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1、7.4 波在传播中的衰减与畸变 7.4 Attenuation and Distortion in Wave Propagation,波在实际线路中传播，总会发生程度不同的衰减和变形。本节主要讲两个因素对波传播的影响： Attenuation and distortion always occurs in wave propagation. This section will focus on two factors of the effects of wave propagation.,7.4.1 线路电阻和绝缘电导的影响 7.4.1 Effects of Wire Resistance a
2、nd Insulation Conductance 7.4.2 冲击电晕的影响 7.4.2 Effect of Impact Corona,本节内容 Contents in this section,7.4.1 线路电阻和绝缘电导的影响 Effects of Wire Resistance and Insulation Conductance,图7-23 单根有损耗传输线的单元等值电路 Fig.7-13 Unit equivalent circuit of single-phase loss transmission wire,考虑导线电阻R0和线路对地电导G0时，单相有损传输线的单元等值电路
3、如图7-23所示。 Considering wire resistance R0 and wire-to-ground Conductance G0, the unit equivalent circuit of single-phase loss transmission wire is shown in Figure 7-13.,线路参数满足条件,（7-41）,时，波在线路中传播只有衰减，不会变形。,While wire parameters satisfiys the above conditions, wave propagated in the transmission wire w
4、ill only be attenuated but not deformed.,因为此时，波在传播过程中每单位长度线路上的磁能和电能之比，恰好等于电流波在导线电阻上的热损耗和电压波在线路电导上的热损耗之比。,Because at this time, the ratio between the magnetic energy and electric energy per unit length is just equaled to the ratio between heat loss of resistance on the current wave and heat loss of r
5、esistance on the voltage wave in the process of wave propagation.,即,所以电阻R0和电导G0的存在不致引起波传播过程中电能与磁能的相互交换，电磁波只是逐渐衰减而不至于变形。,Therefore, the exist of resistance R0 and conductance G0 do not lead to the mutually exchange of electricity and magnetic energy in wave propagation process. The electromagnetic wa
6、ve is just gradual attenuated but not deformed.,式(7-42)叫做波传播的无变形条件，或叫无畸变条件。满足此条件时，电压波和电流波可以写成以下形式： Formular (7-42) is called the wave propagation in the non-deformation conditions, or non-distortion condition. If it meets this condition, the voltage wave and current wave can be written in the follow
7、ing forms.,式中 为衰减系数。实际输电线路并不满足上述无变形条件，因此波在传播过程中不仅会衰减，同时还会变形。此外由于集肤效应，导线电阻随着频率的增加而增加。,is the attenuation coefficient . The actual transmission wire does not meet the non-deformation conditions. So the wave in propagation process will not only be attenuated but also be deformed. In addition, due to th
8、e skin effect wire resistance will be increased with the increase of frequency.,任意波形的电磁波可以分解成为不同频率的分量，因为各种频率下的电阻不同，波的衰减程度不同，所以也会引起波传播过程中的变形。 The electromagnetic waves of arbitrary waveforms can be decomposed into distinct frequency components. The resistances are variety because of distinct frequenc
9、ies. The degree of wave attenuation is different. So it will give rise to the deformation during wave propagation.,7.4.2 冲击电晕的影响 7.4.2 Effect of Impact Corona,在电网中，线路参数随频率而变的特性也会引起行波的畸变。此外，在过电压作用下导线上出现电晕将是引起行波衰减和变形的主要因素。 The characteristic that wire parameters varied with frequency will lead to the
10、distortion of traveling wave in the grid. In addition, under the effect of overvoltage, the appearance of corona on conductor would be the main factors of wave attenuation and distortion.,雷电冲击波的幅值很高，在导线上将产生强烈的冲击电晕。可以认为，在不是非常陡峭的波头范围内，冲击电晕的发展主要只与电压的瞬时值有关。 The amplitude of lightning shock wave is extra
11、ordinarily high. A strong impact corona will be produced on the wire. What can be considered that in range of a gently wave-head, the development of impact corona is mainly related to the instantaneous value of voltage.,但是不同的极性对冲击电晕的发展有显著的影响。电晕外观上是较为完整的光圈。 However, the distinct polarities affected t
12、he development of impact corona significantly. The appearance of corona is a relatively complete aperture.,出现电晕后将导致导线间耦合系数的增大。输电线路中导线和避雷线间的耦合系数k通常以电晕效应校正系数来修正，如（7-43）式所示 After the corona occurs, the coupling coefficient between wires will be increased. The coupling coefficient k between transmission
13、 wire and lightning protective wire is usually modified by correction factor of corona effect. It is shown as formula (7-30).,由于负极性电晕发展较弱，而雷电大部分是负极性的，所以在过电压计算中常以负极性电晕作为计算的依据。 Because the development of the negative corona is weak and most thunder and lightning charges is negative, the negative coron
14、a is usually used as the gist of calculation of over-voltage.,（7-43）,它是几何耦合系数，取决于导线和避雷线的几何尺寸和相对位置；电晕效应校正系数；我国电力设备过电压保护设计技术规程(SDJ7-79)建议按表7-l选取。 It is the geometric coupling coefficient which depends on the geometry and relative position of transmission wire and lightning protective wire. The selecti
15、on of correction factor of corona effect is suggested by Table 7-l according to Chinas “Electrical Equipment Design Procedures of Overvoltage Protection (SDJ7-79)“.,表7-1耦合系数的电晕修正系数k1 Table 7-1 Correction factor of corona coupling coefficient k1,由于电晕要消耗能量，消耗能量的大小又与电压的瞬时值有关，故将使行波发生衰减的同时伴随有波形的畸变。由冲击电晕引
16、起的行波衰减和变形的典型波形如图7-24所示。 As the corona consumes energy, the consumption is related to the instantaneous value of voltage. So it will lead to the attenuation and the distortion of waveforms. Due to the impact of corona, the typical waveforms of attenuation and distortion are shown as Fig.7-14.,图7-24 电晕引起的行波衰减和变形图 Fig.7-24 Attenuation and distortion of traveling wave caused by corona,曲线1表示原始波形，曲线2表示行波传播距离为 l 后的波形，从该图可看出，当电压高于电晕起始电压uk后，波形开始剧烈衰减和变形。 Curve 1 represents the original waveform whil
