继电保护原理与应用(第三版)3.1-3.5(9)

3.2.5 Nomenclature for Current and Voltage电流和电压术语
Unfortunately, there is no standard nomenclature for current and voltage, so confusion can exist among various authors and publications. The nomenclature used throughout this book has proved to be flexible and practical over many years of use, and it is compatible with the polarities of power system equipment.
不幸的是，没有电流和电压的标准命名法，因此在不同的作者和出版物中可能存在混淆。这本书中使用的术语经过多年的使用证明是灵活和实用的，它与电力系统设备的极性兼容。
3.2.5.1 Current and Flux电流和磁通
In the circuit diagrams, current or flux is shown by either (1) a letter designation, such as I or u, with an arrow indicator for the assumed direction of flow; or (2) a letter designation with double subscripts, the order of the subscripts indicating the assumed direction. The direction is thus assumed to be the flow during the positive half-cycle of the sine wave. This convention is illustrated in Figure 3.2a. Thus, in the positive half-cycle, the current in the circuit is assumed to be flowing from left to right, as indicated by the direction of the arrow used with Is, or denoted by subscripts, as with Iab, Ibc, and Icd. The single subscript, such as Is, is a convenience to designate currents in various parts of a circuit and has no directional indication, so an arrow for the direction must be associated with these. Arrows are not required with Iab, Ibc, or Icd, but are often used for added clarity and convenience. It is very important to appreciate that, in these circuit designations, the arrows do not indicate phasors. They are only assumed as directional and locational indicators.