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28 Electrical power systems ± an overview

Fig. 1.21 Real-time environment.

The main power systems software used for the real-time control of the network is
(Wood and Wollenberg, 1984):
. state estimation
. security analysis
. optimal power flows.
These applications provide the real-time means of controlling and operating power
systems securely. In order to achieve such an objective they execute sequentially.
Firstly, they validate the condition of the power system using the state estimator and
then they develop control actions, which may be based on economic considerations
while avoiding actual or potential security violations.
Figure 1.21 shows the real-time environment where the supervisory control and
data acquisition (SCADA) and the active and reactive controls interact with the real-
time application programmes.

1.6.2 Distribution networks
Most distribution networks do not have real-time control owing to its expense and
specialized nature, but SCADA systems are used to gather load data information.
Data is a valuable resource that allows better planning and, in general, better manage-
ment of the distribution network (Go È nen, 1986). The sources of data typically found
in UK distribution systems are illustrated in Figure 1.22. These range from half
hourly telemetered measurements of voltage, current and power flow at the grid
supply point down to the pole mounted transformer supplying residential loads,
where the only information available is the transformer rating. Most distribution
substations have the instrumentation needed to measure and store current informa-
tion every half hour, and some of them also have provision to measure and store
voltage information. Large industrial customers may have SCADA systems of their