RECYCLING OF MINERAL INSULATING OIL Experience of EOS

Tom Larney

Bridges Road Ellesmere Port

Cheshire, CH65 4EQ – United Kingdom

ABSTRACT With a challenging environment of increased demand on utilities to “keep the lights on” in an economic and environmentally friendly manner, within a framework of policies and regulations, asset managers in the UK view reclamation and reclaimed transformer oil as trusted tools to achieve their objectives. OFGEM, the regulatory body has also acknowledged the use of regeneration to improve the health index of key assets. Electrical Oil Services and her predecessor companies have been at the forefront of insulating oil supply, reclamation and on-site treatment for over 60 years in the United Kingdom. Drawing on this long history of close involvement with the UK electricity supply industry this paper seeks to review the closed-loop business model employed in the UK to reclaim customer’s used transformer oil to re-usable reclaimed insulating oil. The latest techniques for in-situ oil regeneration to “deep cleaning” insulation systems to extending the potential life of transformers as well as future options to reclaim used transformer oil in-situ at customer premises are also presented.

1. INTRODUCTION Legal and other environmental requirements such as ISO 14001 and Waste Hierarchy obligations now necessitate waste management and the options of recycling or treating insulating oils to extend use. Utilities are under increasing pressure to meet regulatory targets for both environment (2020) and cost effective energy supply. Based on the continued focus on environmental awareness, increased regulations, cost restraints, effectiveness in managing key assets it is important to review the options available to asset managers in the electricity supply industry. A key factor in recent years has been transformer life extension and the various options to effectively manage insulating oil in a responsible manner. Recycling transformer oil is a well-established trusted and proven method to meet all these objectives. Electrical Oil Services and her predecessor companies have been at the forefront of insulating oil supply, reclamation and on-site treatment for over 60 years. Drawing on this long history of close involvement with the UK electricity supply industry this presentation seeks to review the reclamation of insulating oil at EOS’ facilities in the UK and consider the latest in-situ oil regeneration techniques for “deep cleaning” insulation systems to extending the potential life of transformers as well as future options to reclaim used transformer oil in-situ at customer premises.

2. TRANSFORMER OIL RECLAMATION- UK Electrical Oil Services Ltd (EOS) is the UK's leading supplier of electrical insulating oils, otherwise known as

transformer oils, and associated services to the electricity supply industry, the electrical engineering industry,

and energy-intensive, high voltage, industrial electricity users. The company specialises in the reclamation of

used insulating oils from transformers, switchgear and other oil-filled electrical plant to BS148 condition.

Additional services such as on-site transformer oil reconditioning (purifying) plants known as Mobile

Processing Units (MPUs), in-situ Mobile Regeneration Units (MRU) operate from Stanlow.

The current site was part of the original Lobitus Refinery, Ellesmere Port (Burmah Castrol) which opened in

1934. Refining Operations ceased in 1981.Burmah Castrol set up a storage, reclamation and distribution of

transformer oils business in October 1984 with the key asset being the current reclamation plant. Separately,

Carless operated a similar transformer oils operation in Longport, Stoke. EOS was established on 1st November

1999; formed as a 50:50 joint venture between the electrical oils businesses of Carless Refining & Marketing

Ltd and Castrol UK Ltd. The aim was to create an independent, specialised, stand-alone business to

concentrate on this highly specific niche market of electrical oils and associated services. As a result of this JV,

the Longport site was closed and all operations moved to the Stanlow.

It is the UK's only dedicated transformer oil reclamation plant and is well located to serve the whole of the UK.

This is also the central storage point for the distribution of reclaimed and unused mineral insulating oils. The

site is approximately 12ha or 12,000m² in size and has 60 tanks ranging in size from 45m³ to 2,700m³ with

15,000mt capacity. The number of tanks facilitates the storage and processing of all used transformer oil (UTO)

collected, processed, reclaimed in the 20,000mt/annum capacity plant and final product storage to meet

demand. Environmental Permit number ZP3538MQ issued by the Environmental Agency (EA) gives the

company authorisation to operate a “Transformer Oil Regeneration Plant” installation on the site.

3. WHAT IS RECLAMATION AND RECLAIMED TRANSFORMER OIL

Reclamation [1] is defined as the restoration of oil to a useful state by the removal of contaminants and products of degradation such as polar, acidic, or colloidal materials from used electrical insulating liquids by chemical or adsorbent means. Adsorption is a process in which one substance attracts and holds the other substance tenaciously to its surface area. Most of the contaminants in oil, including water, are polar in nature and are therefore easily adsorbed. Several types of materials are readily available as adsorbents, such as Fuller’s Earth, attapulgite, activated alumina, and molecular sieves. Reclaiming typically includes treatment with clay such as Fuller’s earth or other adsorbents such as alumina or bauxite. Activated bauxite consists principally of hydrated aluminum oxide and is activated by thermal treatment alone. It is then a hard, durable, thermally resistant adsorbent and can be regenerated and reused longer than clays. The activated bauxite is available in bulk in various mesh sizes and is the preferred medium used for percolation of mineral oils at our Stanlow site. Reclamation [2] can also be defined as “any method or process which results in a beneficial change in the oil composition” (restoration of transformer oil that has deteriorated through oxidation) and reclaiming as “removal of acidic and colloidal contaminants and products of oxidation by chemical and adsorbent means. Reclamation and/or reclaiming should not be confused with re-refining which the IEEE[1] defines as “the use of primary refining processes on used electrical insulating liquids to produce liquids that are suitable for further use as electrical insulating liquids. This is a much more intensive technique than reclamation such as hydrogenation and as such, falls outside the scope of reclamation. BS148: 2009[3] defines reclaimed oil as “mineral insulating oil used in electrical equipment which has been subjected to chemical and/or physical processing to eliminate soluble and insoluble contaminants”. The BS 149:2009 Standard further states that “Reclaimed mineral insulating oil is produced by the processing, to a greater or lesser extent, of service degraded used mineral insulating oil. Such oil will have been originally supplied in compliance with either BS 148:1998 (or earlier editions) or BS EN 60296. Due to the variability of service conditions and the changes in original specification since the first edition of BS 148 in 1923, reclaimers may reserve the right to reject used oil if it is considered unsuitable as a feedstock to produce reclaimed oil in accordance with this specification. This British Standard specifies requirements for reclaimed oxidation inhibited and uninhibited mineral insulating oils, as delivered, for use in transformers, switchgear and similar electrical equipment in which oil is required as an insulant or for heat transfer. The UK market for reclaimed insulating oils is dominated by the demand for uninhibited reclaimed oil accounting for 98% of the requirement. Table 1 below is a summary of the general properties of the uninhibited reclaimed oil supplied in the region.

Table 1 General Properties of Reclaimed Insulating Oil

PROPERTY UNIT TEST

METHOD

SPECIFICATION

Min M

ax 1. PHYSICAL

Appearance IEC 296 Clear, no sediment

Viscosity @ -15ºC cSt ISO 3675 800

Viscosity @ 40ºC cSt ISO 3675 13

Closed Flash Point ºC EN 22719 135

Pour Point ºC BS 2000.15 -30

Density @ 20ºC Kg/dm3

ISO 12185 0.89

5 2. CHEMICAL

Neutralisation value Mg

KOH/g BS EN

6021-1

0.03

Corrosive Sulphur BS EN

62535

Non

corrosive

Polycyclic Aromatics

mass

% BS2000

Part 346

3

PCB content mg/kg BS EN

61619

10

Water cont. Bulk

Drums

mg/kg BS EN

60814

20

30

Oxidation stability at

120ºC 164h

Acidity after

Oxidation Sludge

Value

mgKOH/g wt %

BS EN

61125 C

1.2

0.8

3. ELECTRICAL

Dielectric Dissipation

Factor

@ 90ºC

BS EN

60247

0.005

Breakdown Voltage kV BS EN

60156

30

If the current BS148:2009 Standard is compared with the current IEC 60296:2012, the following variances are noted:

Slight difference in viscosity

Pour point

Acidity or neutralization value

DBDS(not specified in BS 148)

PCB content and

Total Furans

4. WHY THE VARIANCE-THE HISTORY OF THE FEEDSTOCK In order to understand the variances between reclaimed transformer oils and the new-generation of unused insulating oils, it has to be considered how the feedstock, that is the quality of the transformer oils produced, sold and used in the electrical industries over the past 30-40 years has developed and the industry it emanated from.

4.1 Historic development of electricity in the UK Godalming, 50km southwest of London was the first town in 1881 in the world to boast an electricity supply generating enough surplus to allow sale of electricity to the public [4] By 1921, there were over 480 authorized suppliers of electricity in England and Wales, who were generating and supplying electricity at a variety of voltages and frequencies. The Electricity (Supply) Act 1926 created a central authority to promote a national transmission system. This system, having a voltage of 132KV, was largely completed by the mid-1930s. The Electricity Act 1947 brought the distribution and supply activities of 505 separate organisations in England and Wales under state control and integrated them into 12 regional Area Boards. Under the same Act, the generating assets and liabilities of a number of companies in England and Wales were also transferred into a single state-controlled body. The Electricity Act 1957 established two new statutory bodies, the Central Electricity Generating Board (CEGB) and the Electricity Council. Under this legislation, the structure of the nationalised electricity supply industry in England and Wales (ESI) had the following features:-

The CEGB produced the vast majority of the electricity generated in England and Wales

The CEGB owned and operated the transmission system and its share of the interconnections with France and Scotland

The 12 Area Boards purchased electricity, almost all of it from the CEGB, and distributed and sold it to customers within their designated areas

The Electricity Council exercised a co-ordinating role for the ESI, providing services in areas of common interest, for example national pay bargaining and certain treasury activities.

In February 1988, HM Government published its proposals for the restructuring and privatisation of the ESI. The Electricity Act 1989 received Royal Assent in July 1989 and the new structure was introduced on 31 March 1990. The CEGB’s assets were transferred to four successor companies:-

The fossil-fuelled power stations were divided between National Power and PowerGen.

The nuclear power stations were transferred to Nuclear Electric.

The national grid, together with two pumped storage power stations were transferred to The National Grid Company.

In addition, the businesses of the 12 Area Boards were transferred to the 12 Regional Electricity Companies (RECs), serving essentially the same regional areas of England and Wales as previously. Shares in the RECs were sold to the public at the end of 1990. In 1991, HM Government partially privatised the ESI, creating National Power. In March 1995, HM Government sold its remaining 40% holding in National Power whilst retaining a special share, which it redeemed in August 2000. In March 2001, the means of trading electricity changed with the introduction in England and Wales of the New Electricity Trading Arrangements (NETA), replacing the Electricity Pool of England and Wales. These arrangements were based on bi-lateral trading between generators, suppliers, traders and customers. They were designed to be more efficient and provide greater choice for market participants, whilst maintaining the operation of a secure and reliable electricity system. Up to March 2005 the electricity industries of Scotland, Northern Ireland and England and Wales operated independently although interconnectors joined all three grid systems together. From April 2005 under the British Electricity Trading and Transmission Arrangements (BETTA), introduced in the Energy Act 2004, the electricity systems of England and Wales and Scotland have been integrated.

4.2. Developments during the 90s

Throughout the 1990’s[5] the UK witnessed a “dash for gas” where previously “rare” natural gas was now allowed to be used as an alternative to coal and oil in conventional power stations. Gas fired power stations sprang up all over the UK with, at the time, a stated expected life span of 15 years. With such a short term investment the majority of the generator transformers specified for these new gas stations were “built to a cost”. In addition these new breed of CCGT power stations were, in the main designed to operate under base load (continuous running) as gas prices were cheap and viewed as plentiful. And so, over 25 years later we witness transformers that were designed to last 15 years, failing, or at the very least showing a degree of insulation wear and tear normally associated with generator transformers twice their age. This degree of insulation degradation is likely due in part to the original design but also, and possibly more significantly, a change in the duty of these transformers – no longer base load operation but on and off load two or three times a day or with long periods of inactivity. Many of these generator transformers, specified for base load operation, were supplied without any forced cooling, relying on the load building up and running at “base load”, steady state for days or weeks at a time. This gives the transformer’s natural cooling sufficient time to “get going” and establish an efficient cooling pattern. Subject the same transformer to a two-shifting regime however and owners have found that by the time the transformer’s natural cooling pattern has been fully established it’s time to switch off the transformer, the result is insulation that for frequent periods has seen operating temperatures without any real cooling effect. Paper overheating, embrittlement and failure can result, with all reflected in the condition of the in-service oil.

4.3. Impact on the Utilities The historical picture painted above largely focuses on the generation sector of the UK market, with the dash for gas, the emerging dominance of the procurement specialist, fewer (and cheaper) construction materials and, it has to be said, a loss of experience and expertise from the industry combined with a lack of investment and training in young engineers who wish to remain at the operational end of our business and not fast tracked into senior management as is often the case. The emphasis is very much on life extension of existing assets over and above outright replacement. When it comes to power transformers with system voltages between 33kV and 132kV, DNOs(Distribution Network Operators) have sought to arrive at a target population that are suitable candidates for investment for life extension – example criteria would be:

The percentage life remaining of the paper insulation (based on furan analysis over time)

Total Acid Number of the oil

Any history of faults

DGA history

Overall physical condition

Availability of spares Many of the transformers identified as candidates for life extension investment are well over 40 years old, they were, however built to exacting BS171 and BEBST2 standards and, just as importantly, most have operated in parallel with a sister transformer with each transformer taking only half the design load. Paper insulation tensile strength as measured through furan analysis remains good with at least “half-life” remaining. With pressure to make generator transformers last longer than their 15-20 years expected life, older conventional and nuclear stations still needed to “keep the lights on” whilst alternatives can be developed and the pressure on the DNOs from OFGEM to extend the life of existing transformers, there is a growing focus on transformer asset management focusing on the insulation system. A transformer’s insulation system ultimately defines the life of the transformer if it is not taken out of service for another reason.

4.4. The UK Electricity Supply Industry Today

An understanding of the current UK electricity supply industry is required as it is the main driver of developments influencing the management of key assets including insulating oil, and therefore the feedstock for reclamation. The creation, maintenance and operation of electricity networks are a matter for network companies, overseen by an independent regulator, the Office of the Gas and Electricity Markets (OFGEM). In the UK, electricity is generated in a number of different ways. The different types of energy and the amount of electricity they create are listed below. Fossil fuels: According to the Energy UK website[6] most of the UK’s electricity is produced by burning fossil fuels, mainly natural gas (30% in 2015) and coal (23%). A very small amount is produced from oil (under 1%). The volume of electricity generated by coal and gas-fired power stations changes each year, with some switching between the two depending on fuel prices. Nuclear: 21% of our electricity comes from nuclear reactors, in which uranium atoms are split up to produce heat using a process known as fission. The UK’s nuclear power stations will close gradually over the next decade or so, with all but one expected to stop running by 2025. Several companies have plans to build a new generation of reactors, the first of which could be running by 2018. Renewable energy: Renewable technologies use natural energy to make electricity. Fuel sources include wind, wave, marine, hydro, biomass and solar. It made up 25% of electricity generated in 2015 - this will rise as the UK aims to meet its EU target of generating 30% of its electricity from renewable sources by 2020. Imports: The UK electricity network is connected to systems in France, the Netherlands and Ireland through cables called interconnectors. The UK uses these to import or export electricity when it is most economical. In 2015, the UK was a net importer from France and the Netherlands with net imports of 13.8 TWh and 8.0 TWh respectively which accounted for 5.8 per cent of electricity supplied in 2015. Total net exports to Ireland amounted to 0.9 TWh. Distribution is managed by the six UK Distribution Network Operators (DNOs) and their 14 separately regulated areas are subject to price control and regulation through OFGEM. OFGEM regulate the electricity markets on a 5 – 8 year cycle. For the period 1st April 2015 to 31st March 2023 RIIO-ED1[7] dictates the revenue available for investment by the DNOs. RIIO (Revenue=Incentives+ Innovation + Outputs),is OFGEM’s framework for setting price controls for network companies. Over the next decade these companies face an unprecedented challenge of securing significant investment to maintain a reliable and secure network, and dealing with the changes in demand and generation that will occur in a low carbon future. As the regulator, OFGEM must ensure that supply is delivered at a fair price for consumers. RIIO is a performance based model for setting the network companies’ price controls. RIIO is designed to encourage network companies to:

• Put stakeholders at the heart of their decision-making process • Invest efficiently to ensure continued safe and reliable services • Innovate to reduce network costs for current and future consumers • Play a full role in delivering a low carbon economy and wider environmental objectives.

Electricity Market Reform Electricity Market Reform (known as EMR) is the Government’s recent programme to respond to the trilemma facing the UK: 1. Decarbonising electricity supply 2. Security of Supply 3. Minimising the cost of energy to consumers

EMR has been legislated for via the Energy Act 2013 and will see the introduction of two new reforms to the energy market, the Contracts for Difference (CfD) and Capacity Market. Explanations of these are provided below: Contracts for Difference (CfDs) CfDs support new investment in all forms of low-carbon generation (renewables, nuclear, CCS) and have been designed to provide efficient and cost-effective price stabilisation for new generation, by reducing exposure to the volatile wholesale electricity price. Low carbon generation projects will apply for a CfD and depending on whether the technology is 'established’ or 'less established’, the project may have to compete in an auction in order to receive a contract. CfDs will require generators to sell energy into the market as usual but, to reduce exposure to changing electricity prices, CFDs provide a variable top-up from the market price to a pre-agreed 'strike price’. At times where the market price exceeds the strike price the generator is required to pay back the difference thus protecting consumers from over-payment. The CfD will be implemented through a bilateral contract between the Generator and the Low Carbon Contracts Company Ltd (LCCC).The payments to be made to generators will be calculated and paid out by the LCCC. The cost of CfDs will be met by consumers via the supplier obligation, a levy on electricity suppliers. Capacity Market The Capacity Market will enhance the security of our electricity supply by ensuring that sufficient reliable capacity is in place to meet demand. In other words, it is an insurance policy to keep the lights on. The Capacity Market works by offering the opportunity to all capacity providers (new and existing power stations, electricity storage and capacity provided by demand side response) of a steady, predictable revenue stream on which they can base their future investments. The cost of the Capacity Market will be met by consumers via the supplier levy on electricity suppliers. This will be minimised due to the competitive nature of the auction process which will ensure the lowest cost provision of capacity to meet the level of security of supply determined by the Secretary of State. In return for this revenue (capacity payments) providers must deliver energy when needed to keep the lights on, or face penalties. The drivers in the ESI can be summarized as follow: Economic drivers

Deregulation and competition policy aimed at ensuring the lowest possible costs for all consumers through a system of price controls

Diversification of energy and fuel sources

The shorter construction times, lower capital costs and quicker payback periods of smaller units

Location of generating plant nearer to demand, thus reducing transmission charges. Technological drivers

Improved technological performance of small-scale generating plant and control technologies. Environmental drivers

Reduction in environmental impact of electricity generation (including acid gases, waste management and carbon dioxide, CO2)

Energy efficiency (although this is also an economic and technological driver)

Increased difficulty – planning, public concerns, in locating large generating units.

Duty of care in terms of waste management and hierarchy and

Standards such as ISO 14001 Duty in relation to the waste hierarchy [8] The Waste (England and Wales) Regulations 2011 No. 988 PART 5 Regulation 12A states that 1. Any establishment or undertaking which imports, produces, collects, transports, recovers or disposes of waste, or which as a dealer or broker has control of waste must, on the transfer of waste, take all such measures available to it as are reasonable in the circumstances to apply the following waste hierarchy as a priority order— (a) Prevention; (b) Preparing for re-use;

(c) Recycling; (d) Other recovery (for example energy recovery); (e) Disposal. 2. But an establishment or undertaking may depart from the priority order in paragraph (1) so as to achieve the best overall environmental outcome where this is justified by life-cycle thinking on the overall impacts of the generation and management of the waste. 3. When considering the overall impacts mentioned in paragraph (2), the following considerations must be taken into account— (a) The general environmental protection principles of precaution and sustainability; (b) Technical feasibility and economic viability; (c) Protection of resources; (d) The overall environmental, human health, economic and social impacts. ISO 14001 ENVIRONMENTAL ISO 14000/14001 is the standard generally adopted in the UK by organisations wanting to ‘prove’ their green credentials. The standard is structured in a similar manner to ISO 9000/9001, and includes subjects such as document control, internal auditing, management review etc., along with those specific to the environment. These include: Legislation: A company must recognise environmental legislation; there will be many items of environmental legislation applicable to every organisation, such as: The Environmental Protection Act, The Environmental Protection (Duty of Care) Regulations, Waste (England & Wales) Regulations 2011, as described above and The Regulatory Reform Fire Safety Order. A Legislative Register needs to list and cross-reference the legislation and be kept up to date. Compliance: You must conduct compliance audits to ensure that your organisation is compliant with applicable legislation. The above 2 items are specific requirements of ISO 14001, but it’s a matter of fact that all organisations need to comply with legislation. Impacts Register: You need to recognise Environmental Aspects (things you do with a relationship with the environment such as: waste disposal, fumes, use of resources, use of chemicals, transport/travel) and determine ‘failure modes’ (e.g. unnecessary use of electricity/fuel, incorrect waste disposal/segregation etc.) along with the resultant impact upon the environment (usually via a standard risk assessment technique.) Duty of Care: Every organisation produces waste, and these waste streams must be recognised and reduced or eliminated if possible/practical. It’s a legal requirement that at least one of the waste streams must be segregated for re-use/recycling (e.g. using waste office paper for ‘note pads’ etc. Waste Transfer or Consignment Notes (Hazardous Waste) must be raised to cover all instances of waste being transferred to another organisation and kept as records. It is not acceptable to mix different types of hazardous waste or to mix with non-hazardous waste, and all waste must be correctly disposed of (e.g. do not pour waste paint/oil etc. to sink/drain without written Consent). Recent legislation requires that waste streams must be analysed against the ‘Waste Hierarchy Triangle’ with the intention of moving away from landfill and progressively towards ‘Prevention by Design’. As can be seen from the market description, it is a complex web of policies and regulations within which the electricity supply industry must operate. The asset manager or site engineer needs to make the decision regarding action to be taken on the key assets including critical transformers, tap changers and switchgear maintenance following assessment of the condition of the equipment. This decision is generally based on the policies of the company which would incorporate all the regulations, legislation and laws applicable as well as the condition assessment of the equipment. Guidance regarding the condition assessment is generally based on IEC 60422[9].

5. INSULATING OIL- CONDITION ASSESSMENT IEC 60422[9] states that the reliable performance of mineral insulating oil in an insulation system depends upon certain basic oil characteristics that can affect the overall performance of the electrical equipment. In order to accomplish its multiple roles of dielectric, coolant and arc-quencher, the oil needs to possess certain properties, in

particular 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 and resistance to oxidation to maximize service life. In service, mineral oil degrades due to the conditions of use. In many applications, insulating oil is in contact with air and is therefore subject to oxidation. Elevated temperatures accelerate degradation. The presence of metals, organo-metallic compounds or both may act as a catalyst for oxidation. Changes in colour, the formation of acidic compounds and, at an advanced stage of oxidation, precipitation of sludge may occur. Dielectric and, in extreme cases, thermal properties may be impaired. IEC 60422[10] suggests limits that can be considered when evaluating the test results during the evaluation of oil in service which are summarized in table 2

Table 2. Classification of oil-in-service

Property Voltage (kV)

Good Fair Poor

Acidity 400/275 <0.1 0.1 – 0.15 >0.15

(mgKOH/g) 132 <0.1 0.1 – 0.2 >0.2

Water (ppm 20ºC)

400/275 <5 5 – 10 >10

132 <5 5 – 15 >15

DDF 400/275 <0.1 0.1 – 0.2 >0.2

132 <0.1 0.1 – 0.5 >0.5

IFT (mM/m) All >28 22 – 28 <22

From insulating oil perspective, in the 1941 edition of the J&P Transformer book [11] the maximum permitted Acid Value for Class A or Class B mineral insulating oil supplied into UK (built) transformers was 0.2mgKOH/g and reflected the limits set out in BS148:1933. Compare this with the limit given in the current version of IEC 60296:2012 of just 0.01 mgKOH/g [12] and it can be viewed how our attitude to transformer oil management has changed in the intervening years. With pressure to make generator transformers last longer than their 15-20 years expected life, older conventional and nuclear stations still needed to “keep the lights on” whilst alternatives can be developed and the pressure on the DNOs from OFGEM to extend the life of existing transformers, there is a growing focus on transformer asset management focusing on the insulation system[13]. Whist there is no doubt that modern mineral insulating oils are carefully refined to ensure top quality and stable performance under exacting conditions it remains a fact that unsuitable specification, poor transformer design, insufficient cooling, poor construction can and do all lead to degradation of insulating systems (oil and paper) and as already discussed it is not uncommon to find relatively young transformers containing highly oxidised insulating oil and low paper strength for one or all of the reasons listed. Mineral insulating oil is supplied as either uninhibited or inhibited, the latter having artificial inhibitors added to the oil in the refinery to give the oil extended resistance to oxidation due to high operating temperatures and exposure to oxygen in air. Inhibitors can and are often added to in-service transformers, particularly following on-site regeneration processes where the oil is already partly aged. During a transformer’s service life heavy acid sludge formation is no longer as common as it was in the 1930s when “new oil” could and was supplied at starting acidities of 0.2mgKOH/g instead of 0.01mgKOH/g (max)[14] specified in today’s standards.

Permanent damage to paper insulation is considered to begin at acid values (TAN) of around 0.08 – 0.1 mgKOH/g with modern transformer asset management practice (based on BSEN 60422:2013) recommending action thereafter [15] depending on the transformers importance to the user. Note there is not always a straightforward correlation between transformer operating voltage and importance to the user, a simple 1MVA 11kV transformer containing 1,200litres of insulating oil could be vital for the production paper in a mill for example and therefore carry a similar importance as a 400kV generator transformer to its’ owners. Figure 1 Figure 2 Neutralisation value versus IFT Curve Acidity over time curve

Figures 1 and 2 are useful practical guides to oil and paper ageing and when to intervene, in this case regenerate the insulating oil in such a manner as to “deep clean” the solid, paper insulation. Both graphs show action points of 0.1mgKOH/g with Figure 1 adding Interfacial Tension as an additional metric. Figure 2 is intended as a graphical representation showing how insulating oil behaves over the years with point A representing the time at which the oils “natural” inhibitors have depleted to such an extent that they can no longer resist the process of oxidation. Point B indicates oil regeneration returning the oil to “as new” but with the addition of an artificial inhibitor to restore the oils oxidation stability.

6. RECLAMATION AT A STATIC PLANT-STANLOW MANUFACTURING CENTRE

Once the decision has been made to replace or reclaim the in-service insulating oil, the UTO(Used Transformer Oil) is collected and transferred to Stanlow for reclamation using Waste Transfer or Consignment Notes (Hazardous Waste) which is raised to cover all instances of the waste being transferred and kept as records. In the UK we have been operating a business model referred to as the “Closed-Loop” model which is based on the principle of collecting all UTO from key customers, reclaim it at the Stanlow works and delivering RTO(Reclaimed Transformer Oil) back at an agreed price or “conversion cost”. The system therefore allows for the management of the UTO of the customers and its reclamation back to a usable product at an agreed price and standard which is the BS148:2009 currently. The UTO is collected in containers ranging from 25lt or 210lt drums, 1,000lt IBC’s or in bulk from 3,000lt to 30,000lt tankers. In most cases, in order to reduce the carbon footprint the RTO to BS148:2009 is delivered when UTO is collected in packaging as agreed with the customer. It is estimated that approximately 18,000mt of UTO was generated in the UK in 2014 of which more than 70% was collected by EOS for reclamation. More than 30,000 drums or 6,000mt of the UTO, mostly from switchgear, was collected in drums and transported to the Stanlow site which necessitate an efficient and well-managed logistic and transport infrastructure. A similar volume of drums of RTO were delivered in most cases.

Once collected the UTO is delivered to Stanlow and a rigorous quality assurance system(See Appendix 1) is undertaken to assure that the material collected is UTO and is fit for reclamation. The QC selection for UTO is based on:

Colour: If visibly poor or highly carbonated then we would segregate to waste or base oil feedstock

Metals: Any oil with metals content >10ppm is rejected to other process stream i.e. Base oil

Silicon: Any oil with content >10ppm is rejected to other process stream i.e. Base oil

PCB: Oil >10ppm PCB is rejected; borderline oil may be used for base oil. Oils above this would be segregated and removed from site to oil treatment facilities or, if >49ppm, to an incinerator.

The main reason for the segregation is to keep a good quality UTO pool and prevent damage to the bauxite in the columns. The volume of the UTO pool maintained at Stanlow is 2,500mt to obtain a uniform feedstock and produce a consistent quality product for use by the customer base. In the graphs below, some of the key characteristics of the UTO feedstock including acidity, DBDS and Sulphur content over the past 5 years is shown and reflects interesting developments during the period. The acidity reflected in Graph 3 ranges from 0.03-0.09 mg KOH/g averaging around 0.06 mg KOH/g which indicates a very low acidity across the UTO intake. This can be explained in that the bulk of the material collected in drums is from our DNO customers returning switchgear oil for reclamation. In addition, not much UTO is returned due to end of life as a result of oxidation or being scrapped but in most cases it is more likely due to transformers being replaced or failing at an earlier stage of their life, rather than that of the oil. In recent years we have also accepted large volumes of UTO as a result of closure of the coal-fired Longannet Power Station in Scotland in March 2016 due to a mixture of old-age, rising transmission costs and higher taxes on carbon. This resulted in approximately a 1,000mt of UTO or acceptable quality in-service oil being sent to EOS for reclamation. With seven nuclear plants to be closed by 2023 in the UK we expect the need for reclamation of acceptable quality UTO to continue. Graph 3 Acidity of the UTO feedstock from 2011-2016

Various research papers have proven the link between the presence of dibenzyl disulphide( DBDS) and the corrosive sulphur phenomena which surfaced in 2004. Our UTO pool was first infiltrated by DBDS in 2013 but due to the size and nature of the pool was restricted to between 8-22 mg/kg as can be viewed in Graph 4. Graph 4 DBDS Content in the feedstock from 2013-2016

Not all sulphur compounds are bad in transformer oils. Some, such as thiophenes and some disulphides, are not only stable, but actually recognised by uninhibited proponents as having good natural antioxidant properties. These may also act as metal passivators and deactivators reducing the catalytic effect on oil oxidation in transformers. The good sulphur content in the UTO pool averages 1,300ppm (mg/kg) which maintains a high level of oxidation stability (See Graph 5). Graph 5 Average Sulphur content(ppm) in UTO feedstock from 2011-2016

It is evident that the properties of the UTO pool reflect the quality and refining processes of the insulating oils

supplied into the UK market for example, by the major Unused Mineral Insulating Oil suppliers. With the new

generation of severely hydrogenated insulating oils resulting in low sulphur levels, it will be interesting to see in the

distant future, the impact on sulphur content and associated oxidation stability. This could result in the need for

inhibition.

From a review of the feedstock and the quality of RTO to BS 148:2009 that can be produced, it is evident that the

quality controls and effectiveness of the reclamation process are critical elements to produce a reclaimed transformer

oil to meet customer and environmental demands.

7. NEW DEVELOPMENTS IN RECLAMATION Although the reclamation process has been operational for many years and now well established as an effective method to produce reclaimed transformer oil on a cost effective basis, it remains a major challenge to improve environmental aspects such as PCB content. IEEE[1] defines PCB (polychlorinated biphenyl) as “A group of chemical compounds characterized by two phenyl (6 carbon) rings with two or more chlorine atoms. When mixed with solvents, PCB fluids were generically called askarel fluids. The commercial introduction of PCBs in 1929 represented a major breakthrough in the technology of dielectric fluids. These compounds were found to have outstanding thermal stability, resistance to oxidation, acids, bases and other chemical agents, as well as excellent electrical insulating characteristics making them ideal for applications in electrical capacitors and in high performance electrical transformers. PCBs gained rapid and widespread acceptance in the electrical industry. In 1966, the discovery of PCBs in environmental samples stimulated concerns that they were a potential toxic hazard. By the early 1970's those hazards had become widely recognised, and this prompted major manufacturers of PCBs to restrict sales to applications in closed electrical systems. All production of PCBs was stopped in 1977. Although PCBs have not been used extensively in general purpose distribution transformers, cross contamination in transformer manufacturing and service facilities over many years has resulted in widespread appearance of relatively small amounts of PCBs in many transformers. We rarely see any UTO with a PCB content much above 10ppm and the average level in our UTO output is around 7ppm. There has however been increasing requirements for a PCB free reclaimed oil to meet the environmental requirements of our customers which necessitate the investment in technology to remove PCB from our feedstock. Hydrogenation, activated carbon bed and solvent extraction are three known commercial technologies used to extract PCB from transformer oil. The viability of these technologies was investigated to evaluate the best option to meet EOSL’s and its markets’ specific requirements, for an uninhibited reclaimed transformer oil: Companies such as Sea Marconi have patented processes employing continuous, multi-stage extraction of PCB's using polyethylene glycols (PEG), which have a selective attraction for PCBs. The most recent decontamination and dehalogenation technique (CDP Process patented by Sea Marconi),uses a solid reagent consisting of a high molecular weight PEG mixture to extract the PCB followed by use of an alkyl (bases) and radical promoter for the chemical conversion of organic chlorine in inert salts. This process normally runs typically at the relatively low temperature of 80-100 °C. EOS’s key requirement was a process that removed the PCB from our feedstock, in addition to any furans but would not impact on the sulphur content in order to allow us to continue to offer uninhibited transformer oil. As a result of such an investment and incorporating the CDP process with our current reclamation process based on bauxite, an uninhibited insulating oil can now be produced, that has the same properties and characteristics as that of most unused insulating oils. In Appendix 2 is a table that compares our range of transformer oils meeting BS148:2009 standard, the new high grade transformer oil and the properties of IEC 60296:2012. It now means that reclaimed transformer oil can be produced from recycled UTO to meet most economic, technical and environmental requirements and targets of insulating oil users for in-service or maintenance requirements.

8. IN-SITU OIL REGENERATION

Although in-situ regeneration has been common practice in North America, Canada, South Africa and parts of Western Europe for many years this technique has only recently started to gain momentum in the UK[13]. The reasons for the slow uptake in the UK are varied but in part it is down to the conservative nature of the UK ESI, the reluctance to add artificial inhibitors to oil after regeneration, some problems with the early design of certain

regeneration units leading to post processing presence of corrosive sulphurs and a reluctance to carry out regeneration work on load which is much the better option for optimum efficiency of the process. Several factors have come together to make the use of in-situ regeneration of oil an attractive proposition for today’s transformer owner.

1. A better design of mobile plants, designed to eliminate the mistakes of earlier regen plants 2. Recognition by OFGEM that oil regeneration is a tool that can be used by the UK DNOs to demonstrate

“Health Index” improvement 3. Pressure by industry insurance companies to test for an remove DBDS contamination found in most UK

transformers filled in the 1990s In-situ regeneration, done correctly can be said to “deep clean” the transformer paper insulation. With enough time, sufficient temperature and ideally, the transformer on load for added heat and vibration the final as left values are usually close to “as supplied” or unused oil as per IEC60296:2013 for acid values (0.01mgKOH/g). Depending on how well all the above variables are met the resultant oil values after 6 Months of operation, allowing time for any residual oil in the paper to leach out remain well within BS148:2009 limits for acidity (0.03mgKOH/g). Typical mobile plants operating in the UK will use bauxite or fullers earth as the adsorbant material (dissolved polar contaminants – acids, soluble sludges, DBDS and indeed water are all polar and will “stick” to the bauxite or fullers earth) which is reactivated on-site (usually overnight) after 30-40,000 litres of oil have been passed through) Connection and disconnection to a transformer can be made whilst the transformer is energized and carrying load providing safety distances are not infringed. In practice many DNOs prefer to have a short outage at the beginning and end of the work to facilitate connection and disconnection. Before the oil in a transformer is admitted to the adsorbant material the oil will first be treated using conventional reconditioning equipment heat, vacuum and fine filtration to a) lower water in oil to acceptable levels (usually 10ppm) and b) to get some additional heat into the transformer. Usually after the first 24 hours the oil will be admitted to the adsorbant beds at a flow rate of 5,000 litres per hour for approx. 8 hours. The beds are then isolated and reactivated overnight. Either a second bed can be used thereafter or the transformer oil is continually reconditioned until the morning when a second “pass” through the adsorbant bed can occur. Typical time on site for starting conditions of 0.15mgKOH/g, water 15ppm will be 7-10 days for a 132kV transformer, 4-5 days for a 33kV transformer. A generator transformer containing 80-100,000 litres can take 20 days or more. Here is one case study carried out over the last 5 years by way of example. Example: TATA Steel – ST9

• Installed circa 1952 • 66kV • 10MVA • Oil Quantity 17,000 litres • DP of paper 420 • No history of faults • DGA normal for a transformer of this age • 5 years of history post regeneration

Graph 6 Graph 9

Graph 7

Graph 8

Left alone and neglected for over 50 years the family of 66kV Supply Transformers at TATA Steel’s Port Talbot works stand testimony to the build quality of transformers in the post war years. Despite its age T9 has a paper strength suggesting just under half life and with the future of UK steel production constantly under scrutiny the capital expenditure necessary for a full blown transformer replacement programme could not be justified at the time (2011). An oil change was considered by TATA steel engineers but the benefits of in-situ regeneration as previously discussed, out-weighed any initial concerns. The transformer was treated off-line and early in the season when ambient temperatures were below 10 °C, despite that the oil temperature coming into the Mobile Regeneration Unit (MRU) reached 50°C with WTI just over 70°C as shown in figure 9 above. It should be noted that this process works best if you can obtain working oil temperatures of 70°C plus which is roughly the Aniline point of insulating oil and enables the oil to become a solvent for oxidation products. As ever, time and temperature remain key to a successful regeneration operation, that and the ability to carry out all necessary tests at site, so all concerned can gauge the progress of the work. Water removal After 115 hours of treatment (partly through the regeneration columns and continuously through the normal reconditioning plant water levels gradually reduced from a starting point of 20ppm to 3 ppm, this form of gradual reduction is typical when outer layers of paper insulation are releasing some of their water into the oil as processing temperature increases. Subsequent samples show a steady increase in water in oil - these samples were taken by site staff and when tested in early 2016 by EOS personnel measured water contents show levels similar to the start conditions in 2011. Such a transformer could benefit from the fitting of a molecular sieve to keep removing water at a slow pace, from the paper insulation. Acidity and other polar contaminants Figures 6, 7 and 8 all show marked improvements in the measured parameters acidity, DDF and IFT and all remain in the “good” column of BSEN60422:2013 5 years after treatment.The transformer was dosed with 0.4% inhibitor at the end of the treatment, this is monitored annually and will help slow down further oxidation in the oil. Topping up of inhibitor should be carried out using concentrate solution, pumped into the top or bottom filter valve with the transformer pumps running or when a reconditioning unit is on site And colour When it comes to assessment of an insulating oil from a sample taken on site (you have to use a clear glass bottle of course) much helpful information can be gathered from an oils general appearance “clear, bright and free from visible contamination” is always a good starting point. Cloudy oil could indicate the sample is close to saturation with water at that temperature, visible contamination in the oil could be a sample error or not. These days unused insulating oil has a water white colour, up until the early 1990s all insulating oil used to fill new transformers was of a “pale straw” colour. In reality colour as a determining factor to an oil’s “quality” is misleading at best, typically reclaimed insulating oil which is widely used by the UK DNOs for all maintenance activities up to 132kV, is perfectly acceptable and fit for purpose alternative to unused oil but it is pale straw in colour. This colour difference is due largely to the greater levels of (good) sulphur in the oil compared to unused oil. Remember that an uninhibited oils’ “natural” ability to withstand oxidation depends largely on the presence of sufficient sulphur in the oil.

It is true, however, that as an oil ages its colour will darken, this is usually down to oxidation but the oil will also change colour depending on how it reacts with the transformer internal construction materials. Oil from older transformers can take on a strong shellac smell from the varnish used on transformer steel for example. When it comes to on-site regeneration of oils as discussed in this paper colour change is a helpful indicator of progress but detailed analysis of acidity, IFT and DDF on site, as part of the service offering should always be the primart indicator of how well the work is going

The two samples shown above relate to recent work undertaken at Little Barford power station in Cambridgeshire. Acidity in this 85,000litre generator transformer was just under 0.3mgKOH/g at the beginning of the on-site treatment. After just over 2 weeks of on-load treatment the oil’s final values were close to unused oil and colour had dramatically improved as a result.

In 2016 there is clearly an emphasis on making transformers last longer, that much is clear. With OFGEM recognizing the benefits of in-situ oil regeneration and accrediting it as a practical tool to help improve the transformer health index such on-site treatment is gaining momentum and acceptance in the UK. The “deep cleaning” effect of professionally carried out on-load oil regeneration has clear benefits over conventional oil changes in downtime, cost and effectiveness. Users and service providers need to work closely and engage professionally when it comes to making strategic decisions regarding particular target transformers.

OTHER USES OF IN-SITU REGENERATION With the technology of in-situ regeneration now well established, increased demand for recycling in Europe and pressure from associations such as GEIR. GEIR is the European Waste Oil Re-refining Industry Association. GEIR member companies are active throughout Europe in supporting the collection of used oils and re-refining these back to valuable lubricant base oils and represents 80% of the waste oil re-refining industry in Europe.

Despite the introduction of the waste hierarchy some years ago, its inadequate implementation across the Member States along with competition for energetic recovery (burning) of waste oils continue to be issues that prevent further re-refining of waste oils across Europe. GEIR proposes the following approach: By 2020:

• An EU-wide target of 95% collection of waste oils of the produced and collectable waste oils in each Member State;

• An EU-wide target of reaching at least 60% of re-refined waste oils of the produced and collectable waste oil in all Member States (target 1);

By 2025:

• An EU-wide target of 100% collection of waste oils of the produced and collectable waste oil in each Member State;

• An EU-wide target of 85% of re-refined waste oils of the produced and collectable waste oil in all Member States (target 2);

The proposed recycling targets for waste oils would contribute to supporting the targets set by the European Union on CO2 emission reductions. Waste oil re-refining contributes to CO2 reductions associated with extracting and processing crude oil. With modern re-refining technologies, CO2 emissions (kg of CO2 per ton of base oil) can be reduced by more than 50% as compared to the conventional production of base oil.

This same principle can be employed by the Electricity Supply Industry (ESI) to meet environmental targets on an economic basis with the use of mobile regeneration units to treat UTO in static tanks at customer sites without the need for transport of any hazardous waste material and the associated incremental impact on CO2 emissions.

9. CONCLUSION

Legal and other environmental requirements such as ISO 14001 and Waste Hierarchy obligations now necessitate waste management and the options of recycling or treating insulating oils to extend use. Utilities are under increasing pressure to meet regulatory targets for both environment (2020) and cost effective energy supply. Based on the continued focus on environmental awareness, increased regulations, cost restraints, effectiveness in managing key assets it is important to review the options available to asset managers in the electricity supply industry. A key factor in recent years has been transformer life extension and the various options to effectively manage insulating oil in a responsible manner. Reclaiming or recycling transformer oil is a well-established proven and trusted method to meet all these objectives.

ACKNOWLEDGEMENT The author would like to thank Mr. Andy Bartram and Mr. Keith Burkin for their support and insightful advice regarding history and applications of reclaimed insulating oils during the past 30 years. Mr. Tony O’Regan is also thanked for his contribution through the years of the environmental legislation applicable to the industry.

REFERENCES [1] p4, IEEE Std C57.637™-2015,IEEE Guide for the Reclamation of Mineral Insulating Oil and Criteria for Its Use [2] p522, Myers, S.D., Kelly, J.J., and Parrish, R.H., A Guide to Transformer Maintenance, Transformer Maintenance Division, S.D. Myers, Akron, OH, 1981 [3] p2, BS148:2009, Reclaimed mineral insulating oil for transformers and switchgear –Specification, The British Standards Institute,2009

[4].History of the UK electricity industry (P. Strange, "Early Electricity Supply in Britain: Chesterfield and Godalming", IEEE Proceedings 1979. [5] p1,Bartram,A.M., On-site Options For Transformer Insulation Management, 2016,Doble Life of a Transformer Proceedings [6] www.energy-uk.org.uk. 2016. Electricity Generation. [ONLINE] Available at: http://www.energy-uk.org.uk/. [Accessed 15 October 2016]. [7] OFGEM, RIIO-ED1 electricity distribution price control – overview of the regulatory instructions and guidance 18th June 2015 [8]www.legislation.gov.uk.2011.WasteRegulations[ONLINE]Availableat:http://www.legislation.gov.uk/uksi/2011/988/regulation/12/made[Accessed 15 October 2016] [9] p10, BSEN 60422:2013, Mineral insulating oils in electrical equipment – Supervision and maintenance guidance, The British Standards Institute, 2013 [10] p29, BSEN 60422:2013, Mineral insulating oils in electrical equipment – Supervision and maintenance guidance, The British Standards Institute, 2013 [11] p80-81, Sigant and Lacey, The J&P Transformer Book, 1941, Eighth edition, Johnson & Phillips ltd [12] p17, International Electrotechnical Commission, Fluids for electrotechnical applications – Unused mineral insulating oils for transformers and switchgear, Edition 4.0, 2012-12 [13] p3,Bartram,A.M., On-site Options For Transformer Insulation Management, 2016,Doble Life of a Transformer Proceedings [14] p17 International Electrotechnical Commission, Fluids for electrotechnical applications – Unused mineral insulating oils for transformers and switchgear, Edition 4.0, 2012-12 [15] p29, BSEN 60422:2013, Mineral insulating oils in electrical equipment – Supervision and maintenance guidance, The British Standards Institute, 2013

APPENDICES 1. Reclaiming process flow chart

2. Comparison of various grades of reclaimed transformer oil with unused oil

Thomas J. Larney was born in South Africa. He received his B.Sc. degree from Johannesburg University (RSA) in 1982 and an M.B.A. from the Post Graduate School of Business (RSA) in 1992.He has more than 30 years’ experience in the Oil and Chemical Industries, having worked for Mobil Oil, Sasol Industries, Sentrachem and Nynas in South Africa and the UK. Tom has for the

past 10 years been Managing Director for EOS, a specialist insulating oils- and services supplier in the UK. He represents ORA(Oil Recyclers Association) on BSI Technical Committee GEL/010,the UK national committee for fluids for electrotechnical applications. It is responsible for specifications, standards and codes of practice for materials, test methods and practical procedures relating to mineral insulating oils and other fluids. He is also a member of CIGRE and represents EOS as member at UEIL and GEIR.