Eaton PLC系统 MPB2-TP CPU模块

Eaton  PLC系统  MPB2-TP  CPU模块

交流输电应用中长地下或海底电缆的电容效应也适用于交流架空线路，尽管程度要小得多。然而，对于长交流架空输电线路，仅用于对线路电容充电的电流就可能很大，这会降低线路向远端负载输送有用电流的能力。

降低交流线路有用载流能力的另一个因素是集肤效应这导致导体横截面上的电流分布不均匀。用直流电工作的传输线导体不会受到任何限制。因此，对于相同的导体损耗(或热效应)，当与HVDC一起运行时，给定的导体可以比AC向负载输送更多的功率。

最后，根据环境条件和采用HVDC运行的架空线路绝缘的性能，给定的输电线路有可能以恒定的HVDC电压运行，该恒定的HVDC电压近似等于其设计和绝缘的峰值交流电压。

交流系统输送的功率由下式定义均方根(均方根)的交流电压，但均方根只有约71%的峰值电压。因此，如果HVDC线路能够以与AC等效线路的峰值电压相同的HVDC电压连续运行，那么对于给定的电流(其中HVDC电流与AC线路中的RMS电流相同)，以HVDC运行时的电力传输容量比以AC运行时的容量高大约40%。

The capacitive effects of medium length underground or submarine cables for AC transmission applications also apply to AC overhead lines, although to a much lesser extent. However, for long AC overhead transmission lines, the current used to charge the line capacitors alone can be large, which reduces the line's ability to deliver useful current to the remote load.

Another factor that reduces the useful current-carrying capacity of an AC line is the skin effect which results in an uneven distribution of current across the cross section of the conductor. Transmission line conductors operating with direct current are not subject to any restrictions. Therefore, for the same conductor loss (or thermal effect), when operating with HVDC, a given conductor can deliver more power to the load than an AC.

Finally, depending on environmental conditions and the performance of the insulation of overhead lines operating with HVDC, it is possible for a given transmission line to operate at a constant HVDC voltage that is approximately equal to its design and insulation peak AC voltage.