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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In the equipment short-circuit duty report, comments and text colors provide indication of problem areas. Figure 3 – Characterization of short circuits and their currents Figure 4 shows an example of the equivalent voltage source at the short-circuit location F as the only active voltage of the system fed by a transformer without or with on-load tap-changer.

This correction factor shall not be introduced for unit transformers of power station units see 3. 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: Currents calculated with equation 74 are larger than the real symmetrical short-circuit breaking.

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. The effective resistance per unit length RL of overhead lines at the conductor temperature 20 “C may be calculated from the nominal cross-section qn and the resistivity p: Short-circuit current of a near-to-generator short circuit with decaying a.

## IEC-60909 Short-Circuit in EasyPower

Equations 84 and 85 are valid in the case of far-from-generator and in the case of near-to- generator short circuits. In meshed networks there are several direct-current time constants. For simplification, it is permitted to use the same value for IC as for the three- phase short circuit.

You can display short-circuit tick marks for initial, breaking and steady state currents. If the highest partial short-circuit crcuit of the power station unit at the high-voltage side of the unit transformer with off-load taps is searched for, choose l-pT.

For high voltage circuit breakers, the peak current is compared with the making capacity and the breaking current is compared with the rated breaking capacity. 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 Impedances between a starpoint and earth shall be introduced without correction factor.

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

### IEC Short-Circuit in EasyPower

The correction factors for three-winding transformers with or without LTC are calculated using the following equations. In the case of figure 4, for instance, to the LV side. It is assumed that the operating voltage at the terminals of the generator is equal to UrG.

Cricuit short-circuit impedances for electrical equipment are modified using impedance corrections factors that are calculated based on section 3. CE1- Instead of: All other static converters are disregarded for the short-circuit current calculation according to this standard.

Example for the estimation of the contribution from the asynchronous motors in relation to the total short-circuit current Time-current characteristic curves showing device curves clipped at the right side and short-circuit tick marks.

EasyPower uses the equivalent voltage source at the short-circuit location, symmetrical components impedance network, and the voltage factor c as described in section 2.

Rated short-circuit voltage of a transformer in per cent Short-circuit voltage of a short-circuit limiting reactor in per cent Rated resistive component of the short-circuit voltage of a transformer in per cent Rated reactive shoet of the short-circuit voltage of a transformer in per cent Positive- negative- zero-sequence voltage Reactance, absolute respectively relative value Synchronous reactance, direct axis respectively quadrature axis Fictitious reactance of a generator with compound excitation in the case of steady-state short circuit at the ciruit poles Xd resp.

Short-circuit duty results displayed in the single line drawing Table 5: The IEC shall not be held responsible for identifying any or all such patent rights. This standard does not cover short-circuit currents deliberately created under controlled conditions short-circuit testing stations. The value should be obtained from the manufacturer. The upstream circuit breakers do not trip instantaneously whereas the most downstream circuit breaker trips fast, enabling selective coordination.

Characterization of short circuits and their currents EasyPower calculates the Peak currents i p based on section 4.

Xk may be neglected. They may be neglected. 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 with earth connection see figures 3c and 3d the application of Ks according to equation 22 may lead to results at the non-conservative side.

These remote currents and voltages are useful for relay setting. The generator impedance shall be transferred to the high-voltage side using the rated transformation ratio t. This is possible if the d. For the short-circuit impedance of synchronous generators in the zero-sequence system, the following applies with KG from equation 1 8: