The role of online DGA in monitoring power transformers

Transformers are a cornerstone of power generation, and as such maintaining their health and performance levels is critical to everything from keeping the lights on to industrial production. They are also among the most valuable assets in electrical power networks, constituting around 60% of substation capital costs.

Having been at the forefront of industrial measurement for over 80 years, Vaisala knows a thing or two about online dissolved gas analysis (DGA). Vaisala has drawn on non-dispersive infrared (NDIR) technology to build a DGA monitor that measures for the seven different types of gas that indicate faults, while some online monitors rely on technologies commonly found in laboratory analysis. In this blog post, we highlight what you need to know when it comes to assessing transformer health, and how you can select a DGA monitor that will provide a comprehensive understanding of your assets’ condition.

Critical fault gases and why they form

In a power transformer, the temperature increases at the location of a developing fault. Thermal stresses resulting from the fault will then lead to the formation of gasses, the type and amount of which will indicate the nature of the fault, allowing owners or operators to take corrective action. The more serious a fault, the more gas will be produced, while larger fault areas will also result in higher gas production.

There are seven key fault gasses, whose levels will need to be monitored closely to give asset owners a comprehensive understanding of transformer health: methane, ethane, ethylene, acetylene, carbon monoxide, carbon dioxide and hydrogen. Different gases will form depending on the fault location and the temperature and materials present at that point in the transformer. It is therefore important that owners of critical assets select a tool that can monitor all of these gases and not just one or two.

Utilizing online DGA monitoring

Traditionally, the power industry relied on the laboratory testing of manually extracted samples of transformer oil. However, this process was slow, open to various sources of sample contamination and provided only a ‘snapshot’ of transformer health at a particular moment in time.

By contrast, online DGA monitoring allows faults to be detected as early as possible, by continuously assessing the levels of these gases in transformer oil. The sophistication of the technology used and its harnessing of digital trends allows operators to detect faults which may be overlooked in manual oil samples. This results in significant cost reductions when it comes to transformer maintenance and repair, as well as minimizing the likelihood of catastrophic failures.

Choosing the ideal online DGA monitor

While a number of online DGA monitors are available to transformer owners and operators, these are not all created equally. Reliable measurement of long-term gas trends is of course a must, but other key considerations when selecting a monitoring device will include its ability to operate in a variety of climatic conditions, a robust design that can be easily fitted to operational transformers, and little need to maintain or monitor the unit itself to ensure its effective operation. 

Cost will of course be another significant factor, but here it is important to consider not just the upfront price of an online DGA monitor, but also the costs associated with its installation and operation over its entire active lifetime. Some online DGA techniques require consumables, such as carrier gases, or have moving parts that require maintenance. Alternatives technologies, such as NDIR, mean no additional installation or maintenance costs, offering operators significant cost savings over the lifetime of the technology.

Online DGA has led to a sea change in how transformers are monitored and serviced. It offers a more practical and effective approach to transformer monitoring, giving owners and operators greater peace of mind in the knowledge that these vital links in the energy network are operating in peak condition.

To learn more about the role of online DGA monitoring for power transformers, watch the webinar:  Online DGA Monitoring of Power Transformers