jimmyboy
Hazard to Others
Posts: 235
Registered: 1-3-2004
Location: Texas
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Mood: No Mood
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How electrical lines work
This is more of a general science question than chemistry - but recently I had a blackout that lasted for two days in our town and was wondering about
redundancy in our local electrical supply. If only one power line is knocked down in a storm does that knock out all the power to everyone down that
line (I've always noticed 3 wires on most electrical posts)
or are the other 2 remaining wires used as backups - I seem to remember something about 3-phase power but the subject is hazy.
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hodges
National Hazard
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Registered: 17-12-2003
Location: Midwest
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As I recall (it's been a while since I read about this), there are several lines which each contain the same AC voltage (sine wave) but each at a
different phase angle. Each home/business is fed by two or more of these lines. Typically about half the load of the home/business is connected
between each of these lines and ground for 120V (US). Appliances requiring a higher voltage (240V US) are connected between the wires vs. between one
wire and ground.
Thus if all the wires are not live, things are not going to work. There is no "backup" in the system. I guess theoretically if only one of
the lines is broken you could get half your house to work - but in practice no doubt things shut down during abnormal conditions such as that to
prevent undesirable things from happening.
This explanation probably was hard to follow and contains inaccuracies, but hopefully it was better than nothing.
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Magpie
lab constructor
Posts: 5939
Registered: 1-11-2003
Location: USA
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Mood: Chemistry: the subtle science.
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residential power distribution
I recently did some research on this as I've always been curious about the aerial transformer on the pole in my backyard.
Also on the pole is a crossbar with 2 bare wires. One wire is a neutral and the other is a fused hot wire at several thousand volts AC. Taps from
these 2 wires go to the primary side of the transformer. The transformer secondary side has three terminals, one of which is called a centertap. The
centertap is also connected to the neutral. The other 2 taps are hot and are at 120 VAC, but are 180 degrees out of phase with each other. All 3 of
these secondary lines are brought to my house. Using the 2 hot lines at an appliance will provide 240 VAC. Using just one of the lines and the
neutral will yield 120 VAC.
This is basically what Hodges has said. So if the hot wire on the crossbar (at several thousand volts) goes out I would not have power at the house
on either hot 120 VAC line. I'm not sure what if anything would happen if the neutral were broken as it is grounded at my house anyway.
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jimmyboy
Hazard to Others
Posts: 235
Registered: 1-3-2004
Location: Texas
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oh yeah thats right - the center of the three is usually the ground wire - so i guess either way if one gets cut then everyone down the line is outta
luck - fat chance that center one would get snapped by itself.
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