IEC 60909 SHORT CIRCUIT CALCULATION PDF

To illustrate its application, the methodology is applied to a study medium voltage network with a variety of distributed generation resources. Distributed generation resources are typically connected to the distribution network, at the low or medium voltage level. Therefore they contribute to the total fault level of the distribution grid. Hence, the basic requirement for permitting the interconnection of distributed generation resources is to ensure that the resulting fault level remains below the network design value. The short-circuit currents is considered as the sum of an a. The Standard distinguishes between near-to-generation and far-from-generation short circuits.

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To illustrate its application, the methodology is applied to a study medium voltage network with a variety of distributed generation resources. Distributed generation resources are typically connected to the distribution network, at the low or medium voltage level.

Therefore they contribute to the total fault level of the distribution grid. Hence, the basic requirement for permitting the interconnection of distributed generation resources is to ensure that the resulting fault level remains below the network design value. The short-circuit currents is considered as the sum of an a. The Standard distinguishes between near-to-generation and far-from-generation short circuits. The methodology includes of a.

In the present, two numerical methods for short-circuit calculations are used: superposition method and equivalent voltage source method. Superposition method gives the short-circuit current only in relation to one assumed amount of the load. Hence, it need not lead to maximum short-circuit current in the system.

For removing this lack, it was developed the equivalent voltage source method [2]. This source is defined as the voltage of an ideal source applied at the short-circuit location in the positive sequence system, whereas all other sources are ignored. All network components are replaced by their internal impedances see Fig.

Equivalent voltage source method In the calculation of the maximum short-circuit currents, the voltage factor c may be assumed equal to cmax, for any voltage levels see Tab. According to Fig.

If any distributed generation unit units is in the grid included, the resulting fault level is the sum of the maximum fault currents due to: the upstream grid, the various types of generators, the large motors connected to the distribution network. The calculation of contribution of the distribution generation units is not included in the IEC Only induction motors are dealt with, whereas the parameter values of synchronous generators provided in [4] are applicable to units of very large size [3].

X d , " X d - subtransient reactance of synchronous machine, K G - correction factor for generators connected directly to the grid.

The value of t depended on the protection and fault. It is needed only for breaking and thermal current calculations. Special case of generator used for variable speed wind turbines is doubly-fed induction generator DFIG. X G for the generator impedance [3]. Four distributed generation stations with total power cca 17 MW are connected to the medium voltage substation.

They are three wind farms with six identical wind turbines and one small hydroelectric plant - SHP with three identical turbines. The data about case study network are given in Table 2. Case study Tab.

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Short Circuit Impedance Calculation | IEC60909

In accordance with the recommendations of this standard, the symmetrical component method is used. This method is the most accurate, then leading to an optimized sizing compared to the other conservative simplified methods. The short-circuit currents are recalculated automatically every time a change likely to alter them is made on the one-line diagram. The first fault current is calculated to determine the touch voltage. The short-circuit currents are used in the following functions: Short-circuit protection: the tripping or melting threshold of the protection is determined in relation to the minimum short-circuit current through this protection, i. Breaking capacity: the aim is to verify that protection devices are able to cut the short-circuit current likely to appear in the area of influence of the protection without deteriorating symetrical short-circuit current within the meaning of the standard IEC Making capacity: the aim is to verify that the breaking devices are able to close on the peak short-circuit current likely to occur when the device closes without deteriorating.

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Calculation of Short-circuit IEC 60909

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