D5-D5A Users Group: Generators, controls lead presentation, discussion topics at annual meeting

Gabe Fleck’s easy demeanor and keen sense of what’s important for operating and maintaining gas-turbinebased generating facilities to the highest standards have helped rekindle the spirit of the 501D5/D5A Users. Attendance at the annual meeting June 11-15 in Memphis tied the alltime high established in 2005. Were it not for several last-minute cancellations, a new record would have been established.

Recall that the D5/ D5A is a relatively small fleet—about 150 engines worldwide. To have nearly half of those machines represented at one meeting spells “success.” Twenty-six owner/operator firms from eight countries and 13 states participated in the diversified program at the Memphis Marriott Downtown, a venue selected after first-choice New Orleans was ravaged by last year’s hurricanes.

The program committee, chaired by Rich Deaver (sidebar), played a major role in the meeting’s success, arranging for formal presentations by OEM (original equipment manufacturer) Siemens Power Generation Inc, Orlando, and by third-party equipment and services providers, which addressed controls upgrades, fire suppression, compressor diaphragm repairs, and gene rat o r issues. Several presentations by users, a series of roundtable discussions, and vendor exhibition rounded out the technical program.

Anyone who has ever attended a D5/D5A meeting knows Fleck, an electrical engineer with Associated Electric Cooperative Inc, Springfield, Mo, always delivers a robust social program and quality fare. The early arrivals on Sunday, June 11, were treated to a first-class welcome dinner courtesy of the user group. Monday was Fleck’s warm-up, get-to-knowyour- colleagues-better program consisting of morning golf an afternoon of informal discussion and evening minorleague baseball game sponsored by Mitsubishi Power Systems, Orlando.

Reception on Tuesday evening was held in conjunction with the vendor exhibition. Wednesday evening, if you weren’t already exhausted from two very busy days in the “classroom” and the vendor fair, there was an invitation from Siemens for a tour of Graceland and dinner at Elvis’ auto museum. Most of the users attended; Elvis was a no-show. After the closed user sessions all day Thursday it was time to kick back for Siemens’ happy hour (really two) at the Isaac Hayes nightclub and then dinner courtesy of Trinity Turbine Technologies LP, Iowa Colony, Tex.

Vendor presentations

Control systems. Sounds like a “fun” meeting, but don’t get the wrong impression. Think of it as a well-balanced conference with rewards for enduring long days of technical presentations and discussions. Reality struck early Tuesday, after a relaxing Monday, when Mitch Cochran of Process Control Solutions LLC, Haddiesburg, Miss (mitchpcs@aol.com) took the podium and began a 78-slide dissertation on lifecycle planning for the WDPF® (Westinghouse Distributed Processing Family) control systems familiar to most D5/D5A users.

Upcoming meetings

Mid-year: January 25, Orlando

Chairman Gabe Fleck and the program committee chaired by Rich Deaver expect a record attendance for the 501D5/D5A Users’ mid-year meeting, Jan 25, 2007 in Orlando, (venue to be announced) based on the success of this past January’s one-day event.

To register, and to keep current on program development, write gfleck@ aeci.org. Review the content of discussions at the last mid-year meeting by accessing “501D5/D5A Users do two days of work in one at mid-year meeting,” COMBINED CYCLE Journal, 1Q/2006, p 80, at www.psimedia. info/ccjarchives.htm.

Annual: June 5-7, Oklahoma City

Block out June 5-7 on your 2007 calendar today. These are the dates of the 501D5/D5A Users’ annual meeting and vendor exhibition at the Cox Business Services Convention Center in Oklahoma City. Hotel accommodations are available at the Renaissance Oklahoma City Convention Center and Courtyard by Marriott. Write Chairman Gabe Fleck (gfleck@aeci.org) for a copy of the preliminary program when it becomes available.

Cochran is an engineer expert at squeezing the last drop of capability from an existing control system, as well as one capable of upgrading your controls to a higher- order system—such as Ovation—when that is the proper strategy. His presentation is summarized in “Lifecycle planning for your DCS,” p OH-80, 2007 Outage Handbook supplement inserted in the middle of this issue.

Fire protection. The benefits of water-mist suppression systems over traditional methods for handling fires were described by Brian Fabel, PE, director of national accounts for Orr Protection Systems Inc, Louisville (bfabel@orrprotection. com). He began by discussing the limitations of gaseous and sprinkler systems most familiar to the D5/D5A user community.

Gaseous systems, Fabel said, require tight enclosures, are expensive to recharge, and are prone to accidental discharges. Some are sized only for one discharge and must be recharged before a unit restart. This can be especially inconvenient when the discharge is accidental. Conventional sprinkler—so-called water spray—typically has a slow response time, can cause thermal shock, and cannot extinguish some types of fires. Also, water consumption is significant and environmental hazards may be associated with run-off.

According to the NFPA Code (National Fire Protection Assn), a mist is a fine spray where droplet size is less than 1000 microns at the minimum design operating pressure of the water nozzle. Specifically, a class 2 mist has an average droplet size of 300 microns or less; class 1, 50 microns or less.

The size difference between sprinkler and mist droplets is significant, Fabel pointed out. For example, one 1000-micron sprinkler droplet is equivalent to 40 class 2 mist droplets and 8000 class 1 mist droplets. This means mist vaporizes much more quickly than sprinkler droplets: If it takes a 1000-micron sprinkler droplet one second to evaporate, a 50- micron droplet will vaporize under the same conditions in 0.003 sec.

Benefits of small droplet size in fire-fighting are several:

  • Ultra-fine droplets create an extensive cooling-surface area and chill the hot burning gases.
  • A high density of mist droplets absorbs and scatters heat radiation, thereby restricting the fire’s ability to spread.
  • Rapid vaporization of the fine mist blocks the entry of oxygen into the fire.
  • A very small quantity of water is used, eliminating the possibility of thermal shock and avoiding runoff and associated cleanup.
  •  Mist is electrically non-conductive.

Water-mist systems originally were developed for shipboard applications where they have been very successful in suppressing fire. A variety of land-based systems (single- and dual-fluid, low to high water pressure, etc) are offered by companies traditionally serving the fire protection market—such as Fike Corp and Chemetron Fire Systems.

Program committee
The program committee for the 501D5/D5A Users is chaired by Richard R Deaver Sr, PE, team leader, project engineering management, Johnson Controls Inc, Trigen Philadelphia Plant. Other members are:

  • Timothy J Luka, CT/plant electrical technical specialist, Springfield (Ill) City Water, Light & Power Dept.
  • Barry Mayhew, maintenance manager, Cardinal Power of Canada LP.
  • Dennis J Oehring, multi-plant superintendent, ProEnergy Services LLC.
  • Matt Konieczka, power solutions engineer, ChevronTexaco Corp.

Fabel spent the second half of his time at the podium describing typical water-mist system designs for powerplant application—GTs and generators in particular (Fig 1). A case history concluded the presentation.

Compressor diaphragms get regular coverage at D5/D5A meetings. If you go back a couple of years into the COMBINED CYCLE Journal archives—3Q/2004, p 82, accessible at www.psimedia.info/ccjarchives. htm—you can get the background on a cracking problem associated with the original R1 diaphragm design. In brief, several machines experienced cracking in the inner shroud vane tenon weld that propagated through the airfoil. Both Siemens and Mitsubishi redesigned the component.

Alan Lovelace, PE, of TRS Services Inc, Houston (alan@trsservices.com) was in Memphis to review diaphragm design, manufacturing, inspection, and repair. One of TRS’s areas of expertise is diaphragm inspection, refurbishment, and repair for the Siemens 501 series of engines. Part of the manufacturing segment of the presentation concerned laser welding practices before year 2000 that didn’t meet expectations. It covered how to inspect for deficient welding in the field, and how to “touch up” poor welds using the TIG process.

Diaphragms sent to the TRS shop for refurbishment are first inspected to determine the scope of work required for restoration. Measurements taken include butt gaps, seal diameters, offset, and drops. Next, the coating is stripped and nondestructive examination (NDE) using magnetic-particle or dye-penetrant techniques is conducted.

Minor indications, Lovelace said, are blended; medium indications are repaired using Inconel 82 weld wire (no heat treatment); major indications are repaired using Type 401 stainless steel with a stress-relief step. He added that the diaphragm should be restrained on a fixture plate during the stress-relief step.

Repair of laser-welded tenons may be required, Lovelace continued, depending on the vintage of the diaphragm. Where multiple tenons are rewelded, the hookfits must be welded and machined concentric (Fig 2).

A review of mods and upgrades was next—including coating options, seal-holder anti-rotation blocks, hookfit coating to close up clearances to the case and/or seal holders, and hot-start mod. Last is designed to open up diaphragm radial clearances to minimize rubs on quick restarts. It results in an efficiency loss and is not recommended for base-load machines.

In closing, Lovelace made these points:

  • The majority of diaphragm repairs are in the minor and medium categories.
  • D5As with diaphragms manufactured prior to 2000 using the laser welding process should be inspected thoroughly and regularly— rows 1, 2, and 3 in particular. Concentrate on the inner and outer shroud tenon welds with a good visual inspection, tap test, and dye-pen check, if possible.
  • Add locking devices to the coverhalf seal holder to stop reverse rotation (Fig 3). Note that this mod still allows base-half seal holders to be rolled out around the rotor if necessary.
  • Choose your repair facility carefully and always compare incoming versus outgoing dimensions. Be sure parts will fit back into your engine before they leave the shop.

Generators

Generators dominated podium time the first afternoon with formal technical presentations. Concurrent meetings were held for users with GTs equipped with Westac (for Westinghouse air-cooled) generators and those with Brush generators. Presenters in the Westac session were Siemens and National Electric Coil (NEC), Columbus, Ohio; those in the companion meeting were Brush Generators Inc, Houston, and NEC.

The D5/D5A Users devote considerable time each conference to generators. In 2005, under Fleck’s leadership, the group launched a Westac Users subgroup within the GT organization to facilitate collaborative problem-solving with Siemens. Fleck said that about 90% of the Westac fleet is driven by a D5 or D5A.

The Brush presentation, conducted by Derek King, general manager (derek.king@houston.rm.fki-et.com), and Mike Watkins, services sales manager (mike.watkins@houston. rm.fki-et.com), was an 85-slide tutorial that could have been considered for continuing education credits. King, a frequent speaker at usergroup meetings, always does a thorough job at the podium. Keep in mind that Brush has extensive experience in GT-based powerplants, having provided more than 600 generators for GE Energy, Atlanta, and Siemens frames worldwide.

King and Watkins started “at the beginning” by reviewing how generators work—that is, how they make electricity. They then dissected the machine and addressed the design, operation, and maintenance of each major part beginning with the exciter. As for overall O&M objectives, their message was simple: “Regarding air, oil, and water supplies, keep them clean; joints and covers, keep them tight.”

After discussing the rotor, bearings, and stator, in turn, the pair ran through a series of case histories that they named “Bad things happen to good generators.” They were an eye-opener and illustrated the importance of proper, regular inspection. Guidance was provided on what to look for in the machine and where. The three photos in Fig 4 that King and Watkins labeled “Going, going, gone” illustrate progressive stages of winding deterioration.

Generator change-out at Borger

King later teamed up with D J Rogers, plant manager, Blackhawk station (Quixx Power Services Inc) to present a case history on the changeout of a Westac generator with a Brush machine. Order was placed at the end of February 2005 and the new machine was in service before the end of the year. King talked about generator design through delivery to the Borger (Tex) site; Rogers addressed the onsite work.

King began with a summary of design features and nameplate information, plus a review of critical features. For example, the plant was concerned about main casing positioning and connections to the starter pack. No changes were required to either the coupling or foundation. Also, could existing main terminal posts be used? What about line and neutral cubicles? “Yes” to both questions; Brush matched the mechanical interface and connections.

The generator was manufactured in the UK and trans-shipped to Rotterdam where it was loaded on an ocean-going vessel bound for Houston). The machine was in Borger six days after the ship docked (Fig 5). Rogers started by reviewing all the planning required to swap-out generators, including:

  • Schedule crane service. Westac load was 367,000 lb, Brush 312,000. Two 300-ton cranes were requested for use in tandem.
  • Contract local vendor support, including mechanical, electrical, and machine shop. Last was required to fabricate four lifting trunions to remove the Westac unit. Each trunion weighed 400 lb.
  • Temporary installation of a backup boiler to accommodate thermal host’s steam needs during generator replacement.
  • Arrange for shipping of the generator from Houston to the plant, including all permits required. The truck contracted was 228 ft long, 16 ft wide, and had a total gross weight of more than 300 tons.
  • Controls and procedural changes included DCS (distributed control system) modifications, new operating procedures, and settings/ performance verification of a new voltage regulator.

Next, Rogers explained that required demolition, and as many other tasks as possible, were completed prior to generator delivery, including the following:

  • Broke couplings and removed starting package.
  • Removed air inlet housing and generator enclosure.
  • Disconnected neutral and lineside electrical cubicles.
  • Removed oil piping and lifted anc i l lary elec t r i cal wi r ing/ instrumentation.
  • Removed Westac generator and repaired/modified foundation to accommodate the Brush machine.
  • Rebuilt access road to plant, provided crane support for offloading and staging.

Commissioning was completed soon after installation (Figs 6, 7). It required coordination with the local utility to conduct pre-service tests, calibrate the automatic voltage regulator, and run load tests. All work was completed within two months and operation through the first winter and summer met expectations. Plant dispatched at up to 70% of its capability during that time.

Other user presentations. The Memphis meeting featured several other user presentations, which always get high marks from attendees. They were:

  • Compressor cleaning challenges, Iqbal Rodak, executive manager, Jubail Energy Saudi Arabia.
  • Torque converter overhaul . Two case histories: one by Jeff Nottingham, plant manager, R W Miller Generating Station, Brazos Electric Power Co-op Inc; the other by Stan Wilhelm, senior CT specialist, Nodaway County Power Plant, Associated Electric Power Co-op Inc.
  • Second major inspection, Barry Mayhew, maintenance manager, Cardinal Power of Canada LP.

Siemens Day

It’s tradition and logical: Siemens Day at all of the usergroup meetings the company supports starts with a review of the OEM’s progress in satisfying customer needs as determined from surveys and interviews conducted by Six Sigma Program personnel. However, the D5/D5A session on improvement actions differed from those conducted previously in that Ron Bauer, Siemens “ambassador of quality” and the company’s six-sigma face to GT users, had accepted a different position within the organization and had been replaced by John R Schuck, director of business excellence.

Transitions can be difficult, but not this time. Schuck—confident, empathetic, and effervescent—had a positive relationship with the audience within minutes. He began with a review of how the company was improving its technical responsiveness, including:

  • Net meetings, online conferences that enable the OEM’s engineers to interface directly with owner/ operators on specific issues of concern when requested by the user group.
  • Plant Optimization Center. It coordinates and manages critical issues and resources for service planning and execution.
  • Field Service Support Center. An engineering help desk that rapidly responds to questions from onsite field engineers during an outage.

Continual improvement in the quality of repairs is a top priority for Siemens. Schuck explained the three keys to success:

  • Customer-focused quality-incident metrics. “Escapes”—quality incidents that impact an internal or external customer—are tracked independently.
  • Greater emphasis on root-cause analysis. Quality data collected during repair operations guide this solution. Executive-level monthly quality-incident reviews raise the visibility of this program, which focuses on eliminating repeat issues by promoting best practices and lessons learned.
  • Accountability.

The Customer Extranet Portal (CEP) gained considerable traction among users between the 2005 and 2006 surveys, membership among D5/D5A owner/operators increasing from 100 to 129. Reasons included enhanced accessibility, more technical documents (service and product improvement bulletins, technical advisories, customer service letters), parts catalogs, contact information for Siemens personnel, outage reports, and the addition of section for GT shop repair reports. The CEP undoubtedly had a significant impact on the substantially higher customer satisfaction ratings regarding the availability of technical information.

Improved content of shop repair reports also has been well received by users. Recent enhancements include greater standardization, more inspection data detail, elimination of acronyms, inclusion of product mods implemented in repairs, better executive summary.

Greater satisfaction was experienced with respect to spare parts. Parts availability was up dramatically (94% of the time a part was requested in 2006 it was available versus 78% 30 months earlier). On-time deliveries also increased.

Customer satisfaction survey results were presented by Harvey Grassian, who has compiled this information since the current program was initiated in 2003. He was pleased with the better response (46%) to Web-based surveys compared to paper ones and with the increasing overall satisfaction rating among D users, now at an all-time high. Significant improvements in customer satisfaction were recorded in the following categories, among others: willingness to recommend Siemens products, D5 parts life, overall availability of Westac generators, shopreport content, all aspects of outage closure (timely and complete final report content, timely and accurate invoices), mods and upgrades delivering expected results, and value of Siemens products.

The highest grade in level of customer satisfaction went to D5 availability/ reliability. The top 10 key areas evaluated also included D5 heat rate and starting reliability, D5A availability/reliability, outage implementation, and workmanship of both generator and GT service personnel.

The availability and reliability report for the D5 fleet was presented by Jeffrey Kain, manager of mature frame product support. Fleet leader among the operating 93 D5s installed since 1982 had logged more than 160,000 hours of operation at the time of the meeting. For the D5As, now actively marketed and sold as the SGT6-3000E, the operating fleet is at 52 units installed since 1996 with the leader at close to 70,000 hours.

Reporting of operating data for the D5 fleet has decreased significantly over the last year as it has for the W251 engines (see article elsewhere in this issue). About half of the D5A units still report, but only about a quarter of the D5s. Both Kain and Chairman Fleck stressed the need for accurate and timely operating data to support the OEM’s efforts in the development of repair technologies, mods and upgrades, rapid problem resolution, adequate spare-parts inventories, etc. The direct value of fleet data to individual users includes the ability to benchmark plant performance against the aggregate.

Duty-cycle analysis of the D5s indicates that about a third of the fleet is on standby, another third peaking, about a quarter of the units are baseload, and the remainder in intermediate-duty service (see sidebar in the W251 Users Group article for definition of terms). Service factor is close to 40% and has remained relatively constant over the last couple of years. The D5 Econopac rings up excellent numbers for availability (over 95%), reliability (over 98%), starting reliability (over 93%), and equivalent-start factor (less than 2), which is why users give the engine their highest satisfaction rating. The foregoing numbers are 12- month rolling averages.

By contrast, half the D5As are on standby, 20% peaking, 20% baseload, and the remainder in intermediate- duty service. Service factor is just over 25%, and like the D5, has been relatively constant over the last couple of years. Reliability of the D5As mirrors that of the D5s, but availability is more than a percentage point higher and starting reliability about three points lower. Equivalent start factor was slightly more than 2. Interestingly, one generator event had the greatest impact on reliability for each model.

Kain said Siemens had initiated a program to improve starting reliability. First step is to identify the most significant common causes for failed starts and then develop corrective measures. At the time of the meeting, engineers had studied eight units with the lowest starting reliabilities in the reporting fleet and data analysis was just beginning.

Three common reliability detractors are vibration, which can be reduced with balancing; slow closure of bleed valves; and no flame. Kain promised an update at the next meeting.

Technical update. Kain was a busy man at the D5/D5A meeting. Following the availability/reliability update and a sip of water, he talked for nearly two hours in bringing users up to date on everything from wet compression to component repair/replacement intervals. Much of this information is sensitive and you only get access to it by attending the annual meeting. Mark your calendar now, as Fleck urged at the beginning of this report, and join the group in Oklahoma City, June 5-7.

Kain devoted 20 minutes or so to the subject of turning-gear time reduction. First he reviewed the issues associated with turning-gear operation, specifically:

  • Rotors will sag and develop runout if maintained in a stationary position. This would result in vibration—possibly vibration severe enough to trip the unit—on startup.
  • High time on turning gear is conducive to disk-serration/blade-root wear. Excessive blade rock may result and seal pins may be liberated. In the extreme, it can contribute to disk cracking.

At the present time, turning-gear operation is suggested 12 hours prior to startup and for 72 hours following shutdown. For units in peaking service, continuous turning-gear operation is recommended.

Siemens is pursuing alternatives to continuous turning-gear operation. Ultimate objectives are to (1) maintain start-readiness without continuous operation, (2) require no pre-start measures, and (3) enable automatic turning- gear operation. An interim objective is to reduce pre-start measures for units that have been off turning gear. Success requires no vibration trips occur on startup or spin-hold.

Kain said that the information engineers need for proper decisionmaking requires extensive engine testing. For example, to maintain start readiness without continuous turning-gear operation, the maximum allowable rotor runout (bow) that will not cause a trip on high vibration during startup must be determined. Next, how long does it take a static rotor to develop the maximum allowable bow?

Evaluation of options available to prevent or periodically remove rotor bow is another task. This could involve intermittent turning-gear operation, periodic spinning of the rotor, and/or periodic repositioning of the rotor. Similar tests must be conducted for different engine models and under a range of ambient conditions. Kain reported that six engines had been tested by mid June and offered some preliminary results. Users were asked to consider supporting the effort by allowing their units to participate in the test program. Join the group in Oklahoma City for an update.

Extending inspection intervals. In the demanding world of deregulated power generation, plant staffs are continually challenged to reduce the cost of operation and to maximize revenue opportunity by increasing availability. One way to achieve both objectives is to extend the intervals between inspections— combustor, hot gas path, and major. Engineers have found that the time between inspections can be as much as doubled without adversely impacting reliability. But careful analysis is required to determine exactly what’s possible for any given unit.

Another way owners may be able to reduce operating costs is to squeeze every possible rpm out of their GT rotors and every cycle/hour of life remaining in other critical components. This can be achieved with a process known as lifetime extension.

Diego Caso presented on both subjects. Rather than cover this material again, refer to Caso’s article, “Operating experience, analytical procedure help OEM extend intervals between GT inspections,” in the 4Q/2005 issue of the COMBINED CYCLE Journal. It can be accessed at www.psimedia. info/ccjarchives.htm. Lifetime extension was covered in the W251 Users Group report, which can be found elsewhere in this issue.

Upgrade packages and other enhancements for the D5 fleet offered in support of the interval- and lifetimeextension programs were described by Kain following Caso’s presentations.

Rotor exchange program. Brad Steinebronn, manager of major and refurbished equipment programs, said there are several reasons a user might need a replacement rotor. One of the most obvious: replace an ageing rotor to allow continued operation of the unit. A rotor exchange also can help mitigate repair risk and allow a unit to return to service quickly compared to alternatives.

The Siemens rotor program was developed to make a limited number of spares available to the operating fleet. Service- run rotors from various frames have been acquired by the company, qualified, and made ready for service. Current stock includes one W251B11-12, one W501D5, one W501FC, and two W501FD rotors. Siemens is looking to add a D5A rotor to the program.

I&C life-cycle support was addressed by Ron Hitzel. It focused on (1) Siemens’ new Web-based T3000 control system designed to replace the Unix-based Teleperm XP (TXP) and earlier controls and on (2) combustor dynamics protection.

Most of the information included in the D5/D5A presentation already has been published in “Upgrading controls to maximize performance, availability,” COMBINED CYCLE Journal, 2Q/2006, p 111. Background on combustor dynamics can be found in “Monitoring—and mitigating— combustion dynamics,” p OH-61, 2007 Outage Handbook supplement inserted in the middle of this issue. ccj