Emergent Generator Re-wedge
Mechanical Dynamics & Analysis (MD&A) performed an emergent generator rewedge for a 260 MW Alstom® generator on-site in Mexico.
The original work scope involved electrical testing of the generator rotor and stator, along with the removal of the retaining rings to inspect the insulation and blocking under the rings.
Upon inspection of the stator, greasing was observed but more imperative, about 80% of the wedges were found to be loose. MD&A experts recommended the replacement of the wedges, including an updated design to an increased number of shorter wedges with a top ripple spring (TPS) system to allow for more uniform compression. The customer accepted this recommendation.
Because this was a new and improved design and there was a very limited outage window in which to perform the work (24 days), original wedge samples were hand-carried internationally across the border to MD&A’s wedge supplier in the USA. MD&A and the customer coordinated logistics to have a customer quality engineer hand-carry the samples to the manufacturing facility.
Samples were delivered for the start of manufacturing within 24 hours despite a snowstorm that canceled connecting flights. The customer representative, stationed at the manufacturing facility, monitored production and quality and reported daily status to the on-site team.
The wedge samples were measured and the newly designed wedge drawings were produced using CAD/CAM software and passed the manufacturer’s engineering review process within hours. A group of wedges were manufactured the next day and were delivered on-site for installation within 48 hours.
In parallel with new wedge manufacturing, MD&A experts were repairing the damaged semi-conductive coating on several bars.
Once the initial batch of wedges was received on-site, they were fitted and minor adjustments were performed. This information was communicated to the wedge manufacturer and incorporated in engineering drawings & remaining wedges.
The wedge manufacturer made and shipped the replacement wedges in batches to allow MD&A to continuously install new wedges while performing other work in parallel, increasing productivity. The collaborative coordination between the customer and MD&A continued as the last batch of wedges was received on-site.
Upon inspection of the generator rotor, it was discovered that the blocking under the retaining ring was cracked. Normally, repairing the blocking would require the removal of the retaining rings. MD&A’s generator specialists developed a method of repair to the blocking that could be performed with the rings in place. This was desired, as removal of the retaining rings can often require the replacement of the ring insulation prior to reassembly.
The customer accepted MD&A’s recommendation and repair method. The cracked blocks were replaced to the customer’s satisfaction. This saved the customer both schedule time and cost. The customer commented that the MD&A generator technician that performed the work “was a true artist” as he shaped the blocking to fit.
This project was completed within 21 days, and below budget.
MD&A is known for our technical expertise, responsiveness, and commitment to customer service. Our willingness to offer pragmatic solutions and our ability to marshal the required resources quickly is well recognized and respected within the industry. In addition to the project described above, MD&A’s capabilities include the overhaul, repair, and supply of parts for steam or gas turbines and generators worldwide.
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