IEC 60909-3:2009 RLV

FOREWORD
1 Scope and object
2 Normative references
3 Terms and definitions
4 Symbols
5 Calculation of currents during two separate
  simultaneous line-to-earth short circuits
6 Calculation of partial short-circuit currents flowing
  through earth in case of an unbalanced short circuit
7 Reduction factor for overhead lines with earth wires
8 Calculation of current distribution and reduction
  factor in case of cables with metallic sheath or
  shield earthed at both ends
Annex A (informative) - Example for the calculation of two
        separate simultaneous lineto-earth short-circuit
        currents
Annex B (informative) - Examples for the calculation of partial
        short-circuit currents through earth
Annex C (informative) - Example for the calculation of the
        reduction factor r[1] and the current distribution
        through earth in case of a three-core cable
Annex D (informative) - Example for the calculation of the
        reduction factor r[3] and the current distribution
        through earth in case of three single-core cables

IEC 60909-3:2009 RLV contains the International Standard and its Redline version. The Redline version provides you with a quick and easy way to compare all the changes between this standard and its previous edition. The Redline version is not an official IEC Standard, only the current version of the standard is to be considered the official document.
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.