is constantly changing.

You would end up with pulse DC at everyone's home.
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Old 09-18-2013, 08:16 PM   #4
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well, let's see . . . if they put diodes on the tranny outputs, that would be, what, a half-wave rectifier on everyone's power supply ? why would they want to spend money on that ?
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Old 09-18-2013, 08:17 PM   #5
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Quote:
Originally Posted by Briancraig81 View Post

Why don't power companys install diodes on the secondaries of there transformers to prevent people from backfeeding them with generators when a power outage happens? I know many lineman have been killed or hurt because of this and while im sure it would be costly I dont understand why they havent done this already?
How many?

I've heard the stories too. But then someone brings up the point that the second you backfeed the grid the generator is going to stall when it attempts to power the load of everything that is still connected (neighborhoods, cities, etc.).

There was a discussion about this at Mike Holt's.

So how many linemen do you know of that definitely died from this?
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Old 09-18-2013, 08:18 PM   #6
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They should install back flow preventers. That would fix the problem.
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Old 09-18-2013, 08:20 PM   #7
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Lightbulb diode

A diode would only supply us with D.C. current and I believe our system is based on A.C.!! ??
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Old 09-18-2013, 08:22 PM   #8
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How many?

I've heard the stories too. But then someone brings up the point that the second you backfeed the grid the generator is going to stall when it attempts to power the load of everything that is still connected (neighborhoods, cities, etc.).

There was a discussion about this at Mike Holt's.

So how many linemen do you know of that definitely died from this?
You are assuming the lines are all made up and cutouts closed.

That is not usually the case when they are working on it.

But I too would like to hear some real numbers.
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Old 09-18-2013, 08:23 PM   #9
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I read a story last year about one who supposedly died, but since you really can't believe anything you read, who knows. I'm sure the pocos would rather blame an accident on anything but themselves in any case. Hard to prove in either case.
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Old 09-18-2013, 08:25 PM   #10
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You are assuming the lines are all made up and cutouts closed.

That is not usually the case when they are working on it.

But I too would like to hear some real numbers.
Yeah, that's what I meant by "everything that is still connected". Usually it's at least the neighborhood but I assume at time it could be an entire town if the problem is at a substation.
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Old 09-18-2013, 10:26 PM   #11
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I dont know of any personally, just stories that ive heard.

Learned something new tonight. I learned about diodes in a basic electronics class in middle school. No one told us they were for DC only.
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Old 09-18-2013, 10:38 PM   #12
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Quote:
Originally Posted by Briancraig81 View Post
I dont know of any personally, just stories that ive heard.

Learned something new tonight. I learned about diodes in a basic electronics class in middle school. No one told us they were for DC only.
They are for creating DC from an AC source, They allow only one polarity
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Old 09-18-2013, 10:54 PM   #13
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So how many linemen do you know of that definitely died from this?
Probably not a lot, but a shiitty way to go! Been a few in British Columbia over the years.

Don't know the details of it.. but even though the gennie might stall out after a few seconds, it's doing around 60 cycles a second. That's putting some real juice on the line, and pumping some current. Boost the juice through the tranny and it's enough to really bite somebody.

Rather than putting a on the line, why don't smart meters just open the line if it senses a backfeed? Must be a good reason why not, because otherwise it seems like an obvious safety feature.
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Old 09-18-2013, 10:58 PM   #14
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Rather than putting a on the line, why don't smart meters just open the line if it senses a backfeed? Must be a good reason why not, because otherwise it seems like an obvious safety feature.
Prolly 'coz if they put one on they open themselves to the liability of having one fail. Its easier to let the lawyers chase down the other guy. Follow the money, not the logic
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Old 09-18-2013, 11:10 PM   #15
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Or probably cause the poco is constantly bridging power from other sources changing the way it is coming from for maintanance purposes.
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Old 09-18-2013, 11:49 PM   #16
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Having done linework, I don't have a lot of sympathy for a knuckle-dragging stump-jumper who bites the big one because of a backfeed.

I realize this sounds somewhat callous, but every lineman has had it drilled into his thick skull at least a million times......"if it ain't grounded, it ain't dead".

Even in the worst of conditions, it takes only a few minutes to ground out the line. If there's no ground available (as is often the case in a storm......), then tie the phases together, but don't just grab hold of a line that could possibly be energized.

I don't always blindly follow all safety rules, but here's what it comes down to; it's your life, you have two choices.

1) Insure that the line is actually dead. This means grounding it, not just opening the cutouts or locking out the breaker.

2) Work it like it's hot.

If you have the self-discipline to operate under the above guidelines, you'll live to enjoy your retirement.
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Old 09-19-2013, 12:05 AM   #17
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Quote:
Originally Posted by Briancraig81 View Post
Might have been discussed before if so I apologize.

Why don't power companys install diodes on the secondaries of there transformers to prevent people from backfeeding them with generators when a power outage happens? I know many lineman have been killed or hurt because of this and while im sure it would be costly I dont understand why they havent done this already?

A bit off the wall but just curious if it could happen. If a trans is back fed its putting hi volt back on the transmission line. If another trans is a block downstream on the same line couldnt that trans become live and (while im sure limited by the amp output of generator) power that house also?

Had a boring day today and figured these would be good to discuss.

We all know the answer to this question is -

BECAUSE IT COSTS MONEY !

The bean counters arn't paid to care about what is practicule or what is safe,
they care only about the bottom line !
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Old 09-19-2013, 07:57 AM   #18
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Quote:
Originally Posted by dmxtothemax

We all know the answer to this question is -

BECAUSE IT COSTS MONEY !

The bean counters arn't paid to care about what is practicule or what is safe,
they care only about the bottom line !
Uuuuhhhhhh....no. It has to do with basic electrical theory bro, that's why. Diodes only allow current to flow in one direction, so like BBQ said, you would get pulsing DC instead of AC.
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