Coordination and comprehensive planning and scheduling were the pivotal keys to success of this complex work that included rings-off generator fields, diaphragms, steam turbine rotors, valves and actuators, and a variety of related items including parts supply.

Consolidated scheduling, communication, accurate reporting and corporate-wide commitment flawlessly united to ensure customer and MD&A-wide confidence in this landmark achievement.

Multiple Divisions

The focal point was the one-stop shop, MD&A’s Turbine Generator Repair Facility in St. Louis, MO, and encompassed various divisions including Generator, Steam Path, Machining Services, as well as the Ohio-based Bearings, Seals and Hydraulics Division.

The precision-based and long-established service and manufacturing capabilities of MD&A joined forces to seamlessly complete each detail of this multifaceted and time-dependent outage.

Scope

Overall scope of work included inspection and repair of 9A4 and 7FH2 generator fields, two HP rotors, HP and IP diaphragms, spill strip supply and installation, two sets of valves and two sets of actuators, and critical parts supply.

Generator

Upon arrival in St. Louis, MD&A completed rings-off testing, inspection and permanent blocking replacement of two steam turbine generator fields. Electrical testing showed unsatisfactory results and mechanical inspection indicated noticeable dishing of the collector rings. These would be honed and polished. Existing amortisseurs showed heat damage and axial cracking, requiring replacement by MD&A.

Existing blocking was replaced with the MD&A strap and tie design. These unique axial blocks have spring forces acting in opposite directions to add interference to prevent any unwanted axial or radial movement of the blocking after installation.

After repairs, the fields were moved to our high-speed balance facility in St. Louis where heat runs with electrical testing were successfully completed. Fields were then moved to machining services for collector ring work scope, including hone and polish. The fields were then final inspected by the Generator Division before returning to site.

Detailed recommendations were prepared for ongoing operation. In addition, MD&A recommended a full rewind at the next rings-off opportunity.

The two gas turbine generator fields also received complete inspection and repair. Mechanical testing indicated noticeable dishing in the collector rings. Slot spring misalignment was found.

Blocking would be replaced with the MD&A strap and tie design. Inspection showed that vent holes for the coils were partially blocked, which can result in reduced hydrogen gas cooling flow, leading to thermal instabilities with the rotor leading to excessive rotor vibration and forced outages.

Our experts performed a unique, patented 7FH2 generator field repair process (top hat modification) that eliminated the axial migration of slot leaf springs that restricted the air flow. Collector rings were honed and polished to correct the dishing.

The following components received non-destructive examination: snap rings, retaining rings, and field wedges. Because these gas-turbine units are hydrogen-cooled, pressure decay testing was performed.

After machining services work was completed, fields were released to the high-speed balance facility, then to the Generator Division for final inspection and shipping preparation.

Steam Turbine Rotors

MD&A conducted detailed inspection and repair of the steam turbine rotors in St. Louis. Upon arrival the rotors were visually, dimensionally and non-destructively inspected. Repairs were conducted and detailed recommendations were made for long-term operation.

Dimensional, run out and non-destructive evaluation (NDE) inspections (including metallurgical evaluations) yielded minor findings that were addressed. Minor indications were identified, reviewed and dispositioned. Low speed balance and a full quality inspection was completed prior to return to service.

Minor repairs completed consisted of:

• Rabbet fit restoration via peening and machining
• Minor bucket repairs were completed by MD&A’s expertly trained bucket technicians
• Deburring and cleaning to remove any stress riser concerns, and
• Low speed balance

All detailed data inspections, repairs and as left conditions, including future repair recommendations were included in final reports to support future planning.

Valves

Example valve repairs, following complete inspection, included the following:

1. Main Stop Valve
   1. Installed new stem & anti-rotation key
   2. Lapped the pressure seal head backseat to achieve a 100% blue contact check
   3. Installed a new stem/disc nut anti-rotation pin and staked, torqued and blue checked to the disc
   4. Machined the pressure seal head gasket face to correct runout and true it to the bushing bore
   5. Ground & polished the main disc seating surface to remove runout and surface imperfections

2. Control Valve
   1. NDE revealed indications in the nitride around the disc OD, a new disc was purchased and installed
   2. New disc nut anti-rotation pin for the was installed and staked into the new disc

3. Turbine End Reheat Stop Valve
   1. Honed pressure seal head bushing tight spots to restore design clearance to the stem
   2. Lap the pressure seal head backseat to achieve a 100% blue contact check
   3. Performed a weld buildup on the pressure seal head casing fit and machined to restore clearance to the steam chest on-site
   4. Machined the pressure seal head gasket face to correct runout and true it to the bushing bore
   5. Ground & polished the main disc seating surface to remove runout and surface imperfections
   6. Installed a new stem anti-rotation pin
   7. Installed a new disc cap bolt

4. Generator End Reheat Stop Valve
   1. Honed the disc bore to restore design clearance to the stem
   2. Honed pressure seal head bushing tight spots to restore design clearance to the stem
   3. Lap the pressure seal head backseat to achieve a 100% blue contact check
   4. Machined the pressure seal head gasket face to correct runout and true it to the bushing bore
   5. Ground & polished the main disc seating surface to remove runout and surface imperfections
   6. Installed a new stem anti-rotation pin

5. Intercept Valve #1
   1. Honed the disc bore to restore design clearance to the stem
   2. Restored the split ring ID to stem OD design clearance and verified
   3. Ground the split ring face in the surface grinder to restore the design stem lift
   4. Stoned the seal ring face to restore the axial clearance upon valve reassembly
   5. Ground & polished the main disc seating surface to remove runout and surface imperfections

6. Intercept Valve #2
   1. Honed the disc bore to restore design clearance to the stem
   2. Restored the split ring ID to stem OD design clearance and verified
   3. Ground the split ring face in the surface grinder to restore the design stem lift
   4. Stoned the seal ring face to restore the axial clearance upon valve reassembly
   5. Ground & polished the main disc seating surface to remove runout and surface imperfections
   6. Installed a new seal ring bolt

At MD&A’s Bearings, Seals and Hydraulics in Ohio, two sets of steam turbine valve actuators (Rexroth and MOOG) were completely refurbished. The refurbishment included disassembly, cleaning, and inspection of all components. All soft parts and sealing parts were replaced, and in some instances some critical components were replaced, and this includes the following: large disc springs, piston shafts, servos, solenoids, LVDT components, packing glands, bushings, piston rings. Additionally, some components were restored using chrome and grind restoration methods to reestablish critical dimensions.

After repairs were complete the actuators were re-assembled, fluid flushed and tested at 110% operating pressure with the same fluid used at site. This ensures that the actuators function properly and ensures that the actuators are leak free during operation.

This testing greatly reduces the need for field troubleshooting and adjustment on site during start-up.

Explore the Benefits of MD&A

These Steam Turbine-Generator Majors and repairs led to their life extension, continued operation and longevity of the plant in the future.

Mechanical Dynamics & Analysis enjoys a firmly-established global reputation as a reliable and trustworthy non-OEM service firm with deep roots in all major OEM products and developments. MD&A’s professionals are up to date on all industry issues and offer these benefits:

• Comprehensive service and precise coordination.
• Multi-talented MD&A personnel in multi-faceted long-established facilities.
• One-stop gas turbine, steam turbine and generator point of contact for estimating, scheduling and project execution.
• Long-term operating assurance and operating guidelines for the owner/operator.
• All backed by MD&A’s world-class corporate commitment.

No job is too complex for MD&A. To discuss and schedule your next turbine generator service and repair project, contact the experienced professionals at MD&A. Call us at (518) 399-3616 today or use our contact form.

The post Quadruple Steam Turbine-Generator Majors with Precision, Breadth, and Coordination appeared first on MDA Turbines.

In the power generation industry, reliability and efficiency are paramount. Gas turbines, such as the 7FA series, are critical assets for utilities, and their performance directly impacts grid stability and profitability. Periodic major inspections are essential to ensure these machines operate within OEM specifications and maintain compliance with environmental and safety standards.

For this combined project, MD&A provided all tooling, supervision and labor to perform the outage work scope.

• 7FA Gas Turbine Overhaul: Complete disassembly of the compressor, combustion, and turbine sections for inspection and refurbishment.
• 7FH2 Generator Inspection: Disassembly and electrical testing of the 7FH2 generator, including stator and field assessments.
• Technical Information Letters (TILs): All TILs were completed.

As part of the outage, the inlet filter house and ducting were visually inspected internally down to the inlet plenum and confirmed to be in sound operating condition.

A customer-supplied, refurbished gas turbine rotor would be installed after MD&A inspection.

Arrival

Once onsite, tooling preparation and disassembly began, working two shifts. All as-found clearances were measured, and initial alignment checks were completed.

Turbine compartment scaffolding and field stands were installed, and preparations were made for removal of both the gas turbine rotor and the generator field.

Throughout disassembly, all reusable materials were identified, stored, and prepared for reuse.

7FA Gas Turbine

Following turbine casing and bearing removal, compressor component inspection and repairs began. Inlet guide vanes (IGVs) were inspected and would be returned to service. IGV inner bushings and spring/thrust washers were replaced. Bearings were replaced as needed.

Oil deflectors and seals were prepared for shipping to MD&A Bearings, Seals and Hydraulics Division in Ohio for inspection and repair. New seals would be required.

Stator compressor blades S1-4 and S5-8 were worn and replaced. Several rows exhibited foreign object damage (FOD) and casing pinch marks, requiring precision blending and vane replacement.

For the combustion section, chamber components revealed wear and coating damage. MD&A experts replaced the following with either new or refurbished parts: liners, flow sleeves, crossfire tubes and retainers, liner caps, FWD cans, TP bull horns and transition pieces. Check valves were also replaced. Fuel nozzles were swapped and flow-tested to ensure proper atomization.

For the hot gas path, First-, second-, and third-stage buckets and nozzles were installed with concentricity and clearance checks verified against OEM tolerances. For the exhaust, flex seals were replaced with new pins installed, and the diffuser was weld-repaired.

A new Bearing T1 was replaced. T3 and T4 bearings were also transported to MD&A Bearings, Seals and Hydraulics division in Ohio, refurbished, returned, and reinstalled. The T1 thrust journal was also replaced.

Degraded gaskets were replaced in the discharge casing, and the casing received blend repairs.

7FH2 Generator

At project start, generator shaft jacking devices and eyebrows were installed. Our team constructed our generator field support platform to allow for easy removal of the field when performing this 7FH2 Generator Major Inspection.

This system addresses the unique challenges associated with the 7FA/7FH2 configuration:

1. The shaft centerline height is 13 feet above machine baseline (grade)
2. The gas turbine inlet ducting and filter house limit crane access.

MD&A’s team removed the turning gear and disassembled the journal bearings, and shipped them to MD&A Bearings, Seals and Hydraulics division in Ohio for refurbishment. Oil deflectors and hydrogen seals were also prepared for shipment.

After end shield and fan blade removal, MD&A experts removed the generator field for covered storage on the turbine deck. The field was inspected, and field windings were found to be clean.

The generator end shields and gas shields were inspected, cleaned, and returned to service.

MD&A performed high-resolution borescope visual inspection of normally inaccessible areas on the generator, outside of the bore region. These areas include under the collector and turbine end retaining rings and the stator end windings, field coil end turns, auxiliary components and stator terminal connections.

The generator stator received visual inspection, insulation resistance testing, winding resistance measurements, DC leakage and RTD tests, and wedge inspection. The field received visual inspection, insulation resistance testing, winding resistance and impedance tests, and turn-to-turn pole balance.

T3 and T4 H2 casings were removed, visually inspected and sent to MD&A Bearings, Seals and Hydraulics division for further inspection and repair. New seals would be installed with refurbished casings.

New T3 and T4 lift oil lines were installed.

Stator testing revealed that more than one-third of the wedges were loose and/or hollow. MD&A experts therefore performed a complete rewedge on the generator stator. A full stator wedge tightness survey map followed.

The new turning gear was installed and aligned, followed by the hydrogen leak check. The gas turbine/generator load coupling was aligned to OEM specifications.

Rewedge on the Generator Stator

Completed Stator: New Rewedge, Painted

Startup

Precision alignment was critical to minimize vibration and extend component life. Rim/face checks were performed and coupling bolts were replaced.

The unit was started on schedule and tuned with no issues.

Long-term recommendations to increase owner/operator confidence in continued operation included monitoring of the T3 area, ongoing inspections of variable inlet guide vanes, filter house visual and mechanical checks (with specific details), water washing frequency, and monitoring CDC (compressor discharge casing) slip issues.

MD&A’s multi-divisional team of experienced technicians and product experts successfully completed the GE 7FA gas turbine major inspection and 7FH2 generator major inspection on schedule. The project demonstrated MD&A’s ability to coordinate cross-divisional resources and execute complex inspection and repair scopes. Detailed recommendations were also provided to support long-term reliability, giving the customer assurance of a well-executed outage and confidence in future full-service operations.

For service of any generator regardless of original design, contact the premier non-OEM service provider to the global turbine-generator market. Call us at (518) 399-3616 today or use our contact form.

The post 7FA Gas Turbine and 7FH2 Generator Major Inspections appeared first on MDA Turbines.

MD&A has an inventory of new or refurbished generator fields in our field exchange fleet, featuring the latest in rewind technologies. Additionally, we have stator rewind kits with stator bars available in stock, ready to support planned or forced outages.

Disassembly and Component Inspection

MD&A’s experts disassembled the generator and inspected critical components in the process.

Our team conducted visual and non-destructive examinations (NDE) on the load coupling Riverhawk bolting. No indications were found – all components successfully passed VT and UT requirements before being returned to service. The unit’s generator bearings were also inspected dimensionally and visually by our technicians before being sent to MD&A’s Bearing, Sealing and Hydraulics Division for refurbishment and sizing to ensure proper fit for the new field journals.

Rotor fan blades were removed, hand-cleaned, and subjected to NDE and visual inspection before being returned to service with new locktabs during the final installation. Hydrogen seal components were also examined, with MD&A providing new seals properly sized to the refurbished rotor configuration and lapped to the refurbished gland specifications.

Our technicians sent the H2 gland seals to MD&A’s Bearing, Sealing and Hydraulics Division for segment replacement and housing refurbishment. Oil deflectors were  modified for insertable teeth design before being reinstalled and aligned to shaft specifications. In addition, our experts removed and replaced the old seal carrier.

Stator Rewind

During this planned outage, MD&A’s team performed a full stator rewind. Our onsite experts performed baseline and post-disassembly ELCID testing to assess stator core iron integrity, with all results indicating acceptable lamination condition. The existing opposing wedge system was then removed by the team.

Our personnel removed series loop connections, circuit ring connections, and top and bottom bars. Core compression flange nuts underwent breakaway torque verification. Several nuts were found to be well below OEM specifications. Our team cleaned the mating surfaces and retorqued all nuts.  Following core tightening, the belly bands were tightened with new shim packs installed.

New 7FH2 bars were installed with proper alignment verification. Our technicians completed electrical testing, which included hi-pot tests at specified voltages, with all phases achieving resistance results within target ranges.

Impressively, this all was completed within 21 days. MD&A has a consistent track record of handling rewinds of this complexity, including core and belly band tightening, within the same timeframe.

Field Spare Rewind

Our team also conducted a field rewind on the 7FH2 generator field. Our technicians disassembled the unit, which included removal of the bore copper and collector rings. The field forging underwent media blasting and comprehensive non-destructive examination (NDE), including magnetic particle testing on the field body and penetrant testing on wedges and retaining rings. All NDE results were satisfactory.

During reassembly, our generator experts installed newly insulated bore copper, main lead studs, and coil components in a controlled, clean room environment. Each coil underwent individual electrical testing before installation and clamping. The field completed a successful bake cycle during which the coils were compressed to their specified diameter via bake clamps.

Throughout the rewind process, MD&A’s engineers performed thorough electrical testing. These tests included: insulation resistance, polarization index, AC impedance, winding resistance, as well as repetitive surge oscillation (RSO), turn-to-turn testing, pole balance, and AC hi-pot. Once fully wound, the field was then high-speed balanced, which included a heat run before the unit was staked, painted, and wrapped for storage.

Reassembly and Alignment

The arrival of the refurbished generator field marked a pivotal moment in the outage. Our team constructed our generator field support platform to allow for easy install of the field. This system addresses the unique challenges associated with the 7FA/7FH2 configuration: 1) the shaft centerline height is 13 feet above machine baseline (grade), and 2) the gas turbine inlet ducting and filter house limit crane access.

During reassembly, MD&A’s technicians performed a 16-point turbine-to-generator alignment. The stator was repositioned to meet OEM specifications. The newly rewound replacement field was then carefully set into place, followed by the installation of lower half bearings with precise tilt and twist measurements recorded.

All of the generator’s systems were returned to service with proper clearances and operational parameters verified.

Conclusion

This multi-faceted scope, including a 7FH2 generator field replacement and full stator rewind, demonstrates the technical complexity and precision required for successful power generation equipment maintenance.

The project required specialized expertise across multiple disciplines. Our ability to coordinate these complex activities with our expert knowledge of OEM specifications and decades of field-proven success exemplifies why power generation customers worldwide rely on MD&A to keep their assets operating reliably.

Call us at +1 (314) 880-3000 today or use our contact form.

The post 7FH2 Generator Field Replacement with Stator Rewind appeared first on MDA Turbines.

Unit disassembly began with MD&A’s Outage Services Division crew mobilizing to site and setting up the outage plan.

During the disassembly, all critical as-found measurements were taken, recorded, and transmitted to both MD&A Engineering and the owner/operator.

After removal of bearings, oil/hydrogen deflectors and seals, eyebrows were installed, end shields lowered and support brackets removed. Hydrogen coolers were removed and MD&A’s experts withdrew the field from the stator core.

A complete list of replacement parts, bolts and gaskets needed for reassembly was prepared. Bearings were inspected and FME protection was installed, as 330H stator bar shipments arrived from MD&A stock.

Stator Rewind and Repairs

The phase connections were stripped and unbrazed from the connection rings which allowed for ease of rewind and much needed replacement, due to known cracking issues in similar models.

Series connections and top bar ties were cut for bar removal. A base-line electromagnetic core imperfection detection (ELCID) test was performed before wedge removal to determine integrity of the as-found core laminations.

The existing tapered wedge system was then removed by traditional methods and MD&A’s procedure. Although the wedge system had recently been given a clean bill of health by another provider during a previous in-situ wedge tap, it was obvious that the entire wedge system was loose, allowing premature aging of the bar ground wall insulation and likely a contributor to the failed insulation.

Series loop connections were removed. Original circuit ring connections were unbrazed and removed showing poor condition, to be replaced with new parts manufactured by MD&A. Top bars were then removed followed by inner radial rings for access to the bottom bars.

After bottom bar removal, core cleaning began followed by a post-disassembly ELCID. During cleaning, MD&A also replaced high-voltage bushings (HVB) with new O-ring seals.

Stator bar installation then began.

All tie materials were saturated with air-dry epoxies for more-solid bonding, limiting any loosening post installation. All bar ties and phase blocking ties were made with epoxy saturated “8-strand” glass roving.

Previous side ripple spring (SRS) abrasion was a concern. MD&A generator engineering improved the SRS design to prevent abrasion issues that have led to premature failure in several similar units. This process was followed on each end of the bar for the top and bottom bars.

Following completion of bottom bar installation and electrical testing, inner radial rings were installed, and resistance temperature detectors (RTDs) were placed in slots. Top bar and side ripple spring installation was completed, followed by full electrical testing.

New slot wedges were installed. Significant attention was given to the wedge system to ensure proper and tight installation. Compression of the top ripple springs (TRS) is a vital part of ensuring that the wedge system is correctly installed. TRS are installed to provide constant force overtime as the slot build materials relax and potentially loosen. The system is designed to make up for this relaxation with their inherent spring forces.

Each wedge was tested with an electronic hardness tester to ensure adequate TRS compression and to use as a baseline for future inspections.

Following wedge installation, a third and final ELCID test was performed to ensure no core laminations were damaged by the wedge installation process, and the original flux probe was installed. Another HiPot was performed to ensure that the bar ground wall insulation had not been damaged by wedging activities.

Series and phase brazing began. Brazing was performed with specialized double-headed torches for heating the plate/bar assembly. The phase and jumper connections were completed with the new plates manufactured by MD&A. Phase connection insulating series cap installation and all blocking completed the generator rewind work.

After completing all brazing work, copper winding resistance was measured to ensure that each of the three phases produced nearly identical resistance, indicating quality braze connections.

Final electrical testing was performed to ensure all components were ready for service.

The MD&A team is confident in the quality of the rewind completed on this generator. The bar ties installed are of the strongest and most durable type available in the industry. The wedge system is tight and the top ripple springs are compressed to 90%.

Reassembly

The generator coupling flange had an indication on the rim, so our Engineering team created a 3D model and performed a stress analysis to confirm it was in a low stress area.  It was recommended to blend out the indication and the 3D model confirmed the final geometry maintained full capability of the coupling flange. The blended area was polished and a final NDE (dye penetrant inspection) of blended area confirmed the indication was successfully removed.

Ongoing inspections included fan blades, bearings, load coupling bolts, hydrogen casings, oil deflectors and all coolers. Bearings were inspected and cleaned.

Hydrogen seals were measured and inspected. Bluing of the seals to the casing determined that lapping was required for acceptable contact.

With hydrogen coolers and shields reinstalled, the field was prepared and inserted into the stator. Inner oil deflector clearances were reset to limit the ingestion of seal oil into the unit.

All axial fan blades were inspected, verified, and returned to service. Six collector fan blades, showing trailing ends tip blends, were replaced.

The load coupling was aligned to OEM specifications.

Return to Service

The global team of MD&A experts returned this 330H generator to full service and renewed owner/operator confidence in its ongoing contribution to dependable electricity demand in the home country.

MD&A stocks stator bar sets for 330H, 324, 7FH2 and several other commonly found generator stator models.  MD&A is ready to mobilize anywhere in the world at a moment’s notice to support your emergent or planned outage needs

Contact the premier non-OEM service provider to the global turbine-generator market. Call us at +1 (518) 399-3616 today or use our contact form.

The post MD&A Completed 330H Generator Stator Rewind appeared first on MDA Turbines.

MD&A provided all project management, inspection and analysis, supervision, labor and tooling for the owner’s dual-unit work scope.

During disassembly of the first unit, MD&A Gas Turbine Services personnel first removed roof sections, recorded thrust and lift checks, removed all relevant casings, and labeled/removed relevant piping/hoses. Half shell readings were taken on the turbine and compressor by recording all rotor and stator tip clearances.

The service run 7FA.04 hot gas path components were inspected and analyzed onsite by specialists from MD&A’s San Antonio Service Center to determine the potential for future component repairs. Our team has extensive knowledge on a range of gas turbine component repairs, including weld repair, blending, dimensional restoration, and machining. They can extend the service life of gas turbine components whose OEM service limit has passed or whose configuration is no longer suitable to operate. These experts provided feedback on the component repairability.

For these outages, the turbines’ first, second, and third stage buckets were removed and replaced with Customer provided components.

Additionally, nozzles and shrouds were removed and exchanged. For the compressor, stage 14 through EGV’s stator vanes were removed; new vanes were drilled and pinned upon installation.

MD&A inspected T1 and T2 bearings and determined replacements were required, in addition to new thrust bearings.

All combustion components were removed and inspected. Transition pieces, liners, flow sleeves, outer bellows, inner crossfire tubes and fuel nozzles were exchanged during reassembly.

The GE® 7FH2 generator was disassembled, including coolers, oil deflectors, gas shields and bearings. Hydrogen casings and seals were removed and sent to MD&A’s Bearings, Seals and Hydraulics Division in Euclid, Ohio for refurbishment.

The generator field was then removed and transported to our Turbine-Generator Repair Facility in St. Louis, MO for a complete field rewind utilizing the existing copper. The rewind process was expedited to allow for the rewound field to be installed in the sister unit. A spare generator field from the Customer’s inventory was installed on the first unit, to support the expedited outage schedule.

MD&A experts inspected the generator stator and found areas of greasing indicated a loose wedge structure and necessitating a full stator rewedge. Core and bellyband tightening was also required.

Stator electrical testing was completed, and electromagnetic core imperfection detections (ELCID) tests were conducted before and after wedge replacement.

MD&A’s Generator Experts replaced the wedges, then completed bellyband and core tightening. With the stator repairs complete, the generator field from owner/operator’s inventory was able to be installed.

During component reassembly, new hydrogen seals and springs provided by MD&A’s Bearings, Seals and Hydraulics facility were utilized.

Following reassembly of the gas turbines and generators, coupling alignments were performed by MD&A technical experts in full collaboration with the Owner/Operator.

MD&A’s Turbine and Generator Controls Division performed a complete inspection of the exciter and inverter equipment, ensuring no issues on return to service. Startup was completed with no operational concerns and full compliance with emissions standards.

Following execution of the first outage, MD&A personnel shifted focus to the sister unit, to complete a nearly identical work scope.

For this unit, turbine first, second, and third stage buckets were replaced as were nozzles and shrouds.

A spare Customer provided Gas Turbine rotor was installed after conducting green rotor inspections and repairs. At startup the green rotor run-in was completed in compliance with industry standards.

As with other unit, all Technical Information Letters were listed as completed, as were all Extra Work Authorizations.

For this unit, the service run generator field was removed for transport to our Turbine-Generator Repair Facility for a complete field rewind utilizing the existing copper. This field would be rewound and returned to Customer after the outage to be held as inventory.

Conclusion

Throughout these major overhauls on two 7F.04 Gas Turbines and 7FH2 Generators, detailed daily written and visual (photographic) job reports and updates documented all current and planned activities, alerts, needs, schedules, recommendations, and resolutions.

For every repair job, large or small, the speed and effectiveness of our response team is matched only by the depth and breadth of our engineering expertise.

Successful completion of these back-to-back projects clearly exemplifies the multi-divisional breadth, versatility, and corporate commitment of MD&A as a premier non-OEM service provider to the global gas and steam turbine-generator market. Call us at (518) 399-3616 today or use our contact form.

The post Back-to-Back Major Overhauls on Two 7F.04 Gas Turbines and 7FH2 Generators appeared first on MDA Turbines.

In fact, MD&A established itself in the beginning as the preferred non-OEM supplier, regardless of original supply or design.

Founded in 1982, MD&A takes great pride in the extensive OEM experience, knowledge, and skills of both its technical experts and management personnel.

A recent case in point: MD&A performed a full stator rewind of a GE® 7A7 generator that suffered an in-service ground fault failure. In order to meet the owner/operator return-to-service schedule for the stator rewind, the owner operator called in MD&A. The rewind was completed on schedule with no safety incidents or concerns, and the unit passed all detailed testing for return to operation.

Specialists from MD&A’s Generator Division arrived on site and completed all site-specific training, walkdowns, and tool staging.

Initial baseline testing, physical measurements, and winding configurations were confirmed. Stator end windings and core were scanned and modeled to aid in the manufacture of new stator bars. To meet the return-to-service schedule, MD&A experts were able to get the new bars quickly.

A baseline electromagnetic core imperfection detection (ELCID) analysis was performed on the stator core iron to determine the integrity of as-found laminations.

The existing wedge system was then removed according to MD&A procedure. Series loop connections were removed and collector-end circuit ring connections were cut.

After bar tie removal, top bars were removed, stacked, and placed in recycling containers. Inner radial ring and bottom-bar ties were then removed, followed by all bottom bars.

Significant levels of partial discharge were noted on several bars with high line-to-neutral voltage potential.

T4 connection ring inspection found material missing at the extension, likely a source of discharge during the generator failure. The T2 ring showed damage at the phase-strap location.

All connection ring pieces were removed and inspected to be repaired and reinstalled. Damaged pieces were replaced with newly-manufactured material. A DC HiPot test was then completed on the circuit rings. A post-disassembly ELCID was also performed to ensure no damage to the core iron, and a loop test confirmed the integrity of the stator core.

For reassembly, binding bands were received and aligned on both ends and made concentric to the core – a vital step for proper bar alignment and consistent felt buildup.

Binding bands were installed and bar installation began. A thin felt layer in each slot served as a bottom breaker between the bar and core iron.

After close-up bar installation, bottom bars were installed and permanently tied with blocking, saturated felt, and saturated roving ties. Side-ripple springs were installed to secure proper seating and avoid any vibrational movement. A bottom-bar Hi-Pot verified the integrity of bar armor insulation.

At this point, a total of 12 new Resistance Temperature Detectors, more accurate than traditional thermocouples, were installed, terminated, and verified. Inner radial rings were installed and top-bar installation began, followed by comprehensive Hi-Pot testing.

For wedging, a tapered low-shrink black canvas (LSBC) wedge and slide design with a top ripple spring was selected for sufficient radial pressing force. Filler was adjusted at each wedge for proper compressive force. Center and body wedges were installed throughout the core, followed by end wedges cut specifically for each of the 72 slots.

Brazing was completed by traditional method and MD&A procedure, and a winding resistance test ensured that the three phases produced similar resistance values. Series, circuit ring, and jumper connections were then installed. The insulating tape used by MD&A ensures no voids or cracks form along the phase breaks during operation, where the voltage potential is the greatest. Series blocking was installed and tied to reduce vibrational movement. Frequency response testing followed.

After the generator stator rewind, comprehensive electrical testing included copper and insulation resistance, final DC HiPot, and DC leakage testing of each phase. All testing results were verified and accepted.

A final crawl-through inspection was completed with the owner/operator. Field installation could begin, and the generator would soon be returned on schedule for dependable, long-term operation.

Once again, MD&A has shown the global electric utility industry its depth of knowledge, finely-tuned technical skills, and repeatedly-proven owner/operator commitment.

MD&A is truly a premier non-OEM service provider to the global gas and steam turbine-generator market. Call MD&A about your next outage today at (518) 399-3616 or use our Contact Form.

The post MD&A Generator Stator Rewind with Timely New Bars appeared first on MDA Turbines.

As a result, over 40 years later, MD&A has evolved from a small firm to a large service provider with over 600 employees reaching more than 100 customers each week during outage season.  The reputation for outstanding service in the US has enabled MD&A to spread globally with parts, repairs, and services on large turbine-generator sets.

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MD&A provided all tooling, supervision, and labor to perform the planned generator major inspection outage scope.

This generator life extension project exemplifies MD&A’s position as a preferred non-OEM one-stop organization throughout the turbine-generator industry.

Generator enclosure

After removal of all attachments, MD&A experts held the critical lift meeting and removed the 24,000 lb generator enclosure and installed all FME covers, removed upper half T4 and T5 bearings, and prepared the base for generator field removal.

The field would be prepared and transported to MD&A’s Turbine-Generator Repair facility in St. Louis, MO. The T4 and T5 bearings and inner and outer oil deflectors would be transported to MD&A’s Bearings, Seals and Hydraulics division in Euclid, OH for inspection and repair.

Scaffolding was then installed for the generator rewind activities.

Coolers were removed from the TEWAC assembly and cooler heads were disassembled. New isomode pads were prepared for the reinstall.

Stator

This was a planned stator rewind, scheduled as preventive maintenance due to significant observed partial discharge. Over time, this could lead to a ground fault condition and forced outage.

A baseline electromagnetic core imperfection detection (ELCID) was performed on the stator core iron to determine the integrity of the as-found laminations.

The existing flat wedge system was removed by traditional methodology and MD&A procedure.

Top bars were then removed without issue, using come-alongs to remove the bars out of individual slots. Bottom bar removal was completed in the same manner. Significant levels of partial discharge were found on several bars.

Following full visual inspection, all connection ring blocking and ties were removed and replaced with new conforming material. A post-disassembly ELCID was performed to ensure no damage to the core iron. Each of the 72 core slots were cleaned of all contaminants and thoroughly inspected.

A core knife test determined the need for complete stator core tightening, completed by MD&A procedure. At the completion of torque activities, an additional ELCID was completed with satisfactory results.

Once received, binding bands were aligned axially and made concentric to the stator core. Three bottom bars were then fit into slots 120 degrees apart to ensure proper alignment. Two top bars were also aligned with the pitch of the bars to ensure the top and bottom bar series plates were properly aligned.

A thin layer of insulation was installed in each slot, and bottom bars were then installed and bottom-bar testing was performed.

A total of six dual-element RTDs were removed during disassembly and were replaced with twelve new dual-element RTDs and operation was verified.

All top bars were then installed, blocked and tied, with no issues.

A tapered wedge and slider design with a top ripple spring was selected to provide sufficient radial pressing forces. Following all winding activities, a final ELCID was performed to ensure no damage to the core iron.

After brazing, a winding resistance test was performed to ensure each of the three phases produced similar resistance values, and all other electrical testing was completed with good results.

Field

Following removal of the generator field the customer opted for a generator field exchange. We sent a refurbished field to site that had been completely rewound with the latest in rewind technology. The field forging had undergone NDE and inspections to ensure long term viability, along with it being high speed balanced with a full heat run to ensure no shorted turns. The exchange of the generator field produced a shorter outage duration which allowed for the customer to be back online sooner.

The original generator field was transported for complete inspection and rewind. On arrival in St. Louis, the field received in-depth visual and mechanical inspection. Three-dimensional scanning and hand mechanical dimensions were obtained.

During disassembly, indications were found on a few field body wedges, and some material damage was found on both retaining rings. All field coils were removed and sent for cleaning.

The cleaned coils were determined fit for service and reinstallation began.

Each installed coil was HI-POT and turn-to-turn tested. A baker surge test was also completed on each coil. During the rewind process, the MD&A standard strap and design blocking was installed. Turn insulation was coated, requiring a rotor bake cycle. After the bake cycle, a full set of electrical tests was completed.

The field was then moved from the clean room to the shop floor to install retaining rings and complete the electrical testing. It was then moved to the high-speed balance facility. After balance, it was staked and painted and prepared for exchange sale.

Isomode Pad 

During this project, the TEWAC assembly was removed. Mating surfaces with the generator enclosure were cleaned and weatherstrips were installed. Generator cooler heads and all piping were cleaned of corrosion and buildups, and new gaskets were installed.

The generator stator was raised to remove the old isomode pads and shims. The MD&A team cleaned the area and installed new isomode pads with pre-existing shims.

The TEWAC assembly was then reinstalled.

Summary

All MD&A inter-divisional work was performed on schedule without any injuries or accidents.

There were no issues with turbine-generator synchronization during startup.

Once again, the MD&A organization drew on its experience and multi-divisional expertise to complete a major inspection and repair project and ensure owner/operation confidence in continued unit operation.

MD&A is truly a one-stop shop! Call MD&A about your next outage today at (518) 399-3616.

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Here are the significant initiatives we have in place to ensure continuous growth and development within our organization.

Mentoring Program and Succession Planning

Kristin Esterby, our Human Resources Director, addressed the critical need for effective succession planning, particularly as many of our seasoned professionals approach retirement. “We’re facing a unique challenge with our workforce,” Kristin noted. “Not only are we navigating the aftermath of the COVID-19 pandemic, but we also have an aging workforce.” This demographic shift necessitates proactive measures to maintain our high standards of service and expertise.

To address these challenges, MD&A has implemented several strategic initiatives:

• Succession and Talent Planning: Our approach focuses on evaluating individual performance, setting clear goals, and creating tailored development plans. This ensures that our employees are prepared to step into critical roles as they become available.
• Mentoring Programs: We are in the process of developing both formal and informal mentoring programs. These initiatives aim to facilitate knowledge transfer between experienced leaders and newer employees, fostering an environment of continuous learning and growth. Technical-specific mentorships are also being established to address the unique challenges of our industry.

Kristin emphasized the importance of these programs in bridging the knowledge gap and ensuring a smooth transition of expertise. “Mentorship is not just about transferring knowledge; it’s about building relationships and creating a culture of support and mutual growth,” she explained.

Learning and Training (LEAP)

One of our most impactful initiatives is the Leading Effectively at Power (LEAP) program. This week-long training event brings together 20-25 leaders from various divisions to enhance their leadership skills. The curriculum covers crucial topics such as finance, legal considerations, and change management. Participants engage in interactive sessions that promote cross-functional learning and collaboration.

Kristin highlighted the dual benefits of the LEAP program: “Participants not only gain insights from our expert instructors but also learn from each other, which is invaluable for their development as leaders.” This collaborative learning environment helps build a cohesive leadership team equipped to handle the complexities of our industry.

In addition to LEAP, we are launching a pilot series called Leadership and HR 101. This program aims to equip our leaders with foundational knowledge in key areas such as human resources and basic management principles. By providing this training, we ensure that our leaders are well-prepared to manage their teams effectively and foster a positive workplace culture.

Engineers in Training (EIT) Program

Charles Monestere, our General Manager of Technical Services, provided insights into the Engineers in Training (EIT) program. Initially, MD&A focused on hiring experienced engineers. However, in 2009, we shifted our strategy to recruit recent graduates, recognizing the value of fresh perspectives and new talent. This structured program combines intensive classroom training with hands-on, on-the-job experience under the mentorship of our seasoned engineers.

Charles outlined the program’s objectives: “We aim to hire about ten new engineers each year. Our goal is to provide them with a comprehensive understanding of our operations and prepare them for long-term careers with MD&A.” The EIT program has grown significantly since its inception, reflecting its success in developing well-rounded engineers who are ready to contribute to our mission.

Personal Experience: Colin Baker

To provide a personal perspective on the EIT program, Colin Baker, a Field Engineer and recent EIT program graduate, shared his journey. “I joined MD&A straight out of college with minimal turbine experience,” Colin recounted. “The EIT program allowed me to learn from experienced engineers and apply that knowledge in the field.” He emphasized the importance of networking and continuous learning, which are integral components of the program.

Colin’s story is a testament to the program’s effectiveness. He highlighted how the EIT program not only provided technical training but also fostered a supportive environment where he could grow both professionally and personally. “The mentorship and hands-on experience I received were invaluable. It helped me build confidence and develop the skills necessary to excel in my role.”

Looking Ahead

At MD&A, we believe that investing in our people is crucial to our long-term success. Through our comprehensive mentoring and training programs, we are preparing our workforce to meet future challenges head-on while fostering a culture of continuous learning and development. These initiatives ensure that we remain at the forefront of the power industry, delivering excellence and innovation.

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