继电保护原理与应用(第三版)3.1-3.5(14)

The various line currents are assumed to flow through this series section as shown, and the voltages are indicated for a specific point on the line section. These follow the nomenclature that was discussed previously. To simplify the discussion at this point, symmetrical or balanced operation of the three-phase power system is assumed. Therefore, no current can flow in the neutrals of the two transformer banks, so that with this simplification there is no difference of voltage between n’ , n or N, n‘’, and the ground plane g or G. As a result, Van = Vag; Vbn = Vbg; and Vcn = Vcg. Again, this is true only for a balanced or symmetrical system. With this, the respective currents and voltages are equal in magnitude and 1208 apart in phase, as shown in the phasor diagram (see Figure 3.3b), in both open and closed types. The phasors for various unbalanced and fault conditions are discussed in Chapter 4.
如图所示，假定各种线路电流流过该串联段，并为线路段上的特定点指示电压。它们遵循前面讨论过的命名法。为了简化这一点的讨论，假设三相电力系统对称或平衡运行。因此，两个变压器组的中性点中没有电流流动，因此通过这种简化，n"，n或n，n""和接地层g或g之间没有电压差。因此，Van=Vag；Vbn=Vbg；和Vcn=Vcg。同样，这只适用于平衡或对称系统。这样，在开路和闭合类型中，各电流和电压的幅值相等，相距1208，如相量图（见图3.3b）所示。第四章讨论了各种不平衡和故障情况下的相量。