Utility
companies have long monitored and controlled electric power generating
operations using computer-based Supervisory Control and Data Acquisition
(SCADA) systems. In an era of deregulation and competition, management
needs more information than ever before, and as quickly as possible,
regarding its own costs, efficiency and the market price of energy.
That need for information is leading to the upgrading and re-engineering
of SCADA systems nationwide with new software and hardware that is more
productive, reliable, and which uses open standards architecture.
The Bath
County Power Station of Virginia Power Company, where MODCOMP recently
completed such an upgrade, provides a good example for study.
Bath
County Pumped Storage Station
The Bath County plant presents unique challenges. While many power
plants are brought on-line and continue to run uninterrupted until
maintenance is required, the Bath County plant is different. It is
a pumped storage hydroelectric plant, designed specifically to help
Virginia Power meet peak demand. Pumped storage is the most economic
method of doing so.
The plant,
located nine miles northeast of Mountain Grove in Bath County, Va.,
has upper and lower reservoirs. Virginia Power pumps water up to the
upper reservoir at night and on weekends; then during the day, it
allows the water to drive generators as it returns to the lower reservoir,
providing 2.1 million kilowatts of peak generating capacity. In effect,
the Bath Power Station is a giant storage battery. So unlike computer
systems in most power generating plants, the Bath County generators
are brought on-line twice a day. That means gathering critical data
for a number of parameters, in real time, for each of six generators.
The older
computer system at the plant was sufficient for monitoring the plant
-- just barely. It was operating at near capacity. It did not allow
the collection and graphic display of data by the Virginia Power's
management team in Richmond. Therefore, the company upgraded the computer
system with MODCOMP's REAL/IX PX operating system, a real-time implementation
of UNIX that runs on Intel-based platforms. The company has more computing
power and greater flexibility to upgrade in the future because the
SCADA system now uses industry-standard hardware and software systems.
Today, the company's servers are running at roughly 40 percent of
capacity; and the data acquisition system is running at just 15-20
percent.
Upgrades
of this sort will become increasingly common as utility companies
strive for a complete understanding of their own power-generation
costs and performance, in real time, to compete more effectively.
Defining
Goals, System Design
Virginia Power began the process of upgrading its SCADA system with
a number of broad goals. Those included:
- Migrating
to standard, open systems with a long useful life
- Maintaining
existing user interfaces whenever possible
- Permitting
future expansion without performance degradation
- Utilizing
the existing I/O infrastructure to contain costs
The new
system runs on two Intel-based host servers, one that is the primary
system and the other a secondary backup and information source. Both
run the same SCADA system software. Operators use the primary system
exclusively; others who need newly acquired data access it through
the secondary server. In case of a hardware failure, plant operators
can fail over to the secondary server. Eight Remote Terminal Units
(RTUs) are connected to the servers. Each of the six generators is
monitored by independent RTUs. One RTU carries common signals for
all six generators and tracks sequence of events with one millisecond
resolution, which is important in the power industry. One RTU carries
common analog signals.
The RTUs
communicate with the host servers over a dual-redundant fiber optic
TCP/IP network. To provide high availability, the network routers
and switches provide automatic network segment failover.
The new
system is far more responsive than its predecessor was. In the past,
the SCADA system scanned operations data every five seconds. The new
system scans every second.
Migrating
to Open Systems
Virginia Power's first goal for the new system was to migrate to standard,
open systems. The SCADA system in place since the 1985 opening of
the plant was based on a proprietary hardware/ software platform.
The new system uses Intel-based computers running the REAL/IX PX operating
system.
This
combination gives Virginia Power's plant longevity. The company's
goal was a system that would last 10-15 years. During that time, disk
drives and other components can be replaced at any time, RAM can be
increased and other upgrades can be made. Individual Intel-based computer
operator workstations can be replaced with new generation hardware
that has faster processors.
The UNIX
operating system platform is compatible with a number of third-party
programs that Virginia Power can integrate into its SCADA or reporting
systems at a later date. The REAL/IX PX operating system enables the
user to acquire and run many "shrink wrapped" applications
that are available for Intel-based UNIX systems.
The REAL/IX
PX operating system combines real-time performance with the benefits
of the UNIX operating system. It features a fully pre-emptive kernel
based on the UNIX System V operating system, symmetrical multiprocessing
and automatic CPU load balancing. The system delivers predictable,
deterministic response rates and fast context switch times, which
are required by mission-critical real-time applications.
Maintaining
User Interfaces, Functionality
Another important requirement was that operator screens display control
data in essentially the same way that operators had viewed that data
for years. The idea was to minimize the impact of the changeover on
daily operations and the need for re-training.
The old
operator display screens were primarily text-based graphics. Re-creating
text-based screens in UNIX is a straightforward matter. But Virginia
Power was also given a doorway to evolve those screens into more meaningful
displays. Now, just a few months after the system's initial use, Virginia
Power's operators are beginning to add more graphic screens with information
presented in a way that's faster and easier for operators to see and
identify. Instead of looking down a tabular list of values, for example,
there are virtual meters that change color and call attention to critical
values. These are display options that were unavailable in the older,
text-based systems.
Existing
applications software functionality was also migrated into the new
SCADA package. The original 10,000-point database, with 6500 digital
inputs and 3500 analog inputs, was imported into the new software.
Utilizing
Existing I/O, Leaving Room to Grow
One of the major challenges for SCADA system upgrades is to make continued
on page 6. Updating SCADA Systems, contnued. the most of existing
resources. In Virginia Power's case, this meant keeping the majority
of the system's previous input/output (I/O) infrastructure. By integrating
the existing MODACS interface over to the new system, we were able
to reduce the cost of the new system by nearly $1.5 million.
With
any system expected to last a decade or more, the owner expects there
to be growth in the number of users, the volume of data that will
be acquired and processed, and more. Already, for example, new data
acquisition points have been added to bring the new total to nearly
14,000 I/O points (from 10,000 previously).
Therefore,
another important feature of the new system is its scalability. The
Virginia Power SCADA system can grow dramatically without substantially
degrading performance. This is true for two reasons. First, there
is excess capacity in the new hardware; host servers are running at
40-50 percent of capacity, and the RTUs operate at 20 percent or less
Ñ and some are just in single digits. So there is plenty of room to
grow on the hardware side and new RTUs can be added as Virginia Power's
requirements change.
Secondly,
the REAL/IX PX operating system ensures that the system will continue
to run in real time. Real-time applications demand that CPU time is
apportioned according to user-defined priorities. The system uses
256 real-time and time-sharing scheduling priorities to control and
allocate system resources. Time-critical processes are ensured immediate
access to the system resources they need.
New
Capabilities
As part of the upgrade, Virginia Power wanted to interface its real-time
control and data acquisition system with a data historian, creating
a historical database for later analysis. The system successfully
integrates OSI's Plant Information (PI) historian, which runs under
Windows NT. The historian can be used to analyze operations data and
generate reports on those analyses.
Another
new capability is remote access for maintenance. System engineers
from MODCOMP can dial into the system, diagnose many problems remotely
and fix them.
That
points out an important element in the evolution of SCADA. In the
past, benchmarks were often based on raw CPU performance --processing
a finite set of information in a set period of time. Today, CPU performance
has increased so far that it has become a secondary issue. So has
reliability; with today's high mean-time-between-failure figures and
fail-over capabilities, people just assume the system will be up at
all times.
So customers
are more concerned with ease of use and maintenance. Remote diagnosis,
software fixes, and upgrades are available almost instantaneously,
24-hours a day.
Where
are SCADA systems headed in the future? First, to more standard protocols.
There are hundreds of protocols used in the utility industries today.
As utilities begin working together in a free-market environment,
we can expect a shakeout.
Secondly,
we can expect to see wide scale integration of SCADA and Geographic
Information Systems (GIS). With GIS, ScadaBase users can have maps
on screen showing generation stations and transmission lines, integrated
with real-time data to pinpoint a disruption of service. It will make
power companies more productive in determining where faults are located
and in dispatching people to effect repair.
That
is just one more example of the ways in which computer systems today
are becoming the critical link in power supply and delivery.
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