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Today's focus on the need for improvement of controls and monitoring for cyclic operation stems from a power industry requirement to assume an ever larger share of the system load change requirements. The source of this need is the significant growth of power sources that provide no assistance in load regulation such as cogenerators and independent power producers.
Management of today's fossil fired power plants must
recognize two broader constraints in addition to simply meeting the
load demand: first - the need for reliable operation with minimum expenditure
of equipment life; and second - the need to conform to environmental
regulations including NOx and other environmental emission limits.
The authors will discuss two approaches currently being
implemented at Entergy's Lewis Creek and Nelson Stations to enable power
plants to provide the best performance achievable with equipment in
service with minimum expenditure of equipment life within the requisite
Implementation will be accomplished through the following
Operating experience with these new strategies will
be shared as available.
INTRODUCTION AND BACKGROUND
The Implementation of Automation Design Concepts is
part of a Joint development program between the Electric Power Research
Institute (EPRI) and Leeds & Northrup Company. EPRI, in order to
commercialize the results of advanced technology in the utility industry
has sought out a number of Joint development projects with major suppliers
to the utility industry under tailored collaboration contracts both
with the utility and the supplier. It is the result of such a tailored
collaboration contract that will be shared with you today.
In the conclusion to the paper Automation Strategies
for Cyclic Operation (reference 1) the author concludes "while
advanced boiler control strategies have provided responsive unit performance
over a wide range limited only by the auxiliaries being controlled,
system extensions to extend the concept of "unit coordination"
are essential to support cycling operation." Additionally the concept
of "extended coordination" is needed to provide the best performance
available with equipment in service with minimum expenditure of equipment
life within the requisite environmental constraints.
A further important consideration has come forward
as these automation design concepts have been implemented with a number
of utility users, that is that the knowledge base for implementing advanced
automation strategies lies with the utility user's plant such as operating
procedures charts and plant operating practice. So an ideal advanced
automation strategy would be one that was very flexible, that could
easily accommodate and encode current plant operating practice and then
could be easily expanded by appropriate utility engineering/plant personnel
as future automation needs are developed. This need is even more
significant today as utilities look for ways to reduce manpower in order
to compete as a supplier of generation capacity in a competitive market.
TASK 1 PLANT AUTOMATION COORDINATOR
Based on these needs, the Plant Automation Coordinator
has been designed to accommodate a full range of automation strategies
from the simple automation of a single auxiliary device to a single
pushbutton start of an entire plant. This flexibility is particularly
important since the level of plant instrumentation and system input/outputs
for the installed distributed control system is already determined at
ENTERGY's Nelson 4 and Lewis Creek 1 and 2 Stations. A second consideration
is to be able to apply automation strategies to assist with the operation
of a limited number of auxiliaries which may be causing operational
problems in the plant.
With this range of requirements for plant start-up
and shutdown in mind three implementation levels are provided for the
plant automation coordinator:
Level 1 Algorithm for control of a single device (device core logic for motor or valve)
Level 2 Algorithm for control of a group of devices associated with a major auxiliary (FD, ID Fan, BF Pump etc.)
Level 3 Algorithm to implement operator guidance messages
to start-up, run and shutdown the plant
Level 1 and level 2 algorithms are resident in the
distributed control systems (DCS) distributed processing units (DPU)
and are accomplished by modifying the existing DPU control strategy
recipe configuration. Level 3 is implemented in the applications processor
which is part of the information management function of the workstation
for the DCS.
Beginning with the plant supervisory level 3, as shown
in Figures 1-4, the operator will follow event level operator guidance
messages which are simply the required actions to be accomplished from
the plant startup/shutdown procedures with checkpoints to confirm that
actions have been completed. Event level operator guidance messages
are organized into thirty groups of twenty-four messages each, to provide
flexible access to the relevant plant operating procedure.
(FIGURE 1, FIGURE 2, FIGURE 3, AND FIGURE 4 NOT SHOWN)
Status of actions can be shown as follows (please note
that color selection can be made in accordance with user color conventions):
Red Actions to be completed
Blue - Completed actions
Yellow - Overrides taken to complete actions following physical verification of acceptable plant status/conditions
Green - Future activities to be completed beyond those currently being processed by the
operator which are shown in red
Explanatory operator guidance HELP messages including
any special advice or cautions as to how to proceed to complete a given
step can be provided as a HELP pop up on the bottom of the CRT screen,
and are available by depressing the HELP key. These HELP messages are
simply for operator guidance and do not replace any of the normal operator
response to alarm activity. Completion of each event action is logged
in the DCS event log, to provide a complete time based record of the
In Figure 1 the event being checked is the status of
the turbine oil system. The help message of Figure 2 includes details
of what is to be checked. Similarly in Figure 3 the event is the test
of the ac hydraulic coupling oil pump. The Figure 4 help explains the
details of this test.
Two operating modes are available from level 3: (1)
a "monitor" or "supervisory" mode where all start/stop
actions are completed manually by the operator in accordance with the
plant procedures, (2) a "control" or "automatic"
mode where required actions are implemented automatically. Provision
for monitor mode/control mode is individually selectable for each step
in the start-up/shutdown procedure.
The ability to override a specified step will allow
the operator to continue with the start-up in the event of a malfunction
of the associated interlocking circuitry. AU override actions will
be logged in the DCS event log.
At Lewis Creek the operator guidance messages are organized
For Nelson 4 the operator guidance messages are organized
Supporting the level 3 operator, guidance messages
will be level 2 or level 1 algorithms as shown in Figures 5 and 6 within
the distributed processing unit, which can be triggered from the level
3 program when the associated sequence steps required to start a major
auxiliary. The current status and progress to completion for the level
2 algorithm is shown on a "pop up" display that can be accessed
from the associated system overview display - airflow/furnace pressure;
feedwater; etc. Similar to level 3, each of the sequence steps can be
placed on "automatic" or "supervisory" mode at the
discretion of the operator. Message background colors (similar to level
3) for each of the steps to be completed by the level 2 sequence are
used to show the actions.
(FIGURE 5 NOT SHOWN)
Level 1 algorithms within the distributed processing
unit are configured to start/stop, open/close-shut any device in the
plant. When on "control" or "automatic" mode, level
1 algorithms can be triggered from level 2 or level 3 programs as appropriate.
The current operating status/condition of the device is shown on a "pop
up" display that can be accessed from any sequence control display
as shown in Figure 6.
(FIGURE 6 NOT SHOWN)
The heart of the level 1 algorithm is the device core
logic subroutine as shown in Figure 7 which is used to start/stop, open/close-shut
start/trip, insert/retract any plant device. This standard logic template
which is a custom algorithm includes the common logic features for any
plant binary device. It also includes user configurable options such
as momentary or maintained start/stop etc., commands or stop an intermediate
Standard core logic features include: lockout capability;
device logic fail alarm in the event of not achieving command status
within a configured time, a change in status without command, a conflict
in status feedback, or power failure without lockout; reset logic to
the existing state of the binary device (part of alarm acknowledge);
auto (remote) mode which allows the device to be operated from higher
level logic; power fail to block a start/open. etc., operation.
In Figure 7 only abbreviated application logic is shown.
More typical examples of application logic and customized logic to specific
device requirements is easily accomplished by the addition of graphically
configured application logic, this logic can be easily added to the
level 1 device core logic as shown in Figures 8 and 9. The graphically
configured custom logic supports a full range of troubleshooting and
self diagnostic ladder logic features such as power flow indication
through and/or gates, timers, set reset functions, input/output status
forcing functions. Alternately standard nongraphical custom logic is
also available for customization on if desired. With these standard
flexible tools, users of the Plant Automation Coordinator can
easily expand and evolve their plant logic systems as may be dictated
by future needs.
Full device status reporting for CRT display pop ups
is available from the level 1 core logic to show: device mode (auto
(remote)/manual (local), lockout); device auto mode inhibit; the status
of the device based on field inputs; the status of outputs commanded
by the operating logic; the status of the device operating logic (lockout,
reset, (directional) in travel, (directional) inhibit or override);
or device power failure - thus the operator will be fully informed of
the exact status of the binary device in question as well as what is
preventing the attainment of the desired status.
Within the "pop up" windows, specific displays can be developed in accordance with the user's graphic
standards and conventions.
The initial implementation of the Task 1 Plant Automation
Coordinator at Nelson 4 and Lewis Creek Stations. shall include
the following Level 1 and Level 2 Automation.
Level 1 Level 2
TASK 2 PROCESS CONSTRAINT COORDINATOR
This algorithm provides for the application of multiple
constraints to set the maximum/minimum generating limits on a plant
as well as the maximum allowable rate (increase or decrease) of load
change that can be accommodated with the current equipment in service.
The sources of constraint conditions include:
- Equipment Life expenditure constraints
- Control System transient constraints
- Equipment Limitation constraints
- Error constraints
Significant advances have been made in the ability
to analyze and diagnose the well being of a power plant on-line as has
been demonstrated at EPRI's maintenance and diagnostic center at Philadelphia
Electric's Eddystone Power Station (Reference 4). The Process Constraint
Coordinator now allows the orderly introduction of constraints from
maintenance and diagnostic programs on unit operations as appropriate
to support best unit availability with minimum expenditure of equipment
life (see reference 3).
Beginning with the unit master station (UMS) display
as shown in Figure 10 which will normally be used to operate the unit,
existence of a constraint condition will be shown by changing the background
color of maximum rate of change setter. By accessing a "pop up"
display from the UMS rate of change setter the major area of the constraining
conditions is shown on the Process Constraint Coordinator graphic (Figure
11). Depending on the number of sources of constraints further access
to detail displays may be required to show the exact source of the limiting
Constraint variables can be: direct process values;
process rate of change values, process value deviation from setpoints
or demands; process deviations from other process values.
The constraint function establishes the allowable unit
rate of chance in each direction as a function of the constraint variable.
A constraint is active when its allowable unit rate of change is less
than that which is set by the operator. The process constraint coordinator
limits the allowable unit
rate of change to whichever constraint calls for the lowest rate of
To fully inform the operator of constraining functions
affecting the ability to change load, a bar chart display is provided
for each constraining function (event limit display functions are noted
in brackets "()" since there is no constraining variable).
Display information includes the constraint variable:
long title; value (constraint time remaining); high/low alarm limits
(not applicable); point alarm condition; the allowable rate of change
for each direction and their relationship to the operator set unit rate
of change; the constraint function point alarm condition when the constraint
is active; and the constraint function point auto/manual status with
hot spots for operator selection.
The constraint coordinator display thus shows the allowable
limit, and the auto/manual status. The operator can then make an informed
decision about the operating constraint consistent with achieving best
unit availability with minimum expenditure of equipment life. Trend
for the limiting stress condition including tag and variable identification
may optionally be provided.
(FIGURE 10 AND FIGURE 11 NOT SHOWN)
The initial implementation of the Task 2 Process Constraint Coordinator at Nelson 4 and Lewis Creek
Stations will include the following constraints:
Constraint Type Constraint
A major benefit associated with the use of the Process
Constraint Coordinator is the ability to calculate online how far a
unit can go at any moment in time and how fast it can get there. Use
of the Process Constraint Coordinator in this way supports the possibility
of intelligent unit dispatch since the real unit performance parameters
are applied to the dispatch functions.
The application of automation design concepts presented
today is scheduled for completion within the next 6 months at ENTERGY's
Nelson 4 and Lewis Creek Stations. Active discussions are proceeding
with ENTERGY to establish the technical details of the scope to be implemented
at each plant. The standardized approaches to plant automation and plant/process
coordination resulting from these two Joint development tasks will be
a major step forward in providing more responsive and more responsive
individual boiler turbine units for the management of system load. 'Me
Authors look forward to reporting upon the results achieved at a future
technical conference including the cost benefits attained and the resultant
return on investment.
1 . R. N. Hubby Automation Strategies for Cyclic Operation, presented
at EPRI Conference on Fossil Plant Cycling, Washington DC, December
2. R. N. Hubby Performance Monitoring for Economic
Dispatch, EPRI Conference on Heat Rate Improvement, Knoxville, TN,
September 26-28, 1989.
3. Richard W. Radtke and Conrad Colson, Northern States
Power Co., Coordination of Unit Equipment Capabilities Into Load
Management Systems, Instrumentation in the Power Industry Volume
31, presented at the ISA Power Symposium, St. Petersburg, FL, May 23-25,
4. W. J. Leonard, Philadelphia Electric Co., Improved
Performance from the Eddystone Unit No. 1 and No. 2, Instrumentation
in the Power Industry Volume 31, presented at the ISA Power Symposium
Ste. Petersburg, FL, May 23-25, 1988.
5. R. N. Hubby Draft
Functional Specification EPRI RP2710-24 Task 1-4, Revision date
6. R. N. Hubby Advances in the Design and Implementation
of Automation Design Concepts (Task 1 and 2) presented at Israel
Section of ISA Technical Conference, Herzilia Israel January 23, 1992.
7. Joseph M. Weiss EPRI, Richard J. Colsher EPRI, and
James J. Hlebik L&N Interconnectivity of Diagnostic Technologies
at the EPRI M&D Center at Eddystone, presented at the Israel
Section of ISA Conference, Tel Aviv, Israel, January 26-28, 1993.
8. Gary A. Cohee ENTERGY and Dave Broske EPRI Implementation of Automation Design Concepts at Entergy's Lewis Creek Units 1 and 2 and Nelson Unit 4, presented at the EPRI Fossil Plant Cycling Conference, New Orleans, Louisiana, September 14-16, 1994.