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Too much power from the grid


By Norm, Section Controls
Posted on Sat Nov 12, 2005 at 04:03:46 PM MST
Is there a device to limit power?

 I seen on the news that some people in Cleveland accidently got too much power ...
a tree branch knocked one wire against another
....burnt up some TVs furnaces fridges..etc.
only those lucky enough that their insurance
covered...even then bad time to be without heat.
  Is there a device that would prevent this for
each individual homeowner?
                 Norm.
Too much power from the grid | 10 comments (10 topical)

Re: Too much power from the grid (3.00 / 0) (#1)
by RP on Sat Nov 12, 2005 at 10:15:20 AM MST

That's called a surge and it's exactly what surge protectors are for.  Most people only think of these in the context of lightning but overvoltage from the power company happens too sometimes.



Re: Too much power from the grid (3.00 / 0) (#2)
by Oso on Sat Nov 12, 2005 at 11:01:08 AM MST

Sounds like a 12kv ( or even higher voltage) got dropped onto the 120V lines.

Service entry surge protectors are available. Costs are generally in the $200-$700 range. If you really want to try to protect the home, I would invest in something in the mid range or higher.  Usually, the more you spend, the better the protection.

Many of the cheaper surge protectors (and particularly surge protection strips) do not do a good job of protecting against a surge of this magnitude. The damage gets done before the strip kicks in. (or burns up).

 



Re: Too much power from the grid (3.00 / 0) (#3)
by Clifford on Sat Nov 12, 2005 at 11:12:07 AM MST

If you look at the power feeding my neighborhood....

High voltage lines at the top of the poles.
These feed transformers
Which in turn feed low voltage lines (110/220V) nearer the bottom of the poles.

I could imagine a localized situation where the high and low voltage lines got crossed causing dangerous overvoltages.

In the country, people often have private transformers feeding only their own residence.  And, with underground wiring, a similar fault would be far less likely.  And, the effects would also be much more isolated.

Protection:
Surge suppressors will, in theory, protect from this kind of an over voltage, but they are normally used at "point of use".  

I believe that "Line Conditioners" are like "super surge suppressors", and could in theory be purchased for a whole house.

UPS devices have surge suppression/line conditioning built in with battery backup.  Normally they are connected to high power consumption devices with limited battery capacity.  However, they come in a variety of sizes and shapes, and some without batteries such as the large industrial centrifugal UPS devices.

One of the issues you will find.
Most residential houses have incoming service rated at 100 Amp x 220V or 200 Amp x 220V.  Depending what kinds of devices you use (home shop, electric heat, electric hot water, etc), one often never gets up to the 200Amp usage.  However, a 200 Amp UPS would be quite a large device, and may actually introduce dangers of it's own.

Of course, in reality, one can lower power consumption to less than 1 KWhr / day, and perhaps less than 1000 or 2000 watts at any one time.




Re: Too much power from the grid (3.00 / 0) (#4)
by Opera House on Sat Nov 12, 2005 at 12:32:17 PM MST

I don't think there is much chance of protecting yourself against that sort of thing.  Ever see those lines sparking on the news?  There is a lot of power behind them and all surge suppressors can only absorb that power for a shortm period of time.  Distributed suppressors at each device are the best way to go.  The more wire and inductance, the better they work.  Incidently, suppresors performance tests are made with 1/4" leads because of this.  Most suppressors don't even start to conduct till you reach about 2,000 volts.  An AC outlet will flash over at 6,000V.



Re: Too much power from the grid (3.00 / 0) (#5)
by richhagen on Sat Nov 12, 2005 at 03:29:05 PM MST

I think that you could if you designed, or bought a system designed to handle such a surge.  The other day, while at work, my duties took me past the Trip-Light plant on the south side of the City.  (very nice folks there)  Since I had to wait there for a bit, the guy in charge of their security, who apparently used to be an electrician or designer for them, gave me a brief overview of the site.  They make surge suppressors, and use a combination of elements to limit surges.  I was impressed with their operation, and happy to see it in my city and not far off some where.  I told him my concerns of lighting on my panels and discussed the use of varistors and other components with him for a bit.  Basically, if you have a suitably designed fuse or breaker up stream that can handle the voltage and amperage, and have sufficient varistors, inductance and capacitance downstream, you should be able to keep the voltage in the house from increasing significantly before the power goes out.  I'll bet they make systems, or at least components for, such a system there.  Rich Hagen
'A Joule saved is a Joule made'
[ Parent ]


Re: Too much power from the grid (3.00 / 0) (#9)
by Opera House on Sun Nov 13, 2005 at 06:30:06 AM MST

Our utility rents a device that goes between the meter and the meter box that is "supposed" to protect you.  They even offer a $5,000 insurance policy against damage if you have one.  They have a couple of big MOVs in them. That might save you from the little stuff.  Frankly, if there was nothing in there the utility company would still make out.  These occurances are very rare and not somthing to design against.  Circuit breakers and fuses will continue to conduct even after they open via plasma conduction as they are not rated for that voltage.  

[ Parent ]


Re: Too much power from the grid (3.00 / 0) (#6)
by Norm on Sat Nov 12, 2005 at 04:31:00 PM MST

  Thanks for all the responses people...maybe one of these days they'll have a device that
will just be a part of the service or like "for a
few dollars more we can install...." it certainly seems a shame the electric company is
quick to claim...not our fault...not our fault!
   I guess what people really need is emergency power...as soon as a storm is immenent you could switch to batteries.                
   Funny as soon as a storm comes along...shut off the computer but leave the TV on so you can
keep posted on the storm ????
                     Norm.
( :>) Norm


Re: Too much power from the grid (3.00 / 0) (#7)
by nothing to lose on Sat Nov 12, 2005 at 11:58:02 PM MST

"Funny as soon as a storm comes along...shut off the computer but leave the TV on so you can keep posted on the storm ????"

Not me. I couldn't sleep just now because the thunder woke me up. The lightning is pretty too. So here I am online enjoying the storm :)

 A TV is normally cheaper than a computer, unless you have a cheapy computer and a serious fancy TV. Also if you blow out a TV you don't really loose any data or half your life like with a computer.

 Well back to the point. Things like the post is about, unreliable power grids and also smart metering and etc.., are more reasons most homes should be going to battery systems and RE.

As was talked about in a post on smart meetering where you pay cheap rates at night and  much higher rates durring peak times, people could put the homes on batteries and inverters. Charge at night durring low rates and run from that power durring daytime peak rates, thus saving money. The other advantages of such a thing would also be power backup for when the grid goes down and surge suppresion from the grid.

 The backup system speaks for itself, if your running from charged up batteries who cares if the grid is down a few hours. The surge suppresion however may not be thought of often. In such a system only the battery charger would actually see the grid power. Would be easy to put chargers on saftey devices so any grid spikes cannot get to the batteries, easier than putting an entire house on one I would think.
 When thinking of the power a house uses, maybe a 100amp service, and maybe for 10 minutes a day the house hits 90amps all at once? Well you have to have those higher amps available 24Hrs just to have them for that 10 minutes, even though the house may only average a load of 20amps the other 23hours 50 minutes of the day.
 With a battery and inverter system you have all clean steady power, backup power, and you can average your usage out over the 24 hours  for charging batteries not just when used as form the grid. Add to that the fact you can make your own power anyway you can and add that to the batteries far easier than adding to the grid power.

I was running some lines of the house from the inverter and batteries, charged from the grid and whatever I could make myself. For me this worked well, that was before I rented the other house. Needing the inverter and batteries at the other house then to keep it off grid I put those lines here back on the grid again.
 For me I loved the system I had, large power items like the fridge, coffee maker, microwave, fans, etc.. were direct to the grid, but could be easily changed to inverter if needed. Items like TV, vcr, dvd, some computer stuff, couple of lights running from the inverter as a giant UPS and getting far better power than from our crap-op grid here. Lights on grid would be flashing and flickering with faulty power, the other lights on the inverter of course were steady and bright.

 And as said, any power I could make from the gennies I was testing and flying at times was extra power I did not buy from the grid. Even without the power I made, the peace of mind, better quality, and steady power was worth the trouble and expense to me anyway.
.
nothing to lose

Spelin and tpying are my strong points, not electronics.



Re: Too much power from the grid (3.00 / 0) (#8)
by Norm on Sun Nov 13, 2005 at 03:30:29 AM MST

   Well the first part about the tv and computer
right now I don't have that big of an inverter to
run the computer or the big tv and shutting down
the outdated computer and leaving on the 32 inch
TV is not my idea...
   One of these days maybe I'll have a couple of batteries....and a (bunch of weight driven generators)...inverters etc.
               ( :>) Norm.
( :>) Norm
[ Parent ]


Re: Too much power from the grid (3.00 / 0) (#10)
by wooferhound on Sun Nov 13, 2005 at 07:09:01 PM MST

 My computer system has a Master Switch that I built to turn on the computer and about 8 other components connected to it. For surge/lightning protection I have 5 varisters wired to the outlets to help absorb the surge before it can get to the computer. but the switch does not simply turn off the power.



The switch disconnects computers Load Wire from the power hot wire and connects it to the neutral wire. So when the switch is in the 'off' position, all the plugs for the computer system are shorted out as shown in the picture above. If lightning comes in on the power line, and is strong enough to jump the gap in the switch, the energy will go equally onto both the hot and neutral. There is no differential of voltage going into the power supplies.

 Of course, If the lightning voltage is strong enough to jump the gap of an 'open' switch, it will probably have enough energy to jump again to any conducting point it decides to. But it makes me think that I'm protecting my system in one more additional way.
W o o f -={(



Too much power from the grid | 10 comments (10 topical)
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