Synchronous Generator Simulation Using LabVIEW (Student Paper)

Transcription

1 Synchrnus Generatr Simulatin Using LabVEW (Student Paper) M. Usama Sardar bstract Cmputer-aided teaching tls have turned ut t be an indispensable element f bth classrm lectures and labratry experiments. The applicatin f market-ready mathematical and database prgramming sftware fr teaching engineering curse utline is well appreciated. This paper presents the utilizatin f LabVEW (Labratry Virtual nstrument Engineering Wrkbench) in intrducing the features f electrical machine simulated at varius pssible cntrl mdes. The undergraduate students need minimal acquaintance f a prgramming language. The examples presented in the paper illustrate hw LabVEW sftware can be applied t simplify sme f the steady-state characteristics f the three-phase synchrnus generatr perating alne. The result f intrducing LabVEW sftware as a teaching tl at the third-year level has been accepted and is nw used as part f the practical sessins fr the electrical machines curse at Ghulam shaq Khan nstitute f Engineering Sciences and Technlgy, Tpi, N.W.F.P. in Pakistan. Keywrds Electric Machines, LabVEW, simulatin, synchrnus generatr.. NTRODUCTON. Need fr a Change in Teaching Methdlgy ODERN prgramming sftwares are equipped with M highly interactive displays, signal prcessing, prttyping, three dimensinal (3-D) plts, X Y graphs, wrd prcessing and data layering t facilitate swift elucidatin and presentatin f results and trends. The direct applicatin f this srt f sftware drastically simplifies simulatin prcedures fr several practicing engineers in additin t undergraduate engineering students. The integratin f the generatr and electrnics t adjust the inherent generatr characteristics creates cmplicatins fr the instructr t make things easier and present the subject matter t undergraduates withut the assistance f sme type f electrnic simulatin tls. successful simulatin tl necessitates time, energy, and prficiency in prgramming languages and general cmprehensin f the peratinal characteristics f the electrical machine and its perfrmance. t is indispensable t emphasize the engineering educatin curriculum with cmputer-aided teaching tls that are interactive as well as educatinal, in rder t keep sustainable interest in the learning prcess fr the students. Fr these reasns LabVEW, a graphical prgramming language was intrduced t initiate the mdificatins in teaching Manuscript received n March 31, M. U. Sardar is with the Faculty f Electrnics Engineering in Ghulam shaq Khan nstitute f Engineering Sciences and Technlgy, Pakistan (phne: ; usamasardar@ htmail.cm). methdlgy at the Ghulam shaq Khan nstitute f Engineering Sciences and Technlgy. B. Cre Technical dvantages f LabVEW The imprtance f LabVEW can be realized by the fllwing statement f the ssciate Directr f Penn State University: "LabVEW is a prgramming language, equivalent t C++, Visual Basic, r any ther language. t is the nly widely accepted graphical prgramming language. Graphical prgramming is a language f the future and carries with it many imprtant prgramming cncepts. feel, it is the respnsibility f universities ( such as Penn State) t expse, at least, every cmputer science and engineering student t these new cncepts."- Sctt Den, ssciate Directr Center fr Electrnic Design, Cmmunicatins, and Cmputing Penn State University. The visual representatins bring prgramming clser t the human side f the human machine interface, just as high-level languages tipped the accessibility scales relative t assembly languages. Mrever, LabVEW has prven t be an invaluable tl in decreasing develpment time in research, design, validatin, prductin test, and manufacturing. Besides this, the majr advantages f LabVEW include ease f learning, using and debugging, the simplicity f using the interface (frnt panel f a LabVEW prgram) particularly fr a user with a little r n knwledge f LabVEW prgramming, mdular develpment, cmplete functinality, available tls and resurces, reliable perfrmance and the capability f cntrlling equipment. There are fur critical elements f the LabVEW develpment platfrm: i) ntuitive graphical prgramming language ii) High-level applicatin-specific tls iii) ntegrated measurement and cntrl-specific capabilities iv) Multiple cmputing targets. LBVEW SOFTWRE S N EDUCTONL TOOL FOR ELECTRC MCHNE CSES n 2006, the faculty f electrnics engineering at Ghulam shaq Khan nstitute f Engineering Sciences and Technlgy intrduced LabVEW sftware n a trial basis with the aim f enhancing interactive teaching and learning f the electric machines curse. Synchrnus generatr simulatin is straightfrward nce the fundamental features f LabVEW sftware are mastered. 392

2 Obviusly, LabVEW sftware is extensively used fr several scientific and engineering applicatins and is nt the nly sftware available. t is easy t use and has numerus built-in functins that facilitate its use in many textbk applicatins. The next sectins will reveal the versatility f adpting LabVEW in evaluating the steady state characteristics f three-phase synchrnus generatr under variable input cnditins. The multiple-chice electrnic menu created by MS ccess sftware as seen in Figs. 1 and 2 given t the student is used t navigate thrugh LabVEW prgrams accrding t the curse utline. Fig. 3 The full equivalent circuit fr a three-phase synchrnus generatr Fig. 1 The interactive electrnic main menu. The Presentatin f the Synchrnus Generatr Characteristics by LabVEW n electrical generatr, the mechanical energy input and the electrical energy utput can be presented in mathematical frm, after presenting the physical peratin f the generatr with the equivalent electric circuit f the 3-ф synchrnus generatr shwn in Fig. 3. The electric circuit is used t facilitate the calculatin f the unknwn quantity, fr instance current r vltage, nce the values f the resistive and inductive cmpnents are given. The values culd be evaluated experimentally by cnducting shrt-circuit and pen-circuit tests n the generatr if that is pssible; therwise, the manufacturer shuld be cntacted fr the infrmatin. The pwer flw, shwn in Fig. 4, within the generatr is tracked by balancing the input and the utput taking int accunt the heat and magnetic pwer lsses. The lsses are quantified by perfrming several standard tests n the generatr. The current flwing in the generatr can be calculated using the equivalent circuit representing the generatr physical elements. The steady-state develped trque and pwer are then evaluated and pltted t reveal the generatr characteristics. The expected efficiency f thse particular parameters can als be pltted. lmst every textbk presents the synchrnus generatr by it's per phase equivalent circuit, as shwn in Fig. 5, and shws hw steadystate current and pwer are estimated. n many cases, the armature resistance and cpper lsses are ignred t simplify the prcedures. Fig. 4 The three-phase synchrnus generatr pwer flw diagram Fig. 2 The multiple-chice submenu fr C synchrnus machines 393

3 Case 1: Effect f adding lagging lads (r inductive reactive pwer lads): f lagging lads are added t a generatr, E a increases. Fig. 6 shws the phasr diagram generated in LabVEW befre adding lads and Fig. 7 shws the phasr diagram generated in LabVEW after the lagging lad is added. Fig. 5 The per-phase equivalent circuit f the synchrnus generatr n many textbk examples, the synchrnus generatr current can be estimated with fairly acceptable accuracy using the abve methdlgy. Example 1 (shwn in the ppendix) presents the standard steps t determine the internal generated vltage using the equivalent circuit fr the synchrnus generatr. B. The Student nteractin with the Sftware The practicality f using LabVEW sftware fr the student is that it will be pssible t input varius cnfiguratins f variables withut any knwledge f text-based prgramming. The use f the built-in functins f the sftware in an interactive way t prduce the cmplete generatr characteristics ver the entire variable range instead f just ne perating pint will be mre infrmative fr the student. This is ne f the advantages ver the numerical examples nrmally presented in the textbk. Therefre, the student can verify all the pssible perating pints alng the generatr characteristics. The LabVEW simulatins stred fr the student in the electrnic database f the curse generate cmplete characteristics ver the whle variable range allwing the student t examine the shape and verify different perating pints. Furthermre, the sftware can be used by the students fr verifying labratry experiments after entering the labratry generatr data and the perating cnditins. The recrded test results fr the labratry machines culd be cmpared fr further verificatin between thery and practice. Fig. 6 Phasr diagram generated in LabVEW befre adding lads. SMULTON CSES T investigate the cmplete generatr characteristics under varying cnditins, the fllwing cases are presented.. Effect f Lad Changes 3 situatins may arise depending upn the type f lad added: Case 1: f lagging lads are added t a generatr, V phase and V t decrease significantly. Case 2: f unity pwer factr lads are added t a generatr, V phase and V t decrease slightly. Case 3: f leading lads are added t a generatr, V phase and V t increase. But in many generatr applicatins, we need t maintain V t as cnstant. S in that case, E a will vary. The LabVEW phasr diagrams fr the 3 cases that arise are given belw: Fig. 7 Phasr diagram generated in LabVEW after adding the lagging lad Case 2: Effect f adding unity pwer factr lads (n reactive pwer lads): f unity pwer factr lads are added t a generatr, E a increases slightly. Fig. 8 shws the phasr diagram generated in LabVEW befre adding lads and Fig. 9 shws the phasr diagram generated in LabVEW after the unity pwer factr lad is added. 394

4 Fig. 8 Phasr diagram generated in LabVEW befre adding lads Fig. 10 Phasr diagram generated in LabVEW befre adding lads Fig. 9 Phasr diagram generated in LabVEW after adding the unity pwer factr lad Case 3: Effect f adding leading lads (r capacitive reactive pwer lads): f leading lads are added t a generatr, E a decreases. Fig. 10 shws the phasr diagram generated in LabVEW befre adding lads and Fig. 11 shws the phasr diagram generated in LabVEW after the leading lad is added. Fig. 11 Phasr diagram generated in LabVEW after adding the lagging lad B. Output Pwer Case 1: Effect f trque angle n utput pwer: Output pwer varies sinusidally with the trque angle if the phase vltage and internal generated vltage are assumed cnstant. This is shwn in Fig

5 Effect f Trque ngle n Output Pwer Effect f Synchrnus Reactance n Output Pwer Fig. 12 Graph generated in LabVEW shwing the variatin f utput pwer with the trque angle Case 2: Effect f phase vltage n utput pwer: Output pwer varies directly with the phase vltage if the internal generated vltage is assumed cnstant. This is shwn in Fig. 13. Effect f Phase Vltage n Output Pwer Fig. 14 Graph generated in LabVEW shwing the variatin f utput pwer with the synchrnus reactance Case 4: Effect f internal generated vltage n utput pwer: Output pwer varies directly with the internal generated vltage if the phase vltage is assumed cnstant. This is shwn in Fig. 15. Effect f nternal Generated Vltage n Output Pwer Fig. 15 Graph generated in LabVEW shwing the variatin f utput pwer with the internal generated vltage Fig. 13 Graph generated in LabVEW shwing the variatin f utput pwer with the phase vltage Case 3: Effect f synchrnus reactance n utput pwer: Output pwer varies inversely with the synchrnus reactance if the internal generated vltage and phase vltage are assumed cnstant. This is shwn in Fig. 14. C. nduced Trque Case 1: Effect f trque angle n induced trque: nduced trque varies sinusidally with the trque angle if the phase vltage and internal generated vltage are assumed cnstant. This is shwn in Fig

6 Effect f Trque ngle n nduced Trque Effect f Synchrnus Reactance n nduced Trque Fig. 16 Graph generated in LabVEW shwing the variatin f induced trque with the trque angle Case 2: Effect f phase vltage n induced trque: nduced trque varies directly with the phase vltage if the internal generated vltage is assumed cnstant. This is shwn in Fig. 17. Effect f Phase Vltage n nduced Trque Fig. 18 Graph generated in LabVEW shwing the variatin f induced trque with the synchrnus reactance Case 4: Effect f internal generated vltage n induced trque: nduced trque varies directly with the internal generated vltage if the phase vltage is assumed cnstant. This is shwn in Fig. 19. Effect f nternal Generated Vltage n nduced Trque Fig. 19 Graph generated in LabVEW shwing the variatin f induced trque with the internal generated vltage Fig. 17 Graph generated in LabVEW shwing the variatin f induced trque with the phase vltage Case 3: Effect f synchrnus reactance n induced trque: nduced trque varies inversely with the synchrnus reactance if the internal generated vltage and phase vltage are assumed cnstant. This is shwn in Fig. 18. Case 5: Effect f mechanical speed f rtatin n induced trque: nduced trque varies inversely with the mechanical speed if the internal generated vltage and phase vltage are assumed cnstant. This is shwn in Fig

7 Effect f Mechanical Speed f Rtatin n nduced Trque Fig. 20 Graph generated in LabVEW shwing the variatin f induced trque with the mechanical speed f rtatin D. Vltage Regulatin Vltage regulatin is a quantity that cmpares the terminal vltage f the generatr at n lad with the terminal vltage at full lad. t is defined by (1): Vnl V fl VR = 100% (1) V fl Case 1: Lagging pwer factr: generatr perating at a lagging pwer factr has a psitive vltage regulatin. Case 2: Unity pwer factr: generatr perating at a unity pwer factr has a small psitive vltage regulatin. Case 3: Leading pwer factr: generatr perating at a leading pwer factr has a negative vltage regulatin. E. Synchrnus Generatr Capability Curves Synchrnus generatr capability curves are used t determine the stability f the generatr at varius pints f peratin. particular capability curve generated in LabVEW fr an apparent pwer f 50,000W is shwn in Fig. 21. The maximum prime-mver pwer is als reflected in it. Fig. 21 Synchrnus generatr capability curve generated in LabVEW als shwing the maximum prime-mver pwer limit V. CONCLUSON LabVEW is a wnderful tl t initiate a simple apprach t evaluate the steady-state characteristics f the synchrnus generatr. The sftware has a high ptential fr the analysis f system perfrmance and can be used in simulatin techniques effectively. The use f the built-in functins f LabVEW in an interactive way t prduce the cmplete generatr characteristics ver the entire variable range instead f just ne perating pint will be mre infrmative fr the student. This is ne f the advantages ver the numerical examples nrmally presented in the textbk. s cmputing languages are nt essential, the undergraduate student can investigate the synchrnus generatr characteristics quickly and easily. PPENDX The fllwing numerical example shws the result f changing the lads n the generatr. t can be bserved frm part (c) f example 1 that E increases when lagging pwer factr lads are added. Similarly, the fact that E decreases when leading pwer factr lads are added is shwn with the help f part (f) f example 1. These results are in cnfrmity with the sectin f the simulatins cases described abve with the help f phasr diagrams generated in LabVEW. Example 1: 480-V, 60-Hz, Δ-cnnected, fur-ple synchrnus generatr has a synchrnus reactance f 0.1 Ω and an armature resistance f 0.015Ω. t full lad, the machine supplies 1200 at 0.8 PF lagging. Under full-lad cnditins, the frictin and windage lsses are 40 kw, and the cre lsses are 30 kw. gnre any field circuit lsses. (a) What is the speed f rtatin f this generatr? 398

8 (b) Hw much is the internal generated vltage f the generatr in rder t make the terminal vltage 480 V at n lad? (c) f the generatr is nw cnnected t a lad, and the lad draws 1200 at 0.8 PF lagging, hw much will the internal generated vltage be t keep the terminal vltage equal t 480 V? (d) Hw much pwer is the generatr nw supplying? Hw much pwer is supplied t the generatr by the prime mver? What is this machine s verall efficiency? (e) f the generatr s lad were suddenly discnnected frm the line, what wuld happen t its terminal vltage? (f) Finally, suppse that the generatr is cnnected t a lad drawing 1200 at 0.8 PF leading. Hw much will the internal generated vltage be t keep V t at 480V? Slutin: This synchrnus generatr is Δ-cnnected, s its phase vltage is equal t its line vltage, while its phase current is related t its line current by the equatin: (a) The relatinship between L = 3the Φ electrical frequency prduced by a synchrnus generatr and the mechanical rate f shaft rtatin is given by the fllwing equatin: 120 f e nm = P Substituting the given values: (b) Since the generatr is at n lad, =0, thus E = V Φ = VT = 480V (c) f the generatr is supplying 1200, then the armature current in the machine is L 1200 = = = PF=0.8 lagging, s = f the terminal vltage is adjusted t be 480V, the internal vltage is given by: E = V Φ + R + jx S = (0.015)( = V ) + ( j0.1)( ) Thus t keep V T = 480V, E must be adjusted t 532V. This shws that E increases when lagging pwer factr lads are added because the value f E was 480V as shwn in part (b). (d) The pwer that the generatr is nw supplying can be fund frm the fllwing equatin: P = ut 120(60) n m = = 1800r / min 4 = 3V csθ T L 3(480)(1200) cs(36.87) = 798kW The mechanical input pwer is given by: Pin = Put + Pelec lss + Pcre lss + P Where it is given that: mech lss + P cre = 30kW and P windage = 40kW The stray lsses were nt specified here, s they will be ignred. n this generatr, the electrical lsses are: Therefre, the machine s verall efficiency is: stray lss 2 2 Pelec lss = 3 R = 3(692.8) (.015) = 21. 6kW S the ttal input pwer t the generatr is: η P in = = kW = in P ut / P 100% = 798/ % = 89.75% (e) f the generatr s lad were suddenly discnnected frm the line, the current wuld drp t zer. Since the field current has nt changed, V T and Vφ must rise t equal E. Therefre, if the lad were suddenly drpped, the terminal vltage f the generatr wuld rise t 532V. Thus V T = 532V (f) f the generatr were laded dwn with 1200 at 0.8 PF leading while the terminal vltage was 480V, then the internal generated vltage wuld have t be: E V = Φ + R + jx = (0.015)( = V S Therefre, the internal generated vltage E must be adjusted t 451V if V T is t remain at 480V. This shws that E decreases when leading pwer factr lads are added because the value f E was 480V as shwn in part (b). CKNOWLEDGMENT First f all, am very thankful t Gd, wh made me able t wrk hard and cmplete my research paper. Specially, wuld like t express my sincere thanks t my supervisr Dr. Laiq Khan wh enlightened me with the cncepts f electric machines in detail and bradened my visin regarding the subject. His help was indispensable in mastering the vast subject f electric machines, in particular synchrnus generatrs. He was generus enugh t give me much f his precius time and his encuragement in writing the paper was vital fr me. He nt nly reviewed the paper but als suggested the necessary crrectins in it. am really grateful t him fr all his help and time. Mrever, am thankful t assistant directr library f GK, Mr. Saleem qbal, fr his help in finding the relevant research papers and bks related t synchrnus generatrs and LabVEW. P ) + ( j0.1)( ) 399

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