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.

The post 7A6 Generator Isomode Pad Replacement with Major and Rewind appeared first on MDA Turbines.

The customer contracted MD&A to perform the inspection and emergent repairs on a tight schedule. Our industry experts completed the work on time maintaining full customer communication throughout the outage utilizing our on-site project management.

For the gas turbine, all combustion and hot gas path components were removed, cleaned, and inspected. All required hardware was provided by MD&A. Our San Antonio Service Center, which is our Gas Turbine Parts Service Facility, refurbished all combustion parts of fuel nozzles, combustion system liners, liner caps, transition pieces, and flow sleeves.

The stage 1 nozzle was replaced with a new assembly. The site team replaced both the right and left stage 1 forward wheelspace thermocouple guide tube assemblies. The stage 2 and stage 3 nozzle segments were also replaced. New shroud blocks and new installation hardware were provided for all stages. Moderate fretting was observed that warranted the replacement of the exhaust frame flex seals.

Simultaneously, MD&A experts removed both turbine-end and collector-end upper half end shields to perform a generator minor inspection consisting of stator and field visual inspections, including in-situ robotic inspections, ELCID, and electrical testing.

The Generator Specialist immediately recognized that the stator had significant connection ring damage that could have led to catastrophic damage had it continued to operate.

The solution: MD&A expeditiously removed, reverse engineered, and replaced the damaged components with no impact on the overall outage schedule (5 days total repair time).

Scoring was identified on both the turbine-end and collector-end journals. The lower half bearings had moderate abrasion/scoring. Minor babbit damage was also noted. The turbine-end and collector-end hydrogen gas and air side seals were found in poor condition and replaced.

Winders were mobilized to perform numerous tie repairs on each end of the unit and connection ring replacement on the collector end with the rotor still in place.

As a result of MD&A’s impact testing and modal analysis, additional blocking and ties were made on the connection rings to ensure the unit will not see this type of problem again.

At project conclusion, comprehensive reports were provided listing each step of the process and its engineering rationale, along with detailed analysis and long-term predictions and recommendations.

MD&A site and shop repair teams worked closely together to deliver first-class service. MD&A provides a one-stop shop solution for turbine & generator services, parts, and repairs.

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

The post Coordinated 7FA Hot Gas Path and 7FH2 Generator Inspection and Repair appeared first on MDA Turbines.

These issues can lead to serious damage to the generator if not addressed. A mechanical failure of both pole to pole connectors could lead to an open circuit on the generator field winding or a generator field ground fault.

MD&A has trained personnel who are qualified to inspect a generator field and identify pole-to-pole cracking issues. We can complete this inspection using a borescope during a minor generator inspection (field-installed) or a major generator inspection (field-removed).

If indications of cracking are found during a borescope inspection, MD&A can make repairs immediately. If no indications are found, MD&A experts can implement the solution as a preventative measure during a future outage.

Have MD&A look at your generator field today. Call our Turbine-Generator Repair Facility at (314) 880-3000 or use our Contact form.

The post Alstom® Generator Pole to Pole Connector Modification appeared first on MDA Turbines.

Once the generator rotor was removed, visual inspections confirmed melted copper turns, damaged insulation, and arcing damage to the rotor forging.

Inspections after disassembly (unwinding) of the generator rotor revealed arcing damage to the inboard side of the collector end retaining ring and to the slot wedge above the ground fault area. The rotor forging was then blast cleaned, clearly revealing the severity of arcing damage to the generator rotor forging slot tooth sidewall.

The unit owner/operator asked MD&A to evaluate and perform an analysis of the damage in support of providing a recommendation for running/repairing/replacing the generator rotor forging.

The slot tooth sidewall arc-damaged and heat-affected material was removed, the forging NDE inspected, material composition confirmed, and the geometry of the rotor forging as well as the excavated tooth sidewall obtained. A detailed stress analysis was performed consisting of both hand calculations and finite element analysis for the damaged geometry. The analysis calculated the damaged tooth stresses under centrifugal load for both normal operational speed as well as over-speed. The results of the analysis revealed the current condition was not acceptable for safe and reliable operation.

Solution: MD&A recommended and performed a local weld repair of the damaged tooth section utilizing a weld filler material that met the base material chemistry, strength, and magnetic permeability of the generator rotor forging.

The welding testing for this repair option not only included the typical base material and weld filler material qualifications, but also actual base material HAZ (Heat Affected Zone) testing utilizing a bore ring sample removed from the coupling end of the rotor forging. The results of these tests were utilized in a final weld repair acceptance and remaining life analysis.

Repair of the rotor included: Initial dimensional inspections, nondestructive testing, and rotor runout checks; Weld prep machining to remove a section of the slot tooth; Preheat and weld buildup of the removed slot tooth section; Post weld heat treatment; Rough machining along with both surface and subsurface nondestructive testing; Final machining, final dimensional checks, final nondestructive testing, and final rotor runout checks. The rotor was then released for winding, final assembly, and balance.

A detailed acceptance/life expectancy analysis was performed on the rotor weld repair. The analysis consisted of a 3D Finite Element stress analysis, fracture mechanics calculations, as well as low cycle fatigue calculations. The results of the analysis offered positive results and increased confidence in the repair performed.

Based on the past and expected future operational parameters of the unit, it was calculated that the original rotor material, the deposited weld material, and the HAZ material would conservatively last for 36, 41, and 16 years, respectively.

The repaired rotor was returned to service without any operational restrictions and it was recommended the rotor forging be inspected after ten years of operation or 150 stop/starts, whichever comes first.

This generator rotor tooth local weld repair allowed the unit owner/operator to return to service much quicker than a full rotor forging replacement option.

MD&A experts are there when you need us! Providing comprehensive refurbishment and repair of generator stators and fields for many different OEMs across the world.

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

The post Generator Rotor Slot Tooth Weld Repair appeared first on MDA Turbines.

Rotor field inspections can either be performed on-site or in a shop environment.  Repairs generally require the rotor field to be transported to a qualified repair facility. 

MD&A has developed a field pulling & support system to address 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.

The MD&A system consists of a modular work platform using adjustable rotor field trolley carts to efficiently and safely extract the field from the stator core, providing a stable work platform for on-site inspections and sufficient length to enable crane access to lift the field for off-site repair transportation.

Key features of the system include:

• Modular design work platform for expedited setup/teardown and efficient transportation on standard trailers
• Overall platform length and height can be adjusted based on site and workscope requirements
• Tongue and groove work platform connections and integrated trolley cart rail system provide seamless transitions between platforms
• Wide walkway wings on left & right sides enable worker & equipment access
• Modular safety rail system allows flexible scaffold stair access based on site arrangement
• Adjustable trolley carts use low-friction, self-guided rollers for safe and fast positioning of the field on the platform
• The system is very stable and is rated for continuous use with steady wind speeds up to 30 mph (with minimum 3x factor of safety)

MD&A offers a complete suite of parts, repairs, and services solutions for gas turbine fleets. We focus on delivering consistent quality and value with fast response, superior communications, and innovative solutions.

Call our MD&A Gas Turbine Services today at +1 (518) 399-3616 or use our Contact form.

The post Generator Field Support Platform appeared first on MDA Turbines.

Electric Generators Review (PDF)

MD&A is an exclusive sponsor and can meet all your generator needs!

See you at the 2018 GUG conference where our experts are presenting again!

For additional generator information or for a quote, call MD&A’s Turbine-Generator Repair Facility today at (314) 880-3000 or use our Contact form.

The post Electric Generators 2018 Annual Review appeared first on MDA Turbines.

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.

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

The post Emergent Generator Re-wedge appeared first on MDA Turbines.

As part of its service offering, MD&A provides turbine-generator owners with the engineering know-how to test, analyze, and resolve bushing operation and failures. MD&A provides both the skilled technicians and the maintenance facilities to disassemble, clean, repair, and recondition or remanufacture multiple high-voltage bushings (HVB), simultaneously.

In one repair scenario, a GE® 4-inch hydrocooled HVB arrived with asphalt leaking from the air side of the bushing.

At the start of a rigorous multi-step process, the bushing first was disassembled and its center conductor removed. Remaining asphalt within the equipment was heated and removed using a combination of thermal exposure and immersion in cleansing solution. Technicians completed the cleaning by hand to ensure that all asphalt was out, and that all oxide, sharp edges, and burrs were burnished away.

Bushing reassembly followed, including fresh asphalt. The equipment then was ready to have its porcelain components machined and repaired. Technicians machined off the old flange and the bushing was placed into a sand blasting tent. The technicians then verified that both the flange and porcelain fit areas were clean before reassembling the equipment.

Electrical and pressure tests were conducted using helium as the pressure agent. No loss of pressure is permitted during these tests. A high potential test was conducted with up to 68kV DC gradually applied and then removed. Doing this allowed technicians to look for current leakage throughout the test.

Just before shipping, the bushing was painted and silver plating applied as needed. One final quality control inspection was completed by an MD&A QC inspector who works separate from the shop personnel who did the work. The bushing then was packed and documented in its shipping crate to verify its secure positioning before leaving the MD&A facility.

MD&A’s also provides comprehensive refurbishment & repair of large utility generator stators and fields. Our large generator repair specialists conduct full scope electrical testing, visual inspections and specialty tests as per customer requirements.

Have MD&A look at your high-voltage bushing today, call our Turbine-Generator Repair Facility at (314) 880-3000 or use our Contact form.

Some typical questions regarding HVB:
Q: What is the typical lifespan of a refurbished bushing?
A: 15 to 20 Years

Q: What is the typical timeframe to refurbish a bushing?
A: Non-Expedited is 7 – 10 days, Expedited 5 – 7 days

Q: Does MD&A stock refurbished bushings?
A: Yes – We will also offer same day swap outs.

Q: How many times can a bushing be refurbished?
A: Once

Q: What percentage of porcelains need to be replaced?
A: 5 – 10% – Due to cracks or damage during flange removal.

The post Expert Repair of Generator High Voltage Bushings appeared first on MDA Turbines.

The utility weighed several repair options. These included rotor welding, which would have been time-consuming and expensive, and field replacement, which presented an unacceptably long lead time and high cost. A third option—stub shaft repair—proved to be the best choice in terms of cost and downtime for the revenue-generating asset. MD&A designed and performed the repair, which involved severing the rotor outboard of the collector-end journal and then installing a bolted-on stub shaft.

As part of the repair, the generator rotor shaft end was removed and the bolted-on stub shaft was fitted in the journal outboard seal area. To ensure that no hydrogen leak would occur around this flange face, an O-ring groove and O-ring were installed. Also, to ensure that the new stub-shaft bolted connection could support the assembly torque, as well as, the exciter that bolts to the shaft, MD&A prepared calculations using the original shaft end bore, the key holding the shrunk-on coupling, and the shrunk-on coupling bolting to the exciter.

Machining of the rotor shaft end included severing the rotor just outboard of the collector-end journal in the middle of the outboard oil seal diameter. Once severed, the shaft-end face was milled, drilled, and tapped to allow for a bolted flange, an alignment female spigot, and an O-ring seal groove.

Machining the new stub shaft included all reverse-engineered features of the original collector shaft end. The forging was bored to the original shaft bore diameter to include the bore plug fit. The flange face was machined to include 14 thru holes and a male spigot fit-in support of bolting up to the original shaft. The shaft was machined to include all the fit diameters for the collector rings, the fan hub, and the shrunk-on coupling. Four radial holes were drilled for the collector ring radial stud assembly.

After it was final-machined, the stub shaft was dimensionally inspected and subjected to a non-destructive examination by MD&A. Before the rotor was returned to the customer, final quality checks were completed, including visual, dimensional and electrical tests.

MD&A provides comprehensive refurbishment and repair of utility generator stators and fields, including high-voltage bushing refurbishment and complete rewinds.

Have MD&A look at your generator rotor today, call our Turbine-Generator Repair Facility at (314) 880-3000 or use our Contact form.

The post Generator Rotor Stub Shaft Repair appeared first on MDA Turbines.