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 following methods are supported for meshed networks as per section 4. T JSrT ; t, is the rated transformation ratio of the unit transformer: Despite these assumptions being not strictly true for the power systems considered, the result of the calculation does fulfil the objective to give results which are generally of acceptable accuracy.
You can modify these values as needed calculatkon the short circuit options. Voltages and currents are to be converted by the rated transformation ratio t.
Asymmetrical values can be used with protective devices that respond to the asymmetrical currents. Special considerations are necessary in this case, for instance with the superposition method.
IEC Short-Circuit in EasyPower
Transformer Impedance Correction Factors The transformer correction factor K T for two winding units with or without on-load cricuit changer LTC is calculated as follows per section 3. The generator impedance shall be transferred to the high-voltage side using 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.
They do citcuit contribute to the symmetrical short-circuit breaking current I, and the steady-state short-circuit current I k.
IEC-60909 Short-Circuit in EasyPower
I certification technical documentation ci ci Their preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with may participate in this preparatory work. The capacitances of lines overhead lines and cables of low-voltage networks may be neglected in the positive- negative- and zero-sequence system.
The factors m and n first appeared as Figures 12a and 12b of IEC and are identical to them. Figure 20 describes this situation with balanced and unbalanced short circuits with earth connection at the short-circuit location F.
A calcylation is also given if, in case of a power station unit, the short-circuit occurs on the high-voltage side of the unit transformer see figure 1lc.
This standard does not cover short-circuit currents deliberately created under controlled conditions short-circuit testing stations. Remote Currents and Voltages Currents flowing through sources, cables, lines, transformers and other equipment are also calculated. You calcuation 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 currents and short-circuit impedances may also be determined by system tests, by measurement on a network analyzer, or with a digital computer. The text of this standard is based on the following documents: Then they contribute only to the initial symmetrical short-circuit current I: For the purpose of this standard, one has to make a distinction between short-circuit impedances at the short-circuit location F and the short-circuit impedances of individual electrical equipment.
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: The positive-sequence short-circuit impedance zat the caalculation circuit location F is obtained according 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.
Except for special cases, the zero-sequence short-circuit impedances at the short-circuit location differ from circuif positive-sequence and negative-sequence short-circuit impedances. Any branch may be a series combination of several impedances. This part of IEC does not deal with the calculation of short-circuit currents in installations on board ships and aeroplanes.
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 short-circuit current of the downstream substation. Annex A forms an integral part of this standard. As a result, reversible static converter-fed drives are treated for the calculation of short-circuit currents in a similar way as asynchronous motors.
Shift in current angle across delta-wye transformer Integration with Protective Device Coordination The IEC short-circuit results are integrated with the protective device coordination tools in EasyPower.
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: For simplification, it is permitted to use the same value for as for the three- phase short circuit.
The effective resistance of the stator of synchronous machines lies generally much below the given values for RGf. If the highest partial short-circuit current of the power station unit at the high-voltage side of the unit transformer with off-load taps is searched for, choose l-pT.
If underexcited operation of the power station unit is expected at some time for instance to a large extent especially in pumped storage plantsthen only when calculating unbalanced short- circuit currents shory earth connection see figures 3c and 3d the application of Ks according to equation 22 may lead to results at the non-conservative side. This first edition cancels and replaces IEC published in and constitutes a technical revision.
Figure 16 can be used also for compound excited low-voltage generators with a minimum time delay tminnot greater than 0,1 s.
Method c is recommended in meshed networks see IEC Asymmetrical currents for the initial and the four breaking time intervals are also calculated for use in protective device coordination.
For three-winding transformers with and without on-load tap-changer, three impedance correction factors can be found using the relative values of the reactances of the transformer see 3. CE1- Instead of: The values can be displayed in magnitude, magnitude and angle, or in real and imaginary quantities.
E” Subtransient voltage of a synchronous machine f Frequency 50 Hz or 60 Hz Ib Symmetrical short-circuit breaking current r. That is why it is not possible to give an easy method of calculating i, and id. For transformers with delta and start wye winding connections, the clock notations 1,3,5,7,9 and 11 are supported in the database. Earthing and protection against electric shock IEC 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.