Grand Coulee Dam: Third Power Plant Overhaul Project |
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| Other TPP-Overhaul Related Projects |
| The following projects will be initiated prior to TPP overhaul, with the work continuing to be performed concurrent with the overhaul outages. This will reduce the total duration of unit outage time for the TPP. |
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| TPP Exciter Replacement |
Excitation equipment for all six generators in the TPP will be replaced with more robust and faster-acting equipment. Design of the present exciters was state-of-the-art when first supplied in the late 1970s but the components have become obsolete and are very difficult to replace. Recently, one of the 800-MVA generators was forced out of service for several days by the failure of a small choke coil in the exciter regulator circuitry. The time of these failures cannot be predicted. Lost revenue is dependent upon time of year and availability of other TPP generators. An average one week forced outage costs about $250,000, if only the affected generator is out-of-service and up to nearly $800,000 if a second generator is also out-of-service. High value month costs (July) would be approximately 4.3 times higher. The TPP generators have a major role in reacting to normal load swings and also in reacting to power system transient conditions such as loss of critical transmission paths. At present, generation dropping (Gen Drop) opens generator breakers and is used to decrease supplied power to compensate for loss of a similar quantity of load. New, faster responding exciters will allow implementation of modern power system stabilizers (PSS) which will enhance the overall stability of the units and power system. Both Gen Drop and PSS can contribute greatly to stability of the Northwest Power Pool transmission system. This project is well underway, with the design complete and the procurement process scheduled to begin in June 2009. |
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| TPP Governor Controls Replacement |
Governor control equipment for all six generators in the TPP will be replaced with more robust and faster acting equipment. As with the excitation equipment, the design of the present governors was state-of-the-art when supplied in the 1970s but the components have become obsolete and are very difficult to replace. The electric-hydraulic governors are showing problems with obsolete electronic components. The printed circuit cards used epoxy-based operational amplifiers (op amps) which are no longer being made. Op amp failures present themselves as unstable oscillations of hydraulic flow and power output; the associated outage times can be as short as 4 hours. However, repairs to the cards require finding a source and purchasing legacy parts or substituting components which must be connected by wire rather than being inserted in the card. Outage times for difficult repairs can approach one week, resulting in power revenue losses similar to those described above in the excitation equipment replacement program. The governor hydraulic systems are adequate and maintainable so the governor replacement will replace only the electronic components and pilot valve. Digital technology will be specified to modernize components and to gain greater flexibility in load/unload rates and the ability to operate the generator stably if the plant becomes islanded. Accomplishing governor work during installation of exciters should minimize construction outage times since the exciter work will be much more time consuming. This project is well underway, with the design complete and the procurement process scheduled to begin in July 2009. |
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| Temporary Construction Facilities |
| The TPP overhauls will involve inspection and refurbishment of all parts before they are re-installed. In most cases, this will involve sandblasting and coating. TPP parts are larger than can be accommodated in the existing sandblasting and painting facilities in the GCPO Industrial Area. In addition, the parts the contractor brings to the project will require temporary storage, and many of them will require finish machining or assembly onsite. It is anticipated that the contractor will construct two temporary buildings to accommodate the paint, sandblasting, storage, machining and assembly needs. Reclamation is currently addressing the NEPA/Section 106 responsibilities associated with the possible temporary buildings. |
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| New Draft Tube Platform |
| The TPP unit overhauls will provide an opportunity to inspect and, if necessary, to repair the draft tubes. A specialize work platform is needed to complete the repairs, and the contractor performing the overhaul work will be responsible for fabricating it. The platform will be suitable for use on all three units undergoing overhauls. |
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| On-going Maintenance Programs in TPP |
| Throughout the execution of the overhaul program there will be operation and maintenance (O&M) work being performed by Reclamation staff. Units will be taken out of service for routine maintenance needs. Some of this work requires the use of the cranes and requires room for parts and equipment. Cavitation repair of turbine runners will be performed as a part of the routine maintenance and electrical testing of various components and will also be performed with repair work done as needed. These O&M activities may conflict with overhaul work. |
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| TPP Operational Constraints |
| There are operational constraints regarding outages for the six units in the TPP. Typically, five of the six units need to be operational during the spring months to pass inflows to prevent total dissolved gas in excess of allowable amounts from being generated by spills. There are additional outage limitations during times of high power demand in July and August and during the winter months between mid-November through mid-February. |
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Last Update: March 11, 2013 10:54 AM |