# IEC 60909-4 PDF

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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In this case special considerations beyond the scope and procedure given in this standard have to be taken into account see for instance 2.

### IEC TR | IEC Webstore

The text of this standard is based on the following documents: These remote currents and voltages are useful for relay setting. Click here to sign up. Short-circuit duty results displayed in the single line drawing Table 5: Enter the email address you signed up with and we’ll email you a reset link.

For dated ied, subsequent amendments to, or revisions of, any of these publications do not apply.

CE1 Idc–l read: For transformers with delta and start wye winding connections, the clock notations 1,3,5,7,9 and 11 are supported in the database. You can insert tick marks arrows in the TCC plot to indicate the short-circuit current through the device. This correction factor shall not be introduced for unit transformers of power station units see 3. In general, two short-circuit currents, which differ in their magnitude, are to be calculated: The estimation according to equation 28 is not allowed in the case of three-winding transformers.

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.

The IEC shall not be held responsible for identifying any or all such patent rights. This is admissible, because the impedance correction factor KTfor network transformers is introduced. Low-voltage motors are to be taken into account in auxiliaries of irc stations and in industrial and similar installations, for example in networks of chemical and steel industries and pump- stations.

Highlighting of buses when voltage is below threshold Figure 7: Steady-state short-circuit current I k Steady-state short-circuit current I k is calculated based on section 4. The effective resistance of the stator of synchronous machines lies generally much below the given values for RGf. Transformer Impedance Correction Factors The transformer correction factor K T for two winding units with or without on-load tap changer LTC is calculated as follows per section 3.

All other active voltages in the system are assumed to be zero. The type of short ic 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.

### IEC Short-Circuit in EasyPower

For simplification, it is permitted to use the same value for as for the three- phase short circuit. Nominal system voltage, line-to-line r.

As a result, reversible static converter-fed drives are treated for the calculation of short-circuit currents in a similar way as asynchronous motors. EasyPower offers a complete and accurate solution to short-circuit calculations in three-phase AC systems using the IEC standard. Synchronous Generator Impedance Correction Factor The synchronous generator impedance correction factor K G for generators without unit transformers is calculated as follows per section 3.

Impedances between a starpoint and earth shall be introduced without correction factor.

## IEC-60909 Short-Circuit in EasyPower

irc The effect of series capacitors can be neglected in the calculation of short-circuit currents, if they are 60909-44 with voltage-limiting devices in parallel, acting if a short circuit occurs. With respect to equation 99 in table 3 the steady-state short-circuit current of asynchronous motors is zero in the case of a three-phase short circuit at the terminals figure 12 and equation This is the 3I0 value 3 times the zero sequence current.

In this case the uec values for RG should be used. The following types of unbalanced short circuits are treated in this standard: This is the only active voltage of the network 1.

E” Subtransient voltage of a synchronous machine f Frequency 50 Hz or 60 Hz Ib Symmetrical short-circuit breaking current r. Breaking currents are calculated at 0.