Hoover Dam and Powerplant

Hoover Dam and Powerplant

The capacity and operational flexibility of the plant also significantly contribute to the stability and reliability of the California, Arizona, Nevada, Utah, and New Mexico electrical grid. The massive rotating inertia of the generation plant at Hoover provides an unusually high ability to sustain system integrity during moderate to severe system disturbances.

The plant contains the unique ability to black start a main 130 MW unit without the benefit of an external system feed. This means the plant can act as a synchronizing source for the rest of the system in the event of a system separation.

The plant acts as a primary source of spinning and non-spinning reserves for the service area. The electrical integration and interconnection of Davis, Hoover, and Parker Powerplants provide maximum generation of power with efficient use of water resources.

The highly developed agricultural base and the complex industrialization of the Pacific southwest benefit greatly from Colorado River hydroelectric energy.

Hoover Dam is a concrete thick-arch structure, 726.4 feet high and 1,244 feet long at the crest. The dam and appurtenant structures contain 4.4 million cubic yards of concrete. Hoover Dam and Powerplant was the first major concrete thick-arch dam constructed by Reclamation. Water for generation is conveyed through four penstocks from four intake structures immediately upstream and contiguous to the dam. Spillway structures use eight 16 foot by 100 foot drum gates which provide for an additional 16 vertical feet of storage capacity in Lake Mead, the reservoir impounded upstream of the dam. Lake Mead is the largest Reservoir in the United States with a total storage capacity of 29.8 million acre-feet.

The Boulder Canyon Project Adjustment Act of 1940 authorized the Secretary of the Interior to promulgate and implement charges for electrical energy generated at Hoover Powerplant. This Act further specified how the revenues resulting from Hoover energy sales were to be applied. The Hoover Powerplant Act of 1984 authorized the uprating of the 17 main generating units and the construction of additional visitor facilities and parking structures and the Hoover Dam bypass bridge. It also changed the funding source from Congressional Appropriations to an Available Receipts Fund (a quasi-revolving fund). The uprating of the units was accomplished through non-Federal funds advanced by 11 power customers.

The dam was originally designated as Hoover Dam by instructions of the Secretary of the Interior dated September 17, 1930. The dam was redesignated Boulder Dam by order of the Secretary dated May 8, 1933. The name Hoover Dam was restored by the Act of April 30, 1947, 61 Stat. 56.

The upper Nevada (NV) penstock tie-rod test was completed with assistance from Denver personnel. The penstock interior was spot coated and the butterfly valve seals were replaced on all of the upper NV unit lateral penstocks. The entire inside of the pipe (elbow, main, and all four laterals) was spot repaired, along with the inside face of the lower 9-foot cylinder gate. Unit turbine overhauls are currently in progress on units N2 and N6 (to be completed by 4/30/2004). Unit N6 turbine has been reconfigured and balanced. All other unit annual inspections were completed this year. Exciter alignments were completed on units A8 and A9. All units are expected to be available for service by May 1, 2004.

Currently overhauling the 2300 volt station service breakers and 17 of 38 such breakers have been overhauled. Electrical board functional relay testing is ongoing. Arc flash analysis is also ongoing with assistance from Denver personnel.

Major piping replacements were completed on both units N2 and N6. In the Arizona 2nd floor pipe gallery, the 400 feet of 6-inch fire main was replaced. The unit N2 cooling water eductor system was also replaced. Extensive painting of all powerhouses piping is ongoing.

The installation of the emergency roadway barriers for the top of dam highway was completed. The relocation of the Nevada checkpoint moving it to 400 feet closer to the dam to accommodate the new road construction for the Hoover Dam Bypass was completed.

Additional work items which address present activities are:

1. The emergency closure test for the upstream cylinder gates was completed in September 2003 confirming that the upper cylinder gate on any penstock at Hoover Dam provides a viable emergency shutoff.

2. In October 2003 re-insulation of the thrust bearing systems for units A8, A9, N2, and N3 were completed. The new insulation systems prevent circulating currents to ground which travel through the bearing surface. Units A8, A9, and N3 had high levels of circulating currents. N3 had old micarta insulation which is known to lose insulation value after many years. This work is part of an ongoing effort to eliminate all potential causes of thrust bearing failures at Hoover Dam.

3. The thrust bearing shim pack on the thrust bearing of A8 was replaced due to complete deterioration of a shim in the shim pack. When A8 was disassembled to eliminate high levels of thrust bearing circulating currents, portions of a shim were missing which gave evidence of mechanical “working” of the components. This work is part of an ongoing effort to eliminate all potential causes of thrust bearing failures at Hoover Dam.

4. One hundred percent coating removal and re-coating of N2 and N6 scroll cases stay vanes, and wicket gates were completed. A small improvement in efficiency will result from this work.

5. A contract was awarded with the Western Area Power Administration to replace 230 KV disconnect A781 on the roof of the Arizona Powerhouse.

6. Additional fall protection cables were added at exposed areas such as main bridge cranes, the cableway tail tower, and access ladders.

7. Topographic maps of downstream river channel between the dam and the spillway discharge area was completed.

8. Visitor Center’s security barrier at plaza was completed.

Elevator hoist ropes on 4 elevators (E1, E2, E5, and E6) will be replaced.

The Arizona penstock lighting contract was awarded which will result in the replacement of the upper and lower AZ penstock lighting systems. Upper AZ will have all new lighting systems which will be completed by September 30, 2004 followed by Lower AZ work to be completed by January 31, 2005.

The contract for the replacement of the station service transformers was awarded and the work is scheduled for the summer of 2004.

The contract for scanning and indexing 36,000 drawings and 43,000 documents has been awarded and should be completed by the end of August.

The contract to repair the 150-ton cableway slack carrier systems will be awarded in April 2004 and the work will be completed in September 2004.

During the 2004-2005 maintenance season the upper AZ lateral penstock butterfly seals will be replaced. This will complete the seal replacements of all butterfly valves. Units A1 and A6 are scheduled for turbine overhauls.

The A8 eductor will be replaced in FY 2005. The unit A1 major overhaul will be completed in FY 2005.

The interior painting of the upper AZ penstock will occur during the 2004-2005 penstock outages.

Hoover Powerplant generators are primarily used for providing a low-cost peaking resource and regulation. Although some end-users receive their entire requirement from Hoover, some wholesale power customers blend their entitlement from Hoover power with other resources. Consequently, Hoover is not a sole source supplier. Contractual arrangements with the power customers provide for Hoover power to be used for "Ramping, Regulating, and Reserves.”

The demand for Hoover power generation is seasonal, with the winter months as the low-demand period. This permits taking out of service one penstock per year for preventative maintenance. Because four generators are normally supplied from each penstock, when the penstock is out of service, so are four generators.

Hoover generation is a direct function of river flow and downstream water demands. Power production is ancillary to flood control, navigation, and irrigation water delivery.

Hoover dam electrical capacity has been reduced due to the on-going drought and decreased lake elevations.