Natural Ester Fluid
Diagnostics
Weidmann 7th Annual Technical Conference
September 17, 2008
BY: C. Patrick McShane and John Luksich
Market Demand Accelerating
¾ More than 130,000 transformers in service
¾ More than 120 power transformers in service
– 200 MVA generator step-up retrofill
– 242 kV reactor new
¾ Recent US Utility announced conversions:
– Alliant Energy: 1P and 3P distribution, Iowa GSU
substation retrofills
– Energy East: 1P and 3P distribution
– Xcel Energy: 1P distribution
– ComEd: 1P pole distribution & networks
– American Electric Power: network
– SMUD: distribution and network
Natural Ester Market Drivers
¾ More desirable environmental profile
¾ Improved insulation system life
¾ Increasing demand for sustainable supply
¾ Smaller carbon footprint
¾ Potential for reduced maintenance, dry-outs
¾ Greatly improves fire safety
– Eliminates key eco/health issues
– Reduces or eliminates m.o. required safeguards
Natural Ester Environmentally Preferred
¾ Rapid and complete biodegradation
– Equal to EPA “ultimately biodegradable” class.
>80% in 10 day. >99% 45 days.
¾ Does not contain hazardous additives
¾ Passes OCED Acute Aquatic Toxicity
– No mortality (trout fry)
¾ Renewable Source contributing to
Sustainability
Insulation System Life Extension
Envirotemp FR3 Mineral Oil
Envirotemp FR3 Mineral Oil
Envirotemp FR3 Mineral Oil
Sealed Tube Test - ML 152-2000
Upgraded Paper 500 hr @ 170°C
Sealed Tube Test - ML 152-2000
Upgraded Paper 2000 hr @ 170°C
Sealed Tube Test - ML 152-2000
Upgraded Paper 4000 hr @ 170°C
500 hours
2000 hours
4000 hours
Fire Safety
FM Global Separation Requirements can be less than
1/10 distance required for mineral oil.
Table 2a. Separation Distance Between Outdoor Liquid Insulated Transformers and Buildings
Horizontal Distance1
Noncombustible Combustible Vertical
Two Hour Fire
Liquid
Volume
Resistant Construction Construction Construction ft Distance ft
Approved Transformer
3
(m)
(m)
ft (m)
ft (m)
or Equivalent
gal (m )
Liquid
5 (1.5)
Yes
N/A
3 (0.9)
Less Flammable
≤ 10,000 (38)
25 (7.6)
25 (7.6)
5 (1.5)
(Approved Fluid)
No
> 10,000 (38)
50 (15.2)
50 (15.2)
15 (4.6)
< 500 (1.9)
5 (1.5)
15 (4.6)
25 (7.6)
25 (7.6)
Mineral Oil
(or
N/A
500-5,000 (1.9-19)
15 (4.6)
25 (7.6)
50 (15.2)
50 (15.2)
unapproved fluid)
> 5,000 (19)
25 (7.6)
50 (15.2)
100 (30.5) 100 (30.5)
1) All transformer components must be accessible for inspection and maintenance.
1
Table 2b. Outdoor Fluid Insulated Transformers Equipment Separation Distance
Approved Transformer Liquid Volume
Distance ft (m)
or Equivalent
gal (m3)
Liquid
3 (0.9)
Yes
N/A
Less Flammable
≤ 10,000 (38)
5 (1.5)
(Approved Fluid)
No
> 10,000 (38)
25 (4.6)
< 500 (1.9)
5 (1.5)
Mineral Oil
(or
N/A
500-5,000 (1.9-19)
25 (4.6)
unapproved fluid)
> 5,000 (19)
50 (7.6)
1) All transformer components must be accessible for inspection and maintenance.
distance from
transformer
distance from
containment
edge
distance from
transformer
distance from
containment
edge
Our History
full-scale accelerated
life tests started
formulation
selected
research
begins
1991
1992
1993
1994
1995
available
to OEMs
first distribution
transformers
retrofilled
1996
Major US utilities
first new
convert 100%
161
kV,
200
MVA
power
for distribution
GSU retrofill
transformer
1997
transformers
available
commercially
1998
1999
first distribution
transformers
installed
utility field
trials begin
2000
first new
mobile
substation
2001
2002
first GSU retrofill
69 kV, 50 MVA
ASTM
natural ester
standard
2003
2004
first new
first new 242 kV
GSU reactor
2005
2006
first utility 100%
conversion for
distribution
US EPA grants
Environmential
Technology
Verification
230 kV
retrofills
2007
2008
100th power
transformer
installed
How to Diagnose
¾Basic chemistry is different between
NE and MO, so….
¾Depending on the property, there can
be significant differences in the
initial and typical service aged values
¾What’s important is to differentiate
between “performance” vs.
“diagnostic” values
Key properties comparisons
¾Similar
– Dielectric strength*
– Dielectric impulse*
– “Color” (ASTD1500)
– Visual Examination (ASTM D 1524)
– Material Compatibility
Key properties comparisons
¾ Higher
–
–
–
–
–
–
–
Acid Number
Dissipation Factor
Dielectric Constant
Kinematic Viscosity
Flash & Fire Points
Relative Density
Water Content (ppm) – Absolute and Relative
Saturation
– Pour Point
Key properties comparisons
¾Lower
– Volume Resistivity
– Interfacial Tension
– Gassing under Electrical Stress D2300
• Corrosive Sulfur
Oxidation
¾Oxidation stability
– Both mineral oil and natural esters oxidize
– The fluids oxidize differently
• Products of mineral oil oxidation form sludge
precipitates
• Products of natural ester oxidation form
oligomers (larger molecules) that stay in
solution
– The long term effect on the transformer is
the same: less efficient heat transfer
Oxidation
2
10
o
Kinematic Viscosity, 100 C (mm /s)
12
8
6
Envirotemp
FR3 fluid
130oC
150oC
mineral
oil
150oC
170oC
170oC
4
130oC
2
0
0
1
2
Equivalent "Normal" Lifetimes
3
4
Oxidation
Mineral oil – 2000 hrs at 170oC
Oxidation
NE fluid – 2000 hrs at 170oC
Cold Temperature
¾Cold temperature performance
– Water saturation
– Viscosity
– Cold start
Water Saturation
5000
Water Saturation Point (mg/kg)
Envirotemp FR3 fluid
from Doble Engineering
4000
mineral oil
from IEEE C57.106
3000
2000
1000
0
20
40
60
80
Temperature (oC)
100
120
D1816 Dielectric Breakdown Strength (kV)
80
70
60
50
40
30
20
Envirotemp FR3 fluid
mineral oil
10
0
0
100
200
300
400
Water Content (mg/kg)
500
600
700
D1816 Dielectric Breakdown Strength (kV)
80
70
Envirotemp FR3 fluid
mineral oil
60
50
40
30
20
10
0
0
20
40
60
80
100
120
140
160
Water Content (% of 20oC saturation)
180
200
Water Saturation
Water Content (mg/kg)
1000
100
20
10
IEEE C57.106 max water content
in new equipment 69 kV and less
mineral oil saturation (IEEE C57.106)
Envirotemp FR3 fluid saturation (Doble Eng.)
1
-20
-10
0
10
20
Temperature (oC)
30
40
50
DGA
Dissolved Gas Analysis
¾ IEEE C57.104 DGA Guide: Key Gases Method
with rate of rise OK, but not Ratio Methods
¾ IEC Duval method recommended
¾ Gas generation & solubility similar to mineral oil
¾ Expect higher proportion of ethane compared to
mineral oil due to basic fluid chemistry
¾ Fine tuning of all limits will come with additional
field data and lab investigations
Field Case History
Alliant Energy - 50 MVA, 69 kV, built 1957, retrofilled 2001
• Dielectric Strength
• Dielectric Strength (1mm converted to 2mm)
• Absolute Water Content
• Relative Water Content
• Dissipation Factor
• Acid Number
• Interfacial Tension
• Dissolved Gases
• Dissolved CO & CO2
• Ethane - The Mischief Maker!
Key Standards
¾ASTM D687-03
– Standard Specification for Natural
(Vegetable Oil) Ester Used in Electrical
Apparatus
¾ New IEEE C57-147-2008
– IEEE Guide for Acceptance and
Maintenance of Natural Esters in
Transformers
New IEEE Standard Guide for NE
¾ Sec 8 - Maintenance of Natural Esters in Transf.
– Field Screening
– Test Limits for service aged fluid
• Currently only properties listed:
• Dielectric Strength
• Fire Point
– Reconditioning
– Reclaiming
– Mixtures of different fluids discussion
• Most are miscible and compatible
• Should be avoided
• Silicone definitely should be avoided, even traces
IEEE Standard Guide for NE
¾ Informative Annex B
–
–
–
–
–
Alternative Oxidation Stability Test
Relative Moisture Saturation
DGA Information
Provisional Guidelines for Trigger Value Limits
Key Properties Mixtures Natural Ester with
Mineral Oil
– Relative Cooling
IEEE Standard Guide for NE
• Table B.5: Provisional Guidelines for
Trigger Value Limits Alternative Oxidation
Stability Test
–
–
–
–
–
Dissipation Factor
Water Content
Flash Point
Color
Viscosity Increase
– Inhibitor Content
Eletronorte
(Brazil)
242 kV Reactor
Alliant Energy retrofill
March 2004, 200 MVA, 161 kV, built 1966, Burlington Iowa
Missoula Electric retrofill
December 2005 8 MVA, 230 kV, built 1980, Montana
Keyspan Energy retrofill
April 2004, 25 MVA, 19 kV, New York City
Summary
¾ Typically the same properties are tested
¾ Some properties are significantly different
¾ Typically same ASTM test methods apply
¾ DGA: Similar faults produce similar gases
– Exception: Ethane is produced “naturally”
¾ Much more field data required to “fine tune”
interpretation from field samples