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Grand Coulee Dam: Third Power Plant Overhaul Project

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This project will involve overhauling turbines G-19 through G-24 in the Third Power Plant. The units have been in service since the mid-1970s and have been heavily used over the years. Their condition has deteriorated to the point that complete overhaul is necessary to ensure these machines will continue to operate reliably. Work will be performed on generators, turbines, shafts, and auxiliary equipment with the overall goal of ensuring another 30 years of dependable service.

Units G-19 through G-21 are equipped with 820,000-horsepower Francis turbines, designed by Dominion Engineering Works, Ltd., and manufactured by Willamette Iron and Steel Company with a runner throat diameter of 34 feet. Units G-22 through G-24 are equipped with 960,000-HP Francis turbines, designed and manufactured by Allis-Chalmers with a runner throat diameter of 32 feet.

Generators G-22, G-23, and G-24 are rated to produce a total of 2,415 Mega-Volt-Amps (MVA) with an annual power production value of over $100 million. The units have begun to show age-related component wear. These units will be overhauled first because they are in worse general condition than units G19-G21. The work will include inspecting, refurbishing or replacing worn mechanical and electrical components, including bushings, seals, controls, and deteriorated wiring. Stator cores or windings for Units G-22, G-23, and G-24 were replaced recently and should not need attention beyond inspection and cleaning. Rotor will be inspected and repaired as needed.

Units G-19, G-20, and G-21 will be up-rated in overall unit capacity with new generator and turbine components. The Third Power Plant (TPP) turbine runners do not appear to need refurbishment since they receive regular cavitation repair and their up-ratings have been determined not to be economically justifiable.

Reclamation is preparing for the overhaul outages by identify specific repair needs, performing detailed analysis, performing design work, and seeking contracts for work to be completed prior to overhaul. A considerable amount of the Planning and Design work is being accomplished in partnership with Architect-Engineering companies under contract with Reclamation. These efforts will result in improved reliability of equipment that is needed to support the overhaul, will identify ways to minimize outage durations, and will reduce the likelihood and magnitude of increases to outage time.

In accomplishing the overhaul a large amount of lay-down space is required for all turbine and generator parts as they are removed. More space is required during the overhauls than for initial construction when parts were delivered as needed. Each unit has several large and heavy items that require special consideration:

  • Upper bracket (diameter approximately 83 feet)
  • Rotor (diameter approximately 58 feet)
  • Main support bracket (diameter approximately 45 feet)
  • Head cover (diameter approximately 35 feet)
  • Operating ring (diameter approximately 25 feet)
  • Three main shaft sections which must be stored in a vertical position

It is expected that these large parts will occupy most of the TPP floor space except for access aisles needed to move smaller components.

In order to refurbish the existing parts, at least two temporary buildings may be erected adjacent to the TPP. One would be for machining and assembly of parts and the other for blasting and painting of parts. The actual sizes of these buildings are not known at this time but are estimated to be at least 120 feet by 120 feet for the machining and assembly building and 60 feet by 120 feet for the blasting and painting building.

 

Last Update: June 25, 2013 11:39 AM