TRNG I HC S PHM K THUT TP. HCM KHOA IN B MN. C S K THUT IN ------------0----------- BIN SON: ThS. NGUYE N TRONG THA NG ThS. LE TH THANH HOANG GIO TRNH K THUT IN TP. HCM Thng01/ 2008 rotor stator dy qun LI NI U KTHUT IN lmtmnhcc squantrngivi sinhvinkhikthut ni chung v sinh vin ngnh in ni ring. c th tip tc nghin cu chuyn su v lnh vc in th sinh vin phi nm vng nhng kin thc ca mn hc ny.K thutinnghincunhngngdngcacchintngintnhm bini nnglng v tn hiu, baogm vic pht, truyn ti, phn phi v s dng in nng trong sn xut v i sng.Ngoi ra mn hc ny cn gip sinh vin khng chuyn ngnh in b sung thm cc kin thc c bn v mch in, cc thit b in, cu to v cc c tnh lm vic ca chng c th vn hnh c trong thc t.Gio trnh c bin son trn c s ngi c hcmn ton v vtl bc ph thng,phninmnvtlicngbci hcnnkhngisuvomtlluncc hintngvtlmchyunghincuccphngphp tnh tonvnhngngdngk thut ca cc hin tng in t. Gio trnh k thut in gm 2 phn:Phn 1. Mch in bao gm 4 chng Phn 2. My in bao gm 4 chng Quyn sch ny trnh by cc kin thc c bn v mch in, phng php tnh ton mch in, dng in xoay chiu hnh sin mt pha v ba pha, cc kin thc v nguyn l, cu to, c tnh v ng dng cc loi my in c km theo cc v d c th v cc bi tp c son theo tng cc chng l thuyt, gip ngi hc c th gii v ng dng vo cc mn hc c lin quan. Giotrnhkthutinnycbinsonvisthamkhocctiliutrongv ngoinc,snggptntnhcaccngnghiptrongbmn.Tuynhingiotrnh cxutbnlnunnkhngthtrnhkhinhngthiust.Rtmongsnggp kin ca cc ng nghip, ca cc sinh vin v cc bn c quan tm n gio trnh ny. Cc tc gi Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMMC LC Trang CHNG 1: NHNG KHI NIM C BN V MCH IN ........................................ 11.1. KHI NIM CHUNG ............................................................................................ 1 1.1.1. nh Ngha V Mch in ................................................................................................... 1 1.1.2. Kt Cu Hnh Hc Ca Mch in ...................................................................................... 1 1.2. CC I LNG C TRNG CHO QU TRNH NNG LNG TRONG MCH IN............................................................................................................................................... 2 1.2.1. Dng in ............................................................................................................................ 2 1.2.2. in p ................................................................................................................................ 3 1.2.3. Cng sut .............................................................................................................................. 3 1.3. CC PHN TC BN CA MCH IN ................................................................. 4 1.3.1. in tr ................................................................................................................................. 4 1.3.2. in dn................................................................................................................................ 4 1.3.3. Cun dy............................................................................................................................... 4 1.3.4. in dung ............................................................................................................................. 4 1.3.5. Ngun c lp....................................................................................................................... 5 1.3.6. Ngun ph thuc .................................................................................................................. 5 1.4. CC NH LUT C BN CA MCH IN .............................................................. 7 1.4.1. nh lut ohm ....................................................................................................................... 7 1.4.2. nh Lut Kirchhoff 1 .......................................................................................................... 7 1.4.3. 1.4.2. nh Lut Kirchhoff 2 ................................................................................................ 8 1.5. BI TP V D CHNG 1 .............................................................................................. 9 1.6. BI TP CHNG I ......................................................................................................... 12 CHNG 2. MCH IN XOAY CHIU HNH SIN MT PHA ..................................... 14 2.1. CC NH NGHA V DNG IN XOAY CHIU HNH SIN .................................... 14 2.1.1. Chu k, tn s, tn s gc ................................................................................................... 14 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCM2.1.2. Tr s tc thi ca dng in .............................................................................................. 15 2.1.3. Gc lch pha gia in p v dng in ......................................................................... 15 2.1.4. Tr s hiu dng ca dng in .......................................................................................... 16 2.2. BIU DIN DNG IN XOAY CHIU HNH SIN BNG VECT ............................. 17 2.3. DNG IN XOAY CHIU QUA IN TR THUN R ............................................... 19 2.4. DNG IN XOAY CHIU QUA CUN DY THUN CM ...................................... 20 2.5. MCH IN XOAY CHIU THUN IN DUNG......................................................... 21 2.6. MCH IN XOAY CHIU GM R - L - C MC NI TIP ......................................... 22 2.7. BIU DIN DNG IN HNH SIN BNG S PHC ................................................... 24 2.7.1. nh ngha v cch biu din s phc ................................................................................ 24 2.7.2. Mt s php tnh i vi s phc ....................................................................................... 26 2.7.3.Biu din cc nh lut di dng di dng s phc ........................................................ 27 2.8. PHNG PHP GII MCH IN XOAY CHIU HNH SIN ...................................... 28 2.8.1. Phng php th vect ................................................................................................... 28 2.8.2. Phng php s phc ......................................................................................................... 28 2.9. CNG SUT ........................................................................................................................ 32 2.9.1. Cng sut tc thi............................................................................................................... 32 2.9.2. Cng sut tc dng ............................................................................................................. 32 2.9.3. Cng sut phn khng ........................................................................................................ 33 2.9.4. Cng sut tiu th v cng sut phn khng trn in tr R .............................................. 33 2.9.5. Cng sut tc dng v cng sut phn khng trn cun dy .............................................. 34 2.9.6. Cng sut tc dng v cng sut phn khng trn t in.................................................. 34 2.9.7. Cng sut biu kin ............................................................................................................ 34 2.9.8. H s cng sut................................................................................................................... 38 2.9.8.1. nh ngha v ngha ca h s cng sut ..................................................................... 38 2.9.8.2. Nng cao h s cng sut ................................................................................................ 39 2.10. BI TP CHNG 2 ........................................................................................................ 41 CHNG 3. CC PHNG PHP GII MCH IN..................................................... 47 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCM3.1. PHNG PHP BIN I TNG NG MCH..................................................... 47 3.1.1. Mch ngun sut in ng ni tip................................................................................... 47 3.1.2. Mch ngun dng mc song song ...................................................................................... 47 3.1.3. Mch in tr mc ni tip ................................................................................................. 47 3.1.4. Mch in tr mc song song ............................................................................................. 48 3.1.5. Mch chia dng in .......................................................................................................... 48 3.1.6. Mch chia p....................................................................................................................... 49 3.1.7. Bin i tng ng in tr mc hnh sao sang tam gic .............................................. 49 3.1.8. Bin i tng ng in tr mc hnh tam gicsao sang ............................................... 50 3.1.9. S tng ng gia ngun p v ngun dng ................................................................. 50 3.2. BI TP CHNG 3 MC 3.1 .......................................................................................... 51 3.3. BI TP CHO P S ....................................................................................................... 61 3.4.PHNG PHP IN TH NT ....................................................................................... 69 3.5. PHNG PHP DNG MT LI .................................................................................. 81 CHNG 4. MCH IN XOAY CHIU BA PHA ............................................................ 86 4.1. KHI NIM CHUNG V MCH IN XOAY CHIU BA PHA ................................... 86 4.1.1. nh ngha .......................................................................................................................... 86 4.1.2. Cch to ra dng in xoay chiu ba pha ........................................................................... 86 4.2. CCH NI MCH BA PHA ............................................................................................... 87 4.2.1. Ni hnh Sao ....................................................................................................................... 87 4.2.2. Ni hnh tam gic ............................................................................................................... 88 4.3. CCH GII MCH BA PHA .............................................................................................. 90 4.3.1. Mch ba pha i xng ........................................................................................................ 90 4.3.2. Cng sut mch ba pha i xng ....................................................................................... 92 4.3.3. Cch gii mch ba pha khng i xng ............................................................................. 98 4.3.4. Cng sut mch ba pha khng i xng ............................................................................ 99 4.4.CU HI N TP CHNG 4 ......................................................................................... 100 4.5.BI TP CHNG 4 ......................................................................................................... 100 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMCHNG 5. MY BIN P .................................................................................................. 104 5.1. KHI NIM CHUNG V MY BIN P........................................................................ 104 5.1.1. nh ngha ........................................................................................................................ 104 5.1.2. Cc i lng nh mc ................................................................................................... 104 5.1.3. Vai tr ca my bin p .................................................................................................... 105 5.2. CU TO V NGUYN L LM VIC ........................................................................ 106 5.2.1. Cu to ............................................................................................................................. 106 5.2.2. Nguyn l lm vic........................................................................................................... 108 5.3. QUAN H IN T TRONG MY BIN P................................................................. 109 5.3.1. Qu trnh in t trong my bin p ................................................................................. 109 5.3.2. Phng trnh cn bng in p cun s cp ..................................................................... 110 5.3.3. Phng trnh cn bng in p cun th cp ................................................................... 110 5.3.4. Phng trnh cn bng sc t ng .................................................................................. 111 5.4. MCH IN THAY TH MY BIN P ....................................................................... 111 5.4.1. Qui i cc i lng th cp v s cp........................................................................... 111 5.4.2. Mch in thay th my bin p ....................................................................................... 112 5.5. XC NH CC THNG S MY BIN P................................................................. 113 5.5.1. Th nghim khng ti........................................................................................................ 113 5.5.2. Th nghim ngn mch ..................................................................................................... 114 5.5.3. Hiu sut my bin p ...................................................................................................... 115 5.6. MY BIN P BA PHA .................................................................................................... 116 5.6.1. Cu to .............................................................................................................................. 116 5.6.2. T ni dy my bin p ba pha......................................................................................... 117 5.7. MY BIN P LM VIC SONG SONG ....................................................................... 118 5.8. CU HI N TP CHNG 5 ........................................................................................ 120 5.9. BI TP CHNG 5 ........................................................................................................ 120 CHNG 6. MY IN KHNG NG B .................................................................... 124 6.1. KHI NIM CHUNG......................................................................................................... 124 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCM6.2. CU TO ........................................................................................................................... 124 6.3. T TRNG QUAY ......................................................................................................... 127 6.3.1. S to thnh t trng quay ............................................................................................. 127 6.3.2. Tnh cht ca t trng quay............................................................................................ 128 6.4. NGUYN L LM VIC.................................................................................................. 129 6.4.1. ng c in khng ng b ........................................................................................... 129 6.4.2. Nguyn l lm vic ca my pht in khng ng b ................................................... 130 6.4.3. Nguyn l lm vic ca ng c khng ng b khi lm vic ch hm in t ...... 130 6.4.4. Cc tnh trng lm vic ..................................................................................................... 131 6.5. CC PHNG TRNH CN BNG IN T ............................................................... 132 6.5.1. Phng trnh cn bng in p stator ............................................................................... 132 6.5.2. Phng trnh cn bng in p dy qun rotor ................................................................. 133 6.5.3. Phng trnh cn bng sc t ng .................................................................................. 133 6.6. MCH IN THAY TH NG C KHNG NG B ............................................ 134 6.6.1. Qui i cc i lng rotor v stator ................................................................................ 134 6.6.2. Mch in thay th ng c KB .................................................................................... 135 6.7. GIN NNG LUNG CA MY IN KHNG NG B ................................ 136 6.8. MOMENT QUAY NG C KHNG NG B ......................................................... 137 6.9. M MY NG C KHNG NG B....................................................................... 139 6.9.1. M my ng c KB rotor lng sc .............................................................................. 139 6.9.2. M my ng c KB rotor dy qun ............................................................................. 141 6.10. IU CHNH TC NG C KHNG NG B .............................................. 141 6.10.1. Thay i tn s ............................................................................................................... 142 6.10.2. Thay i s i cc ........................................................................................................ 142 6.10.3. Thay i in p ............................................................................................................. 142 6.10.4. Thay i in tr ph ni vo rotor................................................................................ 142 6.11. CU HI N TP CHNG 6 ...................................................................................... 143 6.12. BI TP CHNG 6 ...................................................................................................... 143 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMC CH H N NG G 7 7. . MY IN NG B .................................................................................... 146 7.1. CU TO ........................................................................................................................... 146 7.1.1. Phn tnh(stato)................................................................................................................. 146 7.1.2. Phn quay (Rotor)............................................................................................................. 146 7.1.3. Cc b phn ph ............................................................................................................... 147 7.2. NGUYN L LM VIC.................................................................................................. 147 7.2.1. My pht in ng b ..................................................................................................... 147 7.2.2. Phn ng phn ng ca my pht in ng b ............................................................... 148 7.3. M HNH TON HC CA MY PHT NG B .................................................... 149 7.3.1. Phng trnh in p ca my pht in ng b cc li ................................................ 149 7.3.2. Phng trnh in p ca my pht in ng b cc n................................................. 150 7.4. CNG SUT IN T CA MY PHT IN NG B ........................................ 150 7.4.1. Cng sut tc dng ........................................................................................................... 150 7.4.2. Cng sut phn khng ...................................................................................................... 150 7.4.3. c tnh ca my pht in ng b ................................................................................ 151 7.5. S LM VIC SONG SONG CA CC MY PHT IN NG B...................... 151 7.6. NG C NG B ........................................................................................................ 152 7.6.1. Nguyn l lm vic........................................................................................................... 152 7.6.2. iu chnh h s cng sut ca ng c in ng b..................................................... 152 7.6.3. M my ng c in ng b ......................................................................................... 152 7.7. CU HI N TP CHNG 7 ........................................................................................ 153 7.8. BI TP CHNG7 ......................................................................................................... 153 CHNG 8. MY IN MT CHIU................................................................................ 156 8.1. CU TO ........................................................................................................................... 156 8.1.1. Phn tnh (Stator).............................................................................................................. 156 8.1.2. Phn quay (Rotor)............................................................................................................. 156 8.1.3. C gp v chi in .......................................................................................................... 157 8.2. NGUYN L LM VIC.................................................................................................. 157 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCM8.2.1. Nguyn l lm vic v phng trnh cn bng in p ca my pht in mt chiu ..... 157 8.2.2. Nguyn l lm vic v phng trnh cn bng in p ca ng c in mt chiu ....... 158 8.3. QUAN H IN T TRONG MY IN MT CHIU ............................................... 159 8.3.1. Sc in ng phn ng ................................................................................................... 159 8.3.2. Cng sut in t, moment in t ca my in mt chiu ........................................... 160 8.4. PHN LOI MY IN MT CHIU............................................................................ 160 8.4.1. My pht in mt chiu kch t c lp ......................................................................... 161 8.4.2. My pht in kch t song song ...................................................................................... 162 8.4.3. My pht in kch t ni tip .......................................................................................... 163 8.4.4. My pht in kch t hn hp ......................................................................................... 163 8.5. NG C IN MT CHIU ......................................................................................... 164 8.5.1. M my ng c in mt chiu ...................................................................................... 164 8.5.2. iu chnh tc ng c in mt chiu ....................................................................... 165 8.5.3. ng c in kch t song song ....................................................................................... 165 8.5.4. ng c kch t ni tip ................................................................................................... 166 8.5.5. ng c kch t hn hp .................................................................................................. 167 8.6. CU HI N TP CHNG 8 ........................................................................................ 168 8.7. BI TP CHNG 8 ........................................................................................................ 168 TI LIU THAM KHO Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 1. Nhng Khi nim c bn v mch in 1 CHNG 1 NHNG KHI NIM C BN V MCH IN 1.1.KHI NIM CHUNG 1.1.1.nh Ngha V Mch in -Mch in:l mt h thnggm cc thit b in, in tghpli. Trong xy ra cc qu trnh truyn t, bin i nng lng hay tn hiu in t o bi cc i lng dng in, in p. 1.1.2.Kt Cu Hnh Hc Ca Mch in: -Nhnh: l 1 on mch gm nhng phn t ghp ni tip nhau, trong c cng 1 dng in chy thng t u n n u kia. -Nt: l giao im gp nhau ca 3 nhnh tr ln. -Vng (mch vng): l mt li i khp kn qua cc nhnh. Vd1.1:Chomchinnhhnhv(1-1).Hychobitmchintrncbao nhiu nhnh, bao nhiu nt v bao nhiu vng? Gii Mch in trn gm: 3 nhnh: Nhnh 1: gm phn t R1 mc ni tip vi ngun E1 Nhnh 2: gm phn t R2 mc ni tip ngun E2 Nhnh 3: gm phn t R3. 2 nt: A v B 3 vng: Vng 1: qua cc nhnh (1, 3, 1) Vng 2: qua cc nhnh (2, 3, 2) Vng 3: qua cc nhnh (1, 2, 1) Vd1.2:Chomchinnh hnh(1-2).Hychobitmch in trn c bao nhiu nhnh, bao nhiu nt v bao nhiu vng? E1 E2 R1R2 R3 I1 I2 I3 A B Hnh 1-1 E1E2 R1 R2 R3 R4R5 R6 A B C D Hnh 1-2 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 1. Nhng Khi nim c bn v mch in 2 Gii Mch in trn gm: 6 nhnh: Nhnh 1: gm phn t R1 mc ni tip vi ngun E1 Nhnh 2: gm phn t R2 mc ni tip ngun E2 Nhnh 3: gm phn t R3 Nhnh 4: gm phn t R4 Nhnh 5: gm phn t R5 Nhnh 6: gm phn t R6 4 nt (4 nh): A, B, C, D 7 vng: Vng 1: qua cc nhnh (1, 6, 4, 1) Vng 2: qua cc nhnh (2, 5, 6, 2) Vng 3: qua cc nhnh (1, 2, 3) Vng 4: qua cc nhnh (1, 2, 4, 5) Vng 5: qua cc nhnh (4, 5, 3) Vng 6: qua cc nhnh (1, 6, 5, 3, 1) Vng 7: qua cc nhnh (2, 6, 4, 3, 2) Mch in c 2 phn t chnh l ngun in v ph ti. -Ngun in: l cc thit b in dng bin i cc dng nng lng khc sang in nng, v d nh pin, c qui (nng lng ha hc), my pht in (nng lng c hc) -Phti:lthitbinbininnngthnhccdngnnglngkhc.Trns chng thng c biu th bng mt in tr R. -Dy dn: l dy kim loi dng ni t ngun n ph ti. 1.2.CCILNGCTRNGCHOQUTRNHNNGLNGTRONG MCH IN1.2.1.Dng in Dng in l dng cc in tch chuyn di c hng di tc dng ca in trng. Qui c: Chiu dng in hng t cc dng v cc m ca ngun hoc t ni c in th cao n ni c in th thp. Cng dng in I l i lng c trng cho ln ca dng in. Cng dng in ctnhbnglngintchchyquatitdinthngcavtdntrongmtnvthi gian.dtdqI = ( 1-1) n v ca dng in l ampe (A). Bn cht dng in trong cc mi trng : -Trongkimloi:lpngoi cngcanguyntkimloicrttelectron,chnglin ktrtyuvi cc ht nhnvdbtrathnhcc electrontdo.Ditcdngca in trng cc electron t do ny s chuyn ng c hng to thnh dng in. -Trong dung dch: cc cht ho tan trong nc s phn ly thnh cc ion dng t do v cc ion m t do. Di tc dng ca in trng cc ion t do ny s chuyn ng c hng to nn dng in. Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 1. Nhng Khi nim c bn v mch in 3 -Trong cht kh: khi c tc nhn bn ngoi (bc xla, nhit) tc ng, cc phn t chtkhbionhotothnhcciontdo.Ditcdngcaintrngchngs chuyn ng to thnh dng in. 1.2.2.in p in p l i lng c trng cho kh nng tch ly nnglng ca dng in.Trong mch in, ti cc im u c mt in th nht nh. Hiu in th gia hai im gi l in p U. Ta c: UAB = A - B(1-2) Trong :A: in th ti im A B: in th ti im B UAB: hiu in th gia A v B Qui c: Chiu in p l chiu t im c in th cao n im c in th thp. n v in p l vn (V). K hiu: U, u(t). 1.2.3.Cng sut Cng sut P l i lng c trng cho kh nng thu v pht nng lng in trng ca ng in. Cng sut c nh ngha l tch s ca dng in v in p: -Nu dng in v in p cng chiu th dng in sinh cng dng P > 0 (phn t hap thu nng lng)-Nu dng in v in p ngc chiu th dng insinh cng m P < 0 (phn t pht nng lng)nvcngsutlwatt(W).ivimchinxoaychiu,cngthctnhcngsuttc dng nh sau cos . I . U P = (1-3) Trong: U : l in p hiu dng . I : l dng in hiu dng. cos l h s cng sut, vi = +u - +i (vi +u l gc pha u ca in p v +il gc pha u ca dng in). R UAB AB I Hnh 1-3. in p v dng in trn in tr Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 1. Nhng Khi nim c bn v mch in 4 1.3.CC PHN TC BN CA MCH IN: 1.3.1.in tr R: c trngcho hin tng tiu tn nng lng K hiu: Ri R hocn v: O (ohm) 1.3.2.in dn: Y hoc G G= RY1=mho(u) 1.3.3.Cun Dy + K hiu: L: in cm ca cun dy n v: Henry (H)1mH=10-3H in cm L: c trng cho kh nng to nn t trng ca phn t mch in -Tnh cht: gi I l dng in i qua cun dy u: l in p t gia 2 u cun dy ta c: u = L.dtdi(1-4) di/dt: ch s bin thin ca dng in theothi gian -Tnhcht: tcngthc(1-4) inpgia2ucundy t lvi s binthinca dng in theo thi gian. -Lu:Trongmchin1chiuth inpgia2umchinbng0.Trongmch in 1 chiu nu t cun dy th coi nh mch b ni tt 1.3.4.in Dung : +T in: c trng cho hin tng tch phng nng lng in trng. K hiu: C C: in dung ca t in n v: Farad (F) 1F = 10-6F 1nF = 10-9F 1pF = 10-12F Gi u l in p t gia 2 u ca t in Ta c: q= c.utrong : q: in tch trn t dtducdtdq= (1-5) L UL Hnh 1-5 C UC Hnh 1-6 R Hnh 1-4a,b Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 1. Nhng Khi nim c bn v mch in 5 idtdqm =dtdu. c i = (1-6) Tnh cht dng in i qua t t l vi s bin thin ca in p trn t. 1.3.5.Ngun c Lp: ngha ca c lp: l gi tr ca ngun khng ph thuc bt k vo phn t no trong mch. a)Ngun p mt chiu: K hiu:

E: l gi tr ca ngun p n v: Volt (V) b)Ngun p xoay chiu: K hiu:

Mang du + v l v ti thi im gc th t = 0 chiu in p c dng nh hnh v Chiuscinnge(t)itim cin th thpnim cin th cao(ngc chiu vi in p) c) Ngun dng: K hiu: I: l gi tr ca ngun dng, n v Ampe (A) 1.3.6.Ngun ph thuc Ngun p ph thuc:K hiu: E E U Hnh 1-7a, b. Hoc u(t)e(t) hoac Hnh 1-8a, b j(t) Ihoac Hnh 1-9a, b : Ch chiu ca dng in Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 1. Nhng Khi nim c bn v mch in 6 Ngun dng ph thuc:K hiu: + Ngun p iu khin ngun p: (Ngun p ph thuc p) K hiu: VCVS (Voltage control voltage source) Phn t ny pht ra in p U2 ph thuc vo in p U1 (KhiU1 thay i th in pU2 thay i theo) theo biu thc : U2 = oU1o: khng c th nguyn + Ngun p iu khin ngun dng: (Ngun dng ph thuc p) K hiu:VCCS (Voltage controlled curent source) Phn t ny pht ra dng I2 ph thuc vo in pU1 (KhiU1 thay i th dng in I2 thay i theo) theo h thc: I2 = gU1. n v o ca g l Siemen (S) hoc mho (u) + Ngun dng iu khin ngun dng: (Ngun dng ph thuc dng) K hiu: CCCS (Current - controlled current source) Phn tnyphtradngI2phthucvodngI1(KhiI1thayith dnginI2thayi theo) theo biu thc: I2 = |I1|: khng c th nguyn + Ngun dng iu khin ngun p: (Ngun p ph thuc dng)U1 oU1oU1 RU2 Hnh 1-10 U1 gU1g I2 Hnh 1-11 I1 |I1 R I2 Hnh 1-12 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 1. Nhng Khi nim c bn v mch in 7 K hiu: CCVS (Current - controlled voltage source) Phn t ny pht ra in p U2 ph thuc vo dng in I1 (Khi I1 thay i th in p U2 thay i theo) theo biu thc: U2 = R I1 .n v o R l ohm (O) 1.4.CC NH LUT C BN CA MCH IN1.4.1.nh lut ohm: Khi cho dng in i qua in tr R,Ul in p t gia 2 u R theo nh lut ohm ta c: U = I . R (1-7) 1.4.2.nh Lut Kirchhoff 1: (nh Lut Nt) Tng i s dng in ti 1 nt bng 0:= 0 i (1-8) V d 1-3: Cho mch in hnh (1-15) xt ti nt A: theo nh lut Kirchhoff 1 ta c: V d 1-4: Cho mch in hnh (1-16) xt ti nt A: theo nh lut Kirchhoff 1 ta c: I1 RI1RU2 Hnh 1-13 I1 I3 I2 A I1 + I2 + I3 = 0 Hnh 1-15 U R Hnh 1-14 I1 I3 I2 A I1 I2 + I3 I4= 0 I4 Hnh 1-16 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 1. Nhng Khi nim c bn v mch in 8 + Nu ta qui c dng in i vo ntA mang du cng (+), th dng in i ra nt A mang du tr (-) hoc ngc li. 1.4.3.nh lut Kirchhoff 2: Tng i s in p ca cc phn t trong 1 vng kn bt k th bng 0 = 0 u (1-9) V D 1-5: Cho mch in nh hnh (H.1-17) Xt vng 1 (a,b,c,a) theo nh lut Kirchhoff 2 ta c: Uab + Ubc + Uca = 0 Xt vng 2 (a,d,b,a) theo nh lut Kirchhoff 2 ta c: Uad + Udb + Uba = 0 V D 1-6: Cho mch in nh hnh v (H.1-18) Dng cc nh lut c bn tm dng in qua cc nhnh I1, I2 v I3 Gii Ti nt a: theo nh lut Kirchhoff 1 ta c: I1 I2 I3 = 0 (1) Gi s ta xt vng kn l1 (a, b, c, a) theo nh lut Kirchhoff 2 ta c: Uca + Uab + Ubc = 0(2) I1R1 + I2 R2 + (- E1) = 0(2) Kho st vng kn l2 (a, d, b, a) theo nh lut Kirchhoff 2 ta c: Uad + Udb + Uba = 0(3) I3R3 + E2 + (- I2R2) = 0 (3) Gii h 3 phng trnh (1), (2), (3) ta tm c dng in qua cc nhnh I1, I2 v I3. E1 E2 R1R2 R3 I1 I2 I3 a b c d vng 1vng 2 Hnh 1-17 E1 E2 R1 R3 R2 I1 I2 I3 a b c d l1 l2 Hnh 1-18 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 1. Nhng Khi nim c bn v mch in 9 1.5.BI TP V D CHNG 1 Bi 1.1: Cho mch in nh hnh (H1-19) Dng nh lut Kirchhoff 1 v 2 tm i v Uab. Gii Ti nt c: theo nh lut Kirchhoff 1 ta c: 04121 I1= + + I1 = 1 3 = 4 (A) Ti nt d: I2 = I1 + 6 = 4 + 6 = 2 (A) Ti nt e: I2 + 1 = I I = 2 +1 = 3 (A) Vy I = 3 (A) Theo nh lut Kirchhoff 2 ta c: Uab = Uae + Ued + Udc + Ucb = (I).3 + ( I2).2 + ( I1).5 + 12 = 9 4 20 + 12 = 19 (V) Vy Uab = 19 (V) Bi 1.2: Cho mch in nh hnh (H1-20) Dng nh lut Kirchhoff 1 v Kirchhoff 2 tm I v R. Gii p dng nh lut K2 vng (A,E,A) ta c: 2.8 + 8 - 6 - I1.6 = 0 I1 = 618 = 3A ab cd 1A6A 1A+-e O 3O 2O 5O412V I1 I2 I Hnh 1-19 I1 I3I4 I5 O 6V 8 V 6O8O 4O11RA 16AB CV 2IA I 22 =Ea b I1 I3I4 I5 O6V8 V6O8O 4O11RA16A ECV2IA I 22 =Ea b Hnh 1-20 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 1. Nhng Khi nim c bn v mch in 10 p dng nh lut K1 ti A ta c: I3 = I1 + I2 = 3 + 2 = 5A p dng nh lut K2ti vng (B,E,A,B) ta c: I4.11 I2.8 I3.4 = 8V I4.11 2.8 5.4 = 8V I4 = 1144 = 4A p dng nh lut K1 ti B: I5= I4+I3 = 4+5= 9A p dng nh lut K1 ti C: I = 16 I5 = 16 9 = 7A p dng nh lut K2theo vng (C,B,E,C): I4.11 I.R = 2 4.11 7.R = 2 R = 72 44 = 6O p s:I = 7A R = 6O Bi 1.3: Cho mch in nh hnh (H1-21) IIII5632I4I1I-+2A+-18V4A3A634URA B Tm cng dng in chy trong cc nhnh v in p U t trn in tr R. Bit rng I = 1A. Gii Ti nt A theo nh lut Kirchhoff 1: I1 + I + I4 = 0(1) Bit rng:I = 1A I4 = 3A Thay vo (1) ta c: I1 + 1 3 = 0 I1 = 3 1 = 2A Ta c: I1 = I3 + I2 = I2 + 4 I2 = I1 4 = 2 4 = 2 A Ti nt B theo nh lut Kirchhoff 1 ta c: I1 I5 + I6 = 0 Hnh 1-21 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 1. Nhng Khi nim c bn v mch in 11 M: I6 = 2AI5 = I1 + I6 = 2 + 2 = 4Ap dng nh lut Kirchhoff 2 ti vng kn ta c: 6I + 18 + U UB UAB = 0 (2) Trong : UAB =V 12 4 3 = V:UB = V 8 4 2 = Thay vo phng trnh (2) tm c in p t trn in tr R. 4V 18 1 6 8 12 U = + = Bi 1.4: Cho mch in nh hnh (H1-22) I3I2I1BA+-9V60120 20III Tm dng in chy trong cc nhnh I1, I2, I3. Gii Ti nt A theo nh lut Kirchhoff 1 ta c: I1 I2 I3 = 0(1) Vit phng trnh theo nh lut Kirchhoff 2 cho vng I 20I1 + 60I2 = 9 (2) Vit phng trnh theo nh lut Kirchhoff 2 cho vng II 120I3 60I2 = 0(3) Gii h phng trnh (1), (2), (3): I1 I2 I3 = 0(1) 20I1 + 60I2 = 9 (2) 120I3 60I2 = 0(3) T phng trnh (2) ta suy ra: I2 = 6020I 91(4) Ly phng trnh (2) + phng trnh (3) ta c: 20I1 + 120I3 = 9(5) Thay phng trnh (4) vo phng trnh (1) ta c:I10 I6020I 931= 80I1 60I3 = 9(6) Gii h phng trnh (5), (6) ta c: Hnh 1-22 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 1. Nhng Khi nim c bn v mch in 12 Nhn phng trnh (6) vi h s 2 ri cng vi phng trnh (5) ta c: I1 =A 15 . 020 1609 18=++ Thay gi tr I1 = 0.15A vo phng trnh (5) ta c: I3 =A 05 . 012015 . 0 20 9120I 20 91= = Thay gi tr I1 = 0.15A v I3 = 0.05A vo phng trnh (4) ta c: I2 =A 10 . 06015 . 0 20 960I 20 91= = I2 = 0.10A 1.6.BI TP CHNG 1 Bi 1-5: Cho mch in nh hnh (H1-23) O 95500ab+-UoO1I 992I1I2V Dng nh lut K1, K2 tnh U0 v I2 p s: U0 = 95 v I2 = 1,9V Bi 1-6: Cho mch in nh hnh (H1-24) Dng nh lut K1, K2 tnh I1, I2 v I3

p s: I1 = 5A I2 = -11AI3 = I2 I1 = -16ABi 1-7: Cho mch in nh hnh (H1-25) Hnh 1-23 O5abO2I1I31V+-3I1u41O10+-1u10OHnh 1-24 O ab OO 2 I1I31 V3II1 +-8 4 6 2IIIHnh 1-25 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 1. Nhng Khi nim c bn v mch in 13 Dng nh lut K1, K2 Tm I1, I2, I3

p s:I1 = 210.2 =10A;I3 = I1 I2 = 10 (-2) = 12AI2 = -2A Bi 1-8: Cho mch in nh hnh (H1-26) Dng nh lut K1, K2 Tm dng in qua cc nhnh I1, I2, I3 p s: I2 = 2AI1 = 2I2 = 4AI3 = 4 + 2 - 5 =1A Bi 1-9:Cho mch in nh hnh (H1-27) Dng nh lut K1, K2 Tm dng in trong cc nhnh I1, I2 v I3 p s: I2 = 0,1A I1 = 1015.0,1= 0,15A I3 = I1 I2 = 0,15 0,1 = 0,05A O abOO2I1I3I II I24V 5A 6 312Hnh 1-26 O abO O2 I1I4,5V 3 I306010IIIHnh 1-27 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 2. Mch in xoay chiu mt pha 14 CHNG 2 MCH IN XOAY CHIU HNH SIN MT PHA Dnginsinldnginxoaychiubinitheoquyluthmsinbinthintheothi gian. Trong k thut v i sng dng in xoay chiu hnh sin c dng rt rng ri v n c nhiu u im so vi dng in mt chiu. Dng din xoay chiu d dng chuyn ti i xa, d dng thay i cp in p nh my bin p. My pht in v ng c in xoay chiu lm vic tin cy, vn hnh ngin, ch s kinh t - k thut cao. Ngoi ra trong trng hp cn thit, ta c th d dng bin i dng in xoay chiu thnh mt chiu nh cc thit b chnh lu. 2.1. CC NH NGHA V DNG IN XOAY CHIU HNH SIN -Dng in xoay chiu l dng in c chiu v tr s thay i theo thi gian. -Dng in xoay chiu bin thin theo quylut hnh sin theo thigian c gil dng in xoay chiu hnh sin, c biu din bng th hnh sin trn hnh (2-1). i = Imax sin (et + +i)(2-1) trong : i: l tr s tc thi ca dng in. Imax: l gi tr cc i ca dng in (hay l bin ca dng in) e: l tn s gc : l gc pha ban u ca dng in 2.1.1.Chu k, tn s, tn s gc Chu k: L khong thigian ngn nht dng in lp li tr s v chiu bin thin c. Chu k c k hiu l T, n v: giy (s). Tn s: L s chu k m dng in thc hin c trong mt n v thi gian (trong 1 giy). Tn s c k hiu l f. Ta c:f = T1 (Hz)(2-2) n v l hertz, k hiu Hz. Imax i i 0 T et Hnh 2-1. Dng in xoay chiu hnh sin Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 2. Mch in xoay chiu mt pha 15 Tn s gc: L tc bin thin ca dng din hnh sin. Tn s gc c k hiu l e, n v l rad / s. Quan h gia tn s gc v tn s:e = 2. t. f(2-3) 2.1.2.Tr s tc thi ca dng in Tr s tc thil tr s ng vi thi im t, k hiu l i.Trong biu thc (2-1) tr s tc thi ph thuc vo bin Imax v gc pha (et + +i). -Bin Imax l tr s cc i ca dng in i, cho bit ln ca dng in.-Gc pha (et ++i) ni ln trng thi ca dng in ngay ti thi im t. thi im t = 0 th gc pha ca dng inl +i. +igi lgc pha ban u ca dng in. Gc pha ban u + ph thuc vo thi im chn lm gc thi gian. Hnh 2-2 ch ra gc pha ban u +i khi chn cc mc thi gian khc nhau. Hnh 2-2. Gc pha ca dng in ng vi cc mc thi gian khc nhau 2.1.3.Gc lch pha gia in p v dng in Gia s cho dong ien i = Imax sin (et ++i) va u = Umax sin (et ++u).Trong : Umax, +u l bin v gc pha ca in p.Hay bieu dien goc lech pha gia u va i. -ebie u die n goclechphagia2ail ngieu hoachung phaicocungtan so goc, cung ham sin hoac ham cos. -Goc lech pha gia ien ap va dong ien ky hieu la = (et ++i) (et ++u) = 1 2(2-4) Gc ph thuc vo cc thng s ca mch. Khi: > 0 in p vt trc dng in 0 i = 0Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 2. Mch in xoay chiu mt pha 16 V d 2-1: Cho hai i lng iu ha c cng tn s gc u = 100 sin (2t + 600) i = 20 sin (2t + 300) Hy biu din gc lch pha gia in p v dng in. Gii: Ta c: = u i = 600 300 = 300 Vy: u nhanh pha hn i mt gc 300. V d 2-2: Cho hai i lng iu ha c cng tn s gc u = 100 sin (2t + 600) i = 20 cos 2t Hy biu din gc lch pha gia in p v dng in. Gii: Do u v i khng cng dng sin v cos nn ta phi chuyn sang dng cos hoc sin Ta i: i = 20 cos2t = 20 sin(2t + 900) = u i = 600 900 = 300 Vy: u chm pha hn i mt gc 300 +Ch:so snh gclchphagia2ilngiuhath chngphi ccng tns gc; cng dng sin hoc dng cos. 2.1.4.Tr s hiu dng ca dng in Tr s hiu dng ca dng in xoay chiu l gi tr tng ng ca dng in mt chiu khichngiquacngmtintrtrongthigianmtchukth tora cngmtnng lng di dng nhit nh nhau. K hiu bng ch in hoa: I, U, E -Tr s hiu dng ca dng in hnh sin: u,i i u 0 > 0u,i u i t 0 < 0t u,i u i 0 t = 0u,i i u 0 = tt Hnh 2-3. Gc lch pha gia in p v dng in Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 2. Mch in xoay chiu mt pha 17 I = 2maxI = 0,707 Imax(2-5) -Tng t ta c tr s hiu dng ca in p v sc in ng xoay chiu hnh sin l: U = 2Umax = 0,707 Umax(2-6) E = 2Emax = 0,707 Emax(2-7) Ch : phn bit, cn ch cc k hiu: -i, u: Tr s tc thi, k hiu ch thng. -I, U: Tr s hiu dng, k hiu ch in hoa -Imax ,Umax: Tr s cc i (bin ). 2.2. BIU DIN DNG IN XOAY CHIU HNH SIN BNG VECT T biu thc tr s tc thi ca dng in. i = Imax sin (et ++i ) = I 2 sin (et ++i) Ta thy khi tn s cho, nu bit tr s hiu dng I, v pha u +i, th i hon ton xc nh. Vectcctrngbi di (ln,mun)vgc(argument),ttacthdng vct biu din dng in hnh sin (hnh 2-4). di cavectcbiudinbngtr s hiudng,gccavectvi trc Oxbiudin gc pha ban u. K hiu nh sau: Vect dng in: I= I Z +i Vect dng in: U= U Z +u V d 2-3: Hy biu din dng in, in p bng vect v ch ra gc lch pha, cho bit: i = 20 2 sin (et -100)(A) u = 100 2 sin (et +400) (V) Gii: Vect dng in: I= 20 Z -10o

Hnh 2-4. Biu din vect ca in p v dng in x 0 i u U I Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 2. Mch in xoay chiu mt pha 18 Vect in p:U = 100 Z 40o

Biu din chng bng vect trn hnh 2-5. Gc lch pha gia in p v dng in l gc gia hai vect UvIPhng php biu din vect gip ta d dng cng hoc tr cc i lng dng in, in p xoay chiu hnh sin (thc hin cho cc i lng hnh sin c cng tn s goc). V d 2-4: Tnh dng in i3 trn hnh 2-6a. Cho bit tr s tc thi i1 = 16 2sin et; i2 = 12 2sin (et + 900). Gii: p dng nh lut Kirchhoff 1 ti nt ta c: i3 = i1 + i2 Ta khng th cng trc tip tr s tc thi cho, m phi biu din chng thnh vect nh hnh 2-6b. 1I= 16 00 Z 2I= 12 090 ZRi tin hnh cng vect 2 1I I I + =Tr s hiu dng ca dng in I3 l: I3 =A = + 20 16 122 2 Gc pha ca dng in i3 l: 0 3 2I3I1Ix i1 i3 i2 a) b) Hnh 2-6. Vect dng in i3 = i1 + i2 0 x 400 U I -100 100V 20A Hnh 2-5. Vect ca in p v dng in theo v d 2-3 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 2. Mch in xoay chiu mt pha 19 0,751612tg3= =0387 , 36 = +Bit tr s hiu dng I v gc pha u +I ta xc nh d dng tr s tc thi. Vy tr s tc thi ca dng in i3 l: i3 = 20 ( )087 , 36 t sin 2 + .(A) Vicngdngvectbiudinccilngiuha,vccquanhtrongmchin cng nh gii mch in s c cp trong cc mc tip theo.

2.3. DNG IN XOAY CHIU QUA IN TR THUN R Mch in xoay chiu thun in tr l mch in xoay chiu c h s t cm rt nh c th b qua, khng c thnh phn in dung, trong mch ch cn mt thnh phn in tr nh bng n, bp in Gi s cho dng in xoay chiu i = Imax sinet i qua in tr R(2-8) u: l in p t gia 2 u in tr.Theo nh lut Ohm ta c: uR = R . i uR = R . Imax sinetM Umax = Imax . R(2-9) uR = Umax sinet(2-10) So snh biu thc dng in i v in p uR, ta thy: gc lch pha gia in p v dng in: = u i = 0 (Hnh 2-8) Kt lun: u cng pha vi i Hnh 2-7. Mch thun tr uR uR i t 0 x UR y I T/2 T a) iR uR uR, iR, b) Hnh 2-8. th ca mch xoay chiu thun tr Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 2. Mch in xoay chiu mt pha 20 2.4. DNG IN XOAY CHIU QUA CUN DY THUN CM Mch thun cm l mch in c cun dy c h s t cm L kh ln, in tr R kh nh c th b qua. Gi s cho dng in xoay chiu i qua cun dy (hnh 2-9), dng in i c dng: i = Imax sinet(2-11) u: l in p t gia 2 u cun dy DnginbinthiniquacundyLlm xuthinscinngtcmeLvgiahai u cun dy s c in p cm ng uL

t . cos . . I . Ldt) t . sin . I ( dLdtdiL ummL = = = .(2-12) )2t . sin( . U umL L + = (2-13) Vi ULm = Im .L.e(2-14) Trong o:XL = eL(2-15) XL: la cam khang cua cuon day co n v la Ohm() Sosnh biu thc dng in i (2-11) v in p uL(2-13), ta thy: u nhanh pha hn I mt gc 2. o th hnh 2-10 L u uL i Hnh 2-9. Mch in xoay chiu thun cm a) 0 UL I et p, uL, iL iL uL 0 2 t 2t b) Hnh 2-10 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 2. Mch in xoay chiu mt pha 21 2.5. MCH IN XOAY CHIU THUN IN DUNG. Mchinxoay chiuthunindunglmchinch cindungCvin trnhcoi nh khng ng k.Gi s khi c dng in: i = Im.sinet (2-16)quatinthunindungC(hnh2-11),in p trn t in l: ) t . sin( IC .dt . t . sin ICidtCum m C21 1 1 = = =} }(2-17) |.|

\| =2 t . sin UCm ViCm m m CmU . . C I IC .U = =1.(2-18) So snh biu thc dng in i v in p uC, ta thy: -Quan h gia tr s hiu dng ca in p v dng in l: I = C.e.Uc = CC CXUC .U=1(2-19) ViXC = C . 1(2-20) -XC: c gi l dung khng ca t in c n v l ohm (O). -Dng in i v in p uC c cng tn s, dng in i vt trc in p uC mt gc l 2 (hocinpchmsaudngingcpha 2). th vectinpvdngincv trn hnh 2-12a. uuC i C Hnh 2-11. Mch in xoay chiu thun in dung Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 2. Mch in xoay chiu mt pha 22 2.6. MCH IN XOAY CHIU GM R - L - C MC NI TIP Mch xoay chiu khng phn nhnh, trng hp tng qut c c ba thnh phn l R, L, C mc ni tip vi nhau.Gi s khi t in p xoay chiu, trong mch s c dng in l: i = Im.Sin(et) ChytrongnhnhR,L,Cmcnitip,sgyrain pri trnin truR,trnin cm uL, trn in dung uC (hnh 2-13). Cc i lng dng in v in p u bin thin theo hnh sin v cngmt tn s. Do c th biu din chng trn cngmt th vect trn hnh 2-14a. Ta c:u = uR + uL + uC

Hay biu din bng vectC L RU U U U + + =Tam gic vung OAB c cnh huyn l vc t in p tng, hai cnh gc vung l hai in p thnh phn (tc dng v phn khng) c gi l tam gic in p ca mch xoay chiu c R - L - C mc ni tip vi nhau. u uC i R uLuR LC Hnh 2-13. Mch xoay chiu R-L-C mc ni tip0 et IC 0 t/2 t2t p, uC, iC iC pC uC UC a)b) Hnh 2-12. th ca mch in xoay chiu thun in dung Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 2. Mch in xoay chiu mt pha 23 T tam gic in p ta c: 2 2 2 2) U U ( U U U UC L R X R + = + = 2 2) X . I X . I ( ) R . I ( UC L + = 2C L2) X (X R I U + =T ta c: ZU) X X ( RUIC L= +=2 2(2-21) y l nh lut ohm cho mch xoay chiu c R, L, C mc ni tip nhau. Trong : fC 21fL 2 X X XC L = = (2-22) c gi l in khng ca mch. 2C L2) X (X R Z + ==2 2X R + (2-23) c gi l tng tr ca mch. Tbiuthc(2-23)tacthbiudinchngln3cnhcamttamgicvung,trong tngtrZlcnhhuyn,cnhai cnhgcvunglintrRvinkhngX, giltam gic tng tr (hnh 2-14b). Tam gic tng tr gip ta d dng nh cc quan h gia cc thng s R, X, Z v gc lch pha . Gc lch pha gia in p v dng in c xc nh nh sau:RC LRXUU UUUtg= = (2-24a) HayRX XRX tgC L = = (2-24b) Trong mch xoay chiu hn hp (R - L - C mc ni tip) dng in v in p lch pha nhau mt gc . Biu thc in p c dng: u = Um.Sin (et+)(2-25) -Nu XL > XC th UL > Uc , > 0 in p vt trc dng in mt gc (hnh 2-14a), mch c tnh cht in cm. -Nu XL < XC th UL UL v khi UL = UC a C thc +j o -j +1 0 b -1 Hnh 2-16. Mt phng ta biu din s phc Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 2. Mch in xoay chiu mt pha 25 a. Dng i s jb a C + =- Trong :a l phn thc;jb l phn o vi j2 = -1 v a,b l s thc. b.Dng m Z = =-C Ce Cj Trong : C l m un ( ln) ol Agument (gc) i t dng i s sang dng m C= a + jb C= je C = CZTrong : C = abarctg ; b a = + 2 2 V d 2-5: ChoC= 3 + j 4. Hy chuyn sang dng hm mC= CZGii: Ta c:C = 2 2 2 24 3 b a + = += 5 o = 34arctgabarctg == 530 Vy:C= 5Z530 V d 2-6: ChoC= 8 j6. Hy chuyn sang dng hm mC= CZGii: Ta c:C = 2 2 2 26) ( 8 b a + = += 10 o =)86arctg(abarctg == 370 Vy:C= 10Z 370 V d 2-7: ChoC= j10. Hy chuyn sang dng hm mC= CZGii: Ta c:C = 2 2 2 210 0 b a + = += 10 o =)010arctg(abarctg == 2 Vy:C= 10Z900 i t dng m sang dng i s Z = =-C e C CjC= a + jb a =C cos; b =C sino Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 2. Mch in xoay chiu mt pha 26 V d 2-8: ChoC=10Z450. Hy chuyn sang dng i sC= a + jb Gii: Ta c:a = 10. cos450 = 5 2b = 10. sin450 = 5 2Vy:C=5 2 + j5 2 V d 2-9: ChoC=10Z900. Hy chuyn sang dng i sC= a + jb Gii: Ta c:a = 10. cos( 90 0) = 0 b = 10. sin( 90 0) = 10 Vy:C= 0 j10 = j10 2.7.2.Mt s php tnh i vi s phc a. Cng, tr s phc cng(tr)s phc, tabinichngvdngi s ricng(tr)phnthc vi phn thc, phn o vi phn o. V d 2-10: Cho 1C= a1+ jb1 v 2C= a2+ jb2. Hy thc hin php cng (tr) 2 s phc Ta c:C= 1C + 2C= (a1+ jb1) + (a2+ jb2) = (a1 + a2) + j(b1 + b2)C= 1C + 2C= (a1+ jb1) (a2+ jb2) = (a1 a2) + j(b1 b2)V d 2-11: Cho 1C= 8+ j4 v 2C= 2+ j6. Hy thc hin php cng (tr) 2 s phc Ta c:C= 1C + 2C= (8+ j4) + (2+ j6) = (8 + 2) + j(4 + 6) = 10 + j10 C= 1C 2C= (8+ j4) (2+ j6) = (8 2) + j(4 6) = 6 j2 b. Nhn, chia s phc Khi nhn (chia) ta nn a v dng m: Nhn (chia) hai s phc, ta nhn (chia) mun cn argument (gc) th cng (tr) cho nhau. V d 2-12: Cho 1C= 1C Zo1 v 2C= 2C Zo2. Hy thc hin php nhn (chia) 2 s phc Ta c: C = 1C. 2C= 1C . 2CZo1+o2 C = 21CC = 2 1o o Z21CC V d 2-13: Cho 1C=10Z600 v 2C=2Z300. Hy thc hin php nhn (chia) 2 s phcTa c: C = 1C. 2C= 10. 2 Z600+300 = 20Z900 C = 21CC = 210Z600300 = 5Z300 Nhn (chia) s phc cng c th thc hin di dng i s. Khi nhn ta tin hnh nhn bnh thng nh trong php tnh a thc. V d 2-14: Cho 1C = (a + jb) v 2C= (c + jd). Hy thc hin php nhn 2 s phc Ta c:C = 1C. 2C= (a + jb) (c + jd) = ac +jbc + jad + j2bd = (ac bd) + j(bc +ad) Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 2. Mch in xoay chiu mt pha 27 v j2 = -1 Khi chia ta nhn c t s v mu s vi s phc lin hp ca mu s. V d 2-15: Cho 1C = (a + jb) v 2C= (c + jd). Hy thc hin php chia 2 s phc Ta c:C = 21CC = 2 2d cad) j(bc bd) (acjd) jd)(c (cjd) jb)(c (ajd cjb a+ + +=+ +=++ * Qui tc biu din cc i lng in hnh sin bng s phc Ta c th biu din cc i lng hnh sin bng bin phc hoc hiu dng phc: - Mun ( ln) ca s phc l tr s hiu dnghoc bin (gi tr cc i) - Acrgumen (gc) ca s phc l pha ban u. * S phc: 2.7.3.Biu din cc nh lut di dng di dng s phc a. nh lut Ohm i Z =maxI I: bin phc Dng in i(t) = Imax sin(et + i) i Z =2maxII: hiu dng phc biu din sang s phc u Z =maxU U: bin phc in p u(t) = Umax sin(et + u) u Z =2maxUU: hiu dng phc biu din sang s phc S phc R i R I S phc L i jLe = jXL I S phc C i Cj jC =1= jXC I Hnh 2-17 Sc in ng e(t) = Emax sin(et + e)e Z =maxE E: bin phc e Z =2maxEE: hiu dng phc biu din sang s phc Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 2. Mch in xoay chiu mt pha 28 RUI--=b. nh lut Kirchhoff 1 cho mt ntTng i s cc nh phc ca dng in vo hoc ra 1 nt hoc mt mt kn bt k th bng 0: == nKKI10(2-26) Theo nh lut K1 ta c: 1I 2I 3I = 0(2-27) c. nh lut Kirchhoff 2 cho mch vng kn Tngi s cc nhphccaccin p trn ccphn tdctheott c ccnhnh trong mt vng kn bt k th bng 0: = nKKU1= 0 2.8. PHNG PHP GII MCH IN XOAY CHIU HNH SIN gii cc mch in xoay chiu, mt s phng php sau y thng c s dng: -Phng php th vect -Phng php s phc 2.8.1.Phng php th vect Nidungcaphngphpnylbiudindngin,inp,scinngbngvect, vit cc nh lut di dng vect v thc hin tnh ton trn th vect. 2.8.2.Phng php s phc Biudindngin,inp,scinng,tngtrbngsphc,vitccnhlutdi dng s phc.V d 2-16: Cho mch in hnh 2-19a. Bit: U = 100V, R = 10O, XL = 5O, XC = 10O. Hy tnh dng in qua cc nhnh bng phng phap o th vect va bang so phc Gii:a.Phng php th vect Dng in trong nhnh IR =A 1010100RU= =A 205100XUILL= = =A 1010100XUICC= = =2I 3I 1I Hnh 2-18 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 2. Mch in xoay chiu mt pha 29 thvectcamchincvtrnhnh2-19b.Chnphaucainp 0 =u ,vect U trngvitrcOxvdngin I trngphavivectinp U , vect dng in L I chm sau vect in p Umt gc 900, vect dng inC I vt trc vect in p U mt gc 900 Hnh 2-19. Mch in v th vect v d 2-16 p dng nh lut Kirchhoff 1 ti nt A ta c: C L R I I I I + + = Trc tip cng vect trn th ta c I mch chnh. Tr s hiu dngI 2 210 10 + = = 14,14 (A) b.Phng php s phc: biu din cc nh lut bng s phcLp s phc nh hnh 2-20. Hnh 2-20. Bin i s trong v d 1 di dng s phc p dng nh lut Ohm 0 10100 100RUI0R Z =Z= =-- 000 0LL 90 2090 50 1005 j0 100jXUI Z =ZZ=Z= =-- 000 0CC 90 1090 100 10010 j0 100jXUI Z = ZZ= Z==-- R -jXCjXL I U ICIL A IR ... . . RXC XL i u iCiL A iR IL+IC IC I U IR IL 450 a)b) Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 2. Mch in xoay chiu mt pha 30 p dng nh lut Kirchhoff 1 ti nt A: 00 0CRL14 14,14 10 j 10 10 j 0 20 j 0 0 j 1090 10 90 20 0 10 I I I I Z = = + + + + =Z + Z + Z = + + =- - - - Tr s hiu dng cc dng in l: IR = 10 (A) IL = 20 (A) IC = 10 (A) I = 14,14 (A) V d 2-17: Cho i = 10 2 sin(100t + 300) v u = 100 2 sin(314t - 450). Hy biu din u, i di dng hiu dng phc: Gii: Ta c: 030 10 I Z =-= 10(cos300 + jsin300) = 5 3+j5 045 100 U Z =-= 100[cos(-450) + j sin(-450)] = 50 2- j50 2 V d 2-18: Cho mch in nh hnh v. Tm biu thc dng in i Gii: Mun gii bi ton v mch in xoay chiu ta phi chuyn v s hiu dng phc hocbinphc.Khichuynxongtagii gingnhmchinmtchiuvtrkhng ca chng c cng n v l Ohm (). Ta chuyn v s bin phc Tng tr phc ton mch: Z = 4 + j3 = 5Z370(do in tr R mc ni tip vi cun dy L) 0037 50 10ZUIZZ= = = 2Z 370(A) R = 4 L = 30mH u = 10cos100t(V) i Hnh 2-21 R = 4 jLe = j3 U= 10Z00 I Vi e = 100 Hnh 2-22 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 2. Mch in xoay chiu mt pha 31 Vy dng in chy trong mch l: i(t) = 2 cos(100t 370)(A) V d 2-19: Cho mch in nh hnh v. Tm biu thc dng in i Gii: Ta chuyn v s bin phc Tng tr phc ton mch: Z = 6 + j8 = 10Z530(O)(do in tr R mc ni tip vi t in C) 0053 100 10ZUI ZZ= = = 1Z530(A) Vy dng in chy trong mch l: i(t) = 1 sin(2t + 530)(A) V d 2-20: Cho mch in nh hnh v. Tm biu thc dng in i R = 6 u = 10sin2t(V) i F161 Hnh 2-23 R = 6 00 10 U Z = I 8 jcj = (O) Vi e = 2 Hnh 2-24 R = 4 L = 1H u = 10cos(4t+100) (V) i F41 Hnh 2-25 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 2. Mch in xoay chiu mt pha 32 Gii: Ta chuyn v s bin phc Tng tr phc ton mch: Z = 4 + j4 j = 4 + j3 = 5Z370 (O) (dointrRmcnitipvi cundy Lv t in C) 0037 510 10ZUIZZ= = = 2Z270(A) Vy dng in chy trong mch l: i(t) = 2cos(4t 270)(A) 2.9. CNG SUT 2.9.1.Cng sut tc thi + K hiu: p p = u.i(2-28) trong : u: l in p tc thi ti thi im ang xt i: l dng in tc thi ti thi im ang xt + n v cng sut l Watt (W) 2.9.2.Cng sut tc dng Cng sut tc dng cn gi l cng sut trung bnh hay cng sut tiu th. + K hiu: P P = }Tdt . pT01(2-29) V d 2-21: Xt mt mch in gm R, L, C nh hnh v. Tnh cng sut tc dng ton mch. Ta gi:R = 4 jLe = j4 (O) 010 10Z = U I j Cj = (O) Hnh 2-26 Z i1i2 C R i u L Hnh 2-27 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 2. Mch in xoay chiu mt pha 33 u: l in p tc thi t gia 2 u mch in u = Umax cos(et + u) (V) i: l dng in tc thi chy qua mchi = Imax cos(et + i)(A) p: l cng sut tc thi. Theo nh ngha ta c: p = u.i = Umax Imax cos(et + u).cos(et + i) = 2max maxI U[cos(2et + u + i) + cos(u i) ] = 2max maxI U[cos(2et + u + i) + cos ]Vi = (u i) + Cng sut tc dng: P = }Tdt . pT01= ((

+ + +} }T T0max maxdt ) t cos( dt cosTI U022i u = 2TI Umax max.cos.T(V }+ +T0dt ) t cos(i u 2 = 0) P = U.I .cos(2-30) Trong :U = 2Umax: in p hiu dng I = 2Imax: dng in hiu dng cos : h s cng sut : l gc lch pha gia in p v dng in : l argumen caZ = ZZ (gc caZ) 2.9.3.Cng sut phn khng + K hiu: Q Q = U.I.sin(Var)(2-31) + n v: l Var 2.9.4.Cng sut tiu th v cng sut phn khng trn in tr R Gi s cho dng in i = Imax coset i quain tr R. u: l in p t gia 2 u R. Ta c: p = u.i = i2.R P = R. t cos I2 2max Cng sut tc dng: P = } }=T02 2maxT0t.dt cos RIT1p.dtT1P = ((

+}Tmaxdt ). t cos (TR . I022 12 = ((

+} }T Tmaxdt . t cos dt .TR . I0 022 12P = 22R Imax = R.I2(V }Tdt . t cos02 = 0)(2-32) Vi I = 2maxI : dng in hiu dng Cng sut phn khng trn in tr R: Hnh 2-28. Mch thun tr u R uR i Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 2. Mch in xoay chiu mt pha 34 Q = 0(do = 0 nn sin = 0) 2.9.5.Cng sut tc dng v cng sut phn khng trn cun dy Gi s cho dng in i = Imax coset i quacun dy L.u: l in p t gia 2 u cun dy. Ta c:+ Cng sut tc dng trn cun dy: T biu thc P = U.I.cos P = 0 Do gc lch pha gia u v i khi qua cundy thun cm l = 2 nn cos = 0 + Kt lun: Cun dy khng tiu th in nng + Cng sut phn khng trn cun dy: M U = I.XL Vy QL = 2I .XLVi XL = L.e(2-33) 2.9.6.Cng sut tc dng v cng sut phn khng trn t in Gi s cho dng in i = Imax coset i quat in C.u: l in p t gia 2 u t in. + Cng sut tc dng trn cun dy: T biu thc P = U.I.cos P = 0 Do gc lch pha gia u v i khi qua cundy thun dung l = 2 nn cos = 0 + Kt Lun: T in khng tiu th in nng + Cng sut phn khng trn t in: M U = I. XC Vy Qc = 2I . XCVi XC = C1 (O) (2-34) 2.9.7.Cng sut biu kin S Ngoi cng sut tc dng P v cng sut phn khng Q, ngi ta cn a ra khi nim cng sut biu kin hay cng sut ton phn S. S = UI = 2 2Q P + (2-35) L u uL i Hnh 2-29. Mch in xoay chiu thun cm T biu thc QL = U.I.sin = 2 QL = U.Isin = 1 Do T biu thc Qc = U.I.sin = 2 Qc = U. I sin = 1 Do uuC i C Hnh 2-30. Mch in xoay chiu thuan in dung Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 2. Mch in xoay chiu mt pha 35 Cngsut biu kin c trng cho kh nng lam viec cua thit b. Do nha chetao qui nh.QuanhgiaS,P,Q cmtbngmttamgicvung,trongS lcnh huyn v P, Q l hai cnh gc vung gi l tam gic cng sut (hnh 2-31). n v ca S l: VA. T tam gic cng sut ta c: 2 2 2 2) Q Q ( P Q P SC L + = + =PQ tg = cos . S P = sin . S Q = V d 2-22: Cho mch in R - L - C mc ni tip (hnh 2-32).- Tm biu thc dng in i - Tnhcngsuttrungbnhvcngsutphn khng ton mch Gii: Ta chuyn v s bin phc Tng tr phc ton mch: Z = 4 + j4 j = 4 + j3 = 5Z370 (O)(do in tr Rmc ni tip vi cun dy L v t in C) 0037 510 100ZUIZZ= = = 20Z270(A) Vy dng in chy trong mch l: i(t) = 20 cos(4t 270)(A) Cng sut trung bnh: P S Q Hnh 2-31. Tam gic cng sut trong mch in xoay chiu R = 4OL = 1H u = 100cos(4t+100) (V) i F41 Hnh 2-32 R = 4 jLe = j4 (O) 010 100Z = U I j Cj = (O) Hnh 2-33 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 2. Mch in xoay chiu mt pha 36 P = U.I.cos = 0372202100cos = 542202100 = 800 W Ta c th tnh P theo cng thc: P = R. I2 = 4.2220|.|

\|= 800 W Cng sut phn khng: Q = U.I.sin = 0372202100sin = 532202100 = 600 Var Ta c th tnh Q theo cng thc: Q = QL + QC = 2I . XL + ( 2I . XC) = 2220|.|

\|. 4 2220|.|

\|. 1 = 600 Var V d 2-23: Cho mch in R - L - C mc ni tip (hnh 2-34a). Vi U = 127 V, R = 12O, L = 160 mH, C = 127 F , f = 50 Hz.Tnh dng in, in p ri trn cc phn t R, L, C, gc lch pha v cng sut P, Q, S, v th vc t. Hnh 2-34. Mch in v th vect trong v d 2-23 Gii: Tnh dng in: XL =L . f 2 = 2.3,14.50.160.10-3 = 50O XC = 25127.10 2.3,14.50.1fC 216 = = Z = 27,7 25) (50 12 ) X (X R2 2 2C L2= + = +Dng in trong mch: I =A 4,627,7127ZU= =in p trn in tr R: UR = I.R = 4,6.12 = 55,2 V u uC i R uLuR L C UR = 64o20 U UC a)b) UL I Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 2. Mch in xoay chiu mt pha 37 in p trn in cm L: UL = I.XL = 4,6.50 = 230 V in p trn in dung C: UC = I.XC = 4,6.25 = 115 V Gc lch pha : 2,081225 50RX XtgC L===20' 64 0= Vydnginchmphasauinpmtgc640,20.thvectctrnhby trong hnh 2-34b. Cng sut tc dng P: P = I2.R = 4,62.12 = 254 W Cng sut phn khng Q: Q = I2.(XL XC ) = 4,62.25 = 529 VAR Cng sut biu kin S: S = I2.Z = 4,62.27,7 = 584 VA. V d 2-24: Mt cun dy khi t vo in p mt chiu 48V, dng in qua n l 8A, t vo inpxoaychiu120V,50Hz,thdnginquanl12A.Tmintrvin cm ca cun dy. Gii: Trong mch in mt chiu: 6848IUR = = =Trong mch in xoay chiu: 1012120IUZ = = =T tam gic tng tr ta c: 8 6 10 R Z X X2 2 2 2L= = = =Bit: L . f . 2 XL =mH 25,5 H 0,02552.3,14.508f . 2XLL= = = = V d 2-25: Mch in xoay chiu 125V, 50Hz c in tr R = 7,5O ni tip vi t in C = 320 F (hnh 2-35a). Tnh dng in v cc thnh phn ca tam gic in p, v th vect. Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 2. Mch in xoay chiu mt pha 38 Gii: Tng tr ca mch: 10320.10 2.3,14.50.1C . f . 21X6C= = = 12,5 10 7,5 X R Z2 2 2C2= + = + =Dng in trong mch:A 1012,5125ZUI = = =in p trn in tr R: UR = I.R = 7,5.10 = 75 V in p trn t in C: UC = I.XC = 10.10 = 100 V 10' 53 1,3337,510RXtg0 C = === . Dng in vt pha trc in p. th vect hnh II-35b. 2.9.8.H s cng sut 2.9.8.1.nh ngha v ngha ca h s cng sut T tam gic cng sut ta c:P = S.cos = U.I.cos T tam gic tng trta c:cos = ZR=2 2) X X ( RRC L +(2-36) cos c gi l h s cng sut, n ph thuc vo kt cu mch in. H s cng sut c ngha rt ln trong sn xut, chuyn ti v tiu th in.- Mimy in u c ch to vi mt cngsut biu kin nhmc (Sm). T my c th cung cp mt cng sut tc dng l P = Sm.cos. Do mun tn dng kh nng lm vic ca my in v thit b th h s cng sut phi ln. u a)b) UC U UR I uR R C R uC Hnh 2-35. Mch in v th vect trong v d 2-25 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 2. Mch in xoay chiu mt pha 39 -MihtiudngyucumtcngsuttcdnglPxcnh.Khi,dngin chuynti ngdyI= Cos . UP,nuhs cngsutcngbth dngincnglnv iu ny dn n tc hi: Dng in lnphi dng dy dn ln dn n tng vn u t. Tn tht nng lng ng dy ln khi dng in ln vt R I . .2= AA .V th, vic nng cao h s cng sut s lm gim vn u t, xy dng ng dy v lm gim tn tht nng lng chuyn ti. V d 2-26: Vi mt my pht in c Sm = 10.000 KVA Nu cos= 0,7 th cng sut nh mc pht raPm = Sm.cos = 10.000 x 0,7 = 7000 KWNu cos = 0,9 th cng sut nh mc pht ra Pm = Sm.cos = 10.000 x 0,9 = 9000 KW 2.9.8.2.Nng cao h s cng sut Nng cao h s cng sut s tng c kh nng s dng cng sut ngun v tit kim dy dn, gim c tn hao in trn ng dy. Nh vy vi cngmt cngsut biu kin, cos cng ln (ti a cos = 1) th cng sut tc dng P cngln, do cos c trng cho kh nng tn dng ca thit b in bin nng lng ca ngun thnh cng c ch. Mt khc nu cn mt cng sut P nht nh trn ng dy mt pha th dng in trn ng dy l:=cos UPINu cos cng ln th I nh dn n tit din dy nh hn, tn hao in dy trn ng dy b, in p ri trn ng dy cng gim. cos2 22 URPp =Trong sinh hot v trong cng nghip, ti thng c tnh cm khng nnlm cho cosgim thp. nng cao cos, ta dng t in ni song song vi ti. Khi cha b (cha c nhnh t in), dng in trn ng dy I bng dng in qua ti I1, h s cng sut ca mch l cos1. u C U IC t IC IC I It It Z I Hnh 2-36. Nng cao h s cng sut s dng t in Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 2. Mch in xoay chiu mt pha 40 Khi c b (c nhnh t in), dng in trn ng dy I bng I1 + IC . CI I I + =1 T th ta thy: dng in trn ng dy gim, Cos tng, gim. I < I1 ; < 1 ; Cos > Cos1

Khi cha b:Q1 = P. tg1

Khi c bQ = P. tg . Khi ny, cng sut phn khng trong mch gm: Q1 ca ti v QC ca t b. tg P Q tg P Q Q QC C. . = + = + =1 1 ) .( tg tg P QC = 1(1) Mt khc: C U I U QC C C. . . e2 = =(2) T (1) v (2), ta tnh c gi tr in dung C cn thit: ) .(. etg tgUPC =12(F) Vd2-27:MttigmR=6O,XL=8Omcnitip,uvi ngunU=220V(hnh2-37). a)Tnh dng in I1, cng sut P, Q, S v cos1 ca ti. b)Ngitamunnnghscngsutcamchintcos=0,93.Tnhin dung C ca b t u song song vi ti. Hnh 2-37. Mch in v d 2-27 Gii: a) Tng tr ti:Z = 10 8 6 X R2 2L2= + = +Cos1 =0,6106ZR= =Dng in ti I1:I1 = 210220ZU= =Cng sut P ca ti: P = R I2= 6.222 = 2904W Cng sut Q ca ti: Q =XL I2= 8.222 = 3872VAR b) Tnh C: U=220V I1 L R Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 2. Mch in xoay chiu mt pha 41 Cos1 = 0,6 tg1 = 1,333 Cos = 0,93 tg = 0,395 B t cn c in dung l: ) tg .(tgU . PC12 = = ( ) F 1,792.10 0,395 1,333314.220290442= 2.10. BI TP CHNG 2 Bi 2.1: Cho mt mch in R L C nitip t vomt in p xoay chiu: U = 220V,f = 50Hz,R = 9O, L = 0,03H, C = 220F. Tnh: - Tr s hiu dng I v vit biu thc tc thidng in ca mch. - H s cos. Li gii: -XL = e L = 2t.f = 9,42 O -XC = fC C t e 21 1== 14,47 O -Z = 2 2) (C LX X R += 6,60 O -I = 60 , 6220=ZU = 33,3 O -tg = RX XC L = - 29,30 -cos(- 29,30) = 0,87 -Mch c tnh dung mnh hn cm nn : i = 33,3 2 sin( et + 29,30) (A) Bi 2.2:Cho: Biu din : X R Z I U , , , , v th vect quan h dng p GiiTa c :U0=10 I0= 5 nnmch mang tnh cm khng UR UL UC

U R L C Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 2. Mch in xoay chiu mt pha 42 Bi 2.3:Cho mch in nh hnh v Tnh i1, i2 Gii Chuyn sang s phc ta c Theo K1, K2 ta c: m t h phng trnh trn ta c thay vo (1) ta c Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 2. Mch in xoay chiu mt pha 43

Bi 2.4: Cho mch in R L C mc ni tipt vo mt in p xoay chiu c : u(t) = 20sin(2t + 900), R1 = 8O; R2 = 2O;L = 6H; C2 =F41. Tnh:- Tr s hiu dng I v vit biu thc tcthi dng in ca mch. - H s cos ca mch. Li gii: -XL = e L = 2.6 = 12 O -Xc = 4121 1=C e = 2 O -Z =2 10 ) ( ) (2 22 1= + +C LX X R RO -I = ZU= 1 A -cos = ZR R2 1 + = 1 - = 900 - = 450 -i =2sin( 2t + 450)(A) Bi 2.5:Trs dnginvinptrnmtphntcbiudindi dnghiudng phc: 090 2 100 Z = U(V) ; 045 10Z = I(A).Hy biu din u, i di dng tc thi v tnh R, P, Q, S ca mch Li gii -u = 200 sin (et + 900)(V) -i = 10 2sin( et + 450)(A) -P = U.I.cos = 1000 W -Q = U.I.sin = 1000 VAR u(t) = 20sin(2t + 900) R1 L R2 C2 i(t) Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 2. Mch in xoay chiu mt pha 44 -S = 2 2Q P += 1414 VA -R = 2IP = 10 O Bi 2.6: Tr s in p v dng in trn mt phn t c biu din di dng tc thi : u = 200 2 sin (100t + 900)(V) i = 10 2 sin (100t + 600)(A) Hy biu din u, i di dng hiu dng phc (U,I). Tnh R, P, Q, S ca mch. Li gii: - 090 200Z = U (V) - 060 10Z = I(A) -P = U.I.cos = 1000 3W -Q = U.I.sin = 1000 VAR -S = U.I = 2000(VA) -R = 2IP = 10 3O Bi 2.7:innngctruyntmyphtinn ti.Ti v ng dy c cc thng s sau: - Thng s ca ng dy: Rd = 0,5O; Xd= 2,5O - Thng s ca ti: U2 = 220V; R2 = 25O; cos2 = 0.8. Tnh : in p U1, P1, Q1 u ngun ng vi ti c tnh cht cm khng. Li gii -Zt = 22IU = 8,8 O -Sin2 =2cos 1= 0,6 -Rt = Zt. cos2 = 7,04 O -Xt = Zt. sin2 = 5,28 O V ti cm:-ZL = 2 2) ( ) (t d t dX X R R + + += 10,83 O -U1 = I2.ZL = 270,85 V -P1 =) (22 t dR R I += 4712,5 W -Q1 =) (22 t dX X I += 4862,5 Var Bi2.8:HyxcnhinpUvdng in I1, I2, I4.Bit : E1 = 24v; E2 = 12v; E3 = 9v; E4 = 6v R1 = 3O; R2 = 7O; R4 = 3O Rd Xd 2ZU2U1 R1R2 R4 I1I2I4 UE1 E2 E3 E4 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 2. Mch in xoay chiu mt pha 45 Li gii U = E3 = 9 V I1 =39 2411=RU E = 5A I2 =712 922+=+RE U = 3 A I4 =36 944=RE U = 1A Bi 2.9: Hy xc nh in p U v dng in I1, I2, I3, I4.Bit : E1 = 24v; E2 = 12v; E3 = 9v; E4 = 6v R1 = 4O; R2 = 6O; R3 = 3O; R4 = 2O Li gii: u = 4 3 2 1443322111 1 1 11 1 1 1R R R RRERERERE+ + ++ + = 8 V I1 =11RU E = 4 A I2 =22RE U + = 310A I3 =33RU E = 31 A I4 =44RE U = 1 A Bi 2.10: Cho mch in nh hnh v.Bit ch s cc dng c o nh sau: I = 166A; U = 6200V; P = 623KW; Tnh h s cos v tr s tc thi dng inv in p ca mch. Li gii -cos = I UP. = 0,605 = cos 530 -u = 6200 2 sin (et + 530) (V) R1 R2R4 I1I2I4 UE1 E2 E3E4 R3 I3 A W V R X Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 2. Mch in xoay chiu mt pha 46 -i = 166 2sin et(A) Bi 2.11: Cho mch in nh hnh v : Khi cha c t cc dng co ch : P = 1200 W; I = 11A;U = 220 V. Xc nh h s coskhi cha c t. Khi ni t C vo mch th h s cng sut cos = 0,91 . Tnh C v QC ? Li gii + Khi cha c t : -cos 1 = I UP. = 0,496 = cos 60,30 -tg 1 = tg 60,30 = 1,75 + Khi c t : -C =) (.12 etg tgUP( vi cos = 0,91 = cos24,50 tg = tg 24,50 = 0,45) -C =) 45 , 0 75 , 1 (. 2 . 22012002f t= 0,000103F = 103F -QC = - UC IC = - U2.e. C = - 1565,35 Var. Bi 2.12:Chomchinnhhnhv.Ccs o 2 ch nh sau: a) Khi ni t in: I = 115A; P = 665KW; U = 6,4KV b) Khi ct t in: I = 166A; P = 623KW; U = 6,2KV. Tnh thng s R, X ca ti, tr s ca t in C. Li gii a) Khi nit -cos t = I UP. = 0,9035 = cos 25,370 -tg25,370 = 0,474 b) Khi ct t -R = 2IP = 22,6 O -Z = IU = 37,35 O -XL = 2 2R Z= 29,74 O -cost = I UP. = 0,605 = cos 52,750 -tg 52,750 = 1,315 -C =) (.2cotu khongtu etg tgUP = 0,0000434F = 43,4F A W V C K L R A W V C K L R Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 2. Mch in xoay chiu mt pha 47 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 3. Cc phng php gii mch in 47 CHNG 3 CC PHNG PHP GII MCH IN 3.1. PHNG PHP BIN I TNG NG MCH 3.1.1.Mch ngun sut in ng ni tip Etd = RE

-Khicnhiungunpmcni tipta binithnh1ngunp tngngduy nht bng cch chng ta cng (tr khi chng ngc du nhau) li 3.1.2.Mch ngun dng mc song songJtd= RJ -Khicnhiungundngmcsongsongtabinithnh1ngundngtng ng duy nht bng cch chng ta cng (tr khi chng ngc du nhau) li 3.1.3.Mch in tr mc ni tip Trongtrnghpmchincnintrmcnitip,cthbinitngngthnh mch in nh sau: Hnh 3-3. Bin i tng ng cc in tr mc ni tip p dng nh lut ohm ta c :U R1 Rtd U R2 Rn U1 I I U2 Un Et = E1 E2 _ E3 Hnh 3-1 1E2E3E It = I1 + I2 + I3 1I2I3IHnh 3-2 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 3. Cc phng php gii mch in 48 U1 = I.R1 U2 = I.R2 . . . . . . .. Un = I.Rn M U = U1 + U2 + + Un = I(R1 + R2 + + Rn) = I.Rt Trong == + + + =nii n tdR R R R R12 1....Nh vy, i vi mt mch in c cc in tr mc song song, ta c: -Dng in chy qua cc in tr l nh nhau. -in p ca ton mch bng tng in p trn cc in tr. -in tr tng ng ca mch bng tng cc in tr thnh phn. 3.1.4.Mch in tr mc song song Hnh 3-4. Bin i tng dng cc in tr mc song song p dng nh lut ohm ta c :U = I1.R1 = I2.R2 = = In.Rn I = I1 + I2 ++ In = U.(nR R R1...1 12 1+ + + ) =tRU Khi :== + + + =nii n tR R R R R12 11 1...1 1 1 Nh vy trong mch in c cc in tr mc song song th: -in p ri trn cc thnh phn l nh nhau -Dng in qua mch bng tng cc dng in qua cc thnh phn -Nghchocaintrtngngbngtngnghchocaccintrthnh phn. * Hai in tr mc song song Rt =1 22 1.R RR R+ 3.1.5.Mch chia dng in (nh l chia dng) Gi s bit I, R1, R2. Tm I1, I2. I R1R2RnURtd U I1I1I1 I 1R2RTruong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 3. Cc phng php gii mch in 49 Ta c cng thc dng in mch r : 2 121R RRI I+ =2 112R RRI I+ = 3.1.6.Mch chia p (Cu phn th) 3.1.7.Bin i tng ng in tr mc hnh sao sang tam gic:Y A

Hnh 3-6. S bin i sao (Y) tam gic(A) R12 = R1+ R2+32 1.RR R R23 = 13 23 2.RR RR R + +R31 =21 31 3.RR RR R + +NuR1 = R2 = R3 = RY R12 = R23 = R31 = RA RA =3RY R1 R3 R23 R31R12 32 1 2 1 R2 a)b) U1R2R1U2UI2 1222 111R RRU UR RRU U+ =+ = Hnh 3-5 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 3. Cc phng php gii mch in 50 3.1.8Bin i tng ng in tr mc hnh tam gicsao sang : A Y

R1 = 31 23 1231 12.R R RR R+ + R2 =31 23 1223 12.R R RR R+ + R3 = 31 23 1231 23.R R RR R+ + Nu R12 = R23 = R31 = RA Y= = = R R R R3 2 1 3AY=RR3.1.9.S tng ng gia ngun p v ngun dng : Nu IR ='RIth 2 mch tng ng nhau iu kin ngun p v ngun dng tng ng nhau: E = I . RI RS = RI 3 R23 R31R12 2 1 a) R1 R3 2 1 R2 b) 3 Hnh 3-7 ESRRIIRRababRI'RIHnh 3-8 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 3. Cc phng php gii mch in 51 3.2. BI TP CHNG 3 MC 3.1 Bi 3.1: Cho mch in nh hnh v (3-9) Dng php bin i tng ng tm I1 v U O 5 O 20O 12O 40 V 18+U1I Li Gii: t Rt1 gm in tr 20O mc ni tip vi in tr 40O R1 td= 20 + 40 = 60O t Rt2 gm Rt1 mc song song vi in tr 12O R2 td=12 6012 . 60+ = 10O in tr ton mch gm Rt2 mc ni tip in tr 5O Rtd= 10 + 5 = 15O Mch in tng ng : I = 1518 =56A = 1,2A I1=I.12 6012+= 721256= 51A (dng nh l chia dng) U = I1.40 =51 .40 = 8V VyI1 =A51 U = 8V Bi 3.2: Cho mch in nh hnh v (3-10) Dng php bin i tng ng tnh I , I1,U Ni tip Rt1//12O 18VO15Hnh 3-9 V 30+UO 8O 12O 4O 4O 3 O 6O 2O 161I2I3IIHnh 3-10 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 3. Cc phng php gii mch in 52 Li Gii: Ta t R1 gm in tr 8O mc ni tip vi 4O R1= 8 + 4 = 12O t R2 gm in tr 6O mc song song vi in tr 3O t R3 gm R2 mc ni tip vi in tr 4O (nhnh c dng in I chy qua) R2 = 3 63 . 6+ = 2O; R3 = 2 + 4 = 6O t R4 gm R1 mc song song R3 ; v R5 gm R4 mc ni tip vi in tr 12O (nhnh c dng in I2 chy qua) R4=6 126 . 12+ = 4O ; R5 = 12 + 4 = 16O t R6 gm R5 mc song song vi in tr 16O ;v R7 gm R6 ni tip in tr 2OR6=16 1616 . 16+= 8O ; R7= 8 + 2 = 10O I1 =1030 = 3A Mch in tng ng 1I2IO 12 O 2O 16 O 4 V 30A Dng nh l chia dng:I2=I116 1616+=23= 1,5A Mch in tng ng V 30+UO 8O 12O 4O 4 O 2O 161I2I3IIO 2A B Dng nh l chia dng ti nt B: I = I26 1212+=1812.23= 1A p dng nh lut K1 ti B : I3=I2-I = 1,5 1 = 0,5A U = I3.8 = 4V Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 3. Cc phng php gii mch in 53 Bi 3.3: Cho mch in nh hnh v (3-11) Dng php bin i tng ng Tm I v R Li Gii: p dng nh l chia dng ti nt b ta c: 2 = I1.4 88+I1= 3A p dng nh lut K1 ti nt b ta c: I2- I1 - I = 0 (1) I2- 3 - I = 0 (1) p dng nh lut K2cho vng(a,b,d,a):2I2 +10I = 30 (2) nhn (1) cho h s 2 ta c : 2I 22I = 6 Ly pt(2) tr pt(1) ta c : 12I = 30 6 = 24 I = 2A Ta c: R1 td=4 84 . 8+=38O R2 td=R Rtd+1=38 + R p dng K2 cho vng (a,c,d,b) ta c: (Rt1+ R)I1 - 10.I = 0 (38+R).3 10.2 = 0 R = 4O Bi 3.4: Cho mch in nh hnh v (3-12) Tnh cng sut tiu th trn in tr R. Li Gii: Xt bin i tng ng nhnh gm in tr 12O mc song song vi 4O v t l R1 ta c: R1 =12 412 . 4+=3OO 8O 4O 10O 2R V 30abc 1I2IIA 2dHnh 3-11 O 4A 5 O 8O 2O 12O 20RO 4Hnh 3-12 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 3. Cc phng php gii mch in 54 Xt bin i tng ng nhnh gm R1 mc ni tip 2O v t l R2 R2= 2 + 3 = 5O Xt bin i tng ng nhnh gm R2 mc song song vi 20O R3=5 205 . 20+ =4O Xt bin i tng ng nhnh gm R3 ni tip vi 4O t l R4 R4=R3(nt)4O = 4 + 4 = 8O S tng ng 1 A 5O 4O 8 O 20 O 51I2I3I4I p dng nh l chia dng ti nt A ta c: I1=5.8 88+=2,5A = I2(do in tr ca R4 bng vi nhnh c dng in I2 chy qua) p dng nh l chia dng ti nt B ta c: I3=I1.5 2020+=2,5.5 2020+= 2A Mch tng ng 2 RIO 4A 5 O 8O 2O 12O 20RO 4 IR=I3.12 44+=2.12 44+=0.5A PR=R.I2R=12.(0,5)2= 3(W) Bi 3.5: Cho mch in nh hnh v (3-13) Tm cc dng in I1 ,I2 ,I3 bng php bin i tng ng Li Gii: Thay in tr3O v 6O mc song song thnh in tr O =+26 36 . 3 O abOO2I1I3I24v5A 6312hnh(3-13) Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 3. Cc phng php gii mch in 55 Ta c mch tng ng nh hnhO abO3I24v5A122 Bin i ngun dng 5A mc song song vi in tr 2O thnh ngun sc in ng 10v mc ni tip vi in tr 2OTa c mch tng ng ObO3I24v10v12 2 p dng nh lut K2 cho vng kn(2 + 12I3) = 24 10suy ra I3 = 1A Theo K2 ta cng c uab = 2I3 + 10 =12v suy ra I1 = 3abu= 4A ; I2 = 6abu=2A Bi 3.6: Cho mch nh hnh v (3-14) Tnh :I1 ,I2, I3, IX,VX,V1 Li Gii: p dng php bin i tng ng ta c in tr 3O mc song song vi 2 in tr (1O nt 2O) +1V+IO 5 , 1O 6O 42I1I3IV 12 O 5 , 1 Ta c in tr (1,5O nt 1,5O) Mch tng ng +xV+1V+IxIO 3O 1O 2O 5 , 1O 6O 42I1I3IV 12hnh (3-14) Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 3. Cc phng php gii mch in 56 +1V+IO 6O 42IV 1 2O 3 in tr (3Omc song song vi in tr 6O) Ta c mch tng ng +I O 4V 12 O 2 pdng nh lut K2 cho vng knI=612 =2A ; I2=2.93=32A p dng nh l chia dng in ta c : I1=2.96=34A;I=34.63=32A = IX Suy ra :V1= 6. I2= 6. 32= 4v VX = 3. I =3. 32 = 2v Bi 3.7: Cho mch nh hnh (3-15) Tnh I1 , I2 ,Va +Vb Li Gii: p dng php bin i tng ng ta cThay in tr 1 kO ni tip 3k O thnh in tr 4kO v bin i in tr 6kO mc song song vi in tr 3kO thnh in tr 2kO Ta c mch tng ng nh hnh v: +aV+bVO K 1O K 2O K 3O K 4O K 6O K 6 O K 3V 721I2Ihnh (3-15) Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 3. Cc phng php gii mch in 57 O K 2O K 4O K 6V 72O K 2O K 4 Tng t ta c in tr (2kOnt 2kO) mc song song vi in tr4kO c in tr 2kOTa c mch tng ng O K 4O K 6V 72O K 2 p dng nh lut K2 cho vng kn ta c : I= 1272= 6mA p dng nh l phn phn dng in I2= 6.4 44+= 3mA Va = 3mA.2k O = 6v Vb = (3.93).6 = 6v Va + Vb =12v Bi 3.8 : Cho mch in nh hnh v (3-16) Tm dng in i O 122 22OO OOO1abcde(t)ifhnh (3-16) Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 3. Cc phng php gii mch in 58 Li Gii: Dng php bin i tng ng thay 3 in tr mc tam gic gia 3 nh a ,b ,c thnh mch ni hnh sao vi im chung l h Oabcdfh0,81120,40,4OOOO Ta c Rah =O = =+ +8 , 0541 2 22 . 2 Rbh =O = =+ +4 , 0521 2 21 2 Rch =O = =+ +4 , 0521 2 21 2 Thay cc in trni tip trn mt nhnh thnh 1 in trsau li thay 2 in tr mc song song thnh mt in tr Oadf0,81OOOh1,4 2,4 Rhd = O =+884 , 04 , 1 4 , 24 , 1 4 , 2 Ta c mch tng ngTruong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 3. Cc phng php gii mch in 59 Oadf0,81OOh0,884 Rt = Rah + Rhd + 1 = 0,8 + 0,884 +1 = 2,68O Vy mch tng ng nh sau : afOi(t)e(t) 2,68 p dng nh lut K2 cho vng kn ta c i. Rt = e(t) suy rai =) ( 100 sin 23 , 268 , 2100 6 ) (A tt snRt etdtt= = Bi 3.9:Cho mch in hnh (3-17) Tnh I1,I2 v U Li Gii: p dng php bin i tng ng ta c in tr 2O nt 4O Mch in tng ng O 4 O 4O 24 O 121I2I3IO 6V 100 V 100 O 2O 4 2I1I O 4 O 4O 24 O 12+Hnh (3-17) Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 3. Cc phng php gii mch in 60 in tr 6O mc song song vi vi in tr 12O ta cMch tng ng V 100O 4 O 4O 241I2IO 4 in tr 4O nt 4O ta cMch tng ng O 4O 241IO 8V 100I2 p dng nh lut K2ta c:I1= 10100= 10A Phn dng : I2 =10.8 2424+=7,5A Phn dng : I3=7,5.4 412+=4,74A U = I3.2= 4,74.2 = 9,5A Bi 3.10: cho mch in nh hnh v (3-18) Tnh Rab Li Gii: p dng php bin i tng ngta cBin i in tr 6O mc song song vi in tr 3O thnh in tr R1

R1= 6 36 . 3+=918 = 2O Bin i in tr R1 // 2O thnh in tr Rcd Rcd=42 . 2 =1O Bin i in tr 1O nt Rcd nt 6O thnh in tr Rae Rae =168 ). 6 1 1 ( + + = 4O e d O 1O 2O 3O 6O 16O 8O 6abcHnh (3-18) Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 3. Cc phng php gii mch in 61 Bin i in tr 16O nt Rae thnh in tr Rab

Rab= 4+ 16 = 20O 3.3. BI TP CHO P S Dng php bin i tng ng v cc nh lut kirchoff 1 v 2 gii cc bi tp sau: Bi 3.11: Cho mch in nh hnh v (3-19) BitR1 = R2=R5 =10O ,R3 =R6 =50O ,R4 =30O , U =100 v Tnh Ip s: I = 0,3A Bi 3.12: Cho mch in nh hnh v (3-20) Bit R1 =10O ,R2 =5O,R3= 1O,U1 =200v ,U2 =100v ,U3 =50v a/ Tnh Ib/ Tm cng sut pht catng ngunc/ Tm cng sut tiu th ca mch p s : a/ I=23,84A b/ P1 =5686,17 (W) , P2 =576,9(W) ,P3 =4769,14(W) c/ P =6576,7(W) Bi 3.13 : Cho mch in nh hnh v (2-21) U1R2R3R4R5R6RIHnh 3-19 1R2R3RU1 U3 U2 Hnh 3-20 1R2R3R4R5R1U2UHnh 3-21 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 3. Cc phng php gii mch in 62 Bit R1 = 6O, R2=5O,R3 =2O,R4 =3O , R5 =4O, U1 =20 v ,U2 =10 v Tnh dng qua R3

p s: I3 O =2,98A Bi 3.14: Cho mch in nh hnh v (3-22) Cho bit: R1 = 4O, R2= R5= 10O,R3 =2O,R4 =1O ,J1 =25A , J2 =20A ,U =20V Tnh I1 ,I2

p s: I1 =5A , I2 = 10A Bi 3.15: Cho mch in nh hnh v (3-23) Cho bit : R2 = 10O , R3=20O, J=5A ,U =100v Tnh gi tr R1

p s R1 = 20O Bi 3.16: Cho mch in nh hnh v (3-24) Cho bit :R1 = 30O, R2= 10O,R3 = R4 =20O ,U = 50v, J= 5A Tnh dng qua R2

p s : IR2 = -1A Bi 3.17: Cho mch in nh hnh v (3-25) 1R2R3R4R5R+-1J2J1I2IUHnh 3-22 1R2R3R4R5R+-JUHnh 3-25 1R2R3R+-1J UHnh 3-23 1R2R3R4R+-JUHnh 3-24 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 3. Cc phng php gii mch in 63 Bit : R1 = 10O, R2= 20O,R3 =5O,R4 =8O, R5= 4O, U =10v , J =2A Tm dng qua R2 v cng sut tiu th trn np s : IR2 =0,61 A , PR2 =7,466(W) Bi 3.18 : Cho mch in nh hnh v (3-26) Cho bit : R1=4O, R2 =2O, R3 =8O, R4=16O , J1 =10A , J2=5A Tm tng cng sut tiu th v tng cng sut ngunp s : Ptiuth =34,6 W Pngun = 229,41W Bi3.19:Cho mch in nh hnh v (3-27)

Tm I v Ptiu tn

p s: I= 1,25APtiu tn =39,06W Bi 3.20: Cho mch in nh hnh v (3-28) 1R2R3R4R2J1JHnh 3-26 1R2R3R4R+-J5R6R7R8RXUSUHnh 3-28 I+ -O 5O 500100v1ARU 5RUHnh 3-27 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 3. Cc phng php gii mch in 64 Bit : R1= 8,8O, R2 =4O, R3 =16O, R4=10O,R5 = 14O, R6 =8,2O,R7 =12O ,R8 =5,8O 3 , 7XUJ =, nu cng sut tiu tn trn R7 bng 147W .tm US

p s : US =100v Bi 3.21: Cho mch in nh hnh (3-29) Bit R1= 1O, R2 = 2O, R3 =3O, R4=6O=R5, R6 = 16O,R7 = 8O Tnh Rab

p s : Rab = 20 O Bi 3.22: Cho mch in nh hnh (3-30) Bit : R1= 2O, R2 = 12O, R3 =20O, R4= 24O,R5 =12O Tm I ,I1 ,I2 ,I3 ,I4, U1 ,U2 p s : I =3,5A ,I1 =I2 =1,75A , I3 = 0,587A ,I4 = 1,166A U1= 35v ,U2= 14v Bi 3.23: Cho mch in nh hnh v (3-31) Cho bit : R1= 12O, R2 = 4O, R3 = 8O, R4 = 8O,R5 =4O , R6 = 12O, R7 = 24O R8 = R9 = 6O 1R2R3R4R5R6R7RabHnh 3-29 1R2R3R4R1I5R+-2I3I4II1U2U42vHnh 3-30 1R2R3R4R5R6R7R+-I60v8R9RHnh 3-31 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 3. Cc phng php gii mch in 65 Tm Ip s : I =2A Bi 3.24: Cho mch in nh hnh (3-32) O 1O 2O 4O 6O 10O 25A Tm cng sut tiu th trn R =6O p s : P6 =1,5w Bi 3.25:Cho mch in nh hnh (3-33)

O 2O 64A12I1I Tm I1 ,v Up s : I1 = 2A , U1 = 12v Tm U v I1p s : U= 30v ,I1 =2A Bi 3.26: Cho mch in nh hnh (3-34) +-1R2R3R4R5RU Cho bit : R1= R2 = R3 = 3O, R4 =5O, R 5 = 2O ,U=36vTm IR4

p s : IR4 =4A Hnh 3-32 Hnh 3-33 Hnh 3-34 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 3. Cc phng php gii mch in 66 Bi 3.27: Cho mch in nh hnh v (3-35) +-1R2R3R4R5RUI1I2I3I4I Cho bit : R1=1O, R2 =2O, R3 = 4O, R4 =6O, R 5 =3O,U =15vTnh : I, I1 ,I2 I3 ,I4 , Pngun

p s : I =6A , I1=4,5A, I2 = 1,5A ,I3 = 3A ,I4 = 1,5A, Pngun =90W Bi 3.28: Cho mch in nh hnh v (3-36) 1R2R3R4R5Racb36v6R Bit : R1= R4 =R 6 =18O, R2 =R3 = R 5 =9O, Tm Iab ,Iac , Uab ,Ubc

p s : Iab = 6A ,Iac =3A , Uac =18v ,Ubc=18v Bi3.29: Cho mch in nh hnh v (3-37) 1R3R4RR+-U Cho bit:R1 = 1O R4 = 6O, R3 = 3O ,P3O= 300W ,U = 90v Tm R, RP,Pcung cp

p s: R = 3 O, RP = 1350W = Pcungcp Hnh 3-35 Hnh 3-36 Hnh 3-37 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 3. Cc phng php gii mch in 67 Bi3.30: Cho mch in nh hnh v (3-38) 1R2R3R4R5R1I6R+-+-UXUXII Bit: R1 = 4O,R2 = 6O , R3 = 1,5O,R4 = 3O , R5 = 2OR6 = 2O, U = 12V Tm I , I1 , IX , UX

p s: I= 2A, I1 = 34A , IX= 0,667A, UX = 2V 1R2R3R+-3U1U2U+-aIbInI Bi 3.31: Cho mch in nh hnh v (3-39) +-abc1R2R3R4R5R6R1I2IaI

Bit: U1 = 120V ,U2 = 120 ,U3 = 240V,P1 = 1,2W , P2 = 3,6W ,P3 = 9,6W Tm: Ia, Ib , In

p s: Ia= 50A , In = 20A , Ib = 70A Hnh 3-38 Hnh 3-39 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 3. Cc phng php gii mch in 68 Bi 3.32: Cho mch in nh hnh v (3-40) + -1R2R3R+-0U1UaU Bit : R1 = 1O ,R2 = 2O, R3 =3O,Ua = 8vTm U1 , U 0 p s: U1= 24v , U 0 = 12v Bi 3.33: Cho mch in nh hnh (3-41)

Tm I p s : I = 0,93A Bi 3.34: Cho mch in nh hnh (3-42) +I1I2I3I4IO 3 O 6O 2O 4O 1V 15

Tm I 1, I2, I3, I4 , P p s : I 1 = 4,5A , I2 = 1,5A , I3 = 3A , I4 =1,5A , P = 90w Bi 3.35: Cho mch in nh hnh (3-43) V 120+O 6O 6O 2O 2O 3O 14I3II1I2I5I6I Hnh 3-40 O 2V 45O 3O 3O 3O 4O 4O 21IIHnh 3-41 Hnh 3-42 Hnh 3-43 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 3. Cc phng php gii mch in 69 Tnh : I1 ,I2, I3, I4,I5,I6 p s :I1 = 13,333A , I2 = 26,666A,I3=17,7A ,I4 = 8,88A , I5 = I6 = 20A 3.4.PHNG PHP IN TH NT:L tm in th ti cc nt V d 1 : Cho mch in nh hnh v (3-44) Dng phng php in th nt tm dng in qua cc nhnh Li GiiBc 1 :Chn mt nt bt k trong mch v gi l nt gc,thng chn nt c nhiu nhnh ti lm nt gc v in th ti nt gc bng 0.Gi s ta chn 0 lm nt gc U0 = 0VUA =UA0 ( in th ti nt A so vi nt gc)UB = UB0 ( in th ti nt B so vi nt gc) Bc 2 : Dng nh lut kirchhoff 1 vit phng trnh ti cc ntGi s ta kho st ti nt A : theo nh lut K1 ta c :Hnh 3-44 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 3. Cc phng php gii mch in 70 i1 + i2 + i3 = 0(1)Vi i1 = IA

Gii phng trnh (1) v(2) ta tm c in th ti cc nt UA, UB. T ta suy ra dng in qua cc nhnh I1, I2, I3. Theo hnh v ta c :

Nhn xt : vit c trc tip h phng trnh.- Trong mch in ch c ngun dng, nu c ngun p ta phi i sang ngun dng.Bc 1 : Chn mt nt lm nt gc v in th ti nt gc xem nh bng 0Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 3. Cc phng php gii mch in 71 Bc 2 : Vit phng trnh in th nt ti cc nt cn li.- in th ti mt nt nhn vi tng in dn ca cc phn t ni ti nt (A) tr i in th ca nt kia (B) (ni gia hai nt ) nhn vi tng in dn ca phn t chung gia 2 nt bng tng cc ngun dng ni ti nt (A) ( ngun dng mang du + nu n i vo nt v mang du nu i ra khi nt)Bc 3 : Gii phng trnh tm in th ntBc 4 : Tm dng cc nhnh theo nh lut OhmBi 3.36 : Cho mch in nh hnh v (3-45)

Dng phng php in th nt tm I Li Gii :Dng phng php th nt ti a v b ,chn C lm nt gc Uc=0Ta c :

(1) (2) T (1) suy raUb =2Ua 4 th vo (2) Ta c- 3Ua + 4(2Ua -4) = 24Hnh 3-45 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 3. Cc phng php gii mch in 72 Ua =8(V) Ub = 12(V) Vy : Bi 3.37: Cho mch in nh hnh v (3-46)

Tm I v I1? Li Gii :Chn C lm nt gc Uc =0Ta c :

Hnh 3-46 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 3. Cc phng php gii mch in 73 vy: ta c M

Bi 3.38 : Cho mch in nh hnh (3-47) Cho bit :

Tmu,i? Li Gii Mch c v li (bin i tng ng ngun p ni tip in tr thnh ngun dng mc song song in tr) Hnh 3-47 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 3. Cc phng php gii mch in 74 Th nt ti a ta c

Vy :U = R3 . I2 = 2VBi 3.39: Cho mch in nh hnh (3-48) Tm ILi Giip dng phng php th ntChn C lm nt gcTa cUa = 6VV

p dng nh lut K1 ti C Hnh 3-48 Truong DH SPKT TP. HCM http://www.hcmute.edu.vnThu vien DH SPKT TP. HCM - http://www.thuvienspkt.edu.vnBan quyen Truong DH Su pham Ky thuat TP. HCMChng 3. Cc phng php gii mch in 75 Ta c Bi 3.40: Cho mch in nh hnh v (3-49) Tm I ?Li Giip dng phng php in th ntChnc lm nt