# IEC TR 60909-4 pdf free download

**IEC TR 60909-4** pdf free download.Short-circuit currents in three-phase AC systems – Part 4: Examples for the calculation of short-circuit currents.

8 Calculation of three-phase short-circuit currents in a wind power plant

8.1 General

Wind power stations and photovoltaic power stations shall be considered only in case of the calculation of the maximum short-circuit current ‘‘,,iax (see IEC 60909-0). Therefore, the subscript “max” is omitted in the following.

8.2 Problem

A wind power plant with ten wind power station units W is given in Figure 16. The wind power plant is connected by two parallel cables LI and the transformer TWP to the 110 kV network feeder Q.

The initial symmetrical short-circuit currents and the peak short-circuit currents shall be calculated at the short-circuit locations Fl to F14 which are identical to the node numbers 1 to 14.

Three variants are to be regarded:

I) the wind power plant consists of ten wind power station units with doubly fed asynchronous generators (WD);

2) the wind power plant consists of ten wind power station units with full size converters (WF);

3) the wind power plant consists of five wind power station units with doubly fed asynchronous generators (Wi to W5 in Figure 16) and of five wind power station units with full size converter (W6 to WI0).

The lengths of the cables are given in Figure 16. The other equipment data shall be seen from Table 10.

The short-circuit currents at the short-circuit locations Fl to F3 shall be calculated without consideration of these cables, to show the influence of the internal wind power plant cables to the short-circuit currents.

In addition, the symmetrical breaking currents at the short-circuit locations Fl to F3 shall be calculated neglecting the internal wind power plant cables.

The following test network with data of electrical equipment and results for the short-circuit currents in accordance with IEC 60909-0 shall offer the possbility to the designers and users of digital programs to check the results found with their program in comparison to the results given. The results given in Table 22 and Table 23 should be reached， to declare a good correspondence between the calculated results and the given results. This is a necessary but not an overall sufficient condition for the program, because even if this test is fulfilled, other procedures within the program may lead to incorrect results. If there are deviations, they should be smaller than +0,02 %.

Line capacitances are not taken into account because the earth fault factor is smaller than 1,4 (5.2 f) of IEC 60909-0:20 16).

KT is calculated with Formula (12a) of IEC 60909-0:2016 because load flow conditions are not known for the test network.

It is anticipated for the calculation of the impedance correction factor Ksi for the power station unit Si that the generator is operated only in the overexcited region (Figure 7 of

IEC 60909-1:2002).

In the case of negative values for the reactances of three-winding transformers in the positive- sequence or the negative-sequence system, these should not be interpreted as capacitances, especially in the case of the calculation with the equivalent frequency method (8.1.2 c) of IEC 60909-0:20 16). The negative sign may occur for the equivalent reactance (see Figure 6b of IEC 60909-0:2016) of the winding which is situated in between the other two windings in the case of a three-winding transformer (see Table 3 of IEC TR 60909-2:2008, for instance no. 6).

When using the 20 Hz or the 24 Hz method respectively to find the factor K in meshed networks, the impedance correction factors KG, Ks and KT shall be used in the form given (IEC 60909-0).

9.2 High-voltage test network 380 kVIllO kV/30 kVIlO kV

9.2.1 Network topology and data

Figure 20 gives the topology of the three-phase AC test network, 50 Hz, with the busbars 1 to 8 and the electrical equipment. The busbars 1 to 8 shall be the short-circuit locations in the case of three-phase short circuits and the busbars 2 to 5 in the case of line-to-earth short circuits. There are three earth ing points in the 110 kV part of the network: transformer T4, power station unit Si (GI + Ti) and feeder Q2. See Table 20 for the overhead line and cable data.IEC TR 60909-4 pdf download.