Testing of Power Transformers - ABB

1 Testing of Power TransformersRoutine tests, Type tests and Special testsTesting ofPower TransformersRoutine tests, Type testsand Special testsTesting ofPower TransformersRoutine tests, Type testsand Special tests1st Editionpublished byPRO PRINTforABB Business Area Power TransformersAffolternstrasse 44, 8050 Z rich, SCHWEIZT elefon +41 1317 7126, e-Mail: participation of Ake CarlsonJitka FuhrGottfried SchemelFranz WegscheiderLayout/DesignTypesetting/Repr oduction:Pro Print GmbH, D sseldorfTypeface:Neue HelveticaPrinting:InterDruck, B llingenPaper:Bilderdruck matt 135 g/qmTesting of Power Transformersunder participation of Ake CarlsonJitka FuhrGottfried SchemelFranz Wegscheider1st Editionpublished by Pro Print GmbH, D sseldorfISBN 3-00-010400-3 ABB AGAll rights OF Power TRANSFORMERSR emember school days?

2 Nothing caused more excitement thanthe teachers announcement of a test. Because a test confirmswhat you know, if you can apply in real life what you havelearned in a classroom, under strict, rigorous and controlledconditions. It is a chance to demonstrate of Power Transformers seems like a similar experience;and therefore ABB undertook to write this Testing has developed considerably over the pastyears. It evolved from the simple go-no-go verdict into asophisticated segment within transformer manufacturing. In thisbook we have laid down important aspects on transformertesting in order to enhance the understanding of the testingprocedures and its book represents the collective wisdom of over 100 yearsof Testing Power Transformers .

3 It has been written for trans-former designers, test field engineers, inspectors, consultants,academics and those involved in product believes that the knowledge contained in this book willserve to ensure that you receive the best Power transformerpossible. The more knowledgeable you are, the better thedecisions you will rich, October 2003 ABB Business Area Power TransformersPrefacePreface8 Testing OF Power TRANSFORMERSP reface7 Table of transformer Testing ? of concerning this test book172 Dielectric integrity and its / appearing during transformer major insulatiionelectrical for dielectric routine tests27A 2 Appendix28A of winding / of the and methodsfor resistance of the measured in resistance measurements36A 3 Appendix37A requirements on equipment37A of the DC-current of measurement38A (Thomson)

4 Measuring circuit39A of voltage ratio and vectorgroup or phase / of the voltage uncertainty51A 4 Appendix52A and localization of errors525 Measuring the short-circuit voltageimpedance and the load / ot the of the measuring uncertainty65A 5 Appendix66A of relativeshort-circuit voltage (or short-circuit voltage)and winding temperature66A loss separation when windingresistances are not known67A equipment requirements67A error correction69A transformer error correction69A the short-circuit voltage for startingtransformers having an air gap72A for investigation tests72A the no-load lossand no-load / of of the measuring uncertainty918 Testing OF Power TRANSFORMERST able of ContentsTable of Contents9 Testing OF Power TRANSFORMERSA 6 Appendix92A equipment specification92A of the hysteresisand eddy current loss components92A measurements of the iron core93A measuring circuits94A source AC withstand voltage

5 Testor Applied voltage / of the and measuring Uncertainty100A 7 Appendix101A of the capacitive loadcompensation requirements101A requirements for the measuringequipment1028 Induced voltage / of the and test of the load for the inducedvoltage requirements for the of the voltage drop acrossthe protective resistance of sphere-gaps1189 Partial Discharge of of PD measurement on measuring for Investigation of PD of acoustical PD investigation of the PD uncertainty139A 9 Appendix140A of partial discharge140A of quasi-integration143A charge, apparent chargeand measureable charge147A external noise sources149A PD system151A of acoustical PD signals154A of the PD source using analysisof the electrical signals157A shielding16010 Lightning impulse and switchingimpulse of the procedure / the test results and failure impulse measuring system /measuring uncertainty175A 10 Appendix176A Waveshape and its assessment176A Generation of high impulse voltages177A Pre-calculation of impulse waveform180A Test circuit parameters for switchingimpulse test183A Measuring high impulse voltages183A Calibrating the impulse voltage divider ratio190A

6 Use of a Sphere-gap for checking the scalefactor of an impulse peak voltmeter190A Measuring the impulse current193A Earthing the impulse circuit194 Table of ContentsTable of Contents10 Testing OF Power TRANSFORMERSA Switching impulse wave form195A Air withstand196A Impulse voltage stress on Power transformers19611 Temperature rise of the / temperature and test circuit and spot examples and analysisof the measured uncertainty210A 11 Appendix211A Definitions, temperature and temperature-rise211A Other test methods for temperature rise test212A estimating the duration of the temperaturerise test [2]213A Graphical extrapolation to ultimatetemperature [2]214A Oil temperature measurement bymeasuring the surface temperature [61]214A Correction of the injected currentwith non-nominal frequency214A Correction factors according toIEEC [51]215A Conformance of the measured averagewinding temperature rise with the realwinding temperature rise in operation215A Practical examples and analysisof the measured values21612 Measurement of zero-sequenceimpedance(s)

7 On three-phase / of of the zero-sequence procedure228A 12 Appendix230A Example for an unbalanced three-phase system 230A Types of zero-sequence impedance230A Influence of winding connection andtransformer design231A Examples and interpretation23413 Short-circuit withstand of the conditions, Testing techniques andtest connections239A 13 Appendix244A The difference between post-establishedand pre-established short-circuit [105]244A Examples for single-phase test connectionssimulating the three-phase test244A The calculation of the symmetrical short-circuitcurrent according to IEC 60076-5 [5]245A The calculation of the symmetrical short-circuitcurrent Isc according to [50]246A Low-voltage recurrent-surgeoscilloscope method246 Table of ContentsTable of Contents11 Testing OF Power TRANSFORMERS14 Sound level of [7], [51], [106] and measuring uncertainties254A 14 Appendix255A Human perception of sound [106]255A estimating load-sound Power level,and the influence of the load [7]255A Addition of no-load sound and load sound [7]256A Definitions [7]256A Calculation of the environmentalcorrection factor K [51]

8 258A The calculation of sound Power level, example259A Far-field calculations26015 Test on on-load tap-changers anddielectric tests on auxiliary / of the test / procedure [1] / Test of auxiliary equipment [3], [50]26316 Measurements of the harmonicsof the no-load / of measuring circuit [100] measuring 16 Appendix268A The relationship between flux density, no-loadcurrent and harmonic content. [106]268A Example26817 Measurement of insulation / of the measuring circuit /The measuring procedure [51]273A 17 Appendix27418 Measurement of dissipation factor (tan )of the insulation system / of the measuring circuit /The measuring procedure [51]277A 18 Appendix280A Examples280 Index283 References / Bibliography289 Standards290 International Electrotechnical Commission (IEC)

9 290 IEEE / ANSI Standards291 Books291 Technical Reviews292 Editors293 Explanation to the vocabularyThe authors vocabulary in the test book is based on IEC are no really important differences between the vocabularyapplied in IEC and IEEE (ANSI) only exception is the use of the words earth / earthed (according to IEC) and ground / grounded (according to IEEE).Table of ContentsTable of Contents13 Testing OF Power TRANSFORMERS1. Introduction1. IntroductionTesting ofPower Transformers1. Introduction14 Testing OF Power TRANSFORMERS1. Introduction1. transformer Testing ?Tests serve as an indication of the extent to which a transformeris able to comply with a customer s specified requirements;for example: Loading capability Dielectric withstand Further operating characteristicsTests are also part of a manufacturer s internal quality assuranceprogram.

10 A manufacturer s own criteria have to be fulfilled inaddition to requirements specified by customers and requirements are generally combined and published innational and international standards. The primary StandardsOrganizations are IEC and ANSI. These standards are often useddirectly to develop national standards. IEC is the abbreviation forInternational Electro-technical Commission and ANSI stands forAmerican National Standard Institute, the electric area, ANSI has to a great extent delegated thewriting and publication of standards to IEEE, the Institute ofelectric and Electronics Engineers, IEC and IEEE Standards specify the respective tests thatverify compliance with the above requirements; :Temperature rise tests to verify loading capability,see section 11 Dielectric tests to demonstrate the integrity of the transformerwhen subjected to dielectric stresses and possible over-voltages during normal operation, see section and load lo