why do we transmit electricity at high AC voltage?

[Omegachi]

the resistance of the wire if transmitting through a high V?

 

[Omegachi]

nvm, answer is in P=IV and V=IR

 

[MrDudeMan]

simple answer: Power = current^2 * R. R is the resistance in the wire, so the amount of power dissipated through the wire increases exponentially through current. if you transmit 800kV across lines and transform it at the other end to get 120/240/etc. with higher current, you lose MUCH less power in the process.

 

[Varun]

To supplement the previous answer, it also is because more current = thicker wire needed. Change the current into voltage and you require smaller cable to transmit the electricity.

 

[MrDudeMan]

Originally posted by: Varun
To supplement the previous answer, it also is because more current = thicker wire needed. Change the current into voltage and you require smaller cable to transmit the electricity.

oops, forgot to mention that. good catch.

yeah the cost of those wires is pretty steep since they are so long. reducing the diameter is a huge savings, and as Varun said, less current = smaller wire.

 

[Mday]

not to mention AC conversion into lower voltages is easier than with DC.

 

[the splat in the hat]

in english ac high voltage doesnt downfall too much and loose volts/currrent.
dc at high or low voltage has massive downfall.

 

[pm]

Originally posted by: the splat in the hat
in english ac high voltage doesnt downfall too much and loose volts/currrent.
dc at high or low voltage has massive downfall.

Actually, high-voltage direct current (HVDC) is used for many of the largest transmission lines, and for a lot of shorter underwater power lines. AC high-power transmission lines have a fairly large electric field with them that needs to be modulated leading to further I^2*R losses, compared to DC where this field is static.

Historically, HVAC was preferred over HVDC because it's easier to step voltages using transformers, but with recent advances is semiconductors HVDC is increasingly being chosen for very long distance power transmission.

http://en.wikipedia.org/wiki/HVDC

 

[MrDudeMan]

Originally posted by: pm

Originally posted by: the splat in the hat
in english ac high voltage doesnt downfall too much and loose volts/currrent.
dc at high or low voltage has massive downfall.

Actually, high-voltage direct current (HVDC) is used for many of the largest transmission lines, and for a lot of shorter underwater power lines. AC high-power transmission lines have a fairly large electric field with them that needs to be modulated leading to further I^2*R losses, compared to DC where this field is static.

Historically, HVAC was preferred over HVDC because it's easier to step voltages using transformers, but with recent advances is semiconductors HVDC is increasingly being chosen for very long distance power transmission.

http://en.wikipedia.org/wiki/HVDC

From that link...

In a number of applications HVDC is often the preferred option.

* Undersea cables. (e.g. 250 km Baltic Cable between Sweden and Germany [3]).
* Endpoint-to-endpoint long-haul bulk power transmission without intermediate 'taps', for example, in remote areas.
* Increasing the capacity of an existing power grid in situations where additional wires are difficult or expensive to install.
* Allowing power transmission between unsynchronised AC distribution systems.
* Reducing the profile of wiring and pylons for a given power transmission capacity.
* Connection of remote generating plant to the distribution grid, for example Nelson River Bipole.
* Stabilising a predominantly AC power-grid,without increasing maximum prospective short circuit current

Long undersea cables have a high capacitance. While this has minimal effect for DC transmission, the current required to charge and discharge the capacitance of the cable causes additional I2R power losses when the cable is carrying AC. In addition, AC power is lost to dielectric losses.

HVDC can carry more power per conductor, because for a given power rating the constant voltage in a DC line is lower than the peak voltage in an AC line. This voltage determines the insulation thickness and conductor spacing. This allows existing transmission line corridors to be used to carry more power into an area of high power consumption, which can lower costs.

good stuff...learn something new every day

 

[DrPizza]

Awesome info.. I'll carry it over into my physics class this year.