IEC 60909 PDF


This calculation is based on IEC (, c), “Short-circuit currents in three-phase a.c. systems – Part 0: Calculation of currents” and. EasyPower offers a complete and accurate solution to short-circuit calculations in three-phase AC systems using the IEC standard. You can enter. IEC Edition INTERNATIONAL. STANDARD. NORME. INTERNATIONALE. Short-circuit currents in three-phase a.c. systems –.

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This procedure is not allowed when calculating the peak short-circuit current i. The total short-circuit in F1 or F2 figure 13 is found by adding the partial short-circuit current ILrnv, caused by the medium- and low-voltage auxiliary motors of the power station unit.

IEC Short-Circuit in EasyPower

Figure 1 gives schematically the general course of the short-circuit current in the case of a far-fiom- generator short circuit. The values are given in table 1 NOTE The introduction of a voltage factor c is necessary for various reasons. The three impedance correction factors given in equation 13 shall be introduced also to the negative-sequence and to iiec zero-sequence systems of the three-winding transformer.

The values of positive-sequence and negative-sequence impedances can differ from each other only in the case of rotating machines.

For minimum short-circuit calculations the motor contribution is excluded. The symbols represent physical quantities possessing both numerical values and dimensions that are independent of units, provided a consistent unit system is chosen, for example the international system of units SI.

This will display the curve only up to the maximum current the device will see. IEC- lire: Display of short-circuit currents You can view the currents in various formats such as phase currents for A, B and C phases or in symmetrical components: The IEC collaborates closely with the International Organization for Standardization ISO in accordance with conditions determined by agreement between the two organizations.


The correction factor Kso shall also be applied to the zero-sequence system impedance of the power station unit excepting, if present, an impedance component between the star point of the transformer and earth. Figure 16 can be used also for compound excited low-voltage generators with a minimum time delay tminnot greater than 0,1 s.

Transformer secondary short circuits.

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This is the 3I0 value 3 times the zero sequence current. For the calculation of the partial short-circuit current I L 2 feeding into the short-circuit location F2, for example at the connection to the high-voltage side of the auxiliary transformer AT in figure 13, it is sufficient to take: Annex A forms an integral part of this standard.

Earth ground trip functions for low voltage circuit breakers or relays use the symmetrical earth ground current. Their preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with may participate in this preparatory work.

As a result, reversible static converter-fed drives are treated for the calculation of short-circuit currents in a similar way as asynchronous motors. The impedance of the network feeder and the transformer are related to the LV-side and the last one is also corrected with KT see 3. For phase TCC clipping and tick marks, EasyPower automatically selects the asymmetrical currents for low voltage circuit breakers, fuses and electromechanical relays.

Then they contribute only to the initial symmetrical short-circuit current I: IEC Short-circuit currents in three-phase a c.

IEC-60909 Short-Circuit in EasyPower

Calculated Values You can obtain the following values of short-circuit currents at the fault location for both maximum and minimum short circuit currents: 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.


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. NOTE The current in a three-phase short circuit is assumed to be made simultaneously in all poles.

Example HV breaker ratings in the device library Figure 4: Z THV is the impedance of the unit transformer referred to the high-voltage side without correct factor K T. Equations 84 and 85 are valid in the case of far-from-generator and in the case of near-to- generator short circuits.

Short-circuit currents decaying over time Methodology 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.

As per section 4.

While using fuses or current-limiting circuit-breakers to protect substations, the initial symmetrical short- circuit current is first calculated as if these devices were not available. Three-phase short-circuit 6909 for breaking I b at0. He published 17 books in German, English and Turkish and more than 64 international scientific publications.

In this case, it is necessary to distinguish between networks with and without parallel branches see 4. This phenomenon is not dealt with in this standard.