Overview

Embedded generation plant mainly uses conventional electrical machines or power electronic converter circuits. These are described in detail in a large number of excellent text books, e.g. References 1-5. However, compared to stand-alone generators or even large central power station units, there are significant differences in the way that embedded generators are applied and controlled and some aspects of their behaviour assume increased importance due to their position in the power system or the type of prime mover used. In particular, the presence of rotating machines in the distribution network can significantly alter the flow of fault currents and so needs careful attention.

Figure 4.1 shows an embedded generator connected to a radial distribution circuit. The circuit is connected to the transmission system through one or more tap-changing transformers and has loads connected to it at various locations. This arrangement can easily be studied, in as much detail as required (provided data are available), using the computer based methods discussed in Chapter 3. However, for many initial, but only approximate, calculations the network may be represented by a single equivalent impedance connected to an infinite busbar. Section 3.4.2 and eqn. (3.31) showed that, in the per unit system, the magnitude of this impedance is simply the reciprocal of the short-circuit level (without the generator connected), although the X/R ratio of the network must also be known. The terms short-circuit level and fault level are synonymous. The simple representation of Figure 4.1 is particularly useful as the data required...