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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High voltage circuit breaker data comes with the DC time constant. This standard does not cover short-circuit currents deliberately created under controlled conditions short-circuit testing stations.

Factor q for the calculation of the symmetrical short-circuit breaking current of asynchronous motors Example of a meshed network fed from several sources CE1- Instead of: Electric and magnetic devices IEC Factor p for calculation of short-circuit breaking current 1, When calculating short-circuit currents in systems with different voltage levels, it is necessary to transfer impedance values from one voltage 60909-44 to another, usually to that voltage level at which the short-circuit current is to be calculated.

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.

## IEC TR 60909-4:2000

EasyPower calculates the Peak currents i p based on section isc. The values of positive-sequence and negative-sequence impedances can differ from each other only in the case of rotating machines. This part of IEC deals with the calculation of short-circuit currents in the case of balanced or unbalanced short circuits.

I k autre s For increased accuracy, equations 79, 76and 77 can be used. 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. The short-circuit impedances for electrical equipment are modified using impedance corrections factors that are calculated based on section 3. The IEC collaborates closely with the International Organization for Standardization ISO in accordance with conditions determined by agreement between the two organizations.

Examples f o r the calculation of short-circuit currentsi The committee has decided that the contents of this publication will remain unchanged until Voltage sensitivity report for buses with voltage below threshold Transformer Phase Shift The short-circuit calculation provides the phase angle of the branch currents and the bus voltages at various equipment.

### IEC Short-Circuit in EasyPower

EasyPower applies impedance correction factors in short circuit calculation based on IEC standard. These values cannot be used when calculating the aperiodic component id. U, is the nominal voltage of the system; ur, is the rated voltage of the generator; ZGK is the corrected subtransient impedance of the generator; 2, is the subtransient impedance of the generator in the positive-sequence system: Characterization of short circuits and their currents In general, two short-circuit currents, which differ in their magnitude, are to be calculated: For minimum short-circuit currents, the resistances are based on the estimated temperature at the end of the short-circuit condition.

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

### IEC TR | IEC Webstore

Peak current based on method b: From the calculated initial symmetrical short-circuit current and characteristic curves of the fuses or current-limiting circuit- breakers, the cut-off current is determined, which is the peak 609009-4 current of the downstream substation.

Short circuits may have one or more sources, as shown in figures 11, 12, and Q5 This standard meets my needs: 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.

In this case, it is necessary to distinguish between networks with and without parallel branches see 4.

The need for the calculation of minimum short-circuit currents may arise because of underexcited operation of generators low-load condition in cable systems or in systems 69009-4 long overhead lines, hydro pumping stations. In this case, the three-fold zero-sequence current flows through the joint return.

Annex A forms an integral part of this standard.

The following types of unbalanced short circuits are treated in this standard: EasyPower provides the necessary phase angle shift of remote voltages and currents for IEC rated transformers in the IEC short circuit analysis. The following features are supported:. For per unit or other similar unit systems, no transformation is necessary if these systems are coherent, i.

The capacitances of lines overhead lines and cables of low-voltage networks may be neglected in the positive- negative- and zero-sequence system.

The correction factors for three-winding transformers with or without LTC are calculated using the following equations. This first iecc cancels and replaces IEC published in and constitutes a technical revision. Impedances between a starpoint and earth shall be introduced without correction factor.