Basic structure of transmission line

A transmission line consists of conductors, supporting towers and its grounding, insulators, and usually shield wires (overhead ground line). The most commonly'used conductor for HV transmission lines is aluminum conductor steel reinforced (ACSR). For reducing the corona on the surface of the conductors, bundled conductor is used for 500kV line, in which a phase conductor consists of more sub-conductors (four conductors for 500kV line). The shield wires are used to protect the energized conductors from lightning. The supporting poles or towers have different frame structure and must be well grounded. Insulators are used to support the conductor and make it being insulated from the pole or tower and usually are of suspended type. The ground device of a transmission line helps to release and guide lightning current, thus lower the electric potential at the top of poles or towers to protect the line insulator from breakdown or flashover.

Transmission line and distribution line

The high voltage power line through which power is transmitted from power plant's step-up substation to step-down substation is called power transmission line. The voltage classes of 35kV and above are generally used. High voltage distribution line is the power line that transmits the power from step-down substation to distribution transformers. Low voltage distribution line is the line that transmits power from distribution transformer to the users. The normal voltage of power distribution line is 380V

The special sections of the overhead transmission line refer to the sections with large spanning, serious pollution, lightning frequently happening and heavy raining. The overhead line section whose span is l 000m and longer or the height of the pole or tower is l00m and higher is called large spanning line section.

掌握电力线路的物理现象、参数及其相应的公式，熟悉架空线路的主要组成部分及各部分的作用。掌握输电线路的π型等值电路。

1、 线路的电阻、意义及其计算；

2、 线路的电抗、含义及其计算；

3、 线路的电纳、含义及其计算；

4、线路的电导、含义及其计算。