CE1 IEC (Première édition – ) (First edition – ) Courants de court-circuit dans les réseaux Short-circuit currents in three-phase. IEC Edition INTERNATIONAL. STANDARD. NORME. INTERNATIONALE. Short-circuit currents in three-phase a.c. systems –. Buy IEC SHORT-CIRCUIT CURRENTS IN THREE-PHASE A.C. SYSTEMS – PART 0: CALCULATION OF CURRENTS from SAI Global.

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Special considerations are necessary in this case, for instance with the superposition method.

For three-winding transformers with and without on-load tap-changer, three impedance correction factors can be found using the relative values of the reactances of the transformer see 3. Proof of Protective Measures Calcul des iev Part O: The impedances in systems connected through transformers to the system, in which the short circuit occurs, have to be transferred by the square of the rated transformation ratio.

The factor K shali be calculated according to 4.

This is the only active voltage of the network 1. For simplification, it is permitted to use the same value for IC as for the three- phase short circuit. For per unit or other similar unit systems, no transformation is necessary if these systems are coherent, i.

Calculation for an Industrial System The correction factor Ks shall also be applied to the zero-sequence system impedance of the power station unit, excepting, if present, an impedance component between the star point of the transformer and earth.

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The results of the short-circuit current calculation have an acceptable accuracy also in the case of untransposed overhead lines.

The zero-sequence short-circuit impedance at the short-circuit location F is obtained according to figure 5c, if an a.

It is only necessary to choose the branches which carry partial short-circuit currents at the nominal voltage corresponding to the short-circuit location and branches with transformers 609090 to the short-circuit location. In the case of high-voltage feeders with nominal voltages above 35 kV fed by overhead lines, the equivalent impedance 2, may in many cases be considered as a reactance, i.

E” Subtransient voltage of a synchronous machine f Frequency 50 Hz or 60 Hz Ib Symmetrical short-circuit breaking 60990-0 r.

Rated short-circuit voltage of a transformer in per cent Short-circuit voltage of a short-circuit limiting reactor in per cent Rated resistive component of the short-circuit voltage of a transformer in per cent Rated reactive component of the short-circuit voltage of a transformer in per cent Positive- negative- zero-sequence voltage Reactance, absolute respectively relative value Synchronous reactance, direct axis respectively quadrature axis Fictitious reactance of a generator with compound excitation in the case of steady-state short circuit at the terminals poles Xd resp.

Supply to a Factory The factor K shall, be calculated according to 4. Annex A forms an integral part of this standard. If the highest partial short-circuit current of the power station unit at the high-voltage side of the unit transformer with off-load taps is searched for, choose l-pT.

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Nominal system voltage, line-to-line r. Figure 1 – Short-circuit current of a far-from-generator short circuit with constant a. Figure 2 – Short-circuit current of a near-to-generator short circuit with decaying a. Calculation of an LV motor 8. 6090-0 Box to Service Panel This first edition cancels and replaces IEC published in and constitutes a technical revision.

It is not necessary for the product 1, For grounded systems the influence of motors on the line-to-earth short-circuit current cannot be neglected.

Description Reflecting the changes to the all-important short circuit calculations in three-phase power jec according to IEC standard, this 6909-0 edition of the practical guide retains its proven and unique concept of explanations, calculations and real-life examples of short circuits in 660909-0 networks. If the long-term operating conditions of network transformers before the short circuit are known for sure, then the following equation 12b may be used instead of equation 12a.

The deviation depends on the configuration of the network. Calculation of Short-Circuit Currents For these equivalent asynchronous motors, including their connection cables, the following may be used: Figure 3 – Characterization of short circuits and their currents Figure 4 shows an example of the equivalent voltage source at the short-circuit location F as the only active voltage of the system fed by a transformer without or with on-load tap-changer.

Thus the network feeder in figure 4a is represented by its internal impedance Zot, transferred to the LV-side of the transformer see 3. The symbols represent physical quantities possessing both numerical values and dimensions that are independent of units, provided a consistent unit system is chosen, ied example the international system 609009-0 units SI.

## Short Circuits in Power Systems: A Practical Guide to IEC 60909-0, 2nd Edition

The initial symmetrical short-circuit currents riQ,, and riQm, on the high-voltage side of the trans- former shall be given by the supply company or by an adequate calculation according to this 6099-0. The impedances of the equipment in superimposed or subordinated networks are to be divided or multiplied by the square of the rated transformation ratio t. For the effective reactance of the generators, introduce: