STUDY OF THE INFLUENCE OF THE MANUFACTURING PROCESS ON THE MAGNETIC BEHAVIOUR IN TOROIDAL TRANSFORMERS By H PIP Nandasena This thesis was submitted to the Department of Electrical Engineering in partial fulfillment of the requirements for the Degree of Master of Engineering Supervised By Dr. J P Karunadasa Dr. H Y R Perera Department of Electrical Engineering University of Moratuwa Sri Lanka 2004 82483 Abstract Toroidal transformers are manufactured by winding the core material in the form of a continuous strip, to take full advantage by making the direction of preferred orientation coincide with the flux path. However, the manufacturing process influences the magnetic behaviour and affects the quality; quite often leading to a rise in excitation current compared to the design excitation current. In the study, the factors influencing the magnetic behavior in Toroidal transformers are identified and analyzed. The main factors identified are the "Ratio of drum diameter to toroid inner diameter", "Core lathing", "Stress relief annealing" and "Winding pressure" The factor "Ratio of drum diameter to toroid inner diameter" is to study the effect of change of steel drum diameter when making identical toroidal cores to their excitation currents and the "Core lathing" is to study the effect of sharpe edge removing by machining to the excitation current while the factor "Stress relief annealing" is to study the effect of oven type to the excitation current and the "Winding pressure" is to study the effect of different steel brands and winding sequence to excitation current. In order to study the above factors, the sample batch experiments are carried out from the customer orders in a way that production plan is not disturbed. The excitation currents and other related measurements are noted down for the analysis which is performed with the help of MS-EXCEL. The statistical graphical method; a box-plot is used to interpret some variations and comparisons. It is noticed that the excitation currents are high in the initial cores made from a new steel drum and thereby excitation currents are getting reduced. This shows that core making process induces of more irreversible stresses due to plastic deformation at initial cores made from a new steel drum than the later cores. It is also noticed that the excitation currents are increased after machining (core lathing) process. The conclusion is that short circuited steel strips at the lath (or curved) edges cause the increase of eddy currents and thereby increase of excitation current. Further the high excitation currents are observed in the cores which are annealed in the belt oven which is having forced cooling and they are more sensitive to the winding tightness too. The more consistent excitation currents are observed in the box oven when it compares with the belt ovens. The conclusion is that the cores are re-stressed due to the rapid cooling and thereby increase the excitation current. Finally, it is noticed that excitation currents are increased after conductor winding and the level of increase depends on the steel brand. Further, the increase of excitation current is more after the first winding on the core. The conclusion is that pressure exerted by conductor winding stresses the core and thereby increases the excitation current. The first winding on the core is dominant in inducing stresses. Finding the reason for abnormal rise in excitation current (core testing and random test after primary for excitation current are passed but final testing for excitation current is failed) and developing a commonly (design, production and quality) acceptable spreadsheet to determine the excitation current are prerequisites to evaluate the governing factors. Therefore, the abnormal rise in excitation current in the final testing bench is studied and the conclusion is that it is caused by the unbalanced turns in the multithread secondary. The decision support system (to perform extra test or not) for engineers is incorporated in the excitation current calculation spreadsheet, which is developed as part of this study. The excitation current calculation spreadsheet is superior to other tools that are used to determine the excitation current as it considers the magnetic field strength at design flux density, resistive part of the excitation current and corrected mean magnetic path length. Later it is extended to generate production testing instruction sheets too. Declaration To the best of my knowledge and bclict: the work included in this thesis in part or in whole has not been submitted for an~ other academic qualitication at any institution. Stgned by: --~ ·-·· H PIP ~andasena Cet1tiied b). Dr. JP Karunadasa Depatiment ofElectrical Engineering University of M.oratuwa C)ri Lanka l Department ofElectrical Engineering Univcrsit) of Moratuwa Sri Lanka ~ .... II Acknowledgement I wish to express my deep gratitude to all who contributed both directly and indirectly towards the success ofthis research project; , The project supervisors, Dr JP Karuanadasa & Dr HYR Perera, Universit) of Moratuwa, Sri Lanka for the guidance extended right throughout the project. , Prof. JR Lucas, Universit) of Moratuwa. Sri Lanka for the guidance extended for the:>is. , Mr. Bo Lindberg; Managing director of Toroid International (Pvt./.Ltd. for giving the approval. , Mr. Ruwan Dharmasiri, Engineering and Customer Relations Manager of Toroid International (Pvt.) Ltd. for giving the initiation and guidance. , .\tr. Densil Kalupahana, Qualit) Assurance Manager of Toroid International (Pvt.) Ltd and his staff , The design engineers in Toroid Group Mr. Sam Perera 2. Mr. Kapila Warnakulasuri) a 3. Mr Chatura Karunarathna , Trainee engineer, Mr. Chandana Deshapri)a . .,. All the members in the production floor in the both Toroid factories. H.P.I.P ;-Jandasena December 3 l, 2004 ~ ~ \ List of Figures Figure 2.1 BCC lattice------------------------------------------------------------------------------- 5 Figure 2.2 f.CC lattice------------------------------------------------------------------------- 5 Figure 2. 3a Direction magnetisation-Crystal----------------------------------------------------- 5 figure 2 3b Direction eas} magnetisation-------------------------------------------------------- 6 Figure 2. 4 Grain Orientation----------------------------------------------------------------------- 6 Figure 2 5 Gross Process---------------------------------------------------------------------------- 7 Figure 2 . 6 Box Plot---------------------------------------------------------------------------------- 9 Figure 3.1 Permeabilit) variation with ratio D 1 '02-----------------.. J.---------------------ll Figure 3.2 Excitation current \.S ratio core IDtsteel dn1m 00-Test 1----------------------- 13 Figure 3.3 Excitation current vs ratio core ID/steel drum OD-Test 2------------------------14 Figure 4 I Cross-section of toroid---------------------------------------------------------------- 16 Figure 4.2 Edd) current paths f(.n 3 steel strips------------------------------------------------- 17 Figure 4.3a Core Lathing-Test 1---------------------------------------------------------- 18 Figure 4.3b Box plot core lathing-Test 1-------------------------------------------------------- 19 Figure 4. 4a Core Lathing-Test 2------------------------------------------------------------------20 Figure 4 4b Box plot core lathing-Test 2-------------------------------------------------------- 2 1 Figure 4. Sa Core Lathing-Test 3 -----------~------------------------------------------------------ 22 Figure 4. 5b Box plot core lathing-Testing 3---------------------------------------------------23 Figure 5 I Belt oven- and belt oven-3 variations---------------------------------------------- 28 Figure " 2 Box plot tor belt oven-2 and belt oven-3------------------------------------------- 29 Figure 5.3 Belt oven-3 and box oven- I variations-------------------------------------------- 30 Figure 5.4 Box plot for belt oven-3 and box ovcn-1------------------------------------------- 30 Figure 5.5a Box plots box oven- I before I after winding------------------------------------- 31 Figure 5 5b Box plots belt ovcn-3 before I after winding------------------------------------ 32 --· L"' 6 I E . . . ~ · · s I ~ , -rtgure . a xcttatwn currents 111 1-.tppon amp es------------------------------------------- .>) Figure 6.1 b Excitation currents in Poland Samples------------------------------------- 3 5 Figure 6 2a Box plot for excitation currents in Nippon Samples---------------------------- 36 Figure 6.2b Box plot for excitation currents in Poland Samples---------------------------- 36 Figure 6.3 Excitation currents betore I after winding----------------------------------------- 3 7 Figure 6.4a Box plot c.xcitation currents before I after\\ inding----------------------------- 3 7 vi Figure 6.4b Box plot excitation currents after PI winding I after P2 winding------------- 3 8 Figure 7.1 Equivalent circuit of four threads secondary-------------------------------------- 41 Figure 8.1 Equivalent circuit of translormer at no load--------------------------------------- 46 Figure 8.2 Vser interface of e.xcitation current calculation spreadsheet-------------------- 48 Figure 8.3 Excitation current comparisons-MS Steel----------------------------------------- 49 Figure 8.4 Excitation current comparisons-MOl I Steel--------------------------------------- 50 Figure 8 5 Excitation current comparisons-CK ~tee!------------------------------------------ 51 Figure 8 6 Core testing instruction sheet----------------------------------------------------- 52 Figure 8 7 Final testing instruction sheet-------------------------------------------------------- 53 Appendix A .1 Figure AI. Effect of annealing on tensile strength, hardness, ductility and grain size---- 63 ..... vii List of Tables Table 3 .l Results of test 1------------------------------------------------------------------------- 12 Table 3. 2 Results of test 2------------------------------------------------------------------------- J 4 Table 4.1 Core lathing-Test 1-------------------------------------------------------------------- 18 Table 4.2 Core lathing-Test 2---------------------------------------------------------------- 20 Table 4. 3 Core lathing Test 3-------------------------------------------------------------------- 22 Table 4.4 Core lathing test results summary----------------------------------------------- 23 Table 5.1 Main parameters ofbelt ovens---------------------------------------------------- 27 Table 5. 2 Main parameters of box oven~------------------------------------.1 _________________ 2 7 Appendix A Table A 1. RecrystalJization temperatures i()r various metals and alloys------------------- 62 ~ ... ~ \'Ill Contents Declaration ii Abstract Ill Acknowledgement v List of Figures vi List of Tables v iii Chapter !-Introduct ion 1.1 Background-----------------------------------------------------~~---------------------- I 1.2 Thesis objective------------------------------------------------------------------------- 2 I. 3 Thesis Outline--------------------------------------------------------------------------- 2 Chapter 2-Methodology 2. 1 1 n trod ucti on------------------------------------------------------------------------------ 4 2. 2 Literature Rev i e~ ----------------------------------------------------------------------- 4 2.3 Study on Si-Steel Grades------------------------------------------------------------ 4 2 3 1 Crystal/me 5tntcture------------------------------------------------------- 4 2. 3. 2 Grain Orient at ion---------------------------------------------------------- S 2.3.3 Hot-Rolling--------------------------------------------------------- 7 2.3. 4 Cold-Rolling---------------------------------------------------------------- 7 2.4 Identification of the factors Influencing Magnetic Beha\>iour In Toroidal Transformers---------------------------------------------------------------------------- 8 2. 5 Factor Evaluat i 011----------------------------------------------------------------------- 9 2 6 Analysis-------------------------------------------------------------------------------':!'~9 Chapter 3- E ffect of Ratio of D•·um Diameter to Toroid Inner Diameter ---3. I Introduction-------------------------------------------------------------- -------.:::.~ 3. 2 Factor Evaluation---------------------------------------------------------------------- 1 I 3 .2. I Test I (Semi-Auto Winding ~lachine )----------------------------------12 3 .2.2 Test 2 (Full) -Auto Winding Mac hme )-----------------------------13 3.3 Conclusions and Recommendations------------------------------- ---------------- 14 1'\ Chaptea· 4-Effect of Coa·e Lathing 4 .l Introduction-----------------------------------------------------------------------------16 4.2 Eddy Current Losses------------------------------------------------------------------ 16 4. 3 Factor Evaluation---------------------------------------------------------------------- I 7 4. 3. 1 Test 1------------------------------------------------------------------------l 7 4. 3. 2 Te<::t 2-------------------------------------------------------------------------19 4. 3. 3 Test 3-------------------------------------------------------------------------21 5.4 Conclusions and Rewmmendations -----------------------------------------23 Chapter 5- Effect of Sta·ess Relief Annealing S l lntroduction-------------------------------------------------~r-----------------------25 5. 2 Stress Relief Annealing---------------------------------------------------------------25 5. 3 Annealing Ovens-----------------------------------------------------------------------26 5.3 .1 Belt (Tunnel) Oven---------------------------------------------------------26 5. 3 2 Chamber (Box) Oven------------------------------------------------------ 26 5. 4 Factor Evaluation---------------------------------------------------------------------- 2 7 5.4.1 Testing the Dim~rences in Belt Oven 2 and Belt Oven 3-------------28 5.4.2 Testing the Differences in Belt 0\-en 3 and Box Oven 1-------------29 S 5 Conclusions and Recommendations------------------------------------------------ 32 Chapter 6- Effect of\Vinding Pt·essure 6 I Introduction---------------------------------------------------------------------34 6. 2 Factor Evaluation---------------------------------------------------------------------- 3 4 6. 3 Conclusions and Recommendations ------------------------------------------------3 8 Chapter 7-Abnormal Rise in Excitation Current 7. 1 Introduction---------------------------------------------------------------------------- 40 . . ~~ 7. 2 Theoretical Expl ana t 1011---------------------------------------------.....,.------------- 40 7. 2. 1 Four Threads Scenario---------------------------------------------------- 41 7 3 Conclusions and Recommendations------------------------------------------------ 43 X Chaptft' 8-Excitation Currt-nt Sprudsht-ft 8. l 1 ntroducti 011---------------------------------------------------------------------------- 4 S 8 2 C a leu! ation Base-----------------------------------------------------------------------4 5 8 3 Calculation Base Evaluation--------------------------------------------------------- 49 8. 4 Extensions------------------------------------------------------------------------------ S 1 8. 5 Conclusions and Recommendations ----------------------------------------------- 54 Chaptft' 9-Condusion 55 References 59 / Appendix A 60 __, Moo- :XI