By Jim Montague, Executive Editor
If knowledge is power, then detailed and sophisticated information that arrives early enough to prevent problems and even disasters is super-duper power.
For instance, Entergy Corp.'s (www.entergy.com) primary goal for more than 60 years has been to produce electricity safely. Located in Woodlands, Tex., north of Houston, Entergy provides electricity though its Fossil Energy divisional headquarters to 2.8 million customers in Arkansas, Michigan, Louisiana and eight counties in southeast Texas. It generates power using nuclear, coal, oil, natural gas, hydroelectric and wind sources.
"Process safety is our number one priority, and so we focus on it from our CEO on down. Most of our plants are OSHA Star program facilities," says Gary Barnes, superintendent of Entergy's seven-year-old Performance Monitoring and Diagnostics Center (PMDC). "We say that no job is so important that it can't be done safety, and we practice what we preach by emphasizing safety in our training, goals and meetings.”
To aid this safety effort, PMDC monitors Entergy's fossil units for subtle indications developing in its equipment or other operational issues, so it can quickly identify problems when they're smaller, easier to address, less costly, cause little or no equipment outages, and limit the potential for any catastrophic failures. The center uses three main types of software to help Entergy find problems and improve performance, including OSIsoft's PI data historian on all key units to capture data and show how well they're functioning, and General Physics' ETApro to perform thermal calculations for turbine effectiveness, heat balances around heat exchangers, and other tasks that used to be done manually.
In addition, to give it advanced pattern recognition capabilities, PMDC began beta testing SmartSignal's (www.smartsignal.com) EPI*Center software in 2006, and now uses it on 36 units at approximately 16 plants, which represent about 95% of Entergy's total fossil generating capacity. "PMDC monitors our fossil units, and it's been acknowledged as the leading remote diagnostics center in our industry," says Barnes. "In fact, though Entergy's nuclear division is separate from our fossil division, it's implementing PI and SmartSignal's software in our nuclear fleet, and we recommended it to them.”
Jim Gagnard, SmartSignal's president and CEO, adds that, "We originally decided to focus EPI*Center on the process industries because they have continuous manufacturing applications, and so we can use individual historical data to create personalized models for each piece of equipment. For the 300-400 plants that use our technology, it's the data that defines the model, not the software. As a result, we can help users see subtle changes in their unique processes ahead of time, and so some problems never become big ones. In fact, three or four of our customers already have negotiated lower insurance rates by having this early detection of problems in their processes. We have a real-time version of the usual risk-assessment process and can report every five minutes on what's going on that might be abnormal, which make problems a lot easier to fix." (Figure 1)
Little Vibration Reveals Big Crack
For example, shortly after installing EPI*Center on its 411-megawatt Waterford Unit 2 gas/oil generator, Entergy's engineers and operators got an alert from the software that vibration levels on the exciter end of the unit's turbine were slightly elevated, and starting to steadily increase (Figure 2). Barnes says this unit usually runs at 3,600 rpm, and that an ideal vibration level is 1 mil (a unit of vibration equivalent to 0.001 of an inch), though usually operators are satisfied with 2 mils.
"The first notification at 12:30 p.m. was that the unit was running at 3-3.5 mils, which is elevated, but not a lot, because there's not usually a problem until you reach 5-7 mils," explains Barnes. "So, we weren't too concerned, and notified the plant, and continued to watch the situation. However, the vibration level continued to increase until at 5:30 p.m. it reached 6-7 mils, and the decision was made to shut the unit down.
"Because of the early notification from EPI*Center, we were able to learn about the elevated vibrations very early, watch it increase, and then jointly consult with the plant and dispatch center about taking the unit offline. We were able to proceed very calmly and shutdown safely. If we hadn't had this information from the PMDC, then the plant wouldn't have known there was a problem until the vibration level reached 6-7 mils and an alarm went off. As a result, we would have had a lot more critical situation, maybe not enough time to shutdown safely, and possibly have had a catastrophic failure.”
After the safe shutdown, Barnes adds that Entergy's engineers diagnosed and disassembled the unit, and found a 2.5-inch deep crack running 180° around the end of the rotator shaft (Figure 3). Analysis revealed that the new crack was due to stress fatigue from a previous arc gouge that had been repaired several years earlier.
"The consensus of our rotating equipment and generator experts was that, if we hadn't taken this unit offline, then the shaft would have cracked through, and we would have had a catastrophic failure. The 3,600 rpm section would have hit the stationary area, which would have completely wreaked the generator, done serious damage to the turbine, and probably caused hydrogen coolant and oil fires. In other over-speed events, large pieces of metal also have penetrated their facility's shell, and flown up to a half mile away. An incident like this would have caused $40-50 million or more in damage, and this unit would have been down for months, if not years. Because of our safe shutdown, the repair cost only $5 million, and the unit was only down six weeks."