This part of GB/T 18494 deals with the specification, design and testing of power transformers and reactors which are intended for integration within semiconductor converter plants; it is not applicable to transformers designed for distribution of a.c. power in general.
The scope of this part is limited to application of power converters of any power rating. Typical applications are: thyristor rectifiers for electrolysis; diode rectifiers for electrolysis; thyristor rectifiers for large drives; thyristor rectifiers for scrap melting furnaces, and diode rectifiers feeding inverters for variable speed drives. The part also covers the regulating unit utilized in such application as step down regulating transformers or autotransformers. The valve winding highest voltage for equipment is limited to 40.5 kV.
This part is not applicable to transformers for HVDC power transmission.
The standards for the complete converter plant (GB/T 3859, or other standards dedicated to particular fields of application) may contain requirements of guarantees and tests (such as insulation and power loss) for the whole plant, possibly including the converter transformer, auxiliary transformers and reactor equipment. This does not relieve the application of the requirements of this part concerning the guarantees and tests applicable to the transformer itself as a component of the converter plant.
The guarantees, service and type tests defined in this part apply equally to transformers supplied as part of an overall converter package, or to those transformers ordered separately but for use with converter equipment. Any supplementary guarantee or special verification has to be specifically agreed in the transformer contract.
The converter transformers covered by this part may be of the oil-immersed or dry-type design. Unless specific exceptions are stated in this part, the transformers comply with GB 1094 series for oil-immersed transformers, and with GB 1094.11 for dry-type transformers.
Note: For some converter applications, it is possible to use common distribution transformers of standard design. The use of such standard transformers in the special converter applications may require a certain derating. This matter is not specifically covered in this part. It is possible to estimate this derating from the formulae given in 6.2 , and also from GB/T 13499.
This standard deals with transformers with one or more active parts installed in the same tank like regulating (auto)transformer and one or two rectifier transformers. It also covers transformers with transductors and/or one or more interphase transformers.
For any combination not listed above an agreement between the purchaser and manufacturer is necessary regarding the determination and the measurement of the total losses.
This part deals with transformers star Y and delta D and any other phase shifting connections (like zig-zag, extended delta, polygon etc.). Phase shifting windings can be placed on either the regulating or rectifier transformer.
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.
GB 1094.1 Power transformers—Part 1: General (GB 1094.1-2013, IEC 60076-1:2011, MOD)
GB 1094.2 Power transformers—Part 2: Temperature rise for liquid-immersed transformers (GB 1094.2—2013, IEC 60076-2:2011, MOD)
GB 1094.3 Power transformers—Part 3: Insulation levels, dielectric tests and external clearances in air (GB 1094.3-2003, eqv IEC 60076-3:2000)
GB/T 3859.1-2013 Semiconductor converters—General requirements and line commutated converters—Part 1-1:Specification of basic requirements (IEC 60146-1-1:2009, MOD)
GB/T 3859.2-2013 Semiconductor converters—General requirements and line commutated converters—Part 1-2:Application guide (IEC/TR 60146-1-2:2011, MOD)
GB/T 13499-2002 Power transformers—Application guide (idt IEC 60076-8:1997)
3 Terms, definitions and acronyms
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in GB/T 2900.15, GB 1094.1 and GB/T 3859.1, as well as the following apply.
3.1.1
polygon connection
P
the winding connection in which each phase winding consists of two parts in which phase displaced voltages are induced. One part of each phase is connected in series to the other part of a different phase and then closed in a delta (see Annex A)
Foreword i 1 Scope 2 Normative references 3 Terms, definitions and acronyms 3.1 Terms and definitions 3.2 Acronyms 4 Classification 4.1 General 4.2 Normal service conditions 4.3 Unusual service conditions 5 Ratings 5.1 General 5.2 Rated power at rated frequency and load capability 5.3 Rated and service voltages 5.4 Rated current 5.5 Phase displacement and terminal identification for three-phase transformer 5.6 Rating plate 5.7 Units with tertiary windings loaded with filter and compensation 5.8 On-load tap changers 6 Load loss and voltage drop in transformers and reactors 6.1 General 6.2 Determination of transformer load loss under distorted current loading 6.3 Current sharing, losses and hot spot in high current windings 6.4 Effect of geometrical winding arrangement and magnetic coupling between windings on their eddy current losses due to harmonics in transformers with three or more windings wound on the same core limb 6.5 Losses in interphase transformers, current-balancing reactors, series-smoothing reactors and transductors 6.6 Voltage drops in transformers and reactors 7 Tests for converter transformers 7.1 General 7.2 Measurement of commutating reactance and determination of the inductive voltage drop 7.3 Measurement of voltage ratio and phase displacement 7.4 Dielectric tests 7.5 Load loss test 7.6 Temperature rise tests 8 Load noise level with transductors and/or IPT Annex A (Informative) Phase displacement connections and terminal indications of converter transformers Annex B (Informative) Guidelines for design review Annex C (Normative) Correlation between GB/T 18494.1 and GB/T 3859.1 ratings Annex D (Informative) Examples of duty cycles Annex E (Informative) Determination of transformer service load loss at rated non-sinusoidal converter current from measurements with rated transformer current of fundamental frequency Annex F (Informative) Current sharing measurement in high current valve windings Annex G (Informative) Determination of the transformer voltage ratio and phase displacement by the turn ratio measurements Annex H (Informative) Load tests of rectifier transformers equipped with built in transductors Annex I (Informative) Short-circuit test currents and load losses in transformers for single-way converters (total loss injection) Annex J (Informative) Determination of loss in transformer tank due to magnetic field, 3D simulation and guidelines for tank losses evaluation and tank hotspot calculation Bibliography Figure 1 B6U or DB 6-pulse double bridge connection Figure 2 DSS 6-pulse connection Figure 3 Leakage fields for a three-winding transformer with closely coupled valve windings Figure 4 Leakage fields for a three-winding transformer with decoupled valve windings Figure 5 Leakage fields for a three winding transformer with loosely coupled double concentric valve windings Figure 6 Leakage fields for a three winding transformer with both loosely-coupled valve windings in parallel axially-displaced Figure 7 Typical transductor regulating curve (with max voltage drop at zero control current) and tolerance band Figure A.1 Counterclockwise phase displacement Figure A.2 Yd11 connection Figure A.3 Yd1 connection Figure A.4 Example A.1 phase displacement Figure A.5 Example A.2 phase displacement Figure A.6 Zig-zag connection twelve pulse converter transformer Figure A.7 Extended delta connection twelve pulse converter transformer Figure A.8 Polygon connection twelve pulse converter transformer Figure C.1 DB connection ideal rectangular current blocks Figure C.2 DSS Connection rectangular current blocks Figure E.1 Cross-section of a winding strand Figure E.2 Terminal identification for winding connection Yy0y6 Figure E.3 Terminal identification for winding connection Dd0y1 Figure E.4 Valve current DB connection rectangular positive half-wave Figure E.5 Valve side current DB connection rectangular positive and negative half-wave Figure E.6 Valve current DSS connection rectangular shape Figure F.1 Example of valve high current winding and measurement equipment disposition Figure F.2 Transformer windings arrangement Figure F.3 Measurement circuit for the in-phase measurement Figure F.4 Measurement circuit for the in-opposition measurement Figure F.5 Measurements and comparison with the simulations made by finite element method software for the in-phase current distribution Figure F.6 Measurements and comparison with the simulations made by finite element method software for the in-opposition current distribution Figure G.1 Yd1 connection Figure G.2 Yd11 connection Figure G.3 Pd0+7.5 connection Figure G.4 Oscilloscope connection Figure G.5 Oscilloscope with phase B +7.5° lag referring to phase A Figure G.6 Oscilloscope with phase B -7.5° lead referring to phase A Table 1 Connections and calculation factors Table C.1 Harmonics content up to 25th in DB 6 pulse connection (ideal rectangular current waveshape) Table C.2 Harmonics content up to 25th in DSS 6 pulse connection (ideal rectangular current waveshape) Table C.3 Calculation factor comparison example Table C.4 Calculation factor comparison Table D.1 Examples of duty cycles for different applications Table E.1 Specified harmonic currents and phase displacement in the valve windings Table E.2 Resistance measurements at 20 °C winding temperature Table E.3 Specified harmonic currents and phase displacement in the line and valve windings Table E.4 Measurements from test Table E.5 Harmonic currents Table E.6 Harmonic currents Table E.7 Harmonic currents Table E.8 Detailed transformer load losses at rated tap position Table E.9 Harmonic currents Table E.10 Specified harmonic currents and phase displacement in the line and valve windings Table E.11 Harmonic currents Table E.12 Detailed transformer load losses at rated tap position Table F.1 Measurements and comparison with the simulations made by finite element method software for the in-phase current distribution Table F.2 Measurements and comparison with the simulations made by finite element method software for the in-opposition current distribution Table G.1 Single phase ratio measurements
