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B GIO DC V O TO TRNG I HC THNH

KHOA IN TH ----0o0----

N IN T CNG SUT

Gio vin hng dn : Thc s Bi vn Huy Sinh vin thc hin : - inh gia Lim

- quang Bch - Nguyn vn Hin ( 05-03) - Nguyn vn Hin (07-03) - ngc Hng

Lp : CCNTH2 Kha : 5

H Ni, thng 4-2010

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Mc lc

Phn I gii thiu chung

Chng I m u

Chng II Cc phng php m my ng c khng ng b roto lng sc

Chng III cc phng php bo v van

Phn II thit k

Chng I thit k mch ng lc

Chng II iu kin thit k mch

Chng III thit k mch iu khin

Phn III m phng ton b h thng bng phn mm Psim

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TI

THIT K B KHI NG MM NG C KHNG NG B ROTO LNG SC

Thng s ng c: P=120kw n=1490v/pht cos=0.93 Mk/Mm=1.1 Mmax/Mm=2 Ik/Idm=6 J=1.6kg/m2 U1=220/380V Yu cu ni dung thit k n :

- Gii thiu chung v chng loi thit b c giao nhim v thit k - xut cc phng n tng th, phn tch u nhc im ca tng phng n, i

n phng n chn la ph hp thit k mch lc v mch iu khin - Thuyt minh s hot ng ca s km theo hnh v minh ha - Tnh ton m phng mch lc bng phn mm PSim - Tnh ton m phng mch iu khin - Kt lun - Ti liu tham kho

Phn I GII THIU CHUNG

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CHNG I : LI M U

Do yu cu ca cng vic cng nh kh nng lm vic ca mch in khng ng b nn cho n nay n c s dng rng ri nht trong cc ngnh kinh t quc dn vi cng sut t vi chc n hng nghn kiloat. Trong cng nghip thng dng my in khng ng b lm ngun ng lc cho my cn thp loi va v nh, ng lc cho cc my cng c cc nh my cng nghip nh Trong hm m dng lm my ti hay qut gi. Trong nng nghip dng lm my bm hay my gia cng sn phm. Trong i sng hng ngy my in khng ng b cng dn chim mt v tr quan trng :qut gi, my quay a, ng c trong t lnh. Bi n c nhng u im ni bt hn hn so vi my in mt chiu cng nh my in ng b, l : C kt cu n gin, d ch to, lm vic chc chn, vn hnh tin cy. Chi ph vn hnh v bo tr sa cha thp, hiu sut cao, gi thnh h. My in khng ng b s dng trc tip li in xoay chiu do khng cn phi tn km thm chi ph cho cc thit b bin i. Tuy nhin, my in khng ng b ch yu c s dng ch ng c, nn n cng c mt s nhc im l dng khi ng ca ng c khng ng b thng ln (t 4 n 7 ln dng nh mc). Dng in m my qu ln khng nhng lm cho bn thn my b nng m cn lm cho in p li gim st nhiu (hin tng st p li in), nht l i vi li in cng sut nh. Do vn t ra l ta cn phi gim c dng in m my ca ng c khng ng b , c bit l vi ng c khng ng b rto lng sc. Bi v vic tc ng vo ng c rto lng sc kh khn hn so vi ng c khng ng b rto dy qun. Tuy nhin, hin nay vi vic p dng nhng ng dng ca in t th cng vic tr nn d dng hn. ChngII

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Cc phng php m my

2.1-M my ng c in khng ng b: Khi bt u m my th roto ang ng yn, h s trt s=1 nn tr s dng in m my tnh theo mch in thay th bng :

1k2

1 1 2 1 1 2

UI(r C r ) ( C x )

x

T cng thc trn ta thy , dng in khi ng ng c khng ng b ph thuc vo bn thn cu to ca ng c v ph thuc nhiu vo in p li . Trn thc t , do mch t tn bo ha rt nhanh, in khng gim xung nn dng in m my cn ln hn so vi tr s tnh theo cng thc trn, in p nh mc .thng dng m my bng 4 n 7 ln dng nh mc .iu khng nhng lm cho ng c nhanh b hng m cn lm cho in p li mi khi khi khi ng gim nhiu .Do nht thit ta phi lm gim dng in m my . 2.2-Cc phng php m my : Cc yu cu m my c bn :

- Phi c mmen m my ln thch ng vi c tnh c ca ti . - Dng in m my cng nh cng tt . - Phng php m my v thit b cn dng n gin , r tin , chc chn - Tn hao cng sut trong qu trnh m my cng nh cng tt 2.2.1-M my trc tip ng c in rto lng sc : y l phng php n gin nht, ta ng trc tip ng c in vo li in .Khi in p U1 t vo dy qun stato bng in p li (nh hnh v).Do dng in m my ln , nu qun tnh ca ti ln thi gian m my di th s c th lm cho my sinh nhit v nh hng in p li. .

u

2.2.2-H in p m my:

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T cng thc ca dng in m my ta thy, nu gim in p t vo stato khi m my th s gim c dng in m my. Nhng h in p m my th cng s lm cho mmen khi ng gim xung.

2

1 1 2k 2 2

1 1 1 2 1 1 2

m pU rM2 [(r +C r ) (x C x ) ]f

Do ta ch dng phng php ny cho nhng thit b m my c nh. 2.3-Cc phng n: -Ni in khng trc tip vo mch in stato: Khi m my trong mch in stato t ni tip mt in khng, sau khi m my song th in khng ny b ni ngn mch. -Dng bin php t ngu: Ta s dng mt my bin p t ngu, bn cao p ni vi li in, bn h p ni vi ng c in. Sau khi m my song th bin p t ngu c ngt ra khi mch ng lc(ng c ) -M my bng phng php thay i ni -: phng php ny thch ng vi nhng my khi lm vic bnh thng ch u tam gic, khi m my ta i thnh sao. -Dng b iu p xoay chiu ba pha dng ba triac u song song vi nhau. * Phn tch u nhc im ca tng phng php m my: + C bn phng php trn u c tc dng h dng m my nhng trong qua trnh hot ng ca ng c khi dng tng t ngt v mt l do no th 4 phng php trn khng p ng c(khng hn ch c dng ) v vy ta dng b iu p xoay chiu 3 pha. u im ca b iu o xoay chiu 3 pha khi iu chnh gc thch hp ca cc xung iu khin t vo cc thyristor l c th h c in p t vo stasto v do c th hn ch c dng qua ng c. V vn cn tham gia vo mch trong qu trnh hot ng ca ng c . Tuy nhin nhc im ca phng php ny l dng in v in p u khng sin. Nhng do thi gian m my rt nh (t 1-3 giy) nn t vn c th s dng c . V vy ta quyt nh chn phng n dng b iu p xoay chiu 3 pha lm b khi ng cho ng c khng ng b 3 pha rto lng sc. 2.4- Phng php dng b iu p xoay chiu 3 pha: Ta s dng 6 thyristor u song song ngc theo s nh hnh v. Khi ta cp in p xoay chiu vo ba u A, B, C, do cn ph thuc vo gc m van ca cc thyristor nn ta s c 3 dng in p t vo ng c ng vi 3 vng ca gc m van. Cc in p ny u nh hn so vi in p vo .

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T1

A

C

CB

T6 T5T4 T4 T3 T2

2.5- Phn tch hot ng ca b iu p xoay chiu 3 pha: -V ng c khng ng c khng ng b c th coi nh l mt ph ti gm c in p tr v cun cm ni tip nhau, trong o: +in tr rto bin thin theo tc quay. +in cm ph thuc vo v tr tng i gia dy qun rto v stato. + Gc pha gia dng in v in p cng bin thin theo tc quay = (s). -Do tnh cht t nhin ca mch in (c in cm)nn nu trong khong v < m t xung iu khin vo cc van bn dn th cc van ny ch dn dng thi im v= tr i.Do in p ng c khng ph thuc vo gc m .Nu nh vy th ta khng iu chnh vo in p , v vy ta ch t xung iu khin vi gc m > . -Khi v> th ty thuc vo gi tr tc thi ca cc in p dy m c lc c 3 van 3 pha khc nhau dn dng , hay 2 van 2 van khc nhau dn dng: +Nu c 3 van 3 pha khc nhau dn dng.

c'b' ... a'

cba

ZcZbZa

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Khi dng in ti :

dmUi= sin( )

3Z

Um :bin in p dy :Gc lch pha gia in p v dng in giai on ang xt +Nu ch c 2 pha c van dn:

c'b' ... a'

cba

ZcZbZa

Khi ta c dng in ti :

dmUi= sin( )2Z

Ty thuc vo gc iu khin m cc giai on c 3 van dn hoc 2 van dn cng thay i theo. *Khong dn ca van ng vi = 0 600 : Trong phm vi ny s c cc giai on 3 van v 2 van dn xen k nhau nh th di y:

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t

tttttt

Ua

T6

T5

T4

T3

T2T1

ca

b

Khong van dn ng vi = 60 900

t

t

t

t

t

t

t

u

T6

T5

T4

T3

T2

T1

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CHNG III : CC PHNG PHP BO V VAN

3.1 Bo v qu nhit cho van

Khi lm vic vi dng in c dng chy qua trn van c st p, do c tn hao cng

sut P tn hao ny sinh ra nhit t nng van bn dn. mt khc van bn dn ch cho php

lm vic di nhit cho php Tcp cho php no , nu qu nhit cho php th cc van

bn dn d b ph hy. van bn dn lm vic an ton khng b chc thng v nhit ta phi

chn v thit k h thng tn nhit hp l.

Tnh ton cnh tn nhit

Tn hao cng sut trn mt tiristor: P = U.Ilv =1,6.104,3 =166,88 W

Din tch b mt tn nhit: mm

PSK .

Trong : P tn hao cng sut

- chnh lch so vi mi trng.

Chn nhit mi trng l : Tmt = 400C,

Nhit lm vic cho php ca tiristor l Tcp = 1250C

Chn nhit trn cnh tn nhit Tlv = 800C

= Tlv Tmt = 80 - 40 = 400C

km : h s ta nhit bng i lu v bc x. chn km = 8 (w/m2 0C)

Vy ta c din tch ca mi cnh tn nhit:

m 4166,9S 5215

10 8.40 (cm2)

Chn loi cnh tn nhit c36 cnh kch thc mi cnh: a x b = 10 x 10 (cm x cm)

Vy tng din tch cnh tn nhit ca cnh tn nhit: S = 26.5.10.10 = 13000(cm2)

3.2 Bo v qu dng cho van

Trong qu trnh hot ng v lm vic ta phi sa cha v bo dng mch ng lc cng

nh mch iu khin do vy trong mch cn c thm cc thit b bo v ng ngt nh:

aptomat, cu ch, cu dao.

Nh ta bit Ic =208.6A

Ta chn aptomat c thng s v tr s nh sau:

Itt =kmm.Ic = 6 . 208.6 =1251.6A(kmm = 5 7)