Buy IEC/TR Ed. Short-circuit currents in three-phase a.c. systems Part 4: Examples for the calculation of short-circuit currents from SAI Global. The results meet requirements of IEC and match the example provided in IEC TR section 6. The IEC standard terminology is used in the user. The International Electrotechnical Commission (IEC) is the leading global IEC TR , Short-circuit currents in three-phase a.c. systems – Part 4.

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For simplification, it is permitted to use the same value for as for the three- phase short circuit. 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.

In the case of high-voltage direct-current transmission systems, the capacitor banks and filters need special considerations, when calculating a. Low-voltage motors are to be taken into account in auxiliaries of power stations and in industrial and similar installations, for example in networks of chemical and steel industries and pump- stations.

The short-circuit current through any protective device can be used to clip the TCC curve of the device. Impedances between a starpoint and earth shall be introduced without correction factor.

## IEC TR 60909-4:2000

Equations 84 and 85 are valid in the case of far-from-generator and in the case of near-to- generator short circuits. Peak current based on method c: Electric and magnetic circuits IEC 15 1: Annex A forms an integral part of this standard. When calculating short-circuit currents in systems with different voltage levels, it is necessary to transfer impedance values from one voltage level to another, usually to that voltage level at which the short-circuit current is to be calculated.

If the highest partial short-circuit current of the power station ice at the high-voltage side of the unit transformer with off-load taps is searched for, choose l-pT.

### IEC Short-Circuit in EasyPower

For the purpose of this standard, one has to make a distinction between short-circuit impedances at the short-circuit location F and the short-circuit impedances of individual electrical equipment.

Zero-sequence impedance arrangements for the calculation of unbalanced short-circuit currents are given in IEC O 1 marks the positive-sequence neutral reference. Earth ground trip functions for low voltage circuit breakers or relays use the symmetrical earth ground current.

The values of positive-sequence and negative-sequence impedances can differ from each other only in the case of rotating machines. As described in the methodology the solution is obtained using the equivalent voltage source at the short-circuit location, symmetrical components impedance network, and the voltage factor c.

DC component of short-circuit current at breaking times: IEC Short-circuit currents in three-phase a c. The effect of series capacitors can be neglected in the calculation of short-circuit currents, if they are equipped with voltage-limiting devices in parallel, acting if a short circuit occurs.

I is not at all ci Symmetrical currents are applied for relays with DC offset filter. In this case special considerations beyond the scope and procedure given in this standard have to be taken into account see for instance 2.

For breaking current you can choose from 0. Example for the estimation of the contribution from the asynchronous motors in relation to iiec total short-circuit current T k i and the factor K derived in 4.

## IEC-60909 Short-Circuit in EasyPower

This method applies the 1. Asymmetrical currents are calculated as the root mean square of the symmetrical and dc components.

The short-circuit impedances for the examples in figures 1l b and 1I C are given by the following equations: The effective resistance per unit length RL of overhead lines at the conductor temperature 20 “C may be calculated from the nominal cross-section qn and the resistivity p: The influence of various winding-temperatures on RGf is not considered. T JSrT ; t, is the rated transformation ratio of the unit transformer: When a number of short circuits occur with a short time interval in between them, the resulting Joule integral is the sum of the Joule integrals of the individual short-circuit currents, as given in equation 1 Their preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with may participate in this preparatory work.

The equivalent voltage source is the only active voltage of the system. During the initial stage of the short circuit, the negative impedance is approximately equal to the positive-sequence impedance, independent of whether the short circuit is a near-to-generator or a far-from-generator short circuit.

Help Center Find new research papers in: Z S is the corrected impedance of a power station unit with LTC to the high-voltage side. These values cannot be used when calculating the aperiodic component id.

For rotating machines the current contributions to short-circuit decays over time. The initial symmetrical current is calculated based on section 4. The equations 46 and 47 are given for the calculation of and in figure 3c: Short-circuit impedances of a three-phase a. For the effective reactance of the generators, introduce: However, parties to agreements based on this 60099-4 of IEC are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below.

The initial line-to-earth short-circuit current Iil in figure 3d shall be calculated by: You can fault a single bus or all buses in the single-line diagram to view the short-circuit currents at the faulted buses. The results of the short-circuit current calculation have an acceptable accuracy also in the case of untransposed overhead lines. Factor q may also be obtained from figure The capacitances of lines overhead lines and cables of low-voltage networks may be neglected in the positive- negative- and iiec system.

With respect to equation 99 in table 3 the steady-state short-circuit current of asynchronous motors is zero in the case of a three-phase short circuit at the terminals figure 12 and equation