Difference between AC and DC Transmission Systems

The electric power can be transmitted either by using AC transmission system or DC transmission system. Each transmission system has its own advantages and disadvantages. Therefore, to choose the right system for electric power transmission, we need to compare the two systems.

The following table compares and contrasts the AC transmission system and DC transmission system based on different parameters −

ParameterAC Transmission SystemDC Transmission System
DefinitionAn electric power transmission system that uses alternating current to transmit the power is called the AC transmission system.An electric power transmission system which transmits the electric power in the form of DC supply, is called the DC transmission system.
Construction of Transmission LineThe construction of AC transmission lines is more complicated.The construction of DC transmission lines is less complicated.
GenerationIn the AC transmission system, electric power can be generated easily at high voltages.In the DC transmission system, electric power cannot easily be generated at high voltage due to commutation problems.
Number of ConductorsFor the AC transmission, three conductors are required, (for red phase, yellow phase and blue phase).For DC transmission, only two conductors (positive and negative) are required.
Need of TransformerIn the AC transmission, transformer is used for stepping-up or down the voltage.In DC transmission, the transformer cannot be used as the transformer does not work with the DC supply.
Insulation MaterialThe AC transmission requires more insulation material due to more number of conductors.The DC transmission requires less insulation material due to less number of conductors.
Stability and SurgesEffects of stability and surges are found in the AC transmission.The DC transmission is free from the effects of stability and surges.
Factor PresentIn AC transmission lines, the capacitance, inductance and phase displacement are present.In DC transmission lines, the capacitance, inductance and phase displacement do not present.
Effect of CapacitanceIn AC transmission lines, the presence of capacitance causes a continuous power loss.In DC transmission lines, no capacitance is present, thus no power loss.
Effect of InductanceInductance is present in the AC transmission lines causes more voltage drop. Therefore, it has poor voltage regulation.Inductance is not present in the DC transmission lines, hence the voltage drop is less. Therefore, it has good voltage regulation.
Change in Voltage LevelIn AC transmission system, the transformer is used for increasing or decreasing the voltage level.In DC transmission system, chopper and booster are used for increasing or reducing the voltage level.
Skin EffectThe skin effect occurs in the AC transmission system.In case of DC transmission system, the skin effect does not occur.
Corona EffectCorona most exists in AC transmission system.Corona rarely exists in DC transmission system.
Required ComponentsThe main components of AC transmission system are transformer, conductors and insulators.The main components of DC transmission system are rectifier, conductors, insulators and inverter.
CostThe construction and maintenance of the AC transmission system is cheap.The construction and maintenance of DC transmission system is expensive.
Repair and MaintenanceThe repair and maintenance of AC transmission system is simple and easy.The repair and maintenance of DC transmission system is difficult as compared to AC transmission system.
Length of ConductorsThe AC transmission system is used for short distance transmission.The DC transmission is used for transmission of electric power for long distances.
InterferenceThe AC transmission lines interfere the nearby communication lines.The DC transmission lines do not interfere the communication lines.
Dielectric LossThe AC transmission lines have dielectric losses.The DC transmission lines do not have dielectric losses.


From the above comparison, it is clear that the high-voltage DC transmission is superior to the high-voltage AC transmission.

Updated on: 14-Feb-2022

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