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23 On-Line Monitorin g of Liquid-Immerse d Transformer s Andre Lu x Progress Energy 23.1 Benefits ............................................................................. 23- 1 Categories . Direct Benefits . Strategic Benefit s 23.2 On-Line Monitoring Systems......................................... 23-3 Sensors . Data-Acquisition Units . DAU-to-Computer Communications Line . Computer . Data Processing 23.3 On-Line Monitoring Applications................................. 23-4 Power Transformers . Instrument Transformers . Bushings . Load Tap Changers On-line monitoring of transformers and associated accessories (measuring certain parameters or conditions while energized) is an important consideration in their operation and maintenance. The justification for on-line monitoring is driven by the need to increase the availability of transformers, to facilitate the transition from time-based and = or operational-based maintenance to condition-based maintenance, to improve asset and life management, and to enhance failure-cause analysis. This discussion covers most of the on-line monitoring methods that are currently in common practice, including their benefits, system configurations, and application to the various operational parameters that can be monitored. For the purposes of this section, the term transformer refers, but is not limited, to: step-down power transformers; generator step-up transformers; autotransformers; phase-shifting transformers; regulating transformers; intertie transmission transformers; dc converter transformers; high-voltage instrument transformers; and shunt, series, and saturable reactors. 23.1 Benefits Various issues must be considered when determining whether or not the installation of an on-line monitoring system is appropriate. Prior to the installation of on-line monitoring equipment, cost- benefit and risk-benefit analyses are typically performed in order to determine the value of the monitoring system as applied to a particular transformer. For example, for an aging transformer, especially with critical functions, on-line monitoring of certain key parameters is appropriate and valuable. Monitoring equipment can also be justified for transformers with certain types of load tap changers that have a history of coking or other types of problems, or for transformers with symptoms of certain types of problems such as overheating, partial discharge, excessive aging, bushing problems, etc. However, for transformers that are operated normally without any overloading and have acceptable routine maintenance and dissolved gas analysis (DGA) test results, monitoring can probably not be justified economically. 2006 by Taylor & Francis Group, LLC. 23.1.1 Categories Both direct and strategic benefits can arise from the installation of on-line monitoring equipment. Direct benefits are cost-savings benefits obtained strictly from changing maintenance activities. They include reducing expenses by reducing the frequency of equipment inspections and by reducing or delaying active... View Full Document

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