Inoxidable Oil-Paper Insulation
in Free Breathing Power Transformers
Authors:
John Sabau, (Insoil Canada Ltd, Canada)
Issouf Fofana, (ISOLIME, UQAC, Canada)
S Gal, (Transelectrica, Romania)
M. Oltean (SC Smart SA, Romania)
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Introduction
 Power transformers
 the most valuable asset in a substation or plant,
 Indispensable components of high-voltage equipment




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for power generation plants, transmission systems
and large industrial plants.
Unexpected failures
 major disturbances to operating systems,
unscheduled outages and power delivery problems.
Such failures can be the insulation degradation/aging,
result of poor maintenance, poor operation, poor
protection, undetected faults, or even severe lightning or
short circuits
Outages affect revenue, incur penalties and can cost a
company its reputation and its customers.
in extreme cases, they can leave a company facing
financial ruin
The problem
 The Service Reliability of aging transformers
decreases while the number of failing
transformers is growing
 Aging Power Transformers pose an increased
risk of failures and blackouts
 “Power Transformers built in the ’60s and ‘70s
pose a serious strategic issue worldwide.
Catastrophic failures are escalating both in
number and cost including environmental
impacts”
IEEE Electrical Insulation Magazine 2001
3
The consequence
*Cost estimates of an unplanned replacement of a
typical generator step-up transformer
Environmental cleanup
Lost revenue ($500,000/day)
Installation labor and processing
Additional modifications and site work
New transformer unit
$500,000
$10 million
$100,000 – $300,000
$300,000
$2 million – $4 million
Transformer failures can cost up to $15 million, in
addition to an operator’s reputation.
Incentive for electric companies to ensure reliability
and availability throughout the life cycle of these key
assets.
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*Doble Life of a Transformer Seminar - Clearwater, FL, United States
Oil Decaying (1)
MULTIPLES STRESS
ELECTRICAL STRESS
THERMAL STRESS
CHEMICAL STRESS
BREAKDOWN of COVALENT BONDS
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• Some of the hydrocarbon bonds may break and form free radicals: H*, CH3*,
CH2* and CH*,… which then recombine to form:
• soluble/insoluble decay products
• fault gases observed in oil.
Oil Decaying (2)
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The dissolved Oxygen
 Oil in contact with air at atmospheric pressure dissolves 10%
air by volume (Henry’s law).
 The dissolved oxygen content of an oil sample, taken from the
tank of a free-breathing transformer, shows values, between
5,000 and 40,000 ppm
 The omnipresence of oxygen (with the catalytic effect of
copper), heat and water will promote insulating liquid oxidation
even under normal conditions
 According to Fabre and Pichon [1] oxygen increases the rate
of degradation of paper in oil containing 0.3-5% moisture by a
factor of 2.5 and water increases the rate in simple proportion to
its concentration.
Reducing the oxygen from saturation level in the oil (30,000
ppm) to less than 300 ppm reduces the ageing by a factor of
16!
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[1] J. Fabre and A. Pichon, “Deteriorating processes and products of paper in oil. Application to
transformers”, CIGRE, Paper 137, pp. 1-18, 1960.
Limitations of current preventive
procedures
Aggressiveness of oxygen negatively affects the
chemical stability of oil by generating decay products
(detrimental to the solid insulation)
researchers have developed various technical solutions.

Nitrogen sealed type Conservator (Fig 1)

Diaphragm sealed type Conservator (Fig 2)

The Use of Oxidation Inhibitors
N2
N2
Oil
Huile
Indicateur
de niveau
Oil level
indicator
d’huile
Diaphragme
Rubber bladder
Huile
Oil
Cuve du
Transformer
transformateur
tank
Fig 1
Fig 2
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Dessiccateur
de
Dehydrating
Silicagel
breather
Dissolved Oxygen and Moisture
Removal System
To shorten the experimental time frame, a relatively small unit was suitable.
Two 5 MVA distribution transformer were utilized
Expansion
Chamber
Power
Transformer
Tank
Silica
Gel
Nitrogen
Generator
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http://www.insoil.ca/index.php?view=video
Dissolved Oxygen and Moisture
Removal System
30000
Conservator
Oxygen concentration (ppm)
25000
Bottom of the tank
20000
15000
10000
5000
0
0
10
2
4
6
8
10
Period after blanketing (months)
12
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this innovative nitrogen blanketing system gradually decreases
the dissolved oxygen from insulating oil over the experimental
period, while maintaining the “freely breathing” character of the
transformer.
Transformer #1
Dissolved gas Analysis and relative decay products and Turbidity results after 8 years blanketing.
Gas Component
Hydrogen (H2):
Concentration (ppm)
<5
Oxygen (O2):
1450
Nitrogen (N2):
83257
Methane (CH4):
2
Carbon Monoxide (CO):
<25
Carbon Dioxide (CO2):
191
Ethylene (C2H4):
1
Ethane (C2H6):
<1
Acetylene (C2H2):
<1
Total Gas Content % v/v:
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8.47
The level of dissolved carbon dioxide and combustible fault gases also
decreased. The absorbance curves along with the turbidity of the 5 MVA
blanketed unit show little change.
Transformer #2
Dissolved gas Analysis and relative decay products and Turbidity results after 8 years blanketing.
Gas Component
Hydrogen (H2):
Concentration (ppm)
<5
Oxygen (O2):
1083
Nitrogen (N2):
80484
Methane (CH4):
2
Carbon Monoxide (CO):
<25
Carbon Dioxide (CO2):
200
Ethylene (C2H4):
<1
Ethane (C2H6):
<1
Acetylene (C2H2):
<1
Total Gas Content % v/v:
8.15
These analyses confirm the theoretical premises that motivated the
experiment.
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Additional testings
 the Total Acid Number
(TAN) shows slight change
while the interfacial tension
(IFT) is still not a reason for
concern.
 However, an increase the
dissipation factor is
observed. This might be
related to the ability of free
radicals to capture a free
electron and become a
charge carrier
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Economic and Technical considerations
Dissolved Oxygen and Moisture Removal System (DORS)
 Enhances the service reliability
 Eliminates oxidation decay
 Reduces the cost of maintenance
 Proven technology
 Low cost of deployment
 Lower maintenance cost
 Enhanced service reliability (of current transformers)
 Excellent ROI
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Economic and Technical considerations
Contrary to breathing units:

Since the nitrogen supplied by the membrane generator is moisture
free and its flow is in one direction only, frequent changing of depleted
silicagel in the air desiccators filters is no longer necessary.

With the removal of dissolved oxygen in the oil, secondary chemical
reactions with the gases generated under the effect of electrical stress
become impossible which might therefore allows a better
reproducibility and interpretation of dissolved gas analysis (DGA).

The expenses imposed by the reclamation and reconditioning of the
oil may be reduced once the very cause of oxidation of the decay
process affecting the composite solid-liquid insulation is reduced.

The use of antioxidant inhibitors may be unnecessary, including the
laboratory analysis to monitor their declining concentration and the
costs involved in periodic replenishment.
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Economic considerations
Contrary to sealed or rubber bladder units:

Fault gases can freely escape from the transformer.

The system is reparable in situ.

Old transformers may be easily retrofitted.
 The life expectancy of aging transformers is extended. Among all,
the low initial cost and almost maintenance free operation of
membrane nitrogen generators makes this prevention technique
economically affordable.
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Conclusions
 Unlike the current use of oxidation inhibitors which are able only
to retard the oil-paper insulation deterioration process; this
economically affordable procedure successfully prevents the
premature aging of these expensive machines
 Rather than reconditioning or reclaiming service-aged oil in order
to restore its initial properties, the Dissolved Oxygen and
Moisture Removal System (DORMS) open the possibility of
maintaining the initial physical and chemical properties of a liquid
dielectric throughout the lifetime of a power transformer
 By using this system, the oxidation decay of oil-paper insulation
will be hindered and the life expectancy of these expensive
machines considered capital investments in every country
infrastructure, extended, while the mineral insulating oil, a nonrenewable resource, could be given a practically endless life
expectancy.
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Thank you…
Questions &
Answers?
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