Lifecycle planning for your DCSBy Mitch Cochran, Process Control Solutions LLC

The advent of the distributed con-trol system (DCS) in the 1980s brought powerplant control into the digital age, combined the

formerly separate functions of control and data acquisition, and enabled process data to be integrated with enterprise-wide business-manage-ment data. In the 1990s, DCS suppli-ers further enhanced their systems, moving away from proprietary hard-ware and software, and toward more inter-operable, standards-based networks. Net result: Today’s DCS is a reliable, user-friendly product that dominates the controls sector of the electric-power industry.

But all products, no mat-ter how dominant, have a finite lifecycle. This is particularly true for micro-processor-based products. Owner/operators of DCSs, therefore, eventually must address such lifecycle plan-ning problems as lack of manufacturer support, shortage of spare parts, and processor capacity lim-itations. Lifecycle planning also involves evaluation of budgetary constraints as well as corporate strategies regarding future expan-sion.

This article discusses lifecycle planning for one of the most popular DCSs in North America—the WDPF (for Westing-house Distributed Processing Fam-ily), manufactured by Emerson Pro-cess Management’s Power & Water Solutions unit, Pittsburgh, Pa. Note that Emerson purchased the former Westinghouse Process Control Div when Siemens AG acquired that company’s power generation busi-ness. Intent here is to help owners of any make and model DCS decide how long they should retain their existing control system, and at what point they should make the leap to a new system—using the WDPF as an example.

WDPF maintenanceThe WDPF control system has been on the market since the mid 1980s, and is approaching the end of its product lifecycle (Fig 1). That’s not a knock against the product. That’s a fact established by the manufacturer’s product-support policy. Emerson’s policy is to provide a minimum of 10 years of product support. The follow-ing definitions from the original equip-ment manufacturer (OEM) apply:n “Current products” are the most

up-to-date products offered with published pricing, normal lead times, and complete support. Cur-rent products are recommended for new installations.

n “Active products” have been func-tionally replaced by “current prod-ucts,” but remain available with published pricing, normal lead times, and complete support. Active products are intended for expansion of existing systems. Transition to “active product” sta-tus marks the start of the 10-yr product-support commitment.

n “Maintained products” gener-ally are not available for purchase.

Support is available, but is focused strictly on maintenance—replace-ment parts, repairs, and field ser-vice. Emerson encourages owners of products in this category to initi-ate their lifecycle planning.

n “Retired products” are no longer available for purchase. Support is limited, slower, more costly, and subject to material availabil-ity. Transition to “retired product” status marks the end of the 10-yr product-support commitment.The WDPF control system is clas-

sified as a “maintained product,” and is quickly approaching “retired prod-uct” status. At the man-agement level, therefore, WDPF users should be ask-ing themselves: How long—and at what O&M cost—can I maintain my DCS? How much—and in what year—should I budget for a system upgrade?

At the technician level, users should be asking: Are my system backups com-plete and up to date? What can I do to be prepared for a software server crash? Where can I get refurbished WDPF parts? Could I ben-efit from having a plant simulator? What can I do to alleviate memory capacity limitations?

System backups. To prevent the loss of critical configuration software during a hardware or software fail-ure, WDPF systems must be backed up properly. Recovering from a hard-disk crash on an operator WEStation is routine maintenance, requiring only a blank hard drive and the “boot net–install” procedure from the Soft-ware Load Kit U0-8001-2.x.

The software server, however, is the most critical drop in the WDPF system, since all other drops are loaded from the software server. So recovering from a hard-disk crash on the software server is a much big-ger deal. This requires Solaris and

1. Even the most reliable DCS eventually needs to be upgraded, because of such problems as lack of OEM sup-port and shortage of spare parts

Reprinted with permission from the 2007 Outage Handbook supplement to the COMBINED CYCLE Journal, 3Q/2006. PSI Media Inc, 2006

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PROCESSCONTROL 2007OUTAGEHANDBOOKWDPF Release CD-ROMs, back-up tapes, third-party licenses, various custom files and drivers, and more. Many times, if proper back-ups have not been maintained, recovery from a hard-disk crash on the software server cannot be accomplished com-pletely.

The solution: Maintain a “hot-spare” backup hard drive for the soft-ware server. With this action, even the worst-case scenario—recovery from a software server hard-drive failure—becomes routine mainte-nance.

Serial interface QLC cards contain configuration files in battery-backed RAM memory. These files also must be backed up to storage media, in case a QLC card fails.

The WDPF is not self-document-ing. Therefore, all logic drawings—known as “SAMA” drawings because they follow the Scientific Apparatus Makers Assn standards—must be maintained. An “as-built” drawing review may be needed, in order to bring your drawings up-to-date.

All of these maintenance tasks should be performed, at a minimum, during an annual inspection of the WDPF system. At this time, pre-ventive maintenance also should be conducted on the WDPF hardware, to prevent dust, soiling, or normal wear-and-tear from impairing sys-tem reliability. The annual inspec-tion also should include housekeep-ing tasks for the Unix file system, and documentation of processor memory.

Capacity limitations of the WDPF system can hamper system opera-tion and maintenance by making it impossible to add or modify DCS control logic, alarming, or monitoring functions. Lack of available database space in the distributed process-ing units (DPUs) and in the data highway system IDs—referred to as SIDs—are the most common capacity problems encountered with a WDPF control system.

One action that frees up database memory is cleanup of the DPUs. This work does not require any additional hardware, and most of it can be done offsite so that plant downtime is minimized. The cleanup procedure identifies and deletes unused points and obsolete logic. It also identifies alarmable points that could be moved to an empty DPU. A total plant out-age is not required to accomplish this task.

Another option to alleviate capac-ity limitations is to add another DPU processor to the system. Each DPU comprises 120 kilobytes (kB) of database space to which alarms

from other DPUs could be re-located. Adding a DPU with cabinet and Q-Crates makes it possible to relocate I/O points and control functions from other DPUs, as well as moving alarms.

Rebuilding the system point direc-tory can alleviate the problem of SIDs being “maxed out.” In addition to identifying and deleting unused points and obsolete logic, point broad-cast frequencies will be optimized. Preliminary steps can be performed offsite on the DPU source code, but a total plant outage of one to two days is required to load the modified DPU source code and rebuild the system point directory.

Hardware maintenance. Several options are available to users, when it comes to hardware maintenance of the WDPF system. Support from the OEM includes:n Emerson Sure-Serve Contracts.

The OEM of fers repair and exchange services designed to accommodate varying needs and delivery requirements.

n Standard Repair and Return. Under this traditional scenar-io, customers return items for inspection, test, and repair. It is Emerson’s objective to service and return all company-manufactured items within 30 days of receipt.

n 24-Hour Exchange. This option is designed to address customer needs in the event of an emer-gency or other critical situation. A replacement item will be shipped within 24 hours of receiving the malfunctioning part. This level of service can be provided only for in-stock items.

n Advance Replacement allows for critical situations where you must have a replacement item dispatched immediately. Once you call for this service and your purchase order or credit card is received, a refurbished part, if available, will be shipped to you. You will be responsible to ship your serviceable item back to Emerson within 30 days.Users also can tap several non-

OEM suppliers of WDPF spare parts. For example, Sun Microsystems and HP parts—including RAM (ran-dom access memory), hard drives, HP optical drives and optical discs, Ultra-5, and Sparc-5 machines—can be purchased from Sun resellers. These parts also can frequently be found on E-Bay. Used hardware—including data-highway interface (DT Box) and DPU hardware—is available from resellers or custom-ers who have recently upgraded from WDPF. For instance, DeepSouth

Hardware Solutions LLC, Osyka, Miss, buys and sells surplus WDPF parts for powerplant and turbine control systems.

Advanced simulators are invalu-able tools for plant operator train-ing. In addition to learning the basic DCS windowing functions, trainees can gain familiarity with normal operating procedures—such as plant startup and shutdown—and abnor-mal plant situations—such as feed-pump trips, gas-turbine runbacks, and so on.

Simulators also can serve as a valuable maintenance tool. For example, I&C technicians can use them to build or maintain compe-tency in such tasks as loop checks, instrument calibrations, and testing logic modifications prior to actual implementation on the DCS. Final-ly, because the simulator runs on standard control-system hardware, it can double as a “hot-spare” parts bin, thus improving DCS availability when critical—and increasingly dif-ficult to obtain—parts fail.

Time to upgradeDespite the best efforts of the main-tenance crew, a computer-based control system eventually becomes obsolete, and must be replaced. For WDPF users, replacement options include migration to Ovation retain-ing the Q-Line I/O, or a total system retrofit to another DCS technology—such as the Siemens T3000, Foxboro, Bailey, and Honeywell. A compre-hensive control-system assessment will help users decide when it’s time to upgrade. The assessment might include:n System capacity evaluation—an

evaluation of DPU memory and system point directory capacity.

n Interviews with O&M personnel. A questionnaire is a useful tool to quickly assess the system hard-ware configuration. Interviews with operators and maintenance staff can help identify specific areas that need improvement.

n Analysis of historical data. Opera-tions logs and historical data can be used to identify areas where the control system should be opti-mized or upgraded to improve plant availability, efficiency, or emissions.

n The Emerson System Assessment Tool. End-users and owners of WDPF systems can access Emer-son’s automated assessment tool, available on the web at www.wdpf-users.com, for help with their DCS lifecycle planning.Ovation option. Some power pro-

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ducers are doing away with the three-letter acronym that has for decades dominated process control (DCS), in favor of the two-letter acronym that dominates the retail and residential world—PC. Emerson seems to have carried this concept the farthest, with its Ovation product.

First released in 1997, Ovation is a fully PC-based powerplant control system that eliminates proprietary operating schemes and vendor-specif-ic hardware. According to Emerson, Ovation reduces the risk of obsoles-cence often associated with propri-etary control systems, and provides better and more accessible informa-tion than is available through the typical DCS.

For users of existing WDPF sys-tems, an upgrade to Ovation can be accomplished via a complete redraw, or by using Emerson’s “migration tool” which can simplify and speed up the upgrade. The 36-MW San Gabriel Mill Plant, Pomona, Calif, for exam-ple, completed its conversion from WDPF to Ovation during a shutdown lasting only one weekend.

The automated migration tool enables owners of WDPF systems to upgrade to the Ovation system with minimal re-engineering and system retuning (Fig 2). The tool quickly con-verts WDPF graphics and logic codes to Ovation’s open architecture, avoid-ing the lengthy outages needed for the typical modernization project.

Migration to the Ovation system also can provide enhanced system functionality and process efficien-cy while reducing risks related to component obsolescence. If you are

considering upgrading your WDPF system to Ovation, here are general answers to a couple of the questions you’re likely to ask:

Question 1: What are the pros and cons of the migration tool, ver-sus a complete redraw? Answer: The migration tool converts the WDPF DPU source code directly into Con-trol Builder Sheets and database, for import into Ovation. A one-to-one change-out of DPUs is required. Also, some upfront work may be required to get the DPU source code into a format that the migration tool will accept. The migration tool offers a well-proved migration path, and is a good option if documentation is lack-ing, or if schedule or budgetary con-straints dictate the pace of the DCS upgrade.

By contrast, the “redraw” is exact-ly what its name implies. The point database is generated from the WDPF as-built termination lists and Q-Line I/O documentation, and the Control Builder Sheets are redrawn to match the as-built WDPF SAMA logic drawings (Fig 3).

Performing a complete redraw is more expensive because of the addi-tional software engineering that’s required. Two DPUs—which are located side-by-side and perform the same function—can be combined into one controller both to help offset the higher overall cost of a redraw project and to improve control-system reli-ability. A redraw project also offers several advantages over a migration project, which should be considered in your evaluation. These include:n More readable SAMA logic. With

the migration tool, logic is broken up into small bites in order to match WDPF execution order, and signal lines criss-cross the sheet in a visually confusing way.

n Better control-system logic review. With the migration tool, a compre-hensive design review is not per-formed.

n Design modifications easily can be integrated as part of the upgrade process.

n Simulation testing can be per-formed.To compare the costs of a migra-

tion versus a redraw, users may request separate quotes from Emer-son—one for a straight migration and the other for a re-draw. An additional quote from a third-party DCS consul-tant may be required for the as-built documentation and/or simulation development.

Question 2: Which operating system should I choose—Solaris or Windows? Answer: Solaris users often are familiar with Unix and con-cerned about network security, while Windows users want easy connectiv-ity to the plant local area network (LAN) and inexpensive, off-the-shelf computer parts. Other benefits of Solaris include easy recovery from hard-drive failures—with the “boot net–install” option—and X-Window-ing capability—via Hummingbird Exceed. On the other hand, Windows has Expanded Engineering Toolbox functions, which are excellent.

Ovation redraw projectA typical WDPF-to-Ovation redraw project includes the following ele-ments:n Plant walk-down and drawing

collection. A thorough review of the DCS process graphics is per-formed, in conjunction with a plant walk-down, to gain familiarity with the plant systems. Master red-line drawings (SAMA, P&IDs, electrical schematics) are collected. Also, the WDPF software server configuration, along with custom trend groups and any third-party software licenses—such as for Applix, optical drives, and print-ers—is documented and backed up for future reference.

n As-built SAMA logic drawings are the starting point for the software design. Logic drawings are extract-ed from DPU source code.

n As-built termination lists and Q-Line Card slot assignments and addressing documentation will be generated and validated. This information is entered into the Ovation DBID Tool (Database

2. PC-based process control is a DCS upgrade option—one particularly well-suited for WDPF users because of Emerson’s “migration tool” that upgrades to the Ovation system with a minimum of re-engineering and system retuning

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Initial Definition) to generate the initial Ovation point database.

n Network layout/Ovation system architecture design. Fiberoptic runs between buildings and tur-bine enclosures provide isolation from electromagnetic interference and eliminate grounding issues. The 10-BaseT connections make for flexible system architecture. The number and physical locations of fiber runs and network switches must be determined.

n Ovation hardware order. Based on the WDPF system hardware, software design requirements, and Emerson’s recommended net-work layout, the Ovation system hardware order can be placed. The Q-Line I/O hardware need not be replaced, only the human-machine interfaces and the DPU multi-bus chassis and power supplies.

n Spare parts are more economical if complete controller upgrade kits are specified, rather than individ-ual parts. Also, a simulator using Ovation hardware could double as a “hot-spare” parts bin.

n WEStation graphics. Newer WDPF systems with WEStation graph-ics require no additional graphics work. Older WDPF systems with “classic graphics” require a redraw of the process graphics.

n Simulator design. A simulator

model will be developed in order to debug the Ovation software.

n Final design review. Based on the interviews with O&M personnel, review of historical data, and logic review, control-logic modifications or additions to improve plant reli-ability, efficiency, or emissions are reviewed and included in the software design. Any additions or modifications to the logic may need to be reflected in the I/O termina-tion lists and process graphics as well.

n Software submittal to Emerson. All documentation, along with the Software Server backup tape, will be submitted to Emerson and used to implement the Ovation soft-ware.

n Software validation testing. A total plant simulator model facilitates debugging of the software design and implementation. The “loop-back stimulator” reads the outputs from the control system, simulates the process response, and writes the inputs to the control system. A detailed test procedure is an invaluable tool that helps maxi-mize simulation time and ensures that nothing is missed. While the purpose of the simulation test is to validate the software design, maintaining the simulator at the plant for operator training and

as an engineering tool may be an attractive option. This could be done with “virtual controllers” or using actual Ovation hardware.

Installation, commissioningFor both redraw and migration proj-ects, the installation of Ovation’s fiberoptic network can be completed prior to the plant outage in which the total system installation occurs. After all systems are locked out and tagged out, the DPU processors, power sup-plies, WEStations, and WDPF High-way Interface Boxes are removed and the Ovation controllers and WESta-tions are installed and downloaded. With proper planning, a WDPF-to-Ovation upgrade can be completed during a normal gas-turbine com-bustor inspection outage—even on a large 2 × 1 combined-cycle plant.

Commissioning activities are sub-ject to many factors—such as price of fuel and dispatch requirements. Some “hot” commissioning activities include: pre-start simulations, false fire, first sync, load-ramp tuning, and load rejections. Documentation and closeout of the upgrade project includes point database backup, software server backup to tape, and printing the as-built control builder logic. ccj oh

3. A redraw project is an alternative to “migrating” to the Ovation system. It typically is more expensive because of the additional software engineering that’s required, but its benefits include more readable SAMA logic drawings and a better control-system logic review

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