Dr B Pahlavanpour

Senior Techncal Co-ordinator

Nynas Naphthenics LTD

UK

IEC specification and maintenance guide for

mineral insulating oil Dr B Pahlavanpour

Nynas Naphthenics Ltd

UK

Three Important oil related IEC standards

IEC60296, Specification for supply of unused MIO

IEC60422, Maintenance guide for in-service MIO

IEC60599, Interpretation of DGA

Although these standards have maintenance cycle but, if required,

they can be revised if and when require

Reason for revision

During 2005 there was report of some transformer failure due to

copper sulphide formation

IEC, TC10 meeting in Cape Town decision was to revise these two

standard to address this issue,

Also to develop a method for detection of potentially corrosive

sulphur

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Revised IEC60296, 2012 ed

Introduction of corrosive sulphur test methods:

IEC62535

ASTM D1275B

Introduction of IEC60666 test method for:

passivator content

Test method for antioxidant content to 0.01%

Lower level of Furfural in oil (<0.05 ppm)

If passivator is detected then oil should tested for 500 hours for

oxidation stability test (IEC61125C)

Introducing test method for detection of DBDS, limit of <5 ppm

IEC62697

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Table 2 General specification

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No changes to 2003 ed

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Special requirement for special application

(high grade oil)

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IEC 60422 Oil maintenance guide

– A tool for keeping the oil in good condition

Oil tests divided into 3 groups

Routine

Complementary

Special investigative

Different recommended property limits depending on voltage class (also type of

equipment)

< 72.5 kV

72.5-170 kV

< 170 kV

For each measured property 3 levels of assessment

Good No action

Fair More frequent sampling

Poor Action required

Revision of IEC60422

Originally was to address potentially corrosive sulphur in oil

First meeting January 2007

Report to TC10 Test the oil for presence of corrosive sulphur,

corrective actions recommended (i.e change the oil, passivate the

oil)

MT22 members take the opportunity to revise IEC60422 and IEC

central office agreed with this proposal.

To bring it in line with current practice in industry, and address

industries need.

Main changes

Moisture content

Inhibitor content

Passsivator content

DBDS content

Potentially Corrosive Sulphur

Water content

2005 ed. “corrected to 20 ºC” then limit for each category of

equipment

FDIS, “at transformer operating temperature together with

breakdown voltage” .

Consequently higher limits are used

Correction to 20 ºC is transferred to annex (informative).

Water content

(mg/kg at

transformer

operating

temperature)

O, A <15 15 to 20 >20

B, D <20 20 to 30 >30

C, E <30 30 to 40 >40

F Action

necessit

y >40

G Not a routine test.

2005 ed

2013 ed

Inhibitor content

Category Recommended Action Limits

Good Fair Poor

All >60 % of

original

value

40 % to 60

% of

original

value

<40 % of

original value

2005 ed

2013 ed

Passivator content (new)

O, A, B, C,

D, E, F

>70 and stable,

(rate of decrease

<10mg/kg/year)

50-70 mg/kg or

<70 mg/kg,

with a

significant rate

of decrease of

>10mg/kg/year

<50 and

decreasing at

>10mg/kg/year

Interfacial tension

O, A, B, C, D

Inhibited

Uninhibited

>28

>25

22 to 28

20 to 25

<22

<20

E Not a routine test.

F, G Not applicable.

2005 ed

2013 ed

Corrosive sulphur Three corrosive sulphur test are recommended

Introducing new test IEC62535

ASTM D1275B

DIN51353

Category Recommended Action Limits Recommended Action (1) (2)

Good Fair Poor

O, A, B, C, D,

E, F

Non corrosive Corrosive For corrosive oil:

- conduct risk assessment

- reduce the corrosivity of the oil by

adding a copper passivator (e.g. triazole

derivates)

or

- remove the source of corrosivity by

changing the oil [see 12] or by removing

corrosive compounds by mean of

suitable oil treatments.

See NOTE 3.

Passivator content, test method IEC60666, annex B

O, A,

B, C,

D, E, F

>70 and

stable,

(rate of

decrease

<10mg/kg

/year)

50-70

mg/kg or

<70

mg/kg,

with a

significan

t rate of

decrease

of

>10mg/kg

/year

<50 and

decreasin

g at

>10mg/kg

/year

Good: less frequent monitoring

acceptable.

Fair: maintain regular monitoring.

Poor: remove the source of

corrosivity by changing the oil [see

12] or by removing corrosive

compounds by mean of suitable oil

treatments, or

as a short-term solution, top up

with new passivator, to at least

100mg/kg [see 13].

DBDS content

IEC62697-1 is introduce as test method.

No limit for in-service oil as good, fair, bad

Reference to CIGRE Brochure 378 is made

IEC60422, 205 ed.

Table of 2013 ed.

Property Highest voltage for equipment (kV)

<72,5 72,5 to 170 >170

Appearance Clear, free from sediment and suspended matter

Colour (on scale given in ISO 2049) Max. 2,0 Max 2,0 Max. 2,0

Breakdown voltage (kV) >55 >60 >60

Water content (mg/kg)a 20b <10 <10

Acidity (mg KOH/g) Max. 0,03 Max. 0,03 Max. 0,03

Dielectric dissipation factor at 90 °C

and 40 Hz to 60 Hz c

Max. 0,015 Max. 0,015 Max. 0,010

Resistivity at 90 °C (G.m) Min. 60 Min. 60 Min. 60

Corrosive sulphur Non-corrosive

DBDS content (mg/kg) <5

Interfacial tension (mN/m) Min. 35 Min. 35 Min. 35

Total PCB content (mg/kg) Not detectable (< 2 mg/kg total)

Particles - - See Table 9 d

Compatibility

The following functional tests are recommended for each individual oil

and for the mixture:

Foaming

Oxidation stability according to IEC 61125 C, including acidity, sludge

and DDF after ageing. Test time should be according to the oil group as

stated in IEC 60296

Corrosive sulphur and/or potential corrosivity after ageing according to

IEC 61125C