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IS IT THE VILLAIN ?
IS IT THE HERO ?
33.2°C
76.9°C
40
50
60
70
Transformer Oil Laboratory
Corrosive Sulphur
GOMATHY SETHURAMAN

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Sulphur in Transformer Oil
• Unrefined oil may contain :
elemental sulphur,
mercapants, sulphide,
disulphide…ext
• Hydro and acid methods are
used during the refinery
process to remove these
sulphur elements.
• Repetition of the refinery
process may remove the
sulphur, but it can never be
zero.
• Sulphur is a natural element contained in crude oil, which is the
basis of transformer oil.
Source: ESI AFRICA Isuues 4, 2005

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How to Detect Corrosive Sulphur?
Recommended Test Methods -:
ASTM D1275 – Using Copper Strip
DIN 51353 – Silver Strip
ISO 5662 – Copper Strip
TNBR using ASTM D1275 to detect corrosive sulphur in oil
Methodology – Oil sample is purged with nitrogen and a
clean copper strip is placed in the oil under nitrogen blanket.
Then the oil sample is placed in an oven to age at a high
temperature (≈14oºC) for a period of time (≈ 19 hours). The
copper strip is removed from the oil and visually examined
using a standard chart.

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How to Detect Corrosive Sulphur?
The copper strips from the oil are compared to the
ASTM Copper Strip Corrosion Standard

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How to Detect Corrosive Sulphur?
NONCORROSIVE
• Orange
• Red lavender
• Multicolored with lavender
• Blue or silver or both,
overlaid on claret red, slivery,
brassy or gold,
• Magenta overcast on brassy
strip
• Multicolored with red and
green showing but not grey
CORROSIVE
• Transparent black
• Dark grey
• Dark brown
• Graphite
• Lusterless black
• Glossy
• Jet black

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VILLAIN vs HERO
Villain Sulphur : -
“ Elemental sulfur and
thermally unstable sulfur
compound in electrical
insulating oil that can cause
corrosion of certain
transformer metals such as
copper and silver…”
ASTM D 2864
Hero Sulphur : -
“ Relatively stable elemental
sulfur that’s left behind after the
refinery stage acts as natural
antioxidant.
These compound exist in the oil,
and are very useful for improving
oil oxidation stability…”

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Why is it the Villain ?
Sulphur Elements
• Reacts on contact with copper
• Does not require heat to
promote reaction
• Heat makes the reaction more
pronounce
• May lead to copper sulphide
deposition on insulating
paper, thus weakening the
dielectric strength of the
paper.

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RECENT STUDIES CONDUCTED :
• “ There has recently been surprising discovery in small number of
failed transformer and reactors ... deposition of copper corrosion and
copper sulphide…” source Nynas Naphthenics Magazine
• “ Found failure patterns of transformer did not fit the known root
cause… investigation showed that the oil contained elements from
sulphur …” source ESI AFRICA, Issue 4, 2005
• “ Blackened material and foreign deposits were found. Further
investigation showed that the oil contained corrosive element from
sulphur present in the oil…” source ESKOM
Why is it the Villain ?

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Why is it the Villain ?
Examples of Corrosive Sulphur Related Failures
Source : NETA WORLD 2004,
The Negative Effects of Corrosive Sulfur on
Transformer Components

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Why is it the Villain ?
Examples of Corrosive Sulphur Related Failures
Source : DOBLE Engineering
The Evolving Problem of Corrosive
Sulphur in Transformer Oil

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Why is it the Villain ?
Examples of Corrosive Sulphur Related Failures
Source : ABB
The Evolving Problem of Corrosive
Sulphur in Transformer Oil

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CONCLUSION
• The negative effect pertaining to transformers where
corrosive sulphur is present is a relatively a new
phenomena.
• The effect of corrosive / reactive sulfur not only
adversely affect the internal part of the transformer
but also have drastic effects on insulating materials
such as paper.
• Identifying the sources of sulfur contamination and
being able to monitor concentrations of corrosive and
reactive sulfur will help detect problem areas earlier.
• Therefore, a multifaceted monitoring system should be
in place to avoid failures in the power supply.

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Thank You
Contacts:-
Transformer Oil Laboratory
s.gomathy@tnrd.com.my
TNB Research Sdn. Bhd.
No. 1, Lorong Ayer Itam,
Kawasan Institusi Penyelidikan,
43000 Kajang, Selangor, MALAYSIA
Tel: +603-89268818 Fax: +603-89223837