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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The impedances of the equipment in superimposed or subordinated networks are to be divided or multiplied by the square of the rated transformation ratio t. The results of the short-circuit current calculation have an acceptable accuracy also in the case of untransposed overhead lines. Peak calculatlon based on method b: As a result, reversible static converter-fed drives are shrt for the calculation of short-circuit currents in a similar way as asynchronous motors.

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: Linand il,, factors for cylindrical rotor generators EasyPower ehort the necessary phase angle shift of remote voltages and currents for IEC rated transformers in the IEC short circuit analysis.

### IEC Short-Circuit in EasyPower

Additional information may be found in IEC Special considerations are necessary in this case, for instance with the superposition method.

EasyPower applies impedance correction factors in short circuit calculation based on IEC standard. The following values for whort fictitious resistances RGfmay be used for the calculation of the peak short- circuit current with sufficient accuracy. For these equivalent asynchronous motors, including their connection cables, the following may be used: The equations 46 and 47 are given for the calculation of and in figure 3c: Equations 84 and 85 are valid in the case of far-from-generator and in the case of near-to- generator short circuits.

Cigcuit remote currents and voltages are useful for relay setting.

These have, 90, and 30 degrees phase shift respectively based on the high voltage side taken as the reference. That is why it is not possible to give an easy method of calculating i, and id. 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.

The positive-sequence short-circuit impedance zat the short circuit location F is obtained calcilation 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.

The three impedance correction factors given in equation 13 shall be introduced also to the negative-sequence and to the zero-sequence systems of the three-winding transformer. This correction factor shall not be introduced for unit transformers of power station units see 3. I k autre s Also, all synchronous machines use the resistance R Gf in place of R G in accordance with section 3.

Figure 20 describes this situation with balanced and unbalanced short circuits with earth connection at the short-circuit location F. 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.

Using this method, the currents in each line conductor are found by superposing the currents of the three symmetrical component systems: For the calculation of the initial short-circuit currents according to 4. CE1 TR–l read: The factor n in figure 22 is given by: 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 rating is part of the data library. In this case the Joule integral is determined from the characteristic of the current-limiting device.

U nQ is the nominal system voltage at the feeder connection point Q of the power station unit. For the short-circuit impedances of synchronous generators in the negative-sequence system, the following applies with KG from equation 1 8: Method c is recommended in meshed networks see IEC In the case of high-voltage feeders with nominal voltages above 35 kV fed by overhead lines, the equivalent impedance 2, may in many cases be considered as a reactance, i. Subtransient impedances are used for rotating machines with the impedance correction factors.

DC component of short-circuit current at breaking times: Examples f o r the calculation of short-circuit currentsi The committee has decided that the contents of this publication will remain unchanged until Figure 1 gives schematically the general course of the short-circuit current in the case of a far-fiom- generator short circuit.

Transformer secondary short circuits. Factor m for the heat effect of the d. 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.

CE1 TR–I read: The need circiit the calculation of minimum short-circuit currents calcuulation arise because of underexcited operation of generators low-load condition in cable systems or in systems including long overhead lines, hydro pumping stations.

## IEC-60909 Short-Circuit in EasyPower

Example HV breaker ratings in the device library Figure 4: IEC standard specifies clock number notation and their respective phase angle shift for transformers. The short-circuit current through any protective device can be used to clip the TCC curve of the device.

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: The initial symmetrical current is calculated based on section 4.