There are a couple of different ways to determine if a transformer is wet. The traditional way is to pull a fluid sample and send it to a lab for a Karl Fischer Titration test, which will tell you the water content in the fluid in parts per million. When analyzed alongside other data from the transformer (especially temperature) it is possible to calculate the percent saturation--basically the water in the fluid at different temperatures.
Transcription:
There are a couple of different ways to determine if a transformer is wet. The traditional way is to pull an oil sample or a fluid sample. Transformers can be filled with different fluids. The most common is mineral oil, transformer oil, but no matter what the fluid is, it's important to adequately flush that bottom valve. And then depending upon what fluid is in the transformer, it will hold different amounts of moisture. But regardless of the fluid type, those samples are sent to a laboratory and they are tested by an ASTM method for a Karl Fisher titration. And these results that you'll get back are the water content in the fluid. Water content is given in units of parts per million. And then with those parts per million of water that you have, it's very important that you have the temperature.
Temperature will tell you a lot about how wet the transformer actually is. So that temperature should be recorded when the transformer is being sampled. Transformers have the fluid, but they also have a lot of paper insulation and that paper insulation really acts as a sponge for the moisture. So, water is in a flux between that paper insulation and the fluid. So as temperatures increase, the fluids going to hold more moisture. And that's why temperature plays a very important role to actually determine how and what that transformer is. When we have the water content and temperature, we can calculate what we call percent saturation and that's basically the amount of water in the fluid at different temperatures. So, why is percent saturation so important? It's important because it'll actually tell you at what point moisture is in the fluid. And you'll know at what point then you would have free water or if it's still dissolved water.
So that's the traditional way of determining if a transformer is wet. Another way that's much more common now is with the use of a moisture meter. These sensors are installed in transformers or in processing equipment and then they read percent saturation, temperature and then parts per million or water content is calculated from those. So either way you get your water content and your percent saturation. There are industry standards that you can look at to determine what level is too high. So, these standards are usually based on transformer size. So there are generally three different classes of transformers based on voltage and they each have a limit for how much moisture is too much. And in general, the larger the transformer, the smaller amount of moisture you're generally allowed to have. So for example, IEEE one technical society that sets those limits, but laboratories also set limits. And then a lot of individual transformer owners have their own internally set limits as well. Another key is to look at trending. So you won't want to base the decision of whether the transformer's wet on one test result or one reading. You want some history, you'll want to look at, you know, at least two or three samples to determine if the transformer is actually wet. And then if you have an issue that's when you would act on it.
For more information on oil testing packages and the Karl Fischer test, visit: www.sdmyers.com/transformer-s...
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