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For the same generated and transmitted RMS value of power from an electrical power plant station, which transmission line used, assuming having the same wire specification (i.e. wire material conductivity, length, diameter etc) will exhibit the most power losses in the form of heat a DC or an AC line and why?

We assume besides both lines having the same wire specifications also being of the same length and that in the AC power line (50 or 60Hz) there are no intermediate voltage step-up transformers.

What is analytically the contribution of the skin effect on such an AC power (i.e. 50 or 60Hz) line to its power loss? Will this skin effect on the AC line make its losses more than the normal ohmic power loss of the DC line?

I'm asking because I have read assuming that both lines are identical, the power loss to heat per unit length is higher in an AC power line than in a DC power line and try to understand what is the physical reason. Keep in mind that the major reason why AC line was preferred over DC historically and until today is that the voltage can be step-up with transformers allowing longer transmission of electrical power (i.e. voltage drop in the line is a small fraction of the total transmitted).

However, the question remains, does a DC power transmission line have less power loss per unit of length?

Markoul11
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2 Answers2

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Power lines have slightly higher resistance for AC than for DC due to the skin effect.

The wiki article has extensive information on your question, including the AC vs. DC resistance of round wires. In practice, as power wires are stranded, the skin effect losses can be kept very small.

Why is AC still used? You also have to factor in power generation methods, safety, voltage transformation, ... That's where AC wins.

tobalt
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. . . . . does a DC power transmission line have less power loss per unit of length?

An important factor is that for ac the voltage swings between two voltages, $\pm V_{\rm peak} = \pm\sqrt 2 V_{\rm rms}$, which are larger than the equivalent (in terms of power transmission) dc voltage, $V_{\rm dc}=V_{\rm rms} = V{\rm peak}/\sqrt 2$.
At very high transmission voltages this means that insulation becomes a significant challenge particularly in terms of the breakdown of air resulting in corona discharge which represents a loss of electrical power.

Farcher
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