The Role of Online DGA in Monitoring Power Transformers

Senja Leivo
Senior Industry Expert
Nov 2, 2018
Power Generation and Transmission

DGA Online MonitoringTransformers 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

 

 

 

 

 

Senja Leivo

Senja Leivo

Senior Industry Expert

Senja Leivo is the Senior Industry Expert at Vaisala in Finland. Her professional focus is on condition monitoring of power transformers. At Vaisala with her 19 years of experience she is responsible for identifying the strategic trends and new monitoring needs within the industry, as well as bringing customers’ voice close to the Vaisala’s product development. As part of her expert role she is active member in CIGRE working groups.
Senja holds a Master of Science degree in Materials Engineering.

Comment

Paul Pillitteri

Nov 27, 2018
My basic knowledge on the quality and competitiveness of Vaisala transformer products and information is very positive. One recommendation I would volunteer is as follows; " Critical fault gases and why they form" often cause many transformers users great expense when trying to comply with gas-in-oil guidelines from IEEE, IEC or independent companies. It should be noted that all power transformers generate gases (including fault gases) during normal and abnormal operation based on loading, transformer age and ancillary items on the transformer.

Senja Leivo

Dec 5, 2018
Thank you for your valuable comments. It is true that interpretation of DGA may be challenging, because after all each power transformer is unique due to their design and use history.

zushi lin

Dec 4, 2018
do you mean that NDIR monitor have no maintenance cost over 10 years? considering all the mechanical parts used it is difficult to believe that a complex electro/mechanical system that has to measure gases to the ppm level will have no parts failure in 10 years+ that will need repair and maintenance.

Senja Leivo

Dec 5, 2018
Thank you for your question on Vaisala Blog.

Of course, not all NDIR technologies are the same. We can only speak for the Vaisala’s technologies. In the IR measurement technology of the OPT100 DGA monitor, we use only solid components, meaning there are no moving elements in its optical measurement module. All sensor components are manufactured by Vaisala, in own cleanroom, using MEMS technology. In sensors we can tune the IR band pass filters for preferred wave lengths. Also the light source is MEMS based, no filament used there. The sensor components have been extensively tested for life time expectancy significantly over 10 years.

The sensing technology itself includes various automatic proprietary procedures to detect and compensate off ageing of any components like light intensity decrease over years. However, the gas absorption wavelengths do not change as its just fundamental physical phenomenon. By keeping the IR filter properties stable and other components constantly compensated, it is possible to achieve measurements that do not need any factory nor user made site calibration during the years of operation.

What comes to the technology used in oil and gas handling in the OPT100, the only moving parts are magnetic valves and a magnetic gear pump. The specification, capacity and load used in those elements give estimated life time clearly over 10 years as well. Also those components have been heavily tested in conditions and load much over their specification and the actual use in OPT. We have not find any failures in those tests either.

All piping is stainless steel and machined parts high quality aluminum. The pipe fittings used are also the highest grade available on the market, commonly used in extreme-pressure pure gas applications.

All in all, the OPT100 is designed and its components chosen so that we can achieve maintenance free device. Which we truly believe in.

Senja Leivo
Senior Industry Expert

jim ronnie

Dec 5, 2018
A good question leading to a better insight to the difference in "no maintenance" and "failure" in the context of this article. The latter will be determined by the design and show up in MTBF (calculated and demonstrated in life tests/field). Former suggests that the reliability/mtbf is not affected by leaving the units installed without on-going maintenance during this period. Taken to its conclusion then the quality of the on-site installation is an important consideration all other things being equal.

Senja Leivo

Dec 20, 2018
Thank you for your comment. It is a good clarification on the difference between ‘no maintenance’ and ‘failure’. The Optimus™ OPT100 DGA monitor is designed so that it does not need any maintenance actions by user to maintain its measurement performance. However, with modern electronics, it is possible, although unlikely that a component fails, for example. This has been considered in OPT100 development by implementing self-diagnostics procedures which continuously monitor its critical components and operational functions informing the user if any issue arise.
And like you said, obviously the quality of the on-site installation is an important factor as well for reliable long-term online monitoring.

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