Transformer Oil Analysis FAQs

Q1: How often should a transformer be tested?
A1: Transformers need to be tested on a yearly basis, at least. Transformers that are built for a specific purpose such as wind farms, solar farms, electric locomotives and furnace transformers should be tested at shorter intervals.

Q2: Can I use a plastic container for sampling?
A2: No, the whole process starts with a good sample and this must be done correctly. Instead of a plastic container, a new tin or glass syringe should be used. Glass bottles can also be used where there are security requirements, but from a lab safety viewpoint, these sampling containers should only be used in specific cases.

Q3: Can anyone take the samples?
A3: No, for safety and correct sampling technique, please only used qualified samplers. A correctly-taken sample helps provide reliable data.

Q4: How important is the data plate information on the transformer?
A4: This is information is extremely important. The first and most important information is the serial number, as this is used to link all the results in the database. Next, the electrical rating of the transformer is used to determine the specification class, which determines the permissible limits for the test results.

Q5: Can an accurate diagnosis be made on a single set of test results?
A5: No, only in extreme cases.  The diagnosis of transformers is largely based on the trends of repeat samples.

Q6: Do I need to have a full range of tests performed each time?
A6: No, only once a year.  Specialised tests such as PCB, Inhibitor, Passivator, Corrosive Sulphur, Tan Delta or IFT should be conducted annually to determine the condition of the transformer.

Q7:  If the PCB result is higher than the standard, what should be done?
A7: In this case, an oil change is the only treatment that will reduce the PCB level.

Q8: I want to know what the maximum DGA levels can be before action must be taken.
A8: The diagnosis of the DGA levels is complicated and, although there are limits that can be used for alarm purposes, the diagnosis also depends on history, trends, production rates, type of industry/transformer application, age of transformer, etc. 

Q9:  The furanic level of my transformer is close to the 200 level, or lower, what must I do?
A9: The diagnosis of the furanic level is based on the trend and production rates for the furanic components. While a 200 level (or lower) reading is worrying, it does not mean that the transformer is at the end of its lifespan. It does, however, indicate that the transformer could fail prematurely if the condition is not managed. The sampling period for this transformer needs to be shortened and planning for a new transformer may have to begin.

Q10: Do I need to have the furanic level of my tap changer and other switchgear tested?
A10: No, furanic testing only applies to equipment containing paper-based insulation material.

Q11: Do I need to know what type of oil is in my transformer?
A11: YES, each type of oil has its own limits. There may be mineral, natural ester, synthetic ester or silicone oil in use. The transformer will be diagnosed against a mineral oil specification if the oil type is not specified, and this can lead to an incorrect diagnosis.

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email: support@wearcheck.co.za

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