Total Acid Number: Avoiding Potentially Catastrophic Transformer Failure

Shockingly enough, industrial transformers have the potential to reach dangerously high temperatures during extended use. Transformer oil, being stable at high temperatures and having excellent electrical insulating properties, primarily functions to insulate and cool the transformer.

With potentially catastrophic consequences for failure, including damage to components, mechanical failure, ignition risk and outright electrical explosions, it is imperative to keep track of transformer oil quality!

Let’s explore what Total Acid Number is, why it’s regularly analysed in transformer oil and the risks of long-term oxidation.

TAN (Total Acid Number) and the danger of acidity

As previously mentioned, transformers can run at very high temperatures. Extended exposure to heat with the added influence of oxygen can lead to oxidation of the transformer oil. Total Acid Number is a measurement of acidity that is determined by calculating the amount of potassium hydroxide in milligrams.

Should transformer oil become too acidic, the transformer itself can undergo corrosion and result in the formation of sludge and varnish deposits. It is a compounding issue as blockages will stop efficient cooling of the transformer, leading to further breakdown and oxidation of the transformer oil. Should the temperature of the oil reach flash point (released vapour at risk of ignition), there is a great risk of fire.

Calculating TAN

TAN can be calculated through a variety of methods, such as spectroscopy, colour indicating titration or potentiometric titration. We at a1-envirosciences offer a fantastic solution in the form of the Nittoseiko CA/GT-200. A dual-purpose instrument, able to simultaneously measure either colorimetric or volumetric Karl Fischer moisture and potentiometric (TAN).

As mentioned in a previous blog post (An Insidious Contaminant), water in oil also has the capacity to cause severe damage to transformers (or any mechanical instrument containing oil!), so having the ability to test both Karl Fischer and TAN rapidly and accurately is extremely desirable in a range of industries.

As an added benefit, the CA/GT-200 can also be applied to other parameters, such as Total Base Number and a wide variety of matrices such as lubricants, crude oils, fuels and engine oils!


It is crucial, especially given the nature of transformers, that transformer oil quality is regularly tested; not only for Karl Fischer, but also for acidity/TAN. Keeping track of potential impurities will not only guarantee maximisation of transformer lifetime and efficiency, but it also minimises the risk of critical failure and the potentially dangerous consequences associated.

The CA/GT 200 is the ideal solution for consistent and accurate condition monitoring for transformers, with the flexibility to be employed in the analysis of a variety of matrices, thereby offering great value for the investment.

If you’re interested learning more about the applications and benefits of having the CA/GT 200 in your lab, give us a call on 0845 873 8181 or get in touch by email: