Abstract
Power transformers are the most important assets of electric power substations. The reliability in the operation of electric power transmission and distribution is due to the correct operation and maintenance of power transformers. The parameters that are most used to assess the health status of power transformers are dissolved gas analysis (DGA), oil quality analysis (OQA) and content of furfuraldehydes (FFA) in oil. The parameter that currently allows for simple online monitoring in an energized transformer is the DGA. Although most of the DGA continues to be done in the laboratory, the trend is online DGA monitoring, since it allows for detection or diagnosis of the faults throughout the life of the power transformers. This study presents a review of the main DGA monitors, single- or multi-gas, their most important specifications, accuracy, repeatability and measurement range, the types of installation, valve or closed loop, and number of analogue inputs and outputs. This review shows the differences between the main existing DGA monitors and aims to help in the selection of the most suitable DGA monitoring approach according to the needs of each case.
Highlights
IntroductionThe most important and expensive asset in power transmission and distribution networks is the power transformer, so there must have a well-defined maintenance strategy from commissioning to withdrawal to ensure an appropriate level of reliability throughout the operational life of the transformer
The content of FFA in the transformer oil is a very important parameter in the calculation of health index (HI), there are no recommendations for the interpretation of the results in the standards, as indicated by [24,28,38,39], so in each of the studies [15,16,17,19,20,22,23,26,30] a different limit value is taken in the HI calculation
thermal conductivity detector (TCD) = Thermal conductivity detector; gas chromatography (GC) = Gas chromatography; non-dispersive infrared (NDIR) = Non dispersive infrared; fuel cell (FC) = Fuel cell; photoacoustic spectroscopy (PAS) = Photoacoustic Spectroscopy; IC = Solid-state sensor; near infrared (NIR) = Near infrared; IR = Infrared; Fourier transform infrared (FTIR) = Fourier-transform infrared; 1 V = Single valve installation; 2 V = Close loop installation; –: Not indicated by the manufacturer; Blank spaces indicate that monitors do not need consumables or calibration owing to the use or replacement of consumables
Summary
The most important and expensive asset in power transmission and distribution networks is the power transformer, so there must have a well-defined maintenance strategy from commissioning to withdrawal to ensure an appropriate level of reliability throughout the operational life of the transformer. The lifetime management of high-voltage substation equipment is pursued [1], with the aim to manage the risks of the assets of a substation. According to [13], the risk is defined as the “effect of the uncertainty in the objectives,” so risk management of the assets has the purpose to evaluate, create and protect the correct operation of assets throughout the lifetime. The probability of failure refers to the health index of an asset, while the failure consequence evaluates and defines the consequences of a failure event
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