FIELD OF INVENTION:
This invention relates to a process for the estimation of 2-furfuraldehyde in
transformer oils
BACKGROUND OF THE INVENTION:
Electrical power transformers play an important role in power distribution
system In many types of transformers, cellulose based paper and board are used
which serve as dielectric insulation for the electrical windings The windings are
supported on a core, which is immersed m insulating oil For safe and reliable
operation of the transformer, it is necessary to monitor, the quality of insulation
by regularly testing the oil and paper
During the operation of a transformer, thermal degradation of insulation paper
occurs as a natural process Insulation paper in the transformer is subjected to
thermal oxidation and hydrolytic degradation This will result in chain scission
of cellulose and reduction of degree of polymerization (DP) values, resulting in
the formation of CO, CO2 and furan derivatives such as 5-Hydroxy methyl 2-
furfuraldehyde, 2-furfurylalcohol, 2-furoic acid, 3-furoic acid, 2-furfurylmethyl
Ketone, 5-methyl 2-furfuraldehyde and 2-furfuraldehyde Measuring the DP
value of cellulose or determining the level of by products formed on aging are
discussed in The method involved in the measurement of DP-value of
insulating paper is quite laborious and time consuming, further it is not possible
to measure DP value at site to know the condition of transformer insulation The
relative amounts of CO, CO2 and other gases evolved as by products are

determined by Gas Chromatography (GC) to identify the faults inside the
transformer However, because of the interference of the background level
of gasses that are generally present in aged transformer oils, interpretation of the
results obtained by GC is difficult and the condition of the cellulose insulation
cannot be predicted On-line GC has been attempted but it has not been
successful for detecting the 2-furfuraldehyde content at early stages, 1 e there
is a limitation in the detection limits Direct estimation of furfural derivatives by
Ultra Violet (UV) spectrophotometric method is not possible, as all these
derivatives absorb UV radiation in the region 200-300 nm due to n-n* and n-n*
transitions Among the furan derivatives, 2-furfuraldehyde is identified as the
most critical compound which is having direct correlation with DP of paper The
absorption maxima of 2-furfuraldehyde is at 270 nm which is very close to other
furfural derivatives Hence it is difficult to estimate 2-furfuraldehyde in
transformer oil m presence of other furfural derivatives by UV method High
performance Liquid Chromatography (HPLC) is the current method being used
for the detection of 2-furfuraldehyde (FFA) and its derivatives in aged
transformer oil It is quite accurate but requires lengthy extraction procedure and
it is not suitable for field testing Presently, the furfural derivatives as estimated
by IEC-61198 method is quite laborious and time consuming
Apart from the open literature, www uspto gov site has been searched for
patents with a search string 'furfuraldehyde' AND 'transformer oil Two patents
available on this subject are discussed below
1 Patent No 5,646,047-'Method and reagent kit for determining paper
degredation in transformers' and
2 Patent No 6,235,532-'Furfuraldehyde detector and method of
manufacturing the same

Patent No 5, 646,047- This invention pertains to a method and apparatus for
detecting the degree of degradation of paper insulation in a transformer by
determining the concentration of furfuraldehyde in transformer oil This invention
uses halogenated hydrocarbons as solvents which are toxic and health hazard
It was an object of 'Patent No 6,235,532 'Furfuraldehyde detector and method of
manufacturing the same' to mitigate or obviate one or more of the above
disadvantages This invention uses porous solid sensor comprising aniline
acetate entrapped in sol-gel inert matrix Preparation of the sol-gel is
cumbersome and time consuming The invention is silent about determination of
FFA in high aromatic paraffinic oils Minimum concentration of FFA that can be
determined by this method has not been claimed Also, in presence of other
furfuraldehyde derivatives, the accuracy of estimation of 2-FFA and their
interference has not been discussed
Present Status
The current practice involves periodically collecting samples of oil from the
transformer or transformers to be tested, transporting the samples to a
laboratory, usually remote from the transformers, and analysing the samples
using an extraction process with solvents like Acetonitnle, Methanol and Water
and analyzing the extracted furfural derivatives by HPLC following the procedure
as given in IEC-61198 The reagents used during the chemical analysis (and the
fumes produced) are toxic if ingested and therefore great care must be taken
during the laboratory chemical analysis
Present practices therefore do not enable an on-the-spot assessment (or
estimate) of the state of the paper insulation via FFA measurements to be made
The analysis is conducted in a chemical laboratory, sometimes days after the oil
samples were actually collected from the transformers And also, the analysis is

slow and expensive The effect of this delay may sometimes lead to failure of
transformers
Short comings present in the existing prior art are summarized below
1.0 Methods adopted lack accuracy in determining the 2-furfuraldehyde content
and in situ measurement is not possible
2 0 Procedures involved are lengthy, cumbersome and time consuming Also, the
solvents recommended were halogenated hydrocarbons which are toxic and
hazardous to health
3 0 Detection limits of 2-furfuraldehyde content is limited
4 0 As furfural is light sensitive and if the oil is exposed to light, or storage for a
long duration, there is a possibility of change m concentration leading to
erroneous estimation
5 0 Accuracy of estimation of 2-FFA in presence of other furfuraldehyde
derivatives, and their interference has not been discussed
OBTECTS OF THE INVENTION;
An object of this invention is to propose a process for the estimation of 2-
furfuraldehyde in transformer oils,
Another, object of this invention is to propose a reliable technique for direct
determination of 2-furfuraldehyde,
Further, object of this invention is to propose a process for the estimation of 2-
furfuraldehyde with accuracy,

Still further object of this invention is to propose a process for the estimation of 2-
furfuraldehyde from the transformer oil without using the cellulose paper.
DESCRIPTION OF THE INVENTION:
According to this invention there is provided a method for the estimation of 2
furfuraldehyde in transformer oils comprising:
adding glacial acetic acid and aniline to the transformer oil to form a pink
coloured complex at 20°C.
The main object of the present invention is to ovecome the difficulties
encountered in the earlier literature, in estimating the furfuraldehyde content in
transformer oils.
The invention is reliable technique for direct determination of 2-furfuraldehyde
in service aged transformer oil using prototype spectrophotometer, which has
been applied for field-testing. The transformer oils used in India are high
aromatic content (20%) paraffinic oils and also have high sulphur content to the
extent of 1.5%. However, this technique can also be applied for determining the
2-FFA in Naphthenic oils with optimum aromatic content (8%). Minimum
concentration of 2-FFA that can be determined by this method in presence of
other furfuraldehydes to a level of 0.05 mg/ltr with a relative standard deviation
of 0.24%. The present spectrophotometric method relies on the specific reaction
between FFA and the compound aniline acetate which yields a complex with a
bright pink colour, the intensity of which is a characteristic which can be
measured photo-optically and which correlates with the concentration of FFA in
the transformer oil.

In the present invention, a direct rapid spectrophotometric method has been
developed for estimation of 2-furfuraldehyde(2-furfural) in transformer oil at about
20°C by formation of pink coloured complex with aniline acetate having maximum
absorption at 526 nm The bathochromic shift of maximum absorption of 2-
furfural at 270 nm to 526 nm after forming the complex is due to ring opening and
also due to increase of  electron conjugation in the system
Different experiments were conducted with different ratios of aniline and glacial
acetic acid and it is found that the absorption at 526 nm of the complex is highest
when distilled aniline and glacial acetic acid were used in the ratio of 1 9 (v/v)


The absorption is directly proportional to molar concentration and obeys Beer-
Lambert's law The effect of path length on the absorption 2-FFA with Aniline-
Acetic acid complex at 526 nm was also studied and found that the absorption of
2-furfural complex increases with increase in path length of cell A path length of
2 5 cm which is ideal is chosen for the present invention

Number of measurements = 5
The effect of temperature on the stability of the complex was also studied and
found that at 20°C the absorption of 2-furfural-anihine-acetate complex is
maximum and more stable compared to higher temperatures The complex
stability time is dependant on the concentration of 2-furfural present in the oil, viz
0 5 minutes for a concentration of 0 05 mg/ltr and 2 5 minutes for a concentration
of 10mg/ltr


The interference of other furan derivatives were determined quantitatively by
treating the blank transformer oils with these individual compounds and
developing the complex with aniline glacial acetic acid under identical conditions
It was found that 2-furoic acid, 3-furoic acid and 2-furfuryl methyl ketone do not
form any complex, whereas 5-hydroxy methyl-2-furfurldehyde (5-HM 2-FFA), 5-
methyl 2-furfuraldehyde (5-M 2-FFA), and 2-furfurylalcohol developed complex of
negligible intensity as compared to 2-furfuraldehyde Table-4 gives the
percentage absorption of above mentioned derivatives at 526 nm From the
table, it is clear that the absorption of 2-FFA complex is maximum and is 150
times greater than other FFA substitutes, which indicate negligible absorption
values


Experiments were conducted to see the effect of aniline reagent quality on the
absorption value at a maximum wave length of 526 nm Table-5 gives the values
of absorption at different concentrations of 2-FFA with distilled and undistilled
Aniline

Different experiments were also conducted to study the effect of reference
(blank) on the absorption values Consistent maximum absorption values with
aniline glacial acetic acid reagent were obtained with laboratory aged transformer
oil matching with the colour of the service aged sample oil Compared to
naphthenic oils, fresh paraffinic based transformer oils available in India are
yellowish or yellowish orange in colour Service aged transformers oils are mostly
brownish or dark brownish in colour and hence it was necessary to generate

blank oils used for calibration and reference by laboratory ageing the fresh oil in
accelerated environment till the colour matches with the sample oil The effect of
different compositions of reference solutions on absorption of 2-FFA is also
studied Four solutions containing different propositions of aniline, acetic acid,
toluene and transformer oil (aged and fresh) have been prepared The
compositions are shown as R1, R2, R3, and R4 The different compositions of
reference solutions are given in table -6 The effect of different compositions of
reference solutions on the absorption values of 2-FFA complex is given in table-
7 It is observed that the absorption values containing aged transformer values
are found to be consistent and sensitive to even trace levels of 2-FFA in oil

**aged transformer oil to match the colour, *fresh transformer oil
■f


In the present invention a portable spectrophotometer equipped with 2 5cm path
length cell was used The pink color complex was formed by adding 10 ml
solution mixture of distilled aniline and glacial acetic acid in 1 9 ratio and 5 ml of
service aged transformer oil sample and 10 ml of spectral grade toluene The
optical density of this solution was.recorded at 526 nm at temp 20°C with
reference solution prepared as above Calibration curve was generated by using
synthetic mixture containing 2-furfuraldehyde(distilled) in laboratory aged
transformer oil in the concentration range of 0 05-10 mg/liter (oil aged with out
cellulose paper) having the same colour as the service aged sample oil The
values estimated in synthetic blends were determined as per the developed
procedure and the percentage error is calculated (Table-8)


*Number of Measurements 3
The correlation constant determined was 0 9964 The minimum detection limit of
2FFA in transformer oil was found to be 0 05mg/L with RSD 0 24% The
comparative values of 2-Furfuraldehyde determined by the standard IEC method
and the developed method based on Aniline-Acetic Acid complex was found to
be matching for different site transformer oils The comparative values are given
in Table-9

A portable kit comprising aniline and glacial acetic acid can be used at the test
site to determine 2-FFA instantaneously in the sample oil

We claim:
1 A method for the estimation of 2-furfuraldehyde in transformer oils
comprising
adding glacial acetic acid and aniline to the transformer oil to form a
pink coloured complex at 20°C, wherein the ratio of aniline to glacial
acetic acid is standardized as 1.9 (v/v) and the temperature is 20°C
2. The method as claimed in claim 1, wherein the estimation of 2-
furfuraldehyde is preferred without extraction
3 The method as claimed in claim 1, wherein on adding aniline and acetic
acid directly to transformer oil and a pink coloured complex is formed
with 2-furfuraldehyde at 20°C having maximum absorption at 526nm
4 The method as claimed in claim 1, for which a portable
spectrophotometer with a wave length measunng range of 380 to 700nm,
with a fixed path length of 2 5cm, having a provision of blank solution
zero balancing and data storage, is used for estimation.

5. The method as claimed in claim 1 to 4, which can be carried out by a
portable kit comprising aniline and glacial acetic acid.
6. The method as claimed in claim 1, wherein the estimation of
furfuraldehyde in oil can be done in any concentration ranging from 0.05
to 10 Mg/Ltr and above with good reproducibility and repeatability.

ABSTRACT

Title Estimation of 2-furfuraldehyde in service aged transformer oils
The present invention to the development of a new spectrophotometric
technique for predicting the dissolved 2-furfuraldehyde (2-FFA) in transformer
oils It is based on measurement of optical density of a colored complex
formed by the addition of aniline and glacial acetic acid to service aged
transformer oil at 20°C and at a wave length maximum of 526nm In order to
increase the accuracy and minimize the back ground interference, calibration
standards have been prepared by ageing the transformer oil without cellulose
paper in an accelerated way, so that the colour matches with the sample
under testing