Download Citation on ResearchGate | Applying IEC , Fault Current Calculations | Rather than the short-circuit current that would occur in a specific. Applying IEC , short-circuit current calculations. Abstract: Rather than the short-circuit current that would occur in a specific instance, IEC derives. The initial short circuit current for a is as per IEC Equation

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For higher temperatures than 20 OC, see equation 3. Factors ;Iminand il,,for salient-pole generators Breaking currents are calculated at 0. Symmetrical locked-rotor current of an asynchronous motor Rated current of electrical equipment Thermal equivalent short-circuit current d. IEC section 6 provides a sample calculation as a benchmark test for software programs to compare. In this case special considerations beyond the scope and procedure given in this standard have to be taken into account see for instance 2.

I,, is the rated current of the generator transferred to the high-voltage side see 4. For two-winding transformers with and without on-load tap-changer, an impedance correction factor KT is to be introduced in addition to the impedance evaluated according to equations 7 to 9: All network feeders, synchronous and asynchronous machines are replaced by their internal impedances see clause 3.

For per unit or other similar unit systems, no transformation is necessary if these systems are coherent, i. For high voltage circuit breakers, the peak current is compared with the making capacity and the breaking current is compared irc the rated breaking capacity. Highlighting of buses when voltage is below threshold Figure 7: T k i and the factor K derived in 4.

When calculating the partial short-circuit current I: This fault is beyond the scope of, and is therefore not dealt with in, this standard. The peak short-circuit current i, at a short-circuit location F, fed from sources which are not meshed with one another, in accordance with figure 12, is the sum of the partial short-circuit currents: The values can be displayed in magnitude, magnitude and angle, or in real and imaginary quantities.

For other ,values of minimum time delay, linear interpolation between curves is acceptable.

EasyPower compares the short circuit results with protective device short-circuit ratings and displays the results in the text report and in the single line diagram. NOTE The current in a three-phase short circuit is assumed to be made simultaneously in all poles. In this case, the symmetrical short- circuit breaking current Ib is smaller than the initial symmetrical short-circuit current I,”.

Their preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with may participate in this preparatory work.

### IEC Short-Circuit in EasyPower

If Si is used in spite of this in connection with short-circuit calculations, for instance to calculate the internal impedance of a network feeder at the connection point Q, then the definition given should be used in the following form: NOTE The following values for resistivity may be used: In all cases it is possible to determine the short-circuit current at the short-circuit location F with the help of an equivalent voltage source.

In a system of low voltage breakers with ZSI, when the current through any circuit breaker exceeds the short time pickup its restraining signal is sent to upstream circuit breakers. For TCC clipping you can choose one from initial, breaking and steady state currents. Depending on the product f. Calculation of currents 1 General 1.

## IEC-60909 Short-Circuit in EasyPower

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 short-circuit current through any protective device can be used to clip the TCC curve of the device.

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. For minimum short-circuit calculations the motor contribution is excluded.

Ca,culation characteristic curves showing device curves clipped at the right side and short-circuit tick marks.

Example of a meshed network fed from several sources NOTE For some near-to-generator short circuits the value of id. All other active voltages in the system are assumed to be zero. For the short-circuit impedances of synchronous generators in the negative-sequence system, the following applies with KG from equation 1 8: Any branch may be a series combination of several impedances.

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. Transformers having different winding configurations, such as a delta connection on one side and a star wye connection on the other side, have a designated shift in the phase angles of currents and voltages.

EasyPower offers a complete and accurate solution to short-circuit calculations in three-phase AC systems using the IEC standard.