Power system operation and control.pptx.

POWER SYSTEM CONTROL
Lect: 36
Topic: Control system supervision
2nd
Term, Final Year, B.E Electrical
Engineering

Control system supervision
In order to facilitate a smooth operation of the control system,
monitoring and reconfiguration functions are integrated into
and performed by the control system itself.
The monitoring is done on all levels of the system
configuration including the software.
The results of the monitoring are collected in the central
system where they are presented to the operator by means of
the ordinary man-machine equipment.

Control system supervision
The monitoring covers start and restart of the system on all
levels and monitoring of hardware units and communication
channels, failover for the redundant parts of the configuration,
monitoring of software errors, aborts, stall alarms etc.
Validity checks are performed on stored data and on back-up
storage in a redundant configuration.

Start and restart
The functions for start and restart are used for example when
maintenance or repair of a computer or a unit has been done.
When faults have occurred which result in a failover the
restarting functions are activated.
Start-up and restarting routines are implemented both manually
and automatically. A detailed feature is that the
starting/restarting is given an event in the system's database.
The start-up routine normally also provides starting the software
in different modes, e.g. only operating system, start with
different types of database back-up copies and restart of RTUs by
down-line loading of software.

Monitoring of hardware and communication
The automatic on-line monitoring of hardware units and
communication is integrated in the real-time operation.
Diagnostic facilities are often provided which allow further
detailed checking, sometimes on-line and sometimes off-line to
the real-time operation.
The automatic on-line monitoring is normally extensive and
continuous for all vital units of the control system.

Monitoring of hardware and communication
The monitoring objective is to detect faults implying a functional
degradation of the system and, if possible, to point out the type of
fault.
IN SERVICE/OUT OF SERVICE which applies when the operator
requests how the unit shall be used.
OPERABLE/INOPERABLE where the inoperable state defines a unit
with a permanent fault set by the monitoring
DISTURBED OPERATIONS applies to data communication channels
when the number of erroneous telegrams have exceeded a limit
value

Software and data checking
Software functions are monitored in different ways. Principally,
functions exist which detect and/or prohibit software aborts
and locking.
Monitoring for program aborts is done by the operating system
itself which aborts the execution of a program, if a non-
authorized operation is requested.
Data errors are also monitored

System maintenance
The system maintenance in general involves three tools which
are now integrated into the control systems:
Diagnostic test facilities for hardware, software and database
checking
Database, generation functions for the data, the displays and
the reports
Software development including net only programming, linking
etc. but also routines for test and integration into the system

Database maintenance
The database management system normally includes programs
for generation and maintenance of the database, its structure
and content.
This means that, e.g., a description of the power system is
specified by the utility. The data are normally read by database
generation programs and translated, to items which are stored
into the database.
Changes in the database can usually also be performed by an
operator as a dialog at his console. The formats of all display
pages and their organization are included in the database.

In modern control systems database maintenance can be
performed on-line, i.e. together and simultaneously with the
supervision of the power process (this implies a dual concept).
It is of utmost importance that this does not interfere in any
way with the supervisory functions.
Special emphasis must therefore be put on the testing facilities
so that all changes can be thoroughly tested before they are
entered into the real-time system.

lf the real-time database is generated off-line or if a study
database is generated on-line there are no inconsistency
problems. lf, however, the real-time database is generated on-line
there are several possible problems especially in a dual computer
environment.
In dual computer systems, database generation is usually
performed in the back-up computer. The problems arise in
conflicts between generation programs and real-time updating of
the back-up computer's database.

Another problem when generating databases in real-time is that
the operator must be able to test the generation and to
disapprove if the new database is incorrect. When disapproving,
the old database must be reinstalled.
One way of achieving this is to use the failover facility in a dual
computer system. when the generation is finished in the back-up
computer, a manual failover is requested.
The new database will now reside in the primary computer. If the
logging to the back-up of all regenerated files is stopped in this
testing phase, the old database, now in the back-up computer, will
not be destroyed

lf the operator finds that the generation is satisfactory he can
demand synchronization of the generated files from primary to
back-up and the old database will be destroyed.
Logging to back-up can now be resumed for all files. lf, on the
other hand, the generation is in any way erroneous a new
failover is initiated and synchronizing is performed.
The old database will in this case overwrite the new database
and generation can be restarted from the beginning.

Program development tools
A computerized control system for network dispatch and
control typically contains hundreds of programs, subroutines
and functions, all in different forms such as source code, object
code, load format etc.
The programs can be written in languages such as Fortran,
Pascal and Assembler, in one language or using a couple or all
these languages within the same software system.
In order to maintain existing programs and to develop new
ones, facilities must be provided to handle this effectively.

Development
All software development is normally carried out using the
back-up computer in a dual computer system. Testing of the
changed programs is also performed in the back-up.
Any errors made that were not discovered during compilation
or assembly can then be detected without influencing the
primary computer and thereby the control system functions.
Extensive tests can be performed on the new program since
the whole database is updated and available.

Power system operation and control.pptx.

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