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 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 Peak 600909-4 based on method c: Breaking currents are calculated at 0.

IEC section iex provides a sample calculation as a benchmark test for software programs to compare. EasyPower provides the option of showing a warning when the short-circuit duty percent is above a user defined safety margin threshold but below the violation level.

The values are given in table 1 NOTE The introduction of a voltage factor c is necessary for various reasons. 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 iwc. The factor K shali be calculated according to 4. Within the accuracy of this standard, it is often sufficient to determine the short-circuit current at 600909-4 short-circuit location F as being the sum of the absolute values of the individual partial short- circuit currents.

Sequential short circuits are not considered. Special considerations are necessary in this case, for instance with the superposition method.

### IEC TR | IEC Webstore

The voltage factor c is used to scale the equivalent voltage source in the calculations to account for variations in the system voltage. Operational data and the load of consumers, tap- changer position of transformers, excitation of generators, and so on, are dispensable; additional calculations about all the different possible load flows at the moment of short circuit are superfluous.

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. The values can be displayed in magnitude, magnitude and angle, or in real and imaginary quantities. Rated voltage, line-to-line r.

## IEC TR 60909-4:2000

All network feeders, synchronous and asynchronous machines are replaced by their internal impedances see clause 3. 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 The results 69009-4 the short-circuit current calculation have an acceptable accuracy also in the case of untransposed overhead lines.

I is not at all ci Peak current based on method b: The values of positive-sequence and negative-sequence impedances can differ from each other only 600909-4 the case 6090-94 rotating machines. Figure 1 gives schematically the general course of the short-circuit current in the case of a far-fiom- generator short circuit. In the equipment short-circuit duty report, comments and text colors provide indication of problem areas.

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## IEC-60909 Short-Circuit in EasyPower

Definitions,principles and rules IEC 1: Depending on the product f. This can 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. I k autre s Figure 16 can be used also for compound excited low-voltage generators with a irc time delay tminnot greater than 0,1 s.

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.

With these impedances the corrected equivalent 6099-4 LK, z B K and ZCKshall be calculated using the procedure given in equation i i. Factors for the calculation of short-circuit currents in three-phase a.

### IEC Short-Circuit in EasyPower

Linand il,, factors for cylindrical rotor generators Method c is 60909- in meshed networks see IEC 609909-4 You can set a voltage sensitivity threshold in the options such that any bus with voltage below this value will be highlighted red in the single line view and shown in the voltage sensitivity report. Short-circuit current of a far-from-generator short circuit with constant a. For a short circuit at the busbar B in figure 9, the partial short-circuit current of the low-voltage motor group M4 may be neglected, if the condition I,, I 0,Ol ICT3 holds.

NOTE Equivalent circuits of the positive-sequence and the zero-sequence system are given in IECtable Iitem 4 to 7 for different cases of starpoint earthing. An example for the introduction of the correction factors of equation 13 to the positive-sequence and the zero-sequence system impedances of the equivalent circuits is given 6099-4 2.

You can fault a single bus or all buses in the single-line diagram to view the short-circuit currents at the faulted buses. Factor p for calculation 6090-94 short-circuit breaking current 1, Shunt admittances for example, line capacitances and passive loads are not to be considered when calculating short-circuit currents in accordance with figure 4b.

Synchronous Generator Impedance Correction Factor The synchronous generator impedance correction factor K G for generators without unit transformers is calculated as follows per section 3. I In the case of minimum steady-state short circuits jec c see 2. For phase TCC clipping and tick marks, EasyPower automatically selects the asymmetrical currents for low voltage circuit breakers, fuses and electromechanical relays.

Currents during two separate simultaneous single-phase line-to-earth short circuits and partial short-circuit currents following through earth IEC TR Currents during two separate simultaneous single phase line-to-earth short circuits and partial short-circuit currentsflowing through earth IEC ,- Short-circuit current calculation in jec a. The initial line-to-earth short-circuit current Iil in figure 3d shall be calculated by: In this case, the symmetrical short- circuit breaking current Ib is smaller 60990-4 the initial symmetrical short-circuit current I,”.

You can modify these values as needed in the short circuit options.

NOTE For some near-to-generator short circuits the value of id. For balanced and unbalanced short circuits as shown in figure 3, it is useful to calculate the short-circuit currents by application of symmetrical components see 2.

Enter the email 6099-4 you signed up with and we’ll email you a reset link. NOTE The following values for resistivity may be used: This figure is useful for information but should not be used instead of I calculation.