Gas analysis series | Why it’s important to monitor oxygen in transformers

When proactively managing your wind farm’s transformer assets, it’s important to consider many of the external factors that could be accelerating the transformer aging process which will subsequently lead to unplanned or premature failures. Together with water and temperature, Oxygen is one of the three key elements responsible for accelerating the aging process. In the following blog we breakdown oxygen’s role in transformer degradation and how the correct transformer monitoring solution can help reduce its impact on your transformers lifespan.

The role of oxygen in the degradation of a transformer

Oxygen (O2) enters the transformer due to continuous breathing caused by oil volume changes with load and temperature variations. At the same time O2 is also naturally consumed by the transformer due to the aging and degradation process. The rate of ingress and increase of O2 depends on the oil protection system type and integrity, while the rate of consumption that results in O2 decrease depends on the speed of degradation.

Where there is a failure of the sealing system, for example caused by a membrane rupture, O2 will increase. By comparing O2 readings and their trend with the sealing characteristics, this can easily be detected.

On the other hand, if the insulation is degrading over time and consuming O2, O2 levels will decrease and by comparing it with CO and CO2 data, this can also easily be detected.

Why is it important to monitor oxygen online?

• It detects insulation aging and allows you to calculate aging speed and an estimate of remaining life, combined with temperature and moisture effect (ref IEC60076)
• It detects failures in the sealing system
• It is more reliable than a laboratory test, where results are strongly affected by manual sampling mistakes, leading to non-repeatable trending.
• Oxygen/Nitrogen is now used to calculate DGA condition according to IEEEc57.104:2019

How to monitor oxygen levels

There are three key ways to monitor oxygen online:

1. A gas-chromatographer
2. An electrochemical sensor in contact with oil
3. An optical sensor in contact with oil

Kelvatek’s total transformer monitor, TOTUS applies the third method, an optical sensor, which is very sensitive to O2 regardless of the sealing type and provides very accurate and consistent measurements.

TOTUS provides a direct solution to oxygen monitoring

There are monitors available on the market, that due to technical limitations, cannot measure oxygen levels, and their suppliers propose alternative methodologies. When looking at transformer monitor suppliers, it’s important to consider that insulation aging and sealing failures both involve O2.

By purchasing a monitor that accurately detects O2 levels you will be able to measure these two phenomena. Any alternative method will be an indirect estimation. For example, monitoring the total gas pressure while beneficial when detecting large leaks, has no advantage over the direct measurement of O2 which is the main gas of interest when there is a leak. Additionally, total gas pressure will not be sensitive enough to detect small leaks or aging consumption when compared with O2 measurements, because O2 is only a portion of the total gas pressure.

In all cases, if O2 is the key parameter, measuring O2 is the best choice.

In conclusion, understanding and monitoring oxygen levels is crucial for the effective management of transformer assets. Accurate O2 measurement not only helps detect insulation aging and sealing failures but also ensures the longevity and reliability of your wind farm’s transformer assets preventing costly failures and ensuring project uptime.