IEC TR 60909-4:20 21是一份技术报告，旨在为IEC 60909-0在50 Hz或60 Hz三相交流系统中计算短路电流提供帮助。 本文件不包括附加要求，但支持正序、负序和零序系统中电气设备的建模（第4条）、低压系统（第5条）、带异步电机的中压系统（第6条）和电站机组及其辅助网络为大量中压异步电机和低压电机组供电（第7条）中计算的实际执行。 第5、6和7条中给出的三个示例与IEC TR 60909-4:20 00中给出的示例相似，但根据IEC 60909-0，替换它。第8条中给出的示例是新的，反映了IEC 60909-0:20 16新6.8的引入。 第9条给出了测试网络的电路图和数据以及根据IEC 60909-0进行的计算结果，以提供在用用于计算短路电流的数字程序得出的结果与高压网络中的给定结果之间进行比较的可能性，该高压网络具有电站单元、发电机、异步电动机和线路，具有四个不同电压等级380 kV、110 kV、30 kV和10 kV。 第二版取消并取代了2000年出版的第一版。本版构成技术修订版。 与上一版相比，此版本包括以下重大技术变更: a)适应IEC 60909-0:20 16； b)增加了计算风力发电站机组短路电流的示例； c)纠正错误。

IEC TR 60909-4:2021 which is a Technical Report, is intended to give help for the application of IEC 60909-0 for the calculation of short-circuit currents in 50 Hz or 60 Hz three-phase AC systems.
This document does not include additional requirements but gives support for the modelling of electrical equipment in the positive-sequence, the negative-sequence and the zero-sequence system (Clause 4), the practical execution of calculations in a low-voltage system (Clause 5), a medium-voltage system with asynchronous motors (Clause 6) and a power station unit with its auxiliary network feeding a large number of medium-voltage asynchronous motors and low-voltage motor groups (Clause 7).
The three examples given in Clauses 5, 6 and 7 are similar to those given in IEC TR 60909-4:2000 but they are revised in accordance with IEC 60909-0, which replaces it. The example given in Clause 8 is new and mirrors the introduction of the new 6.8 of IEC 60909-0:2016.
Clause 9 gives the circuit diagram and the data of a test network and the results for a calculation carried out in accordance with IEC 60909-0, to offer the possibility for a comparison between the results found with a digital program for the calculation of short-circuit currents and the given results for and in a high-voltage network with power station units, generators, asynchronous motors and lines in four different voltage levels 380 kV, 110 kV, 30 kV and 10 kV.
This second edition cancels and replaces the first edition published in 2000. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous edition:
a) adaption to IEC 60909-0:2016;
b) addition of an example for the calculation of short-circuit currents of wind power station units;
c) correction of errors.