501 D5/D5A Users Group: Issue #1

IEEE standards may not sufficiently address grounding issues in rotor, stator windings

There are two, unfortunately common, generator-winding failure modes that the IEEE standards overlook: the fracture of a rotor (field) conductor and the fracture of a stator conductor. This article describes these types of failures, discusses associated negative impacts of them, and recommends corrective actions.

   On rotor windings, IEEE Standard C37.102 implies that a single ground may not be a major concern, except for exposure to a double ground. But on turbine/generator rotor windings, experience has shown that single grounds, which result from the fracture of a rotor-winding electrical conductor, can cause dangerous burning of rotor forgings. more

Engine vibration continues as a top concern of 501D5-D5A Users

The 501D5-D5A Users can be characterized as an intimate group, historically attracting about two-score attendees to its annual conferences and vendor fairs, fewer at the "mid-year" meetings in January. Most attendees have been repeat participants, several from far-away places like Korea and Indonesia, with the typical user knowing perhaps half of the owner/operators in the room. more
Hawaiian Electric advances the use of biodiesel as a gas-turbine fuel
State-mandated renewable portfolio standards are designed to shift the production of electricity from fossil fuels and nuclear power to wind, solar, biomass, and other green alternatives. The standards differ among the three-dozen states that have established RPSs with regard to the percentage of kilowatt-hours that must be produced from renewables by a given year. Hawaii has the most challenging rules in the nation, requiring its utilities to produce 40% of their net electricity sales from renewable resources by the end of 2030 (25% by the end of 2020). more
Consider replication to verify metallurgy of buckets/blades after restoration heat treatment

To achieve the creep rupture life expected from a gas-turbine bucket/blade, and to ensure reasonable mechanical properties, the airfoil's microstructure must have the ideal shape and distribution of its constituent phases, reminded John P Molloy, PE, of M&M Engineering Associates Inc, Leander, Tex, in a telephone call to CCJ's offices.

   The primary beneficial phases of interest are the gamma-prime and carbide constituents, he said.  The first probably is the most scrutinized phase during microstructural evaluation, and often is used to determine if a blade requires refurbishment. Carbide shape and distribution is similarly important, but often takes a back seat to the gamma prime in condition assessment. more

501D5-D5A users share major maintenance, repair experience
During the closed session at the recent 501D5-D5A Users Group meeting, discussion transitioned from engine vibration concerns to maintenance outages, experience with conventional and extended-life parts, repairs and coatings, etc-a cornucopia of subject matter. One attendee with a pending major inspection polled the group for experiences in using contractors for this work. Standard practice at his facility has been to perform maintenance outages with plant personnel under the direction of an OEM technical advisor. This has worked well over the years, but a multitude of projects would prevent staff from doing the work on the upcoming major. He was leaning toward hiring the OEM or Mitsubishi to perform the outage. What was the group's experience? more

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