IEC 60909-3:20 09规定了高压三相交流电中不平衡短路预期短路电流的计算程序。在标称频率50 Hz或60 Hz下运行的系统，即: -隔离中性点或谐振接地中性点系统中两个单独同时线路对地短路期间的电流； -在固体接地或低阻抗接地中性点系统中单线对地短路的情况下流过大地的部分短路电流。 当确定电站（发电站或变电站）和架空线路杆塔处的感应电压或接触电压或阶跃电压以及地电位上升时，使用通过这些程序计算的电流。给出了一根或两根地线架空线路折减系数的计算程序。本版构成技术修订版。与上一版相比的主要变化是: -引入了新的程序，用于计算护套或屏蔽的折减系数，以及通过地和三芯电缆或三根两端接地的金属非磁性护套或屏蔽的护套或屏蔽的电流分布； -在新订的第7条中，修正并给出了计算有地线架空线路折减系数的资料； -引入新的第8条，用于计算两端接地的金属护套或屏蔽三芯电缆的电流分布及折减系数； -新的附件C和D提供了在两端接地的金属护套和屏蔽电缆的情况下计算折减系数和电流分布的示例。本出版物应与IE一起阅读 C 60909-0:20 01。 新的！IEC 60909-3:20 09也可作为IEC标准+60909-3:20 09提供，其中包含国际标准及其红线版本，显示了与前一版本相比技术内容的所有变化。

IEC 60909-3:2009 specifies procedures for calculation of the prospective short-circuit currents with an unbalanced short circuit in high-voltage three-phase a.c. systems operating at nominal frequency 50 Hz or 60 Hz, i. e.:
- currents during two separate simultaneous line-to-earth short circuits in isolated neutral or resonant earthed neutral systems;
- partial short-circuit currents flowing through earth in case of single line-to-earth short circuit in solidly earthed or low-impedance earthed neutral systems.
The currents calculated by these procedures are used when determining induced voltages or touch or step voltages and rise of earth potential at a station (power station or substation) and the towers of overhead lines. Procedures are given for the calculation of reduction factors of overhead lines with one or two earth wires. This edition constitutes a technical revision. The main changes with respect to the previous edition are:
- New procedures are introduced for the calculation of reduction factors of the sheaths or shields and in addition the current distribution through earth and the sheaths or shields of three-core cables or of three single-core cables with metallic non-magnetic sheaths or shields earthed at both ends;
- The information for the calculation of the reduction factor of overhead lines with earth wires are corrected and given in the new Clause 7;
- A new Clause 8 is introduced for the calculation of current distribution and reduction factor of three-core cables with metallic sheath or shield earthed at both ends;
- The new Annexes C and D provide examples for the calculation of reduction factors and current distribution in case of cables with metallic sheath and shield earthed at both ends.

This publication is to be read in conjunction with IE C 60909-0:2001.

NEW! IEC 60909-3:2009 is also available as IEC Standards+ 60909-3:2009 which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.