Incoming visual and mechanical inspections were first completed, as well as a runout inspection in the lathe which resulted in machining the turbine end journal to fix high runout in this area.

As found electrical data was then collected on the generator field by completing a 500V winding insulation “Megger” test, an AC impedance test and testing for shorts within the field winding.

After testing, the retaining rings were removed, and a full blocking inspection was performed. Significant blocking damage was found which resulted in replacing the entire blocking scheme with the MD&A recommended blocking.

Additional damage was found during wedge removal, which revealed 320 wedges with significant arc damage of about 2-3 arc marks per wedge. The wedges were successfully repaired by removing a thin amount of material from the effected wedge face. After which, they were cleaned and underwent non-destructive evaluation (NDE.)

With the wedges and copper completely removed, the field was glass bead blasted and underwent NDE. HiPot testing was then performed on the inboard and outboard collector rings as well as the respective bore copper with satisfactory results.

Prior to reassembly, the copper coils were sent out for blast cleaning. The rotor body and the field body wedges were glass bead blasted. The field body was then cleaned, followed by additional NDE. The non-destructive examination revealed multiple arc marks throughout the field forging body. A formal recommendation was made to remove these indications which was accepted by the Customer.

Repairs involved machining a relief to both sides of the dovetail where the wedges meet, as well as changing the #1 slot wedges from steel to aluminum, which incorporate larger end radii. The field then underwent a second NDE which resulted in no indications.

After each coil was checked and installed, they were AC Hi-Pot tested and turn-to-turn tested. A baker surge test was also completed on each coil to ensure that there were no shorts present in the winding. The turn insulation was then coated on one side with heat-cured glue, which required a bake cycle of the rotor after winding.

After the bake, a full set of electrical tests were completed including a 500V Megger test, a winding resistance test, an AC impedance test, a pole balance test, an RSO and a complete DC turn to turn test. A full set of electrical tests were also completed after the retaining ring insulation was installed and repeated after the retaining rings were installed. All results were satisfactory.

After a heat run and electrical testing were completed in our high-speed balance facility, the field was staked and painted and prepped for shipment. Before the field was shipped, a final outgoing Megger test was completed.

The generator field rewind was then complete with a Rotor Slot Dovetail Repair.

MD&A is a full-service OEM alternative for generator service, parts, and repairs with an over 30-year track record of successful generator stator and field repairs. We focus on delivering consistent quality and value with fast response, superior communications, and innovative solutions that meet or exceed OEM alternatives.

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

The post Field Rewind with a Rotor Slot Dovetail Repair appeared first on MDA Turbines.

The blockage of the radial ventilation passages results in reduced hydrogen gas cooling flow, which can lead to thermal instabilities with the rotor leading to excessive rotor vibration and forced outages.

View the video to see how you can have our experts repair your 7FH2 Generator field. For additional information call MD&A’s Generator Division today at (314) 880-3000 or use our Contact form.

The springs migrate axially within the slot:

Also, see MD&A’s Solution for 7FH2 & 324 Stator End Winding Dusting Issues

See all our Gas Turbine Services offerings from major inspections to capital parts to control systems!

The post MD&A 7FH2 Spring Migration Repair appeared first on MDA Turbines.

Our reputation for accuracy and reliability in power plant services has spanned over 30 years. Our technical expertise and effective project management will get the job done on time and within budget.

MD&A provided our customer with a replacement 7FH2 generator field. MD&A’s gas turbine maintenance team removed the original generator field from the site and shipped it to our St. Louis turbine-generator repairs shop for refurbishment. As well as, we sent the new generator field to St. Louis for a complete test and inspection, and high-speed balance before being brought to site.

The scope of work also included:

• The replacement generator field was removed from a unit in storage, and sent to the St. Louis Repair facility, and subsequently installed at the customer site.
• The unit was re-assembled with a new 7FH2 field with the existing #4 bearing installed and a new #3 bearing. Both were cleaned and measured, before installation.
• All new oil deflectors were used on both ends, inner and outer.
• The coupling faces were cleaned, inspected, and found to be in good condition. MD&A performed a 16-point alignment.
• New hydrogen seals were lapped and installed with existing cases.
• The air shields were cleaned and reinstalled and torqued to OEM specifications.
• The generator air test was performed, and the results were within acceptable limits.

After MD&A performed its checks, the unit started up without issues.

The gas turbine maintenance team replaced the faulty field with the new one under very difficult circumstances during the peak of the outage season. MD&A made this project happen in a few weeks from start to finish.

MD&A also performed minor repairs on the customer’s steam turbines as well, including a turning gear replacement and thrust bearing adjustment.

MD&A’s specialized services range from Combustion, Hot Gas Path and Major Inspections, as well as, Compressor & Turbine Rotor Repairs to Plant Performance Testing and Analysis. We also provide turbine internal alignment to your gas turbine, along with vibration analysis and balance (low-speed & high-speed.)

Call our Gas Turbine Services today at (518) 399-3616 or use our Contact form.

The post 7FH2 Gas Turbine Generator Repair appeared first on MDA Turbines.