MD&A was contracted to perform a Generator Major inspection, to provide a GE® 7FH2 Generator Field Replacement and perform an onsite Stator Rewind. The scope included full disassembly, mechanical inspection, maintenance and replacement of related components to accommodate the new rotor. The generator field that was extracted onsite received a field rewind and high speed balance, and was placed into the MD&A’s field exchange fleet.
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.
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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.
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