Efficient transformer monitoring
Why trend analysis with MSENSE® DGA 2/3 is sufficient
Monitoring transformers and tap-changers is crucial for operational safety and early fault detection. While multi-gas DGA systems are often considered the most comprehensive solution, practical experience shows that continuous trend analysis with simple sensors such as the MSENSE® DGA 2/3 is not only sufficient but also significantly more cost-effective.
Oil testing is still very often carried out only once every one to two years in the laboratory – in between, the condition of the equipment remains largely unknown. Multi-gas sensors provide a detailed analysis of the entire gas spectrum, but they are expensive. And even when multi-gas sensors are used, a laboratory analysis is usually carried out to validate the results when the sensor issues a warning or alarm message. Online DGA systems such as the MSENSE® DGA 2/3, on the other hand, continuously provide trends for critical gases such as hydrogen (H₂) and carbon monoxide (CO), which are produced during thermal and electrical faults and when paper degradation begins.
Costs/Benefits of Various DGA Monitoring Techniques
| DGA Monitoring Technique Used |
Number of Avoided Failures per Year |
Avoided Costs in M$ per Year |
| None | None | None |
| Laboratory DGA | 2 | 7 |
| Monitors M1, M2 | 4 | 13 |
| Monitors M3 to M9 | 5(+0.8) | 18(+24) |
Table 1: CIGRÉ D1/A2 Technical Brochure TB 783, DGA monitoring systems, Chapter 2.7
Good to know
The estimated total costs over the service life of an online DGA sensor also favor single/dual gas systems. They show a significantly better ratio of total costs to investment costs.
Recessed installation of MSENSE® DGA 2/3
The new option of recessed installation of the MSENSE® DGA 2/3 also makes it easier to retrofit existing systems. With a simple double screw connection, the sensor can be installed up to 20 cm outside the transformer tank – without the need for a ball valve with no loss of measurement quality.
- Transformer wall
- Gate valve (or other type of valve)
- Double screw connection
- MSENSE® DGA 2/3 and
- Oil convection in the transformer
Conclusion
Trend analysis with the MSENSE® DGA 2/3 is a practical, cost-effective, and reliable solution for condition monitoring and early fault detection. It offers everything you need for effective monitoring—without the complexity and costs of a multi-gas system.
Results of two exciting case studies
400 kV single-phase GSU transformer, 267 MVA
400 kV single-phase GSU transformer, 267 MVA
Findings:
- Increase in hydrogen concentration
- An oil sample was taken. Laboratory analysis confirmed an increased hydrogen concentration and showed an increased acetylene concentration.
- A partial discharge measurement indicated a fault on the high-voltage side of a bushing.
Investigation result: A potential connection on the high-voltage side of a bushing was defective.
Figure 4: Data recording online DGA sensor, H2 increase
380 kV single-phase GSU transformer, 600 MVA
380 kV single-phase GSU transformer, 600 MVA
Findings:
- Continuous increase in hydrogen concentration and other hydrocarbon components.
- Concentrations exceeded the limits for Condition 4 according to IEEE C57.104.
- An oil sample was taken. Laboratory analysis results confirmed the trend.
Investigation results: There was mechanical contact between the core and the tank. This led to a ground fault. A hot spot developed, which caused a ground cable to melt.
Figure 5: Data recording online DGA sensor, H2 increase and increase of other hydrocarbons
Conclusion of the case studies
A comparable trend development and thus the same information content could have been achieved by monitoring the H2 content using a single/dual gas sensor alone – at significantly lower costs.
