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For some year past, the transmission of electric power by DC has been receiving the active consideration of engineers due to its numerous advantages.Advantage
. It require only two conductors a compared to three for AC transmission.

. There is no inductance, capacitance, phase displacement and surge problem in Dc transmission.

. Due to the absence of inductance, the voltage drop in a Dc transmission line is less than the AC line for the same load and sending end voltage. For this reason, a DC transmission line has better voltage regulation

. There is no skin effect in DC system. Therefore entire cross-section of the line conductor is utilized .

. For the same working voltage, the potential stress on the insulation is less in case of DC system than that in AC system. Therefore, a DC line required less insulation.

. A DC line has less corona loss and reduces interference with communication circuits.

. The high voltage DC transmission is free from the dielectric losses, particularly in the case of cables .

. In DC transmission, there are no stability problems and synchronizing difficulties.

Disadvantage

. Electric power cannot be generated at high DC voltage due to communication problems.

. The DC voltage cannot be stopped up for transmission of power at high voltages

. The DC switches and circuit breakers have their own limitations .