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c 0 M M r s s r 0 N
r r c T R 0 T E c H N r 0 u EN T E R N A T T 0 N A L E
(affili6e
l'0rganisationnternationaleeNormalisationlS0)
R E C ( l M M A N l l A T I t l NE
L A
C E I
I N T E R N A T I ( l N A LL E C T R ( l T E C H N I C A Lt } M M I S S I ( } N
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Publication22
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Publication22
. - _ v
Guide
our
amaintenance
des uilessolanles
et
asurueillance
en eruice
Maintenance
nd uperuision
uide
for nsulatingilsnseruice
Droits
e eproduction
6serv6s
Copyrightall r ights eserved
Bureauentrale aCommissionlectrotechniquenternationale
1, ue eVarembd
Oendve,
uisse
)
,}
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R6vision de
la
pr6sente publication Revision
of
this
publication
L€ contenu technique des
publications
de
la CEI est cods- The techrdcal content of
IEC
publications
is kept under
tafiment revu
par
la Commission a.fin d'assure
qu'il
reflete constant
review by
the IEC, thus ensufing that the content
bien l'€tat actuel de 1a echnique, reflects current technology.
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l'6ta-
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blissement
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peuvent
editions and amendment sheets may be obtained from IEC
etre obtenus auprCs des
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consultant les documents ci-dessous:
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c 0 M M r s s r 0 Nt r c T R 0 T E c H N r 0 u EN T E R N A T t 0 N A L E
(affili6e
l'0rganisationnternationaleeNormalisationlS0)
R E C ( ) M M A N D A T I l l NEL A C E I
I N T E R N A T I ( l N A LL E C T H O T E C H N I C A L( ) M M I S S I ( } N
(aff i l iated
o the nternationalrganizationor Standardizati onlS0)
I E C R E C ( ) M M E N I l A T I ( l N
Publicalion
22
Premi i re
d i t ion F i rs t
d i t ion
1 9 7 3
Guide
our
des
lamaintenance
huiles
solantes
et a
surueillance
en
eruice
Maintenance
nd uperuision
uide
for nsufalingilsnseruice
PERP''ST
KAAN
IIMBAGA
r..rtriiol-r..
{ETF,I\IAGAAN
No.
Ageoda
qW
T a n g g a l
, 9
- - 9 -
Dro i ts
e eproduct ion
eserv6s
Copyr igh t
a l l iqh ts
eserved
Aucune ar t ie
e ce t t e
pub l r ca t ron
e
peu t
e t re
epr0 r lU i t e
i L r t i l i s6e
ous
No
par t
o f
t h rs
pub l i ca t r0n
ay
be reproduced
r
u t r l i zed
n any
que lque
orme
que
ce soi t t r t
pa r
aucun
procede ,
lec t ron iq r i e
u
mEca-
form
t r r
any
means ,
lec t r0nic
r mechan ica l ,
nc lud ing
ho t ocopy ing
n t que ,
compr is
a
pho t ocopre
t esmicrol i lms,
ans
'accord
cr i t e
' ic l i teur .
and
microf i lm,
i t hou t
e rm iss ion
n
wr i t ing
rom he
pub l i sher .
Bureau
entral
e
a
Commission
lectrotechnique
nternationale
1, ue
e
Varembd
6eneve,
uisse
iii:Ji
,
34 0
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- 3 -
CONTENTS
FonrwoRo
PnrnlcE
Clause
1.
Introduction
Scope
Oil deterioration
and recommended
ests .
3.1. Deterioration
of
oils
in
service
3.2.
Special ests
Frequency
of examination
of oils in service
Action to
be taken
Criteria
7. Test
methods
.
7.1.
Sampl ing
7.2.
Electric
strength .
7.3.
Water
content
7.4. Dielectric
dissipation
actor .
7.5. Resistivity
7.6. Neutralization
value
7.7.
Sediment
and
precipitable
ludge
7.8. Flashpoint .
7
9.
Interfacial
ension
7.10. Dissolved as
.
7 l l .
Co lour .
7.12. Appearance
7.13.
Oxidation stabil i ty .
7.14.
Compatibility
.
7.15.
Other field
tests
AppExorx
A1
-
Application to
oils in transformers
AppeNolx
A2
-
Application
to
oils in switchgear
Apprxolx B
-
General
procedure
or handling,
reconditioning
and
Frcung I
Page
)
5
2.
a
7
7
7
7
l 1
1 3
1 3
1 5
l 5
1 5
l 5
t 5
l 5
r 7
1 7
l 7
t 9
1 9
t 9
l 9
1 9
t 9
t 9
l 9
4.
5 .
6.
replacing
oi l
2 l
23
25
32
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- 5 -
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
MAINTENANCE AND SUPERVISION GUIDE
FOR
INSULATING
OILS IN
SERVICE
FOREWORD
l) The
formal
decisions
r agreements
f
the IEC
on
technical
matters,
prepared
by
Technical
Committees
n
which
al l
the National
Committees aving
a special
nterest
herein
are
represented,
xpress,
s nearly
as
possible,
n
international
consensus
f opinion on
the
subjects ealt
with.
2) They have the form
of
recommendations
or
international
use and they
are acceptedby the
National
Committees n
that sense.
3)
In
order
to
promote
nternational
unification, he IEC
expresseshe
wish that
all
National
Committees hould
adopt
the
text
of the IEC recommendation
or their national
ules n
so
far
as national
conditionswill
permit.Any
divergence
between
he
IEC recommendations
nd
the
corresponding ational ules
should,as
far
as
possible,
e clearly ndicated
in
the
atter.
PREFACE
This
recommendation
has
been
prepared
by Sub-Committee
10A, Hydrocarbon
lnsulating
Oils, of
IEC Technical
CommitteeNo. 10,
Liquid and
Gaseous
Dielectrics.
The drafts
were
discussed uring the mee tingsheld
in
Tehran
in
1969
and
in Brussels
n
1970.
As a
result of this latter
meeting
a new draft,
document l0A(Central
Office)14,was
submitted to
the National
Committees or approval under the Six Months'Rule in October 1971.
The
following
countries
voted explicitly in favour
of
publication:
Australia
Poland
Austria
Portugal
Belgium
Romania
Canada
South Africa
Czechoslovakia
Srveden
France
Switzerland
Germany
Turkey
Israel
Union of Soviet
Italy SocialistRepublics
Japan
United
Kingdom
Netherlands
Yugoslavia
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2.
- 7 -
MAINTENANCE
AND
SUPERVISION
GUIDE
FOR
INSULATING
OILS
IN
SERVICE
lntroduction
Many countries
possess
odes
or
the maintenanceof
insulating oils
in
service.
A comparative
examination
of
these documents
has
made it
possible
o
propose
an
International Guide.
The
values
of
the various characteristics
mentioned
therein
should be
consideredas
indicative
only.
In
fact, for
the
proper
interpretation of
results,
account
has
to
be
taken of various
factors,
such
as
the conditions
of use,
he type of eq uipment,
and
the
generalprogression
f
the
oil 's
charac-
terist ics.
Reference
hould
also be
made to the equipment
manufacturer's nstructions.
lt is
not intended
hat the
contents
of
this documentshould
give
he
full
detailsof
the instruc-
tions which are
necessaryo
deal
with all
types of oil-filled equipment
of all sizes.The
intention
is to give a common basis on which more complete codes may be prepared when these are
necessary.
In the
present
Guide,
the
causes
of oil
deterioration are discussed,
nd
recommendationsare
made
for
the various
tests. ndications
are also
given
regarding
the type
of
treatment
to
which
the
oil should
be subsequently
ubjected,
f
applicable.
Scope
This Guide
applies
o mineral oils, both
uninhibitedand
inhibited againstoxidation,
n
service,
under
normal operating
conditions,
n
transformers,switchgearand
similar electrical
equipment
where oil
sampling
is
permissible.
These oils
are of
the
same
type as
those
described
n IEC
Publication 296: Specification or New Insulating Oils for Transformersand Switchgear.
Application
of
the recommendationsof
this
document
to oil
in transformers of
low
power
or
voltage
<
I
MVA
or
{
36
kV)
may require
variation in the
light
of
local
economic
circumstances
(see
preliminary
remark
No. 2 in Appendix
Al).
Oil
deterioration
and recommended
ests
Deterioration
of oils
in
service
In
service,
nsulating
oils
are subject
to normal deterioration
due
to the
conditions
of use.
For example, n many applications the oil is in contact with the air. It is therefore subject to
oxidation
reactions
accelerated
y
temperature
nd
the
presence
f
catalysts
solid
ron and copper,
dissolved
metallic compounds).
As a
result, here
s
a change
n colour, and acid
products
are
formed. The dielectric
dissipation
factor may
increase
and,
at an advanced
stage
of oxidation, sepafation
of sludge
may
occur.
In certain
special
cases,
other
changes
n
the
characteristicsof
the oil
may
be
a sign of abnormal
deterioration
of certain
other
materials used
n the
construction
of
the
equipment.
All these
changes
may
affect
both solid
and
liquid
insulating
materials,
interfere with
the
proper
functioning of
the
electrical
equipment,
shorten ts
working
life
and,
n
some
cases,
ncrease
the no-load
osses.
3.
3 . 1
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9 -
Any
kind
of deterioration
of
an
oil
is made
evident
by changes
n
one or
more
of the
character-
ist ics
mentioned
below.
The
appearance
f an
odour and a
change n colour,
although not
being of a decisive
nature,
may,
by
comparison, ive
useful ndications
about the trend
of c hange n
an oil.
The following contaminants nay be found in insulatingoils in service.
3 .1 .1
Wate r
Water
may
originate from
the
atmosphere
or be
produced
by the
deterioration
of insulating
materials.
ts
presence
s
harmful; it may
reduce he
electricstrength
and the resistivity
of
the
oil
and
accelerate
he
deterioration
of
insulatingpaper.
Irlote.
-
Resistivity
and
dissipation factor
are
adversely
affected by
undissolved water
and to a much lesser
extent
by water in
solution,
but a decrease
of
resistivity
may
sometimes
be observed
with no
appreciable rise
in
dissipation factor.
3.1.2
Solid
porticles
i.e.
sediment,
eeSub-clause
.7.)
Solid particlesmay be classif iednto four categories, ccording o their origin:
l)
Insoluble
oxidation
or degradation
roducts
of
solid or
l iquid
insulating
materials.
2) Deteriorationproducts
due to
condit ionsof service
f
the
equipment:
carbon, metal,
metallic
oxides.
3) Various
products
resulting
rom inadequate
leaning
of
the
equipment
before
being
put
into
service.
4)
Fibres
of diverse
origins.
The
presence
f these
particles
normally
reduces he
electricstrength
of
the
oil
and, in
addition,
deposits
hinder heat-exchange,
hus
encouraging urther
deterioration
of the insulating
materials.
3.
.3
Polar
substances
These
are oil-soluble
compounds
esulting
rom
oxidation
of
the
oil
itself,
or from the
solution
in the
oil of
external
contaminants
r materials
used n
the construction
of
the
equipment.
Measurements
f the
dissipation actor
and to a
lesser
extent,
resistivity
and
interfacial
ension
of the
oil
enable
such
contamination o
be detected
nd
periodically
assessed.
A
comparison
of th e rate
of changeof the neutralizatio n
alue with
that
of one
of
these hree
characteristics ives,
o some
extent, an
indication
of the
probable
cause
of the
deterioration
of
the
oil.
For
example,
a
high
value
of dissipation actor
associated
with a low
neutralizationvalue
may
sometimes
be considered
as an
indication
of
oil contamination
other than
of oil origin.
a) Dielectric dissipation
factor
This
characteristic
s
very
sensitive o the
presence
n
the oil
of solublecontaminants
and ageing
products.
Changes n
this
characteristicmay
be
monitored
evenwhen the
oil is heavily
con-
tarninated.
his
determination s
therefore
of special nterest.
b) Resistit,ity
For
any
given
oil,
there
s
generally
a
relationship
between
dissipation
actor
and resistivity:
if the
dissipation
actor
increases,
here is
a reduction in
resistivity.
Useful
additional
information
can be obtained
when it is
possible
o
do the
resistivity
est
at
both
ambient emperature
nd 90
"C.
A satisfactory
esult
at
90'C coupled
with
an unsatis-
factory
value
at
the
lower
temperature
s an indication
of
the presence
f water
or
cold
pre-
cipitable material,
without
undue chemical
deterioration
or
general
contamination.
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3 . 1 . 4
3 . 1 . 5
3 . 1 . 6
3 . r .7
3.2
3 .2 . r
-
l l
-
Unsatisfactory
results
at both temperatures indicate
a
greater
extent of contamination than
a
poor
value at the lower
temperature
only, and that the
oil is
therefore
less likely to
be
restored o
a satisfactory evel
by
drying and
low
temperature iltration.
The
measurement
of
resistivity
can be
more
easily carried out on site than that
of dielectric
dissipation actor.
c) Interfocial
tension
This characteristic
changes airly rapidly
during
the
first stagesof ageing.Afterwards,
the rate
of change
decreases
s
the
values hemselves
ecome ower.
For this reason,
he results
are difficult to interpret
especiallywhen the
oil
is
heavily
con-
taminated.
Organic
acidity
The
acid
products
formed
by
the
oxidation of the
oil actively encourage
deterioration
of
insulating
paper
and
pressboard.
t is therefore
essential o
detect and
monitor
this
process.
The determination
of organic acidity
by
measurement
of the neutralization
value is the most
convenientand direct method of assessinghe chemicalageingof an oil. The presence f dissolved
COr in the
oil
(see
Sub-clause
.1.6.)apparently ncreases
his
acidity, but dissolved
CO,
content
is considerably
educed f
vacuum treatment
s
applied
to the
oil.
Precipitable
sludge
This
refers
to
sludge
which
is
precipitated
by
adding
n-heptane
o the
oil
but which may
be
subsequently
dissolved
by the solvent
specified n the test method
(see
Sub-clause
7.7.2.).
The
presence
of such a deposit,
consisting of
products
formed
at an advanced
stageof oxidation, is
undesirable
and
is
a
premonitory
sign of insoluble
sludge.
Dissolved gases
Under normal
service
conditions, the
production
occurs
of only small
quantities
of
CO,
CO,
and
very small
quantities
of hydrogen
and hydrocarbons.
Large
amounts of
dissolved
gases,
other
than
atmosphericcomponents,may
be
an
indication
of
an
incipient
fault in the
equipment.
Light
hydrocarbons
Light hydrocarbons
are formed during the
degradation
of oil
under the influence
of
heat,
and/or
electrical stresses.
arge
amount of
these
hydrocarbons
may
be
an
indication
of an
incipient
fault in the
equipment.
The
presence
f some ower hydrocarbon
deterioration
products
may
be detectableby measuring
he flash-point
of the
oil.
Special
tests
Oxidation
stability of
inhibited oils
Inhibited
oils
do
not
deteriorate
more
than slightly
as
ong
as
he active
nhibitor
is
still
present.
For
a
given
oil, the
induction
period
is
generally proportional
to the
active inhibitor
content,
provided
that the
inhibitor
has
been added
to
a
new
non-aged
oil. The
oxidation
test for
new
inhibited
oils enables
he induction
period
of
an oil
to
be
easily
measured
by
means
of determi-
nation
of volatile acids
developed.
This test,
applied to
a used oil
previously
tested,
will indicate to
what
extent the induction
period
has
been reduced.
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t 3 -
3.2.2
Compatibility
of
insulating oils
Compatibility
tests may
be
required to deterrnine
he
feasibility of
mixing rrew oils of different
type
and
origin
or new oil with
oil
in
service,
f
the make-up is
more than
5\ .
These ests are of particular interest in the case of inhibited oils.
The
main characteristics
f
the mixture, including oxidation
stability,
must not
be
less avour-
able
than those of
the worst
individual oil.
4.
Frequency
of examination
of oils
in
service
This
dependson
the
power, loading, construction and other
service
conditions
of
the
equip-
ment.
Hence, it is
not
possible
o
lay
down
a
general
rule applicable
to all
types
of oil-filled
equipment.
By way of a
guide,
tables showing
the application and
frequency
of
tests
suitable
for
different
types
of equipment
are
given
in Appendices
Al and
42.
Generally,
check
measurements
an
be
carried out on
the basis
of
paragraphs
l),
2)
and 3)
below, which apply particulary to transformer oils:
1)
Check
periodically
characteristics,
t
intervals
as
suggested
n Appendix A1, unlessotherwise
defined by
manufacturer.
2) It desired,check at
more frequent
intervals
those
characteristics
eterminable on site.
3)
If rapid deterioration or acceleration
n the
process
of
deterioration
s observed, ecommend:
a)
to confirm
the last value by
means of a
further test
on
a
fresh sample;
b)
to inform the manufacturer of
the equipment;
c)
to
check
the
condition
of
the oil
rnore frequently,
according
o the
size
of the equipment
and
the
degree
of deterioration
observed.
As regards
oil
in switchgear, t
may
be
sufficient
to
check
the electric
strength either
periodically
or after a
given
number of operations.
5.
Action
to be taken
The
following casesare
considered as a
function
of
the degree of
deterioration
of the
oil:
a) The characteristics
re
normal: no action
is necessary.
b)
Only
the value of
the
electric
strength
is
too low:
remove
water and solid
particles
by
re-
conditioning (e.g. filtering, centrifuging or vacuum dehydrating) (see Appendix B, Sub-
clause83.2).
The efficacyof
the treatment should be
controlled.
In
casesof high
humidity
of
transformer
oil,
it may
be
necessary lso
to
dry
out
the insulation of
the
active
part
of
the transformer.
c)
One
or
more
characteristicsof
the oil change
rapidly:
supplementary
ests
of
the
oil
(see
Sub-clause
.3) .
d) Several
characteristicsare
unsatisfactory:
according
to
economic
factors
and
local circum-
stances,
t should be decided
to
examine
the oil more
thoroughly,
to
reclaim
the oil or
to
replace
t
altogether.
In
caseswhere
oil
is
reclaimed
or replaced,
the
equipment
should be
thoroughly flushed
before
refilling,
with special attention
to the
windings,
to
minimize contamination
of
the
new
oil by ageingproducts (Appendix B).
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1 5 -
If
the
oil has
been eclaimed,
ts
characteristics
hould
be checked
and, f
necessary,
ts
oxidation
stability
should
be reinforced
by addition
of inhibitor.
The characteristics
of reclaimed
oil
should
be verified
after
addition
of
inhibitor.
if this
is
applicable.
It is
always
advisable
also to
carry
out a laboratory
test
before reclamation
of the
used
oi l
in order to ensure hat the treatment s appropriate.
Note-
General
rocedure
or reconditioning
f oil
by several
rocesses
s
given
n
Appendix
B.
A
guide
of
reclaiming
as
been
ublished
*
6.
Criteria
The values
of
perrnissible
lirnits
for the
different
criteria
listed
in
Appendices
Al
and
A2
are
given
for
guidance
only
and they
should
be interpreted
n
terms
of the
type
and
size
of the
apparatus.
Depending
on
such
type
and
size,not
all
of the
tests
given
n these
Appendices
need
to
be done.
As a generalrule, severalcharacteristics ave to be unfavourable n order to justify rejection
of
an oil
unless,
f
course, he
electric
strength
s
below the
limits given.
n
such
a case,
rrespective
of
the
values
of
the
other
characteristics,
ppropriate
action is
essential.
7.3
Test
methods
Sampling
Under
consideration
v IEC.
Electric
strength
See
EC Publication
156:
Method
for
the
Determination
of the
Electric
Strength
of Insulating
Oils.
Water
content
See
SO
Recommendation
R
760.
Note.-
Temperature
f
the
oil and transformer
perating
onditions
must
be noted
at the
time
of sampling
(see
EC
sampling
nethod).
D e
ect
ic
dissipation
actor
See EC
Publication
250:
Recommended
Methods
for the
Determination
of
the
Permittivity
and Dielectric
Dissipation
Factor
of Electrical
Insulating
Materials
at Power,
Audio
and Radio
Frequencies
ncluding
Metre
Wavelengths,
and IEC
Publication
247:
Recommended
Test
Cells
for Measuring
the
Resistivity
of
Insulating
Liquids
and Methods
of
Cleaning the
Cells.
Carry
out the measurement
at
90
"C
and
power
frequency.
7"
7.1
7.2
7.4
*
See
IEEE
Guide
for
Acceptance
and
Engineers
March 1969
(IEEE
No.
Maintenance
of
Insulating
Oil in
Equipment
".
Inst.
of
Elestrical
and Electronics
64),
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7 .5
- t 7 -
Resistit,ity
See EC Publications
3 Recomntertded
ethods
of
Test
or
Volume
and SurfaceResistivities
of Electr ical
nsulat ing
Mater ia ls,
nd IEC Publ icat ion24T.
Carry
ont
the
nteasurement
t 90
C
after
a d.c. voltage
gradient
of 250
V/mm has
beenapplied
for one minute.
l''lote.
Another
cmperature
ay
bc
chosen.
See
elationship
resistivity-ten-rperatLlrc",
igurc
1,
page
32.)
Netrtralization
yalue
See EC
Publ icat ion
96,
Clause l .
Sedinrcnt
antl
precipitable
sludge
7.6
7 .7
7 .7 .1
Scope
This
method
covers
he
detemrination
f
sediment
nd of
precipitable
ludge n
used nsulating
o i ls .
Sediment:
any
solid
substauce
hich is insoluble
n the
oil after
dilution with
n-heptane
an d
in the
solvent
mixture
mentioned
below.
Precipitable
sludge;
oil
deterioration
prodircts
or contarrir-rants,
r
both, which
become
insoluble
uporl
di lut ion
of
the
oil with
n-heptane
under
prescribed
onditions
but which
ar e
solr , rb le
n the
hereunder-ment ioned
olvent
nixture.
7.1.2
Procedure
Thoroughlyagitate he satttple f usedoil in the originalcontainer .rntil ny sedinelt is homo-
gerreously
uspended
n the
oi l .
Weigh
approximatively
0
g
of
oil
to the
nearest
,1 g,
in
a stoppered
onical
lask
apd intro-
duce
a volutne
of n-heptane
orresponding
o l0
nrl for
each
granrme
of
oil
taken.
Tl-roroughly
mix
the
sarnple
lnd solvent
and
allow to
stand l-r
he
glass
lask,
n
the
dark, for
18-24
hours.
If
er
olid deposit
s
observable,
i l ter the
solution
hrough
a
tared
Grade
4
sintered lass
rucible
with the
assistance
f
vacuum,
insing
he
flask
with lresh
n-heptane
o
ensure
omplete
ransfer
of
the precipitate
o
the
crucible.
Wash the
crucible
ar-rd
recipitate
with heptane
until
free
rom
oil.
Allow
any heptane
o
evaporate
nd
then
dry
the
crucible
n
an
oven
at 100-110
C
for
one hour,
cool
in
a desiccator
nd
weigh;
calculate
he increase
n
weight
of the
crucible
as a
percentage
of
the
weight
of
oil
taken.
Denote
his
value,
epresenting
he otal
of
insoluble
material
suchas a
sedirrrent
nd
precipitable
sludge,
as
"A".
Dissolve
he
precipitated
sludge
n the
crucible
by treatrnent
with the
rninirnum quantity
of
a
Irlixtttre
of equal
parts
of toluene,
acetone
and alcohol
(either
ethanol
or isopropapol
nay
be
Itsed.
a
purity
of
95
being
satisfactory
n
either
case),
at approximately
50
'C,
until no
more
n'ill
dissolve,
ud
collect
he
washings
n
an
accurately ared
flask. Disti l
offthe
solvent;visual
exatninatiotr
f the
flask
coutent
at this
stage
will
show
whether
any residue
i.e.
precipitable
sludge
n
1he
oi l )
is
present.
This n-ray
ltf f ice;
f however
a
quantitative
alue
s reqr-rired,
ry
the
flask
n
an
oven at 100-
ll0'C
for
one hour,
cool
in
a
desiccator
nd weigh.
Calculate
he
weight of residue
n the
flask
as a
percentage
f the
weight
of oil taken.
Denote
such
value
as
"8".
The difference A-B", if any, will represent sediment" n the oil.
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- 1 9 -
7.8
Flash point (closed
cup)
See
EC
Publication
296A:
First
supplement
o Publication
296
(page
25).
Field
test:
suitable
equipment
s
commercially
available.
7.9 Interfacial tension
See
EC Publication
296,
Appendix.
Field
test: interfacial
tension
of
electrical
nsulating
oils
of
petroleum
origin
against
water
may
be determined
more
easily
n
the
field
by the
drop-weight
method.*
7.10
Dissolved
gas
Under
consideration.
7. l l
Colour
Any
applicable
National
Standard
or
petroleum
products
may
be
used.
See SO Recommendation S 2049.
7.12
Appearance
See EC
Publication
296,
Clause
6.
7.13
Oxidation
stability
Uninhibited
oils:
see
EC
Publication
74: Method
for
Assessing
he
Oxidation
Stability
of
Insulating
Oils.
Inhibited
oils
under
consideration.
7.14
Compatibility
The
main
characteristics
ncluding
oxidation
stability
are
determined
on
a
mixture
of
the
new
oil
and the
used
oil.
The ratio
of this
mixture
is
the
same
as that
effectively
chosen
n
practice.
If this
ratio
is
not
known
at
the
laboratory,
ests
are to
be
made
with
a mixture
containing
one
part
of
new
oil
and
one
part
of
used
oil.
7.15
Other
field
tests
See
eference
n
footnote,
page
15.
*
As examplea descriptionof this method is given n ASTM Method D 22g5-6g.
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a
d
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r r 6 =
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M s €
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c F *
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: : F :
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b o . Y
6 p 9
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- 2 3 -
APPENDIX A2
INTERPRETATION OF TESTS ON OIL
IN SWITCHGEAR
AND ASSOCIATED APPARATUS *
Characteristic
measured: Electric strength
Testmethod: IEC 156
Test
venue:
Field or
laboratory
Equipment voltage
Breakdown
voltage
equired
Permissibleimit:
>l7okv
>
30
kv
<
l70kv >
20kv
Frequencyof
test: Seemanufacturer's
specification
Action
if
outside
permissible
limit: Reconditioning r
replacement
f
the
oil.
t
Excluding ap changeequipmentof
power
transformers.
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8 1 .
- 2 5 -
APPE,NDIX
B
GENERAL
PROCEDURE FOR
HANDLING, RECONDITIONING
AND
REPLACING
OI L
Scope
The scope
of this appendix is
to
give general
principles
that can
be applied
to
l-randling,
e-
condit ioning
and
replacingof insulatingoils.
The
general
naintenanceules
o
be
followed may
be
found
either
n
IEC
publications
ssued
by
those Committeesdealing
with
a
given type
of
equipment,
or in manufacturer's nstructions.
The
rnain
precautions
o
take in handling, replacing and
for
processing
o improve charac-
terist icsof the oil are described.
There are
two types
of cleaning
processes:
a)
Reconditioning:
This
involves
a
process
o elirninate, nly by
physical
means,
olid
particles
rom the
oil and
to
decrease
water content to an acceptable
evel.
b) Reclaiming:
This involves a
process
o
eliminate
rom the oil al l contarninants,
nsoluble
and
dissolved,
to obtain, at
the
end
of
the
process,
n oil
with
similar
characteristics
o those chosen
or
the new
product.
In this appendix,only the caseof " Reconditioning will be exarnined. he applicabilityof
the " Reclaiming
of
the
oil dependson economic
and
local fact ors which
are
not considered
in
this document.
If
"
Reclaiming
"
is
considered
o
be
desirable,
ecommendations
may
be
found in
a
suitable
document
(see
ootnote,
page
15).
Handling
To
ensuresatislactoryservice, he utmost care
n handling the
oil before
filling into the equip.,
ment
is
essential.
Drums
used
or transport
and
storage
should be
kept
under
cover. In
practice,
owing to contamination n the containers,difficulty may be experiencedn maintaining the purity
of
the
oil when it
is transferred rom
one
vessel o
another,
and
once
a vesselor drum
has
been
filled with moist
oi l , i t
is
difficult
to
clean. Oil-handling equipment
pipework,
pumps)
should
be
kept
clean and
free from moisture. Before
use,
his
equipment should be
carefully
inspected
to
ensure
hat i t is free rom
dirt and water. and
flushed
with clean
oil.
When oil
is
stored n drums, these
should be
placed
n
such
a
posit ion
that
there is
a
head
of oil on
the
bung or
plug
to
prevent
he entry
of
water
during storage.
However,
t is recogmzed
that
storageof
oil in
drums s not alwayssatisfactory, nd
transfer
of such oil
to
electr ical quip-
ment through a
suitable
reatment
plant
is recommended.This
also applies
o
oil
in
drums
which
have
been
bent
or
otherwise
damased n transit or storase.
B2.
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and
solids
rom
oil include
several ypes
The
best choice
of temperature
or
purification
depends
on circumstances. f
vacuum
treat-
rnent
is
employed to remove
water, temperatures
up to
80
oC
are advantageous ; f
not,
it is
advisable
to limit
the
temperature
to
60
oC
to
prevent
oxidation.
If
it is
desirable o reduce
precipitable
sludge
or
free
water without
vacuum treatment),
cold treatment may
be appropriate.
B3.2
Reconditioning
rocesses
83.2.1 Filters
Filter devicesare generallybased upon the principle
of
forcing
oil
under
pressure
hrough
absorbing material
such
as
paper.
Filters
of this type
are capable of removing
contaminants
n
suspension,
but they
cannot remove
them
effectively when
they
are dissolved
or
in
colloidal
form. These
devices
will
not
remove
air
and in
fact
tend to
aerate
he
oil.
The water-removing
ability
of the filter
is
dependant
upon
the
dryness
of the filter media.
When filtering
oi l
containing
water,
the filter
medium rapidly
comes nto
equilibrium
with the
water content
of
the
oil.
A continuous
ndication
of
the
water content
of the
outgoing
oil
is
very
helpful o fol low
the
efficiency
of the
process.
83.2.2
Centrifuges
83 .
8 3 . l
83.2.3
- 2 7 -
Reconditioning
*
G
eneral consideratiorts
The
physical
means
hat
are used or removing
water
of filter, centrifugeand vacuumdehydrator.
Another means or separatingcontaminants n suspension s the continuous centrifuge. n
general,
he
centrifuge
can handle
a
much greater
concentration
of contamination than
can
the
conventional
ilter
but cannot
remove
some of
the
contaminants
as completely
as
a
filter.
Conse-
quently,
the
centrifuge
s
generally
ound
in
use
for
rough
bulk
cleaning where
large
amounts
of
contaminated
il are to
be
handled.
Frequently,
he
output
of the
centrifuge s
put
through
a filter for
the final
clean
up .
Vacuum
dehydrators
The
vacuum
dehydrator
s
an efficientmeans
of
reducing
he
gas
and
water content
of an
insulating
oil
to
a very low
value. There
are two
types
of vacuum
dehydrator,
both of them
functioning
at elevated
emperature
or
a short time. In
one
method,
he treatment s accomplished
by
spraying
the
oil into
a vacuum
chamber; in
another, the
oil is
allowed to flow
over
a
series
of
baffies
nside
a vacuum
chamber
thus formins
thin
fllms.
If the
oil contains
solid
matter,
t is
advisable
o pass
t
through
processing
nder
vacuum.
The
operation
of vacuum
dehydrators s
continuous.
n
addition
dehydrators
will
degas he
oil and remove the
more
volatile
acids.
some kind
of a
filter
befbre
to
removing
water, vacuum
*
See reference
n footnote,
page
15 .
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83.3
8 3 . 3 . 1
- 2 9 - -
Application
o electricalequipment
Direct
purification
The
oil
is removed
hrough
a
purilying plant
into
suitable
containers
nd,
when
the
electrical
equipment s to be refilled,passed hrough the purifier again nto the equipment.This method
should
be used
or
switchgear. t
is
suitable,
oo, for the
smaller
ransformer,but care
s
needed
to
ensure
hat the
core and windingsare
thoroughly cleaned.The oil-containing
housing
of
th e
equipmentshould also
be
well cleaned, y
meansof
oil originating
rom the
purifier.
The direct
purification
method requires
auxiliary
oil containers, nd
drums are sclrnetimessed.
83.3.2 Purificalion
by
circulation
The oil
is
circulated
hrough the
purifier,
being
taken
frorn the
bottom of
the
tank
of
th e
electr ical
equipment
and
redelivered o
the top.
The
return
delivery should be
made
smoothly
and horizontally at or near the surlace evel o avoid, as ar as possible,mixing cleanedoil with
oil which has
not
yet passed
hrough
the
purifier.
The circulation
method
s
particularly
useful
for removing
suspendednternalcontaminat ion
n
equipment, ut
al l adher ingcontaminat ion
will
not
necessarily
e
rernoved.
Experience
as shown that i t is
generallynecessary
o pass he total
volume
of
oil
thror.rgh
he
purif ier
not
less
han three imes,
and equipment
of appropriate
capacity
should be chosenwitl-r
th is n mind.
The inal
amount
passed
i l l depend n
the
degree f
contaminat iou,
nd
he
process
must
be continued
unti l a
sarnple
aken from the
bottom of
the
electr icalequipment,after
the
oil
has
been
allowed
o
sett le
or
a
few hours,
passes
he
electr icstrength
est.
The circulationshould
preferably
be
performed
with
the
electr ical
quipmentdead,and
this
is
essential hen using
a
purifier
which aerates
he
oil.
In
an emergency,
transformermay
be
left
alive while circulation s proceedingprovided that there is a closed systemof piping so that
aeration
of oil
is
avoided, but
this is not recommendedon transformers or vol tages
above
I I kV. Aeration
occurs
mostly with centrifugal
separators,
ther
than those
operating
under
vacuum,
and should
aerat ion
have occurred,
he
oi l shouldbe al lowed
o
stand
or some ime
before
he
equipment s macl e ive,
according
o
the manufacturer's ecommendation.
84.
Replacement
The dirty oil is replacedwith cleanoil. This method s usefulwhen dealingwith smallquantities
of oil in the smaller
circuit-breakers nd
isolating-switch
hambers.
A
small extra
quantity
of
clean
oil
is
needed
o rinse he interior
of
the tank
and
the
immersed
parts.
It
is
essential
ha t
the
tank
and
the
surfaces
f
conductorsand
insulators
be
kept free from fibres,
and
from moisture
from
the
hands
of
the
working
personnel;
uch
moisture
can easily
provide
suff icient
ontami-
nation
to lower
the
electric
strensth
of
the new
oil below
standard.
There
should be
as
ittle
aerationas
possible
uring
the f i l l ing
of
tanks
and, as
far
as
possible,
the
end of
the
delivery
pipe
shouldbe
held
below
he
surface f
the
oil
in
order
o
avoid
splashing;
alternatively , he tanks
should
be
filled from the
bottom. There
should be a standing
period
of
not less
han
one hour to
al low de-aerat ion efore ommissiorr ing
he
equipment.
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3 l -
B5.
Precautionsn
the handlingand disposal f
mineral nsulatingoils
The
oils
with which
the
present
document
is
concerned are
mineral hydrocarbon
(pet-
roleum)
oils.
Whilst no
special isk s are
involved
in
the handling
and use of
mineral insulating
oils
(whether
inhibited or not), attention s drawn to the need or personalhygiene washingof skin and clothing
which
has
come
into contact
with oil) by
personnel
dealing
with
these
products.
When
used oil
has
o
be disposedof, certain
precautions
are
necessary
o
avoid
risk
of environ-
mental
pollution.
In most
countries,official advice
s
available on
these opics
and
legal
requirements
must
be
applied.
If the
precautions
and
regulations
applicable
o handling
and disposalof
industrial
and
other
lubricants
e.g.
utomobile rankcase rainings) re applied
o mineral nsulating
oils,
no problems
should arise.
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E
d
o
.9'
.ir;
' P - . F
q U ,
o ( t
.O
C)
E E .
100 0
0 . 5
0.2
- 3 2 -
Tem p6ra tu re
e l ' hu i le ,
C
O i l
t e m p e r a t u r e ,
C
Etat de
I'huile isolanted6termin6
par
la r6sistance
n courant continu.
Condit ionof
insulat ine
i l
as
determined v d.c.
resistance.
120
Acceptable
Mauvais
Bad
Frc. l .
-