From Short-Circuit Currents

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...

Products & Services
Telecom Transformers
Telecom transformers are used in applications which require high bandwidths and fast switching speeds. They isolate the signal between primary and secondary grounds. This product area includes DSL, xDSL, T1, E1, ISDN, LAN, WAN, Ethernet, ATM and modem transformers.
Current Sense Transformers
Current sense transformers are used to detect and measure current. There are two basic types of products: switch-mode transformers for power conversion applications, and precision-measurement transformers for instrumentation applications.
Gate Drive Transformers
Gate drive transformers are used to modify the voltage level to a gate. They also provide impedance matching and voltage isolation.
Switch Mode Transformers
Switch mode transformers (switching transformers) are used mainly in switching power supplies and DC-DC converters. They provide a storage element for transferring energy from input to output in discrete packets as required in switching power supplies, regulators and converters.
Pulse Transformers
Pulse transformers interface a pulse forming network (PFN) and a load. They match the impedance of the load to the PFN in order to maximize power-transfer efficiency.

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...

9.1 General The calculation of short-circuit currents in d.c. auxiliary installations, e.g., in power plants and substations is dealt with in IEC 61660-1. Contrary to the approach for the calculation...

5.4 Power system with isolated neutral The operation of power systems with isolated neutrals is applicable to systems with nominal voltages up to 60 kV, however the main application is seen in power...

5.6 Handling of neutrals on HV-side and LV-side of transformers Special attention must be placed while selecting the type of neutral handling on HV-side and LV-side of transformers. The neutral...