Online DGA Monitoring of Power Transformers

Qualitrol Duval Triangle Dissolved Gas Analysis Lab Accuracy Diagnostics

Online Dissolved Gas Analysis (DGA) Monitoring of Power Transformers

What are the technology options available when planning to deploy online Dissolved Gas Analysis (DGA) on Power Transformers? A look at why accuracy of the DGA result is so important to success in any online DGA monitor.

Technology for Online Dissolved Gas Analysis

Originally developed as a laboratory technique, involving manual sampling and laboratory analysis in a Gas Chromatography instrument, online DGA use is now a common sight in electrical substations.

Various core technologies are employed in online gas monitors for dissolved gas analysis.  For multigas monitors it can be divided into two groups

  1. “Gas Chromatography” based monitors
  2. “Infra-Red” (plus additional secondary sensors) based monitors eg. PAS

Both technologies face the same challenges: How to track in real time changing gas content over very long periods of time (years or even decades) in sometimes harsh environments and with a high degree of accuracy which is why Methods for On-line Dissolved Gas Analysis of Electrical Insulating Fluids, is such a great read. To check it out, click here.

Online Dissolved Gas Analysis

Planning to employ online DGA Monitoring? How does online DGA monitoring of power transformers create value for electrical substation asset managers?

One of the core objectives of any substation asset manager is to ensure the availability of major assets for as long as possible, while at the same time knowing and planning for when they will finally need to be replaced.

  • Availability is tied to effective maintenance
  • Replacement planning is based on understanding when maintenance is no longer financially prudent

Online DGA is a tool for supporting both.

Online DGA is often considered to be a solution, in its own right. “If you deploy online DGA you have covered your needs for DGA” However this is not actually the case; Online DGA is just a tool to aid in decision making. The real value of online DGA is not in the data, but in the electrical asset managers use of that information to make informed decision.

For reference, please see Michel Duval’s Triangle above. How does one ensure accurate date? With a complex analytical system such as an Online DGA monitor you do it through calibration.

Looking for more information on Michel Duval and his diagnostic tools? Qualitrol has worked extensively with Michel Duval and has covered both the topics of the Triangle in this on-demand webinar and the Pentagon. Both of which can be accessed below:

Dissolved Gas Analysis Systems and Solutions

Monitor calibration is essential for an accurate online DGA system and here’s why!

As noted above there are two core technologies employed for multigas online DGA monitoring.

  1. Gas Chromatography
  2. Infra-Red (plus additional secondary sensors)

For any DGA system based off Gas Chromatography calibration is a routine part of its operation. In GC systems a known gas standard is introduced into the Gas Chromatograph every few days and the sensors are recalibrated. This ensures that the monitor is always operating off a recent calibration and so provides for lifetime accuracy of the DGA monitor

InfraRed based systems (PAS, FTIR, etc) are much more complex to calibrate; True calibration is only every possible in a laboratory environment. For this reason, online systems are either designed to sacrifice calibration entirely or have a routine maintenance cycle that involved replacement of the Infra-Red Spectrometer (and all the secondary sensors). Where replacement of the core sensors is a component of ensuring continued accuracy, this is typically performed every 5 years, and this leave multiple years where the state of calibration is unknown.

For more information on this topic, please read the following paper titled, Analysis of Gases Dissolved in Electrical Insulating Fluids, Technologies and the Importance of Accuracy” which can be found by clicking here.

Power Transformer Monitoring and Dissolved Gas Analysis

Online Dissolved Gas Analysis is an important element of any Transformer monitoring solution.

The key requirement of the technique is detection and diagnosis of the health of the transformer. Where accurate diagnosis is expected accurate data is critical. Inaccurate DGA data can lead to incorrect conclusions and the wrong decision being made, potentially risking a catastrophic outcome.

In this environment an online DGA system capable of providing lifetime accurate DGA data provides a distinct advantage over one that relies on occasional spectrometer replacements or no calibration at all.