Transmission lines according to the structure can be divided into overhead transmission lines and underground transmission lines

Transmission lines according to the structure can be divided into overhead  air circuit breaker  lines and underground power lines. Former by the line towers, conductors, insulators, etc., set up on the ground; latter mainly cable, laid in the ground (or water). Transmission sent by the current nature can be divided into HVDC and AC  electric meter . 1880s successfully achieved first HVDC, after due not to mention the high voltage limits (transmission capacity and the transmission voltage roughly proportional to the square) late 19th century was replaced by AC transmission. AC transmission success ushered in the 20th century, the era of electrification. Since the 1960s, the development of power electronics technology, there are new developments in HVDC and AC transmission matched to form a hybrid AC-DC power system.