Electrical Power System Essentials

1.9 POWER SYSTEM STRUCTURE

The graphical layout of the three-phase power system is often displayed as a single-line equivalent or as a one-line diagram. Such a one-line diagram gives only an overview of the topology of the power system. The components are identified by means of standardized symbols and not by models built up from lumped circuit elements (as is the case with the equivalent line-to-neutral diagram as introduced in Section 1.5 (Equivalent Line-to-neutral Diagrams)). The symbols used in such a one-line diagram are shown in the list of symbols. Sometimes lumped circuit elements appear in a ‘one-line diagram’. An example of such a ‘one-line diagram’ is Figure 5.28 (Section 5.5.3 (Unified Power-Flow Controller (UPFC))): it shows a device used in the power system for sophisticated control actions. The lumped elements in the diagram show what is actually inside the device.

Figure 1.37 One-line diagram of a section of a power system [15].

A one-line diagram which schematically displays part of the structure of a power system is shown in Figure 1.37. The one-line diagram shows a clear vertical structure: a relatively small number of large power stations supply the transmission network (380 kVand 150 kV). Besides some large industrial consumers that are connected to the higher voltage levels (150 kV), most of the power is transported and distributed to the consumption centers ...