IEC 60909-3 : 3.0

SHORT-CIRCUIT CURRENTS IN THREE-PHASE AC SYSTEMS - PART 3: CURRENTS DURING TWO SEPARATE SIMULTANEOUS LINE-TO-EARTH SHORT CIRCUITS AND PARTIAL SHORT-CIRCUIT CURRENTS FLOWING THROUGH EARTH

International Electrotechnical Committee

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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
  5.1 Initial symmetrical short-circuit current
      5.1.1 Determination of M[(1)] and M[(2)]
      5.1.2 Simple cases of two separate simultaneous
            line-to-earth short circuits
  5.2 Peak short-circuit current, symmetrical short circuit
      breaking current and steady-state short-circuit
      current
  5.3 Distribution of the 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
  6.1 General
  6.2 Line-to-earth short circuit inside a station
  6.3 Line-to-earth short circuit outside a station
  6.4 Line-to-earth short circuit in the vicinity of a station
      6.4.1 Earth potential U[Etn] at the tower n outside
            station B
      6.4.2 Earth potential of station B during a line-to
            earth short circuit at the tower n
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
  8.1 Overview
  8.2 Three-core cable
      8.2.1 Line-to-earth short circuit in station B
      8.2.2 Line-to-earth short circuit on the cable between
            station A and station B
  8.3 Three single-core cables
      8.3.1 Line-to-earth short circuit in station B
      8.3.2 Line-to-earth short circuit on the cable between
            station A and station B
Annex A (informative) Example for the calculation of two
        separate simultaneous line-to-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

Abstract

Describes 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.