The success of a user group meeting depends on the steering committee’s ability to attract meaningful participation by owner/operators, OEMs, and third-party equipment and services providers. For third-party participants, user groups generally are the most efficient way to reach customers. Most of these vendors are small, with a single salesperson (sometimes the business owner) and may not offer more than a couple of products and services.
For owner/operators, the evening vendor fair conducted at virtually all user-group meetings is the most efficient way to for them to touch hardware and learn about products and services of value that they might not hear about otherwise. Most groups also allocate time for presentations by third-party providers, which often provide more details than OEMs might. Obviously, that’s because not-well-known companies must do so to pique your interest.
At STUG 2015, six vendors presented Tuesday, six Wednesday. Presentations were organized in two back-to-back 45-min sessions, each with three break-out rooms. The editors profiled six of the presentations below.
VENDOR PRESENTATIONS
Roadmap to Mark IV/V control system survival
Abel Rochwarger, GTC
Rochwarger, Gas Turbine Controls’ chief engineer, walked attendees through the company’s program for keeping Mark IV and V control systems in service without compromising the availability and reliability of critical generating assets. He also discussed GTC’s support network for the Mark IV, V, VI, and VIe.
A highlight of the presentation was the speaker’s simple approach for determining how many spares of specific control cards to have on hand. His thinking: In a forced-outage situation, fixed costs apply, gas costs may apply (take or pay), and power may have to be purchased at a higher (spot) price to fulfill commitments. Easy to see how you might have a negative margin. The challenge: How to mitigate exposure.
Rochwarger showed users his ABC curve to help decide what is cheap to have and can save the day. You can plot the curve easily using the following information: Vertical axis is value, in percent; horizontal axis is items to procure as a percentage of the total number of items. Starting at 0%/0% extend a line through the following points: 70% value/20% items, 90/50, and 100/100. This defines the ABC curve. What you find is that 50% of the items you might ordinarily stock only have a 10% value for outage recovery.
Another consideration, Rochwarger said, is how many parts should the plant stock to be “safe?” He noted that a simplified statistical deviation based on a binomial distribution suggests as a rule of thumb the square root of the number of units in operation, “n.” Correct application of the square root of “n” rule requires consideration of the costs of the forced outage and storage space, and projected inventory costs based on ABC curve results. Other variables come into play as well—such as the shelf life and warranty of critical spares. And, he reminded, don’t forget common sense.
At that point in the presentation, Rochwarger tooted the GTC horn suggesting users evaluate supply-chain reliability as part of their analysis. He said GTC has an unparalleled inventory of Mark IV and V cards, cores, and parts ready to ship within 24 hours or sooner with circuit integrity confirmed by live panel test (purchaser gets a Certificate of Conformance). Emergency courier service is available, he continued, and field engineering service can be provided within 24 hours. Card repair and exchange services are available as well.
Rochwarger recommended a periodic health check for Mark V, VI, and VIe control systems. The typical exam takes two days per turbine, he said. Here’s a short list of procedures carried out:
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Alarm troubleshooting and clearing.
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Verify control constants to specifications.
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DC power supply health check.
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File cleanup.
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Battery health check.
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Cleanliness/cooling,
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Junction box and terminal-board tightness check.
Among the benefits: long-standing issues are resolved, sequencing modifications are made, and a full report of the proceedings is presented. Access presentation.
Extending generator service life
Paul Heikkinen, TGM
Heikkinen’s presentation on Tuesday was a welcome relief from the mind-numbing detail on shop equipment and workplace practices presented by some representatives of turbine OEMs earlier in the day. He knows the kind of information owner/operators need to grow in their jobs and delivered it without commercial interruption.
Heikkinen has been around generators and motors since he was a child, working in his father’s electrical shop while others his age were out playing ball. The logical place to begin given attendee experience ranging from a year to decades is with exploded views of a generator rotor and stator so everyone was on the same page regarding nomenclature and how these critical components were constructed.
Logic also suggests that knowing what components can have the most significant impacts on generator life is a good place to begin your assessment of current condition and life expectancy. Heikkinen started with the rotor and showed that insulation deterioration is likely to drive its ageing. He quoted experts who said, “Insulation in service is exposed to high temperature, high voltage, vibration and other mechanical forces, as well as environmental conditions. These various factors act together and individually to wear out or age the insulation.”
One of Heikkinen’s slides identifies the Top 10 failure modes for generators. Missing from the material posted to the Power Users website is a supporting slide for each failure mode that digs into the details on how to identify that problem and mitigate it. Time constraints prevented the speaker from covering such details at the STUG meeting; it would have required a couple of hours.
Here’s a snapshot of the information Heikkinen has compiled: The leading failure mode on the summary slide, thermal ageing of stator core, stator windings, and/or rotor windings, is caused by inadequate cooling. The supporting slide asks the following:
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Why do I have this problem? Possible answers include (1) heat-exchanger failure, malfunction and/or improper operation, (2) clogged air filters, (3) inadequate hydrogen pressure, etc.
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How do I know I have this problem? Possible answers include (1) elevated stator slot RTD temperatures, (2) smell of hot or burning insulation in air-cooled generators, etc.
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How do I test for this problem? Possible online alternatives include PDA, flux probe, ac impedance; offline alternatives include insulation resistance, polarization index, El CID, etc.
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How do I prevent this and extend generator service life? Possible courses of action: operate generator within design parameters, adjust operating parameters to compensate, etc.
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Obviously, the support slides provide valuable checklists for finding the source, in this case, of inadequate cooling, for problem verification and for issue correction.
Access to Heikkinen’s material can help you recognize emerging issues and extend generator service life through proper operation, routine maintenance, and quality repairs. For more information, email the speaker at paulh@turbinegenerator.com.
New generators, old problems
Jamie Clark, AGTServices Inc
The title of this presentation was right on: The equipment problems of yesterday do recur in new plants. You can ask why, but not get satisfactory answers. The ageless generator consultant, Clyde Maughan, who began his career with GE, tells the story of being asked for his opinion on a particular generator problem and giving a quick—and correct—answer that left some very knowledgeable people stunned. The obvious question, “How do you know that?” The reply, “We solved that design problem in the late 1950s.”
The point, of course, is that companies change direction and a lot can be lost in the process. In this instance, GE furloughed many hundreds of engineers to cut cost. The boss got to keep his job, but the product line suffered. Happens as well among plant owners, some of whom buy and sell generating assets willy-nilly; personnel get discouraged, the continuity of decision-making is compromised, and old problems are recreated.
Clark began with an overview of stator issues in the winding, core, end-winding support system, wedge system, etc. For the stator winding he covered the causes and effects of contamination, loose ties, broken ties, loose blocking, corona activity, and movement. Stator core issues discussed included contamination, loose through bolts, loose (or absent) belly bands, mechanical damage, and movement. Obvious is that contamination has negative impacts on all components. Clark had it at the top of his list of discussion items for the field, too. Others included blocked cooling circuits, turn shorts, field grounds, and loose blocking.
You can access a wealth of information on all the areas discussed by Clark with a keyword search at the top of the page or by accessing content from the recent Generator Users Group (GUG). It’s impossible to cover all that material here. But you certainly want to encourage plant personnel to access the speaker’s presentation on the Power Users website. The six dozen photographs and illustrations presented are among the best ever seen by the editors. Their value in training new hires and for refreshing the recollections of O&M personnel before a generator inspection cannot be over-estimated.
Electromagnetic signature analysis testing
James Timperley, PE, Doble Engineering Co
The speaker, an IEEE Fellow, is recognized by colleagues as the “father” of the current approaches to EMI (electromagnetic interference) testing. Timperley spent the first 38 years of his career with American Electric Power, the last nine with Doble, which to date has applied EMI Diagnostics to more than 1150 generators, about 900 transformers, more than 600 bus systems, and well over 1000 motors.
The NDE technique has been used to support the need for condition-based maintenance of high-voltage (2400 V and above) equipment since 1980. It monitors radio-frequency (RF) energy from electrical activity at defects to detect and identify many types of system and equipment-related problems. Trending data over weeks or months is not required for accurate condition assessment. Non-intrusive data collection, in real time, while equipment remains in service offers economic and safety benefits to all powerplants.
Timperley reported that almost 80% of the components tested have revealed no problems requiring attention at the time of the test. This is good news because the test method allows users to avoid allocating maintenance resources for healthy equipment. EMI Diagnostics is efficient, providing maintenance recommendations with the first test.
The speaker reviewed some of the conditions identified via EMI Diagnostics—such as stator-bar slot discharges, loose stator wedging, winding contamination, exciter issues, etc. He then ran through 11 case studies attesting to the value of the technique—excellent material for an in-plant training program.
Here’s one example Timperley presented: An inspection of connections in the grounding cabinet and at the generator neutral were recommended during the next outage. Operation without a grounded neutral is not advised. The old shaft ground was not working and a new copper braid was installed, eliminating shaft currents through the gearbox and inboard bearing. The carbon-shaft ground had not been maintained and no longer prevented shaft currents. The copper braid retrofit solution prevented additional bearing and gearbox damage. Access presentation.
Isolated phase bus inspection and maintenance best practices
Gary Whitehead, Electrical Builders Inc
High-voltage electrical gear has emerged as a top interest area among gas-turbine users. Whitehead called to the group’s attention that the failure to inspect and maintain isophase bus duct (IPB) can lead to problems no plant manager wants. His presentation begins with the basics—a primer of sorts—to familiarize attendees having no experience beyond the generator with equipment that’s important to know. This included an overview on the two basic types of IPB—continuous and non-continuous.
Whitehead then got into the causes of IPB failures and how to avoid them, the starting and ending points being a robust inspection and maintenance program. Safety is stressed; no one wants to make a mistake around live bus duct.
Readers can access the complete presentation on the Power Users website or get the CCJ ONsite summary here.
Improving reliability, operator consistency, and efficiency for cycling CCGT plants
David Davis and Ray Boucher, Real Time Power Inc
The highlight of Davis’ presentation—in the opinion of CCJ ONsite’s editors—was the company’s automated software solution for computing the optimal run schedule for thermal energy storage (TES) systems in both day-ahead and real-time markets. The idea is to increase profitability by exploiting daily pricing patterns to chill water in off-peak hours and then provide turbine inlet-air cooling in peak demand periods to boost output and improve heat rate.
Davis said TES systems often are operated using default running schedules based on vendor design calculations, which do not account for the actual prices of electricity and natural gas, or weather conditions, or the thermodynamic state of the plant. The high variability in external and internal conditions during plant operation, he continued, implies that a fixed operating policy is sub-optimal in real-world situations.
The Real Time Power presentation was not available for posting on the Power Users website at the time this report was released. You can get CCJ ONsite’s article on the software solution here.
