Significance of the Topic
The analysis of dissolved gases in transformer oil is a critical diagnostic tool for the early detection of insulation degradation and thermal faults in high-voltage equipment. Monitoring gas concentrations allows maintenance teams to predict potential failures, optimize service intervals and extend transformer lifetimes.
Study Objectives and Overview
This application note presents a workflow for dissolved gas analysis in mineral oil using ASTM D3612 Method C (headspace sampling) on the Bruker TOGA Analyzer. The goal is to demonstrate full separation, reliable quantification and excellent repeatability for key fault gases.
Methodology and Used Instrumentation
The protocol employs a closed-vessel headspace sampler (SHS-40) to partition gases from oil into an argon headspace. After calibration with a Morgan Schaffer standard, the volatile fraction is directed through:
- A Hayesep P precolumn
- A Carboxen-1000 micro packed column
- A micro packed Molsieve column
- Thermal Conductivity Detector (TCD) for H2, O2 and N2
- Flame Ionization Detector (FID) with methanizer for CO, CH4, CO2 and C2–C3 hydrocarbons
Main Results and Discussion
Chromatograms from both TCD and FID channels show baseline separation of seven target analytes. Repeatability tests (n=7) on a transformer oil sample yield relative standard deviations below 3.1 % for N2, CH4 and CO2, meeting the precision window defined in ASTM D3612. Back-flush timing ensures removal of higher hydrocarbons (C4+).
Benefits and Practical Applications
The described headspace-GC method offers:
- Non-destructive extraction of dissolved gases
- Rapid sample throughput with automated headspace injection
- High sensitivity and linearity for fault gas quantification
- Compliance with international standards for transformer maintenance and safety
Future Trends and Applications
Emerging directions include coupling headspace techniques with mass spectrometry for trace-level detection, integrating real-time monitoring sensors in transformer bushings and developing advanced data analytics to correlate gas profiles with specific fault types.
Conclusion
The Bruker TOGA Analyzer combined with SHS-40 headspace sampling enables robust, standard-compliant analysis of dissolved gases in transformer oil. The method delivers full component separation, accurate quantification and excellent repeatability, making it a reliable solution for asset health monitoring.
References
1. ASTM Standard D3612-02, Analysis of Gases Dissolved in Electrical Insulation Oil by Gas Chromatography, Method C, ASTM International
Content was automatically generated from an orignal PDF document using AI and may contain inaccuracies.
Insulating fluids, generally mineral oils, are used in
transformers. Under normal, mild conditions there is
very little decomposition.
Occasionally however (localized or general) overheating
of the oil occurs and decomposition products are formed.
If the concentration of these gases reaches a critical point,
the chances of catastrophic transformer failure are high.
The ASTM D 3612 method1 describes in detail three
different routes.
A. Vacuum Extraction.
The gases are extracted from the oil via a vacuum
extraction device and analyzed via gas chromatography.
B. Stripper Column Extraction.
Dissolved gases are extracted from a sample of oil by
sparging the oil with the carrier gas on a stripper column
containing a high surface area bead. The gases are then
flushed from the stripper column into a gas chromatograph
for analysis.
C. Headspace Sampling.
An oil sample is brought into contact with a gas phase
(headspace) in a closed vessel purged with Argon.
Application Notes #283028
Transformer Oil Gas Analysis with the Bruker TOGA
Analyzer equipped with the Bruker Headspace Sampler.
Gases in Transformer
Oil Analysis
As a result, a portion of a gas dissolved in the oil is
transferred to the Headspace.
This application note describes Method C.
Instrumentation
Gas Chromatograph
• Bruker TOGA Analyzer based on 450-GC
Headspace Sampler
• SHS-40 Headspace Analyzer
GC control and data handling
• Compass CDS software
Figure 1. TOGA analysis, TCD channel.
Materials and Reagents
“True North” DGA Oil Standard by Morgan Schaffer:
Hydrogen
88 ppm
Oxygen
11163 ppm
Nitrogen
40368 ppm
Methane
96 ppm
Carbon monoxide
89 ppm
Carbon dioxide
123 ppm
Ethylene
90 ppm
Ethane
92 ppm
Acetylene
84 ppm
Table 2. TCD, FID, Methanizer settings.
Table 1. Column oven settings.
Safety Class 1
Rate (°C/min)
Step (°C)
Time (min.)
Initial
50
5.0
10.0
75
0.0
20.0
220
10.25
Total Time
25.0
Table 3. Valves.
Time
(min)
(1) Gas
Sampling
Valve
(2) Series
bypass
Sample
Event
A
Initial
Fill
Series
OFF
OFF
3.0
Fill
Series
OFF
ON
4.2
Fill
Bypass
OFF
ON
TCD
Ar reference flow
10 mL/min
Temperature
200°C
Filament temperature
254°C
Carrier gas
N
2 /Ar
Total Time
25.0
FID
Temperature
300°C
Ar makeup flow
20mL/min
H
2 flow
10mL/min
Air flow
300mL/min
Methanizer
Temperature
400°C
Figure 3. Schematic overview hardware.
Figure 2. TOGA analysis FID channel.
Sample Preparation
The Morgan Schaffer Calibration Standard is carefully
transferred into the headspace vial.
The gases are extracted from the oil by means of a
headspace sampler and injected onto a short Hayesep
P precolumn and then to a micro packed Carboxen-1000
column. The fraction containing Hydrogen, Oxygen,
Nitrogen, Carbon Monoxide, and Methane will elute direct
from the Carboxen-1000 column to the micro packed
Molsieve column. Hydrogen, Oxygen and Nitrogen are
detected by the TCD. Carbon Monoxide, and Methane are
detected by the FID, after passing the Methanizer. When
the Molsieve column is bypassed, Carbon Dioxide and the
C
2 -C3 isomers are eluting from the Carboxen-1000 column
and detected by the FID after passing the Methanizer.
The back flush time is set to completely elute the C
3
isomers. C
4 and higher are back flushed.
Extraction, Method Parameters:
Conditions
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Bremen · Germany
Phone +49 (0)421-2205-0
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[email protected]
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Results and Discussion
Chromatograms of both TCD and FID channels are shown
in Figure 1 and Figure 2. The complete hardware
configuration (SHS-40/TOGA) is shown schematically in
Figure 3.
Repeatability is tested by analyzing multiple samples from
the same source. Data can be found in Table 4.
Table 4. Repeatability data.
Run
N
2
Peak Area
CH
4
Peak Area
CO
2
Peak Area
1
692201
609
369764
2
696712
606
365757
3
669175
584
361535
4
678626
592
361783
5
709715
577
364403
6
702775
576
376105
7
724545
607
393602
n
7
7
7
Average
696249.9
593.0
370421.3
St.Dev.
18640
14.4
11414
RSD (%)
2.68
2.43
3.08
A graphic representation of the data is shown in Figure 4
and Figure 5.
Figure 4. Repeatability results of a Transformer Oil.
Figure 5. Repeatability results of a Transformer oil.
Besides the analytical result also the window specified in
the ASTM D 3612 method is presented.
From the data presented in Table 4, Figure 4 and Figure 5 it
is clear that the repeatability of the system is well within the
window specified by the ASTM D 3612.
Conclusion
Full separation of all components of interest, easy and
reliable quantification results with very good repeatability
was achieved.
The analysis of dissolved gases in transformer oil according
to ASTM D 3612, Method C, can be performed perfectly
with the Bruker Transformer Oil Gas Analyzer (TOGA
Analyzer) in conjunction with the Bruker SHS-40
Automated Headspace Sampler.
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References
1. ASTM Standard D 3612 - 02, “Analysis of Gases Dissolved in
Electrical Insulation Oil by Gas Chromatography. Method C”,
ASTM International, West Conshohocken, PA, www.astm.org
