继电保护原理与应用(第三版)3.1-3.5(12)

电压（总是下降）由（1）带有双下标的字母表示；或（2）在假定处于相对高电位的点处显示的小加号（）指示器表示。因此，在正弦波的正半周期内，电压降由使用的两个下标的顺序表示，或从“”指示器到电位差的另一端。如图3.2a所示，其中两种方法均显示。最好在电压降名称的两端显示箭头，以避免可能的混淆。同样，最重要的是要认识到，电路图中的这两个名称，特别是如果使用箭头，只是位置和方向指示灯，而不是相量。
It may be helpful to consider current as a ‘‘through’’ quantity and voltage as an ‘‘across’’ quantity. In this sense, in the representative Figure 3.2a, the same current flows through all the elements in series, so that Iab Ibc Icd IS. By contrast, voltage Vab applies only across nodes a and b, voltage Vbc across nodes b and c, and Vcd across nodes c and d.
将电流视为“通过”量，将电压视为“穿过”量可能会有所帮助。从这个意义上说，在代表性的图3.2a中，相同的电流流过串联的所有元件，因此IbaIbcIcd为零。相比之下，电压Vab仅适用于节点a和b，电压Vbc适用于节点b和c，而Vcd适用于节点c和d。
3.2.6 Phasor Diagram相量图
With the proper identification and assumed directions established in the circuit diagram, the corresponding phasor diagram can be drawn from the calculated or test data. For the circuit diagram in Figure 3.2a, two types of phasor diagrams are shown in Figure 3.2b. The top diagram is referred to as an open type, where all the phasors originate from a common origin. The bottom diagram is referred to as a closed type, where the voltage phasors are summed together from left to right for the same series circuit. Both types are useful, but the open type is preferred to avoid the confusion that may occur with the closed type. This is amplified in the following section.