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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Bruker Daltonik GmbH
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
