BY DAVID P. STOCKTON,
JOHN R. BLAND, JR.,
TODD MCCLANAHAN,
JIM WILSON, DAVID L. HARRIS,
& PATRICK MCSHANE
F
IRE
SAFETY,
FIREWALLS,
deluge systems, and fluid containment are some of the fire protection problems users face when
installing mineral oil filled transformers. Aging
substation infrastructure, environmental protection, and resource sustainability are other growing
issues. To address these concerns, natural ester fluids are being utilized for their superior fire, environmental, and life-extension properties. Natural
ester fluid offers the highest fire point of any insulating fluid at 360 °C and a flawless fire safety
record through ten years and more than 45,000
installations. Natural ester fluid is manufactured
IEEE INDUSTRY APPLICATIONS MAGAZINE JAN j FEB 2009 WWW.IEEE.ORG/IAS
from seed oil and biodegradable additives, mak-
68
ing it readily biodegradable in the case of a spill.
The combination of fire safety and biodegradability typically eliminates the traditional need for
Digital Object Identifier 10.1109/MIAS.2008.930887
© PHOTODISC
Safety, reliability, and environmental
performance of natural ester fluids
1077-2618/09/$25.00©2009 IEEE
incorporated less-flammable transfirewalls and deluge systems and can
former fluids in 1978. Qualifying
reduce spill containment, reporting,
fluids must meet a minimum criteand remediation requirements. PropNATURAL ESTER
rion of 300 °C open-cup fire point.
erties unique to certain seed oils help
FLUIDS CAN BE
Figure 1 shows the fire and flash
to slow down the insulation aging rate
points of mineral oil and natural
and to stabilize the electrical performREJUVENATED,
ester, less-flammable fluids.
ance of the transformer [1].
Because of this series of environmenThis article presents information on
RECYCLED, AND
tal regulations and liability risks involvthe safety, reliability, and environmental
ing nonedible oils such as mineral oil, an
performance of natural ester transformer
READILY
extensive research and development profluids by acquainting the readers with
gram began in the early 1990s. Rethe history of transformer fluids and
DISPOSED.
searchers concluded that natural esters
also explores how the industry has
could be chemically enhanced to overarrived at the current technologies of
come the initial barriers of inferior oxidanatural ester fluid. The properties of
natural ester fluids are explained and then compared side by tion stability, pour point, permittivity, and viscosity values.
According to the IEEE specification, when a new insulaside with conventional mineral oil fluid.
This article outlines two refinery case studies. The tion system is developed, it is recommended to test the sysfirst case study is from a refinery in Texas City, where nat- tem following the C57.100 standard, also known as the
ural ester transformers were chosen for a new wet gas Lockie method. This method is known as Standard for Thermal
scrubber project. The second case study is from a refinery Evaluation of Oil-Immersed Distribution Transformers Life Test
in Memphis, Tennessee, where natural ester fluid was [17]. This method uses actual transformers (Figure 2).
used to retrofill an in-service, large-power transformer.
These two case studies show the applicability of natural
ester fluids in new and retrofilled distribution and power
class transformers
400
Flash Point
350
300
250
200
150
Mineral Oil
Natural
Ester Fluid
Flash Point
155
330
Fire Point
165
360
1
Transformer fluid flash and fire points.
2
Lockie-accelerated aging transformer test facility.
Authorized licensed use limited to: IEEE Xplore. Downloaded on January 7, 2009 at 11:14 from IEEE Xplore. Restrictions apply.
IEEE INDUSTRY APPLICATIONS MAGAZINE JAN j FEB 2009 WWW.IEEE.ORG/IAS
Temperature (°C)
Fire Point
History of Transformer Fluids
In the United States, the first distribution class transformer
was constructed in 1885 and was of dry-type construction;
it used air as the dielectric coolant. Although smaller and
more efficient mineral oil transformers were patented in
1882 by Elihu Thomson, it was not until 1892 that General Electric produced the first-known liquid-filled transformer. Shortly after 1899, the key mineral properties were
identified, and oil refineries began manufacturing this special transformer mineral oil [2].
For many decades, transformer users have recognized
the benefits of liquid-filled transformers in comparison
with dry-type transformers: overloadability, contamination resistance, surge protection, efficiency, space savings,
noise levels, complete diagnostic capabilities, temperature, and expected life are some of the superior characteristics of these.
From 1929 to 1977, polychlorinated biphenyl (PCB)filled transformers were commonly used, promoting fire
safety in addition to the common liquid-filled transformer
benefits. In 1976, the Toxic Substance Control Act [3] targeted the PCBs with extensive Environmental Protection
Agency (EPA) regulation to follow the most recent
changes in 1998 [4], [5]. Following a government ban of
the further production and commercialization of PCB fluids due to environmental concerns, users turned to mineral
oil and less-flammable fluids [6], [7].
Mineral oil, however, did not provide the necessary fire
protection. The American National Standards Institute
(ANSI) has published a Guide for Substation Fire Protection
[8], stating that the minimum recommended distance to a
building is 30 ft for mineral-oil-filled transformers greater
than 333 kVA because of the increased fire risk.
Originally referred to as high fire-point fluids until
1984, the National Electric Code (NEC) formally
69
Normative Annex A of this standard
defines a sealed tube aging procedure for
testing when it is not practical to test an
actual transformer. Using this method,
the insulation system must meet a minimum of 50% retained tensile strength
for an equivalent of 65,000 h, 25%
retained tensile strength for an equivalent of 130,000 h, or a degree of polymerization (DoP) greater than 200 for an
equivalent of 150,000 h. Detailed results
of this test are shown in a condensed format in Table 1 [18].
MINERAL OIL FIRES
CAN PROPAGATE
TO NEARBY
EQUIPMENT AND
BUILDINGS.
TABLE 1. TEST PARAMETERS FOR TRANSFORMER-ACCELERATED
AGING EVALUATION AND RESULTS [19].
Test Cell
A
B
C
167
175
183
1,302
721
407
21
21
21
Hours
6,510
3,604
2,036
Years equivalent
105
105
105
10,186
6,623
328
271
Target hottest-S pot
temperature (°C)
Standard required
expected life*
Years equivalent
Standard test method
required life**
Actual times to failure***
11,400 þ 1,190
Hours
Years equivalent
464
Environmental and sustainable characteristics are increasingly important.
Natural ester fluids have been tested
for biodegradability and can be classified in the most favorable EPA classifications of ultimately biodegradable
and readily biodegradable ester fluids
[20], [21]. These fluids have also been
tested for acute aquatic toxicity with
zero trout mortality through the
standard test period of 96 h at 1,000
mg/kg [22], [23]. However, EPA
SPCC essentially does not differentiate
100
15,000
75
10,000
25
5,000
0
0
0
1,000
2,000
3,000
4,000
Time at 170 °C (h)
Mineral Oil
Natural Ester Fluid
Degree of Polymerization
20,000
Retained Tensile Strength (% of Unaged)
1,200
Tensile Strength (lb/in2)
IEEE INDUSTRY APPLICATIONS MAGAZINE JAN j FEB 2009 WWW.IEEE.ORG/IAS
Natural Ester Fluid Properties
Environmental Safety
Hours
70
Because of the extremely favorable
results of this testing, further testing
was conducted. Figures 3 and 4 show
the significantly slower aging rate of
thermally upgraded kraft paper in natural ester fluid when compared with
mineral oil. ANSI defines the end of
life of a transformer as 25% retained
tensile strength for distribution transformers and 50% retained tensile
strength for power transformers.
Using DoP, end of life is defined as
being less than or equal to 200. Both
of these figures show the data results
from tests performed at 170 °C. It has
been estimated that thermally upgraded kraft paper in natural ester
fluid will have the same life in an 85
°C temperature rise transformer as that
of an identical paper in a 65 °C temperature rise mineral-oil-filled transformer [19].
1,000
800
600
400
200
0
0
1,000
2,000
Natural Ester Fluid
Calculated from IEEE Loading Guide (Error Bars = 1σ)
4
3
Aging rates (as tensile strength) of thermally upgraded
paper in natural ester and mineral oil [19].
4,000
Time at 170 °C (h)
Mineral Oil
Calculated from IEEE Loading Guide (Error Bars = 1σ)
3,000
Aging rates (as DoP) of thermally upgraded paper in
natural ester and mineral oil [19].
Authorized licensed use limited to: IEEE Xplore. Downloaded on January 7, 2009 at 11:14 from IEEE Xplore. Restrictions apply.
between oils while some state regulations do differentiate.
Additionally, natural ester fluids
are classified under the Edible Oil
Regulatory Reform Act [16]. The
complete combustion products are carbon dioxide and water. The fluid can
be rejuvenated, recycled, and readily
disposed.
ANOTHER ADDED
FEATURE OF
NATURAL ESTER
FLUIDS IS THE
SOLUBILITY OF
WATER IN THE
FLUID.
Fire Safety
because of the proven fire-safety record
of less-flammable liquids. Code listing
requirements are now equal to or more
flexible than those listed for silicone
oils [14], [15].
FM Global increased the maximum fluid volume from 1,000 to
10,000 gal of an approved, lessflammable fluid-filled transformer
for a given minimum clearance distance that is considered to be equivalent safeguard as firewalls and
fire-suppression systems [24]. This
change allows the users to lessen the
separation distance for both equipment to buildings (Table 2) and equipment to equipment (Table 3).
TABLE 3. OUTDOOR LIQUID-INSULATED EQUIPMENT-SEPARATION DISTANCES [24].
Approved
Transformer
or Equivalent
Liquid
Approved, lessflammable fluid
Unapproved fluid
Horizontal Distance, ft (m)
(Based on Construction Type)
Liquid Volume,
gal (m3)
2-h Fire
Resistant Noncombustible
Vertical
Distance,
Combustible
ft (m)
Yes
N/A
3 (0.9)
3 (0.9)
3 (0.9)
5 (1.5)
No
10,000 (38)
5 (1.5)
5 (1.5)
25 (7.6)
50 (15.2)
>10,000 (38)
15 (4.6)
15 (4.6)
25 (7.6)
50 (15.2)
5 (1.5)
15 (4.6)
25 (7.6)
25 (7.6)
N/A
<500 (1.9)
500–5,000 (1.9–19) 15 (4.6)
>5,000 (19)
25 (7.6)
25 (7.6)
50 (15.2)
50 (15.2)
50 (15.2)
100 (30.5)
100 (30.5)
Authorized licensed use limited to: IEEE Xplore. Downloaded on January 7, 2009 at 11:14 from IEEE Xplore. Restrictions apply.
IEEE INDUSTRY APPLICATIONS MAGAZINE JAN j FEB 2009 WWW.IEEE.ORG/IAS
There are a percentage of substation
transformer fires that are eventful,
often resulting in oil fires that are
difficult to extinguish and are very
costly to control. These mineral oil
fires can also propagate to nearby
equipment and buildings, creating a very large problem and risk. It is costly to control the fire, perform Relative Performance
the necessary safety and clean-up processes, and repair A commonly occurring problem of transformers using carthe equipment; however, the downtime for these bon-based fluids is the development of coking on conducactions to occur is perhaps the most costly of all.
tors and switch contacts. Coking tendency tests indicate
These fires can be avoided by using a natural ester, that the natural ester fluid resists coke formation on hot
less-flammable dielectric coolant. Factory Mutual (FM) metals [25]. A paper presented at the 2006 IEEE Power
Global became the first nationally recognized testing Engineering Society (PES) Transmission and Distribution
laboratory (NRTL) to list these less-flammable fluids (T&D) conference showed that stationary contacts had by
[9]. Underwriters Laboratories (UL) then, in 1984, far the most stability during accelerated life test when
developed a new standard for transformers, combining tested with natural ester [26].
the fire resistance of lessflammable fluids with the transTABLE 2. OUTDOOR LIQUID-INSULATED EQUIPMENT-SEPARATION
former-protection schemes [10],
DISTANCES [24].
[11]. There are currently ten
Approved
listings of less-flammable diTransformer
Liquid Volume,
Distance,
electric coolants by FM Global
or Equivalent
gal (m3)
ft (m)
Liquid
and UL [10], [12].
Yes
N/A
3 (0.9)
Approved,
In 1994, FM Global also
less-flammable
adopted transformer installation
No
10,000 (38)
5 (1.5)
fluid
guidelines that combined an ap>10,000 (38)
25 (7.6)
proved, less-flammable fluid with
transformer protection per their
Mineral oil or
N/A
<500 (1.9)
5 (1.5)
Approval Standard 3990 [13].
unapproved fluid
5005,000
25 (7.6)
FM Global’s initial installation
(1.919)
requirements based on specific
heat-release rates have been elimi>5,000 (19)
50 (15.2)
nated for this class of material
71
tend to polymerize, causing a
Another added feature of natural
gradual increase in viscosity. Natural
ester fluids is the solubility of water in
esters are designed for use in sealed
the fluid. Figure 5 shows a solubility
THE NATURAL
transformers [18].
chart of water in both mineral oil and
Natural ester has the tendency
natural ester fluids. This allows the
ESTER FLUID
for thin films of the fluid to polyfluid to remove more moisture away
merize on hot surfaces exposed to air
from the insulating paper, resulting in
RESISTS COKE
much more quickly than mineral
improved dielectric performance,
FORMATION ON
oil. These films have excellent
elimination of the possibility of vapor
dielectric properties but can inhibit
bubble formation during sudden overHOT METALS.
mechanical operation and increase
load, and a reduction in the paper
the power factor of the coil, and
aging rate. It also reduces or elimishould thus be avoided. This does
nates the need for periodic, transnot become an issue unless an
former dry-out services.
The natural ester maintains higher dielectric strength, impregnated core and coil assembly are removed from
especially at cold temperatures, because of its more fa- the fluid and stored for several weeks [25].
Doble Engineering developed the power factor valvorable saturation curve compared with mineral oil (see
Figure 5). However, the pour point temperature is signifi- ued oxidation (PFVO) and sludge-free life (SFL) tests
to resolve the issue of testing oxidation stability of
cantly higher than mineral oil.
transformer fluids [28].
72
The historically based opinions that natural esters did
not have sufficient oxidation stability properties were
commonly derived from results of tests such as ASTM D
2112 and D 2440. When these test methods are applied
to natural esters, they perform very poorly because of the
nature of the tests. The tests are used to check the inhibitors used in the mineral oil but are not indicative of inservice performance.
The reason for the attention to oxidation stability is
due to the degradation products of mineral oil precipitating as sludge. However, natural esters oxidize much
differently because of the chemical composition of the
fluid. Rather than a sludge precipitant, natural esters
5,000
Water Saturation Point (mg/kg)
IEEE INDUSTRY APPLICATIONS MAGAZINE JAN j FEB 2009 WWW.IEEE.ORG/IAS
Oxidation Stability
4,000
3,000
2,000
Case Study 1: New Distribution
Transformer Installation
History or Project Scope
Following a fatal explosion at the largest oil refinery in
Texas City, Texas, the refinery is currently initiating an
extensive maintenance and modernization program. The
company’s five-year, US$1 billion focus on the future plan
is promoting the highest levels of safety, reliability, and
environmental performance in equipment installation and
upgrades [29].
One such investment was a wet gas scrubber project to
reduce sulfur oxide and nitrogen oxide emissions from the
fluid catalytic cracking units, which required ten liquidfilled transformers.
The wet gas scrubber being installed was to replace an
existing system using an electrostatic precipitator. Earlier,
the electrostatic precipitator was using an existing
double-ended substation, and the equipment was required
to remain in service while the wet gas scrubber system was
being installed. This meant that the real estate was at an
extreme premium, with very little room to work while
installing the new system.
Original Specification
1,000
0
20
40
60
80
Temperature (°C)
A–
Saturation (T ) = 10 ·
100
120
B
273 +T
Natural Ester Fluid: A = 5.3318, B = 684
From Double Engineering
Mineral Oil: A = 7.0895, B = 1,567
From IEEE C57.106
When specifying the transformers for this project, the
customer and the electrical contractor extended bid
opportunities to multiple equipment manufacturers,
specifying mineral oil as a standard, with natural ester
fluid as an alternate. Although the consultant was relatively familiar with natural ester products, the customer
was not initially aware of the option and the benefits
inherent with such a fluid.
Findings with Natural Ester Fluid
5
One hundred percent water saturation versus temperature
of natural ester fluid [26] and mineral oil [27].
Following the receipt of proposals for the liquid-filled
transformers, the consultant began reviewing the pricing and options. The natural ester-filled transformers
were consistently higher on purchase price. After
further investigation, it was found that there were additional benefits in using natural ester-filled transformers
Authorized licensed use limited to: IEEE Xplore. Downloaded on January 7, 2009 at 11:14 from IEEE Xplore. Restrictions apply.
that would help to justify and offset
these purchase costs.
Health, Safety, Security,
and Environment
Because of the company’s increased
safety awareness, there were very
stringent installation procedures for
liquid-filled transformers. According
to the health, safety, security, and environment (HSSE) policy, the customer
was required to install a deluge system
and containment for every new liquidfilled transformer installation.
Option 1: Fire Deluge System
NATURAL ESTERS
ARE DESIGNED
FOR USE IN
SEALED
TRANSFORMERS.
The refinery was not amenable to a
fire deluge system for several reasons. It is required to test the system
periodically. To perform this test,
the transformers must be deenergized. Since these are the main power
feed transformers for the entire refinery, this was not an option. Additionally, the refinery was concerned
about spraying the equipment with
water containing chlorine and other
additives.
Option 2: Firewalls Between Transformers
Final Installation and Future Transformers
Case Study 2: Retrofilled Power
Transformer
History or Project Scope
The refinery had two existing mineral-oil-filled power
transformer units feeding the electrical distribution system. The transformers were base rated 25 MVA, with a
maximum rating of 46.6 MVA. The primary voltage was
161 kV delta connected, stepping down to a service voltage of 12.47 kV wye connected. The two transformers had
been purchased in 1980.
The refinery’s insurance company, FM Global, evaluated the two units and determined that the units were
too close to one another. The separation distance was not
sufficient for mineral oil transformers. The insurance
company presented two options to the refinery: fire deluge
system and firewalls between transformers.
This option was very carefully evaluated. In the end, it was
determined that in the case of a spill and a fire the firewalls
would merely channel the propagating fluid fire toward
the rest of the substation, further spreading the fire and
destroying more equipment.
Other Options: Less-Flammable Fluids
The plant electrical engineer began researching other
methods for fire safety. While researching the FM
Global guidelines, it was found that less-flammable
fluids can be used to significantly reduce the separation distances between equipment as shown in Table 2.
The refinery approached FM Global with the option of
retrofilling both the units with an approved natural
ester, less-flammable fluid. FM Global readily accepted the option.
When discussing this retrofilling option with the
transformer original equipment manufacturer (OEM), it
was found that the equipment was not required to be
derated and that the mineral oil and natural ester fluids
are completely compatible.
Future Transformers
An additional power transformer was purchased for the
refinery, and natural ester fluid was specified for the unit.
The refinery plans to purchase all future units with natural
ester fluids.
Conclusions
The growing demands for improved fire safety, source
material sustainability, environment friendliness, and
asset life extension have driven the research and development efforts of natural ester, less-flammable fluid. The
majority of performance characteristics of natural ester fluids are far superior to those of conventional mineral oil,
including fire safety, material compatibility, electrical and
thermal characteristics, and a significant reduction in
insulation aging rate.
The two case studies presented in this article have
shown the applicability of a natural ester fluid in both new
and retrofilled power and distribution transformers. In
addition to being used in outdoor applications, natural
ester fluid-filled transformers are becoming more commonly used indoors because of their proven fire-safety
performance and code-compliance options.
The largest disadvantage to natural ester fluid-filled
transformers is the first cost price differential of
Authorized licensed use limited to: IEEE Xplore. Downloaded on January 7, 2009 at 11:14 from IEEE Xplore. Restrictions apply.
IEEE INDUSTRY APPLICATIONS MAGAZINE JAN j FEB 2009 WWW.IEEE.ORG/IAS
The idea of the alternate natural ester fluids was
presented to the customer. During this presentation,
items such as fire safety and environmental performance were the biggest decision drivers.
With the flawless fire record in more than 45,000
applications over ten years, the HSSE group recognized
the safety benefits [25]. Because of this, the group made
the decision not to require fire deluge systems for the new
natural ester-filled transformers.
Equally, the group evaluated the biodegradation properties of the natural esters. After being presented with
information showing that the fluid is greater than 99%
biodegradable after 21 days, the HSSE group made the
decision that containment was not required for these natural ester-filled transformers [20], [21].
After the requirement for tire deluge systems and
containment were removed from the natural ester, lessflammable fluid-filled transformers, the prices were
reevaluated. The installation cost savings for natural
ester-filled transformers easily justified the small purchase price difference.
In this application, the natural ester fluid not only met
all focus-on-the-future objectives but also reduced the
total installation cost of the transformers while saving
space on a project where real estate was at a premium.
For all future installations of liquid-filled transformers,
the refinery has adopted a policy of natural ester, lessflammable fluid-filled transformers.
73
[17] Standard for Thermal Evaluation of Oilapproximately 10–15% more than
Immersed Distribution Transformers, ANSI/
the conventional mineral oil. HowIEEE Standard C57.100-1986, 1986.
THE
NATURAL
ever, the fluid offers a significant life
[18] C. P. McShane, G. A. Gauger, and J. Lukcycle value for users, justified with
sich, ‘‘Fire-resistant natural ester dielecESTER MAINTAINS
tric fluid and novel insulation system for
the performance advantages of the
its use,’’ in Proc. IEEE/IAS Transmission
fluid.
HIGHER
and Distribution Conf., New Orleans, LA,
Electrical groups, including mem1999.
bers of IEEE Petroleum and Chemical
[19] C. P. McShane, ‘‘Vegetable-oil-based dielecDIELECTRIC
tric coolants,’’ IEEE Ind. Applicat. Mag.,
Industry Committee (PCIC), have
pp. 34–41, May/June 2002.
helped to develop new standards for
STRENGTH,
[20] Office of Prevention, Pesticides, and
natural ester dielectric fluids. An
Toxic Substances, ‘‘Fate, transport, and
ESPECIALLY AT
American Society for Testing and
transformation test guidelines: OPPTS
Materials (ASTM) standard for the
835.3100 aerobic aquatic degradation,’’
COLD
U.S. Environmental Protection Agency,
acceptance of new natural ester dielecWashington, DC, EPA Publication, 712tric fluids was issued in 2003 [30]. An
TEMPERATURES.
C-98-075, Jan. 1998.
American National Standard Institute
[21] Office of Prevention, Pesticides, and Toxic
(ANSI)/IEEE standard guide for the
Substances, ‘‘Fate, Transport, and Transformation Test Guidelines: OPPTS 835.3110
acceptance and maintenance of natural
ready biodegradation,’’ U.S. Environmental Protection Agency,
esters is in the balloting process [31]. As more users adopt
Washington, DC, EPA Publication, 712-C-98-076, Jan. 1998.
this technology, user groups must also work to help [22] OECD,
‘‘Test no. 203: Fish, acute toxicity test,’’ in OECD Guidelines
develop database information, especially for preventative
for the Testing of Chemicals, Section 2: Effects on Biotic Systems, Paris
maintenance purposes.
Cedex, France: Organization for Economic Cooperation and Develop-
Acknowledgments
We gratefully acknowledge the contributions of Jerry
Corkran, John Luksich, Peter Stenborg, Kevin Rapp, Jonathan Piel, Larry Bucholtz, Henry Hecker, Roger Bengtson, Jeff Schneider, Ray Schmidt, Dave Vetterick, and Jim
Harrison.
IEEE INDUSTRY APPLICATIONS MAGAZINE JAN j FEB 2009 WWW.IEEE.ORG/IAS
References
[1] (2001, June). Envirotemp FR3 Fluid. Cooper Power Systems Bulletin
00092 [Online]. Available: http://www.cooperpower.com/Library/
pdf/00092.pdf
[2] F. M. Clark, Insulating Materials for Design and Engineering Practice.
New York: Wiley, 1962.
[3] Toxic Substance Control Act. U.S. Public Law 94-469, 1976.
[4] PCB Regulations, Environmental Protection Agency, Part 761, 40
CFR, 1979.
[5] Disposal of Polychlorinated Biphenyls (PCBs), Environmental Protection
Agency, Parts 750-761, 40 CFR, 1998.
[6] M. Earley, ‘‘Minimizing the hazards of transformer fires,’’ Fire J.,
pp. 73–74, Jan./Feb. 1988.
[7] D. A. Hallerberg, ‘‘Less-flammable liquids used in transformers,’’
IEEE Ind. Applicat. Mag., vol. 5, pp. 50–55, Jan./Feb. 1999.
[8] IEEE Guide for Substation Fire Protection, IEEE Standard 979-1994, 1994.
[9] Factory Mutual Approval Guide. Norwood, MA: Factory Mutual
Research Corporation, 1979.
[10] ‘‘R-temp fluid UL classification marking,’’ in Gas & Oil Equipment
Directory. Chicago, IL: Underwriter’s Laboratories, 1984.
[11] S. D. Northrup, ‘‘Protection of transformers for prevention of rupture, explosion, and fire,’’ presented at the Edison Electric Institute
Transmission and Distribution Conf., Fort Worth, TX, 1985.
[12] Factory Mutual Approval Guide. Norwood, MA: Factory Mutual
Research Corporation, 1999.
[13] Less and Nonflammable Liquid Insulated Transformers, Factory Mutual
Research Corporation Approval Standard Class Number 3990.
[14] ‘‘Loss prevention data sheet 5-4/14-8,’’ Norwood, MA: Factory
Mutual Research Corporation, 1997, revised 1998.
[15] NEC Requirement Guidelines, 1999 Code Options for the Installation of
Listed Less Flammable Liquid Filled Transformers. Waukesha, WI:
Cooper Power Systems, 1999.
[16] Edible Oil Regulatory Reform Act, Public Law 104-55, 1995.
ment, 1992.
[23] ‘‘Final report: Acute trout toxicity testing for two Envirotemp FR3
formulations,’’ GlobalTox Int. Consultants, Guelph, ON, Canada,
Dec. 1, 1999.
[24] ‘‘5-4 transformers,’’ Section 2.3.1.1.1 Separation Distance,
Property Loss Prevention Data Sheets, Factory Mutual Global,
May 2003.
[25] C. P. McShane, J. Corkran, K. Rapp, and J. Luksich, ‘‘Natural ester
dielectric fluid development,’’ presented at the IEEE/PES Transmission Distribution Conf. and Exposition, Dallas, TX, 2006.
[26] L. Lewand, ‘‘Laboratory evaluation of several synthetic and agricultural-based dielectric liquids,’’ in Proc. Doble Int. Client Conf., 5th ed.
Boston, MA, 2001.
[27] IEEE Guide for Acceptance and Maintenance of Insulation Oil in Equipment, IEEE Standard C57.106-2002, 2002.
[28] F. S. Oliver, ‘‘Doble power factor valued oxidation tests,’’ in Doble
Conf. Minutes, Insulating Fluids, 10-401, pp. 1–9, 1960.
[29] BP Investigation Team, ‘‘Fatal accident investigation report, isomerization unit explosion final report,’’ BP North America, Houston,
TX, 2005.
[30] Standard Specification for Natural (Vegetable Oil) Ester Fluids for Use in
Electrical Apparatus, ASTM D 6871-03, 2004.
[31] Proposed Standard Guide for Acceptance and Maintenance of Natural Ester
Fluids in Transformers, IEEE Standard C57.147.
[32] L. Dix and P. Hopkinson, ‘‘Tapchangers for de-energized operation in
natural ester, mineral oil, and silicone,’’ presented at the IEEE/PES
Transmission and Distribution Conf., Dallas, TX, 2006.
David P. Stockton (dstockton@cooperpower.com) and Patrick
McShane are with Cooper Power Systems in Waukesha, Wisconsin. John R. Bland, Jr., is with BP Texas City Refinery.
Todd McClanahan is with Valero Refining in Memphis, Tennessee. Jim Wilson is with Jacobs in Houston, Texas. David
L. Harris is with Waukesha Electric Systems in Wisconsin.
McClanahan and Harris are Members of the IEEE. McShane
is a Senior Member of the IEEE. This article first appeared as
‘‘Natural Ester Transformer Fluids: Safety, Reliability, and
Environmental Performance’’ at the 2007 Petroleum and
Chemicals Industry Conference.
74
Authorized licensed use limited to: IEEE Xplore. Downloaded on January 7, 2009 at 11:14 from IEEE Xplore. Restrictions apply.