还必须注意，给定的短路电流是使用
假设变压器上游功率为750 MVA，忽略
母线或断路器连接的阻抗。
表格指的是之前规定的条件；的信息
断路器的选择仅根据使用电流和
预期短路电流。为了正确选择，其他因素包括
作为选择性、后备保护，决定使用限制断路器
还必须考虑其他因素。因此，设计工程师必须
进行检查。

例子：
假设需要确定断路器A1/A2/A3的尺寸，在三个断路器的低压侧
英国630 kVA 20/0.4 kV变压器
%等于4%和输出馈线
63-400-800 A的断路器B1/B2/B3：
ABB |电气设备421
2电气设备保护
2.4变压器的保护和切换
根据表2，对应于3x630 kVA变压器相关的行，
可以看出：
A级断路器（变压器低压侧）
•trafo I
r
（909 A）是流经变压器断路器的电流；
•母线I
b（2727 A）是变压器可以承受的大电流
供给
•trafo馈线I
k
（42.8 kA）是要考虑的短路电流值
选择每个变压器断路器的开断容量；
•T7S1000或X1N1000是变压器断路器的尺寸；
•In（1000 A）是变压器断路器（电子）的额定电流
用户选择的版本）；
•小值0.91表示
CBs T7S1000和X1N1000的电子版本。
B级断路器（出线馈线）
•母线I
k
（64.2 kA）是由于所有
三台变压器；
•对应于63 A，读取断路器B1 Tmax XT1H160；
•对应400 A，读取断路器B2 Tmax T5H400；
•对应于800 A，读取断路器B3 Tmax T6H800或
Emax X1N800。
所做的选择没有考虑歧视/支持
要求。请参阅相关章节以了解适用于
各种情况。

tables refer to the previously specified conditions; the information for the selection of circuit-breakers is supplied only with regard to the current in use and the prospective short-circuit current. For a correct selection, other factors such as selectivity, back-up protection, the decision to use limiting circuit- breakers etc. must also be considered. Therefore, it is essential that the design engineers carry out precise checks. It must also be noted that the short-circuit currents given are determined using the hypothesis of 750 MVA power upstream of the transformers, disregarding the impedances of the busbars or the connections to the circuit-breakers. Example: Supposing the need to size breakers A1/A2/A3, on the LV side of the three transformers of 630 kVA 20/0.4 kV with uk % equal to 4% and outgoing feeder circuit-breakers B1/B2/B3 of 63-400-800 A: ABB | Electrical devices 421 2 Protection of electrical equipment 2.4 Protection and switching of transformers From Table 2, corresponding to the row relevant to 3x630 kVA transformers, it can be read that: Level A circuit-breakers (LV side of transformer) • trafo I r (909 A) is the current that flows through the transformer circuitbreakers; • busbar I b (2727 A) is the maximum current that the transformers can supply; • trafo feeder I k (42.8 kA) is the value of the short-circuit current to consider for the choice of the breaking capacity of each of the transformer circuit-breakers; • T7S1000 or X1N1000 is the size of the transformer circuit-breaker; • In (1000 A) is the rated current of the transformer circuit-breaker (electronic release chosen by the user); • the minimum value 0.91 indicate the minimum settings of the L function of the electronic releases for CBs T7S1000 and X1N1000. Level B circuit-breakers (outgoing feeder) • busbar I k (64.2 kA) is the short-circuit current due to the contribution of all three transformers; • corresponding to 63 A, read circuit-breaker B1 Tmax XT1H160; • corresponding to 400 A, read circuit-breaker B2 Tmax T5H400; • corresponding to 800 A, read circuit-breaker B3 Tmax T6H800 or Emax X1N800. The choice made does not take into account discrimination/back-up requirements. Refer to the relevant chapters for selections appropriate to the various cases.