Advantages and disadvantages of DC (Direct current) transmission

Less number of conductors needed as DC transmission requires two conductors where as a three phase AC transmission requires three conductors.
There is no skin effect in DC and hence the cross section of entire conductor is fully utilized. Thus the effective resistance of the conductor in DC is less than that of AC.
There are no effects of inductance, capacitance and phase angle displacement on the lines in DC transmission.
The DC transmission has better voltage regulation. Due to the absence of inductance the voltage drop is comparatively less in DC than that of an AC system.
The corona effect and interference with communication circuits is less in DC.
There are no stability and synchronizing problems in Direct Current transmission.
The potential stress on the conductors is less in DC transmission and hence it requires less insulation.

Difficulty of generating the DC at high voltage because of the commutation problems.
The voltage in DC system cannot be easily stepped up for high voltage transmission. Whereas in AC system it can be easily done with a transformer.
Moreover DC circuit breakers and switches offer more limitations.