继电保护原理与应用(第三版)3.1-3.5(21)

通过变压器的电流和电压基本上是同相的，因为通过变压器的磁化电流和阻抗降非常小，可以忽略不计。这对于这些定义来说是正常的和实际的。
The current transformer (CT) polarity markings are shown in Figure 3.5. Note that the direction of the secondary current is the same, independent of whether the polarity marks are together on one side or on the other.
电流互感器（CT）极性标记如图3.5所示。请注意，二次电流的方向是相同的，与极性标记是在一侧还是另一侧在一起无关。

FIGURE 3.5 Polarity markings for CTs. 图3.5电流互感器的极性标记。
For CTs associated with circuit breakers and transformer banks, it is a common practice for the polarity marks to be located on the side away from the associated equipment.
对于与断路器和变压器组相关的CT，极性标记通常位于远离相关设备的一侧。
The voltage-drop rule is often omitted in the definition of transformer polarity, but it is an extremely useful tool to check the phase relations through wye–delta transformer banks, or in connecting up a transformer bank for a specific phase shift required by the power system. The ANSI=IEEE standard for transformers states that the high voltage should lead the low voltage by 308 with wye–delta or delta–wye banks. Thus, different connections are required if the high side is wye than if the high side is delta. The connections for these two cases are shown in Figure 3.6. The diagrams below the threephase transformer connection illustrate the use of the voltage-drop rule to provide or check the connections. Arrows on these voltage drops have been omitted (preferably not used), for they are not necessary and can cause confusion.