Environmental Engineering Reference
In-Depth Information
33 kV
Primary
substation
11 kV
Distribution
transformer
PCC
400 V
Embedded
Generator
Figure 6.1
Example embedded generator
tion network. An example of an embedded generator in a distribution network is shown in
Figure 6.1 .
Distributed generation alters the power fl ows in distribution networks and breaks the tra-
ditional one - way power fl ow from the high to the low voltage layers of the power system.
In some circumstances, a distributed generator can be accommodated into a distribution
network without diffi culty, but occasionally it can cause a variety of problems. This chapter
examines these issues.
6.1.2 Point of Common Coupling ( PCC )
A basic requirement in connecting any generator to a power system is that it must not
adversely affect the quality of electricity supplied to other customers on the network. With
this in mind, it is useful to identify again the
point of common coupling
(PCC).
Offi cial defi nitions vary, but in simple terms the PCC is the point where the generator is
connected to the public network as shown in Figure 6.1. In other words, the PCC is the point
on the network, nearest to the generator, at which other customers are, or could be, connected.
Thus, the exact location of the PCC can depend on who owns the line between the generator
and the rest of the network. The importance of the PCC is that it is the point on the public
network at which the generator will cause most disturbance.
6.1.3 Connection Voltage
The distribution system in the UK includes 400 V, 11 kV, 33 kV and 132 kV; other countries
have similar voltage levels. As mentioned in Section 5.7.4, the fault level at the point of
connection which is a measure of network strength, is an important design parameter, not
only for predicting currents under fault conditions, but also for predicting performance under
normal operating conditions and in particular, voltage rise.
The fault level at the PCC is very important when considering connecting a generator
because it largely determines the effect that the generator will have on the network. A low
fault level implies a high network source impedance, and a relatively large change in voltage
