Why do we use Alternating Current (AC) instead of Direct Current (DC) in power lines?

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The majority of today’s electronics either do or can run on DC current, and must be converted from AC, which comes out of wall-outlets, in order to run. In addition, DC is safer – according to IEC 60479, it takes about four times as much DC current to kill a man than AC current. So why do we use AC? There are three main reasons:

  1. AC electricity loses less power over power lines than DC.
  2. It’s easier to change the voltage of an AC current, and the higher the voltage, the less power is lost. This is why non-residential power lines are more dangerous than residential power lines: they have a much higher voltage to reduce power loss over long distances.
  3. It’s easier to convert from AC to DC than the other way around. A DC power supply consists of a transformer, a capacitor, and a few diodes, all of which are cheap and non-mechanical (no moving parts). A non-mechanical DC-to-AC "inverter," however, is not so simple (which was doubly true before the invention of the transistor).

There are also historical reasons – see the War of Currents.

Additional Reading:


  1. sheeba says:

    thank u…………….


  2. Andreas says:

    I'm not so sure about your first reason: on a pure ohmic load a DC voltage will lead to the same losses as the corresponding AC RMS voltage (per definition). But a landline is not purely ohmic, it is also a capacitive load (also a minor inductive part, but we can neglect that for 50Hz lines). The reactive power that is needed because of the landline capacitance also has to be produced and is basically "wasted".

    If using the same landline, AC also has the disadvantage of leading to skin-effect, so the same "wire" has a higher ohmic resistance for AC (but ok, we have ways to deal with this).

    Those are the reasons why we get more and more HV-DC landlines.

    You are clearly right on the second point, at the time of the invention changing a DC voltage was pretty much impossible, which a transformer was very easy to build. Transforming to a higher voltage leads to lower currents and voltage drops on the landline, therefore less power loss.

  3. Erin says:

    Magnetic fields do not physically repel birds, nor attract them for that matter. Haven’t you ever seen birds perched on a power line?

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