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
The estimated total costs over the service life of an online DGA sensor also favor single/dual gas systems. They show a better ratio of total costs to investment costs.
| DGA-System | Invest1[€] | Life cycle[Jahre] | Costs/Year[€] | Costs in 15 Years[€] | Total costs[€] | Ratio Total costs/Invest |
| MSENSE® DGA 2 | ~5.500 | 15 | 275 | 4.125 | 9.625 | 1,75 |
| MSENSE® DGA 3 | ~6.800 | 15 | 340 | 5100 | 11.900 | 1,75 |
| MSENSE® DGA 5 | ~15.000 | 15 | 1125 | 16.875 | 31.875 | 2,125 |
| MSENSE® DGA 9 | ~26.000 | 15 | 1950 | 29.250 | 55.250 | 2,125 |
1depends on the configuration of the device
Estimation of the total lifetime costs of an online DGA sensor.
| Costs per year: | |
| MSENSE® DGA 2 | 5% of Invest |
| MSENSE® DGA 3 | 5% of Invest |
| MSENSE® DGA 5 | 7,5% of Invest |
| MSENSE® DGA 9 | 7,5% of Invest |
Figure 1: Estimation of the total lifetime costs of an online DGA sensor
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.
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
