Identifying Transformer Faults with DGA

Imagine trying to explain power transformer fault detection to your child’s second grade class or to a CFO who does not have a technology background.  The conversation might start like this: “like a doctor takes a blood sample from your body to detect an illness, an engineer may take an oil sample from a transformer to detect a problem or fault inside the transformer.” Okay, that was the easy part! Now how do you explain what to do with that oil sample and why it is important to the utility? DGA and Fault-Related Gases Dissolved gas analysis (DGA) is used to identify faulty transformers and to monitor transformers that are under stress or behaving abnormally. The key to trouble detection is understanding that abnormal heat and electrical discharges cause the production of fault-related gas ...

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Transformer Reliability and Dissolved-Gas Analysis

Authors: J.J. Dukarm and M. Duval 2016 CIGRE Canada Conference October 17, 2016 Dissolved gas analysis (DGA) is widely used for transformer condition screening and assessment. Conventional DGA practice is to employ statistically derived limits for combustible gas concentrations and their increments or rates of increase for the purpose of classifying a transformer’s condition as acceptable, suspicious, or abnormal. The DGA condition assessment, in the form of numeric “condition codes,” is sometimes used as part of a transformer health index for prioritizing of testing and maintenance or for asset management functions such as replacement planning. The basis of this condition classification scheme is the seemingly reasonable assumption that higher fault gas levels must repre ...

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TDCG, TCG, ETCG, ESHL, etc.

TOA4’s gas analysis report contains several alphabet-soup items which are explained here along with a couple of related items. In each case we start with the text label you see on the page or report, then the database field name, then the explanation. Most of this is general information about dissolved-gas analysis (DGA) in power transformers and other oil-filled apparatus, so even if you don’t use Transformer Oil Analyst (TOA) software, this may be of interest. But first a word about units. Dissolved-gas concentrations in insulating oil are usually expressed as parts per million by volume (ppm), which is the same as microliters of gas per liter of oil. Gas-in-gas concentrations are usually expressed as percent by volume. One percent by volume is ten thousand ppm. All of these volumes are ...

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TOA4’s DGA Summary Report

One of the download links at the bottom of the equipment list page provides a DGA Summary report in .csv format. To use the summary report, first filter and sort the equipment list to show the equipment you want to include in the report. Then click the “Export DGA report data” link to download the report. Like all .csv files, it can be viewed and edited in a spreadsheet. For each equipment item contained in the equipment list as filtered and sorted, the report contains a row of data consisting of basic equipment information, the latest DGA sample date and re-sample date, gas concentrations, and the DGA condition code, diagnosis, and “chinese summary”. So far, we are aware of two different uses for this report, described below. Example 1: Problem report for maintenance personnel First, be s ...

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TOA4’s Fluid Quality Index (fqindex)

The S. D. Myers Inc. laboratory reports the ratio of interfacial tension (IFT) and acid number as an indicator of the extent of oxidation of insulating oil. This ratio is the inspiration for TOA4’s Fluid Quality Index, which is calculated with an extra factor of 1000 to ensure that typical values of the index are not tiny decimal fractions. Here is the formula: fqindex = 1000*acidnum/ift Here, acidnum is the acid number (mg KOH/g), and ift is the interfacial tension (mN/m). The fqindex is calculated so that low values are good and high values are bad. Clean new oil has an fqindex below 1.0, and when fqindex reaches 10, the oil is in poor condition. While fqindex is good for trending the approximate oil quality and for detecting sudden changes which may need investigation, the acidity and I ...

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TOA4 Online Q&A

What is the difference between kv_ratings and ratedkv in TOA4? The ratedkv field — a “legacy” field inherited from TOA3 — is numeric and designates the rated kV of a piece of equipment, or the highest rated winding kV of a transformer. The kv_ratings field is text and can be used to display multiple winding kV’s, usually separated by slashes; it was introduced in TOA4 as a companion to mva_ratings, which is also text. For analysis purposes, does it matter which of the two fields we use? You can use either, both, or neither, as you like. Other than the fluidtype, equipnum/serialnum, and apprtype, all the equipment information that the analysis needs is implicit in the analysis norms that you assign to the equipment. Over the years we have discovered that the equipment “nameplate” informatio ...

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TOA4 In-Service Equipment Filter

Each equipment item has an “In-service” checkbox – visible when editing the item – which should be checked if the equipment is in service and unchecked if the equipment is not in service, i.e., retired or permanently de-activated. In an equipment import or export file, this field is called “in_service” and has a value of 1 (true) or 0 (false). The default value, if no value for in_service is specified when the equipment is imported for the first time, is 1. The “In-service items only” checkbox below the Apparatus Type filter at the top of the equipment list page activates a filter which excludes all equipment items for which in_service is false. This prevents, for example, all the failed equipment from occupying the top of the list when you are sorting by Assessment or Next DGA. The “In-se ...

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TOA4 Online Mobile Access

If you are a TOA4 Online user and have a web-enabled cell phone, Blackberry, or PDA, you might like to try out TOA4’s new mobile access feature. Point your phone’s web browser to the TOA4 Online address, but add “/m” at the end of that address. Some cell phone companies aren’t very good with handling “https”, so if your phone complains about the security certificate, try using “http” instead. You still have to log in using the same ID and password that you normally use for TOA4 Online. If you use the mobile access feature, we would appreciate some feedback on how it treats you and what we should do to make it more useful for you. Here are some example pages. The “home” page (not shown) is an abbreviated equipment list, which is always filtered to keep the list short. Items with an abnormal ...

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Honey, I deleted all my data!

Early one Monday morning a TOA4 Online user reported, not too cheerfully, having “accidentally” deleted all of the equipment (and therefore all of the test data too) from her company’s TOA4 database. Anything we could do? at all? I could hear her boss’s heavy breathing in the background. Yes, of course, we could fix it, but I had to go find Farmer Neil, our server administrator, who was far out on the land with his dynamite, air compressor, and jackhammer preparing the still-frozen soil for this year’s planting of canola (hey, this is Canada). Pushing the hood of his parka back and mopping his forehead with a large red hankie, Neil just said, “Yep, we’ll get her all fixed up in no time. Have to work my way closer to the farm house, though, because my wireless isn’t too good this far out, e ...

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Common TOA4 Import Problems

When you are trying to import test data into your TOA4 Online account, there can be various reasons why either TOA4 refuses to accept the data file or some of the data records don’t get imported. Here are some cases that users have encountered so far: File upload fails 1. Error parsing data file. Usually, this means that you have clicked the wrong thing and tried to upload a spreadsheet (.xls) or word processing (.doc) file. Sometimes it means that the file has been corrupted and contains non-text gibberish. Import operation fails 1. Missing or mis-named required columns. For example, if the apparatus type (apprtype) column is not found, neither equipment nor test data can be imported. Often it turns out that the column is not missing, but its name is spelled wrong. 2. Missing sampledate c ...

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