Routine Maintenance of Electric Generating Stations

AGENCY:

Tennessee Valley Authority (TVA).

ACTION:

Notice of availability.

SUMMARY:

TVA is announcing the availability of a technical report, Routine Maintenance of Electric Generating Stations (February 2000). This report describes common practices on the TVA electric power system and elsewhere in the electric utility industry that are necessary to maintain the efficiency, reliability, and availability of steam electric generating units.

ADDRESSES:

A copy of this report may be obtained by contacting Jerry L. Golden at (423) 751-6779; email address: jlgolden@tva.gov. TVA is currently planning on posting this report on TVA's website www.tva.gov.

FOR FURTHER INFORMATION CONTACT:

Jerry L. Golden, Manager Production Technology, at (423) 751-6779.

SUPPLEMENTARY INFORMATION:

Background

Under section 14 of the TVA Act, 16 U.S.C. 831m, TVA is directed to collect data and report on practices, methods, facilities, and equipment and the economic integration of plants and systems “best suited to promote the public interest, efficiency, and the wider and more economical use of electric energy.” In accordance with this directive and authority, TVA reported on its generating unit maintenance practices and experiences in a report entitled, TVA's Power Plant Maintenance Program, Philosophy and Experience, T. H. Gladney and H. S. Fox (April 1972). Today, TVA is announcing the availability of an updated report on utility maintenance practices, Routine Maintenance of Electric Generating Stations, Jerry L. Golden (February 2000).

Congress has tasked TVA with the development and conservation of the resources of the Tennessee Valley region in order to foster the region's economic and social well-being. One component of TVA's regional resource development program is the generation, transmission, and sale of electric power. TVA's electric power system now serves approximately 8 million people in parts of seven southeastern states.

TVA has more than 65 years of experience in maintaining various kinds of power-generating technologies. These technologies include hydro-electric units, nuclear units, combustion turbines, a pumped storage facility, and 11 coal-fired power plants. TVA's coal-fired power plants consist of 59 units with a diverse mix of burner types and configurations. The size of units currently being operated ranges from 125 megawatts to 1,300 megawatts (nameplate capacities). These boiler types and sizes are typical for more than 90 percent of the coal-fired boiler fleet in the United States. TVA's February 2000 technical report describes common utility maintenance practices and philosophies and provides case studies of a number of maintenance projects on the TVA system and elsewhere.

Other Information and Report Summary

A steam-electricity generating unit is a complicated machine consisting of thousands of separate parts and components that must be operated together in an integrated fashion to produce electricity. Like any complex mechanical system, a electricity-generating unit may suffer impaired performance caused by defects in design or manufacture, extreme operating conditions, normal wear of components, or catastrophic failure. This impaired mechanical performance affects the economic performance of the unit and employee safety. To ensure reliable integration of the thousands of different parts and continued reliable performance, TVA and other electric power systems must have an active generating unit maintenance program.

Maintaining integrated operation of all components is difficult because of the large number of components and the varying stresses on components. Failure of a component can affect unit operating efficiencies and can even prevent the unit from operating at all. This is true regardless of the size of the component. A critical electric relay, sensing device, or valve can shut a unit down as easily as the failure of a unit component such as an economizer or a reheater.

The maintenance, repair, and replacement of unit components are necessary to achieve reliable and safe operation of a generating unit throughout its useful life. To do this, TVA and other electric utilities routinely conduct maintenance activities that are proactive, reactive, and predictive. Proactive maintenance practices try to forestall component failure and degradation. This includes such things as lubricating equipment, replacement of fluids, and the regular replacement of gaskets. Reactive maintenance practices correct a component failure or degradation when it occurs. Such reactive maintenance can be limited to specific component elements, include surrounding or adjacent elements that may have suffered the same stress, or involve the replacement of an entire component. Predictive maintenance takes advantage of the most recent advancements in assessment and measurement technologies. Through predictive maintenance practices, TVA and other utilities try to predict when a component element or entire component may fail or suffer unacceptable degradation. Utilities then replace elements and components in advance of actual failure so that damage to other components is reduced and generating units are not suddenly lost.

It has been routine practice within TVA and the utility industry for decades to replace components and systems with state-of-the-art equipment and materials to ensure that the most reliable and efficient equipment is used rather than original equipment or components that may not only be obsolete but no longer even available on the market. TVA's 1972 maintenance report described the routine use of improved materials and designs, and this practice continues throughout the industry today.

TVA's 2000 maintenance report provides case studies of four typical utility maintenance practices: replacement of cyclones, reheaters, economizers and forced draft fan systems. Based on a review of data from the TVA and other coal-fired utility systems, TVA found that replacement of cyclones occurred as early as 10 years after initial operation of a unit to as late as 37 years after initial operation. Reheaters were replaced from 5 to 44 years after initial operation. Economizers were replaced from 6 to 55 years after initial operation. The conversion of forced draft fan systems to balanced draft systems has occurred at units from 4 to 36 years after initial operation.

TVA concludes that components are routinely replaced throughout the lives of units and can occur very early after initial operation of a unit. The many factors that influence equipment or component replacement include design or fabrication errors, unanticipated operating conditions, operational errors, and technology advancements.