Hardware and Functional Development of Protection Devices and Systems - Digital Signal Processing in Power System Protection and Control - page 25

future). Complete protection of a power system component can now be provided
by only a few integrated relays (e.g. 3 relays, each with about 15 protection
functions, needed for protection of a larger generating unit).
Most of the present-day relays are combined protection and control units. The
protection devices provide control of many circuit breakers, function of key-
operated switching authority, feeder control diagram, status indication of feeder
devices at graphic display, measured-value acquisition, signal and command
indications, P, Q, cos u and meter-reading calculation, measured-value recording,
event logging, switchgear statistics, switchgear interlocking, etc.
There exist a clear tendency towards:

• Substation Integration—integration of protection, control and data acquisition
functions into a minimal number of platforms to reduce capital costs, reduce
panel and control room space and eliminate redundant equipment and databases.
• Substation Automation—deployment of substation and feeder operating func-
tions and applications ranging from SCADA and alarm processing to integrated
volt/var control in order to optimize the management of capital assets and
enhance operation and maintenance efficiencies with minimal human

intervention.

One can observe a process of converting the substation structure of traditional
protection and substation control being a conglomeration of often totally different
devices (relays, meters, switchboards and RTUs), constituting a centralized solu-
tion with extensive parallel wiring, control with mimic display, pushbuttons,
position indicators, interposing relays, local/remote switch, into a modern coor-
dinated protection and substation control system characterized by:

• decentralized protection and control structure,
• a few multifunctional, intelligent devices of uniform design,
• a few serial links used instead of extensive parallel wiring,
• control of the substation takes place with menu-guided procedures at a central
Visual Display Unit workplace.

Today's trends in substation automation technology is related to substation
(local) control as well as remote control. Modern integrated protection and control
substations apply a lot of Intelligent Electronic Devices (IEDs) that can build an
open communication systems, operated centrally with a PC, with communication
to higher level control centre [ 9 ].
In wider sense the structure of power system control is a hierarchical structure
with vertical connections, depicted schematically in Fig. 3.13 . Modern protection
and control systems within substations offer also horizontal links, utilizing the
common data bus for extensive data exchange between feeder/object level devices
(Fig. 3.14 ).
The substation IEDs are either LAN enabled or are connected to the data bus
through the Network Interface Module devices. A lot of information is stored in
the Data Concentrator. The substation data can be remotely accessed from outside,
time referenced (GPS) and used in SCADA applications. The operational and