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Electric Power grid questions

by Charles123
Tags: electric, grid, power
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Feb17-12, 08:36 PM
P: 140
Utility poles have a grounded wire. Is this just for lightening? Is not connected the neither one of the 3 phase wires, is it? Is the static electricity wire always present, and is it grounded (at every pole, or every x poles)? What does the multi-grounded neutral wire do, and has it always have to be present? The 3 phase wires are only grounded at destination when electricity is being consumed?
If domestic consumers receive just one phase current, why there are 3 wires coming from the pole to the house?
Is ground always the return path for electrons? Is there a ground connection at every house directly or at the nearest utility pole?
In power plants the wires in the generator are connected to the ground, to close the circle?
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Feb18-12, 06:03 PM
P: 276
1. The ground is actually a neutral (which is different but similar). Using a neutral allows a 3-phase system to operate at a higher voltage while still allowing 1-phase pick-off. The 1-phase requires the neutral for shock safety. Neutral is at ground potential but not ground itself except at key points of distribution.

2. Houses may have 3 wire because it is 3-phase down to the junction box. The 1-phase used in the house is just one leg of the 3-phase. Electric dryers usually are 3-phase (in the US/Canada at least). Some house only have 2 wires because they have 1 phase service and the one phase was picked off at the pole.

3. Ground is simply a return based on the potential (voltage) of the system. Electron or positron/hole; it wouldn't actually matter what the carrier charge is.

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Feb19-12, 01:36 PM
P: 140
Thank you for your answer. I read the Wikipedia article, and It help understand new things, but it didn't really answered my questions... Maybe I failed to understand it properly, I don't know...

Feb19-12, 04:33 PM
P: 78
Electric Power grid questions

In USA, three phase to homes is rare ... more so than in many other places in the world. This is in part due to the way the lower 120 volt service is handled.

In many places where the distribution voltage is stepped down to a three phase system with 208/120 volts, homes will get TWO of the phases, giving them a 120/208 volt combination. This is more common in large apartment/condo buildings where there is economy in using a large three phase transformer.

In other places, the distribution just picks off one distribution phase, and steps the voltage down using a split phase transformer, providing 120/240 volts in a form with "2 phase lines" (at 180 degree phase angles) to the home. In other places, two distribution phases may be used to derive the 120/240 volts for the home.

I did say three phase to the home is rare in USA. However, my grandfather's house (built in 1961) did have three phase power. The stove and water heater did not heat as well since they were operating at 208 volts. Apparently they did not get 208 volt versions or heating elements.

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