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 −

Parameter	AC Transmission System	DC Transmission System
Definition	An 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 Line	The construction of AC transmission lines is more complicated.	The construction of DC transmission lines is less complicated.
Generation	In 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 Conductors	For 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 Transformer	In 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 Material	The 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 Surges	Effects of stability and surges are found in the AC transmission.	The DC transmission is free from the effects of stability and surges.
Factor Present	In 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 Capacitance	In 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 Inductance	Inductance 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 Level	In 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 Effect	The skin effect occurs in the AC transmission system.	In case of DC transmission system, the skin effect does not occur.
Corona Effect	Corona most exists in AC transmission system.	Corona rarely exists in DC transmission system.
Required Components	The main components of AC transmission system are transformer, conductors and insulators.	The main components of DC transmission system are rectifier, conductors, insulators and inverter.
Cost	The construction and maintenance of the AC transmission system is cheap.	The construction and maintenance of DC transmission system is expensive.
Repair and Maintenance	The 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 Conductors	The AC transmission system is used for short distance transmission.	The DC transmission is used for transmission of electric power for long distances.
Interference	The AC transmission lines interfere the nearby communication lines.	The DC transmission lines do not interfere the communication lines.
Dielectric Loss	The AC transmission lines have dielectric losses.	The DC transmission lines do not have dielectric losses.

Conclusion

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