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1、3.1 液体电介质的极化与损耗 3.1 Polarization and loss of liquid dielectrics,3.1.1 液体电介质的极化 3.1.1 Polarization of liquid dielectrics 3.1.2 液体电介质的损耗 3.1.2 Loss of liquid dielectrics,本节内容 Contents in this section,3.1.1 液体电介质的极化 3.1.1 Polarization of liquid dielectrics 液体电介质的介电常数： The dielectric constant of liquid
2、dielectrics:,要由电介质的微观参数（N、）求得介电常数 ，必须先求得电介质的有效电场 。一般液体电介质的有效电场强度和宏观平均电场强度是不相等的。 To obtain dielectric constant from the dielectric micro-parameters (N,), you must first get the dielectric field intensity . Generally, liquid dielectric strength of the effective electric field and macro-average electri
3、c field is not equal.,电介质中某一点的宏观电场强度，是指极板上的自由电荷以及电介质中所有极化分子形成的偶极矩，共同在该点产生的场强。 The macro-field strength of a point in the dielectric is defined as the field strength co-generated here by the free-electrons as well as all the dipole moments of the dielectric polarization molecules in the plate .,这样，电介
4、质中任一点电场强度，便等于极板上自由电荷面密度在该点产生的场强/ 与束缚电荷面密度/ 在该点产生的场强-/ 之和，即 Thus, the dielectric field strength of any point in the dielectric equals to the field strength / generated by the free-charges surface density of the plate plus the field strength -/ generated by the bound-charges surface density / , that i
5、s,由于偶极矩间的库仑作用力是长程的，有效电场强度的计算很复杂。洛伦兹（Lorentz）首先对有效电场作了近似计算。 The calculation of effective field strength is complicated because the coulomb force between dipole moments is long distance. Lorentz has presented an approximative calculation method.,下面对液体电介质的有效电场强度和介电常数作一些分析。 The followings are some analy
6、sis of effective field strength and dielectric permittivity.,非极性液体和弱极性液体电介质极化中起主要作用的是电子位移极化，其极化率为e，介电常数与折射率n仍近似保持麦克斯韦关系，即 Nonpolar and slight-polar liquid dielectric mainly depend on the function of electron displacement polarization with the polarizability of e, dielectric permittivity and refracti
7、ve index n still comply with the Maxwell relationship,非极性和弱极性液体电介质 Non-pole and inferior pole liquid electrolyte,这类液体介质的介电常数一般在2.5左右，有四氯化碳、苯、二甲苯、变压器油等。 Permittivity of these liquid keeps about 2.5, including carbon tetrachloride, benzene, xylene, transformer oil, etc.,（3-1）,对于非极性和弱极性液体介质，它们的分子在外电场作用
8、下，所感应的偶极矩大小相等，且沿电场方向排列。又由于液体无一定的形状，分子在空间各处出现的几率相等，因而在洛伦兹球内分子的分布可以看作是对称的，球内分子对中心O分子作用的场强 ，所以非极性和弱极性液体介质的有效电场强度 As for nonpolar and slight-polar liquid, the molecules will induce the dipole moment with same value and array in the direction of electric field by the effect of external electric field. An
9、d because of the non-shape characteristic of liquid, the molecules appearance odds is equal in space, which makes the distribution of molecules in Lorentz-ball can be regarded symmetrical and the field strength of centric-molecule O is . Thus, the effective field intensity can be given as follows:,上
10、式称为莫索缔（Mosotti）有效电场强度，将其代入克劳休斯方程式(2-13)，得到非极性与弱极性液体介质的极化方程为 This formula is called Mosotti effective electric-field intensity that can be substituted into Clausius Equation Eq(2-13) to obtain the polarization equation of nonpolar and weak-polar liquid dielectric:,式(3-3)称为克劳休斯莫索缔（Clausius-Mosotti）方程，
11、简称克-莫方程。 Eq (3-3) known as the Clausius - Mosotti Equation.,(3-3),极性液体介质包括中极性和强极性液体介质这类介质在电场作用下，除了电子位移极化外，还有偶极子极化，对于强极性液体介质，偶极子的转向极化往往起主要作用，介电常数远大于折射率平方n2，即 。 Polar liquid medium include mid-polar and high-polar liquid dielectric, which will execute electron displacement polarization and dipole pola
12、rization in the effect of electric field. As for high-polar liquid dielectric, the dipole orientation polarization plays the major role, and dielectric is far beyond square of refraction index n2 , that is .,2. 极性液体电介质 Polar liquid dielectrics,极性液体分子具有固有偶极矩，它们之间距离近，相互作用强，造成强的附加电场，故洛伦兹球内分子作用的电场 0，莫索缔
13、有效电场也就不适用。 Polar liquid molecule of inherent dipole moment and the distance between them is so short that the interaction is strong, which leads to strong additional electric field, so the electric field 0 by the effect of molecules in Lorentz-ball. As a result, Mosotti effective electric field is n
14、ot available here.,极性液体电介质 与电源频率有较大的关系。频率太高时偶极子来不及转动，因而 值变小，如图3-1所示。 Polar liquid dielectric associated with the power frequency closely, namely dipole cannot rotate in such a short time if the frequency was so high, which makes become smaller (in Fig 3-1).,图3-1 极性液体电介质的r与频率的关系 Figure 3-1 Relations
15、between r and frequency of polar liquid dielectric,其中 相当于直流电场下的介电常数，ff1以后偶极子越来越跟不上电场的交变， 不断下降；当频率f=f2时，偶极子已经完全跟不上电场转动了，这时只存在电子式极化， 减小到 ，常温下，极性液体电介质的 36。,is equal to the permittivity in direct current field, when ff1, dipole can hardly keep up with the alternation of electric field and continuously d
16、ecreases. When f=f2, dipole definitely cannot catch up with the alternation ,then electron polarity exists only and reduces to . At normal temperature, polar liquid dielectric has a 36.,温度对极性液体电介质的 值也有很大的影响：如图3-2所示。 Temperature also has a great influence on the value of , as shown in Fig 3-2.,图3-2 极性液体电介质的r与温度的关系 Figure 3-2 Relations between r and temperature of polar liquid dielectric,当温度很
