Environmental Engineering Reference
In-Depth Information
(f ) FACTS
The way PWM converters can be controlled to act as capacitors or inductors was discussed
in Section 4.5.6. FACTS are power electronic converters capable of adjusting the angle and
magnitude of the voltage of a network mode. They are capable therefore of regulating the
active and/or the reactive power fl ow at a mode.
(g) RE Generator Interfaces
In Chapter 4 it was seen that in order to maximize effectiveness or because of absolute neces-
sity the majority of renewable energy generators are interfaced to the grid through a power
conditioning converter. This has the added advantage that if the converter is of the PWM
type it can contribute to the voltage regulation at the PCC.
5.6 Load Flow and Power System Simulation [2, 3]
5.6.1 Uses of Load Flow
Section 5.4 looked at the maths describing an individual overhead line or underground cable.
Mature power systems are likely to have thousands of such lines, all interconnected. The
same basic maths applies to each and every line, but now the equations must be solved
simultaneously. Structured procedures for such calculations are known as load fl ow .
A basic load fl ow calculation provides information about the voltages and currents and
complex power fl ows throughout a network, at a particular point in time, with a given set of
load and generation conditions. Additional information, such as losses or line loadings, can
then be easily calculated.
Load fl ow analysis is an essential tool that provides the following vital information for the
design as well as the operation and control of power systems:
checking whether equipment run within their rated capacity;
checking that voltages throughout the network are kept within acceptable limits;
ensuring that the power system is run as effi ciently as possible;
ensuring that the protection system will act appropriately under fault conditions and that
under likely contingencies the system will remain secure and operational;
assisting in the planning of the expansion of conventional and renewable generation and
the necessary strengthening of the transmission and distribution system to meet future
increases in power demand.
Load fl ow calculations are central to the numerous software packages available for power
system simulation, including PSS/E and DIgSILENT. Most such packages also include many
additional functions, such as the following:
Fault analysis determines the currents that will fl ow in the event of a short circuit. Such
information is critical in the design of switchgear and protection systems.
Unbalanced analysis allows modelling of networks where the three phases are not perfectly
balanced. This is particularly relevant in networks where single-phase loads are
connected.
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