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2017-PPIC-0263
Methanol as an Ageing Marker for In Service Transformers
Charles E. Bare 11
Stanley Y. Merritt
Member, IEEE
Highground Services, Inc.
601 N. Mechanic St.
Franklin, VA23851, USA
cbare@highgroundservices.com
Abstract - Measurement of transformer remaining useful life has
long been a goal for responsible asset management. Most testing
laboratories offer furan concentration testing as a suitable method.
The interpretive method of choice is usually the Chendong equation
expressed in practical terms as degree of polymeri zation of the
paper with new paper at about 1000 and end of life at around 300.
Typical mill transformers have insulation ratings expressed as 55°
C rises for plain kraft or 65° C which corresponds to thermally
upgraded kraft paper (TUP). It has been determined that TUP
paper does not produce Furans and thus provides a false indicator
of the cellulose breakdown. There are several papers currently in
circulation that have demonstrated that a measurement of Methanol
(MeOH) may be a better method to determine ageing of the TUP
insulation and also for transformers with regular kraft paper
insulation. The objective of this paper is to provide an overview of
the reasons why furans should not be used as the basis for
measuring degradation of thermally upgraded paper, why methanol
should be so used, and to compare actual furans and methanol test
data for service aged transformers in a process industry application
Index Terms-Cellulose Insulation, DGA, Dissolved Gases, Furanic
Compounds, Methanol (MeOH), Polymeri zation, Thermally
Upgraded Kraft Paper (TUP)
I.
INT RODUCTION
Many and probably most mill substation transformers are
rated for a 65 degree rise of average winding temperature
over a 30 degree ambient. Using the thermal model of IEEE
standard C57 .91-2011 the resulting hotspot temperature will
be 110 deg C. The only insulating paper that is rated for 110
deg C is thermally upgraded paper such as "Insuldur" or
"Thermo ZA". There are good reasons to use thermally
upgraded paper other than the temperature rating,
particularly since its oxidation consumes water and
neutralizes acid
It has long been accepted that a different interpretation of
furan concentration must be applied to thermally upgraded
paper as compared with plain kraft. There is a modified
Chendong equation for thermally upgraded paper. Recently,
however, several technical papers have been published that
support the belief that at temperatures near the rated value of
110 deg C. there is actually no furan produced by
degradation of thermally upgraded paper.
We were able to find 4 research papers which reported aging
tests of thermally upgraded paper in oil which produced no
Senior Member, IEEE
Highground Services, Inc.
601 N. Mechanic St.
Franklin, VA 23851 , USA
smerritt@highgroundservices.com
detectable furans at temperatures from 105 to 170. (See
Table 1, we were not able to find any research reports of
ageing tests which did produce detectable furans at these
temperatures.
Table 1- Su mortinl! R esearc hPapers
Source
TUP
Temp.
2FAL
Paper
Range
Ref 5
Insuldur
70,90,1 ND
Luundgard
10,130
Ref 8
Manning
60
to ND
lalbert
220
130
Ref 3
Thermo
140,15
ND
Yamagata
ZA
5,170
Ref 7
NS
105,
ND
CIRED
122,
0695
130
11.
DP
Retained
NS
Methanol
ppb
NS
NS
1000
50%
NS
50%
1000
TYPICAL SCREENING AND DGA SCREENING
A typical test report from a reputable laboratory on a mill
transformer with thermally upgraded paper will show furans
at less than 100 ppb and will conclude that therefore loss of
useful life is less than a year. We have seen this from 3 well
known test laboratories. In light of the available literature it
seems more likely that the reason no furans were found is
that thermally upgraded paper does not produce furans in
measurable quantities as a degradation product and absence
of furans does not provide reliable indication about condition
of the paper.
Fortunately, there appears to be a better way to go. CIGRE
has a working group to assess the use of methanol as a
marker since it is produced by both plain kraft and thermally
upgraded paper. A report of this working group is included
as Re£ 6. (Ryadi)
PARAPHRASED FROM A 2016 REPORT BY A MAJOR
TESTING LABORATORY
Furanic Compound Diagnostics (most recent sample): New
insulation with a high degree of mechanical strength will
typically have a Degree of Polymerization (DP) of 10001300. "Middle Aged" paper is approximately 500 and paper
with less than 250 is in its "Old Age. " Severely degraded
insulation with a DP of 150 or less will have very little
mechanical strength and may result in a transformer failure.
The above estimations are based on a study by Chendong of
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2017-PPIC-0263
GSU transformers filled with mineral oil. Estimated Average
Degree of Polymerization
(DP): >1003 Estimated Operating Age of the Equipment:
<1.0
Diagnostics:
DGA Key Gases / Interpretive Method: PER IEEE C57.I042008 (most recent sample)
Hydrogen within condition J limits (J 00 ppm). Methane
within condition J limits (J20 ppm). Ethane within condition
J limits (65 ppm). Ethylene within condition J limits (50
ppm). Acetylene within condition J limits (J ppm). Carbon
Monoxide within condition J limits (350 ppm). rDCG within
condition J limits (720 ppm). Carbon Dioxide: Condition 2
Indications of overheated cellulose insulation (2500 ppm).
(1) DP: >1003 Estimated Operating Age of the
Equipment: <1. 0
(2) Carbon Dioxide: Condition 2 Indications of
overheated cellulose insulation (2500 PPM)
How can both of these statements apply to the same
transformer at the same time?
Unpacking the background for these conflicting statements:
(l)ls based on the measured furan concentrations of less
than 10 ppb
(2)ls based on ANSl/IEEE Std. C 57.104
(3)There is a growing body of literature (see references)
which supports the following argument:
(a) If a transformer is rated for 65 deg rise the
insulation is thermally upgraded paper which is
produced by a pulping process which
impregnates the paper with a nitrogenous
compound usually dicyandiamide.
Most
modern transformers use thermally upgraded
paper (TUP) which entered general use about
50 years ago.
(b) The referenced process of analysis is based on
plain kraft paper which could be used in a 55
deg C rise transformer but not in a 65 deg C
transformer
(c) Some degradation products of plain kraft paper
are (CO +C02), H2O, and furans
(d) Some degradation products of TUP are (CO +
C02) in quantities about 5 times that for plain
kraft, and NH3. H20 is consumed and not
produced. If any furans are produced they are
very quickly consumed by the NH3. A recent
paper by engineers from a major European
OEM states shows in laboratory tests So the
high (CO + C02) and the low furans are both
simply due to the fact that the insulation is TUP
and neither can be relied on as an indicator of
life remaining or life used. The logical
statement (obviously a disconnect) from the
report would be " We could not detect
measurable quantities of a compound which is
not produced by the degradation of the actual
insulation, therefore we are confident that the
insulation is essentially like new".
(4)The same body of literature shows that methanol is
produced by degradation of both plain kraft and
TUP and is stable in the transformer mineral oil
environment. It presents extensive reports which corelate methanol concentration with mechanical
strength of the paper.
(5)The authors of many of the papers are with Canadian
and European firms and other reputable entities. It
is not possible to dismiss use of the methanol
marker for life estimation as unproven or too novel
to consider. At least 2 major testing laboratories,
one in Europe and one in the USA can test oil
samples for methanol.
(6)CIGRE has a working group addressing the issue.
See their report below:
Ill. METHANOL AS A MARKER
The CIGRE report is shown below: (Ref. 6)
CONDITION ASSESSMENT
Presented by: Mohamed Ryadi (EDF-R&D)
Principal investigators: Jocelyn Jalbert, Marie-Claude
Lessard and Mariela Rodriguez-Celis (Hydro-Quebec-IREQ)
"Is there enough experience to consider MeOH as a new
marker fOr early stage paper degradation in transfOrmers?
Many papers promoting the use of methanol as a marker for
early stage paper degradation have been written since 2007.
These fundamental papers described different laboratories
ageing studies which validate the reliability of methanol
(MeOH) as a chemical marker for cellulose paper
degradation. Indeed, it has been demonstrated that MeOH
can be produce from both standard and thermally upgraded
Kraft papers under different ageing conditions. The authors
demonstrated the direct relationship between the scission of
the glycoside bond of the cellulose chain and the MeOH
generation.
In the particular transformer application, Hydro-Quebec and
Electricite de France now use this marker on a regular basis
for the residual life estimation and the diagnostic of cellulose
abnormal ageing. For example, Hydro-Quebec experienced a
cooling problem on an OF AF transformer insulated with
Insuldur thermally upgraded paper. After the analysis of the
cellulose chemical markers: ~ 100 ppb of2-furfural (2-FAL)
was found compared to ~650 ppb of MeOH. Based on the 2-
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2017-PPIC-0263
FAL concentration, the cellulose insulation seems to be well
preserved but the MeOH concentration revealed that the
cellulose has suffered from this lack of cooling.
groups and methanol from the depolymerization of
cellulose during the ageing of paper/oil systems. Part 2:
Cellulose,
thermally-upgraded insulating papers.
In 2007, EDF performed analysis by measuring MeOH
content in oil of some transformers in order to detect units
with signs of thermal ageing. A follow up during two years
of one suspected unit, a transformer equipped with standard
Kraft paper insulation, showed a relatively high level of
methanol and 2-F AL. Indeed, the methanol concentration
was higher than 1000 ppb and more than 2000 ppb of2-FAL
were found. The post-mortem analysis performed by
measuring the degree of polymerization (DPv) of 40 paper
samples coming from different areas of the winding gave an
average DPv of about 300. A correlation between DPv of
paper samples and the chemical markers concentrations,
previously observed, was confirmed.
5. Denos Y. , Tanguy A. , Guunic P., Jalbert 1., Gilbert R ,
Gervais P., Ageing diagnosis by chemical markers:
influence of core-type and shell-type technology, Cigre,
Paris, August 2010.
6.1. Jalbert, C. Rajotte, M. Ryadi and P. Guuinic, Alcoholbased ageing chemical markers for the diagnosis of
transformer cellulosic insulation, CIGRE, Kyoto, 2011.
7.1. Jalbert, R Gilbert, Y. Denos and P. Gervais, Methanol :
A novel approach to power transformer asset
management, IEEE Power Delivery, vol. 27, No. 2,
April 2012.
8. USBR Fist 3-31 Transformer Diagnostics
" What are the known drawbacks and advantages related to
the MeOH utilization when comparing to 2F AL?"
What is the activity in the U.S . regarding the use of
methanol as an ageing marker?
The advantages of using MeOH over 2-FAL are the direct
relationship with the cellulose chain scission no matter the
insulation paper is a standard or a thermally upgraded Kraft
paper. The early detection in the transformer oil helps to
follow the trend at the beginning of the transformer
operation and/or determine abnormal ageing occurring with
the cellulose insulation . It has been also demonstrated that
MeOH is a stable compound over the transformer
temperature operation range.
Like moisture in oil, MeOH is highly influenced by the oil
temperature and in the future, it will be very important to
correct the concentration at a given temperature to obtain the
real trend . However, at a less extend, 2-FAL is also
temperature dependent.
IV. READING LIST OF RELATED PAPERS
A reading list of papers related to the use of methanol as a
chemical marker of insulating materials degradation can be
found below.
l. Jalbert, 1. , Gilbert. R , Tetreault, P., Morin , B., LessardDeziel, D. Identification of a chemical indicator of the
rupture of 1 ,4-~-glycosidic bonds of cellulose in an oilimpregnated insulating paper system, Cellulose, 14:295-
309, 2007.
2. Gilbert, R , Jalbert, 1., TetreauIt, P. , Morin , B. , Denos, Y.
Kinetics of the production of chain-end groups and
methanol from the depolymerization of cellulose during
the ageing of paper/oil systems. Part 1: standard wood
Kraft insulation. Cellulose, 16:32 7-338, 2009.
3.1. Jalbert, R Gilbert, Y. Denos and P. Gervais, Chemical
markers for the determination of power transformer
insulating life, a step forward, Proceeding of the 76th
Annual International Doble Client Conference, 2009.
4. Gilbert, R , Jalbert, 1. Duchesne, S, TetreauIt, P., Morin,
B. , Denos, Y. Kinetics of the production of chain-end
17:253-269, 2010.
1. What is IEEE doing? The Insulation Life Committee is
planning for a 30 minute presentation by the Chair on
methanol.
2 What is ASTM doing? There is a working group on
standards for evaluating methanol concentration.
3. What are the testing laboratories doing?
We have found only one laboratory which tests for methanol.
4. There are no recognized standards for correlating
methanol level with DP and remaining useful life. There
are some papers with good pedigrees on which one could
base a conclusion.
5. The authors have project responsibility for remammg
useful life estimates using methanol on 7 industrial units
with thermally upgraded paper. There is good historical
data on these units using carbon oxides and also furan
measurements. Samples were drawn in late October 2016
and a report is given below.
V.
CASE HISTORY OF LIFE MARKERS ON
INDUSTRIAL TRANSFORMERS
Below are tabulated data of aging markers, recorded over a
period of 10 years on 7 industrial distribution transformers
which use thermally upgraded paper. Acid number, 1FT,
moisture, and DBV are impeccable and so are not shown.
CO and C02 levels in many cases exceed Condition 2 and in
some cases Condition 3 per IEEE Std. 104. Some of the test
reports concluded on this basis that severe overheating had
occurred. It is more likely that instead the numbers are high
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2017-PPIC-0263
because thermally upgraded paper produces more CO + C02
than plain kraft paper.
Furans are essentially zero and some reports concluded that
the paper was therefore like new. It is more likely that the
data only shows that thermally upgraded paper produces
essentially no furans.
Methanol shows a measurable level which indicates that very
little life has been used. Since no published standards are
known to exist, the paper CIRED PAPER 0695 has been
used as a basis for evaluation. It indicates that if methanol
concentration is less than 500 ppb then DP is more than 900.
The highest methanol concentration is less than 200 ppb so
the indication is that very little life has been used.
As a check on the use of markers it should be noted that
under actual operating conditions, the highest hot spot
temperature can be shown to be about 80 deg C. The
acceleration factor for 80 deg C hotspot is 0.07. If end of life
is taken as 50 % retained tensile strength then the
acceleration factor should be applied to 7.42 years giving a
life of 106 years in the absence of water and oxygen. The
transformers have been in service for about 16 years,
therefore one could say that 2 years maximum of useful life
may have been used. A caveat, which is satisfied, is that all
the factors in the liquid screen are exemplary. Also, low
oxygen must be assured and is so assured by use of a
nitrogen blanket in the headspace.
T able 2- Carbon Monoxide (CO)
7/ 13
3436
7032
8217
2900
4244
2779
4410
10/ 12
3101
6040
8253
2652
3802
2452
4150
4/ 12
1992
4193
5842
1937
2770
1708
3237
5/6
1286
3984
3192
1287
1359
858
1788
5/5
1014
2653
3281
1069
1139
695
1540
5/4
1221
2589
4047
13 30
1373
809
In tables 2 and 3 the Italics mdlcate a pomt which
Condition 2 or 3 for co and C02.
1585
IS
m
Table 4 expresses condition levels of concern as defined by
IEEE ANSI Standard C 57-104.
Table 4- C 57- 104 C on dT
I IOn L eve Is ~or E va I uatlOn ppm
Condition
CO
CO2
1
0-350
0-2500
2
351-570
2501-4000
3
571- 1.400
4001- 10.000
4
1.400
10.000
Table 5- Furans
MMIYY
BI
Cl
Dl
El
FI
10/16
0
0
4/16
0
0
10/15
0
0
10/14
0
0
4
4
7/13
Al
I
8
3
3
GI
2
10/12
1
4
I
I
1
3
1
MM/YY
Al
BI
Cl
Dl
El
FI
GI
4/12
< 10
< 10
< 10
< 10
<10
<10
<10
10/16
283
350
69
308
315
100
291
5/6
NR
NR
NR
NR
NR
NR
NR
4/16
275
97
5/5
NR
NR
NR
NR
NR
NR
NR
10/15
402
157
5/4
NR
NR
NR
NR
NR
NR
NR
10/14
591
357R
7113
761
754
724
537
703
479
618
10/12
528
625
700
526
666
380
564
MMIYY
Al
BI
Cl
Dl
El
FI
GI
4112
784
727
796
838
943
589
554
10/ 16
43
67
154
36
55
39
122
5/6
296
464
520
320
386
273
265
5/5
273
398
412
194
220
143
211
5/4
352
468
591
349
344
321
254
Table 3- Carbon Dioxide (CO2)
MM/YY
Al
BI
Cl
01
El
FI
GI
10116
2611
5880
3089
2474
3450
2079
3428
4116
3271
1931
10115
3974
2582
10114
3133
1928
Tab le 6- Methanol (MeOH)
VI. CONCLUSION
The CO and C02 concentrations are in many instances in
Condition 2 or 3, justifYing extreme concern per IEEE Std.
104. A judgement call was made that the high levels were
actually due to the fact that TUP produces much more CO +
C02 than kraft, and no special measures were taken.
Similarly, the low furan levels were not accepted as proof
that the insulation was like new. In 2016 the methanol levels
on all units were tested. Since there is not yet an ANSIIIEEE
standard for evaluation, CIRED Paper 0695 Fig. 9 was used
978-1-5090-5288-2/17/$31 .00 © 2017 IEEE
2017-PPIC-0263
Page 5 of 7
for evaluation. This showed that all units are at the
beginning of the linear range ofthe plot ofDP as indicated
by methanol concentration and that the average DP is about
950. It will now be possible to track DP as the transformers
age in service. By comparison, even iffurans were produced
the level would not rise to a significant point until the DP
had dropped to the 600 - 700 point. The goal of an objective
test to confirm calculations and to provide real time tracking
ofDP has been met.
VII.
REFERENCES
(1) Methanol as a New Aging Marker of Oil- Filled
Transformer Insulation , CIRED Paper 0695 , 23d
International Conference on Electricity Distribution Lyon
15-18 June 2015 (Perrier et al).
SUMMARY
Test data for thermally upgraded paper in inhibited oil at
105,122, and 130 deg C. shows no detectable 2 FAL even
though significant depolymerization occurred. By contrast,
significant concentration of methanol was measured.
(2) Atanasova
http://www.elp.com/articles/powergrid_ international/print/v
0Iume-16/issue-3/features/ carbon -oxides-in-theinterpretation-of-dga-in-transform ers.html
CARBON OXIDES IN THE INTERPRETATION OF DGA
IN TRANSFORMERS
Partial text
Generally, CO formation shows temperature dependence
and in cases of absence of a severe fault (no acetyleneO is
mainly derived from the insulating fluid. The C02 content
indicates degradation of solid insulation. As a consequence,
a growing trend ratio of C02/CO seems to be a better
indicator of solid insulation degradation than carbon oxide
alone. The usually used range of 3 to 10 should be further
specified and in the case of closed-type transformers,
revised. For closed type systems, or transformers working on
a steady high load, ratios of 0.6 t05 often have been
observed with no fault indication
(3)Yamagata
http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=4580
450&url=http%3A%2F%2Fieeexplore.ieee.org%2Fxpls%2F
abs_all .jsp%3Farnumber%3D4580450
DOl: 1O.1109/CMD.2008.4580450
or
http://www.tandfonline.com/doi/pdtllO.5370mCEE.2011.1.
2.181
EVALUA TION
OF
AGING
FOR
UPGRADED PAPER IN MINERAL OIL
THERMALLY
Partial text
The (CO + C02) content with a percent DP retention value
of 45 % was roughly 1.1 ml/g paper for the Kraft insulation
paper but roughly 5.3 ml/g for the Thermo-ZA a difference
by approximately a factor of 5. This is a point that will
require care if the (CO + C02) content is selected as a
degradation indicating component for maintenance
management of a transformer employing thermally upgraded
insulation paper. Nevertheless, (CO + C02) content
promises to be employable for degradation analysis.
Thermo-ZA generates a larger amount of (C02 +CO) than
Kraft insulation paper. It was confirmed experimentally that
such larger quantity is due to (C02 +CO) produced by
thermal degradation of Thermo- ZA 's dicyandiamide
additive.
It has been reported that heating of thermally upgraded
insulation paper in oil produces hardly any 2-FAL. This
suggests that ammonia (NH3) is generated through
hydrolysis reactions of the additives, and the 2-FAL is
consumed through reactions with the NH3 [lO}. Below is put
forward a 2-FAL consumption mechanism Involving
pyrolysis reactions of the dicyandiamide - the Thermo-ZA 's
main additive. Fig. 9 shows the main decomposition
reactions produced by heating of dicyandiamide. First of
all, heating of dicyandiamide generates NH3 and melamine
as the principal decomposition products. Then reactions
take place between the NH3 and 2-FAL, generating
furfuramide as a byproduct and consuming the 2-FAL.
(4) Lewand
http://www.doble.com/content/products/EnergizeMagazineOctober-2006.pdf
PRACTICAL EXPERIENCE GAINED FROM FURANIC
COMPOUND ANALYSIS
Partial Text
Studies at .. . .... have consistently shown that 90 - 95 % of
samples from transformers with thermally upgraded
insulation have less than about 100 mg/L of 2-furfural.
However, for a similar population study of oils from service
aged transformers with Kraft paper insulation, the 95 %
norm was 2057 mg/L.
The amount and type of furanic compounds is different for
Kraft and TU-Kraft paper. A comparison of the relative
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2017-PPIC-0263
composition of by-products formed under the
controlled laboratory conditions is given:
same
. 0'1
Tabl e 7- Percent Composition to Paper Bsypro d ucts ID
I
COMPOUND
HMF
FOL
FAL
AF
23.3
60.4
KRAFT
0.4
0.1
19.8
2.0
TUK
72.5
4.4
Chemicals in the insulation used for thermal upgrading such
as dicyandiamide significantly reduce the concentration of
furanic compounds in the oil. Data from a furanic compound
analysis should be treated carefully. As described in the
paper upon which this article is based, ....... has developed
a scheme for determining the difference between normal and
accelerated aging based on the insulation type and
preservation system present. The categories are as follows :
a. Kraft paper insulation andfree breathing
conservator
b. Kraft paper insulation and sealed system
c. TU-Kraft paper (chemical addition) and free
breathing conservator
d. TU-Kraft paper (chemical addition) and sealed
system
It has been found that transformers in these categories
produce different amounts offuranic compounds at varying
rates and should not be grouped together as a single
population.
Using rates of accumulation, aids in determining if a fairly
new transformer may have an abnormal overheating
condition much sooner than concentration limits alone. For
example, if a new transformer (sealed wl TUK insulation)
within the first six months of operation produces
a
concentration of 35 microgramlliter in most cases it would
be assumed to be operating normally, since it is less than
100 microgramlliter. However, the 2-furfural accumulation
rate is 70 microgramlL/year, which is excessive and
indicative of accelerated heating of the cellulose insulation.
(5) Lundgaard
hUp://sintef.org/uploadpages/268450/Iundgaard.pdf
AGING OF OIL IMPREGNATED PAPER IN POWER
TRANSFORMERS
Partial text
The effects of moisture, oxygen, and acidity upon the aging
of Kraft and thermally upgraded ("Insuldur® ") papers have
been studied in detail. The results for Kraft are consistent
with the kinetic model and parameters proposed earlier by
Emsley et al., and with the principle that moisture promotes
acid-hydrolysis by causing carboxylic acids to dissociate.
Moisture is released during the aging of Kraft and, hence,
its aging is auto-acceleratory. In contrast, Insuldur
consumed moisture under the same conditions, aged more
slowly, and its aging was less accelerated by added
moisture. 2-Furfuraldehyde (2FAL), which is a dehydration
product of pentosans and, hence, an index of moisture
production, is also released from Kraft during aging, but not
from Insuldur. Acids are, however, producedfrom both types
of paper. Theoretical explanations for these findings are
proposed, and their practical implications for transformer
maintenance are discussed.
Insuldur has performed impressively in this investigation. It
contains additives which consume water by reacting
chemically with it, and organic bases which partially
neutralize the acids. This increases its lifetime by a factor of
about three compared to Kraft.
Insuldur upgraded paper does not produce as much 2FAL as
Kraft paper and, hence, 2FAL can not be used as an
indication of aging in papers of all types.
6. Report ofCIGRE Working Group A2 Ryadi et al
http://www.cigre.org/var/cigre/storage/original/applicationId
d8dfaf508249fD 14f420cd53954c7a2 .pdf
7 CIRED Paper 0695 Methanol as New Aging Marker of Oil
Filled Transformer Insulation Perrier et al
8 Kinetics of the production of chain-end groups and
methanol from the depolymerization of cellulose during the
aging ofPaper/Oil Systems Part 2 Gilbert et al
VIII. YITA
Stanley Y. Merritt (M'95- SM'99- LSM'09)
received the B.S and MS degrees in
electrical engineering from the University
of Tennessee, Knoxville, TN, USA . He is a
Consulting Engineer with Highground
Services, Inc., Franklin, VA, USA. He has
specialized in transformer life extension,
short circuit and stability studies, industrial switchgear, and
motor control for many years. He was also a designer of
marine and aircraft power conversion products for the
General Electric Co., earning two US patents for inverter
circuits. He is the author of numerous conference papers for
the IEEE Pulp and Paper Committee. Mr. Merritt is a
Registered Professional Engineer in Virginia.
Charles "Carl " E. Bare 11 received
B.S.E. T and ME.M degrees from Old
Dominion University, Norfolk, VA , USA .
He retired from the US Navy with 25
years maritime experience as an
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electrician and (Chief) engineering officer. He is currently
a consulting maintenance engineer and project manager
with Highground Services, Inc., Franklin, VA, USA
978-1-5090-5288-2/17/$31 .00 © 2017 IEEE
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