Grand Coulee Dam: Third Powerplant Overhaul Project

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Projects to be Completed Prior to the Overhauls

Replacing 500 kV Cables with Overhead Lines

The degraded condition of high voltage cables that transmit power from the TPP and across the dam to the switchyard constitutes an unacceptable risk for loss of generation. The nine oil-filled cables for G-19, G-20, and G-21 have been operated near or above their continuous current rating for 30 years. Because they cross the river in a common underground tunnel, failure of one cable has the potential to destroy all nine cables and take all three generators out of service for at least one year. It was just such an event in the other tunnel carrying G-22, G-23, and G-24 cables which forced those units off-line in 1981. It took a year to install temporary overhead lines to get G-23 and G-24 back on-line, and until 1985 for installation of the permanent replacement cables to be completed.

Replacing these cables with overhead transmission lines will remove the potential of one cable failure causing the loss of 2,100MVA or more of generation. A conservative estimate of lost power sales revenue for one year of outage of three TPP units is over $139 million. If the value of availability is considered, the loss is estimated to be $177 million. Both of these values assume by-pass lines can be designed and installed within 12 months.

Modifying the Fixed-wheel Gate Repair Chamber for Blasting and Painting

This project will modify the chamber to allow blasting and painting of TPP fixed-wheel gate components and be in compliance with Life Safety and Electrical Codes. At present, the wiring is not explosion-proof, ventilation is inadequate, separation from dam galleries is inadequate, and lighting is inadequate. All these factors lead to potential violations of code requirements if work is undertaken during seasons when blasting and painting cannot be done outdoors. Fixed-wheel gates from the six TPP penstocks can be moved by gantry crane from their individual chambers to this modified chamber for repair or refurbishment.

The project is well underway, with planning and VE studies completed, and final design scheduled for completion in May 2009. The next phase, procurement, will cover purchasing, installing, and commissioning the new equipment using traditional procedures.

Rehabilitating TPP Cranes

There are six cranes which will see heavy use during the TPP unit overhauls. There are three upper bridge cranes, one 2,000-ton lower bridge crane, one draft tube gantry crane, and one forebay gantry crane. It is imperative that they all be in excellent working order prior to the overhaul work for use by contractors and the GCPO in order to prevent unplanned crane outages that could result in costly delays in the overhaul schedule.

Repairs and upgrades of these cranes in preparation for overhaul was the subject of a crane consultants’ inspection and report that was completed in September of 2008. This TPP work is intended to be combined with rehabilitation of other facility cranes as long as the TPP work can be completed prior to the generator overhaul contract.

The consultants’ recommendations have been reviewed and utilized to prepare preliminary design concepts. The concepts have undergone Value Engineering (VE) study to ensure that needed function and value were addressed in selecting the final alternatives for design.

New Material Storage Building

Overhaul of the TPP turbines and generators requires lay-down space for all turbine and generator parts as they are removed. These and other incidental parts will occupy nearly all of the TPP floor space. There are a variety of spare parts and pieces presently being stored in the TPP that need to be removed in order to provide the needed overhaul lay-down space. These valuable and easily damaged spare parts need to be kept in a secure, covered, and heated storage space. The proposed new storage building will be built to provide this space in a location convenient for movement of materials to and from the TPP. Preliminary plans for this building include a 100-foot by 200-foot floor area with 30-foot walls, 30-foot by 28-foot door (same opening as the north TPP door), insulated walls and ceiling, heating and cooling, forced ventilation, power, compressed air, and a life safety system with fire suppression.

The GCPO facilities are considered part of a historically significant area. As such, this new storage building cannot detract from the overall appearance of the area. The storage building will be much smaller than the TPP and will retain the historical context of the site.

The general size and requirements of the building have been established and the VE study has been completed. Design of the building is scheduled to begin in June 2009.

Asbestos and Lead Paint Abatement

The Contractors performing work on existing equipment need may encounter asbestos or lead paint on some of the existing components. This is typically not an issue for components manufactured after 1980, however, these units were completed prior to that year for the most part. Tests have confirmed that lead and asbestos do exist. The units will be cleaned prior to the overhauls by Reclamation and contractors who specialize in this field. The overhaul Contractors must be prepared with appropriate safety equipment, procedures, and trained staff to test for, handle and dispose of hazardous materials should they be encountered.

Permitting and Coordinating Activities

National Environmental Protection Agency (NEPA) compliance must be considered for all activities associated with the TPP overalls. Impacts to the environment need to be defined and addressed appropriately. Additionally, the GCPO facilities are considered part of a historically significant area. As such, any activity that could impact the overall appearance of the area could have an adverse effect and should be avoided if possible, and mitigation for the action applied if the action is unavoidable.

TPP 236 MVA Transformer Replacement

New transformers will replace the six single-phase 236-MVA transformers comprising the generator step-up transformer banks for generators G19 and G20. These banks of transformers have been in continuous service since 1975. Identical transformers in an adjacent bank were replaced in 2002 because of deteriorating conditions. When these types of transformers deteriorate they produce flammable gases within the cooling oil. Close monitoring is required to prevent gas build up and the potential for explosion. Due to potential for explosion, access to this transformer area has been restricted. An explosive failure could damage cable circuit terminations and adjacent transformers which would compound immediate power loss and lengthen recovery time. Spares for these transformers are not available in the Northwest. Design for this project is complete and the procurement process is scheduled to begin in July 2009.

Rehabilitation of Two TPP Elevators

There are two freight and personnel elevators which will be in continual use during the TPP overhauls. One elevator is in the Turbine Erection Bay at the southern end of the TPP and the other in the Generator Erection Bay at the northern end of the TPP. It is imperative that both are in excellent working order prior to the overhaul work in order to reduce potential for elevator outages and costly delays in the overhaul schedule. Scoping for this project has been initiated and design is scheduled to begin in July 2009.

Last Update: June 10, 2009 2:10 PM