## 3.1 General

In general, equipment in power systems are represented by equivalent circuits, which are designed for the individual tasks of power system analysis, e.g., for the calculation of no-load current and the no-load reactive power of a transformer, the no-load equivalent circuit is sufficient. Regarding the calculation of short-circuits, voltage drops and load characteristic a different equivalent circuit is required. The individual components of the equivalent circuits are resistance, inductive and capacitive reactance (reactor and capacitor), voltage source and ideal transformer. Voltage and currents of the individual components and of the equivalent circuit are interlaced by Ohm's law, which is valid for the three-phase system (RYB-system) as well as for the system of symmetrical components (012-system). A detailed deduction of the mathematical methods and equations is not given within the context of this section of the book, but only the final equations are quoted. For further reading, reference is made to [1], [13].

[1]Schlabbach, J.: Electrical power system engineering (Elektroenergieversorgung). 2nd revised edition, VDE-Verlag. Berlin, Offenbach/Germany, 2003. ISBN 3-8007-2662-9.

[13]Balzer, G., Nelles, D., and Tuttas, C.: Short-circuit current calculation acc. VDE 0102 (Kurzschlu stromberechnung nach VDE 0102). VDE-technical reports, Vol. 77. VDE-Verlag, Berlin, Offenbach/Germany, 2001. ISBN 3-8007-2101-5.

## 3.2 Equipment in a.c. systems

### 3.2.1 General

Impedances of equipment are calculated based on name plate data, from manufacturer's data or from geometrical arrangement. For the calculation of impedances of generators, power plants, step-up and step-down transformers, correction factors are necessary. The calculation equations as per Tables 3.1 3.11 are...

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##### Topics of Interest

4.1 Types of short-circuits In three-phase a.c. systems it has to be distinguished between different types of short-circuits (s.-c.), as outlined in Figure 4.1. Figure 4.1: Types of short-circuits...

1.1 Objectives This book deals with the calculation of short-circuit currents in two- and three-phase a.c. systems as well as in d.c. systems, installed as auxiliary installations in power plants and...

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8.1 General Several factors for the calculation of short-circuit (s.-c.) currents have been introduced in previous sections, the origin of which will be explained within this section. Voltage factor...

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