“IEC” short-circuit calculation

This paper analyzes how to calculate the three-phase and single-phase short-circuit currents present in type TT and TN power networks, and the three-phase and two-phase currents in type IT power networks, for low voltage electrical plants with a radial type of layout. The following are considered in the calculation: the transformer and generator contribution (the same or different); the motor contribution; and the impedance of the medium voltage network, cables, busbars and other components known to the designer. With regard to the transformer and network contribution, the calculation takes into account the recommendations of the IEC909[C], VDE 0102, and Teil 1[E] UTE NFC 15-100 [O]/C 15-105 [P] Standards and with regard to the motor and generator contribution, the indications in the IEC363[A] Standards and in R. Roeper´s [L] text. The main reason for this paper is to give, step by step, a complete method for the calculation of critical short circuit situations, especially if the power source and load are working within electrical limits