This calculation is based on IEC (, c), “Short-circuit currents in three-phase a.c. systems – Part 0: Calculation of currents” and. EasyPower offers a complete and accurate solution to short-circuit calculations in three-phase AC systems using the IEC standard. You can enter. IEC Edition INTERNATIONAL. STANDARD. NORME. INTERNATIONALE. Short-circuit currents in three-phase a.c. systems –.

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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. It is assumed that the operating voltage at the terminals of the generator is equal to UrG.

Calculations are simplest for balanced short circuits on radial systems, as the individual contributions to a balanced short circuit can be evaluated separately for each source figures 12 or I 1 unacceptable, marketing specialist other Calculated Values You can obtain the following values of short-circuit currents at the fault location for both maximum and minimum short circuit currents: Short-circuit current-limiting reactors shall be treated as a part of the short-circuit impedance.

The transformer correction factor K T for two winding units with or without on-load tap changer LTC is calculated as follows per section 3. In the case of unbalanced short circuits, the impedance correction factor KSOfrom equation 24 shall be applied to both the positive-sequence and the negative-sequence system impedances of the power station unit.

For minimum short-circuit currents, the resistances are based on the estimated temperature at the end of the short-circuit condition. 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.

Calculation with Impedance Corrections You can fault a single bus or all buses in the single-line diagram to view the short-circuit currents at the faulted buses. Voltage Factors c The voltage factor c is used to scale the equivalent voltage source in the calculations to account for variations in the system voltage. These have, 90, and 30 degrees phase shift respectively based on the high voltage side taken as the reference. Also, all synchronous machines use the resistance R Gf in place of R G in accordance with section 3.

This postulates that the electrical equipment has a balanced structure, for example in the case of transposed overhead lines. For a synchronous generator use Rm see 3.

For the effective reactance of the generators, introduce: Currents flowing through sources, cables, lines, transformers and other equipment are also calculated. They do not contribute to the symmetrical short-circuit breaking current I, and the steady-state short-circuit current I k. Special methods to calculate i, with sufficient accuracy are given in 4. The total short-circuit current in F1 or F2 figure 13 is found by adding the partial short-circuit current IL,, caused by the medium- and low-voltage auxiliary motors of the power station unit.

In some special cases, it could happen that the decaying short-circuit current reaches zero for the jec time, some cycles after the short circuit took place.

### IEC Short-Circuit in EasyPower

Supply to a Factory In this case the Joule integral is determined from the characteristic of the current-limiting device. 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.

The impedance correction factor shall be applied also to the negative-sequence and the zero- sequence impedance of the transformer when calculating unbalanced short-circuit currents. E” Subtransient voltage 06909 a synchronous machine f Frequency 50 Hz or 60 Hz Ib Symmetrical short-circuit breaking current r.

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

Symmetrical locked-rotor current of an asynchronous motor Rated current of irc equipment Thermal equivalent short-circuit current d. For the short-circuit impedance of synchronous generators in the zero-sequence system, the following applies with KG from equation 1 8: Then they idc only to the initial symmetrical short-circuit current I: For TCC clipping you can choose one from initial, breaking and steady state currents.

For transformers with delta and start wye winding connections, the clock notations 1,3,5,7,9 and 11 are supported in the database.

Examples f o r the calculation of short-circuit currents’ IEC The factors m and n first appeared as Figures 12a and 12b of IEC and are identical to them.

This correction factor shall not be introduced for unit transformers of power station units see 3. Definitions,principles and rules IEC 1: Each branch short- circuit current can be calculated as an independent single-source three-phase short-circuit current in accordance with equation 29 and the information given in 4.

Enter the exact the reason is: The initial symmetrical current is calculated based on section 4. Short-circuit equipment duty report Voltage Ice Analysis Short-circuit on any bus results in voltage drop in other near buses in the system. Display of short-circuit currents You can view the currents in various formats such as phase currents for A, B and C phases or in symmetrical components: The IEC shall not be held responsible for identifying any or all such patent rights.

The superposition method gives the short-circuit current related to the one load flow presupposed. The comparison of results is summarized below. The following methods are supported for meshed networks as per section 4. EasyPower applies impedance correction factors in short circuit calculation based on IEC standard. The impedance of the network feeder ief the transformer are related to the LV-side and the last one is also corrected with KT see 3.

## IEC-60909 Short-Circuit in EasyPower

This 609099 lead to a situation where the partial short-circuit currents are too small to operate any further protection device, particularly in the case of minimum short-circuit currents. This part of IEC does not deal with the calculation of short-circuit currents in installations on board ships and aeroplanes. For grounded systems the influence of motors on the line-to-earth short-circuit current cannot be neglected.