THE EFFECT OF VARIATION OF NONLINEAR LOAD ON POWER FACTOR OF THE AC SUPPLY NETWORK

Transcription

1 Number Vlume Jue 00 Jural f Egieerig THE EFFECT OF VARATON OF NONLNEAR LOAD ON POWER FACTOR OF THE AC SUPPLY NETWORK By Mr. Mhammed Abdulla Abdulsada, Electrical Egieerig Dept. Faculty f Egieerig \ Tbruk Omar Al-Mukhtar Uiversity Praf. Dr. Ali A. Al-killidar & Dr. Ziad Al-Azawi Electrical Egieerig Dept. Cllege f Egieerig Uiversity f Baghdad ABSTRACT The aim f this paper is t evaluate the effect f the cverter system the pwer factr f the supply etwrk.therefre a -phase, -pulse, bridge cverter is assembled ad cected t a pwer supply thrugh a -phase ac vltage regulatr.the theretical aalysis is simulated usig Furier series aalysis ad Fast Furier Trasfrm ( FFT algrithm. The experimetal measuremets f distrti factr, displacemet factr ad ttal pwer factr are recrded. The experimetal results are shw t be cicidet with the theretical results. The csiderati f pwer factr imprvemet relative t distrti ad displacemet factrs is discussed. الخالصة إن الهدف من هذا البحث هو تأثير مغير القدرة عمى معامل القدرة ( factr pwer لمشبكة المجهزة. لذلك تم تجميع و ربط مجهز قدرة مستمر ثالثي الطور ذو ست نبظات و باستعمال منظم فولتية في الطرف المتناوب. استخدمت طريقتان لمتحميل النظري و هما : تحميل سمسمة فورير ( aalysis Furier series و تحويل فورير السريع ( Trasfrm Fast Furier. تم distrti factr و معامل القدرة و استنتاج النتائج العممية لمعامل اإل ازحة ( factr displacemet و معامل التشويه ( تم مقارنة النتائج النظرية مع النتائج العممية. تم مناقشة طرق تحسين معامل القدرة و ذلك عن طريق تحسين معامل اإل ازحة و معامل التشويه. 55

2 A.A. Al-killidar Z.Al-Azawi M.A.Abdulsada The Effect Of Variati Of Nliear Lad O Pwer Factr Of The Ac Supply Netwrk KEYWORDS: pwer factr, displacemet factr, distrti factr, harmic currets, pwer factr crrecti, effect f dc iductace. NTRODUCTON Pwer factr has icreasigly becme a tpic f discussi whe specifyig lads ad ac\dc pwer surces. Whe large liear lads are cected t utility systems, sigificat harmic currets are prduced. The cverter harmics cause icreased heatig f the utility ad ther custmer equipmet ad ca lead t system resace. Therefre, the harmics eed t be take it accut i varius system evaluatis[l. Cividi, 99].Harmics ca be defied as a siusidal cmpet f a peridic wave r quatity havig a frequecy that is a itegral multiple f the fudametal frequecy [ EEE stadard 59 99, 99].The harmics fr a -pulse cverter, 50 Hz fudametal frequecy are the fifth (50 Hz, the seveth (50 Hz, the eleveth (550 Hz etc. The mst ticeable prblem assciated with electrical rectificati was the iheretly pr pwer factr f the pwer system. The pwer factr f a circuit is uiversally defied as the rati f the active r average pwer, i watts, t the apparet pwer r prduct rms vlt times rms ampers at the termials". The abve defiiti is based the assumpti that lads the system have lier vltage-curret characteristics ad that harmic distrti f the curret ad vltage is t sigificat. With these assumptis, the pwer factr is equal t the displacemet factr. Harmic distrti i the curret ad vltage caused by AC/DC cverters i the system chages the way pwer factr must be defied[w. Shepherd ad P. Zad, 979]. this case, the ttal pwer factr is defied as the rati f the ttal pwer iput, i watt, t the ttal vlt-amperes i the circuit, the ttal pwer factr made up f tw cmpets; displacemet ad distrti factrs. The displacemet factr is the rati f the active pwer f the fudametal wave, i watt, t the apparet pwer, i vlt-amperes [P. Filipski S.,99].This is the pwer factr that is measured by meterig. The distrti factr is that part assciated with the presece f harmic curret ad vltage [EEE stadard 59 99, 99]. The assciati f ttal pwer with displacemet ad distrti factrs is imprtat because it highlights the factrs which determie the verall pwer factr f a system. A pr pwer factr ca be the result f either a sigificat phase differece betwee the vltage ad curret at the lad termials, r it ca be due t a high harmic ctet r distrted/disctiuus curret wavefrm. Pr lad curret phase agle is geerally the result f a iductive lad such as a iducti mtr, pwer trasfrmer, lightig ballasts, welder r iducti furace. A distrted curret wavefrm ca be the result f a rectifier, variable speed drive, switched mde pwer supply, discharge lightig r ther electric lad. The pwer factr crrecti (PFC ca be made if the distrti factr ad displacemet factr are imprved. The distrti factr is icreased by reducig the harmic currets frm eterig the mai system by prvidig a shut filter f lw impedace t the harmic frequecies. These shut filters als supplies all r part f the reactive pwer csumed by the cverter, the remaider beig supplied by shut capacitr baks Which used t imprve the displacemet factr. A large umber f tplgies ad ctrl strategies are implemeted t achieve rectificati i -phase supply with high pwer factr[h. Ma, etal, 997 ; Y. Jag ad M. Jvavic, 998]. 55

3 Number Vlume Jue 00 Jural f Egieerig The bjective f this paper is t aalyze the supply ttal pwer factr f the -phase, -pulse, ac\dc bridge cverter with the use f -phase ac vltage regulatr theretically ad experimetally. * DSPLACEMENT FACTOR, DSTORTON FACTOR AND TOTAL POWER FACTOR The agle betwee the fudametal supply vltage ad the fudametal cmpet f the supply lie curret is kw as displacemet agle (. The csie f the iput displacemet agle is the displacemet factr (cs. The displacemet factr ca be als defied as the rati f the active pwer t the fudametal apparet pwer. The distrti factr is defied as the rati f the rms amplitude f the fudametal cmpet f the iput supply lie curret, t it is ttal rms amplitude, that is: cs L ( The ttal pwer factr is defied as the rati f the ttal active pwer iput, i watt, t the ttal apparet pwer i the circuit, that is: Ttal active pwer iput ( W PF Ttal apparet pwer iput ( VA * POWER FACTOR UNDER LNEAR AND NONLNEAR LOADS The liear lad is that lad draw a siusidal curret wave whe supplied by a siusidal supply vltage. Oly the fudametal cmpet f the supply vltage ad lie curret are exist. The active iput pwer culd be described as: P e ( t. i ( t. d t E si t. si ( t d t 0 0 Which leads t: P = E.. cs φ ( The apparet pwer will be give by : 5

4 A.A. Al-killidar Z.Al-Azawi M.A.Abdulsada The Effect Of Variati Of Nliear Lad O Pwer Factr Of The Ac Supply Netwrk S = S = E. (5 By defiiti the ttal pwer factr is give by: P P PF S S cs ( t ca be deduced that i the liear lads the ttal pwer factr is equal t the displacemet factr. the case f liear lad the curret draw frm the mai supply vltage is -siusidal (distrted ad ca be represeted by Furier summati f the fudametal ad harmics cmpets: ( t si( t h h si( ht The active pwer draw frm the supply system due t each harmic cmpet f curret is give by: h (7 P h 0 E si (. si ( ht dt 0 t h h (8 That meas the active pwer trasferred ly by cmbiati f vltage ad curret cmpets f the same frequecy The ttal rms lie curret ad ttal apparet pwer is give by: L h h h h (9 S E. L E. h h (0 By the use f Eq. (, the ttal pwer factr will be : PF h h. cs.cs L ( 55

5 Number Vlume Jue 00 Jural f Egieerig Thus, the pwer factr f liear lad is made up f prduct f tw cmpets: displacemet Factr ( cs φ ad the distrti factr ( \ L which assciated with the harmics preset. Sice, by defiiti, L is greater tha due t the presece f harmics curret cmpet, the distrti factr is less tha uity ad hece the pwer factr is less tha uity eve i thse cases where cs has it is maximum value f uity. The distrti pwer ( D is created by the cmbiati f vltage ad curret cmpets f harmic curret. Oly fudametal frequecy pwers (P, Q ad S ca be represeted by a triagle phasrs as shw i Fig..a.The ttal apparet pwer ad distrti pwer are ly umerical values. The distrti pwer is perpedicular t the plae P, Q ad S, s that the ttal apparet pwer (S is cvetial t represeted gemetrically by a three dimesial represetati (space diagal as shw i Fig..b[Task Frce, 99]. S Q P a. b. Fig. Pwer phasr diagram ( a liear lad ( b liear lad. * POWER FACTOR N TERMS OF FOURER SERES COEFFCENTS The ttal pwer factr ca be calculated als by usig the Furier series aalysis. Fr a peridic -siusidal curret (ωt f a peridicity π radias the Furier cefficiet a ad b fr the peak value f the fudametal lie curret are: a 0 b 0 i( t.cs t dt i( t.si t dt ( ( 55

6 A.A. Al-killidar Z.Al-Azawi M.A.Abdulsada The Effect Of Variati Of Nliear Lad O Pwer Factr Of The Ac Supply Netwrk The rms value f fudametal lie curret ( is give by: ( a b / ( The displacemet factr ca be shw t be: cs cs ta a b a b b (5 The distrti factr is give by: cs a b L ( The ttal pwer factr is fud t be : PF b L (7 * MODELNG AND ANALYSS OF AC\DC CONVERTER At lw ac level etwrk ( i.e. 0. Kv, -phase, -pulse, AC\DC bridge cverters are recmmeded whe dealig with pwer up t 50 Kw. case f high dc curret, it is preferable t ctrl the supply ac vltage by meas f -phase ac vltage regulatr as shw i Fig..This allw the thyristrs t ctrl the lwer primary curret, which results i simpler mre ecmical pwer circuit. Let the ac supply phase vltages be: Fig. Circuit cfigurati f ac vltage regulatr with -phase bridge rectifier. 55

7 Number Vlume Jue 00 Jural f Egieerig V V V A B C E E E si( t si( t si( t (8 The crrespdig lie-t-lie supply vltage be: V V V AB BC CA E E E si( t si( t 7 si( t (9 The perati f this mdel f AC\DC cverter is depeds the firig agle values. O varyig the firig agle α frm 0 t 0 as measured frm zer trasit f the phase vltage, there is ctrl the thyristrs cducti. The thyristrs start t be ctrlled fully after wt = π \ f the trasit f the phase vltage. Durig this perid, the trasfrmer is subjected t balace -phase supply vltages. At ay istace f time, tw dides cduct e i the psitive half ad the ther i the egative e. Fr the rage f α, 0, there are certai perids whe three thyristrs cduct ad ather whe tw thyristrs cduct simultaeusly. This particular mde f perati is represeted the tati mde \. t may be ted that the perid durig which three-thyristrs cduct simultaeusly decrease as the firig agle is retarded ad whe the firig agle is r mre threethyristrs simultaeus cducti ceases. This perati f the circuit describe as mde \, exteds ver the firig agle rag frm t 90. Last mde f perati is referred t as mde 0\ describe the perati fr firig agle rag frm 90 t 50 which disctiuus cditi is ccur. Fig. shws the wavefrms f secdary ad supply lie currets fr differet mdes f perati. * CALCULATON OF DSPLACEMENT FACTOR, DSTORTON FACTOR AND TOTAL POWER FACTOR The displacemet, distrti ad ttal pwer factr at the supply side ca be evaluated i terms f Furier cefficiets. The displacemet factr ca be fud by usig Eq.(5 ad the Furier cefficiets ad give by: 55

8 A.A. Al-killidar The Effect Of Variati Of Nliear Z.Al-Azawi Lad O Pwer Factr Of The Ac M.A.Abdulsada Supply Netwrk 5 ( si ( 5 cs ( 9( si ( cs ( 7 0 cs ( 0 si ( cs ( 9( 0 cs Si By Cmbiati f Eq. ( ad the Furier cefficiets,results i the fllwig expressi fr distrti factr: ( si ( 5 si ( 5 cs ( 9( cs ( ( 0 cs ( ( si ( cs ( 9( 0 cs cs Si The supply ttal pwer factr is btaied by usig Eq. (, r ca be expressed as the prduct f Eq. (0 ad ( ad give by: ( si ( cs ( 0 0 Si P F

9 Number Vlume Jue 00 Jural f Egieerig Fig. Secdary ad supply lie currets fr differet firig agles. 55

10 A.A. Al-killidar Z.Al-Azawi M.A.Abdulsada The Effect Of Variati Of Nliear Lad O Pwer Factr Of The Ac Supply Netwrk - Simulati ad Experimetal Results The Harmic curret magitudes are evaluated usig tw methds; Furier series ( FS decmpsiti ad Fast Furier Trasfrm ( FFT.The FFT methd described the curret wavefrm i the time dmai ad ca easily be perfrmed via cmputer sftware t arrive at the cstituet harmics. The MatLap sftware is used t cmpute the FFT f the supply lie curret ad the cmplete data vectr iput takes exactly e perid t sample. The samplig rate is take t be 80 sample per cmplete perid ( i. e. 80 sample\ 0 msec.. A -phase, -pulse,. Kw is assembled ad cected t 0. Kv pwer supply thrugh -phase, ac vltage regulatr (fig.(. The driver iput sigal t the firig circuit is i the rage ( 0-. which prvides a firig agles frm zer t50. A 5 KVA, delta\star trasfrmer f 9 turs rati ( step dw is used ad the lad is a pure resistive f 0.5 Ω. Fig. shws the experimetal wavefrm f the supply lie curret ad the crrespdig frequecy spectrum. The displacemet, distrti ad ttal pwer factrs cmputed by tw simulati methds ad these results ad the experimetal results are shw i Fig. Fig.. Frm Fig., it ca be see that the displacemet factr has a maximum value f 0.9 at uctrlled regi ( α 0. This is due t the supply curret is apprximately i phase with the supply phase vltage. With firig agle icreases the displacemet factr is rabidly decrease because the firig agle shifts the supply curret wavefrm ad this icrease the displacemet agle, hece, decrease the displacemet factr. The chages i the distrti factr values with the icrease f the firig agles are small as shw i Fig.5. Fr firig agle greater tha 70, the harmic currets begi t effect the values f distrti factr ad this affect icreases as the firig agle icreases. The distrti factr is equals t 0.9 at α = 70 ad decrease t 0.8 at firig agle equals t 0. Als, the fudametal cmpet f experimetal results is fud t be greater tha the theretical results, especially at higher firig agles, ad this explai the reas f sigificat reducti i the distrti factr f the experimetal results. Frm Fig., the maximum ttal pwer factr is 0.9 which is measured at ctrl agle ad reaches zer at α =

11 Number Vlume Jue 00 Jural f Egieerig Fig. Experimetal wavefrms f the supply lie curret ad crrespdig frequecy spectrum. 55

12 A.A. Al-killidar Z.Al-Azawi M.A.Abdulsada The Effect Of Variati Of Nliear Lad O Pwer Factr Of The Ac Supply Netwrk Fig. Simulati ad experimetal results f displacemet factr. Fig.(5 Simulati ad experimetal results f distrti factr. 55

13 Number Vlume Jue 00 Jural f Egieerig Fig.( Simulati ad experimetal results f pwer factr. CONCLUSON this paper, the ttal pwer factr f the -phase, -pulse, ac\dc cverter with -phase ac vltage regulatr at the supply side is aalyzed theretically ad experimetally. The theretical aalysis fr the harmic curret, ad ttal pwer factr are simulated usig Furier series aalysis ad Fast Furier Trasfrm ( FFT algrithm. A. Kw ( v \ A, -phase, AC DC cverter is assembled ad the experimetal measuremets f harmics amplitudes, ttal pwer factr ad ther parameters were carried ut. Frm the results f distrti factr, displacemet factr ad ttal pwer factr it ca be deduce that the agreemet betwee experimetal ad simulati results is fair but there are small differeces betwee them. This is because f cmmutati effect, errrs i measurig exactly the values f firig agle, ad the istrumet iaccuracies. The imprvemet f the distrti factr, ad csequetly the pwer factr, is recmmeded fr firig agle greater tha 70, while the displacemet factr imprvemet is required fr firig agle greater tha 0. Frm abve csiderati, it ca be ccluded that the distrti factr des t cause pr pwer factr fr firig agle less tha 70 ad the factr that sigificatly effects the pwer factr is the displacemet factr. Fr firig agle greater tha 70, bth the distrti ad displacemet factrs are respsible f lwer pwer factr. 5

14 A.A. Al-killidar Z.Al-Azawi M.A.Abdulsada The Effect Of Variati Of Nliear Lad O Pwer Factr Of The Ac Supply Netwrk The mdel f AC DC cverter,which csidered i this paper, is preferable t be used at lw vltage level etwrk t prduce lw dc vltage, high dc curret. This allw the thyristrs t ctrl the lwer primary curret, which results i simpler mre ecmical pwer circuit. REFERENCES H. Ma, etal, 997, Review f high perfrmace three phase pwer factr crrecti circuits, EEE Tras. O dustry electrics, Vl., N., Aug., PP 7-5. EEE stadard 59 99, 99, EEE recmmeded practices ad requiremets fr harmic ctrl i electrical pwer systems. J. Arrillaga, et al, 997 Pwer system harmic aalysis, Ld: Wiley. L. Cividi, 99, " Pwer factr, harmics distrti, causes, effects ad csideratis " 'th iteratial cferece telecmmuicati eergy, Oct., pp P. Filipski S.,99, " Plyphase apperet pwer ad pwer factr uder distrted wavevrme cditi ", EEE Tras. O Pwer Delivery, Vl., N., July, PP - 5. R. D. Heders ad P. J. Rse, 99, Harmics: the effect pwer quality ad trasfrmer, EEE Tras. O dustry Applicatis, Vl.0, N., May\Jue, PP Task Frce Harmics Mdelig ad Simulati, 99, mdelig ad simulati f the prpagati f harmics i electric pwer etwrks, EEE Tras. O Pwer delivery, Vl., N., Ja.,PP 5-. V. K. Mehta, 998, Priciple f pwer system, S. Chad ad Cmpay ltd., dia. W. Shepherd ad P. Zad, 979, Eergy flw ad pwer factr i siusidal circuits, Cambridge uiversity press. Y. Jag ad M. Jvavic, 998, A cmparative study f sigle switch, three phase, high pwer factr rectifier, EEE APEC 98 Cferece recrd, part, PP

15 Number Vlume Jue 00 Jural f Egieerig LST OF SYMBOLS = Firig agle. Cs φ = displacemet factr. Cs δ = Distrti factr. D = distrti pwer. Ed = Average direct vltage. E = ac supply lie-t-eutral vltage (rms. h = rder f harmic. i ( t = stataeus supply curret. d = Average value f dc lad curret. dm = crest value f dc lad curret. l = fudametal cmpet f L. l = fudametal cmpet f L, assumig zer phase ctrl. L = supply lie curret (rms. K = teger.,,,, P = Active iput pwer. PF = ttal pwer factr. R = Resistace f dc lad. S = Ttal apparet pwer. S = fudametal cmpet f apparet pwer. T = Trasfrmer turs rati. V A, V B, V C = stataeus lie-t-eutral -phase supply vltages. V AB, V BC, V AC = stataeus lie-t-lie -phase supply vltages. 55