Oil in Service

7/28/2019 Oil in Service

1/23

Maintenance of in-service mineral

insulating oil

Dr B Pahlavanpour, Nynas UK

Subjectmatter,Name, Division2 2012-11-03

Functional Requirements for Oil

An insulant

A heat transfer and cooling medium

An arc quenching medium for tapchanger diverter switches and oil

filled switchgear

Must be compatible wi th the materials used in electrical

equipment


Oil Condition monitoring

Monitoring and maintaining oil quality is essential to ensure the reliable

operation of oil-filled electrical equipment.

Codes of practice for this purpose have been established by electrical

power authorities, power companies and industries in many countries.


2/23


Transformer Failure

Before 1930

Lack of transformer oil maintenance

many kinds of oil in useLack of specification for manufacture of oil

Lack of standard for determining oil quality

Lack of understanding of what transpires inside

a transformer as it ages

Nynas-20125 2012-11-03

In Privatized Electricity Industr y

5 hours forced ou tage = 30 days loss of revenue

availability is more important than reliability


Why Oil Maintenance?

Insulating oil in-service is subjected to heat and air

Oil oxidation deterioration

If a certain amount of oil deterioration is exceeded, there is inevitably

some erosion of safety margins and the question of the risk of

premature failure has to be considered.

While the quantification of the risk can be very difficult, a first stepinvolves the identification of potential effects of increased deterioration.

Unused mineral oils are limited resources and should be handled with

this in mind.


3/23


Maintenance standard

IEC60422 Mineral insulating oils in electrical equipment Supervisionand maintenance guidance.

IEEE C57, 106 IEEE Guide for acceptance and main tenance of i nsulatingoil in equipment.

Utility, organisation standards TGN158

Current situation of IEC6042



Aim

Prevent forced outage

Eliminate unnecessary maintenance

Provide the appropriate amount of maintenance at right time

Prevent premature ageing


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Basic oil characteristics required for reliable performance

High dielectric strength to withstand the electric stresses imposed in

service

Sufficiently low viscosity so that its ability to circulate and transfer heat

is not impaired

Adequate low-temperature properties down to the lowest temperature

expected at the installation site

Resistance to oxidation to maximise service life


IEC60422 recommendation

Three group of tests are recommended:

Routine tests (Group 1)

Complementary tests (Group 2)

Special Investigative tests (Group 3)


Routine tests (Group 1)

Minimum tests required to monitor the oil and to ensure that it is

suitable for continued service. If the results obtained from these tests

do not exceed recommended action limits usually no further tests are

considered necessary until the next regular period for inspection but,

under certain perceived conditions, complementary tests may be

deemed prudent.


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Complementary tests (Group 2)

These are additional tests, which may be used to obtain further

specific information about the quality of the oil, and may be used to

assist in the evaluation of the oil for continued use in service.


Special Investigative tests (Group 3)

These tests are used mainly to determine the suitability of the oil for

the type of equipment in use and to ensure compliance with

environmental and operational considerations.


Group one tests

Property Group Method

Colour and appearance 1 ISO 2049

Breakdown voltage 1 IEC 60156

Water content 1 IEC 60814

Acidity (neutralization value) 1 IEC 62021-1 or

IEC 62021-2

Dielectric dissipation factor (DDF)

and resistivity

1 IEC 60247

Inhibitor content 1 IEC 60666


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Group 2 tests

SedimentSludge

2 Annex C of IEC 60422

Interfacial tension (IFT) 2 ASTM D971

EN 14210

Particles (counting and sizing) 2 IEC 60970


Group 3 tests

Flash point 3 ISO 2719

Compatibility 3 IEC 61125

Pour point 3 ISO 3016

Density 3 ISO3675

Viscosity 3 ISO 3104

Polychlorinated biphenyls (PCBs) 3 IEC 61619

Corrosive sulphur 3 IEC 62535ASTM D1275B

DIN 51353

Dibenzyl disulfide (DBDS) content 3 IEC 62697-1

Passivator content 3 Annex B of IEC

60666

Oxidation stability 3 IEC 61125


Oil sampling

It is essential that every effort be made to ensure that samples are

representative of the insulating oil in equipment

Sampling should be performed by an experienced person, who has

received adequate training, in accordance with IEC 60475.

Where available, manufacturers instructions should be followed.


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8/23


Evaluation of mineral insulating oil in new equipment

Property Highest voltage for equipment (kV)

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) 20


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Frequency of examination of oils in service

It is impossible to lay down a general rule for the frequency of

examination of oils in service which will be applicable to all possible

situations that might be encountered.

Property Equipment category

O A B C D E F G

Group 1 (Routine

Tests) years

1 to 2 1 to 3 1 to 4 2 to 6 1 to 2 2 to 6 2 to 6 2 to 6

Group 3 (passivator content) 6 month or less, depending on the rate of

decrease and the absolute value.

Maintenance of in-service insulating oil26 2009

CMI = (P - F)/2

P= Time of detecting an upcoming failure

F= Moment of failure

Condition monitoring interval, CMI


Oil tests

Field tests

Only limited number of tests can be performed

Obtain a prompt estimation of oil condition

Establish the classification of service-aged oils

Eliminate any changes to the oil samples properties due to

transportation to a laboratory and/or storage of oil samples

Laboratory tests

More accurate

A complete examination scheme of recommended tests can be

performed


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Classification of the condition of oils in service

oils in service may be classified as:

Good

FairPoor

based on the evaluation of significant properties


Good

Oil in normal condition; continue normal sampling

No corrective action is require


Fair

Oil deterioration detectable;

more frequent sampling recommended


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Poor

Oil deterioration abnormal

schedule effective actions


Corrective action

Two types of contamination / deterioration of the oil can be considered

physical

chemical

Each one requires a different remedial action


Important point:

Where a test result is outside the limits recommended value

should be compared with previous results and

fresh sample obtained for confirmation before any other action is

taken.

If rapid deterioration or acceleration in the rate of deterioration is

observedmore frequent tests should be instituted promptly and/or

appropriate remedial action should be taken.

It may be desirable to consult the manufacturer of the equipment


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Colour and appearance

All

equipment

Clear and

without

visible

contamination

Dark and/or

turbid

As dictated by

other tests.

Dark colour is a symptom

of chemical contamination

or ageing.

Turbidity is a symptom of

high water content.


Breakdown voltage (kV)

O, A, D >60 50 to 60 50 40 to 50 40 30 to 40


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variation in saturation water content with oil

temperature and acidity

0

50

100

150

200

250

0 10 20 30 40 50 60

oil temperature during operation (C)

saturation

watercontentofoil(m

g/kg

)

saturation water content in unused oil (l og Ws =

7.0895 - 1567/T)

typical saturation water content in oxidised oil with

acidityof 0.3 mg KOH/g


0,00

1,00

2,00

20 30 40 50 60 70 80 90 100

ts (C)

Correction

factor

st04,0e24,2f

Sampling oil temperature above 20 C


Moisture correction factor


14/23


Sampling oil temperature below 20 C

T

15670895,7LogWs

% Saturation= (mg/kgof water/ Ws)x 100

Percent saturationwater in oil

Condition of cellulosic insulation

0 5 % Dry insulation

6 20 % Moderately wet, low numbers indicate fairly dry to

moderate levels of water in the insulation. Valuestoward the upper limit indicate moderately wet

insulation21 30 % Wet insulation

> 30 % Extremely wet insulation

Source : IEEE C57.106:2002 (B6)


Effect of temperature

0

5

10

15

20

25

30

35

1 2 3 4 5 6 7 8 9 10 11 12

Time

Watercontent(ppm)

0

10

20

30

40

50

60

Temperature(C)

wa ter ppm wate r ppm 2 0 oi l te mp

Loaded Loaded Loaded

Loaded


Acidity (mgKOH/goil)

O, A, D 0,15

B, E 0,20

C 0,30

F, G Not a routine test.

Good: Continue normal sampling

Fair: More frequent sampling. Check the presence of

sediment and sludge.An inhibited oil that reached fair values

has possibly lost its oxidation protection.

Poor: Starting from a value of 0,15, Reclaim the oil or change

the oil


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Dielectric dissipation factor at 40 Hz to 60 Hz at 90 C

O, A 0,20

B, C 0,50

D 0,03

E 0,30

F, G Not a routine test.

Good: Continue normal sampling.

Fair: More frequent sampling. Check other parameters.

Poor: Reclaim oil, change the oil


Resistivity (Gm)

O, A >200 20 to 200 60 4 to 60 800 250 to 800 60 7 to 60 10 3 to 10 3 0,2 to 3 50 10 to 50 3 0,4 to 3


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Inhibitor content

Good Fair Poor

>60 % of

original value

40 % to 60 %

of originalvalue

70 and stable,

(rate of

decrease


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Interfacial tension (mN/m)

O, A,

B, C,

D

Inhibit

ed

Uninhi

bited

>28

>25

22 to 28

20 to 25


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Flash point

AllCategories

Maximum decrease 10

Equipment may requireinspection. Investigate.


Do nothing

Risk of failure

Establish rate of deterioration

Establish type of contamination

Physical

Chemical

Take corrective action

Options for equipment owner


Summary of typical actions

Key factors Symptoms Corrective actions

Physical - High water content- Low breakdown voltage value

- High particles content

- Turbid (not clear)

- Reconditioning

Chemical - High colour value- Low IFT

- High acidity value- High dissipation factor value

- Presence of sediments or sludge, or both

- Low inhibitor content, for inhibited oil

- Low passivator content for passivator

containing oil

-Reclaiming

-- or change the oil

Restore original additive

concentration according to

recommendations

PCB PCB contamination detectable - Refer to local regulations

Corrosive

Sulphur

- Oil corrosiveness Perform risk assessment andcorrect as necessary

- Passivation

- Oil change

- Reclaiming


19/23


Reconditioning

Reconditioning is a process that eliminates or reduces physical

contamination by means of physical processes (filtration, drying,

degassing etc.)

Reconditioning reduces the particle and water content of the oil

The process may also remove some dissolved gases and other

components such as Furanic compounds

it is recommended that the oil should not be vacuum treated at

temperatures over 85C.

If it is desirable to reduce particles or free water, cold treatment at

atmospheric pressure may be appropriate.


Conditions for processing inhibited and/or passivator containing

mineral insulating oils

Temperature (C) Minimum Pressure (Pa)

40 8

50 15

60 30

70 80

80 200

85 280


Vacuum Treatment of Insulating Oil

Pressure [Pa]

Working Temperature [C]

100000

10000

1000

100

10

1

0 40 50 65 100 150 200 250 300 350

Water Insulating Oil Working Point


20/23


Removing water from liquid and solid insulation

On-line methods

Advantages:

Possible

fortransform

ers

that

cannotwithstand

vacuum

Transformer

remains inservice

Disadvantages:

Off-line methods

Advantages:

Efficiency

Speed

Disadvantages:

Transformer hasto be taken

out of

service for theduration

of the process

Cost


Reconditioning equipment

Filter

Filtering equipment usually forces oil under pressure through

absorbing material such as paper or other filter media.

Centrifuge

use for rough bulk cleaning where large amounts of contaminated

oil are to be handled.

Vacuum dehydrator

It is an efficient means of reducing the gas and water content of a

mineral insulating oil to very low values


Oil reconditioning application t o electrical

equipment

Direct reconditioning

The oil is passed through a purifier and then stored in suitable

clean containers

Reconditioning by circulation

The oil is circulated through the purifier, being taken from the

bottom of the tank of the electrical equipment and re -delivered tothe top

It is useful for removing suspended contaminants


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Oil Reclamation

This is a process that eliminates or reduces soluble and insoluble polar

contaminants from the oil by chemical and physical processing.

The resulting product should be evaluated on critical parameters

Reclamation of oils of moderate to high acidity will usually result in oils

with a lower oxidation resistance than the original new oil

IEC developed new standards for reclaimed oil IEC62701


Replacement of oil in electrical equipment

Lower than 72.5 KV

A small extra quantity of oil is needed to rinse the interior of the tank

and the immersed parts

It is essential that the tank and the surfaces of conductors and

insulators be cleaned effectively and subsequently be kept free from

fibres

Possibly up to 10% of the original oil m ight remain adsorbed in the

solid insulation and its contaminants may take some time to migrate

into the new oil


Replacement o f oil in tr ansformers rated 72,5 kV

and above

Use manufacturers recommendation

Removed used oil from main tank as much as possible

Rinse the winding with clean hot unused oil (hot flashing)

Apply vacuum with care (manufacturers recommendation)


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Passivation

Metal passivator is added as a stock solution, dissolved in insulating

oil

The stock solution can be added via an oil processing unit or other

suitable equipment.

This treatment is recommended for unused and in-service insulating oil


Renewal of additives

Oil reclamation remove oxidation inhibitors

Additives shall be replaced in the reclaimed oil after the reclaiming

process and before the equipment is re-energized

The most widely used additives are 2,6-di-tert-butyl-paracresol (DBPC)

and 2,6-di-tert-butyl-phenol (DBP).

Metal passivators will also be reduced or removed due to their polar

nature.


Decontamination of oils containing PCBs

Contaminated oil may change and replaced by unused oil

There are several processes and techniques available for either on-

site and off-site decontamination of PCB contaminated oils

All PCB dec ont aminati on m etho ds, ei ther off -sit e or o n-si te, have

to be applied by skilled companies complying fu lly with local

regulations.


23/23


Dehalogenation process

Several process are available

Dehalogenation processes using sodium and lithium derivatives

Dehalogenation processes using polyethylene glycol and potassium

hydroxide (KPEG)

Dehalogenation in continuous mode by closed circuit process

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Oil in Service