# power distribution?

Discussion in 'General Electronics Chat' started by Mathematics!, Apr 7, 2009.

1. ### Mathematics! Thread Starter Senior Member

Jul 21, 2008
1,022
4
Ok , I am curious how the power company distributes it electricity.
What I want to understand is how does the power company distribute it's electricity for miles and miles without the voltage drop to be signifigant?

I have been told that the power company's generator generates a voltage of 200KV. But then I can figure out what the voltage dropped is be the length of the wire and gage.

Curious to know what AWG gage they use from the power generator to the substation to the powerline to the home. They must be different.

Anybody know?

I know in home's I used as high as 6 gage but I believe the powerlines at the pole outside are 1/0 but not sure.

I am curious to know the gages so I can calculate the voltage drops.

I know what every voltage gets to the transformer bucket must be stepped down/or up to 240 volts between the two hot black wires and 120 between any black and the center tabed white neutral wire.

Assume we are in the United States because I know they do thing's differently else where.

And curious to know what is the biggest wire gage made for use?

Last edited: Apr 7, 2009
2. ### PRS Well-Known Member

Aug 24, 2008
989
35
Ohms law and the power dissipation interact. Take a power of 7 watts. You can get that with 1 amp and 7 volts or you can get that with .1 amp and 70 volts, or .001 amp and 700 volts. Do you see how you can get the same power by increasing the voltage and decreasing the current?

The size of wire is related to the size of current. High current takes fat wire, small current takes skinny wire. This principle, and the ease of transformers to make the transformation, is why we use AC current in residential, commercial and industrial applications.

As for the exact sizes of wire involved I can't tell you offhand.

3. ### Mathematics! Thread Starter Senior Member

Jul 21, 2008
1,022
4
Yes but we are talking about 3 phase AC not DC.

So V = |V| sin(1/60 * t)
I = |I| sin(1/60 * t )
Because it has a frequency of 60 cycles per second

So power is P = VI = |V||I| sin(1/60 * t) *sin(1/60 * t )

But I am still curious is if ac voltage drop will be the same as dc voltage drop in a wire.

For example say I have a 14 gage wire length is 100 feet do I get the same voltage drop using either a 10 volt battery or a 10 volt ac generator?

They must mean by 200KV is the root mean square rms (i.e the equivalent dc for the ac )

So I guess we can do the voltage drop calculations in terms of the equivalent dc.

But I just didn't know if the ac provided flucations or less voltage drop over a certain time.

4. ### thingmaker3 Retired Moderator

May 16, 2005
5,072
6
Same voltage drop whether AC or DC.

Here's why: We measure AC using the "RMS" value. This is the value which dissipates heat equivalent to the same magnitude of DC. So, by definition, the wires will dissipate the exact same power.

5. ### recca02 Senior Member

Apr 2, 2007
1,211
0
AC has more voltage drop in wires if one considers skin effect (one reason why HVDC seems better). AC are preferred due to ease in stepping up.
Generators typically generate around 15.75 KV (in India) then voltage is stepped up to 220KV/400KV. The more the voltage for the same power the lesser the current, meaning lesser I*I*R losses.

6. ### thingmaker3 Retired Moderator

May 16, 2005
5,072
6
Have you calculated skin effect at 60Hz? It is 0.336 inhces. In any power line with this or smaller radius, DC and AC resistance at 60Hz will be identical.

Note also that current does not simply cease to flow at skin depth - it is a reference - the point at which current density has fallen to 37% of the surface.

For a ratio of AC to DC resistance in round wire, use:

r^2 / (2rS - S^2) where r = radius of the conductor and S = skin depth.