High-voltage direct current or HVDC transmission system emerged in 1930s when mercury vapor rectifier came into existence. Presently, HVDC transmission system is a mature technology and has had a fundamental influence in both long-distance transmission and in the interconnection of various systems. Transmission of power in DC form instead of AC and at high voltage is a new technology that has turned out to be more economic and simpler in operation. This new technology is HVDC transmission that works as the backbone of an electric power system. An HVDC link maintains a strategic distance from the disadvantages and limitations of AC transmission. HVDC transmission suggests that the AC power, which is generated at a power plant, is changed into DC power before it gets transmitted. In this paper, a brief study of HVDC transmission systems is presented. The applications and advantages of HVDC transmission systems are also outlined.