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
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
q w (t ) = A0 - kt + Be - t/Tw 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
POWER TRANSFORMERS –
Part 2: Temperature rise for liquid-immersed transformers
1 Scope
This part of IEC 60076 applies to liquid-immersed transformers, identifies power transformers according to their cooling methods, defines temperature rise limits and gives the methods for temperature rise tests.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
IEC 60076-1, Power transformers – Part 1: General
IEC 60076-8:1997, Power transformers – Part 8: Application guide
IEC 60085:2007, Electrical insulation – Thermal evaluation and designation
IEC 61181:2007, Mineral oil-filled electrical equipment – Application of dissolved gas analysis (DGA) to factory tests on electrical equipment
IEC Guide 115:2007, Application of uncertainty of measurement to conformity assessment activities in the electrotechnical sector
Bibliography
[1]IEC 60076-7:2005, Power transformers – Part 7: Loading guide for oil-immersed power transformers
[2]IEC 60296:2003, Fluids for electrotechnical applications – Unused mineral insulating oils for transformers and switchgear
[3]IEC 60567:2005, Oil-filled electrical equipment – Sampling of gases and of oil for analysis of free and dissolved gases – Guidance
[4]IEC 60599:1999, Mineral oil-impregnated electrical equipment in service – Guide to the interpretation of dissolved and free gases analysis
[5]IEC 60836:2005, Specifications for unused silicone insulating liquids for electrotechnical purposes
[6]IEC 61099:2010, Insulating liquids – Specifications for unused synthetic organic esters for electrical purposes
[7]IEEE C57.91:1995, IEEE Guide for loading mineral-oil-immersed transformers
[8]CLC/TR 50462:2008, Rules for the determination of uncertainties in the measurement of the losses on power transformers and reactors
[9]CIGRE WG 06-ST 12:1982, Final report concerning the temperature rise test on oil- immersed transformers with analysis of gases dissolved in oil
[10]CIGRE WG 12.09:1994, Dissolved-gas analysis during heat-run tests on power transformers