Environmental Engineering Reference
In-Depth Information
400 kV
~
~~~~~~~~~~~
Generators
Transformers
132 kV
~
~
33 kV
11 kV
Loads
400/230 V
Figure 5.4
One - line diagram showing 'voltage layers' in a large power system
5.2.2 Transmission and Distribution Systems
It is usual to refer to the higher voltage levels as the
transmission system
and the lower voltage
levels as the
distribution system
, but the exact usage varies from country to country. In
England and Wales, the 400 kV (plus some sections at 275 kV) is regarded as the transmission
system, while the 132 kV and all layers below are the distribution system. In Scotland, many
sections of 132 kV are regarded as transmission.
The term
national grid
usually means the transmission network. However, the term
grid
is often used loosely to describe the transmission and distribution networks. In
particular,
grid - connected
means connected to any part of the network, but is used
increasingly to mean small generators connected directly to the low voltage distribution
system.
Nearly all generation that is currently installed is connected to the transmission system and
is called
centralized generation
. Thus, traditionally, power always fl ows to the consumers
