During the disassembly and replacement of all flexible leads, it was observed that some of the assemblies were too short. The customer arranged for the removal of all asbestos-containing material associated with the flex lead assemblies. This allowed the new flexible leads to be fit and drilled, which created a more uniform bolting configuration with a larger contact surface.

The installation process also involved properly torquing the stainless-steel bolts, distribution plates, and nuts. Textolite barriers were installed over the flexible leads and were secured in place with glass tape. The final assembly was then insulated using fusible rubber tape, with an outer layer of raw glass tape, varnished and then tag painted.

Two sets of Generator Stator electrical tests were performed, pre and post flexible lead replacement. The Customer requested that both sets of tests be performed with the unit assembled and under a pressurized carbon dioxide blanket. There were negligible differences between the before and after readings, and all values were consistent with past testing results.

Additionally, MD&A’s experienced team performed on-site testing and inspections of the Generator Stator and Field during a scheduled minor outage, which included visual inspections and a complete series of electrical tests.

A comprehensive visual inspection of the Generator Stator’s Bushing Box revealed a large crack in T3’s Stand Off Insulator (SOI). Once the customer arranged for the removal of the potential asbestos-containing material, the flexible leads, tubular lead, and clamshell were removed, and the old SOI was replaced. The SOI, tubular lead, and clamshell were loosely assembled to ensure proper alignment. All the components were fit checked to be stress-free.

Once all components were verified to be in proper alignment, the SOI and tubular lead were secured in place. The clamshell was blue checked at the HVB (High Voltage Bushing) and tubular lead contact surfaces. Once all component assemblies were verified, the bolting hardware underwent an initial torque. All bolting hardware was torqued a second time, 24 hours later. The assembly was then insulated using fusible rubber tape, with an outer layer of raw glass tape, varnished and then tag painted.

The following series of electrical tests were performed on the Stator while under a pressurized CO2 blanket:

• Winding Copper Resistance
• 5000VDC Insulation Resistance
• DC Leakage
• Hipot
• RTD Resistance and Insulation Resistance Testing
• Flux Probe Resistance Reading
• HIT Skid (Vacuum and Pressure Decay Testing)

A series of electrical tests were also performed on the Field while under a pressurized CO2 blanket, including:

• Winding Copper Resistance
• 500VDC Insulation Resistance
• AC Impedance Testing

All electrical tests were found to be in accordance with OEM Specifications.

Upon completion of the job scope, and a thorough review of inspection observations and test data with the customer, the unit was returned to service.

MD&A is proud to have served the needs of the customer on repair and parts replacement for their generator, providing exceptional quality of workmanship that met their expectations.

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. We focus on delivering consistent quality and value with fast response, superior communications, and innovative solutions.

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

The post Generator Flex Lead Replacement 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.