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The IEC collaborates closely with the International Organization for Standardization ISO in accordance with conditions determined by agreement between the two organizations. For simplification, it is permitted to use the same value for IC as for the three- phase short circuit.

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In some special cases, it could happen that the decaying short-circuit current reaches zero for the first time, some cycles after the short circuit took place. In the case of high-voltage direct-current transmission systems, the capacitor banks and filters need special considerations, when calculating a.

The following types of unbalanced short circuits are treated in this standard: The factor K shall, be calculated according to 4. In general, the calculation according to 4. Help Center Find new research papers in: For large transformers the resistance is so small that the impedance may be assumed to consist only of reactance when calculating short-circuit currents. In all cases it ief possible to determine the short-circuit current at the short-circuit location F with the help of an equivalent voltage source.

Within the accuracy of this standard, it is often sufficient to determine the short-circuit current at the short-circuit location F as being the sum of the absolute values of the individual partial short- circuit currents. The positive-sequence short-circuit impedance zat the short circuit location F is obtained according to figure 5a, when a symmetrical system of voltages of positive-sequence phase order is applied to the short-circuit location F, and all synchronous and asynchronous machines are replaced by their internal impedances.

Impedances 2, between the starpoint of transformers and earth are to be introduced as 3 2, into the zero-sequence system without a correction factor.

The correction 609009-1 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. The calculation of the three-phase peak short-circuit current i, applies to the line conductor and to the instant at which the greatest possible short-circuit current exists.

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Phasor diagram of a synchronous generator at rated conditions The superposition method gives the short-circuit current related to the one load flow presupposed. I cochez tout ce qui convient Je iiec lehn: Except for special cases, the zero-sequence short-circuit impedances at the short-circuit location differ from the positive-sequence and negative-sequence short-circuit impedances.

Additional information may be found in IEC Depending 06909-1 the application of the results, it is of interest to know the r. Factor m for the heat effect of the d. The IEC shall not be held responsible for identifying any or all such patent rights. Thus the network feeder in figure 4a is represented by its internal impedance Zot, transferred to the LV-side of the transformer see 3.

Short circuits may have one or more sources, as shown in figures 11, 12, and 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 Figure 2 - Short-circuit current of a near-to-generator short circuit with decaying a.

The estimation according to equation 28 is not allowed 60909- the case of three-winding transformers. The impedances and z o L of low-voltage and high-voltage cables depend on national techniques and standards and may be taken from IEC or from textbooks or manufacturer's data. This postulates that the electrical equipment has a balanced structure, for example in the case of transposed overhead lines.

For higher temperatures than 20 OC, see equation 3.

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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 6009-1 transformer without or with on-load tap-changer. In a near-to-generator short circuit, the short-circuit current behaves generally as shown in figure 2.

The results of the short-circuit current calculation have an acceptable accuracy also in the case of untransposed overhead lines. All other static converters are disregarded for the short-circuit current calculation according to this standard. Calcul des courants Part O: For 609099-1 short-circuit impedances of synchronous generators in the negative-sequence system, the following applies with KG from equation 1 8:

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