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When Tri-State Generation and Transmission
Association Inc. set out to upgrade the legacy control
system at its 110-megawatt Nucla Generating Station,
the organization solicited bids from several vendors.
After thoroughly evaluating the vendors’ bids and
equipment, Tri-State turned to a trusted and familiar
name – Emerson Process Management Power & Water
Solutions.
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Weighing the Options
Tri-State is a nonprofit,
wholesale power supply cooperative that provides electricity
to 44
member distribution systems serving major parts of Colorado,
Nebraska, New Mexico and Wyoming. The Nucla plant, which
was originally commissioned in 1959 with a capacity of 36
megawatts, expanded to 110 gross megawatts with the installation
in 1987 of the world’s first ACFB (Atmospheric Circulating
Fluidized Bed Combustion) boiler. Emerson’s WDPF distributed
control system monitored and controlled this boiler, as well
as the balance of plant.
A few years ago, the desire for an
enhanced control system combined with some difficulty
in finding certain replacement components spurred Tri-State
to weigh the different migration options that were
available. According to Jerry Saunders, a senior electrical
engineer for Tri-State, the decision to migrate from
the plant’s
WDPF control system and Numa Logic controllers to Ovation,
a state-of-the-art system that utilizes commercially
available (non-proprietary) off-the-shelf hardware,
communications and software, made sense both technologically
and economically.
“The
other vendors demonstrated their equipment for us, but
in the end it boiled down to the fact that we would have
to change 580 I/O modules for about 6,000 I/O points,” said
Saunders.
On the other hand, under the Emerson migration
plan, the Nucla facility would retain the modules for the
approximate 5,000 I/O points associated with the WDPF system;
only the 800 I/O points tied into the plant’s vintage
Numa Logic controllers required new modules and retermination. |
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For Tri-State, the choice was clear. “With
Emerson, we could take advantage of the latest technology
while still maintaining the vast majority of our investment
in I/O, logic and graphics,” said Saunders.
Emerson, which has designed, delivered and has maintained
WDPF systems for more than 20 years, provides customers with
a straightforward migration path. This approach enabled Nucla,
which replaced 15 WDPF controllers with Ovation controllers
and five single-screen operator stations with dual-screen
operator consoles, to realize Ovation’s enhanced functionality
while retaining existing graphics, operator control schemes,
I/O, wiring, terminations and cabinetry, as well as their
investment in system engineering.
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Emerson’s migration path allows
WDPF customers like Tri-State to retain much of their
investment by allowing them to keep existing I/O cards,
field cabling, terminations and cabinets; as well as
their system engineering investment in control logic,
graphics and the database. |
During migration, WDPF engineering tools are replaced by
a fully integrated set of advanced software programs that
create and maintain Ovation control strategies, process graphics,
point records, report generators and system-wide configurations.
For example, the Ovation Control Builder, one of these advanced
software programs, is layered on a commercially available
CAD program that utilizes standard SAMA symbols containing
embedded control algorithms. When building or modifying logic
drawings in the control builder, the control code is automatically
generated and tested and then downloaded to the controller.
The software also allows on-line visual tracking of logic
in operation to quickly spot problems. One of the advantages
of utilizing this method is that the actual control logic
running in the system by definition matches the drawings,
eliminating the configuration management issues of older
systems.
Tri-State migrated their WDPF ladder logic to Ovation
ladder logic due to time and other constraints, according
to Terril Daniels, a technical support specialist for
Tri-State, who added that the ability to gain the advantages
of a more robust control system with minimal re-engineering
was very important. “We could take advantage of
Ovation’s enhanced capabilities – such as
trending and historical data – while maintaining
our investment,” said Daniels. “That was
a boon to us.”
Under Budget, On Schedule
According to
Saunders and Daniels, while the primary migration project
is completed, the plant is continuing to enhance its control
system. For example, last year, Emerson and Tri-State G&T
personnel installed two data links and added a WAVE (Web
Access View Enabler) Server. With the WAVE Server, customers
like Tri-State can remotely view process data through a direct
LAN/WAN connection or via secure Internet access, enabling
key personnel to trend information and troubleshoot plant
control systems from any location. In addition, plans call
for the Nucla station to add another data link that will
tie a PLC running the coal handling system into the Ovation
system. “With Ovation, it is easy to do,” said
Daniels.
According to Daniels, all aspects of the migration project,
which took place in September 2001, went smoothly. “This
is one of the first times I’ve been around an upgrade
where everybody liked it. It turned out really great for
us,” he said.
“The project came in under budget, on schedule and
we all worked well together as a team.”
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