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 environmental constraints.

Implementation will be accomplished through the following task development:

1. The Plant Automation Coordinator which provides expert best operating practice for plant start-up and shutdown supervision with optional equipment automation available for critical plant operations.
   
2. The Process Constraint Coordinator to provide the easy incorporation of plant operating constraints, plant life expenditure, environmental and regulatory constraints in to the real-time operating strategy of boiler control. By the dynamic on-line calculation of maximum allowable unit rate of change and maximum and minimum operating limits based on available equipment in service and life expenditure and environmental restrictions, intelligent automatic unit dispatch is readily achievable.
   

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 start-up.

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 as follows:

Group #	Group Title	Number of Steps
1	Boiler Start-up Procedure	24
2	Main Turbine Start-up (prior to Roll on Steam)	11
3	Main Turbine Start-up (rolling on steam)	2
4	Main Turbine Pre Start	11
5	Main Turbine Cold Start Rolling Procedure	21
6	Main Turbine Hot Start Rolling Procedure	9
7	Unit Synchronization	11
	TOTAL	89

For Nelson 4 the operator guidance messages are organized as follows:

Group #	Group Title	Number of Steps
1	Boiler Cooling Water Start-up	24
2	Circulating Water Start-up	10
3	Circulating Water System Fill	8
4	Circulating Water Pump Start	10
5	Main Condensate System Start-up	24
6	Fill Main Boiler - Cond Booster Pump Fill	10
7	Fill Main Boiler Aux BFP Fill	9
8	Fill Main Boiler - Main BFP Fill	24
9	Vent Valves on 8th Elevation	5
10	Purge Furnace	16
11	Establish Air Flow	15
12	Light Off Gas Burners	19
13	Establish Flash Tank Pressure	15
14	MAX 1000 Start-up Guide - Ramping	16
15	Roll and Synchronize Turbine	19
16	Shutdown Steps 1-15 to 250 MW	15
17	Shutdown Steps 16-26 to 170 MW	11
18	Prepare to Start Deramp	21
19	Reserve Shutdown	6
20	Boiler Leak Cool Down	7
21	Boiler Off-line/Tuning Gear Tagout	10
22	Break Vacuum	8
23	Shutdown - Condensate Pumps	6
24	Shutdown - Bearing Cooling Water	6
25	Shutdown - Circulating Water Pumps	7
26	Shutdown - Inservice Status Procedure	2
	- Stator Cooling Water System
	- EHC System
	TOTAL	324

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 position.



Additional optional logic features include: directional inhibits to block an operation, override to achieve a specified status upon command.

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.






The level 1 core logic supports a full range of CRT operator display features within standard customer specified control pop ups including: two pushbuttons for directing device status; two mode select pushbuttons for device auto (remote/manual (local) mode selection; one pushbutton to reset logic in alarm condition to the existing state of the binary device; an optional pushbutton to STOP the device at an intermediate position.

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

		Level 1	Level 2
Quantity	Auxiliaries	Device Control	Group Control
2	FD Fans	2	1
2	Circulating Water Pumps	2	1
1	Main Boiler Feedpump	1	1
1	Start-up Boiler Feedpump	1
2	Condensate Pumps	2	1

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 conditions.

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 change.

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 Description

Constraint Type	Constraint Description
Equipment Life Expenditure	Turbine Metal Temperature Rate of Change
	Boiler Header Temperature Rate of Change
	Boiler Drum Temperature Rate of Change*
Control Transient	Load Demand Error
	Superheat Temperature Error
	Superheat Temperature Approaching Saturation*
	Reheat Temperature Error
	Reheat Temperature Approaching Saturation*
	Throttle Pressure Excessive Error
	Fuel Control Excessive Error
Equipment Limits	Fuel Regulating Equipment at a maximum/minimum limit (function of # burners in service and burner pressure)
Event Constraint	Boiler Water Purity
*Lewis Creek only	Sliding Pressure Mode*

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.

CONCLUSIONS

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.

REFERENCES

1 . R. N. Hubby Automation Strategies for Cyclic Operation, presented at EPRI Conference on Fossil Plant Cycling, Washington DC, December 4-6, 1990.

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, 1988.

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 1/15/92.

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.