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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International, governmental and non-governmental organizations liaising with the IEC also participate in this preparation. Short-circuit impedances of a three-phase a.

## IEC TR 60909-4:2000

I,, is the rated current of the generator transferred to the high-voltage side see 4. Click here to sign up. 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: Systems at highest voltages of kV and above with long transmission lines need special consideration.

In the case of high-voltage direct-current transmission systems, the capacitor banks and filters need special considerations, when calculating a. 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.

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: 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.

Regardless of the time of short-circuit occurrence, the discharge current of the shunt capacitors may be neglected for the calculation of the peak short-circuit current.

In all cases it is possible to determine the short-circuit current at the short-circuit location F with the help of an equivalent voltage source. Currents flowing through sources, cables, lines, transformers and other equipment are also calculated. Normally, the steady-state short-circuit current Ik is smaller than the symmetrical short-circuit breaking current 1.

### IEC Short-Circuit in EasyPower

The short-circuit current through any protective device can be used to clip the TCC curve of the device. For minimum short-circuit currents, the resistances are based on the estimated temperature at the end of the short-circuit condition.

At this date, the publication will be 0 reconfirmed; 0 withdrawn; 0 replaced by a revised edition, or 0 amended. It 609094- assumed that the operating voltage at the terminals of the generator is equal to UrG.

## IEC-60909 Short-Circuit in EasyPower

Each branch short- circuit current can be calculated as an independent single-source three-phase short-circuit current in accordance with equation 29 and the information given in 4. The upstream circuit breakers do not trip instantaneously whereas the most downstream circuit breaker trips fast, enabling selective coordination. This will display the curve only up to the maximum current the device will see. The correction factors for three-winding transformers with or without LTC are calculated using the following equations.

The factor K shall, be calculated 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.

Figure 21 – Factor m for the heat effect of the d.

### IEC TR | IEC Webstore

Also, all synchronous machines use the resistance R Gf in place of R G in accordance with section 3. Breaking currents are calculated at 0.

The positive-sequence short-circuit impedance zat the short 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.

This does not exclude the use of special methods, for example the superposition method, adjusted to particular circumstances, if they give at least the same precision. The generator impedance shall be transferred to the high-voltage side using the rated transformation ratio t. The factor K shali be calculated according to 4.

In this case, the three-fold zero-sequence current flows through the joint return.

The factors m and n 609009-4 appeared as Figures 12a and 12b of IEC and are identical to them. Peak current based on method b: In all cases I L is equal to Ikv,because the short circuits are far-from-generator short circuits see 1.

Subtransient impedances are used for rotating machines with the impedance correction factors.

This factor is also used in calculating impedance correction factors. Calculations are simplest for balanced short circuits on radial systems, as the individual contributions to a balanced short circuit can be evaluated separately for each source figures 12 or In this case, it is necessary to distinguish between networks with and without parallel branches see 4. With respect to equation 99 in table 3 the steady-state short-circuit current of asynchronous iex is zero in the case of a three-phase short circuit at the terminals figure 12 and equation IEC standard specifies clock number notation and their respective phase angle shift for transformers.

Short-circuit current of a far-from-generator short circuit with constant a.