Comprehensive Generator Stator and Field Rewind

Mechanical Dynamics & Analysis (MD&A) recently completed a generator stator and field rewind on a GE® 7A3 generator during a planned customer outage. All stator work was completed on-site, and the field rewind was performed at our Turbine-Generator Repair facility in St. Louis, MO.

Stator Rewind

MD&A performed a complete rewind of the generator stator during this outage. The rewind kit supplied by MD&A included new stator bars, connection rings, and end winding support components.

The rewind process began with the removal of the stator wedges and stator bars. Following bar removal, the stator slot walls and core vent ducts were cleaned and prepared for bar installation. The core was both visually inspected and electrically tested using an Electromagnetic Core Imperfection (ELCID) test to identify any shorted laminations that could lead to future overheating and damage. ELCID tests were performed three times throughout the rewind process with no relevant indications found.

New bottom bars and connection rings installed

The winding installation included replacement of the original end winding supports and connection rings. Additionally, Glaskyd sausage (conforming material) was installed in place of the original radial rings between the top and bottom bars in the end winding. Conductive side ripple springs were installed to ensure proper electrical contact between the slot wall and the bar. Following bar installation, a contact measurement test was performed to ensure the bars were properly grounded to the core.

New connection rings were then installed, all series and phase connections were brazed using induction heating. The bars were appropriately blocked, and the series loops were insulated with two-piece molded caps filled with insulating epoxy filler. Following stator slot wedge installation, all final electrical tests were completed with excellent results.

Field Rewind

Once removed from the stator, the generator field was identified with damaged end-winding blocking. The field was then sent to our Turbine-Generator Repair Facility in St. Louis, MO.

Incoming electrical testing was completed once the field arrived in St. Louis, confirming multiple shorts within the field winding. After the retaining rings were removed and the unit was inspected, MD&A recommended a full rewind to remove the shorted turns and properly adjust the end-winding blocking. After the rewind was authorized by the customer, the unit was stripped and cleaned. During this time, all removed components underwent a complete visual and NDE inspection. Indications were noted on one of the snap rings. Ultimately, the customer elected to have both snap rings replaced at the same time.

After the copper windings were removed, electrical testing was completed on the bore copper and collector rings with acceptable results. The coils were blast cleaned and inspected. Following inspection, the coils were deemed suitable for continued operation and returned to service. The wedges were blast cleaned and sent for NDE inspection. The field body was blast cleaned and underwent NDE inspections. All NDE results were satisfactory, and the field body was repainted. The field forging and field body wedges were returned to service.

Removal of copper coils from field

After each coil was re-installed, an AC Hi-Pot test was performed, and an AC turn-to-turn test was completed. A baker surge test was then completed on each coil to ensure that there were no shorts present in the winding.

The turn insulation was coated on one side with heat-cured glue. This glue required a bake cycle of the rotor after it was wound. After the bake, a full set of electrical tests were completed and the unit underwent a high-speed balance, two heat runs (with a flux probe test after each heat run). All test results were acceptable.

MD&A is a full-service, OEM-alternative for generator service, parts and repairs with a 35+ year track record of successful generator stator and field repairs. All inspections and necessary repairs are completed by our experts in a timely manner that allows units to be placed back online on an expedited basis.

Call MD&A today for any generator repair at +1 (314) 880-3000 or use our Contact form.

View the video to see how you can minimize costly outages by having our expert technicians perform your next full stator rewind.

 

 

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