继电保护原理与应用(第三版)3.1-3.5(24)

FIGURE 3.6 Voltage-drop polarity rule useful in checking or connecting wye–delta transformer banks: (a) Wye-connected side leads, delta-connected side 30°. (b) Deltaconnected side leads, wye-connected side 30°.
图3.6用于检查或连接Y形-三角形变压器组的电压降极性规则：（a）Y形连接侧引线，三角形连接侧30°。（b） 三角形连接侧导线，Y形连接侧30°。
Because the ANSI=IEEE standards have been in existence for several years, most transformer banks in service today follow this standard, except where it is not possible because of preexisting system conditions. Many years ago, in the absence of a standard, many different connections were used. Some of the older references and textbooks reflect this.
由于ANSI=IEEE标准已经存在了好几年，目前大多数运行的变压器组都遵循这一标准，除非由于先前存在的系统条件而不可能。许多年前，在没有标准的情况下，使用了许多不同的连接。一些旧的参考文献和教科书反映了这一点。
3.5.2 Relay Polarity继电器极性
Relays involving interaction between two input quantities from the power system may have the polarity marking that is necessary for their correct operation. There are no standards in this area, so if the polarity of the relay connections is important, the relay manufacturer must both specify the polarity markings and clearly document their meaning. Relays that sense the direction of current (or power) flow at a specific location and, thereby, indicate the direction of the fault, provide a good practical example of relay polarity. Directional units are usually not applied alone, but rather, in combinations with other units, such as fault sensors or detectors. A common practice is to use the output of the directional-sensing unit to control the operation of the fault sensors, which often is an instantaneous or an inverse-time–overcurrent unit, or both units together. Thus, if the current flow is in the desired operating direction (trip direction) and its magnitude is greater than the fault sensor’s minimumoperating current (pickup), the relay can operate. If the current is in the opposite direction (nontrip or nonoperate direction or zone), no operation can occur even though the magnitude of the current is higher than the pickup threshold current.