Regeneration of used insulating oil

Presented by

Stanislav Sukhar

8 Sadovskogo Street, Poltava, Ukraine, 36034Tel/Fax: +380532241211www.gcequipment.cominfo@gcequipment.com

Agenda• Our Agents – Drallim Industries Ltd• Introduction to Regeneration• Ageing of Oil and Cellulosic Materials• Remedial Actions (Oil Purification, Oil

Regeneration)• Regeneration Plant Design and Operation• Applications of Regeneration Plants• Historic Data• Summary

Our UK Agents - Drallim Industries Ltd• Drallim Industries Ltd, our UK agents were formed in 1957

• Now has 3 divisions of Utilities, Aerospace & Industrial - Staff of 62

• Located at St Leonards on Sea, East Sussex

• Service Engineers in Staffordshire & East Sussex

• Manufacturers of OILMON cable monitoring Systems (<400kV)

• Representatives for:- GlobeCore - Oil Regenerations & Purification Systems

MTE – Transformer Oil-in-Gas monitoring Systems

High Voltage Inc – VLF, Power Freq. & DC HV Test Equipt

IRIS – Partial Discharge Monitoring Systems

Introduction

• At present, more than 40 % of transformers in use are over 25 years old

• Replacement of all aging transformers in not possible due to high cost

• Timely oil regeneration will prolong the life of a transformer

• Oil Regeneration with sorbent reactivation is the most efficient and environmentally friendly process to date.

Ageing of Oil and Cellulosic MaterialsOil chemistry

• Very complex structure• Generally most compounds in oil are still not fully

known and understood.• Oils composed mostly of hydrocarbons (>99%)

however some minor components created as a by-product of aging (hydro-peroxides, ketones, carboxylic acids, aldehydes, phenols) have a major impact on it’s properties.

Functions of Transformer Oil

• Oil provides heat transfer - acts as a cooling medium• Oil protects the solid insulation - acts as a barrier

between the paper and damaging effects of oxygen and moisture

• Oil can be tested to give an indication of the conditions inside the equipment-acts as a diagnostic tool for evaluating solid insulation

• Oil provides a dielectric strength - acts as a part of insulation together with paper and board.

Inhibited and Uninhibited oils• Inhibition is the addition of DBPC-2,6-Diteriary-Butyl-

para-Cresole• Percentage is 0,3% by weight• Inhibited oil relies on the ability of antioxidant to

suppress the oxidation• Uninhibited oil must contains sulphur compounds

which act as antioxidants• Correctly formulated inhibited oil has long technical

life as long as there is sufficient inhibitor left• Uninhibited oil will start to oxidize and produce acids

early in its life but will age in predictable way.

Paper Insulation

• Provides mechanical strength, dielectric strength and mechanical spacing

• Board and paper insulation consist of three main components: cellulose, hemicellulose and lignin

• Degradation of it’s main component cellulose has the greatest effect on its mechanical properties

• Life of the transformer is determined by the state of cellulose insulation

Transformer has no moving parts apart from on load tap changers and regulating transformers

But it does move due to:• Mechanical vibration, • Switching surges, • Line surges and • Limited short circuits.

Dielectric Clearance

Normal Load

The paper wrapping & spacers withstand this movement when the Transformer is new.

Dielectric Clearance

Surge Load

This is the type of stress transformer windings undergo

IEEE defines Transformer’s end of life as 75% loss in paper tensile strength (DP).Beyond this point transformer may not reliably withstand the next surge load or short circuit.

But how does Transformer’s paper insulation lose strength?• Because of moisture presence• Because of oxidation taking place

within the Transformer• Due to overheating

• Residual absorbed moisture left in by the manufacturer

Moisture is available to the cellulose primarily from three sources

• Moisture formed by thermal degradation during service life

• Moisture absorbed through unmaintained breathers

The following bad conditions form in the Transformer from oxidising oil, then take up residence in the paper insulation:

• Water soluble acids• Low molecular weight acids• Fatty acids• Water (free)• Moisture (dissolved/ emulsion)• Visible sludges of asphaltene• Dissolved sludges of asphaltene• Peroxide Gas• Alcohols

• Metallic soaps• Aldehydes• Ketones• Lacquers• Colour pigments

Transformer’s paper insulation acts just like the paper in a car’s oil filter – it filters these decay products out

of the oil and holds them, DESTROYING TRANSFORMER’S PAPER

INSULATION

Action of heat & moisture in the development of cellulosic degradation

What happens?Simple - End of life of a transformer.

Remedial ActionsCurrent Choices

•Purchase new oil-standard procedure worldwide•Purchase regenerated / reclaimed oil (not available in all countries but available in UK, South Africa, Thailand, Australia, Brazil etc.)•Utilize mobile on site Purification Plants•Utilize mobile on site Regeneration Plants

Advantages of Oil Treatment over Oil changesEnergized Transformer De-energized Transformer

No power supply interruption Power supply interruption to consumer

No loss of money Loss of money

No environmental, hazard due to oil spillage or PCB contamination

Environmental nightmare. High possibility of oil spillage. Transport limitations if PCB contaminated

No exposing of core to atmosphere Dangerous exposure of core to water/air absorption. Re-gasketting of top cover

Not dependent on climatic conditions Field work only done under favourable climatic conditions

Not labour intensive – 1 plant operator after set-up

Skilled and labour intensive operation

Complete flushing of transformer and core achieved

Core leaches out contaminated products to new oil

Oil Purification and Regeneration

• Oil Purification forms an important part of regular, preventative transformer maintenance. In the process of purification, water, dirt and gasses are removed from transformer oil.

• When oil in a transformer reaches a stage (due to aging process) where purification / degassing is no longer efficient, the oil must be changed or regenerated. Regeneration is the complete treatment of oil to like new condition.

High Vacuum Purification

• Internationally accepted way to purify Transformer oil.

• Dissolved water removed down to 3ppm.• Gas removed down to 0,1% of volume.• Dirt removed down to 0,2 micron.• Plants manufactured in stationary, mobile and

portable combinations.• Very effective, simple to operate.

On-line Oil Purification

• Effective way to treat transformer oil.• Process can be done on energized and de energized

transformers.• Before filtration takes place full laboratory analysis is

required on the oil especially for on line operations.• Final oil tests are required after filtration is

completed.

Important Oil Purification Facts Summary

• 97% of the water in a transformer is in the paper in the transformer.

• Oil purification only removes water from the oil and not from the paper-only extended period of purification can dry out the paper in a transformer.

• Purification using a vacuum process reduces combustible gas in the oil.

Important Facts Continued

• By regular purification, oxygen is reduced which is a driver of the oxidation process happening in the oil.

• Regular purification also removes combustible gas which again is a driver of oil decay

• Correct micron filtration removes any dust, rust or other particles in the oil

High Vacuum Oil Purification Plant

Oil Regeneration

• Regeneration-treatment of old aged oil back to like new condition

• Normally done using Fuller’s Earth systems.• Fuller’s Earth systems have shown to be most cost

effective to date.• Can be mobile or stationary.• Latest designs are environmentally friendly.

• Breakdown voltage• Acid number• Surface tension• Dielectric loss tangent• Oxidation stability

Oil Regeneration Improves:

Typical Oil Parameters After RegenerationParameter Test Methods Standard Value

BS 148:2009Before

regeneration After regeneration

Appearance Visual Clear, free from sediments and suspended matter Cloudy brown Clear and

transparentAcid number, mg КОН/g

IEC 296; ASTM D-664 ≤ 0.03 0.63 0.01

Corrosive sulphur ISO 5662; ASTM D-1275 Non Corrosive Present None

Moisture content, ppm

IEC 733; ASTM D-1533 ≤ 20 170 5

Breakdown voltage, kV

IEC 156; ASTM D-1816 ≥ 30 11 73

Dielectric loss tangent at 90ºС

IEC 247; ASTM D-924 ≤ 0.005 4.0 0.001

Gas content, % IEC 60599; ASTM D-3612 --- 12 0.1

Surface tension, mН/m, at 25ºС

ISO 6295; ASTM D-2285 --- 22 45

Mechanical contaminants size, micron

Clear, free from sediments and suspended matter 50 0.2

Oxidation stability:mg КОН/g

IEC 1125А; IEC 1125B; IP-307 ≤ 1.2 --- 0.2

Regeneration of used insulating oil

• All mineral oils can be regenerated successfully to be used over and over again

• Regeneration of oil can be done in stationary-tank to tank or mobile equipment in energized or de energized transformers.

• Still the most cost effective way to treat oil to be used again in electrical equipment safely and reliably

• No limit on the amount of times oil can be regenerated

When is the Correct Time to do Oil Regeneration?

•Every 10 years•When oil colour changes from a dark yellow to light orange.•Marked increase in Tan delta (power dissipation factor) and reduction in IFT values•Increase in oil acidity values

0.08 .2 .4 .6 .8 1.0 1.2 1.4 1.6

NEUTRALIZATION NUMBER mg KOH/gm Oil

IN

TERF

ACIA

L TE

NSI

ON

DYN

E/cm

2

40353025

2015105

0

Neutralization Number versus Interfacial Tension Curve

Recommended regeneration treatment to

commence

Good Oil

Prop A Oil

Marginal Oil

Bad Oil

Extremely Bad Oil

Very Bad Oil

Fuller’s Earth Method

• The current best known and improved method of transformer oil regeneration, is treatment with Fuller’s Earth.

• Modern Plants use a special high performance Fuller’s Earth to achieve maximum performance and efficiency from installed earth to return old aged oil to like-new condition.

• Fuller’s Earth is a naturally occurring absorbent clay

• Easily absorbs impurities from oil• Crystalline structure – can absorb large

quantities of acid• Can absorb up to 25% water by weight• Porosity of up to 125m2/gram

Properties of Fuller’s Earth

Flow Schematic of Disposable Fuller’s Earth System

Old Disposable System Design Used Oil

Regenerated Oil

Compressed Air Purge Evacuation

Fuller’s Earth Dump

New Fuller’s Earth

Not cost effective or environmentally friendly Old Technology

• Reactivation of Fuller's Earth is fully automated and enables the Regeneration Plant to process oil again and again using the same Fuller's Earth.

• Fuller's Earth does not need to be removed from the Regeneration Plant for a period of up to 2-3 years.

Latest MethodFuller’s Earth Reactivation

Typical Modern Oil Regeneration Plant

Flow Schematic for Stationary Oil Regeneration Plant

Flow Schematic for Mobile Oil Regeneration Plant

Major Advantages of using On site and On line Regeneration Plants

• Extension of life of oil filled transformers-most important aspect.

• Extension of oil life-second most important.• Transformer is energised-no loss of revenue or

inconvenienced customers• Easy to do, one operator.• No oil transportation concerns • No cross contamination problems example PCB or

silicon concerns

• There is no concern about the availability of oil to regenerate because all the oil is currently installed in transformers.

• Not subject to international oil prices.• Very effective process with low operating costs.• Equipment to do regeneration was developed in

South Africa and is now available from European manufacturers.

Major advantages of using on site and on line regeneration plants continued

Oil Processing in Energized Transformer

Advantages continued

• Client retains his existing oil - retains the asset.• No oil cross contamination or mixing.• Oil will meet current international standards.• Clean out of the transformer – removal of sludge

deposits from transformer windings and insulation.

Damage from the Sludge

• Sludge if left will settle on the cooler parts of the transformer.

• It penetrates the voids in insulation board.• Starts to attack the metals that are unprotected.• Can build up in the cooling path - preventing oil flow,

increase in operating temperature.

Desludging of Paper Insulation

• Regeneration plants are capable of removing sludge deposits from transformer windings and insulation

• Achieved by increasing circulating oil temperature to the aniline point, which is usually around 80 ºC

• Dissolved deposits of sludge are removed by the sorbent before oil is returned to the transformer.

History of on site regeneration

• Started in 1965 in the USA and UK.• Modern mobile regeneration plants

(automated reactivation process 1990 South Africa, 1991 UK)

• Over 120 modern reactivatable plants sold worldwide since 1990.

• 2009 Oil Regeneration Technology transfer from Fluidex to GlobeCore

Historic DataTable below shows averaged data from 247 transformers treated by ABB in Norway and Sweden with 3 mobile regeneration units.

Classification Oil Property Acidity

(mg KOH/g) Colour BDV (kV/2,5mm)

DDFat 90°C

IFT(mN/m)

Before Regeneration 0,157 4,1 68 0,0812 23,5

After Regeneration 0,009 1,5 80 0,0033 46,0

Follow-up(Approx 6-9 months) 0,014 1,6 74 0,0063 42,3

IEC 60422Std Specification 0,03 2,0 55-60 0,010-0,015 35

Key: DDF - Dielectric Dissipation Factor BDV - Breakdown Voltage IFT - Interfacial Tension.

Summary• On-line regeneration restores the oil’s

properties to close to those of new oil.• The changes in properties (due to

recontamination from degraded products in the solid insulation) during the first years in service after treatment are small.

• Oil is not a renewable resource and the new technology causes much less waste of oil and sorbent than traditional methods.

• Thousands of transformers successfully treated worldwide.

Company Information• Globe Core is a manufacturer of Transformer

Oil Purification and Regeneration Plants• Production Facilities – Poltava, Ukraine• Sales Offices – Ukraine, USA

Worldwide Sales

Company Information

GlobeCore’s UK Representatives are:-

Drallim Industries Ltd

For Further Information please contact us at:- Drallim Industries Ltd,

Drury Lane, St Leonards-on-Sea,East Sussex, TN38 9BA, UK

Tel: 01424 205140 Fax: 01424 202140E: sales@drallim.com Web: www.drallim.com

Thank you for your timePresented by

Stanislav Sukhar

8 Sadovskogo Street, Poltava, Ukraine, 36034Tel/Fax: +380532241211www.gcequipment.cominfo@gcequipment.com