Mechanical Dynamics & Analysis (MD&A) was contracted to bring its expertise to a planned major outage of a GEC Alsthom® / Alstom Generator in the United Kingdom.
The unit is part of a steam-and-gas installation with the steam turbine located between the gas turbine and the generator.
This project exemplifies not only MD&A’s global turbine generator service commitment, but also its reputation as a worldwide service provider with extreme attention to all details, and expertise on all system components regardless of age or original equipment manufacturer.
Alstom® Generator
After generator rotor removal, MD&A experts performed onsite generator stator testing, including visual inspections of end windings, end winding support and core in addition to back iron areas.
Initial inspection showed areas of oil pooling and greasing that were cleaned by MD&A. Inspections of the core laminations did not show any evidence of heating, damage, fretting or movement. No greasing of slot wedges was found, and no debris was found in the core areas.
MD&A’s baseline pressure decay test results indicated that the unit did have significant leaks in the stator winding cooling system.
Electrical and mechanical testing in this project also included winding insulation and polarization index, ELCID core iron testing, wedge mapping, bump testing, and qualitative thermocouple function tests, among others.
Hose Replacement
As part of this system outage, the owner/operator contracted MD&A to replace all generator Teflon cooling water hoses and perform the associated tests and inspections. All Teflon cooling hoses were manufactured by MD&A’s Turbine-Generator Repair Facility in St. Louis, MO, and were onsite well ahead of the need date.
The owner/operator requested that MD&A replace all the seals at all terminal locations. This additional work included replacement of all O-ring seals in the terminal connections (4 per terminal).
The radial O-ring that seals the interface between the gas-side terminal and the top of the bushing was the primary leak point. Further, there is a separate connection point above the bushing that has an identical connection point with two identical seals. All four seals were replaced on all six terminals.
Hoses were installed with new O-ring seals and connection points were contoured with mica/epoxy then insulated with mica tape saturated with air-dry epoxy. An outer layer of glass tape was applied to the insulation before painting.
MD&A testing with localized helium tracer gas followed by pressure decay testing indicated that the leaks were repaired.
MD&A HIT Skid
Using the MD&A Hydraulic Intensity Test (HIT) Skid, the full scope of testing listed in TIL-1098 (Stator Bar Water Leaks)was performed including blowdown, dry-out, vacuum- and pressure-decay testing, and helium tracer gas investigation.
The MD&A HIT Skid was placed on top of the generator on a custom-built scaffold to conserve limited turbine deck space.
Specific testing included evacuation and drying of stator windings, pressure and vacuum decay, helium tracer gas, capacitance mapping of all stator bars, and ultrasonic flow testing of the stator cooling water system (SCWS) following hose replacement.
Doppler Flow testing, end-winding frequency response (Bump) testing, wedge tightness mapping, winding resistance, and electromagnetic core imperfection detection (ELCID) tests were also performed. Follow-up recommendations were prepared for the owner/operator.
The unit was then prepared for return to service.
If your next project needs assurance that every system detail has been both tested and expertly serviced for long-term continued operation, talk to the global industry experts at MD&A regardless of system age or original equipment supplier.
MD&A is a premier, non-OEM service provider to the worldwide steam and gas turbine generator industry. Call us in the U.S. at +1 (518) 399-3616 today or use our contact form.
