voltage question.....

hello Forum,

a question regarding the way voltage "works" in a particular transmission
application.

In the mountains, I have seen power transmission power lines that use only
one metal wire. The second wire (return wire) is represented by earth,
i.e., the first wire is stuck straight into the ground.
Isn't that equivalent to complete the circuit with a incredibly large
resistance that dissipates a lot of power?
 
In cars, the chassis is used as the return wire, but that is a very good
conductor....earth is not such a great conductor to put in series in a
circuit.

Power=V*I. I guess that in this type of application they don't care about
the current I. But aren't they trying to transfer the largest amount of
power  as possible?

thanks
fisico32

fisico32 <marcoscipioni1@gmail.com> wrote:
 
> a question regarding the way voltage "works" in a particular transmission
> application.
 
> In the mountains, I have seen power transmission power lines that use only
> one metal wire. The second wire (return wire) is represented by earth,
> i.e., the first wire is stuck straight into the ground.
> Isn't that equivalent to complete the circuit with a incredibly large
> resistance that dissipates a lot of power?
(snip about cars)

Not if the current is low and the voltage is high.
 
> Power=V*I. I guess that in this type of application they don't care about
> the current I. But aren't they trying to transfer the largest amount of
> power  as possible?

Maybe, but some want to transfer the most power per unit wire cost.

-- glen

fisico32 wrote:

> hello Forum,
> 
> a question regarding the way voltage "works" in a particular transmission
> application.
> In the mountains, I have seen power transmission power lines that use only
> one metal wire. The second wire (return wire) is represented by earth,
> i.e., the first wire is stuck straight into the ground.
> Isn't that equivalent to complete the circuit with a incredibly large
> resistance that dissipates a lot of power?

Properly done ground connection has resistance less then 1 Ohm. This 
resistance is independent from the length of the ground path.


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com

fisico32 wrote:
> hello Forum,
> 
> a question regarding the way voltage "works" in a particular transmission
> application.
> 
> In the mountains, I have seen power transmission power lines that use only
> one metal wire. The second wire (return wire) is represented by earth,
> i.e., the first wire is stuck straight into the ground.
> Isn't that equivalent to complete the circuit with a incredibly large
> resistance that dissipates a lot of power?
>  
> In cars, the chassis is used as the return wire, but that is a very good
> conductor....earth is not such a great conductor to put in series in a
> circuit.
> 
> Power=V*I. I guess that in this type of application they don't care about
> the current I. But aren't they trying to transfer the largest amount of
> power  as possible?

You ought to be asking your questions in a more general forum if you can 
find one. Considering the extent of general knowledge arrayed here, 
there may not be one.

Resistance is proportional to length and inversely proportional to cross 
section. The effective cross section of an earth return can be very low. 
the greater the distance between end points, the greater the average 
effective cross section, so that the resistance remains fairly constant, 
on the order of a few ohme at most.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������

On Nov 6, 2:33&#4294967295;pm, "fisico32" <marcoscipio...@gmail.com> wrote:
>...........
> The second wire (return wire) is represented by earth,
> i.e., the first wire is stuck straight into the ground.
> Isn't that equivalent to complete the circuit with a incredibly large
> resistance that dissipates a lot of power?
>
>....earth is not such a great conductor to put in series in a
> circuit.

Perhaps the heat dissipated in the earth by the
return current is a major cause of global warming
and the melting of the polar ice caps?

Jerry Avins wrote:

> Resistance is proportional to length and inversely proportional to cross 
> section. The effective cross section of an earth return can be very low. 
> the greater the distance between end points, the greater the average 
> effective cross section, so that the resistance remains fairly constant, 
> on the order of a few ohme at most.

One interesting implication of that is the effective path of current 
goes at the depth ~ 1/2 of the end-to-end distance. So the system 
behaves like big loop. This is how VLF antennas work.


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com

On 11/6/2009 3:49 PM, dvsarwate wrote:
> On Nov 6, 2:33 pm, "fisico32"<marcoscipio...@gmail.com>  wrote:
>> ...........
>> The second wire (return wire) is represented by earth,
>> i.e., the first wire is stuck straight into the ground.
>> Isn't that equivalent to complete the circuit with a incredibly large
>> resistance that dissipates a lot of power?
>>
>> ....earth is not such a great conductor to put in series in a
>> circuit.
>
> Perhaps the heat dissipated in the earth by the
> return current is a major cause of global warming
> and the melting of the polar ice caps?

That and the heat generated by the use of energy.  The heat from all the 
combustion engine radiators, shed using equipment cooling fans on 
electrical equipment, radiated by cooling fins, shed by power plant 
cooling towers, etc., etc.   All that heat goes somewhere.

I suspect if everybody just shut all the computers and servers off for a 
few days we'd descend into another ice age.

;)

-- 
Eric Jacobsen
Minister of Algorithms
Abineau Communications
http://www.abineau.com

As far as I'm aware in the UK the neutral is always a wire but
sometimes the earth might be from an earth rod for remote places. The
problem with an earth rod is it's resistance depends on the type of
ground. If you live somewhere soggy you're ok but in the desert you
have problems. It's resistance can be well over 1 ohm and for that
reason you always have to install an rcb on the incoming mains if
you're using an earth rod.

Fully Half Baked wrote:
> As far as I'm aware in the UK the neutral is always a wire but

There's much you're not aware of.

> sometimes the earth might be from an earth rod for remote places. The
> problem with an earth rod is it's resistance depends on the type of
> ground. If you live somewhere soggy you're ok but in the desert you
> have problems. It's resistance can be well over 1 ohm and for that
> reason you always have to install an rcb on the incoming mains if
> you're using an earth rod.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������

On Fri, 06 Nov 2009 14:33:26 -0600, "fisico32"
<marcoscipioni1@gmail.com> wrote:

>hello Forum,
>
>a question regarding the way voltage "works" in a particular transmission
>application.
>
>In the mountains, I have seen power transmission power lines that use only
>one metal wire. The second wire (return wire) is represented by earth,
>i.e., the first wire is stuck straight into the ground.
>Isn't that equivalent to complete the circuit with a incredibly large
>resistance that dissipates a lot of power?

Imagine earth as if it's an arbitrarily large reservoir of electrons.
You can take or give as many as you want on each end; actual electrons
need not move (much). So that's not an incredibly large resistance, in
fact can be made as small as a couple of hundreds of milli-ohms.
-- 
Muzaffer Kal

DSPIA INC.
ASIC/FPGA Design Services

http://www.dspia.com