CONTENTS
FOREWORD 5
1 Scope 7
2 Normative references 8
3 Terms and definitions 8
3.1 General 8
3.2 Terminals and neutral point 9
3.3 Windings 10
3.4 Rating 11
3.5 Tappings 13
3.6 Losses and no-load current 15
3.7 Short-circuit impedance and voltage drop 16
3.8 Temperature rise 17
3.9 Insulation 17
3.10 Connections 17
3.11 Test classification 18
3.12 Meteorological data with respect to cooling 19
3.13 Other definitions 19
4 Service conditions 20
4.1 General 20
4.2 Normal service conditions 20
5 Rating and general requirements 22
5.1 Rated power 22
5.1.1 General 22
5.1.2 Preferred values of rated power 22
5.1.3 Minimum power under alternative cooling modes 22
5.1.4 Loading beyond rated power 23
5.2 Cooling mode 23
5.3 Load rejection on transformers directly connected to a generator 23
5.4 Rated voltage and rated frequency 23
5.4.1 Rated voltage 23
5.4.2 Rated frequency 23
5.4.3 Operation at higher than rated voltage and/or at other than rated
frequency 24
5.5 Provision for unusual service conditions 24
5.6 Highest voltage for equipment Um and dielectric tests levels 25
5.7 Additional information required for enquiry 25
5.7.1 Transformer classification 25
5.7.2 Winding connection and number of phases 25
5.7.3 Sound level 26
5.7.4 Transport 26
5.8 Components and materials 26
6 Requirements for transformers having a tapped winding 27
6.1 General – Notation of tapping range 27
6.2 Tapping voltage – tapping current. Standard categories of tapping voltage
variation. Maximum voltage tapping 27
6.3 Tapping power. Full-power tappings – reduced-power tappings 30
6.4 Specification of tappings in enquiry and order 31
6.4.1 General 31
6.4.2 Constructional specification 31
6.4.3 Functional specification 32
6.5 Specification of short-circuit impedance 32
6.6 Load loss and temperature rise 33
7 Connection phase displacement symbols 34
7.1 Connection and phase displacement symbols for three-phase transformers
and for single phase transformers connected in a three phase bank 34
7.1.1 Connection symbol 34
7.1.2 Phase displacement in clock number notation 34
7.1.3 Windings not intended to be loaded 35
7.1.4 Reconnectable windings 35
7.1.5 Examples 35
7.2 Connection and phase displacement symbols for single phase transformers
not in three phase bank 37
7.2.1 Connection symbol 37
7.2.2 Phase displacement in clock number notation 38
7.2.3 Windings not intended to be loaded 38
7.2.4 Reconnectable windings 38
8 Rating plates 39
8.1 General 39
8.2 Information to be given in all cases 39
8.3 Additional information to be given when applicable 40
9 Safety, environmental and other requirements 41
9.1 Safety and environmental requirements 41
9.1.1 Liquid leaks 41
9.1.2 Safety considerations 41
9.2 Dimensioning of neutral connection 42
9.3 Liquid preservation system 42
9.4 DC currents in neutral circuits 43
9.5 Centre of gravity marking 43
10 Tolerances 43
11 Tests 44
11.1 General requirements for routine, type and special tests 44
11.1.1 General 44
11.1.2 Routine tests 46
11.1.3 Type tests 46
11.1.4 Special tests 47
11.2 Measurement of winding resistance 47
11.2.1 General 47
11.2.2 Dry-type transformers 47
11.2.3 Liquid-immersed type transformers 48
11.3 Measurement of voltage ratio and check of phase displacement 48
11.4 Measurement of short-circuit impedance and load loss 48
11.5 Measurement of no-load loss and current 49
11.6 Measurement of zero-sequence impedance(s) on three-phase transformers 50
11.7 Tests on on-load tap-changers ─ Operation test 51
11.8 Leak testing with pressure for liquid immersed transformers (tightness test) 51
11.9 Vacuum deflection test for liquid immersed transformers 51
11.10 Pressure deflection test for liquid immersed transformers 52
11.11 Vacuum tightness test on site for liquid immersed transformers 53
11.12 Check of core and frame insulation 53
12 Electromagnetic compatibility (EMC) 53
13 High frequency switching transients 54
Annex A (informative) Check list of information to be provided with enquiry and order 55
Annex B (informative) Examples of specifications for transformers with tappings 59
Annex C (informative) Specification of short-circuit impedance by boundaries 63
Annex D (informative) Examples of three-phase transformer connections 64
Annex E (normative) Temperature correction of load loss 67
Annex F (informative) Facilities for future fitting of condition monitoring systems to
transformers 68
Annex G (informative) Environmental and safety considerations 69
Bibliography 70
Figure 1 – Different types of voltage variation 30
Figure 2 – Illustration of 'clock number' notation 35
Figure 3 – Illustration of 'clock number' notation for transformers with open windings 37
Figure 4 – Illustration of 'clock number' notation 39
Figure C.1 – Example of specification of short-circuit impedance by boundaries 63
Figure D.1 – Common connections 64
Figure D.2 – Additional connections 65
Figure D.3 – Designation of connections of three-phase auto-transformers by
connection symbols (auto-transformer Ya0) 66
Figure D.4 – Example of three single-phase transformers connected to form a three-
phase bank (connection symbol Yd5) 66
Table 1 – Tolerances 44
Table B.1 – Example of combined voltage variation 60
Table B.2 – Example of functional specification with HV voltage variation 61
Table B.3 – Example of functional specification with LV voltage variation 62
Table F.1 – Facilities for condition monitoring 68
POWER TRANSFORMERS –
Part 1: General
1 Scope
This part of IEC 60076 applies to three-phase and single-phase power transformers (including auto-transformers) with the exception of certain categories of small and special transformers such as:
–single-phase transformers with rated power less than 1 kVA and three-phase transformers less than 5 kVA;
–transformers, which have no windings with rated voltage higher than 1 000 V;
–instrument transformers;
–traction transformers mounted on rolling stock;
–starting transformers;
–testing transformers;
–welding transformers;
–explosion-proof and mining transformers;
–transformers for deep water (submerged) applications.
When IEC standards do not exist for such categories of transformers (in particular transformer having no winding exceeding 1000 V for industrial applications), this part of IEC 60076 may still be applicable either as a whole or in part.
This standard does not address the requirements that would make a transformer suitable for mounting in a position accessible to the general public.
For those categories of power transformers and reactors which have their own IEC standards, this part is applicable only to the extent in which it is specifically called up by cross-reference in the other standard. Such standards exist for:
–reactors in general (IEC 60076-6);
–dry-type transformers (IEC 60076-11);
–self-protected transformers (IEC 60076-13);
–gas-filled power transformers (IEC 60076-15);
–transformers for wind turbine applications (IEC 60076-16);
–traction transformers and traction reactors (IEC 60310);
–converter transformers for industrial applications (IEC 61378-1);
–converter transformers for HVDC applications (IEC 61378-2).
At several places in this part it is specified or recommended that an 'agreement' should be reached concerning alternative or additional technical solutions or procedures. Such agreement is made between the manufacturer and the purchaser. The matters should preferably be raised at an early stage and the agreements included in the contract specification.
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 60076-2, Power transformers – Part 2: Temperature rise for liquid-immersed transformers
IEC 60076-3:2000, Power transformers – Part 3: Insulation levels, dielectric tests and external clearances in air
IEC 60076-5:2006, Power transformers – Part 5: Ability to withstand short circuit IEC 60076-10:2001, Power transformers – Part 10: Determination of sound levels IEC 60076-11:2004, Power transformers – Part 11: Dry-type transformers
IEC 60137:2008, Insulated bushings for alternating voltages above 1 000 V
IEC 60214-1:2003, Tap-changers – Part 1: Performance requirements and test methods
IEC 60296:2003, Fluids for electrotechnical applications – Unused mineral insulating oils for transformers and switchgear
IEC 60721-3-4:1995, Classification of environmental conditions – Part 3: Classification of groups of environmental parameters and their severities – Section 4: Stationary use at non- weatherprotected locations
ISO 9001:2008, Quality management systems – Requirements
Bibliography
IEC 60050-421:1990, International Electrotechnical Vocabulary – Chapter 421: Power transformers and reactors
IEC 60060 (all parts), High-voltage test techniques
IEC 60068-3-3, Environmental testing – Part 3: Guidance – Seismic test methods for equipments
IEC 60076-4, Power transformers – Part 4: Guide to lightning impulse and switching impulse testing – Power transformers and reactors
IEC 60076-6, Power transformers – Part 6: Reactors
IEC 60076-7, Power transformers – Part 7: Loading guide for oil-immersed power transformers
IEC 60076-8:1997, Power transformers – Part 8: Application guide
IEC 60076-10-1, Power transformers – Part 10-1: Determination of sound levels – Application guide
IEC 60076-12, Power transformers – Part 12: Loading guide for dry-type power transformers
IEC 60076-13, Power transformers – Part 13: Self-protected liquid-filled transformers
IEC/TS 60076-14, Power transformers – Part 14: Design and application of liquid-immersed power transformers using high-temperature insulation materials
IEC 60076-15: 2008, Power transformers – Part 15: Gas-filled power transformers
IEC 60076-16, Power transformers – Part 16 : Transformers for wind turbines application 1
IEC 60270, High voltage test techniques – Partial discharge measurements
IEC 60310, Railway applications – Traction transformers and inductors on board rolling stock
IEC 60529:1989, Degrees of protection provided by enclosures (IP Code)
IEC/TR 60616:1978, Terminal and tapping markings for power transformers
IEC/TS 60815 (all parts), Selection and dimensioning of high-voltage insulators intended for use in polluted conditions
IEC 61378 (all parts), Convertor transformers
IEC 61378-1, Convertor transformers – Part 1: Transformers for industrial applications
IEC 61378-2, Convertor transformers – Part 2: Transformers for HVDC applications
IEC 62032, Guide for the application, specification, and testing of phase-shifting transformers
IEC 62262, Degrees of protection provided by enclosures for electrical equipment against external mechanical impact (IK code)
ISO 3:1973, Preferred numbers – Series of preferred numbers
ISO 2178:1982, Non-magnetic coatings on magnetic substrates – Measurement of coating thickness – Magnetic method
ISO 2409:2007, Paints and varnishes – Cross-cut test
ISO 12944 (all parts), Paints and varnishes – Corrosion protection of steel structures by protective paint systems
ISO 14001, Environmental management systems – Specification with guidance for use
ISO 14122 (all parts), Safety of machinery – Permanent means of access to machinery
ANSI/IEEE C57.12.00, General requirements for liquid-immersed distribution, power and regulating transformers
ANSI/IEEE C57.12.90, IEEE standard test code for liquid-immersed distribution, power and regulating transformers
IEEE C57.142, Guide to describe the occurrence and mitigation of switching transients induced by transformer, switching device, and system interaction
CIGRE Brochure 156, Guide for customers specifications for transformers 100 MVA and 123 kV and above
CIGRE Brochure 204, Guide for transformer design review
CIGRE Brochure 343, Recommendations for Condition Monitoring and Condition Assessment Facilities for Transformers