Transformer Oil Gas Analysis via Headspace Sampling (ASTM D3612)
Application Note
INTRODUCTION
Insulating fluids, generally mineral oils, are used in
transformers. Under normal, mild conditions, there is
very little decomposition. However, occasionally
localised or general heating of the oil occurs and
decomposition
products
are
formed.
If
the
concentration of these gases reach a critical point,
the chances of catastrophic transformer failure are
high. ASTM D3612 describes in detail three different
routes for transformer gas analysis.
During Vacuum Extraction gases are extracted from
the oil via a vacuum extraction device and analysed
using gas chromatography (GC). Stripper Column
Extraction details the extraction of dissolved gases
from a sample of oil by sparging the oil with the
carrier gas, onto a stripper column containing a high
surface area bead. The gases are then flushed from
the stripper column into a GC for analysis. The final
method is Headspace Sampling in which an oil
sample is brought into contact with the headspace in
a closed vessel sparged with argon. As a result, a
portion of gas dissolved in the oil is transferred to the
headspace. This application note describes the final
method; Headspace Sampling.
EXPERIMENTAL
The SCION TOGA Analyser comprised of a SCION 456
GC with FID and TCD detectors. A headspace sampler
in sample loop mode was also used. Figure 1 details
the schematic overview of the TOGA Analyser.
Table 1 details the analytes of interest obtained from
an injection of a commercial oil standard.
The calibration standard is carefully transferred into
the headspace vial. The gases are extracted from the
oil by means of a headspace autosampler and
injected onto a short porous polymer precolumn and
then onto a micro packed spherical carbon molecular
sieve column. The fraction containing hydrogen,
oxygen, nitrogen, CO and methane will elute directly
from this column onto the packed SCION Molsieve
column. Hydrogen, oxygen and nitrogen are detected
by the TCD. CO and methane are detected by the FID,
after passing the methaniser. When the molsieve
column is bypassed, CO2 and the C2-C3 isomers elute
from the porous polymer column and are detected
by the FID (after passing through the methaniser).
The back flush is set to completely elute the C3. C4+
are backflushed. Tables 2a and 2b detail the method
parameters used throughout this application note.
Analyte
Conc (ppm)
Hydrogen
88
Oxygen
11163
Nitrogen
40368
Methane
96
Carbon Monoxide
89
Carbon Dioxide
123
Ethylene
90
Ethane
92
Acetylene
84
Table 1. Commercial oil standard components
AN0030
Fig 1. Schematic operation of the TOGA Analysis
Table 2a. Analytical conditions of the GC
Condition
Oven
50°C (5 mins), 10°C/min to 75°C, 20°C/min to 220°C
TCD
200°C, Filament 254°C, Air 10mL/min, Carrier N2/ Ar
FID
300°C, Ar makeup 20mL/min, H2 10mL/min,
Air 300mL/min
Methaniser
400°C
Time (min)
GSV
Series
Bypass
Sample
Event A
Initial
Fill
Series
OFF
OFF
3.0
Fill
Series
OFF
ON
4.2
Fill
Bypass
OFF
ON
Table 2b. Valve settings
RESULTS
Chromatograms of both TCD and FID are shown in
Figures 2 and 3.
Repeatability was tested by analysing multiple
samples from the same source. Table 3 shows the
repeatability data whilst Figures 4 and 5 show
graphic representation of the repeatability of the
TOGA analyser.
Fig 2. TOGA Analysis; TCD channel
Fig 3. TOGA Analysis; FID channel
Run
N2
CH4
CO2
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
Ave
696249.9
593
370421.3
RSD %
2.68
2.43
3.08
Table 3. Peak area repeatability values
Fig 4. Repeatability data N2 and CO2
N2
CO2
CH4
Fig 5. Repeatability data CH4
The repeatability data shown above is well within
the defined limits specified by ASTM D3612 (N2
<5%, CO2 <4%, CH4 <4%).
CONLUSION
Full separation of all components of interest with
easy and reliable quantification results in very
good repeatability using the SCION Transformer
Gas Oil Analyser. The analysis of dissolved gases in
transformer oil according to ASTM D3612, method
C, can also be performed perfectly with the SCION
TOGA analyser with headspace sampler.
SCION Instruments HQ
SCION Instruments NL BV
Livingston Business Centre,
4462, Goes,
Kirkton Road South, Livingston,
Stanleyweg 4.
EH54 7FA, Scotland, UK.
The Netherlands
Tel: +44 1506 300 200
Tel: +31 113 348 926
www.scioninstruments.com
www.scioninstruments.com
H2
O2
N2
