Environmental Engineering Reference
In-Depth Information
down through the distribution system. Traditionally, distribution systems are designed with
this in mind.
5.2.3 Example Networks
The transmission system shown in Figure 5.5 covers the length and breadth of the UK main-
land. It is a single AC power system and therefore has the same frequency throughout. There
is a similar, but smaller, transmission system that covers Ireland, including Northern Ireland.
It also operates at 50 Hz nominal, but the frequency is not tied to the UK mainland system.
There is a high voltage DC (HVDC) link from Scotland to Northern Ireland which allows
power to be transferred in either direction, but does not require that the two systems are run
in synchronism. There is a similar, but higher capacity, HVDC link between England and
France. France is interconnected with its neighbouring countries so effectively there is a
continuous connection between the most northern tip of Scotland and the most southern tip
of Italy.
Most major European countries generate electricity approximately equal on average to their
national demand. Nonetheless, interconnections with neighbouring countries are very valu-
able for effi cient operation. Of particular note is Denmark, where the impressive penetration
of wind power is facilitated by such interconnections.
Returning to the British Isles, many of the islands around the coast are now connected by
under-sea cables and enjoy electricity with a cost and reliability similar to that on the main-
land. More remote islands have standalone systems, usually with a heavy dependence on
diesel fuel.
Figure 5.6 shows in greater magnifi cation the north Wales network that includes only the
upper voltage layers. The 400 kV transmission network matches (roughly) that shown in
Figure 5.5. Transformers transfer power from the 400 kV to the 132 kV network which in
turn supplies the major towns. Further transformer substations feed power down to the 33 kV
network, which takes power to the smaller towns. Figure 5.7 shows the much denser 11 kV
network layer which takes power to villages, hamlets and even individual farms. Finally, the
even denser 400/230 V network (not illustrated) distributes power to individual properties, as
shown schematically in Figure 1.12 .
Further information regarding the UK power system can be found in Reference [1].
5.3 Voltage Control
Consumer loads comprise mainly heating and lighting elements, motors, electronic equipment
providing audiovideo services, computers and controllers, battery charging facilities for por-
table equipment and fi nally electrochemical services mostly for industrial applications. All
these 'loads' are designed to provide their service from a nominally fi xed voltage supply.
Utilities are therefore obliged by law to provide electricity at consumer terminals at a voltage
that does not deviate from the nominal value by more than a few percent with a maximum
of
10% not being uncommon. For this to be achieved at the extremities of the distribution
network the voltage of all nodes moving up through the layers of increasing voltage in the
distribution and transmission system should be kept close to their nominal value. As the
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