BS EN 60909-0:2016
$215.11
Short-circuit currents in three-phase a.c. systems – Calculation of currents
| Published By | Publication Date | Number of Pages |
| BSI | 2016 | 80 |
This part of IEC 60909 is applicable to the calculation of short-circuit currents
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in low-voltage three-phase AC systems, and
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in high-voltage three-phase AC systems,
operating at a nominal frequency of 50 Hz or 60 Hz.
Systems at highest voltages of 550 kV and above with long transmission lines need special consideration.
This part of IEC 60909 establishes a general, practicable and concise procedure leading to results which are generally of acceptable accuracy. For this calculation method, an equivalent voltage source at the short-circuit location is introduced. This 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. The superposition method gives the short-circuit current related to the one load flow presupposed. This method, therefore, does not necessarily lead to the maximum short-circuit current .
This part of IEC 60909 deals with the calculation of short-circuit currents in the case of balanced or unbalanced short circuits.
A single line-to-earth fault is beyond the scope of this part of IEC 60909 .
For currents during two separate simultaneous single-phase line-to-earth short circuits in an isolated neutral system or a resonance earthed neutral system, see IEC 60909‑3 .
Short-circuit currents and short-circuit impedances may also be determined by system tests, by measurement on a network analyser, or with a digital computer. In existing low-voltage systems it is possible to determine the short-circuit impedance on the basis of measurements at the location of the prospective short circuit considered.
The calculation of the short-circuit impedance is in general based on the rated data of the electrical equipment and the topological arrangement of the system and has the advantage of being possible both for existing systems and for systems at the planning stage.
In general, two types short-circuit currents, which differ in their magnitude, are considered:
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the maximum short-circuit current which determines the capacity or rating of electrical equipment; and
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the minimum short-circuit current which can be a basis, for example, for the selection of fuses, for the setting of protective devices, and for checking the run-up of motors.
The current in a three-phase short circuit is assumed to be made simultaneously in all poles. Investigations of non-simultaneous short circuits, which may lead to higher aperiodic components of short-circuit current, are beyond the scope of this part of IEC 60909 .
This part of IEC 60909 does not cover short-circuit currents deliberately created under controlled conditions (short-circuit testing stations).
This part of IEC 60909 does not deal with the calculation of short-circuit currents in installations on board ships and aeroplanes.
PDF Catalog
| PDF Pages | PDF Title |
|---|---|
| 6 | English CONTENTS |
| 9 | FOREWORD |
| 11 | 1 Scope |
| 12 | 2 Normative references 3 Terms and definitions |
| 17 | 4 Symbols, subscripts and superscripts 4.1 General 4.2 Symbols |
| 19 | 4.3 Subscripts |
| 20 | 4.4 Superscripts 5 Characteristics of short-circuit currents: calculating method 5.1 General |
| 21 | Figures Figure 1 – Short-circuit current of a far-from-generator short circuit with constant AC component (schematic diagram) |
| 22 | Figure 2 – Short-circuit current of a near-to-generator short-circuit with decaying AC component (schematic diagram) |
| 23 | 5.2 Calculation assumptions Figure 3 – Characterization of short-circuits and their currents |
| 24 | 5.3 Method of calculation 5.3.1 Equivalent voltage source at the short-circuit location |
| 25 | Figure 4 – Illustration for calculating the initial symmetrical short-circuit current in compliance with the procedure for the equivalent voltage source |
| 26 | 5.3.2 Symmetrical components Tables Table 1 – Voltage factor c |
| 27 | 6 Short-circuit impedances of electrical equipment 6.1 General 6.2 Network feeders |
| 28 | Figure 5 – System diagram and equivalent circuit diagram for network feeders |
| 29 | 6.3 Transformers 6.3.1 Two-winding transformers 6.3.2 Three-winding transformers |
| 31 | 6.3.3 Impedance correction factors for two- and three-winding network transformers Figure 6 – Three-winding transformer (example) |
| 32 | 6.4 Overhead lines and cables |
| 33 | 6.5 Short-circuit current-limiting reactors 6.6 Synchronous machines 6.6.1 Synchronous generators |
| 35 | 6.6.2 Synchronous compensators and motors 6.7 Power station units 6.7.1 Power station units with on-load tap-changer |
| 36 | 6.7.2 Power station units without on-load tap-changer |
| 37 | 6.8 Wind power station units 6.8.1 General 6.8.2 Wind power station units with asynchronous generator |
| 38 | 6.8.3 Wind power station units with doubly fed asynchronous generator |
| 39 | 6.9 Power station units with full size converter 6.10 Asynchronous motors |
| 40 | 6.11 Static converter fed drives 6.12 Capacitors and non-rotating loads 7 Calculation of initial short-circuit current 7.1 General 7.1.1 Overview |
| 41 | Table 2 – Importance of short-circuit currents |
| 42 | Figure 7 – Diagram to determine the short-circuit type (Figure 3) for the highest initial short-circuit current referred to the initial three-phase short-circuit current when the impedance angles of the sequence impedances Z(1), Z(2), Z(0) are identical |
| 44 | Figure 8 – Examples of single-fed short-circuits Figure 9 – Example of a multiple single-fed short circuit |
| 45 | 7.1.2 Maximum and minimum short-circuit currents Figure 10 – Example of multiple-fed short circuit |
| 46 | 7.1.3 Contribution of asynchronous motors to the short-circuit current |
| 47 | 7.2 Three-phase initial short-circuit current 7.2.1 General |
| 48 | 7.2.2 Short-circuit currents inside a power station unit with on-load tap-changer |
| 49 | Figure 11 – Short-circuit currents and partial short-circuit currents for three-phase short circuits between generator and unit transformer with or without on-load tap-changer, or at the connection to the auxiliary transformer of a power station unit and at the auxiliary busbar A |
| 50 | 7.2.3 Short-circuit currents inside a power station unit without on-load tap-changer |
| 51 | 7.3 Line-to-line short circuit 7.4 Line-to-line short circuit with earth connection |
| 53 | 7.5 Line-to-earth short circuit 8 Calculation of peak short-circuit current 8.1 Three-phase short circuit 8.1.1 Single-fed and multiple single-fed short circuits |
| 54 | Figure 12 – Factor κ for series circuit as a function of ratio R/X or X/R |
| 55 | 8.1.2 Multiple-fed short circuit |
| 56 | 8.2 Line-to-line short circuit 8.3 Line-to-line short circuit with earth connection 8.4 Line-to-earth short circuit |
| 57 | 9 Calculation of symmetrical breaking current 9.1 Three-phase short circuit 9.1.1 Symmetrical breaking current of synchronous machines |
| 58 | 9.1.2 Symmetrical breaking current of asynchronous machines Figure 13 – Factor μ for calculation of short-circuit breaking current Ib |
| 59 | 9.1.3 Symmetrical breaking current of power station units with doubly fed asynchronous generator 9.1.4 Symmetrical breaking current of power station units with full size converter Figure 14 – Factor q for the calculation of the symmetrical short-circuit breaking current of asynchronous motors |
| 60 | 9.1.5 Symmetrical breaking current of network feeder 9.1.6 Symmetrical breaking current in case of multiple single-fed short-circuits 9.1.7 Symmetrical breaking current in case of multiple-fed short circuits |
| 61 | 9.2 Unbalanced short-circuits 10 DC component of the short-circuit current |
| 62 | 11 Calculation of steady-state short-circuit current 11.1 General 11.2 Three-phase short circuit 11.2.1 Steady-state short-circuit current of one synchronous generator or one power station unit |
| 64 | Figure 15 – Factors λmin and λmax factors for cylindrical rotor generators Figure 16 – Factors λmin and λmax for salient-pole generators |
| 65 | 11.2.2 Steady-state short-circuit current of asynchronous motor or generator 11.2.3 Steady-state short-circuit current of wind power station unit with doubly fed asynchronous generator 11.2.4 Steady-state short-circuit current of wind power station unit with full size converter 11.2.5 Steady-state short-circuit current of network feeder 11.2.6 Steady-state short-circuit current in case of multiple single-fed short circuits |
| 66 | 11.2.7 Steady-state short-circuit current in case of multiple-fed short circuits 11.3 Unbalanced short circuits 12 Short circuits at the low-voltage side of transformers, if one line conductor is interrupted at the high-voltage side |
| 67 | Figure 17 – Transformer secondary short-circuits, if one line (fuse) is opened on the high-voltage side of a transformer Dyn5 |
| 68 | 13 Terminal short circuit of asynchronous motors Table 3 – Factors α and β for the calculation of short-circuit currents with Formula (96), rated transformation ratio tr = UrTHV/UrTLV |
| 69 | 14 Joule integral and thermal equivalent short-circuit current Table 4 – Calculation of short-circuit currents of asynchronous motors in the case of a short circuit at the terminals |
| 70 | Figure 18 – Factor m for the heat effect of the DC component of the short-circuit current (for programming, the formula to calculate m is given in Annex A) |
| 71 | Figure 19 – Factor n for the heat effect of the AC component of the short-circuit current (for programming, the formula to calculate n is given in Annex A) |
| 72 | Annex A (normative) Formulas for the calculation of the factors m and n |
| 73 | Annex B (informative) Nodal admittance and nodal impedance matrices |
| 74 | Figure B.1 – Formulation of the nodal admittance matrix |
| 75 | Figure B.2 – Example Table B.1 – Impedances of electrical equipment referred to the 110 kV side |
| 77 | Bibliography |
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