考虑线路参数依频特性的特高压半波长交流输电线路行波传播分析

Analysis of Traveling Wave in UHV Half-wavelength Transmission Lines Considering Frequency Dependent Characteristics

为分析类似特高压半波长线路的超长线路上行波传播特点,在考虑线路参数依频特性的条件下,对线模行波与零模行波在不同故障距离上所体现出的波速差异进行了理论研究。从理论推导与仿真验证两个方面指出:故障点无法解耦而导致的"模混杂"会造成从故障点反射至线路两端的零模行波包含由线路两端反射至故障点的部分线模行波,渗透进入零模通道的线模行波会使计算得到的零模平均波速趋近于线模平均波速;随着传播距离的增加,零模行波与线模行波的差异逐渐增大,在传播距离达到3 000 km时,零模行波所含高频量极少,波形平缓,利用高频量进行标定的方法容易失效。分别利用小波模极大值与行波幅值10%作为波到时刻判据对零模行波到达时刻进行了标定,指出波到时刻的定义与标定方法有关,且随着传播距离的改变,平均波速也会出现较大变化,不能以单一波速进行测距计算。

In order to study the characteristic of traveling wave on ultra-long transmission line which is similar to half-wave length line, we analyzed the difference of wave speed of air mode and earth mode in distinct fault distance after taking the frequency-dependent characteristics of transmission lines into consideration. Theoretical analysis and simulation results show that the traveling waves in the air mode and earth mode can refract to passageways of each other, so the air mode traveling wave in the earth mode will increase the calculated mean wave speed of earth mode traveling wave, with the impossibility of decoupling fault point. Compared with the air mode traveling wave, the earth mode traveling wave is smoother with radiation length increasing. Therefore, calibration of the earth mode traveling wave is far more difficult in half-wavelength transmission systems if the traveling distance is longer than 3 000 km. In order to illustrate that the arriving time of wave is related to the calibration method, the maximum value of the wavelet transform modulus and the 10% wave amplitude are used to calibrate the earth mode traveling wave. The simulation results also show that the average wave speed is much different with the change of traveling distance, and simply using the single traveling wave speed cannot fit the demand of fault location.