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Laboratory Accreditation: Accuracy and Precision

By in General, Laboratory Diagnostics | February 25, 2019

 

This article was co-authored by Denis Lafrance, Melissa Carmine-Zajac and Lance Lewand.

 

There are a variety of tests that provide information about the development of acute problems and changes in the long-term condition of the health of transformers. Tests such as those for dissolved gas-in-oil analysis (DGA), furans, water content and oil quality provide a tremendous amount of information for making operational and maintenance decisions about transformers. However, it’s vital that the data collected is accurate and test results are repeatable to receive actionable results.

Determining Accuracy

Accuracy is how close results are to the true value. For DGA analysis, gas-in-oil standards can be prepared to a high level of accuracy by using pure gases or primary standards that are prepared gravimetrically to 1.0% or better accuracy. Gas-in-oil standards can be prepared to verify results which confirm gas extraction and measurement are occurring in a manner that retains accuracy within 5-10% of the true value. Knowing that the results are accurate permits greater confidence in decision making.  Morgan Schaffer’s laboratory is accredited to ISO 17034 for its True North (Gas-in-oil standards) and Atlantis (water in oil) standards, which are available in various dielectric liquids. These standards are used at Morgan Schaffer’s laboratory and are commercially available to allow laboratories to determine accuracy. Doble prepares standards for its laboratories through the use of ASTM methods. Laboratory users can determine how accurate their laboratories are performing their analyses by either using their own standards or Morgan Schaffer’s.

Importance of Repeatability

To analyze oil data, it is important to assess the trend for changes in properties or characteristics over time. Repeatability, the ability for the same laboratory to achieve the same results on the same sample, is needed to be reasonable for early detection, as well as efficient decision making. If the variation in results is too high, it is more difficult to determine when real changes are occurring. Diagnostics will be needed to add more tolerance, therefore slowing down decision making. This may result in missing problems until they are too far advanced for maintenance, and in the worst cases culminate in an unplanned outage or catastrophic failure.

Doble/Morgan Schaffer laboratories verify repeatability as part of their accreditation to the ISO 17025 standards. Doble/Morgan Schaffer laboratories are dedicated to providing repeatable and accurate results that enable the electric power industry to make decisions based on data they can rely on.   Utilities need to know and prove that their apparatus are operating reliably, that they can maintain them and extend the service life of their assets in a knowledgeable way. The best practice is to have reliable oil data analyzed based on accurate absolute values, repeatable trends, and benchmarked against a database of similar apparatus and their performances.

 

Need more information on laboratory testing? An overview of tests covered by Doble/Morgan Schaffer laboratories is available on our website.

 

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Doble Engineering Company

Doble Engineering Company