TABLE OF CONTENTS A summary of relevant data of equipment is given in IEC 60909-2:1992. The data are based on a survey carried out by IEC TC 73. In some countries this document does not have the character of a standard.
Impedances of power system feeders, respectively, their initial short-circuit power are difficult to determine as typical values, the structure of the power systems (cable or overhead line system), the voltage levels or the application task, i.e., for rural, urban or industrial power supply can vary in a wide range. Typical ranges of the initial short-circuit power (three-phase short-circuit) are given in Figure 13.1 for a power system with different voltage levels.
Transformers are constructed with defined rated power with respect to their application. In low-voltage and to a certain extent in medium-voltage systems, transformers are build with standard rated power and standard impedance voltage. Transformers in high-voltage systems, sometimes also in medium-voltage systems, have to meet special application conditions, such as the internal standard of the utility with special defined values for rated power, impedance voltage and ohmic losses. It should be noted in this respect that the minimisation of the impedance voltage is limited by the minimal insulation thickness of the windings. Typical values for the impedance voltage of transformers are outlined in Figure 13.2. Figure 13.3 gives data for the...
