Difference between AC and DC and its advantages/disadvantages

Sep 9, 2017   //   by admin   //   Knowledge Base  //  No Comments

As the name suggests, this paper explains about what AC and DC is and difference between the two and their advantages and disadvantages. To look at it more carefully, lets first brief ourselves with concepts.


AC: this is a short form used for Alternating current. But due to heavy usage it is popularly known as AC. While DC is a short used for Direct Current. Both the terms are used to refer to voltage or electric signals and not are in particular are currents.

These terms are used for the current or voltage in a circuit.

About Alternating Current or AC:

AC is a specific type of electric current wherein the direction of the current’s flow is reversed on regular basis. This means that current flows in one direction and reverses its own direction. The voltage is hence continually changing between positive (+) and

negative (-). Alongside is a picture depicting the graph of flow of current from + to -.
The rate at which the flow changes the direction is referred to as frequency. This can be understood as no of upward and downward cycles per second which is

measured in Hertz or Hz.
Use: it is utilized largely for powering devices and bulk transfer of power.

About Direct Current or DC:
DC as the name suggests always flows in one, uniform direction. The DC voltage is

always either positive or always negative. However there could be increase of decrease in the voltage but the direction of the flow remains unchanged. The graph here represents the Direct current voltage.


  1. Reactance: DC ensures no reactance in the line. It can transmit to high power through the capacity of the line, providing higher capacity utilisation of generators.
  2. Power: the DC system, power is the real component. The transmission system operator need not worry about sufficiency of the reactive power to maintain the stability and security of the system. The absence of the reactive power translates to higher power transfer capacity of line and higher capacity utilization of generators.
  3. Frequency: In DC system, there is no frequency variation, this transient stability during clearing and switching is no more a problem.
  4. Susceptance: DC system doesnt introduce susceptance along the line thus removing the effect of charging the current and over voltage in the system. This also translates to higher capacity of the higher power transmission specially for underground and submarine cables. This is cost saving through installation of inductive shunt reactors.

Basic Differences between AC and DC

1. Cost effective: DC is expensive and dangerous at times, since the risk of the damage is high. However AC is rather cost effective in generating and transmiting using the transformers without risking the devices power is offered to.

  1. Voltage: AC can be generated in high voltage. However DC cant be generated at high voltage since sparking begins at commuator which can damage the system. Also, DC systems, the voltage must be generated in the right amount else there is wastage of supply of voltage.
  2. Long distance: DC are poor carriers of voltage current and transmit in long distances. Large amounts of power is lost due to resistance of the wire. But through the use of transformer, efficient transformation of electric power over the long distance lines is possible.
  3. Resistance: DC system offers lower resistance than AC system, thus it will have lower line losses. AC has higher resistance in the wire and hence it is also called as “skin effect”.

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