IEC 60909-3-2003 pdf free download – Short-circuit currents in three-phase a.c. systems – Part 3: Currents during two separate simultaneous line-to-earth short circuits and partial short- circuit currents flowing through earth.
This part of lEC 60909 specifies procedures for calculation of the prospective short-circuitcurrents with an unbalanced short circuit in high-voltage three-phase AC systems operating atnominal frequency 50 Hz or 60 Hz, i.e.
a) currents during two separate simultaneous line-to-earth short circuits in isolated neutral orresonant earthed neutral systems;
b) partial short-circuit currents flowing through earth in case of single line-to-earth shortcircuit in solidly earthed or low-impedance earthed neutral systems.
The currents calculated by these procedures are used when determining induced voltages ortouch 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 in the electrical installations on board ships or aeroplanes,orc) 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 calculationof line-to-earth short-circuit currents during two separate simultaneous line-to-earth shortcircuits and partial short-circuit currents through earth from electrical installations,leading toconservative’ results with sufficient accuracy. For this purpose，the current is determinedby considering an equivalent voltage source applied at the short-circuit location with allother sources set to zero. The procedure is suitable for determination by manual methodsor digital computation.
This standard is an addition to lEC 60909-0.General definitions，symbols and calculationassumptions refer to that publication.Special items only are defined or specified in thisdocument. This does not exclude the use of special methods,for example the superpositionmethod, adjusted to particular circumstances, if they give at least the same precision.
As stated in lEC 60909-0, short-circuit currents and their parameters may also be determinedby system tests.
The calculation of the short-circuit parameters based on the rated data of the electricalequipment and the topological arrangement of the system has the advantage of beingpossible both for existing systems and for systems at the planning stage.
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 editionof the referenced document (including any amendments) applies.
lEC 60909-0:2001，Short-circuit currents in three-phase a.c. systems – Part 0: Calculationof currents
3Terms and definitions
For the purposes of this standard,the following definitions apply.
3.1
two separate simultaneous line-to-earth short circuits
line-to-earth short circuits at different locations at the same time on different conductors ofa three-phase AC system having a resonant earthed or an isolated neutral.
3.2
initial short-circuit currents during two separate simultaneousline-to-earth short circuits IkEE
r.m.s. value of the initial short-circuit currents flowing with the same magnitude at bothlocations at the instant of the two separate simultaneous line-to-earth short circuits.
3.3
total earth current lEtot at the short-circuit location
r.m.s. value of the earth current at the short-circuit location flowing through the earthingsystem of a station (power station or substation) or the footing resistance of an overhead linetower far away from a station and through earthed conductors to earth (Figures 4 and 5).Such conductors may be earth wires of over-head lines or sheaths, shielding or armouring ofcables.
3.4
earth current IETn..
r.m.s. value of the earth current causing the potential to rise above earth at an overhead linetower n in the vicinity of a station
3.5
earth current LEBn
r.m.s. value of the earth current causing the potential to rise above earth UEen of station B, incase of a line-to-earth short circuit at an overhead line tower n in the vicinity of the station B
3.6
partial short-circuit current through earth r-3L0)
part of the total current flowing through earth remote from the short-circuit location andthe earthing system of a station,where the distribution of the total current between earthedconductors and earth is nearly constant. Its magnitude depends on the reduction factor r.IEC 60909-3 pdf download.