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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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. Short-circuit current-limiting reactors shall be treated as a part of the short-circuit impedance.

### IEC TR | IEC Webstore

The factor K shall, be calculated according to 4. When an impedance is present between the starpoint of the generator and earth, the correction factor KG shall not 6909-4 applied to this impedance. For higher temperatures than 20 OC, see equation 3. 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.

Any branch may be a ifc combination of several impedances.

The initial short-circuit current at the short-circuit location F is the phasor sum of the individual partial short-circuit currents see figure Factor q may also be idc from figure You can display short-circuit tick marks for initial, breaking and steady state currents.

For transformers with delta and start wye winding connections, the clock notations 1,3,5,7,9 and 11 are supported in the database. In the calculation of short-circuit currents, those medium-voltage and low-voltage motors may be neglected, provided that, according to the circuit diagram interlocking or to the process reversible drivesthey are iecc switched in at the same time.

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 currents and partial short-circuit currents for three-phase short circuits between generator and unit transformer with or without on-load tap.

## IEC TR 60909-4:2000

With respect to equation 99 iiec table 3 the steady-state short-circuit current of asynchronous motors is zero in 609909-4 case of a three-phase short circuit at the terminals figure 12 and equation The type of short circuit which leads to the highest short-circuit current depends on the values of the positive-sequence, negative-sequence, and zero-sequence short-circuit impedances of the system.

For undated references, the latest edition of the normative document referred to applies.

When calculating the partial short-circuit current I: For breaking current ice can choose from 0. If synchronous motors have a voltage regulation, they are treated like synchronous generators.

### IEC Short-Circuit in EasyPower

In a system of low voltage breakers with ZSI, when the current through any ied breaker exceeds the short time pickup its restraining signal is sent to upstream circuit breakers. Each branch short- circuit current can be calculated as an independent single-source three-phase short-circuit current in accordance with equation ice and the information given in 4. This method applies the 1. Electric and magnetic circuits 60909- 15 1: Asymmetrical values can be used with protective devices that respond to the asymmetrical currents.

This can lead to a situation where the partial short-circuit currents are too small to operate any further protection device, particularly in the case of minimum short-circuit currents. The decaying aperiodic component id. Symmetrical currents are applied for relays with DC offset filter.

## IEC-60909 Short-Circuit in EasyPower

With these impedances the ic equivalent impedances LK, z B K and ZCKshall be calculated using the procedure given in equation i i.

The following values for the fictitious resistances RGfmay be used for the calculation of the peak short- circuit current with sufficient accuracy.

Ik Steady-state short-circuit current r. In some special cases, it could happen that the decaying short-circuit current reaches zero for the first time, some cycles after the short circuit took place. During the initial stage of the short circuit, the negative impedance is approximately equal to the positive-sequence impedance, independent 6090-4 whether the short circuit is a near-to-generator or a far-from-generator short circuit.

Skip to main content. A contribution 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.

Ied 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.