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IEC 60076-2 Edition 3.0 2011-02 INTERNATIONAL STANDARD NORME INTERNATIONALE Pow

IEC 60076-2 Edition 3.0 2011-02 INTERNATIONAL STANDARD NORME INTERNATIONALE Power transformers – Part 2: Temperature rise for liquid-immersed transformers Transformateurs de puissance – Partie 2: Echauffement des transformateurs immergés dans le liquide INTERNATIONAL ELECTROTECHNICAL COMMISSION COMMISSION ELECTROTECHNIQUE INTERNATIONALE X ICS 29.180 PRICE CODE CODE PRIX ISBN 978-2-88912-346-9 ® Registered trademark of the International Electrotechnical Commission Marque déposée de la Commission Electrotechnique Internationale ® colour inside This is a preview - click here to buy the full publication – 2 – 60076-2  IEC:2011 CONTENTS FOREWORD ........................................................................................................................... 4 1 Scope ............................................................................................................................... 6 2 Normative references ....................................................................................................... 6 3 Terms and definitions ....................................................................................................... 6 4 Cooling methods .............................................................................................................. 8 4.1 Identification symbols .............................................................................................. 8 4.2 Transformers with alternative cooling methods ........................................................ 9 5 Normal cooling conditions................................................................................................. 9 5.1 Air-cooled transformers ........................................................................................... 9 5.2 Water-cooled transformers .................................................................................... 10 6 Temperature rise limits ................................................................................................... 10 6.1 General ................................................................................................................. 10 6.2 Temperature rise limits at rated power .................................................................. 10 6.3 Modified requirements for special cooling conditions ............................................. 12 6.3.1 General ..................................................................................................... 12 6.3.2 Air-cooled transformers ............................................................................. 12 6.3.3 Water-cooled transformers ........................................................................ 13 6.4 Temperature rise during a specified load cycle ...................................................... 13 7 Temperature rise tests .................................................................................................... 13 7.1 General ................................................................................................................. 13 7.2 Temperature of the cooling media ......................................................................... 13 7.2.1 Ambient temperature ................................................................................. 13 7.2.2 Water temperature ..................................................................................... 14 7.3 Test methods for temperature rise determination ................................................... 14 7.3.1 General ..................................................................................................... 14 7.3.2 Test by short-circuit method for two winding transformers.......................... 14 7.3.3 Test modification for particular transformers .............................................. 15 7.4 Determination of liquid temperatures ..................................................................... 16 7.4.1 Top-liquid temperature .............................................................................. 16 7.4.2 Bottom and average liquid temperatures .................................................... 17 7.5 Determination of top, average and bottom liquid temperature rises ........................ 18 7.6 Determination of average winding temperature ...................................................... 18 7.7 Determination of winding resistance at the instant of shutdown ............................. 19 7.8 Determination of average winding temperature rise at the instant of shutdown ............................................................................................................... 19 7.9 Determination of the average winding to liquid temperature gradient ..................... 19 7.10 Determination of the hot-spot winding temperature rise ......................................... 20 7.10.1 General ..................................................................................................... 20 7.10.2 Determination by calculation ...................................................................... 20 7.10.3 Direct measurement during the temperature rise test ................................. 20 7.11 Uncertainties affecting the results of the temperature rise test............................... 21 7.12 Dissolved gas-in-oil analysis ................................................................................. 21 7.13 Corrections............................................................................................................ 21 Annex A (informative) Hot-spot winding temperature rise determination for OFAF and OFWF cooled transformers based on the top-liquid temperature in tank ................................ 23 Annex B (informative) Methods to estimate the hot-spot winding temperature rises.............. 25 This is a preview - click here to buy the full publication 60076-2  IEC:2011 – 3 – Annex C (informative) Techniques used in temperature rise testing of liquid-immersed transformers ......................................................................................................................... 30 Annex D (informative) Dissolved gases analysis for the detection of local overheating ......... 39 Annex E (informative) Application of optical fibre sensors for winding hot-spot measurements ...................................................................................................................... 43 Bibliography .......................................................................................................................... 47 Figure B.1 – Temperature rise distribution model for ON cooling methods ............................ 26 Figure B.2 – Value of factor Q as a function of rated power and strand height (W) ............... 27 Figure B.3 – Typical liquid flow paths in a disk winding with diverting washers ...................... 28 Figure C.1 – Recommended circuit for transformers with a low resistance winding using two separate direct current sources, one for each winding ........................................... 32 Figure C.2 – Alternative recommended circuit using only one direct current source for both windings........................................................................................................................ 32 Figure C.3 – Average winding temperature variation after shutdown ..................................... 33 Figure C.4 – Extrapolation of the cooling down curve, using the fitting curve ( ) w 0 w t/T Be kt A t − + − = θ .......................................................................................................... 38 Figure E.1 – Optical fibre sensor application for a disk winding of core type transformer ....... 45 Figure E.2 – Optical fibre sensor application for a transposed cable of core type transformer ........................................................................................................................... 45 Figure E.3 – Modality of optical fibre sensor application in the winding spacer of core type transformer ................................................................................................................... 46 Figure E.4 – Optical fibre sensor application for high voltage winding of shell type transformer ........................................................................................................................... 46 Table 1 – Temperature rise limits .......................................................................................... 11 Table 2 – Recommended values of temperature rise corrections in case of special service conditions ................................................................................................................. 12 Table 3 – Exponents for the corrections of temperature rise test results ............................... 22 Table A.1 – Hot-spot winding temperature rises for some specific transformers determined from conventional heat run test data combined with calculated hot-spot winding temperature rise, and from direct fibre-optic measurements ..................................... 24 Table C.1 – Example of cooling down curve calculation spreadsheet .................................... 37 Table D.1 – Minimum detectable value SD of gases in oil ...................................................... 40 Table D.2 – Admissible limits for gas rate increases ............................................................. 41 Table E.1 – Minimum recommended number of sensors for three-phase transformers .......... 43 Table E.2 – Minimum recommended number of sensors for single-phase transformers ......... 43 This is a preview - click here to buy the full publication – 4 – 60076-2  IEC:2011 INTERNATIONAL ELECTROTECHNICAL COMMISSION ____________ POWER TRANSFORMERS – Part 2: Temperature rise for liquid-immersed transformers FOREWORD 1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with may participate in this preparatory work. International, governmental and non- governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for Standardization (ISO) in accordance with conditions determined by agreement between the two organizations. 2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international consensus of opinion on the relevant subjects since each technical committee has representation from all interested IEC National Committees. 3) IEC Publications have the form of recommendations for international use and are accepted by IEC National Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any misinterpretation by any end user. 4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications transparently to the maximum extent possible in their national and regional publications. Any divergence between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter. 5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any services carried out by independent certification bodies. 6) All users should ensure that they have the latest edition of this publication. 7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and members of its technical committees and IEC National Committees for any personal injury, property damage or other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC Publications. 8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is indispensable for the correct application of this publication. 9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent rights. IEC shall not be held responsible for identifying any or all such patent rights. International Standard IEC 60076-2 has been prepared by IEC technical committee 14: Power transformers. This third edition cancels and replaces the second edition published in 1993. It is a technical revision. This edition includes the following significant technical changes with respect to the previous edition: a) the standard is applicable only to liquid immersed transformers; b) the winding hot-spot temperature rise limit was introduced among the prescriptions; c) the modalities for the temperature rise test were improved in relation to the new thermal requirements; d) five informative annexes were added in order to facilitate the standard application. This is a preview - click here to buy the full publication 60076-2  IEC:2011 – 5 – The text of this standard is based on the following documents: FDIS Report on voting 14/669/FDIS 14/676/RVD Full information on the voting for the approval of this standard can be found in the report on voting indicated in the above table. This publication has been drafted in accordance with the ISO/IEC Directives, Part 2. A list of all parts of the IEC 60076 series can be found, under the general title Power transformers, on the IEC website. The committee has decided that the contents of this publication will remain unchanged uploads/Geographie/iec-60076-2-ed-3-0-pdf.pdf