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Energised transformer oil processing

Presentation for

Eilat - November 2012

Enviro Power Services LimitedTRANSFORMER LIFE EXTENSION SPECIALISTS

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What do you see?

Ageing asset ? Liability?

Or 20 years+ more reliable, service?

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Expected component lifeExpected component life(Bathtub curve)(Bathtub curve)

Failure Rate

Time

Initial work upHigh incidence / likelihood of failure

Useful operational life

“Old age”Increased risk of failure

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Why do transformers fail?Why do transformers fail?

85% of transformer failures occur due to weakened solid

insulationIn the windings! *

Paper life = Transformer life

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1000

250

Degre

e o

f poly

merisa

tion

0 25 50 75

Effect of contamination on the deterioration curve for paper insulation

Age in years

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Why do transformers fail?Why do transformers fail?

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Root cause?

As cellulose (paper) ages it becomes weaker.

The build up of contaminants in the paper insulation accelerate ageing,

further weakening the paper insulation and increasing the risk of failure.

Solution?

Eliminate or minimise the contamination at the earliest possible stage.

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1000

250

Degre

e o

f poly

merisa

tion

0 25 50 75

Age in years

Initial deterioration rate

By decontaminating the paper insulation regeneration slows the deteriorationRate and restores it to the original rateBy periodically regenerating the transformer the potential life of the paper canBe greatly extended!

End of life

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What limits Paper insulation (Cellulose) life ?

The primary factors that affect the paper insulation life are:-

•Heat

•Access to Oxygen

•Moisture absorbed in the paper

•The build up of Oxidation by-products:- Acids, Keytones, Peroxides etc.

•Sludge

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The progression towards insulation failureControlling FactorsControlling Factors

Dissolved moistureDissolved moisture HeatHeat

Oil impregnated paper(Cellulosic insulation)Oil impregnated paper(Cellulosic insulation)

Insulation FailureInsulation Failure

Corona (glow discharge)


Conduction & Ionisation(Partial discharge)


Chemical degradation(acids, peroxides, 02, Furanics etc.


Mechanical degradationMechanical degradation

Dielectric degradationDielectric

degradationAcids

(polar materials)Acids

(polar materials)Added

MoistureAdded

Moisture

CELLULOSE DEGRADATION CELLULOSE DEGRADATION

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Dielectric degradationDielectric degradation

Acids(polar

materials)

Acids(polar

materials)

CELLULOSIC DEGRADATION




Acids(polar

materials)

Acids(polar

materials)

Failure prediction

Failure prevention Life extension.

ACT NOW!

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The three key steps

1. Assessment – What conditions exist now, how much life remains?

2. Correction – What remedial actions can we take? Inspect, repair,

process?

3. Condition monitoring – what to test and when?

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ASSESSMENT ASSESSMENT

How much life is left in your transformers?How much life is left in your transformers?

=

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ASSESSMENT ASSESSMENT

Have there been any events in theHave there been any events in theTransformer’s history that might affectTransformer’s history that might affect

The remaining life of the paper insulation?The remaining life of the paper insulation?

We need to look back in time and indentifyWe need to look back in time and indentifyAny events that may have caused hot spotsAny events that may have caused hot spots

Bearing in mind that these may well NOT haveBearing in mind that these may well NOT haveCaused alarms to be triggered by Caused alarms to be triggered by Conventional analysis / diagnosis.Conventional analysis / diagnosis.

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Gas signatures

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Off circuit tap changer showing burnt contacts

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Historical perspective.

“Standards” have come to be used as acceptance limits

“Standards” for transformer oil are based upon

How the oil behaves as a dielectric medium

NOT primarily the effects on the entire insulation system

• Intended to be used as a basis for the development of ownspecific standard.

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IEC 60422 -2005Mineral insulating oil in electrical equipment – supervision and

maintenance guide

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The progression towards insulation failureControlling FactorsControlling Factors

Dissolved moistureDissolved moisture HeatHeat

Oil impregnated paper(Cellulosic insulation)Oil impregnated paper(Cellulosic insulation)









Dielectric degradationDielectric

degradationAcids

(polar materials)Acids

(polar materials)Added

MoistureAdded

Moisture

CELLULOSE DEGRADATION CELLULOSE DEGRADATION

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Show Movie clip

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Transformer Oil Regeneration

For Against

Well established and proven technique Must be performed by knowledgeable and experienced service.

Non intrusive – No outage necessary Plant must be engineered correctly bearing in mind the chemical and physical forces and processes at work

Environmentally friendly - Produces little to no waste products

Process must be controlled to prevent contamination of transformer with corrosive products.

Re- uses limited resource (Naphthenic oil)

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What remedial processes can we use?

Condition Method Effectiveness

High moisture Vacuum purificationOff line

Limited

Vacuum purificationOn line

Effective, needs to be supported

High acidity Vacuum purification Ineffective

RegenerationOff line

Limited

Energised regeneration

Highly effective

Sludge Hot Oil Cleaning Highly effective

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Contaminants removedWater, Gases and particulates.

Vacuum purification

Incoming oilAcid LacquerSludge PeroxidesAlcohol Oxygen Water

Outgoing oil

Acid LacquerSludge PeroxidesAlcohol

Corrective actions

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Corrective actions

Incoming oilAcid LacquerSludge PeroxidesAlcohol Oxygen Water

Outgoing oil

Clean, dry, contaminant free oil

Acid LacquerSludge PeroxidesAlcohol OxygenWater ALSO particulates and gases

Regeneration

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Contamination.

Both the oil and the paper insulation

Acidity

Sludge(begins to form at acidity levels as low as 0.1mgKOH/g)

Not always visible.Prevents effective cooling

Attacks and degrades cellulose.

Other polar compounds

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Why is acidity so important?Why is acidity so important?

• When acid forms it leads to sludge formation and deposition

0.05mgKOH/g 0.1mgKOH/gx250

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0.15mgKOH/g 0.3mgKOH/g

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Transformer: 60MVA, built 1958, oil capacity 54,000lt

Analysis: DGA – OK, Acidity – 0.23mgKOH/gm, IFT – 14

Power factor – 0.2133, OQI - <200, Furan derived DP - 420

Transformer investigation

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Transformer investigation

Results of DP tests carried out on paper samples showed a range of DP from 344 - 560

These transformers (2) was scrapped and replaced at a cost of

> £ 3 million.Appropriate remedial processing would have given 10 -

20 years additional life deferring the capital expenditure significantly and reducing the risk of

failure.

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The costs and the hazards involved in changing the oilAre considerable.

1.Cost of new oil

2.Outage to drain, flush and recharge

1.Disposal of old oil

2.Does not remove any of the contamination from the paper insulation

5. Stresses paper that may already be weak.

Why not just change the oil?Why not just change the oil?

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Transformer drained and refilled – note sludge deposits unaffected

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After re-energisation, sludges diffuse into new oil.

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• Non – intrusive (no outage required!)

• Active components, cooling paths and solid (cellulose) insulation decontaminated

• Paper insulation (cellulose) deterioration is retarded

• Transformer life is extended.

Energized transformer oil regeneration

a process overview

35

Why is energized regeneration better?

• The oil remains in the transformer, so no additional stress for the paper.

• The oil is the carrier for the contaminants and is the best solvent for them, and wherever the oil flows the regenerated hot oil cleans.

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Hot, regenerated oil is returned to the transformer And the cycle repeats until the oil is fully restored and

the insulation is decontaminated.

Regeneration

Heating &

coarse filter

Fine filtration

Dying &

degassing

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Limitations of 1st generation plants.

Made from mild steel. The concentration of the acidic and other aggressive chemical compounds

in the adsorbent columns causes severe corrosion – Fe2O3 This can be transported back, inadvertently, to the

transformer. The filtration available in these plants cannot filter out at the molecular level.

A transformer would never be put in service without the interior of the tank being coated!

Lack of control over process temperatures.

Causes damage to adsorbent and incomplete reactivation leading to faulty processing

Not built to pressure vessel specifications

Has led to vessel failures and fires.

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Latest generation plants by EPSFeatures.Manufactured in Stainless steel alloys. The use of carefully selected and researched stainless steel alloys has enabled us to ensure there is no production of corrosion products, eliminating the potentially hazardous carry over to the transformer.

Design improvement By building the adsorbent columns to a pressure vessel specification the inherent safety of the systems is improved and the failures experienced in the first generation equipment have been eliminated.

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Comparison of effectiveness of oil change and Energised processing

Oil Change Energised processing

Removes sludges from windings, cooling pathways and internal structures

No Yes

Decontaminates paper insulation

No Yes

Restores oil to new condition

Partially. Old oil residues (10%) and sludges will contaminate new oil

Yes

Stresses tank seals joints and gaskets

Yes No

Subjects older paper insulation to stress

Yes No

Extends asset life No Yes

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Cost comparison between oil change and energised processingOil change Cost GBP Processing Cost

Outage Drain – 15 hrsHot oil flush – 24 hoursVacuum – 24 hours +Refill – 20 hoursStanding time post fill – 24 hoursTotal - 107 hoursLoss of earnings @ £15k/hr

£1,605,000.00

Normally no outage is required this depends upon safety clearances

Nil

New oil New virgin oil for fill (80klt) @£1.8/ltOil for flush 40klt @ £1.8/lt

£144,000.00

£72,000.00

Top up +/- 0.1% = 100lt

£180.00

Inhibition Not required Nil Done as part of process

Nil

Manpower costs

Depending upon rate and number of personnel but estimate for team of 4 for time 2 skilled two 2 semi skilled

£5,350.00 Included in processing costs

Nil

Oil handling Storage and conditioning of drained oil

£5,000.00 Not required Nil

Disposal of used oil

Sold to recyclers @ £0.25/lt80,000 lt+ flush oil 40,000lt

-£30,000.00 Not required Nil

Cost of processing

Not relevant Nil Depending condition

£120,000.00

Total £1,801,350.00 £120,180.00

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400kV Supergrid transformer. Winding insulation test results before and after regeneration.

Insulation status

Before processing After processingHV - E 450MΩ 2250MΩHV - LV 700MΩ 1750MΩLV - E 350MΩ 3500MΩ

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Winding insulation test results before and after regeneration.5 x 12.5MVA distribution transformers

Manufactured in 1976

Insulation status

Before processing After processingHV - E 90MΩ 1300MΩHV - LV 100MΩ 1550MΩLV - E 100MΩ 1400MΩ

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Energised transformer oil regeneration (HOC) will:-

Remove contamination from the paper insulation and

improve insulation capability Restore the oil to an “as new”

condition Extend the life of a transformer

Reduce the risk of failure

Energised transformer oil regeneration will not:-

Improve the tensile strength of the paper insulation

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