IEC 60909-3:2003 pdf download.Short-circuit currents in three-phase a.c. systems
I Scope
This part of IEC 60909 specifies proceduies for calculation of the prospective short-circuit currents with an unbalanced short circuit in high-voltage three-phase AC systems operating at nominal frequency 50 Hz or 60 Hz, i.e.
a) currents during two separate simultaneous line-to-earth short circuits in isolated neutral or rcsonant carthcd ncutra! systcms;
b) 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).
This standard does not cover:
a) short-circuit currents deliberately created under controlled conditions as in short-circuit testing stations, or
b) short-circuit currents iii the electrical installations on board ships or aeroplanes, or
c) single line-to-earth faults in isolated or resonant earthed systems.
The object of this standard is to establish practical and concise procedures for the calculation of line-to-earth short-circuit currents during two separate simultaneous line-to-earth short circuits and partial short-circuit currents through earth from electrical installations, leading to conservative results with sufficient accuracy. For this purpose. the current is determined by coiisideninij an equivalent voltaqe source applied at the shunt-circuit location with all other sources set to zero. The procedure is suitable for determination by manual methods or digital computation.
This standard is an addition to IEC 60909-0. General definitions, symbols and calculation assumptions refer to that publication. Special items only are defined or specified in this document. I his does not exclude the use of special methods, for example the superposition method. adjusted to particular circumstances. if they give at least the same precision.
As stated in IEC 60909-0, short-circuit currents and their parameters may also be determined by systerii tests.
The calculation of the short-circuit parameters based on the rated data of the electrical equipment and the topological arrangement of the system has the advantage of being possible both for existing systems and for systems at the planning stage.
2 Normative reference
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments ) applies.
IEC 60909-0:2001，Short-circuit currents in three-phase a.c. systems - Part 0: Calculation of currents
3.1 two separate simultaneous line -to-earth short circuits
ine-to-earth short circuits at different iocations at the same time on different conductors of a three-phase AC sysierm having a resonani ear thed or an isoiaied neuirai.IEC 60909-3 pdf download.