BS EN 60909-3:2010 PDF

1   Scope and object This part of IEC 60909 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.:

a) currents during two separate simultaneous line-to-earth short circuits in isolated neutral or resonant earthed neutral systems;

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) and the towers of overhead lines. Procedures are given for the calculation of reduction factors of overhead lines with one or two earth wires. The standard does not cover:

a) short-circuit currents deliberately created under controlled conditions as in short circuit testing stations, or

b) short-circuit currents in the electrical installations on board ships or aeroplanes, or

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