IEC TR 62874 Edition 1 0 201 5 05 TECHNICAL REPORT Guidance on the interpretation of carbon dioxide and 2 furfuraldehyde as markers of paper thermal degradation in insulating mineral oil IE C T R 6 2[.]
I E C TR 62 ® Edition 201 5-05 TE C H N I C AL RE P ORT G u i d an ce on th e i n terpretati on of carbon d i oxi d e an d -fu rfu ral d e h yd e as IEC TR 62874:201 5-05(en) m arkers of paper th erm al d eg rad ati on i n i n s u l ati n g m i n e ral oi l T H I S P U B L I C AT I O N I S C O P YRI G H T P RO T E C T E D C o p yri g h t © I E C , G e n e v a , S wi tz e rl a n d All rights reserved Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either IEC or IEC's member National Committee in the country of the requester If you have any questions about I EC copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or your local I EC member National Committee for further information IEC Central Office 3, rue de Varembé CH-1 21 Geneva 20 Switzerland Tel.: +41 22 91 02 1 Fax: +41 22 91 03 00 info@iec.ch www.iec.ch Ab ou t th e I E C The I nternational Electrotechnical Commission (I EC) is the leading global organization that prepares and publishes I nternational Standards for all electrical, electronic and related technologies Ab o u t I E C p u b l i ca ti o n s The technical content of IEC publications is kept under constant review by the IEC Please make sure that you have the latest edition, a corrigenda or an amendment might have been published I E C Catal og u e - webstore i ec ch /catal og u e The stand-alone application for consulting the entire bibliographical information on IEC International Standards, Technical Specifications, Technical Reports and other documents Available for PC, Mac OS, Android Tablets and iPad I E C pu bl i cati on s s earch - www i ec ch /search pu b The advanced search enables to find IEC publications by a variety of criteria (reference number, text, technical committee,…) It also gives information on projects, replaced and withdrawn publications E l ectroped i a - www el ectroped i a org The world's leading online dictionary of electronic and electrical terms containing more than 30 000 terms and definitions in English and French, with equivalent terms in additional languages Also known as the International Electrotechnical Vocabulary (IEV) online I E C G l os sary - s td i ec ch /g l oss ary More than 60 000 electrotechnical terminology entries in English and French extracted from the Terms and Definitions clause of IEC publications issued since 2002 Some entries have been collected from earlier publications of IEC TC 37, 77, 86 and CISPR I E C J u st Pu bl i s h ed - webstore i ec ch /j u stpu bl i sh ed Stay up to date on all new IEC publications Just Published details all new publications released Available online and also once a month by email I E C C u stom er S ervi ce C en tre - webstore i ec ch /csc If you wish to give us your feedback on this publication or need further assistance, please contact the Customer Service Centre: csc@iec.ch I E C TR 62 ® Edition 201 5-05 TE C H N I C AL RE P ORT G u i d an ce on th e i n terpretati on of carbon d i oxi d e an d -fu rfu ral d eh yd e as m arkers of paper th erm al d eg rad ati on i n i n s u l ati n g m i n e ral oi l INTERNATIONAL ELECTROTECHNICAL COMMISSION ICS 29.040.1 ISBN 978-2-8322-2661 -2 Warn i n g ! M ake su re th a t you obtai n ed th i s pu bl i cati on from an au th ori zed d i s tri bu tor ® Registered trademark of the International Electrotechnical Commission –2– I EC TR 62874: 201 © I EC 201 CONTENTS FOREWORD I NTRODUCTI ON Scope Norm ative references Significance General Thermal and mechanical degradation of paper General 2 I m pact of tem perature 3 I m pact of hum idity and oxygen 3 Sym ptoms of paper ageing in insulating oil 3 General 3 Volatile by-products 1 3 Soluble by-products 1 3 I nsoluble by-products 1 Operational parameters influencing paper therm al ageing 1 Role of oil type and condition Fault conditions that may affect thermal ageing Maintenance operations that m ay affect thermal ageing indicators 3 General 3 Effects of oil reconditioning 3 Effects of oil reclamation 3 Effects of oil change Monitoring protocol 4 General 4 Parameters 4 Basic monitoring 4 2 Complem entary m onitoring 4 Recomm ended testing frequencies Typical values of paper ageing sym ptoms 5 General 5 Fam ilies of equipm ent Estim ation of paper thermal degradation and ageing rate 6 General approach 6 Practice Actions Annex A (informative) Typical values tables A General warning A 2-FAL typical values A 2.1 General A 2.2 Famil y: GSU (generation step-up units) A 2.3 Famil y: network transmission units 20 A 2.4 Famil y: large distribution units 20 A 2.5 Famil y: industrial distribution units 20 A 2.6 Famil y: LVDC units 21 I EC TR 62874:201 © I EC 201 –3– A Carbon dioxide typical values 21 A 3.1 General 21 A 3.2 Famil y: GSU (generation step-up units) 21 A 3.3 Famil y: network transmission units 21 A 3.4 Famil y: large distribution units 22 A 3.5 Famil y: industrial distribution units 22 A 3.6 Famil y: LVDC units 22 Bibliograph y 23 Figure – Schematic diagram showing rate of ageing k, depending on different ageing mechanisms Figure – Relationship between mechanical properties of insulating paper and paper degree of pol ym erization (DP) [5] Figure – Exam ple of flow-chart for the estimation of paper degradation conditions Table A – 2-FAL typical values for GSU transformers, filled with uninhibited m ineral oil (based on a population of 860 units) Table A – 2-FAL typical values for GSU transform ers, filled with inhibited m ineral oil (based on a population of 76 units) Table A – 2-FAL typical values for network transmission transform ers, filled with uninhibited m ineral oil (based on a population of 845 units) 20 Table A – 2-FAL typical values for large distribution transform ers, with open breathing conservator, filled with uninhibited mineral oil (based on a population of 07 units) 20 Table A – 2-FAL typical values for large distribution transform ers, with sealed conservator, filled with uninhibited m ineral oil (based on a population of 288 units) 20 Table A – 2-FAL typical values for industrial distribution transformers, filled with uninhibited m ineral oil (based on a population of 885 units) 20 Table A – 2-FAL typical values for LVDC transform ers, filled with uninhibited m ineral oil (based on a population of 360 units) 21 Table A – CO typical values for GSU and excitation transformers, filled with uninhibited mineral oil (based on a population of 098 units) 21 Table A – CO typical values for network transm ission transformers, filled with uninhibited mineral oil (based on a population of 435 units) 21 Table A – CO typical values for large distribution transform ers, filled with uninhibited mineral oil (based on a population of 291 units) 22 Table A 1 – CO typical values for industrial distribution transformers, filled with uninhibited mineral oil (based on a population of 556 units) 22 Table A – CO typical values for LVDC transformers, filled with uninhibited mineral oil (based on a population of 273 units) 22 –4– I EC TR 62874: 201 © I EC 201 INTERNATI ONAL ELECTROTECHNI CAL COMMISSI ON G U I D AN C E O N T H E I N T E RP RE T AT I O N O F C ARB O N D I O XI D E AN D - F U RF U R AL D E H YD E AS M AR KE RS O F P AP E R T H E RM AL D E G R AD AT I O N I N I N S U L AT I N G M I N E R AL O I L FOREWORD ) The I nternati on al Electrotechni cal Comm ission (I EC) is a worl d wid e organization for stan dardization com prisin g all n ation al el ectrotechnical comm ittees (I EC National Comm ittees) The object of I EC is to prom ote internati onal co-operation on all q uestions concerni ng stand ardi zati on in the el ectrical an d electronic fi elds To this en d and in additi on to other acti vities, I EC pu blish es I nternational Stan dards, Techn ical Specificati ons, Technical Reports, Publicl y Avail abl e Specificati ons (PAS) an d Gu ides (h ereafter referred to as “I EC Publication(s)”) Th ei r preparation is entrusted to tech nical comm ittees; any I EC N ational Comm ittee interested in the subj ect dealt with m ay partici pate in this preparatory work I nternational, governm ental an d n on governm ental organ izations l iaising with th e I EC also participate i n this preparation I EC collaborates closel y with the I ntern ational Organi zation for Stand ardization (I SO) in accordance with ditions determ ined by agreem ent between th e two organi zati ons 2) The form al decisions or ag reem ents of I EC on tech nical m atters express, as n early as possible, an i nternati onal consensus of opi nion on the rel evant subjects since each technical com m ittee has representati on from all interested I EC N ational Com m ittees 3) I EC Publications have the form of recom m endations for intern ational use an d are accepted by I EC National Com m ittees in that sense While all reasonable efforts are m ade to ensure that th e technical content of I EC Publications is accu rate, I EC cann ot be h eld responsi ble for th e way in which th ey are used or for an y m isinterpretation by an y en d u ser 4) I n order to prom ote intern ational u niform ity, I EC National Com m ittees und ertake to apply I EC Publ ications transparentl y to the m axim um extent possible i n their national an d regi on al publicati ons Any d ivergence between an y I EC Publication and the correspondi ng national or regi on al publicati on sh all be clearl y in dicated in the latter 5) I EC itself d oes n ot provi de an y attestation of conform ity I n depend ent certificati on bodies provi de conform ity assessm ent services and, in som e areas, access to I EC m arks of conform ity I EC is not responsi ble for any services carri ed out by ind ependent certification bodi es 6) All users shou ld ensure that th ey have the l atest editi on of thi s publicati on 7) No liability shall attach to I EC or its directors, em ployees, servants or ag ents inclu din g in divi dual experts an d m em bers of its tech nical com m ittees and I EC Nati on al Com m ittees for any person al i nju ry, property d am age or other dam age of any nature whatsoever, wheth er di rect or indirect, or for costs (includ i ng leg al fees) and expenses arisi ng out of the publ ication, use of, or relian ce upon, this I EC Publicati on or any other I EC Publications 8) Attention is drawn to th e N orm ative references cited in th is publ ication Use of the referenced publ ications is indispensable for the correct applicati on of this publication 9) Attention is drawn to the possibility that som e of the elem ents of this I EC Publication m ay be the su bject of patent rig hts I EC shall not be held responsibl e for identifyi ng any or all such patent ri ghts The m ain task of I EC technical com mittees is to prepare I nternati onal Standards H owever, a technical committee m ay propose the publication of a Technical Report when it has collected data of a different kind from that which is normally published as an I nternational Standard, for exam ple "state of the art" I EC TR 62874, which is a Technical Report, has been prepared by I EC technical comm ittee 0: Fluids for electrotechnical applications The text of this standard is based on the following docum ents: Enqui ry draft Report on votin g 0/903/DTR 0/91 7A/RVC Full inform ation on the voting for the approval of this Technical Report can be found in the report on voting indicated in the above table I EC TR 62874:201 © I EC 201 –5– This publication has been drafted in accordance with the I SO/I EC Directives, Part The committee has decided that the contents of this publication will rem ain unchanged until the stability date indicated on the I EC website under "http: //webstore.iec.ch" in the data related to the specific publication At this date, the publication will be • • • • reconfirmed, withdrawn, replaced by a revised edition, or am ended A bilingual version of this publication m ay be issued at a later date –6– I EC TR 62874: 201 © I EC 201 INTRODUCTION The cellulosic solid insulation of transform ers and other electrical apparatus is subject to thermal degradation during their operational lifetim e This results in a progressive loss of paper’s m echanical properties, such as tensile strength, which are related to the duration of the technical life of the equipm ent [3,4] During its thermal degradation process (also called “ageing” in this Technical Report), cellulose forms several by-products, some of which m ay be detected by means of insulating oil’s chem ical anal ysis [1 ,2] The concentration and rate of increase of those by-products can be used as a tool to estim ate the progress of paper therm al degradation in transform ers and other electrical apparata in service For this reason, I EC technical comm ittee has prepared this Technical Report for the m onitoring of insulating oil parameters related to cellulose ageing and the interpretation of results, as a guidance to the therm al degradation evaluation of insulating paper This Technical Report is based on the evaluation of cellulose ageing by-products content in insulating oil, and their rate of formation during the life of the oil-immersed electrical equipm ent Statistical reference values reported in Annex A of this Technical Report are based on data collected by TC1 The final report of CI GRE WG D1 01 TF1 [7] was taken as a source of inform ation concerning m echanisms and param eters influencing the formation of furanic com pounds NOTE Methods for the estimation of actual deg ree of pol ym erization (DP) val ues of paper, which are wi del y available in literature, were n ot appli ed within this Techn ical Report This is due to the fact that a num ber of different m odels have been developed an d reported, and they often l ead to different results Moreover, th e appl icability of th ose m odels h as not been sufficientl y proven by com parison with field experience to be incl uded into an I EC stand ard Health and safety This Technical Report does not purport to address all the safety problems associated with its use I t is the responsibility of the user of the Technical Report to establish appropriate health and safety practices and determin e the applicability of regulatory limitations prior to use The m ineral oils which are the subject of this Technical Report should be handled with due regard to personal safety and h ygiene Direct contact with eyes may cause slight irritation I n the case of eye contact, irrigation with copious quantities of clean running water should be carried out and m edical advice sought Some of the tests specified in this Technical Report involve the use of processes that could lead to a hazardous situation Attention is drawn to the relevant standard for guidance Environment This Technical Report involves mineral oils, chem icals and used sam ple containers The disposal of these item s should be carried out in accordance with current national legislation with regard to the im pact on the environment Every precaution should be taken to prevent the release into the environment of mineral oil _ Figu res in squ are brackets refer to the Bibliograph y I EC TR 62874:201 © I EC 201 –7– G U I D AN C E O N T H E I N T E RP RE T AT I O N O F C ARB O N D I O XI D E AN D - F U RF U R AL D E H YD E AS M AR KE RS O F P AP E R T H E RM AL D E G R AD AT I O N I N I N S U L AT I N G M I N E R AL O I L S cop e I EC TR 62874, which is a Technical Report provides guidance for the estim ation of consum ed thermal life of transformers' cellulosic insulators, through the anal ysis of som e com pound dissolved in the insulating mineral oil A com parison between anal ytical results of 2-furfural (2-FAL) and carbon oxides and their correspondent typical values estim ated for different fam ilies of equipment gives inform ation on the estimated thermal degradation of papers The ageing rate of insulating papers can be evaluated, in short time ranges (e.g year), by regularl y monitoring 2-FAL and carbon oxides content in the oil and by comparing them to typical rates of increase A statistical approach for the estimation of paper therm al degradation, and the evaluation of ageing rate is given Typical values for concentrations and rates of increase of the parameters related to paper ageing were extrapolated from a statistical database collected, and are reported in Annex A They m ay be used as a rough guide, but they should not be considered as threshold values This Technical Report is onl y applicable to transformers and reactors filled wi th insulating mineral oils and insulated with Kraft paper The approaches and procedures specified should be taken as a practical guidance to investigate the therm al degradation of cellulosic insulation, and not as an algorithm to calculate the actual degree of polymerization (DP) of papers The paper thermal life evaluation protocol described in this Technical Report applies to mineral oil impregnated transformers and reactors, insulated with Kraft paper An y equipm ent filled with insulating liquids other than m ineral oil (i e esters, silicones) or insulated with solid materials other than Kraft paper (i.e TU P – therm all y upgraded Kraft paper, synthetic pol ym ers) is outside of the scope of this Technical Report This Technical Report is applicable to equipment that has been submitted to a regular monitoring practice during the service, and for which maintenance and fault history is known N o rm a t i ve re fe re n c e s The following docum ents, in whole or in part, are normativel y referenced in this docum ent and are indispensable for its application For dated references, onl y the edition cited applies For undated references, the latest edition of the referenced docum ent (including an y amendments) applies None –8– I EC TR 62874: 201 © I EC 201 S i g n i fi c a n c e G e n e l This Technical Report describes a statistical approach to paper thermal life evaluation This means that all typical values are obtained from populations of transform ers belonging to the sam e famil y for technical characteristics and application (see Annex A) The approach used to collect statistical data, described in , can be applied by utilities or owners having a large population of units, to calculate individual reference values related to a specific famil y of transform ers or reactors This is very important because different population of transformers (i e operating in different clim ates or under different operational conditions) may have different typical values NOTE For an extensi ve survey on furanic com pounds as m arkers for diagnosis of paper insulati on d eg radation, see CI GRE Brochu re 494/201 [7] 3 T h e rm a l an d m e c h a n i c a l d e g d a t i o n of p ap er G e n e l There are main factors: design and m aterials, contam inants in the insulation system and operational conditions, that will determ ine the ageing of a transformer [1 , 2] For the solid insulation – paper and pressboard – it m eans a combination of mechanical and dielectric perform ance, which are interlinked and synergetic For a transformer, in the context of thermal ageing, it is the mechanical strength of the paper that m atters The ageing of paper results in a decreased m echanical strength and is assumed to reduce the ability of the transformer to withstand short circuit stress This, however, has not been statisticall y demonstrated, yet Tensile strength, elongation and folding strength all decay with time, and more quickl y at higher temperatures The m echanical performance of cellulosic insulation is given in term s of tensile index or degree of pol ymerization (DP), which are strongly influenced by ageing The DP value is an average value of chain lengths of the cellulose molecules given as a number of glucose rings in a cellulose chain I t is measured through m easurem ent of the viscosity of a paper solution, according to I EC 60450 [8] It is more convenient to perform DP than tensile index, because of the lim ited am ount of paper accessible for tests; therefore it is widel y used for the evaluation of the cellulosic ageing status There are three main processes of degradation: – h ydrol ysis; – oxidation; – pyrol ysis 2 I m p a c t o f t e m p e t u re Temperature affects the rate of degradation This fact is reflected in I EC 60076-7 [3] and IEEE Std C57.91 [4] transform er loading guides I EC 60076-7 [3] suggests in accordance with Montsinger that the life of a transformer can be described according to Equation (1 ): Life duration = e − p × θ (1 ) – 12 – I EC TR 62874:201 © I EC 201 The high-load of a transform er, impl ying elevated operating temperatures, promotes the paper therm al degradation process, observed with som e types of transform ers that are often overloaded (shunt reactors, H VDC, generator step-up (GSU ) in therm al power plants (TPP), high voltage inter-tie transmission transform ers) The type of cooling, in terms of cooling media (water or air) and type of flow applied (forced or natural convection), affects efficiency of heat rem oval, thus influencing the rate of paper thermal degradation The m ost efficient cooling can be achieved by appl yin g water as coolant in forced oil flow For exam ple, it was observed in m ost cases that the degree of paper degradation with GSU transformers in h ydro power plants (H PP) is lower than with therm al power plant GSU units, having a similar service duration These findings are correlated to different types of cooling (OFWF versus ON AF and OFAF), hours of service and loading history of HPP and TPP units [6] Am ong different transformer sub-types, air-breathing transform ers are subj ected to more intensive paper degradation than sealed ones, due to higher oxygen and moisture content Elevated concentrations of oxygen and water accelerate the paper degradation process Since the paper degradation process is temperature driven, every environm ental and operational condition that may affect the tem perature can also modify the degradation rate of the solid insulation An elevated environmental tem perature or a high loading can thus increase the rate of paper degradation, resulting in a sudden increase of 2-FAL, CO , CO and other by-products 3.5 Role of oil type and condition Oil type m ay affect the ageing rate of paper I nhibited oils show a lower tendency to form acidity, and the oxidation process is slackened; the effect of oxygen in the paper oxidation process is reduced Transform ers im pregnated with inhibited oil m ay show a lower content of 2-FAL if compared with units insulated with an uninhibited oil, even if showing the sam e degree of pol ym erization (DP) of the paper The effect of passivators (triazole derivates) in the ageing of celluloses is still not well defined By definition, metal passivators m ay induce a lower rate of the oil degradation process by deactivating the copper catal yst in oxidation processes, therefore slowing down the paper degradation process, but influence of metal passivators on 2-FAL concentration in the oil may not be straightforward Some laboratory studies have shown that papers impregnated with oils to which a passivator has been added, m ay have a lower tendency to form furanic com pounds; this m ay lead to optimistic estimation of ageing in presence of triazolic passivators The ageing condition of the oil may also affect the partition of furanic compounds between solid and liquid insulation; acidic oils m ay result in an increased 2-FAL concentration in oil, due to its augmented capability to extract polar com pounds from the paper 3.6 Fault conditions that may affect thermal ageing I n transformers where the degradation mechanism may be either thermal or electrical, the rate of paper degradation m ay increase rapidl y as a consequence of significant tem perature rise High energy thermal and electrical faults involving excessive currents circulating through the insulation and large current follow-through lead to extensive destruction and carbonization of paper I n presence of local therm al degradation due to a fault, the estimation of the paper’s consum ed thermal life may becom e very difficult, since the extension of the paper volum e I EC TR 62874:201 © I EC 201 – 13 – involved is unknown, and temperature may have strong variations even over a short tim e I nvestigations on the presence of thermal faults through DGA should always accom pan y therm al life evaluation, to avoid m isleading conclusions High energ y electrical faults (discharges of high energ y) usuall y involve a very sm all volume of paper, so that the contribution to the detected concentration of furanic com pounds is negligible I n case of discharges with paper invol ved, a sharp increase of carbon oxides is observed, rather than an noticeable increase of 2-FAL The formation of cellulose by-product has not been found to be related to partial discharges 3.7 3.7.1 M aintenance operations that may affect thermal ageing indicators General Maintenance operations on the oil m ay affect (partiall y or totally) parameters used as indicators of cellulose therm al ageing (see 3) Their effects should be taken into account during the estimation of the total 2-FAL concentration, and in evaluating the rate of increase of the thermal ageing indicators 3.7.2 Effects of oil reconditioning Oil reconditioning may reduce 2-FAL concentration in oil, depending on the duration/efficiency of the treatm ent Oil reconditioning normall y does not significantl y affect 2-FAL, gas and moisture concentration in cellulose On-line degassing or long-term reconditioning may reduce moisture in paper The equilibrium of 2-FAL distribution between oil and paper is restored in a time depending on temperature, cooling and oil circulation Dissolved gases and water dissolved in oil are mostl y removed by vacuum degassing In the m onths following a reconditioning, the rates of increase of 2-FAL, dissolved gases and m oisture should not be considered as an indicator of increased ageing rate, the equilibrium being forced therm od ynamicall y through the increase of concentration in the oil 3.7.3 Effects of oil reclamation Reclaiming the oil has m ajor effects on the concentration of 2-FAL Furanic com pounds are polar and they are alm ost com pletely rem oved by fuller’s earth and other adsorbing m edia After an oil reclamation the trend of furanic com pounds should be carefull y recorded (with frequent sampling) to monitor the increase of 2-FAL, taking into account new equilibrium conditions NOTE For effects of reclam ation on dissolved gases an d m oisture see 3.7.4 Effects of oil change Oil change has m ajor effects on the concentration of 2-FAL, as well All the by-products dissolved in the oil are rem oved N evertheless, after an oil change a new equilibrium between solid and liquid insulation is dependent on temperature, cooling and oil circulation After an oil replacem ent the trend of furanic com pounds should be carefully recorded (with frequent sampling) to monitor the increase of 2-FAL, taking into account new equilibrium conditions NOTE For effects of oil chan g e on d issolved g ases and m oisture see – 14 – I EC TR 62874:201 © I EC 201 Monitoring protocol 4.1 General A regular monitoring of param eters related to therm al ageing of cellulose is strictl y required for the estim ation of paper ageing condition and its rate of therm al degradation N o evaluation should be done and no action should be taken on the basis of a single determination Evaluation based on a few samples close to the end of the operational lifetime will not lead to reliable conclusions; the approach for the estimation of paper therm al degradation reported in this Technical Report cannot be applied if a regular m onitoring was not perform ed during the life of the equipment 4.2 Parameters 4.2.1 Basic monitoring Param eters for a basic m onitoring are (see 3): – furanic compounds; – DGA (dissolved gas analysis) NOTE The use of DGA as a m onitoring tool is solel y add ressed to the scope of this Technical Report, i e the estim ation of paper ageing dition For the applicati on of DGA as a tool to intercept or reveal faulty ditions of transform ers, refer to I EC 60599 [1 4] 4.2.2 Complementary monitoring Parameters for com plem entary m onitoring are (see 3): – – – – – 4.3 water content in oil; acidity; inhibitor content (for inhibited oils onl y, refer to I EC 60666 [1 3] for the detection method); passivator content (for passivated oils onl y, refer to I EC 60666 for the detection method); particle counting Recommended testing frequencies The following sampling and testing frequencies are recomm ended for paper therm al degradation monitoring, depending on the age of the equipment and the results of previous estimations of paper therm al degradation In case of indications of typical or low paper thermal degradation: – basic m onitoring every to years I n case of indications of high paper therm al degradation or high rates of paper therm al degradation, or in case of suspect of abnormal paper ageing due to high loading, defective or insufficient cooling or severe environm ental conditions: – basic and complementary m onitoring at least twice per year In case of evidence of severe thermal degradation, or if DGA shows presence of thermal faults (T1 -T2): – refer to I EC 60599 for DGA interpretation and sam pling frequency I EC TR 62874:201 © I EC 201 5 5.1 – 15 – Typical values of paper ageing symptoms General Typical values are calculated for 2-FAL and carbon dioxide, for different fam ilies of equipment listed in The sam ple population is divided in age ranges as follows: – – – – units units units units with with with with service service service service age age age age lower or equal to year; higher than year and lower or equal to years; higher than years and lower or equal to 30 years; higher than 30 years For each age range two reference values are calculated: – the lower value corresponds to the value wh ere 90 % of the population falls (90 th percentile) – the higher value corresponds to the value wh ere 98 % of the population falls (98 th percentile) While calculating typical values for a famil y of equipment, it is highly recomm ended to follow the above listed criteria, taking into account also the following recomm endations: – – – – discard values m easured just following an oil reconditioning, reclaiming or replacem ent; discard values measured on units having been out of service for a long period; consider onl y values m easured with units at constant power load (equilibrium conditions); the reliability of laboratories perform ing the anal ysis is of outmost importance While calculating typical rate of increase (RoI ) values for a famil y of equipment, it is highl y recomm ended to follow the above listed criteri a: – consider onl y values sam pled with a reasonable time gap (> months), to reduce the effects of test reproducibility; – RoI should be preferably measured on a set of to values obtained with regular sampling, eventuall y using the m oving average to reduce the effects of statistical fluctuations Famili es of equipment For a better estimation of paper thermal degradation, equipment is classified in families, having different typical values of the param eters related to thermal degradation of paper Fam ilies of equipm ent are: – reactors – power transform ers • GSU (generation step-up units) • network transmission • large distribution (> M VA) – rectifiers • HVDC • LVDC – furnace transformers – industrial/distribution (< MVA) – 16 – I EC TR 62874:201 © I EC 201 Moreover, when a sufficient am ount of data is available, each famil y is divided in sub-fam ilies on the basis of design parameters (conservator breathing m ode) and type of oil (i nhibited or uninhibited) 6.1 Estimation of paper thermal degradation and ageing rate General approach NOTE The procedu re for esti m ation of paper th erm al degradation descri bed in this Tech ni cal Report is based on the statistical evalu ation of a popul ation of transform ers The approach to the estimation of paper therm al degradation proposed here is addressed to suppl y general information on the thermal degradation conditions and (if possible) on the rate of degradation Paper therm al degradation may be evaluated by m eans of com paring the value of parameters related to therm al degradation to the typical values obtained by the population of equipment Transformers and reactors having undergone m ajor repair, oil change and/or reclamation, or having shown sym ptom s of thermal faults should be evaluated very carefull y, for the reasons described in A unique set of threshold values for furanic com pounds or carbon oxides cannot be established, due to the large variation of typical values resulting from different databases Nevertheless, a statistical evaluation m ay be done on a selected population; thus, on the basis of typical values calculated as described in 5: – LOW thermal degradation is associated with values lower than the 90 th percentile of the appropriate famil y of transform er, for the corresponding service age; – TYPI CAL thermal degradation is associated with values between 90 th and 98 th percentile of the appropriate fam il y of transformer, for the corresponding service age; – HI GH therm al degradation is associated with values higher than the 98 th percentile of the appropriate famil y of transform er, for the corresponding service age Units in LOW ageing condition can be assum ed as having a paper therm al degradation lower than the one that should be expected on the base of the actual age of service Units in TYPI CAL ageing condition can be assum ed as having a paper therm al degradation close to the one that should be expected on the basis of the actual age of service Units in HI GH ageing condition can be assum ed as having a paper therm al degradation higher than the one that should be expected on the basis of the actual age of service All reference values described in Annex A were obtained from a databank of units where 90% of the population has a service age of less than 35 years Thus, all considerations relative to the ageing condition and the paper thermal degradation should refer to an average life of transform ers of 30 to 40 years 6.2 Practice Follow the m onitoring protocol described in Clause regularl y Examine the maintenance and fault history of the equipm ent, and give particular attention to events which m ay have influenced the content of cellulose degradation by-products (see to 7) or to fault conditions which may jeopardize the evaluation of paper therm al ageing (see 6) I EC TR 62874:201 © I EC 201 – 17 – Verify to which of the fam ilies defined in (or other fam ilies eventually identified) the unit belongs Establish actual values and rates of increase of 2-FAL and carbon dioxide in the unit, and refer to typical values in order to identify the condition of the unit in terms of ageing condition and/or ageing rate Figure reports a flow-chart of the whole practice procedure Sampling protocol Thermal degradation: low Results Thermal degradation: typical Ageing rate: low Actions: Thermal degradation: high Compare with typical value Deeper investigations Compare with typical rol Ageing rate: high Ageing rate: typical Deeper investigations Increase sampling frequency contact manufacturer IEC Figu re – Example of flow-chart for the estimation of paper degradation conditions NOTE I f 2-FAL eval uation and CO evalu ation produce different results, a conservati ve approach su gg ests considering th e worst cond ition of th e two obtained I n this case, a m ore frequ ent m onitori ng is recomm ended for a better assessm ent EXAMPLE One network transm ission un it filled with uni nhi bited m ineral oil, with years of service, shows the following data: – 2-FAL concentration = 2, m g/kg – CO concentrati on i n oil = 500 μ l /l Tables A , A and A appl y to this example Search i n th e col u m n [1 < Y ≤ 30] wh ere th e actual values fall in comparison with reference values 2-FAL value indicates a TYPI CAL ageing, CO value indicates a LOW ageing The unit should be considered in TYPI CAL ageing condition, with a recommendation to continue a regular m onitoring to confirm this evaluation Actions A transformer or reactor found in H I GH ageing conditions or with a H I GH ageing rate may require an action to rectify the critical factor – 18 – I EC TR 62874:201 © I EC 201 I t is recommended to keep the unit under regular and strict monitoring to confirm the presence of abnormal paper therm al degradation I n case of abnormal paper thermal degradation, refer to the m anufacturer before taking an y decision I EC TR 62874:201 © I EC 201 – 19 – Annex A (informative) Typical values tables A.1 General warning Data reported in Annex A shall not be considered as thresholds or lim its They are given as examples of typical values for some families of equipm ent, and are not exhaustive or com prehensive of all transform er types Users having a sufficient number of units to calculate specific typical values and rates of increase are encouraged to build their own tables of values and to refer to them for evaluation A.2 2-FAL typi cal values A.2.1 General Typical values of 2-FAL concentration (Conc , expressed in mg/kg) and rate of increase (RoI , expressed in m g/kg/y) are listed in the following tables Each table refers to the famil y of equipment and oil type described in the related note NOTE Values reported as N A (not available) were n ot calculated, because th e n um ber of cases in the popul ation was too exi guous A.2.2 Famil y: GSU (generation step-up uni ts) NOTE I n A 2, no d istinction is m ade between u nits with open conservator an d un its with sealed conservator A.2.2.1 Sub-fami ly: GSU i mpregnated with u ninhibited oil Table A.1 – 2-FAL typical values for GSU transformers, fil led with uni nhi bited eral oil (based on a popul ation of 860 u nits) Age → Percentile ↓ Conc RoI Conc RoI Conc RoI Conc RoI 90° < 0, 05 < 0, 01 0, 0, 04 2, 0, 30 3, N A 98° < 0, 05 < 0, 01 ,0 0, 4, 0, 70 6, N A A.2.2.2 30 Y Sub-fami ly: GSU i mpregnated with inhibited oil Table A – 2-FAL typical values for GSU transformers, filled with inhibited mineral oil (based on a population of 76 units) Age → Percentile ↓ Conc RoI Conc RoI Conc RoI Conc RoI 90° N A N A 0, N A 0, 80 0, 25 N A N A 98° N A N A 0, N A ,5 0, 60 N A N A 30 Y – 20 – A.2.3 I EC TR 62874:201 © I EC 201 Fam ily: n etwork transmission units Table A – 2-FAL typi cal values for n etwork transm issi on tran sformers, fil led with uni nhi bited mineral oil (based on a population of 845 u nits) Age → Percentile ↓ A.2.4 A.2.4 30 Y Conc RoI Conc RoI Conc RoI Conc RoI 90° 0, 0, 01 0, 0, 06 ,6 0, 25 2, 0, 98° 0, 0, 02 ,1 0, 3, 0, 80 4, ,1 Famil y: large d istribution units Sub-fami ly: l arge di stri bution u nits with open conservator Table A – 2-FAL typi cal values for large distribution transformers, with open breathing conservator, filled with u ninhi bited mineral oil (based on a popu lation of 07 uni ts) Age → Percentile ↓ Conc RoI Conc RoI Conc RoI Conc RoI 90° < 0, 05 < 0, 01 0, 0, 20 ,5 0, 30 N A N A 98° 0, 0, 03 3, 0, 50 4, 0, 80 N A N A A.2.4.2 30 Y Sub-fami ly: l arge di stri bution u nits with sealed conservator Table A.5 – 2-FAL typical values for large di stri bution transformers, with seal ed conservator, fi ll ed with u ninhibited mineral oi l (based on a popu lation of 288 units) Age → Percentile ↓ Conc RoI Conc RoI Conc RoI Conc RoI 90° < 0, 05 N A 0, 0, 02 ,6 0, 40 N A N A 98° 0, N A 0, 85 0, 04 5, 0, 70 N A N A A.2.5 30 Y Famil y: industrial di stri bution u nits Table A – 2-FAL typi cal values for indu strial distribution transformers, filled with uni nhi bited eral oil (based on a popul ation of 885 u nits) Age → Percentile ↓ Conc 90° 98° 30 Y Conc RoI 0, 30 N A N A ,1 N A N A I EC TR 62874:201 © I EC 201 A.2.6 – 21 – Family: LVDC units Table A.7 – 2-FAL typical values for LVDC transformers, filled with uninhibited mineral oil (based on a population of 360 units) Age → Percentile ↓ Conc RoI Conc RoI Conc RoI Conc RoI 90° N A N A 0, 80 0, 30 ,0 0, 30 N A N A 98° N A N A ,4 0, 80 3, 0, 80 N A N A A.3 A.3.1 30 Y Carbon dioxide typical values General Typical values of carbon dioxide concentration (Conc., expressed in μ l /l ) and rate of increase (RoI , expressed in μ l /l/y) are listed in the following tables Each table refers to the fam il y of equipm ent and oil type described in the related note NOTE Valu es reported as N A (not availabl e) were n ot calculated, because the n um ber of cases in th e populati on was too exig uous Due to lack of data no division of data is described according to type of preservation system (open-breathing vs sealed/nitrogen blanketed) that may affect CO concentration I t is highl y recomm ended to make such division for individual data bank anal ysis NOTE Typical valu es an d typical rates of increase for carbon oxi des that are reported i n I EC 60599 differ from the on es listed in th e foll owi n g tables This is du e to the different approach used in this Technical Report, where typical values are calculated for specific age i ntervals, and are aim ed solel y at the estim ation of paper therm al deg radation For the application of DGA as a tool to intercept or reveal faulty ditions of transform ers, refer to I EC 60599 A.3.2 Family: GSU (generation step-up units) Table A.8 – CO typical values for GSU and excitation transformers, filled with uninhibited mineral oil (based on a population of 098 units) Age → Percentile ↓ Conc RoI Conc RoI Conc RoI Conc RoI 90° 000 N A 000 500 000 500 000 N A 98° 500 N A 000 000 1 000 000 000 N A A.3.3 30 Y Family: network transmission units Table A.9 – CO typical values for network transmission transformers, filled with uninhibited mineral oil (based on a population of 435 units) Age → Percentile ↓ Conc RoI Conc RoI Conc RoI Conc RoI 90° 000 N A 000 N A 000 N A 000 N A 98° 000 N A 000 N A 1 000 N A 000 N A 30 Y – 22 – A.3.4 I EC TR 62874:201 © I EC 201 Family: large distribution units Table A.1 – CO typical values for large distribution transformers, filled with uninhibited mineral oil (based on a population of 291 units) Age → Percentile ↓ Conc RoI Conc RoI Conc RoI Conc RoI 90° 000 N A 000 N A 000 N A 000 N A 98° 500 N A 000 N A 000 N A 000 N A A.3.5 30 Y Family: industrial distribution units Table A.1 – CO typical values for industrial distribution transformers, filled with uninhibited mineral oil (based on a population of 556 units) Age → Percentile ↓ Conc RoI Conc RoI Conc RoI Conc RoI 90° 500 N A 500 N A 500 N A 000 N A 98° 500 N A 500 N A 000 N A 000 N A A.3.6 30 Y Family: LVDC units Table A.1 – CO typical values for LVDC transformers, filled with uninhibited mineral oil (based on a population of 273 units) Age → Percentile ↓ Conc RoI Conc RoI Conc RoI Conc RoI 90° N A N A 000 N A 500 N A N A N A 98° N A N A 500 N A 500 N A N A N A 30 Y I EC TR 62874:201 © I EC 201 – 23 – Bibliography [1 ] CI GRE WG D1 01 0, Brochure 323/2007, Ageing of cellulose in m ineral-oil insulated transformers [2] L Lundgaard, W Hansen, D Linhj ell & T Painter, (2002), “ Ageing of Oil Impregnated paper in power transformers ”, I EEE Trans Pow Del , Vol 9, No , 2004, pp 230-238 [3] I EC 60076-7, Power transformers – Part 7: Loading guide for oil-immersed power [4] I EEE Std C57 91 -1 995 I EEE Guide for loading Mineral-oil-imm ersed Transform ers [5] Lawson, M A Simm ons, P S Gale “Therm al ageing of cellulose paper insulation” I EEE Transactions on Electrical I nsulation, Vol EI -1 2, N o , Feb 977, pp 61 -66 [6] J Lukic, A Bojkovic, V Rajakovic, K Drakic, D.Jovanovic, D.Teslic “Monitoring I nsulating Paper Degradation With H igh Performance Liquid Chrom atograph y Determ ination of Furan Com pounds”, Regional Conference and Exhibition on Electricity Distribution, CI RED, H erceg Novi, Montenegro, October 2004, R-3 , p 72 [7] CI GRE WG D1 01 TF1 3, Brochure 494/201 2, Furanic Compounds for Diagnosis [8] I EC 60450, Measurement of the average viscometric degree of polymerization of new [9] I EC 60567, Oil-filled electrical equipment – Sampling of gases and analysis of free and dissolved gases – Guidance [1 0] I EC 6081 4, Insulating liquids – Oil-impregnated paper and pressboard – Determination [1 ] I EC 60970, Insulating liquids – Methods for counting and sizing particles [1 2] I EC 61 98, Mineral insulating oils – Methods for the determination of 2-furfural and [1 3] I EC 60666, Detection and determination of specified additives in mineral insulating oils [1 4] I EC 60599, Mineral oil-impregnated electrical equipment in service – Guide to the interpretation of dissolved and free gases analysis transformers and aged electrical papers of water by automatic coulometric Karl Fischer titration related compounds _ I N TE RN ATI O N AL E LE CTRO TE CH N I CAL CO M M I S S I O N 3, ru e d e Va re m bé P O B ox CH -1 1 G e n e va S wi tze rl a n d Te l : + 41 F a x: + 22 91 02 1 22 91 03 00 i n fo @i e c ch www i e c ch