Difference between AC and DC currents

Difference between AC and DC current
  • Ability to lower or increase voltage
    • Electricity is transmitted over long distances at very high voltages (and thereby proportionately reduce the current). According to Joule’s Law, energy losses are directly proportional to the square of the current – thus, the reduced current flowing through the line reduces the heating losses in the conductors. That’s why mains power is transmitted at many hundreds of thousands of volts, and is only stepped down to the 110V or 230V that you’re used to when it is near your building.
    • Before the advancement in power electronics and High-voltage direct current (HVDC), it was impossible to economically step up DC to a voltage suitable for transmission. Without stepping up, transmitting to even few 100 meters was extremely lossy and long distance transmission was impossible.
    • However, a transformer can step up or step down AC voltages with ease. This easy nature made everyone adopt AC system and now the whole world has its electrical infrastructure designed for AC.
  • Losses by way of movement
    • In DC, there is a movement of free electrons in a specific direction which causes heating of the conductor and leads to loss of energy.
    • While in AC, there is no actual movement of free electrons. Rather they just keep oscillating at their initial position. Due to this, negligible heating is there, and thus, least loss of energy.
  • In recent times however, power electronics has made significant advancements and its now possible to step up and step down DC using HVDC converter stations – and the world is slowly moving towards HVDC transmission.
  • This is because with Direct Current – the current flowing in one direction all the time, and so is not impeded by this inductance, and has negligible capacitive losses – on the other hand, there are huge losses in HVAC due to the skin effect.

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