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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RL is the line resistance for a conductor temperature of 20 OC, when calculating the maximum short-circuit currents. IkP Steady-state short-circuit current at the terminals poles of a generator with compound excitation Initial symmetrical short-circuit 6099-4 r.

EasyPower uses the following c factors as the default for maximum and minimum short-circuit conditions. Q5 This standard meets my needs: At this date, the publication will be 0 reconfirmed; 0 withdrawn; 0 replaced by a revised edition, or 0 amended.

The impedance of the auxiliary transformer AT in figure 13 is to be corrected with KT from 3. This 06909-4 the 3I0 value 3 times the zero sequence current. Special considerations are necessary in this case, for instance with the superposition method. If the 60909–4 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. 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.

In existing low-voltage systems it is possible to 6090-4 the short-circuit impedance on the basis of measurements at the location of the prospective short circuit considered.

This is the only active voltage of the network 1.

During the initial stage of the short circuit, the negative 6099-4 is approximately equal to the positive-sequence impedance, independent of whether the short circuit is a near-to-generator or a far-from-generator short circuit. Sequential short circuits are not considered. For the examples in figures 1Ib and 1 IC, the initial symmetrical short-circuit current is calculated with the corrected impedances of the generator and the power station unit see 3.

All network feeders, synchronous and asynchronous machines are replaced by their internal impedances see clause 3. Short-circuit duty results displayed in the single line drawing Table 5: For the calculation of the initial short-circuit currents according to 4.

If only overexcited operation is expected, then for the calculation of unbalanced short-circuit currents the correction factor Ks from equation 22 shall be used for both the positive-sequence and the negative-sequence system impedances of the power station unit. The total short-circuit current in F1 or F2 figure 13 is found by adding the partial short-circuit current IL,, caused by the medium- and low-voltage auxiliary motors of the power station unit.

Synchronous machines generators, motors, or compensators with terminal-fed static exciters do not contribute to I k in idc case of a short-circuit at the terminals of the machine, but they contribute to l k if there is an impedance between the terminals and the short-circuit location.

The values of p in equation iecc apply if synchronous machines are excited by rotating exciters or by static converter exciters provided, for static 609909-4, the minimum time delay tminis less than 0,25 s and the maximum excitation voltage is less than 1,6 times rated load excitation-voltage. Additional information may be found in IEC The text of this standard is based on the following documents: IEC section 6 provides a sample calculation as a iiec test for software programs to compare.

Special methods to calculate i, with sufficient accuracy are given in 4. The initial line-to-earth short-circuit current Iil in figure 3d shall be calculated by: Medium-voltage motors have to be considered in the uec of maximum short-circuit current see 2. However, parties to agreements based on this part of IEC are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below.

These values cannot be used when calculating the aperiodic component id. Neglecting the -zero-sequence capacitances of lines in earthed neutral systems leads to results which are slightly higher than the real values of the short-circuit currents.

This fault is beyond the scope of, and is therefore not dealt with in, this standard. All other static converters are disregarded for the short-circuit current calculation according to this standard.

The short-circuit current through any protective device can be used to clip the TCC curve of the device. The value should be obtained from the manufacturer. Breaking currents are calculated at 0. These have, 90, and 30 degrees phase shift respectively based on the high voltage side taken as the reference. The IEC shall not be held responsible for identifying any or all such patent rights. I librarian researcher I design engineer safety engineer ci Q7 Please assess the standard in the I following categories, using testing engineer ci the numbers: These remote currents and voltages are useful for relay setting.

Equations 84 and 85 are valid in the case of far-from-generator and in the case of near-to- generator short circuits. Currents flowing through sources, cables, lines, transformers and other equipment are also calculated. This procedure is not allowed when calculating the peak short-circuit current i.

## IEC TR 60909-4:2000

The resistive component uRrcan be calculated from the total losses PkiTin the windings at the rated current IrT, both referred to the same transformer side see equation 8. If there are several transformers with slightly differing rated transformation ratios trT1trT Then they contribute only to the initial symmetrical short-circuit current I: Fuses and low voltage circuit breakers ratings are compared with initial currents.

The IEC collaborates closely with the International Organization for Standardization ISO in accordance with conditions determined by agreement between the two organizations. The values of positive-sequence and negative-sequence impedances can differ from each other only in the case of rotating machines.

High voltage circuit breaker data comes with the DC time constant. Within the accuracy of this standard, it is often sufficient to determine the short-circuit current at the short-circuit location F as being the sum of the absolute values of the individual partial short- circuit currents.

### IEC Short-Circuit in EasyPower

This part of IEC deals with the calculation of short-circuit currents in the case of balanced or unbalanced short circuits. For the effective reactance of the generators, introduce: When calculating unbalanced short-circuit currents in medium- or high-voltage systems and applying an equivalent voltage source at the short-circuit location, the zero-sequence capacitances of lines and the zero-sequence shunt admittances are to be considered for isolated.

The method described above is for 3-phase short circuit. In a system of low voltage breakers with ZSI, when the current through any circuit breaker exceeds the short time pickup its restraining signal 6090-4 sent to upstream circuit breakers. Rated short-circuit voltage of a transformer in per cent Short-circuit 60909- 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 component of 6099-4 short-circuit voltage of a transformer in per cent Eic, 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 terminals poles Xd resp.