ENGINEERING SOFTWARE

Automating Production of Loop and Terminal Block Wiring Diagrams Cuts Design Time for Power Plant Retrofit by Hundreds of Man-hours

PPL Generation, LLC was able to cut hundreds of man-hours off the design time for a power plant retrofit by using software that automatically produces loop and terminal block wiring diagrams derived from database information. Previously, loop and terminal block wiring diagrams were drawn by hand in a CAD system. Whenever the design changed, a great deal of time was spent identifying all the affected drawings and updating them.

PPL Generation's Instrumentation and Control (I&C) group streamlined this process by installing software that can generate drawings from information in equipment lists, instrument indexes, and cable schedule databases. "With this approach we spend most of our time inputting design information in the database as it becomes available. Then, in the final two weeks, we have the software generate the drawings," explains Frank Lyter, a senior control systems engineer at PPL Generation. "This is obviously much faster than creating them by hand. But delaying the creation of drawings also means that mid-project design changes cause only minor delays because they are dealt with before the drawings are produced."

PPL Generation, LLC, is a subsidiary of PPL Corp. (formerly Pennsylvania Power & Light). With its sister company, PPL Global, LLC, PPL Generation owns and operates facilities in northeastern and western United States, Latin America, and Europe with generating capacity of 10,000 megawatts and 2,700 megawatts under development. Power plants are low cost, use multiple fuels (coal, natural gas, oil, uranium, and water) and are strategically located to provide PPL access to various markets.

Plant Description and Recent Projects
PPL Generation first used the new loop and terminal block wiring diagram method to retrofit the company's Montour Steam Electric Station. Located one mile northeast of Washingtonville, Pennsylvania, this is a coal-fired facility consisting of two ABB CE tangentially fired units with a total of 1,500 megawatt generating capacity. Unit 1 began commercial operation in 1972 and Unit 2 became operational the following year. A recent retrofit was done in 2000 when the plant installed a new selective catalytic reduction (SCR) system and replaced the electrostatic precipitator on Unit 2. Two, 5,000hp Induced draft, booster fans were also added at the same time to overcome the additional pressure drops of the SCR and precipitator.

Traditional Design Techniques
For this retrofit, the I&C and Electrical design groups were required to design and implement a control system consisting of multiple pressure transmitters, flow transmitters, thermocouples, limit switches, analyzers, and motor control devices. The new equipment was to be tied into an expanded and upgraded Max Control Systems Distributed Control System. In all, there were 1,023 inputs and outputs, split about evenly between the SCR system and ID fan system. In the past, the group would have used AutoCAD or MicroCadam to produce the instrument loop and terminal block wiring diagrams, for these systems.

Production of standard CAD typically involved the engineers preparing loop sketches and draftspersons in turn generating the final loop drawings, terminal block drawings and cable lists. Preparation of the final design documents involved significant repetitive manual entry of information for a given instrument installation. For example, loop drawings include field instrument tagging and descriptions, multiple terminal strips and DCS tagging and termination information. The same information would normally be manually transcribed on related terminal block and cabinet wiring drawings.

In addition to the time required to create and revise drawings, the I&C and drafting groups spent a great deal of time ensuring consistency between all the documents related to a project. "In the past, it was up to the individual who changed a wiring diagram, for instance, to determine all the other places where that information appeared and change those as well," says Lyter. "We spent a lot of time trying to avoid the problems that occur when changes are made on one document and not on supporting documents."

Design Process Evaluation
In preparation for the coming deregulation in the electric industry, PPL Generation's I&C group was looking for ways to operate more efficiently. They saw the limitations of the existing schematic production process and knew that was an area where automation could have a significant effect. "For the last six or eight years, even though we have been using CAD to generate the final product, the drawings, we have been doing much of our work in databases," explains Lyter. "That's where we compile information such as lists of instruments, cable schedules, and so on. Since we were essentially doing the design work in a database already, it didn't make sense to have to repeat the effort again on the drawings."

That led the group to look for software that could take database information and use it to generate and plot drawings automatically. In addition to this functionality, the group specified that the software run on top of AutoCAD since that is the in-house CAD program as well as the one used by many of PPL Generation's vendors. The AutoPLANT Instrumentation Workgroup from Rebis, Walnut Creek, California, was the only program they found that met both requirements. "This program was the only AutoCAD add-on software that was truly database-oriented rather than just CAD-oriented," says Lyter.

Customizing the process
Prior to using the new software on the Montour plant retrofit, the I&C group spent some time planning how to use it most efficiently. They set up the software's databases to meet their data conventions. They also customized the termination and loop diagrams. The drawings were simplified so that those who would be doing the actual wiring would see only the end of the cable they are interested in, rather than both ends as in the default drawing. They also increased the size of the text on the drawings to better meet the needs of the people in the field.

Once this preliminary work was done, the group began designing the SCR and ID fan systems. The job involved placing instruments and devices and setting up all the wiring between them, from transmitters to local termination boxes to larger cables, then to the control system termination cabinet and the I/O modules.

Rather than drawing these devices and the connections in CAD, they designed the systems in the AutoPLANT database. "By doing the design this way, we were able to ignore the intermediate points initially," explains Lyter. "We could just indicate in the database that transmitter A went to channel 1 on a given card." Although this information could have also come from intelligent process and instrumentation diagrams (P&IDs) created in AutoPLANT, the process design was being provided by an Architect/Engineering (AE) firm and group opted to accept hardcopy P&IDs and database-style instrument lists.

Design Implementation
Once the database was completed, the software was directed to generate and plot the loop diagrams and terminal block drawings automatically. Detailed instrument wiring and termination data was transferred from the cable schedule database to automatically annotate the loop diagram. Other information, such as manufacturer, model number, range, location, panel and calibration information can be obtained from the master instrument database. With the software, I&C group designers were able to assign cable termination, title block, and other data to a series of loop numbers by editing input screens. This reduced transcription errors, increased the speed of drawing revisions, and increased control over the drafting process. Similarly, termination drawings were automatically generated from the end device and terminations indicated in the database. "Eighty percent of the job involved using the database structure to fill in the design information. The last 20 percent was where we started producing the field documents," says Lyter. "Since we made sure the database was correct, we had confidence that the field documents would also be correct.

"In the past we had to check across four or five documents to make sure they were all consistent. When the information came from the same database, we did not have to worry," says Lyter. For example, if an instrument were added to a terminal block drawing, it would also be necessary to change the loop drawing. With traditional CAD drawings, that step could be overlooked. "Now when we make this type of change, we just regenerate the appropriate loop and affected terminal block drawings and we know it's correct," says Frank Lyter.

Project Savings
The man-hour savings in the design of the project were certainly significant, but the largest contribution to the project was the savings realized by having extremely accurate design documents during the construction phase. As a result of the accurate documentation, startup and testing of the new equipment went very smoothly. Some minor problems were encountered during field testing of the equipment, but the problems were due to system designs, instrument loop designs or equipment problems and not problems due to wiring errors or inconsistencies across multiple design documents.

Lyter estimates that by producing the documentation this way, the group was able to complete the design of the retrofit using 600 to 800 fewer man-hours than if they had used the previous method of drawing in AutoCAD. The savings during the construction phase are difficult to estimate, but the project was constructed and started up on schedule.

Future Work
PPL Generation is planning to install an SCR and electrostatic precipitator on Montour's Unit 1 next year. Together the two SCRs will remove about 90 percent of the remaining nitrogen oxide leaving the boiler while the upgraded precipitators will remove almost all of the plant's coal ash from the stack gas.

The I&C group is well prepared to handle this and other retrofits. "With this new method of generating design documentation automatically from the database, we can quickly implement new air quality equipment such as what we installed in Montour," says Lyter.

"The efficiencies we gain from our use of AutoPLANT will help PPL continue to meet its commitment to conduct its business in an environmentally responsible manner," he concluded.