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Reclamation research to define unit maintenance costs

The U.S. Department of the Interior’s Bureau of Reclamation is conducting research to develop better maintenance cost information for its turbine-generator units. Reclamation is especially interested in quantifying maintenance costs associated with units that are used more frequently to provide ancillary services, such as spinning reserve and regulation that supports power system automatic generation control (AGC).

A primary objective of the research, referred to as “Maintenance Costs and Hydro Turbine Operational Flexibility Project,” is to determine the cost of operating a unit in the “exclusion zone,” says Steve Stitt, automation team leader in Reclamation’s Hydroelectric Research and Technical Services Group. This zone represents generation levels at which the unit experiences increased vibration and noise (referred to as the rough zone), as well as high cavitation levels.

Hydro plant operators avoid operating a unit in the rough zone in an effort to reduce needed repairs and extend life. Yet, it is often necessary to force units to cross their rough zones several times daily to provide regulation for the power system. This regulation requires that the generator react quickly to maintain AGC functions and to account for changing loads that are not predicted by hourly generation schedules, Stitt says. In addition, high spinning reserves force power plants to operate at less than optimum efficiency.

The relationship between operation in the exclusion zone and actual machine condition/damage is largely unknown, Stitt says. Consequently, the cost of operating within the exclusion zone is poorly understood. Improved knowledge of the operation-damage relationship can better quantify the operating costs at generation levels below optimum efficiency.

To analyze this relationship, Reclamation compared the relative cost of increased maintenance resulting from operating at decreased efficiency to provide ancillary services to the additional revenue gained from providing these services. The analysis found that providing ancillary services can easily overcome an estimated 25 percent increase in maintenance downtime and equipment wear. From these results, operating a unit at levels necessary to provide ancillary services and performing repair or replacement as needed appears to be an economically viable approach.

Reclamation says the next step in its research is to gather data from a variety of power plants that are used to supply ancillary services. Damage occurring at these plants will be analyzed to determine the linkage to operating conditions. Then, where possible, exclusion zone cost models will be proposed that do not drastically affect present operations, in an effort to more accurately relate increased costs to unit generation levels.

Ideally, cost models will be developed that will allow Reclamation to prioritize use of the units at a particular plant in an effort to minimize maintenance costs.

– For details about this research, contact Steve Stitt at (1) 303-445-2316; E-mail: sstitt@do.usbr.gov.

Using drogues to conduct research on fish passage

The U.S. Geological Survey (USGS) is using an instrument called a drogue to gather data on fish movement paths and timing in the tailrace of hydroelectric projects. Drogues (or drifters) are water-following instruments that consist of a surface float attached to a drag element. The drag element has a large surface area and is designed to follow surface currents. The float is designed to minimize wind influences.

Drogues traditionally have been used in oceanographic studies to monitor major ocean currents and eddies. USGS determined that drogues are a useful tool for egress evaluations at hydro projects because they are relatively inexpensive, collect detailed path information, and can be deployed in locations where access is limited because of safety concerns.

To gather data, the surface float on the drogues that the USGS employs contains a global positioning system (GPS) unit that records drogue position each second as it drifts through the tailrace. USGS releases drogues into fish passage locations at the dam and correlates their egress times with those of juvenile salmon over a variety of test conditions and passage routes.

USGS is using drogues at two hy- dro projects on the Columbia River: 1,812.8-MW The Dalles Dam and 2,160-MW John Day Dam.

At The Dalles, USGS used drogues to measure egress for fish passing the north and south spillways. Research using drogues and juvenile chinook salmon revealed longer egress times through the south spillbays than through the north spillbays. Egress delays were caused by entrainment in lateral currents along the spillway or by deflection into low-velocity areas where predators tend to congregate, USGS reports.

At John Day, USGS compared egress from the juvenile bypass during high and low spill conditions. The most common egress path during low spill was directly downriver, compared with a path perpendicular to river flow during high spill. This indirect travel route resulted in significant increases in egress time, according to USGS.

EPRI conducting research on large power transformers

EPRI is conducting several research studies relating to power transformers. The overall goal of this research is to provide tools for more reliable operation of these transformers, says Nick Abi-Samra, P.E., senior technical executive with EPRI.

Current EPRI research projects in this area include:

– Continuing sponsorship of an effort to use metal-insulator-semiconductor (MIS) sensors in transformers. These devices are low-cost solid-state detectors of hydrogen. EPRI is pursuing work to deploy these sensors to monitor acetylene. Both hydrogen and acetylene release are indicative of impending transformer failure. Early investigations in this area began in 2004; work is scheduled to be completed in 2009.

– Work to make load tap changers (LTC) more reliable. LTCs, which regulate the voltage of a transformer, are among the leading reasons for failure in large transformers. EPRI’s research on LTCs covers problems related to design, operation, diagnosis, and maintenance. The most recent work focuses on developing advanced techniques for analyzing various types of gas dissolved in the insulating fluid of an LTC, to determine the health of the transformer. In addition, EPRI is examining on-line monitoring of the headspace in an LTC for both fault gases and gases generated by tracers in the contacts to provide an alert related to contact wear.

– Leadership of a project to assemble a standardized transformer database. The database will provide utilities with data and information to assist in developing a strategy for repairing, refurbishing, or replacing an aging transformer fleet. This research will result in a risk-informed strategy for operating and maintaining transformers. Work on this project began in late 2006, and results are expected by December 2007.

– For more information on this research, contact Nick Abi-Samra, (1) 650-619-7229; E-mail: nabisamra@ epri.com.

Project gathers data on pre-stressed anchors in dams

More than 20,000 anchor tendons have been successfully installed in about 400 dams in North America over the past 40 years. This is one of the findings from Phase 1 of the National Research Program on Rock Anchors for Dams.

The goals of this program – being conducted by Donald A. Bruce, PhD, president of Geosystems L.P., and John S. Wolfhope, P.E., principal with Freese and Nichols Inc. – are to:

– Produce a definitive and detailed list of all North American dam anchor projects;

– Trace the evolution of practice via codes and specifications analysis; and

– Assess the market for post-tensioned anchors on large dams and hydropower facilities.

To complete Phase 1, researchers gathered information on every pre-stressed anchoring project completed on North American dams. Data includes dam name, location, year anchored, number of anchors installed, the type of anchor tendon (bar, strand, or wire), strand/bar size, number of strands per tendon, and average length of the anchors.

At the end of 2006, complete data had been gathered on 260 dams. An additional 40 were nearly complete (missing one or two pieces of information), and 100 were incomplete (missing more than two pieces of information). Bruce and Wolfhope hope to fill in the missing information by the summer of 2007.

Phase 2 of this research project began in January 2007. This phase focuses on reviewing and analyzing the engineering and performance aspects of pre-stressed anchors in dams. In particular, research will focus on reviewing available load measurement data that demonstrates the performance of installed anchor systems over their service life. Phase 2 research is scheduled to be complete by December 2008.

Phase 1 research was financed by the Association of Drilled Shaft Contractors, Freese and Nichols, Geosystems, Boart Longyear Company, Sumitomo Steel Wire Corporation, and Sumiden Wire Products Corp. The researchers are seeking funding for Phase 2.

– For more information, contact John Wolfhope at (1) 512-617-3118; E-mail: jsw@freese.com.


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