Visvesvaraya Technological UniversityJnana Sangam Belgaum-590014

A seminar on

“Testing for Corrosive Sulfur Effect in transformer oil ” Submitted in partial fulfillment of the requirement for the award of the degree

Bachelor of Engineeringin

Electrical & Electronic’s Engineering

presented by

SHIVAKUMAR.S(USN: 1GC08EE049)

Under the guidance of

Mr. Faheem Ahmed Khan

Department of Electronics and Electronic’s Engineering Ghousia College of Engineering Ramanagara –562159 2011-2012

Asst. Prof, Dept. of E&E, GCE, Ramanagara

G

HO

US

IA C

OLLEG

E O

F E

NG

INER

RIN

G

Dep

artm

ent

of

Ele

ctro

nic

s an

d E

lect

ron

ic’s

En

gin

eeri

ng

INTRODUCTIONOver the past several years there have been a number of failures of power transformers and reactors, due to formation of copper sulfides on conductors and insulating materials.

The conductive copper sulfide reduces the dielectric breakdown voltage of the solid insulation. This can result in a dielectric puncture through the paper insulation. The failures have occurred after the apparatus have been in service for a year or more, often several years.

Dep

artm

ent

of

Ele

ctro

nic

s an

d E

lect

ron

ic’s

En

gin

eeri

ng

G

HO

US

IA C

OLLEG

E O

F E

NG

INER

RIN

G

G

HO

USIA

CO

LLEG

E O

F EN

GIN

ER

RIN

G

Dep

artm

ent

of E

lect

roni

cs a

nd E

lect

roni

c’s

Eng

inee

ring •At normal operating

temperatures the corrosion process will take time to form conductive sulfides.

•This problem in the transformer is difficult to detect and manage, because the failures have occurred without prior evidence of abnormal gassing behavior.

•This problem is mainly present in the large power utilities.

• Less in the industrial and commercial users with oil-filled electrical equipment, but the same issues can arise.

•One of the most frequently asked questions is “Which apparatus is most susceptible?” •In response to the above question, Doble has developed the following list.(1) Units that have the following characteristics a)Manufactured from 1999 to present. b) Operate at high temperatures over long periods of time. c)Are either gas blanketed or have a sealed conservator system. d)Have oils that fail the corrosive sulfur .2)Those unit that do not have

completely enameled or varnished conductors.

G

HO

US

IA C

OLLEG

E O

F E

NG

INER

RIN

G

Dep

artm

ent

of

Ele

ctro

nic

s an

d E

lect

ron

ic’s

En

gin

eeri

ng

Dep

artm

ent

of

Ele

ctro

nic

s an

d E

lect

ron

ic’s

En

gin

eeri

ng

G

HO

US

IA C

OLLEG

E O

F E

NG

INER

RIN

G3)In the fast several years, in response to this problem, there has been a great deal of research activity in developing new test to help identify oils with the potential to have corrosive sulfur problems

. some of the tests are in various stages of development and are broken down into two groups. 1. Oil tests.2. Transformer Electrical test.

OIL TESTS: These test is to determining if corrosive sulfur compounds are present in the oil or not.

Identifying sulfur compound that are presently stable but may become corrosive under conditions that exist in the transformer.

A listing of some of the oil tests used with descriptions follows.

G

HO

US

IA C

OLLEG

E O

F E

NG

INER

RIN

G

Dep

artm

ent

of

Ele

ctro

nic

s an

d E

lect

ron

ic’s

En

gin

eeri

ng

1)Corrosive sulfur in oil: This test ages 220mls of oil in contact with a copper

strip in a sealed vessel for 48 hours at 150 deg C as shown.

The primary purpose of the test is to determine if any corrosive sulfur compounds present in the oil.

G

HO

US

IA C

OLLEG

E O

F E

NG

INER

RIN

G

Dep

artm

ent

of

Ele

ctro

nic

s an

d E

lect

ron

ic’s

En

gin

eeri

ng

If the corrosive sulfur compounds present in the oil, then the oil will react with the copper strip to turn it gray or black as shown below.

Noncorrosive Strip Corrosive Strip

In the above figure the lift side is the strip before immersed in the sealed vessel & right side is the strip after removal from the sealed vessel after 48 hours at 150 deg C.

This is a very routine test.

G

HO

US

IA C

OLLEG

E O

F E

NG

INER

RIN

G

Dep

artm

ent

of

Ele

ctro

nic

s an

d E

lect

ron

ic’s

En

gin

eeri

ng

G

HO

US

IA C

OLLEG

E O

F E

NG

INER

RIN

G

Dep

artm

ent

of

Ele

ctro

nic

s an

d E

lect

ron

ic’s

En

gin

eeri

ng

This test is performed by gas chromatography with sulfur selective detection and covers the detection of volatile sulfur-containing compounds.

This test can be used to isolate specific sulfur compounds, some of which may or may not be responsible for corrosive sulfur attack.

There are thousands of sulfur compounds, and this test does not have the ability to cover them all.

It is usually not considered a routine test and mostly used for research purposes.

2)Sulfur speciation:

There are several tests that can be used for the detection of total sulfur in oil.

This test determines the total amount of sulfur in the oil.

But in this method it does not determine whether or not the compounds being detected are corrosive.

This is a routine test, but it only provides information on how much sulfur in the oil.

3)Total sulfur in oil: G

HO

US

IA C

OLLEG

E O

F E

NG

INER

RIN

G

Dep

artm

ent

of

Ele

ctro

nic

s an

d E

lect

ron

ic’s

En

gin

eeri

ng

Mercaptans are sulfur compounds that can be very corrosive.

This is a potentiometric titration test that is used to determine the concentration of mercaptans compounds.

From this test it is not able to identify specific compounds.

This test is used in the fuel and lubrication industries often and is starting to be used in the transformer oil industry.

The problem with mercaptans is that some of them are highly volatile and thus not easily sampled.

It is presently not routine test.

.

G

HO

US

IA C

OLLEG

E O

F E

NG

INER

RIN

G

Dep

artm

ent

of

Ele

ctro

nic

s an

d E

lect

ron

ic’s

En

gin

eeri

ng

4)Mercaptans in oil:

5)Doble Covered Conductor Deposition (CCD) Test, Doble Test

Then they are placed in 20 mL headspace vials. Oil is added and then the vials are sealed as shown below.

This test is conducted by taking an abraded copper road and wrapping new Kraft paper insulation around the rod as shown in the figure below.

G

HO

US

IA C

OLLEG

E O

F E

NG

INER

RIN

G

Dep

artm

ent

of

Ele

ctro

nic

s an

d E

lect

ron

ic’s

En

gin

eeri

ng

CONT……

• A stainless steel needle of a particular diameter is then pierced through the spectrum of one vial and left there to allow air ingress during testing as shown in figure.

• The vials are then tested at 140 deg C for four days.

• At the end of the test cycle , the vials are removed and the copper rods with paper retrieved.

G

HO

US

IA C

OLLEG

E O

F E

NG

INER

RIN

G

Dep

artm

ent

of

Ele

ctro

nic

s an

d E

lect

ron

ic’s

En

gin

eeri

ng

Cont….. The paper is then removed from the copper as shown in the

figure below.

• Then washed in a solvent to remove the oil.

• The road is inspected to determine if it has been tarnished by corrosive sulfur, and the paper is inspected to determine if deposition as occurred.

• The presence of deposition in the paper is important as most of the recent transformer failures have been due to copper sulfide deposits in the paper causing a severe reduction in dielectric strength.

• The resulting “deposition,” whether heavy, moderate, or light, means that the interaction of the copper and oil with the paper insulation.

• This is becoming a very routine test.

G

HO

US

IA C

OLLEG

E O

F E

NG

INER

RIN

G

Dep

artm

ent

of

Ele

ctro

nic

s an

d E

lect

ron

ic’s

En

gin

eeri

ng

ConclusionThese test will be used to screen out or

identify oils that may not be suitable.

G

HO

US

IA C

OLLEG

E O

F E

NG

INER

RIN

G

D

epar

tmen

t o

f E

lect

ron

ics

and

Ele

ctro

nic

’s E

ng

inee

rin

g

THANK YOU

G

HO

US

IA C

OLLEG

E O

F E

NG

INER

RIN

G

Dep

artm

ent

of

Ele

ctro

nic

s an

d E

lect

ron

ic’s

En

gin

eeri

ng