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Moisture in Transformers - Part 3

The three most common ways to reduce the moisture levels in a wet transformer are: a Field Vacuum Dry-Out, where heat and direct vacuum are applied to the transformer tank after the unit is completely drained of fluid; a Factory Dry-Out, where a transformer is removed from service, drained normally, and then transported to a repair facility; and by using an Online Dryer, such as a DryMax.    

Moisture in Transformers - Part 2

Moisture may exist in a transformer in several forms. 1. Water vapor in the gas space of the transformer. 2. Water dissolved in the oil. 3. Free water suspended as droplets in the oil. 4. Emulsified water contained in the decay products of oil oxidation. 5. Water absorbed into and adsorbed onto the solid insulation. 6. Free water that has settled to the bottom of the transformer. Paper has more affinity for moisture than oil does. Once wet, moisture removal is the corrective action that should follow. However, before moisture removal, it is important to first evaluate how the transformer became wet. 

Liquid Power Factor - Part 3

For in-service insulating liquids, we recommend running liquid power factor at both 25°C and 100°C on all mineral oil-filled transformers except, perhaps, for very small distribution class transformers such as small pad mounted or pole mounted units. Liquid power factor is particularly important when D1816 dielectric breakdown voltage is also performed, since the results from the power factor may indicate the cause(s) of poor Dd1816 results. 

Liquid Power Factor - Part 2

The values we obtain from liquid power tests indicate certain conditions in a transformer, allowing us to determine which condition, moisture, oil oxidation, or contamination, is causing the result. The values we use to classify liquid power factor results for in-service oil are the same for all primary voltage classes of equipment.

Furan Testing - Part 7

There are oil processing and transformer maintenance procedures that will significantly change the content of furans. If the unit is subjected to reclamation/regeneration using an adsorbent system such as Fuller’s Earth, alumina, or one of the other reclaiming adsorbents that can be reactivated, the degree to which furans will be removed will depend on how well the reclaiming job was performed.      

Furan Testing - Part 6

Very high levels for furan test results may indicate substantial damage to the insulating system. The calculations that we perform to estimate the condition of the solid insulation by using the furans analysis results is performed in a two-step approach to estimate a DP and calculate insulation life remaining.

Furan Testing - Part 5

The significance of the furan test results depends, in part, on the reason for testing the unit in the first place. If you have baseline data, or if you have other past history, any increase in total furans, and especially the presence of specific furans other than 2-furaldehyde, may be significant. Even a small increase may indicate a significant, suggesting ongoing breakdown in the solid insulation. When we do not have a history of furans analysis to follow up on other abnormal results or for a baseline determination, we have to make our judgement and recommendations based on complete information and some general guidelines.

Furan Testing - Part 4

There are a couple of situations where performing the analysis on insulating liquid during every routine sampling and testing interval is appropriate.

Furan Testing - Part 3

While knowing the state of the solid insulation is critical information for any transformer, it may not be the best use of resources to always run furans as a routine test. There are three very important times for performing analysis of insulating liquids for furans.   

Furan Testing - Part 2

Interpreting the results of furanic compounds can tell us whether the paper has broken down and, maybe even more importantly, whether it still is breaking down. SDMyers tests for five different furanic compounds. Increases in the concentrations of these compounds indicate that the paper is breaking down. Further, the particular furanic compounds present provide some useful information on what conditions caused the paper to break down, and may even indicate whether those conditions are still present.

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