Environmental Engineering Reference
In-Depth Information
Figure 5.2
Transformer: 132 to 33 kV. (Courtesy of Murray Thomson)
Figure 5.3
One - line diagram
Lastly, and by no means least, a great deal of switchgear is installed as suggested in Figure
1.14. This allows sections of the system to be isolated for operational and maintenance pur-
poses, or on the occurrence of faults.
5.2.1 Single - phase Representation
The Appendix explains in detail the reason why three-phase is exclusively used for the gen-
eration and transmission of electrical power. It is also shown that as long as the three phases
are balanced, calculations can be performed by considering just one of the phases. Thus, it
is common to draw just one phase in circuit diagrams. To achieve this, delta-connected com-
ponents are represented by their equivalent star and a neutral conductor may be drawn in,
even when there is no neutral in reality.
To simplify drawings even further, it is common to omit the neutral return and represent
a three-phase generator supplying a load as in the
one - line diagram
of Figure 5.3. This one-
line shorthand is universally used by power system engineers both to represent schematically
and perform calculations in balanced power systems.
A one-line diagram of a power system is shown in Figure 5.4. The different voltage levels
found in a large power system may be thought of as layers, each one feeding the one below
it by way of transformers.
