OEM presenters focus on helping 501D5-D5A users maximize unit reliability, availability

The 501D5-D5A Users and Siemens Energy work well together. There are squabbles to be sure, but the group’s steering committee of Chairman Gabe Fleck, Lonnie Grote, and Barry Mayhew has been working closely with key members of the Siemens team—Mark Kamphaus and Jeff Kain, in particular—for the last decade, allowing the participants to develop meaningful professional and personal relationships. 

Program development for the users’ meetings is a collaborative process with the information needs of owner/operators as the primary objective. OEM presentation topics for the mature D5 and D5A engines lately are rapid-fire updates on equipment solutions in development and continuing issues, making the program lively and compelling. The goal: Maximize reliability, availability, and operational flexibility while meeting expectations with regard to emissions, efficiency, and safety.

To illustrate: At the group’s 19th annual meeting in Tucson, June 2-4, Siemens speakers covered four topics in an hour on one morning (including Q&A), six more in an 80-min afternoon session, and then a few more, plus a vibrant open discussion session, in two hours the following day. All the material presented is available to registered users via the OEM’s Customer Extranet Portal; if you are unsure how to access the CEP, contact your Siemens representative.

There’s no time for daydreaming at this conference. First-timers (one-third of the nearly 40 Tucson attendees) can get “lost” on unfamiliar topics, but user-only discussions strategically positioned between the OEM sessions provide the background and perspective on important issues to ensure all attendees benefit from the information disseminated. No question goes unanswered.

Fleet stats, technical advisories. Kain, manager of technical integration for the D5 and D5A engines, introduced the Siemens program to the group and updated attendees on fleet-wide statistics. Reliability, availability, and starting reliability continued to meet expectations. Technical advisories were reviewed next—including upgrade of the exhaust bearing removal tool, publication of a technical bulletin on the rubbing issue associated with the last three rotating stages of the turbine section, and recommendations for dealing with rotor vibration. Last includes relocation of the exhaust-bearing vibration probes.

An update on cracking of inlet-manifold splitter plates and struts experienced by some users included a reminder on the availability of an inspection service bulletin (SB4-13-037-GT-EN-01) as well as enhancements to mitigate cracking. A cutback mod to minimize the probability of splitter-plate cracking is available for side-entry units, the group was told; a solution for top-entry units is under development. The mod has been used successfully on 501F and G engines. Likewise, the bolted-strut mod for 501F and G engines also is available for the D5 and D5A fleets.

Turbine axial rubbing has been experienced by some users. The OEM’s investigation of the issue, which began more than three years ago, indicates rubbing is the result of a permanent loss of axial clearance caused by vane deflection and blade-ring distortion. Also that rubbing occurs primarily during startup because of the thermal growth differential between the turbine shaft and the casing.

The ongoing project suggests the following operating changes may help affected owner/operators mitigate rubbing:

      • Over-cool disc cavities 2 and 3. This is believed to reduce the rate of permanent displacement.

      • Follow OEM guidelines regarding a hold at full-speed/no load during startup.

      • Slow down the engine load ramp rate.

Work continues in the monitoring and analysis of data and of evaluating potential improvements.

A tutorial on combustion system basics closed out the morning session. The drawings and explanations of system design and operation were particularly valuable for first timers, but also a good refresher for most of the others. The value of automated combustion tuning was part of the discussion.

Spin cooling and turning-gear operation took center stage after lunch. Tough to keep attendees engaged following a D5-D5A noontime feast that included a dozen or more dishes, but this was a hot topic of interest to virtually all attendees. Spin cooling was recommended to help avoid possible rotor thermal issues. Users were told the temperature gradient experienced when spin cooling is not included in the shutdown process can cause upward bowing of the cylinder and loss of blade-tip clearance at the rotor mid-section. Damage to airfoils and the casing can occur.

Recommended was a 5-min spin cool on shutdown, an hour on turning gear, another 5-min spin cool, and then turning gear until disc-cavity temperatures drop below 150F. Periodic turning-gear operation, or a high-speed spin for a few minutes before restart, likely will prevent high vibration on startup.

The speaker suggested the following three options to maintain rotor health after cool down:

      • Stay on turning gear (TG) to prevent rotor bow and keep the unit in a state of operational readiness. But keep in mind that extensive turning-gear operation can cause serious wear issues.

      • Take the unit off TG. This can cause a temporary rotor bow, requiring pre-start measures. Recommendation: 12 hours on turning gear before restart, or one hour on TG followed by a 5-min spin.

      • Turning-gear time reduction by periodically moving the rotor 180-deg from its previous position. One unit using this method over the last several years reduced its time on TG by more than 95%.

Rotor and casing inspection and evaluation. Ongoing work in RCIE indicates that at about 100,000 hours of service, wear and tear of rotor components becomes noticeable. The speaker said that’s the time to get the rotor into the shop to “reset the clock.” Here are some of the things that might be found at the second major:

      • Torque-tube indications.

      • Baffle-seal groove wear.

      • Compressor disc embrittlement—specifically in the 12Cr material used to make discs for Rows 12-19. The users were told embrittlement reduces a material’s resistance to crack propagation and that crack-initiation events may include one or more of the following: forging inclusions, low-cycle fatigue (LCF), heavy corrosion, foreign or domestic object impact on airfoils or the wheel, disc migration. 

Data from RCIEs are compiled by the OEM and analyzed to help both Siemens and customers make better risk assessments and better decisions regarding component repair/replacement.

Moisture reduction in the casing is important to reduce deterioration of units forced to spend long periods of time on standby. A warm-air purge was one solution recommended. It reduces the humidity of air inside the GT during turning-gear operation by raising the temperature of air (electric heater) circulated through the unit. Another method is to use a desiccant wheel to pull moisture out of the air inside the GT (used on one 501G). This requires installation of a damper or deployment of a duct balloon inside the inlet air house.

Bolted compressor rotor. Compressor rotors for D5 and D5A engines have shrunk-on discs—not conducive to fast starting. The first bolted rotor for the D5 and D5A frames (Fig 1), similar in design to the 501F rotor, has been retrofitted on the D5 at Capstone’s Cardinal Power in Canada. Benefits include a straighter rotor, improved material (low alloy steel) and longer life, the capability to start within 10 minutes, and an a 2-MW increase in unit output with no change in heat rate. Commercial acceptance of the rotor was in May 2015.

Siemens 1, 2

The Siemens presenter discussed the 64 thermocouples and 14 strain gauges installed on the rotor to monitor its performance over time (Fig 2). Data are transferred to the OEM’s engineers via an advanced telemetry system. Cardinal Power’s maintenance manager, Barry Mayhew, presented on the complete upgrade project during the user-only portion of the program. Siemens reported that all clearances, vibration, temperatures, and other parameters of interest were within specs.

Rocky Road. An OEM presentation on the last day of the meeting detailed the upgrade of the gas-only 3 (D5A) × 0 Rocky Road Power Station, East Dundee, Ill, to include black-start capability. The project, completed in only eight months (three days ahead of schedule), required a considerable electrical analysis and design effort to assure the functionality required by the grid operator (PJM). This work included identifying which of the existing electrical equipment could be reused.

The speaker noted challenges imposed by (1) cold weather, (2) the additional engineering and procurement effort required because of scope changes, and (3) having to perform the T3000 and E3000 retrofits in parallel. Here are some of the project highlights:

      • Two diesel/generators were installed to power the nominal 2000-hp starting motors and 1000-hp gas-compressor motor drivers serving each of the D5As. Having two diesel/generators instead of one provides more inrush-current capability than one unit of equivalent output, the presenter said.

      • Soft-start motors for the gas compressors because the existing auxiliary transformers were not able to serve all auxiliaries at one time using standard motors.

      • The compressor motor control center was arranged for dual feed.

      • The diesel/generator delivers power to the 13.8-kV unit bus during a black start.

Lessons learned included the following:

      • Do black-start test and commissioning plans early in the design review stage.

      • Have separate site leads for I&C and electrical work (one person did both at Rocky Road) to improve onsite communication.

      • Allow the installation contractor to schedule and manage selected onsite services to simplify project execution.

      • Avoid design changes after contract award to not jeopardize on-time delivery of equipment. At Rocky Road, design changes caused the short-circuit study to become the critical path and delayed peer reviews. The delayed short-circuit study results also forced schedule delays for onsite services.

      • Consolidation of day-to-day MV switchgear functions with black-start functions created challenges for installation and control schemes.

 

 

 

 

 

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