khoi dong dong co

7/30/2019 Khoi dong dong co

1/72

Li ni u

Mt trong nhng mc tiu quan trng hng u m ng v Nh

nc t l tin trnh cng ngh ho , hin i ho t nc.

tin hnh cng ngh ho , hin i ho cc doanh nghip cn

phi tin hnh xy dng li cc nh my , c s sn xut, trang thit b

my mc a cng ngh hin i ho vo sn xut . Hn th na , vn

hnh tt cc nh my cn phi c mt i ng cng nhn k thut c trnh

chuyn mn cao.

L mt sinh vin sp tt nghip Khoa in ngnh T ng ho

trng i Hc Bch Khao H Ni , em hiu rng t ng ho nghipcng nghip ng vai tr ht sc quan trng trong s pht trin ca ngnh

cng nghip Vit Nam. Trong t thc tp tt nghip ny em c thy

gio TS. V Minh Chnh hng dn em thit k n tt nghip vi

ti l : " Thit k b khi ng ng c khng ng b ba pha ".

bi bao gm 3 chng :

Chng I: Gii thiu v ng c khng ng bChng II: Gii thiu v tnh ton b bin i.

Chng III: Xy dng v thit k mch iu khin.

hon thnh tt c n, em c s gip rt nhiu ca

khoa in trng i Hc Bch Khoa H Ni v c bit l s gip

tn tnh ca thy gio TS. V Minh Chnh. Sau mi tun lm n em

hiu c cu to v nguyn l hot ng ca ng c khng ng b.

V qua em bit cch tnh ton v thit k b khi ng ng ckhng ng b . l nhng kinh nghim qu bu gip em vng tin hn

trong cng vic sau ny . Mc d ht sc c gng nhng ti ca em

vn cn nhiu thiu st , em rt mong c s ch bo ca cc thy .

Em xin chn thnh cm n!

Sinh vin

Chng I:Gii thiu chung v ng c khng ng b

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I- Gii thiu chung v ng c khng ng b .

1. Gii thiu chung :

ng c khng ng b l my in xoay chiu, c tc rto khctc stato . T trng quay c th l 1 pha , 2 pha hoc 3 pha, tu thuc

vo cu to dy qun stato l 1 pha, 2 pha hoc 3 pha. Theo cu to dy

qun rto , ng c khng ng b c chia lm 2 loi: Rto lng sc v

rto dy qun ng c khng ng b lng sc c cu to n gin, vn

hnh v bo qun d dng , tin cy cao , gi thnh r , nn c ng

dng rng ri trong thc t. ng c khng ng b rto dy qun c cuto phc tp vn hnh v bo qun kh hn, tin cy km hn, gi thnh

cao hn nhng n c u im l c th a in tr ph ngoi vo

ci thin tnh nng m my v iu chnh . Tc do n khng c

s dng cho nhng ni no c cu dao v m my v iu chnh tc

m ng c lng sc khng p ng c.

Tuy nhin ng c khng ng b c nhc im l iu chnh tc

v khng ch cc qu trnh qu kh khn ring vi ng c rto

lng sc , cc ch tiu khng ng b.

2. Cu to

2.1. Phn tnh ( Stato)

Trn stato c v, li st v dy qun.

a/ V my:

V c tc dng c nh li st v dy qun, khng dng lm

mch dn t. Thn v my lm bng gang . i vi my c P tng i

ln ( 1000kw) thng dng tm kim loi lm thnh v.

b/ Li st.

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Li st l phn dn t, v t thng i qua li st l t thng quay nn

gim tn hao, li st c lm bng li thp k thut in dy 0,5 mm

ghp li. Khi ng kinh ngoi li st nh hn 0,9mm . Th dng c tm

trn ghp li. Khi ng knh ngoi ln hn 0,9mm th phi dng cc tm

hnh r qut ghp li :

(hnh I.1).

Mi l thp k thut in u c ph sn cch in trn b mt

gim tn hao do dng in my gy nn.

Nu li st ngn th c th ghp thnh khi , nu li st di th ghp

thnh tng thp ngn , mi thp t 6 - 8 cm t cch nhau 1 cm thng

gi cho tt , mt trong ca l thp c s rnh t dy qun.

c/ Dy qunDy qun stato c t vo cc rnh ca li st v c cch in

tt vi li st.

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2.2. Phn quay Rto.

C 2 b phn chnh: Li st v dy qun.

a/ Li st.

Li st dng l cc l thp k thut nh stato , li st c p trc

tip trn trc ng c hoc ln mt gi roto ca ng c pha ngoi ca l

thp c s rnh t dy qun.

b/ Dy qun to

Phn lm 2 loi chnh: Loi rto kiu dy qun v loi roto kiu

lng sc.

- Loi rto kiu dy qun: Roto c dy qun ging dy qun stato.

Trong ng c c trung bnh tr ln thng dng dy qun kiu sng 2

lp v bt c nhng dy u ni kt cu ca dy qun trn rto cht

ch. Trong my in c nh thng ng tm mt lp. Dy qun 3 pha

ca roto thng u hnh sao cn ba u kia c ni vo ba rnh trtthng lm bng ng t c nh mt u trc v thng qua chi than

c th u vi mch da? Bn ngoi . c bit ca roto kiu dy qun l

c th thng qua chi than a in tr ph vo mch in roto ci

thin h s cng sut ca my khi my lm vic bnh thng. Dy qun

roto c ni ngn mch.

- Loi roto kiu lng sc , kt cu ca loi dy qun ny rt khc,vi dy qun stato trong mi rnh ca li st roto t vo thanh dn bng

ng hay nhm di ra khi li st v c ni tt li hai u bng 2

vnh ngn mch bng ng hay nhm lm thnh mt ci lng gi l lng

sc.

Dy qun rto lng sc khng cch in vi li st . ci thin

tnh nng m my trong my cng sut ln. Rnh roto c th lm thnh

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dng rnh su hoc lm thnh hai rnh lng sc kn trong my c cng

sut nh , rnh rto thng c lm cho i mt gc so vi tm trc.

2.3. Khe h.

V rto l mt khi trn nn khe h u . Khe h trong ng c khng

ngb rt nh ( t 0,2 1 mm ) . hn ch dng in t ho ly t li

ln v nh vy mi c th lmcho h s cng sut ca my cao hn.

II- Nguyn l lm vic ca ng c KB 3 pha.

Sau khi ni thng cun dy stato vi ngun in 3 pha , th s sn

sinh ra t trng quay.

Nu t trng quay theo chiu kim ng h th theo quya tc bn

tay phi dy dn ca roto pha cc N ct t trng , dng in cm ng

i theo chiu xuyn t mt giy ra. Dy dn ny chu tc dng ca lc

s lm cho roto quay theo chiu kim ng h . Tng t nh vy pha

cc S , roto chu tc dng ca lc cng quay theo chiu kim ng h . Cc

lc in t to thnh mt mmen in t i vi trc quay, do lmcho rt quay theo chiu quay cu t trng quay.

Tc quay ca N2 ca roto lun lun nh hn tc quay ca n1

ca t trng quay ( tc quay ng b ). Nu tc quay ca roto t

n tc quay ng b th khng cn c s chuyn ng tng i gia

n v t trng na. Dy in ca rto s khng ct ng sc do sc

in ng cm ng , dng in v momen in t ca n u bng 0 . Do ta thy roto lun quay theo t trng quay vi tc n2 < n1 .

5

N

S

n1

F

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Nguyn l lm vic ca ng c khng ng b.

Ta gi ng c khng ng b v tc quay n2 ca roto khng

bng tc quay ng b ca trng quay ca roto .

Trong : n1 - n2 : L hiu s tc quay ca ng c KB.

T s gia hiu s tc quay vi tc quay ng b gi l

trt . K hiu l S :

1

21

n

nn

S

=

Khi ng c KB 3 pha trng thi ph ti nh mc th trt

ca n rt b ( 0,02 0,06).

Sau khi ni thng cun dy stato ca ng c KB vi ngun in

xoay chiu 3 pha , qua tc dng ca t trng quay s truyn in nng

cho rto . Hin tng ny ging nh t trng bin i xoay chiu

trong li st ca MBA truyn in nng t cun s cp cho s cp cho

cun th cp. Do khi dng in trong roto tng ln th dng in trong

stato cng tng ln.

Momen in t (M) ca ng c KB t l thun vi tch ca t

thng quay () v thnh phn tc dng ca dng in roto (I2 cos 2 )

M = CM . I2 cos 2

CM: L hng s momen ca ng c KB

i vi mt ng c ch to hon chnh th n l mt tr s xc

nh khng i, th tr s cng thc trn v c bn khng thay i

nn momen in t ca ng c KB tu thuc vo dng in I2 ca roto

v h s cng sut cos 2 ca mch in roto.

- Khi n1 - n2 gim th I2 gim.

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Khi bt u khi ng ng c , roto cha quay , do hiu s tc

quay n1 - n2 = n1 , lc ny dy dn ca roto ct t trng quay vi tc

ln nht . Khi roto bt u quay th tc tng i ca dy dn roto

ct t trng quay gim xung, n1 - n2 gim xung do I2 gim .

- Khi n1 - n2 gim th cos 2 tng ln .

Mch in rto tng ng vi mt cun dy qun trn li st n

cng c cm khng, ln ca cm khng t l thun vi tn s ca dng

in trong roto . Cm khng cng nh th cos cng ln . Tn s ca dng

in trong roto gim khi n1 - n2 gim -> cos tng.Ta thy quan h gia momen in t v trt kh phc tp ,

l mt ng cong quan trng biu th c tnh vn hnh ca ng c

KB cho ta thy trt khi momen in t thay i.

- Mmax : Momen cc i

- Mx : Momen khi ng

- Mm : Momen nh mc

- Sth : trt ti hn.

ng cong momen ca ng c KB

7

M

Sth

S =

1

Mm

Mmax

Mkdd

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Sau khi u ng c vi ngun in thi im bt u khi ng

S = 1 , lc ny I2 ln nht, cos nh nht gi l momen khi ng. Nu

Mk ln hn momen cn trn trc ca ng c th roto s quay v tng

dn tc , momen in t ca ng c cng tng dn theo on ng

cong BA ln ti im A, sau khi t n momen cc i Mmaxli gim dn

theo on ng cong AO .

Khi M = Mcn th ng c s quay theo mt tc khng i v vn

hnh n nh theo on ng cong OA.

Khi ng c lm vic n nh OA , nu tng momen cn ( tng

ph ti) th tc quay ca ng c gim xung ( S tng ln ) lm cho

momen in t tng ln . Do to nn s cn bng mi vi momen cn,

nu ph ti tng ln n mc lm cho momen cn vt qu momen cc

i.

Nu ph ti tng ln n mc lm cho momen cn vt qua momen

cc i , th tc quay ca ng c s gim xung nhanh chng cho nkhi dng li. Do phm vi lm vic n nh ca ng c ch hn ch

trong on ng cong OA.

Khi ng c lm vic lin tc v lu di, trn trc ng c truyn ra

mt momen nh mc. Momen nh mc ca ng c phi nh hn

momen cc i. Nu khi thit k cho momen nh mc gn bng momen

cc i , th khi hi qu ti mt t ng c s dng li ngay. Do ng

c phi c mt kh nng qu ti nht nh , kh nng qu ti l t s gia

momen cc i v momen nh mc k hiu

38,1max ==dmM

M

Trn y ta xt khi in p ca ngun in khng thayi, nu in

p thay i th t cng thc :

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9/72

M= CM . .I2.cos 2

Ta thy: V v I2 u thay i theo in p U nn M bin i

theo U2 . Nh vy in p c nh hng kh ln i vi momen in t

ca ng c KB.

in p thp th dng in trong stato tng ln c th lm chy ng

c , do cc ng c c ln u c thit b bo v in p thp ( hoc

km in p ).

III- c tnh c bn ca ng c khng ng b.

* Phng trnh c tnh c .

thnh lp phng trnh c tnh c ca ng c khng ng b

ta da vo thay th vi cc gi thit sau:

- 3 pha ca ng c l i xng.

- Cc thng s ca ng c khng ng b khng i.

- Tng dn mch t ho khng thay i, dng in t ho khng

ph thuc ti m ch ph thuc vo in p t vo stato ng c.- B qua cc tn tht ma st, tn tht trong li thp.

- in p li hon ton sin i sng ba pha

Ta c s thay th.

U1f

1I X1T

1I'X

R

1R X'2

R'2S

Trong :

U1f: in p pha t vo stato

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I, I1,I'2 : Cc dng in t ho, stato v dng in roto qui i v

stato

X,X1,X2: in khng mch t ho , in khng tn stato v in

khng tn roto qui i v stato.

R,R1,R2: Cc in tr tc dng ca mch t ho ca cun dy stato

v roto qui i v stato.

S: trt ca ng c, c trng cho tc quay ng c KB

vi t trng quay.

p

fW

p

fn

n

nn

W

WWS

2;

6000

0

0

0

0

==

==W0: Tc t trng quay.

: Tc gc ca ngc

f: Tn s in p ngun t vo stato

p: S i cc t ng c.

Da vo s thay th ta tnh c dng in stato

( )

( )

++

+

++

=

++

+

++

=

221

2

21

221

221

2

21

2211

''

11

''

11

XXS

RR

XRU

XXS

RR

XRUI

f

f

(1-11) phng trnh c tnh dng in stato

- Khi =0 -> S = 0

Dng khng ti

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I1 = 10221

IXR

U f =+

- Khi = 0 -> S = 1

-> I1 =( ) 2221

22

1

'

1

nm

f

XRRXR

U

+++

+

Gi l I1 ngn mch.

-> I'2 = ( )nm

nm

f IXRR

U 222

21

1 ''

1. =

++

S

0

I'2nm 1nmI' 1'I I'1

(Hnh 1.5)

Cng sut in t chuyn t stato sang roto

P12 = Mt. 0

Mt: Momen in t ca ng c

Nu b qua cc tn tht ph th Mt = M= M

Cng sut c chia thnh 2 phn

Pc: Cng sut a ra trn trc ng c

P2: Cng sut tn hao ng trong roto

P12 = Pc +P2

-> M0 = M+P2

-> P2 = M.( 0 - ) = M0.S

Mt khc : P2 = 222 '.'.3 RI

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Nn: M =SW

RI

.

'.'.3

0

222

Thay I'2 tnh c trn vo ta c:

SXS

RRW

RUM

nmo

f

.'

'.3

2

2

2

1

221

+

+

=

Biu thc trn l phng trnh c tnh c ca ng c KB

Kho st : bng cch gii 0=s

M

d

dta xc nh c cc im cc tr.

Tr s ca M v S ti im cc tr k hiu l Mth v Sth

221

2'.nm

th

XR

RIS

+=

Thay vo phng trnh c tnh ta c.

( )2211

21

.2

.3

nmo

f

th

XRRW

UM

+=

Du (+) ng vi ch ng cDu (-) ng vi ch my pht

thFM 0

SthF

Mth

thFS

S

M

Hnh 1.6: th c tnh c ca ng c KB

Khi nghin cu h truyn ng vi ng c KB. Ngi ta quan

tm n trng thi lm vic ca ng c nn ng c tnh c thng

biu din khong tc 0 S Sth

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S

M

0

Sth

0M

TN (R =0)f

fR =0

mM M th

Hnh 1.7

c tnh c bn ca ng c KB = f (M) trong ch ng c

n gin phng trnh c tnh c:

thth

th

tht

SaS

S

S

S

SaMM

.

.1(.2

++

+=

Trong :2

1'R

Ra =

i vi cc ng c cng sut ln thng R1 rt nh so vi Xnm lc

ny c th b qua R1, coi R1 = 0 ; a.Sth = 0 ta c.

S

S

S

S

MM

th

th

th

+=

.2

Trong :

nm

f

th

nm

th

XW

UM

XRS

..2

.3

'

1

21

2

=

=

IV - Cc phng php m my ca ng c KB

iu kin m my l: Mm>Mco ( momen cn ban u trn trc my)

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Khi m my thng Im ( 5 - 7 ) Im . V vy nu cng mt lc c

nhiu ng c m my th dng in tng t li in quc gia vo x

nghip s ln -> Mmc gim. Thi gian m my tm ln -> aptomat tng b

tc ng -> mt in ton x nghip -> ta phi tm cch gim dng m

my.

Tu theo tnh cht ca ti v tnh hnh ca li in yu cu v m

my i vi ng c in cng khc nhau. Ni chung khi m my ng

c cn xt n yu cu c bn sau:

- Phi c momen 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 qu trnh m my cng thp cng tt.

1. M my ng c KB roto lng sc.1.1. M my trc tip.

ng trc tip ng c vo li in nh cu dao. y l phng

php m my n gin nht nhng lc m my trc tip, dng in m

my ln, thi gian m my qu ti th c th lm cho my nng v nh

hng n in p li.

Nu ngun in tng i ln th nn dng phng php m myny v m my nhanh, n gin. Phng php ny ch dng trong nhng

ng c c cng sut nh hoc cng sut ng c v cng nh so vi

cng sut li in.

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Hnh 1.8

1.2. M my bng phng php h in p.

a/ Ni in khng ni tip vo mch in stato.

LU

D2

D1

Hnh 1.9:H p m my bng in khng.

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Khi m my trong mch in stato t ni tip mt in khng ta

hon tt vic m my bng cch ng cu dao D2 th in khng trn s b

ngn mch. C th iu chnh tr s m in khng c c dng in

m my cn thit. Do c st p trn in khng nn in p t vo ng

c Ut s gim i v nh hn in p li UL.

Gi s :ck

dck

UU 1= ( kck >1)

Gi dng in m my v mmen m my trc tip l Im v Mm sau khi

thm in khng vo , dng in m my cn li Im

Im =ck

m

dcckdc

dc

k

I

ZK

U

Z

U==

.

1

V mmen m my t l vi bnh phng ca in p nn :

2ck

mmck

k

MM =

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17/72

b/Dng in p t ngu h in p m my.

UL

1D

2DT

D3

Hnh 1.10: H p m my bng bin p t ngu

Trong s : T l bin p t ngu,bn cao p ni vi li in , bnh p ni vi ng c. Sau khi m my xong th ta ct T ra bng cch

ng cu dao D2 v m D3 .

My bin p t ngu ni Y - Y c im trung bnh tnh ni t.

Trong my bin p th BAkI

I

U

U'

2

1

2

1 ==

Mt khc da vo s ta thy:U1 = Ue ; U2 = Uc ; Iml = I1 ; Imc = I2 .

-> Uc =bak

U1 ( Ging phng php cun khng )

Imc =ba

m

k

I

Iml = 22

'' ba

m

ba

mdc

ba k

I

k

I

k

I

==

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18/72

-> Mmba = 2ba

m

k

M

Phng php ny thy dng in m my ly t li vo nh hn

rt nhiu so vi phng php m my trn. Mt khc khi ly t li vo 1dng in m my bng dng in m my ca phng php trn th

phng php ny c mmen m my ln hn . y chnh l u im ca

phng php dng bin p t ngu h bin p m my.

c/ M my bng phng php Y -

Phng php ny thch ng vi nhng my khi lm vic bnh

thng u tam gic. Lc m my chuyn sang u Y. Nh vy in p i

vo 2 u mi pha ch cn31U .

Khi m my ng cu dao D1 cn cu dao D2 th ng xung di

im m my du Y khi my chy ri th ng cu dao D 2 v pha trn

my u tam gicTheo phng php ny ta c : Khi u

Im = Im =dc

d

dc

mZ

U

Z

UI 3.33 1 ==

Khi u Y :

3

3

13

1

mmY

mmY

m

my

MM

II

I

I

=

=

=

( V in p t ln dy qun gim 3 ln ).

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19/72

3. M my ng c khng ng b roto dy qun.

M my bng cch a in tr ph vo roto

3K

2K

1K

R f1

f2R

f3R

SW

Aac

eeg

b

d

f

W0

0Mc 2M M1

Hnh 1.11

Phng php ny ch dng vi nhng ng c roto dy qun v c

im ca loi ng c ny l c th thm in tr vo cun dy roto . Khi

in tr roto thay i th M = f(S) cng thay i. Ta iu chnh in tr

mch in roto thch hp th s c trng thi m my l tng.

Khi c in tr ph Rf th ta c:

( ) ( ) 2212

21 ''' XXRRR

UI

f

mrf

++++=

( ) ( )[ ]2212

211

22

'''.2

)'(..3

XXRRRf

RRUpM

f

f

mrf++++

+=

Nh vy khi c in tr ph th ImRf gim v MmRf ln .

Sau khi my quay gi mt mmen in t nht nh trong qu

trnh m my ta ct dn in tr ph.

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20/72

Khi ta ct dn cc in tr ph th s lm thay i tc ng c t

ng M = f(S) ny sang M = f(S) khc . Sau khi ct ht in tr ph th

tc t n im lm vic sau 3 cp in tr khi ng

Nh vy dng ng c khng ng b roto dy qun c th t

c momen m my ln, dng in m my nh nn ta thng dng

nhng ni no m my kh khn , yu cu m my cao. Cu to phc

tp , bo qun kh khn, gi thnh cao... l nhc im ca ng c

khng ng b roto dy qun .

V. Xy dng mch lc

* S mch lc

C

RN RN

K

A B C

AP

1 2K 3K

20


21/72

* Nguyn l hot ng

Khi ng Aptomat vo, ngun in qua b bin i a n khi

ng ng c. B khi ng bao gm 6 Thyristor mc song song ngc

c mch RC bo v hin tng qu in p trn Thyristor. Nh b bini ny ta h thp c in p trc khi a n khi ng ng c.

Khi ng c chy, mun ct b bin i ra khi h thng

khi ng ta n vo nt M. Khi K c in v ko cc tip im K ng

li ct b bin i ra khi ng c.

4 - nh gi nhn xt v la chn .

Trc khi khi ng ng c khng ng b 3 pha nu ngt mch

in 1 pha ca stato th ng c cng khng khi ng c . Nhng

trong qu trnh vn hnh , nu dy chy ca mt pha no b t th

ng c vn tip tc quay th mmen cn trn trc ng c cha thay i ,

nh vy dng in trong mch in ca hai pha cn li s tng ln t

ngt dn n hu qu l ng c b nng ln qu mc v b hng, do

cn phi c bit . Ch khi vn hnh ng c khng ng b 3 pha c

hin tng b t cu ch ca mt pha no khng .

Sau khi khi ng nu ct mch in cun dy khi ng th ng

c vn c th tip tc quay , iu chng t rng cun dy khi ng

khng c tc dng na . Do trong ng c khng ng b 1 pha ngita thng lp 1 cng tc ly tm , sau khi quay n s t ng ct mch

in ca cun dy khi ng .

Nhn xt:

Ngi ta s dng ng c khng ng b trong truyn ng v

cng c th iu khin n c c mi yu cu mong mun nh tc

khng i, momen khng i hay hm ng c.

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S lm mt ng c thng tu thuc vo dng xoy khng kh

trong khe, do qut lp trn trc ng c to nn . Khi ng c quay vi

tc nh hn nh mc th hiu qu lm mt ln hn -> phi gim

momen hay dng thng gi cng bc nh thit b bn ngoi to nn.

Vic gim cc tn hao ca truyn ng lm tng hiu xut chung v

tit kim nng lng.

* La chn phng php khi ng

T cc phng php khi ng trn ta thy phng n 4 l phng

n thch hp nht . Trc ht ta i phn tch tng phng n thy c

u nhc im cng nh phm vi ng dng ca n.

* Cng dng ca ng c khng ng b .

Do kt cu n gin , lm vic chc chn , hiu xut cao , gi thnh

h nn ng c khng ng b l mt trong nhng loi ng c in c

dng rng ri nht trong cc ngnh kinh t quc dn vi cng sut vi

chc n vi nghn kw . Trong ngnh cng nghip thng dng ng ckhng ng b lm ngun 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 nh gi. Trong nng nghip dng lm my bm

hay my ch bin nng sn phm. Trong i sng hng ngy, my in

khng dng b cng dn chim mt v tr quan trng: Qut gi , my quay

a ... Tm li theo s pht trin ca nn sn xut in kh ho va , tng ho v sinh hot hng ngy ... Phm v ng dng ca my in

khng ng b ngy cng rng ri.

Tuy nhin ng c khng ng b cng c nhng nhc im nh :

Cng sut ca ng c khng cao lm v c tnh iu chnh tc khng

tt nn vic s dng ng c khng ng b c phn b hn ch .

22


23/72

- Phng php khi ng trc tip.

u im: Phg php ny n gin chi vic ng trc tip ng c

vo li in .

Song n ch ph hp vi nhng ng c c cng sut nh hn 50kw

. Cn vi yu cu , ng c my bm c P = 250 kw , ta khng s dng

c phng php ny .

- Phng php dng cun khng mc ni tip vo.

Phng php ny cng d thc hin , ch vic ng AP1 v sau thi

gian khi ng AP2 t ng li .

Tuy nhin phng php ny thng xut hin tia la in gy nguy

him cho ngi vn hnh . Thm vo phng php ny khi ng theo

cp in p -> rt tn , thit b cng knh , gi thnh cao => khng s

dng

- Phng php Y -

i vi phng php ny ch thch hp vi loi ng c ng b lloi ng c c cp i ni Y - l 380/600 => ng c bm l 380/220

-> khng thch hp.

- Phng php dng Thyristor.

T vic phn tch trn ta thy phng php ny l ti u nht, dng

phng php ny va h c in p ( dng iu p xoay chiu song

song ngc ) thm vo khi ng m , khng pht sinh tia la in , c

th huy ng cng sut nh , iu khin c cng sut ln, vn hnh n

gin, an ton v tin cy cao.

23


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Chng II

Cc b bin i xung p

Cc b bin i xung p c chc nng bin i mc in p .

Nguyn l bin i xung p l dng mt phn t kho ni ti vo ngun

trong mt thi gian nht nh tx trong khong t 0 - T ta thay i c gi

tr trung bnh ca in p gia ti trong chu k T .

Nguyn l bin i in p ny c u im c bn l:

C th thay i gi tr in p trong mt phm vi rng m hiu sut

ca b bin i rt cao v tn tht trong b bin i ch yu l trn pn t

ng ct rt nh.Cc b bin i xung p xoay chiu.

Cc b bin i xung p xoay chiu , dng iu chnh gi tr in

p xoay chiu vi hiu sut cao. Xung p xoay chiu ch yu s dng cc

Thyristor mc song song ngc hoc Triac thay i gi tr in p

trong na chu k ca in p li theo gc m -> T thay i c

gi tr hiu dng ca in p ra ti .* Cc s van .

Xung p xoay chiu s dng cc s van c bn nh sau. Cc s

ny l tng ng nhau trong chc nng iu chnh in p xoay

chiu

G

a/ Thyristor u song song ngc b/ Cu Diot c/Triac

24


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Ta nhn thy trong 3 s trn th s a c s dng nhiu nht v :

Nh ta bit van bn dn ph hp nht cho bin i xung p xoay

chiu l Triac v y l loi duy nht cho dng xoay chiu i qua n . Tuy

nhin ngi ta thng dng Thyristor u song song ngc thay cho

Triac, lc ny mi Thyristor theo mt chiu nht nh nn tng li dng

qua cm Thyristor l xoay chiu . Thm vo vic m cho kho

Thyristor d hn Triac.

Cn i vi s b, nu thay Thyrystor bng mt trazitor th c th

thc hin c iu chnh in p bng phng php iu ch rngxung mo na chu k in p li. Tuy nhin tn hao cng sut trong

s ny cao hn cc s a, c.

I. Xung p xoay chiu 1 pha

1. Trng hp ti thun tr

a. S nguyn l

UT1T

R(2T)

i

cU2i

T2UT

~U

i 1

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b. Dng in p

2i

Uc

tU

iU

0

0

0

22U

2

2

y

i1

i

c. Cng thc tnh ton

* Gi tr hiu dng ca in p trn ti

=

dUUC2)sin2(

1=

2

2sin)(2 +U

* Gi tr hiu dng ca dng ti

R

U

R

UI CC ==

2

2sin)(2 +

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* Cng sut tc dng cung cp cho mch ti.

P = Uc.Ic =( )

2.

2sin22.2

R

U +

* Gi tr trung bnh dng qua Thyristor

- Dng in qua Thyristor ch tn ti trong mt na chu k -> nn

tr s hiu dng dng qua Thyristor l :

IT =

2

2sin)(2

22

+=

R

UIc

- Tr s trung bnh dng qua Thyristor

* Dng qua Thyristor trong mt chu k c dng: Vi 0 < Itb = TI

2

* in p ti a t trn van : UTmax = Umax = U2

d/ Nguyn l lm vic ca mch xung p xoay chiu mt pha vi

ti thun tr.

- Khi T1 m th mt phn ca na chu k dng , in p ngun t

ln mch ti , khi T2 m th mt phn ca na chu k m in p ngun

t ln mch ti.

Gc m c tnh t thi im i qua gi tr 0 ca in p ngun ( V)

Khi dng in ti : it = sin2

U vi


28/72

=> Ngay c trong trng hp ti thun tr li in xoay chiu vn

phi cung cp mt lng cng sut phn khng.

T cng thc tnh P ta thy : Bng cch lm bin i gc t 0

ta c th iu chnh c cng sut tc dng cung cp cho mch ti t gi

tr cc i:

Pmax = 02

R

U

2.Trng hp ti thun cm

a/ S nguyn l :

~U

T

U2T

i 2 Uc

T1TU

1i

tZ

b/ Dng in p

28


29/72

2

2

0

0

0

Ui

Ut

cU

i1

i

2

2i

i2

+

c/ Cng thc tnh ton

* Gi tr hiu dng ca dng in ti.

==

22

22 )cos(cos

1.

2.

1d

L

UdiIc

->

2sin3)2cos2)((2.

++= =

L

UIc

* Gi tr hiu dng ca in p trn ti

->

2sin3)2cos2)((2 ++= UUc

* Cng sut mch ti tiu th ( cng sut phn khng )

P = Uc . Ic =( )

.

2sin3)2cos2)((22

L

U ++

d/ Nguyn l lm vic ca XAAC 1 pha vi ti thun cm.

Khi = cho xung m T1 , dng in ti tng dn ln v t gi tr

cc i sau gim xung v t gi tr 0 khi = .

Khi Thyristor T1 m , ta c phng trnh.

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0cos.

2

sin..2

IL

Ui

tUdt

diL

+=

=

Hng s tch phn I0 c xc nh theo s kin : Khi = th i =0 . Cui cng ta nhn c biu thc ca dng in ti.

)cos(cos2

=L

Ui

Gc c xc nh bng cch thay = khi i = 0 -> = 2

Khi = + cho xung m T2

s lm vic nghim chnh khi ti thun cm phi tho mniu kin :

+ -> Do gc phi nm trong gii hn :

2

Dng in ti l dng gin on do dng i 1 , i2 to nn . Khai trin

Fourier ca n bao gm thnh phn sng c bn ( i) v cc thnh phn

sng hi bc cao

Thnh phn sng c bn lch chm sau in p ngun (V) mt gc

l2

c lp vi gc m

3. Trng hp ti (R+L)

a. S nguyn l

Zt

i 1

UT1T

cU2i

T2UT

~URt

b. Dng in p :

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U

c

2

TU

Ui

0

0

0

+

2i

i

1

c. Cng thc tnh ton :

* Gi tr hiu dng ca in p nhn c trn ti :

Uc = U .

2

2sin)(2sin +

* Gi tr hiu dng ca dng in ti :

2

2sin)(2sin.

)(22

+

+

==

LR

U

Z

UI cc

* Cng sut tc dng cung cp cho mch

+

+==

2

2sin)(2sin.

)(.

22

2

LR

UIUP cc

Phm vi iu chnh gc iu khin

Vi ti tr khng , in p ra ti thay i t 0 n bng in p

ngun th phm vi iu chnh gc iu khin :

Biu thc ca dng i c dng

+=

tgeLR

Ui ).sin()sin(.

).(

222

Biu thc trn ng trong khong t ( - ) =

Gc c xc nh bng cch thay = v t i=o

Sin ( - ) - sin ( -)

tge

= 0

ViRL

RZtg L ==

II- Xung p xoay chiu 3 pha

Qu trnh hot ng ca XAAC 3 pha phc tp hn nhiu so vi 1

pha v cc pha nh hng mnh sang nhau v cn tu thuc vo nhiu

yu t : s u van, gc iu kin c th , tnh cht ti .

Thng thng ,khi phn tch s hot ng ca s ta phi xc

nh lc no c 3 pha cng dn , lc no ch c 2 pha dn cng nh

khong dn ca cc van .

Nu mi pha ch c mt van dn th ton b in p 3 pha ngun

u ni ti

Nu ch 2 pha c van dn th mt pha ngun b ct khi ti -> do

in p a ra ti l in p dy no ang c van dn

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Khng c trng hp ch c mt pha dn dng

Ta lu rng trong h thng in p 3 pha, dng c th chy qua c

3 pha hoc ch qua 2 pha

Khi dng chy qua c 3 pha th in p trn mi pha ng bng in

p pha

Khi dng chy qua c 2 pha th in p trn pha tng ng bng2

1

in p dy

Sau y ta phn tch s hot ng ca s qua cc trng hp

sau :Vi 0 060 : Ch c cc giai on 3 van v 2 van cng dn

Vi 600 090 : Ch c cc giai on 2 van cng dn

Vi 900 0150 : Ch c cc giai on 2 van dn hoc khng c

van no dn c

1. S u Y c trung tnh

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2. S ti u Y khng trung tnh

3. S ti u

34


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Quy lut chung: mi thi im trong mt pha ch c th c mt

van dn -> trong mch s lng van ng thi dn ln nht l 3 van .

Trn hnh v ch trnh by dng in p ti u sao c trung tnh , ti

u khng c trung tnh v ti u sao.

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iii. Dng in p

1. = 0 - 600.

Trong phm vi gc ny s c cc giai on 3 van v 2 van dn xen

k nhau

aU

T1

2T

3T

4T

5T

6T

ab c a

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* Cng thc tnh ton

* Gi tr hiu dng ca in p pha ti.

Uan =

2

2sin

4

3

2.

1

.2

U

* Cng sut P:

=

++++

+

++

2

2

22

2

23 3

2

3

22

2

222

3

sin

4

sin

3

sin

4

sin

3

sin

.

3ddddd

R

Udm

-> P =

+

8

2sin

46.

.3 2

R

Udm

Nguyn l hot ng ca s XAXC 3 pha

Dng 6 Thyristor u song song ngc u vi ti thun tr, ti u

theo hnh sao v cch ly vi ngun = 30

+Trong khong : = 1 2

Van mt nng pha A ; Van6 dn pha B ; van 5 dn pha C ->

dng c th chy qua 3 pha -> C UZA = UA

+ Trong khong : = 2 - 3

Van mt dn pha A ; van 6 dn pha B -> dng c th chy qua 2

pha -> c UZA = 1/2. UAB


Van 1 dn pha A ; Van 2 dn pha C ; Van 6 dn pha B

-> UZA = 1/2. UAB


Van 1 dn pha A ; Van 2 dn pha C -> UZA = 1/2. UAB


Van 1 dn pha A ; Van 2 dn pha C ; Van 3 dn pha B

-> UZA = UA

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2. Trng hp : = 600 - 900

Trong phm vi ny lun ch c cc giai on 2 van dn :

Ua

A

ABU

2 2

UAC

B C A

=75 =600 0 0

=60

0

=120

T 1

2T

T3

T4

T5

5T

th in p pha A , = 750,gc dn ca Thyristor khng i

* Cng thc tnh ton

* Gi tr hiu dng ca in p qu ti.

Uan =

++

2cos

4

32sin

4

3

3.

4

3.2U

* Cng sut:

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39/72

P =

++

2cos

16

32sin

16

3

12

3 2

R

Udm

3. Trng hp : 900 < < 1200

* Dng in p

T5

5T

4T

3T

T2

1T

=150

=45000

=45=105

aU

* Cng thc tnh ton

Trong trng hp ny ch c cc giai on 2 van dn hoc khng

van no dn c

P =

+

+ +

32 32

222

3

sin

4

sin

.

3dd

R

Udm

39


40/72

-> P =

++

2sin

16

12cos

16

3

424

5

.

.3 2

R

Udm

40


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4 - nh gi v nhn xt

Qua cc phng php trn ta thy:

a. S ti u Y c trung tnh :

u im:

- S ging ht 3 mch iu p 1 pha iu khin dch pha theo

in p li do in p trn cc van bn dn nh hn v in p t vo

van bn dn l in p 3 pha. Cc van u in trung tnh nn s van

gim i mt na.

Nhc im: Tuy nhin phng php ny i hi ta phi ra ng 6

u dy m b khi ng ca ta khng ph hp. Chnh v vy ta khng s

dng s ny.

b. S ti u :

Hin nay s ti u l s thng dng nhng v s khng

c im trung tnh nn ta khng s dng s ny.c. S ti u Y khng c im trung tnh:

Qua cc s trn ta nhn thy s ny l s p ng c

y nhng yu cu m ti t ra. Chnh v vy ta la chn s

ny.

S ny c nhiu im khc vi s c dy trung tnh . y

dng in chy gia cc pha vi nhau nn ng thi phi cp xung iu

khin cho 2 Thyristor ca 2 pha mt lc .

Tuy nhin s ny cng c hn ch l vic cp xung iu khin

nh th i khi gp kh khn trong mch iu khin, ngay c khi vic i

th t pha ngun li cng c th lm cho s khng hot ng

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IV- Tnh chn v bo v van:

1. Cc iu kin tnh chn v bo v van .

* Cc iu kin bo v van:

- Khi chn van ta phi ch ti cc thng s bi cho , y ta

c :

P = 250 (kw) , cos = 0,85 , U = 380/220 , km theo cc yu cu

sau y i vi van l :

- in p ngc ln nht Ungmax

- Gi tr trung bnh cho php i vi dng in Itb

- iu kin lm mt cho van

- H s d tr dng in , in p.

* iu kin lm mt cho van:

- V van bn dn rt nhy cm vi nhit , nn khi lm vic nu

nhit mt ghp vt qu nhit cho php th d trong thi gian rt

ngn cng c th ph hng thit b bn dn . Chnh v vy m ta phi cnhng bin php lm mt m bo an ton cho cc van bn dn .

Thng thng ta c 3 phng php lm mt sau.

- Lm mt t nhin : dng cnh tn nhit v thng gi t nhin ,

phng php ny t hiu sut 25%-30%.

- Lm mt bng thng gi cng bc : bng cch lp qut gi vo

cnh tn nhit vi tc 15 m/s , hiu sut s dng 30% - 40%.- Lm mt bng nc : Cho nc chy tun hon qua van, hiu sut

ca phng php ny l 90%.

- Cn c d kin bi ta chn phng php lm mt bng thng

gi cng bc vi tc qut l 12 m/s.

* in p ngc ln nht t ln van l :

Ungmax = 6 U2 = 6 .220 = 538,9 (V)

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*in p van cn c l :

Uv = ku.Ungmax = 1,6.38,9 = 862,2 (V)

Ku - l h s d tr in p

* Dng in ti l :

It = cos..3dm

dm

U

P

Thay s vo ta c :

It = 85,0.380.3

250000

= 447 (A)Dng in trung bnh qua van l :

Itbv = 2242447

2==

It(A)

Thay s vo ta c :

Ibv = =%354.1.224

896 (A)

Ki =1,4 l h s d tr dng in

Vi cc s liu trn m bo an ton ta chn van TB- 320 vi cc

thng s ca van nh sau :

Gi tr dng ti trung bnh cho php i vi dng in :I = 630(A)

in p ngc ln nht : Ungmax = 1000 (V)

in p ri trn van : U = 1 (V)

Thi gian kho : toff = 100 (s)

Dng iu khin : Ik = 300A

in p iu khin : Uk = 7 (V)

dt

di= 50 (A)

dt

du

= 100 (V/

s)

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2. Bo v van khi vn hnh :

- Thyristor rt nhy cm vi nhit , qu in p nh mc c th

lm hng van . V vy ta phi c nhng bin php bo v cho van

- Thng thng c hai nguyn nhn :

-Nguyn nhn ni ti : Do s tch t trong cc van bn dn , khi

kho Thyristor bng in p ngc gy ra sc in ng cm ng rt ln

trong cc in cm.Gia cc Ant v Katt ca Tiristor xut hin qu p.

-Nguyn nhn bn ngoi: nhng nguyn nhn ny thng xy ra

ngu nhin nh khi ng ct khng ti my bin p , khi cu ch bo v

nhy , khi c sm st...

bo v qu in p ngi ta thng dng mch R- C u song

song vi Thyristor bo v qu in p do tch t in tch khi chuyn

mch gy nn.

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chng iii :

thit k mch iu khin

I- S khi ca mch iu khin

Trong :

Ucm : in p iu khin(in p 1 chiu)

Ur : in p ng b, hoc in p xoay chiu

Hiu in p Ucm Ur c a vo khu so snh lm vic

nh mt

Trig . Khi Ucm Ur = 0 th Trig lt trng thi, u ra ca n

nhn c mt chui xung hnh ch nht.

Khu 2 l mt a hi mt trng thi n nh

Khu 3 l khu khuch i xung.

Khu 4 l khu bin p xung.

Bng cch tc ng vo Ucm ta c th iu chnh c v tr ca

xung iu

khin tc l iu chnh c gc m.

Ur

Uc

S 1T

1 2 3 4

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II- Cc nguyn tc iu khin.

C hai nguyn tc iu khin c bn sau y:

1- Nguyn tc iu khin thng ng tuyn tnh

Trong nguyn tc ny ngi ta dng hai in p l:

- Dng p ng b Ur c dng rng ca , ng b vi in p t trn

- ant- catt ca Thyristor.

- in p iu khin Uc l in p mt chiu c th iu chnh c

bin .

Tng i s ca Ur+ Uc c a ti u vo ca nt khu so snh.

Nh vy bng cch lm bin i Uc ngi ta c th iu chnh c

gc m

Khi Uc = 0 ta c = 0

Khi Uc < 0 ta c > 0

Khi Uc v c quan h : = maxUrUc

Ngi ta ly Ucmax = Urmax . Vy = maxUcUc

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2- Nguyn tc iu khin thng ng ARCCOS.

Theo nguyn tc ny ngi ta cng dng hai in p:

- in p ng b Ur vt trc in p ant- catt ca Thyristor mtgc

bng /2.

( Vi UAK= Asin(t) th Ur= B cos(t) )

- in p iu khin Uc l in p mt chiu c th iu chnh c

bin

theo hai hng : dng v m. ( hnh v)

(Ur+U

c)

Uc

Uc

2U

c

t

Ur

47


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Tng i s (Ur+Uc) c a n u vo ca mt khu so snh

Khi Ur+Uc= 0 th ta nhn c mt xung u ra ca khu so snh

Uc+ Bcos = 0Khi = arccos(/) . Ngi ta ly = Ucmax.

Khi Uc= 0 th = /2.

Khi Uc= Ucmax th =

Khi Uc= -Ucmax th = 0

Nh vy : Khi cho Uc bin thin t (-Ucmax) n (+Ucmax) th bin

thin t

0 n .

UU

Ur

0t

Uc

Ur

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III - Chc nng v nhng yu cu c bn i vi h thng

iu khin

Mch iu khin c cc chc nng sau :

- iu khin c v tr xung iu khin trong phm vi na chu k

dng ca in p t trn ant, ca tt, Thyristor.

- To ra c cc xung iu kin m c Thyristor ( xung iu

khin thng c bin t 2 n 10V, rng xung tx = 20 n 100 s

i vi thit b chnh lu, tx 10 s i vi thit b bin i tn s cao)

rng xung c xc nh theo biu thc :

tx =dtdi

Idt

/

Trong : Idt - dng duy tr ca Thyristor

di - tc tng trng ca dng ti

dt - thi gian xy ra s tng trng ca dng ti

H thng iu khin cc thit b bin i dng hnh thnh v to

ra cc xung iu khin c dng xung v so snh rng xung nht nh,

phn b chng theo cc pha v thay i thi im a xung kch thng

vo cc van ca b bin i.Cc yu cu c bn ca h thng iu khin ccb bin i ph

thuc vo dng phn t, cc ch lm vic ca chng v c tnh ca

ti. V vy cc yu cu chnh cn c ca mch iu khin l:

m bo pht xung vi cc yu cu m van:

- bin Uc.

- rng xung(tc).

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- Sn xung phi ngn(ts= 0,5 1ms)

- m bo tnh i xng i vi cc knh iu khin.

Cc xung iu khin phi m bo i xng theo pha. Nu khng mbo i xng cc xung iu khin th cc Thyristor ca b bin i nhiu

pha s gy ra s khng cn bng v gi tr trung bnh ca dng chy qua

cc Thyristor .

Vi s iu khin cc Thyristor trong s chnh lu nhiu pha

th lch pha cho php ca cc xung iu khin cc knh khc nhau

U

1s

tc

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phi trong phm vi t 10 30 ng vi cng mt gi tr in p iu

khin.(hnh v)

- m bo cch ly gia mch iu khin v mch lc.

Bin p xung thng c s dng nh mt khu truyn xung cuicng tng khuch i so snh ti xung. in p chu ng gia s cp

51

10 30

6001200

18000

0

V1

V2

V3

2400

3000

V5

V4

V6

3600


52/72

v th cp ca my bin p phi t c t 1500V n 2000V khi s

lm vic vi in p li in 1240 VAC.

- m bo ng quy lut thay i v pha ca xung iu khin .

y l yu cu m bo phm vi iu chnh ca gc iu khin

.

V d: i vi chnh lu c iu khin hoc cc s bin i xung

p xoay chiu , thng thng i vi chnh lu iu khin th gc iu

khin phi thay i c trong phm vi 100 1700.

- C th hn ch c phm vi iu chnh ca gc khng ph

thuc vo s thay i ca in p li.

- Khng gy nhiu i vi cc h thng iu khin in t khc

xung quanh.

- C kh nng bo v qu p , qu dng, mt pha v bo hiu khi

c s c.

IV. Xy dng mch iu khin

1. Khu ng pha

y l khu to in p dng xung vung c pha ng pha vi in

p ngun , thc hin c iu ny ta s dng IC khuych i thut

ton trong xy dng mch iu khin.

- in p ngun nui: V= 5 18

-Hiu in th gia cng o v khng o U= 25(V)

-Nhit vn hnh: T=-250 850C

a. S cu trc chn

+V

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53/72

3 7

6

2 4

- V

Hnh 3.1

Nhn vo c tnh khuych i ta thy Ur , Uv2 rt nh -> i vi

cc KP ch cn mt bin thin rt nh ca Uv cng gy ra Ubh u ra do

ta u b khuych i thut ton khng c ni tip nh hnh di y

th n l mt khu so snh c c tnh truyn t th 2

Ur =

>U xung ra mang phn m u ra ca khu ng

pha ta c xung c hai na m dng ng pha vi in p ngun xoay

chiu

c. Cng thc tnh ton khu ng pha

Uth cp ba = U2=12v a vo D1,D2

Us cp ba =U1=220v

U=I vU

8,1012.9,0222

==

Chn R0=1k

Id = mAR

Ud8,10

10

8,103

==

Gi tr in p ngc t ln iot D1 ,D2 :

Ung= 17.2 2 =U v

Chn D1,D2 loi IN 4007 c Ung=50 v

in tr R2 hn ch dng in i vo khuch i thut ton 0A1

thng chn R1sao cho dng in i vo khuch i thut ton Iv < 1mA

Do R1K

I

Ud

v

8,1010

8,103

==

in p U2= sin..2 2U

Chn nh bng 50 di iu chnh ln, ta c :

U0= 5,15sin..2 02 =U v

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55/72

Chn in tr R2,VR3 theo phn p sau:

U0=32

33

32

.15.5,1.

VRR

VRvVR

VRR

E

+=

+

-> R2 + VR3=10VR3

-> R2= 9VR3

-> R2 =9(k )

Chn VR3=1k

2. Khu to rng ca.

a. S nguyn l : b. Dng in p

c. Nguyn l hot ng

Bng T1 dng lm ngun dng np cho t C, nh cch mc theo

s baz chung nn dng IC rt n nh. Khi T2 b kho t C s c

np in bi dng IC = const v tuyn tnh. Khi a xung vo m T2, T2

m v t C s phng in qua T2

55

R6D4

OA2

C1

D3

U4

U3

R5

R4


56/72

d. Cng thc tnh ton

* Tnh dng in np ca t C1 :

Chn OA2 l loi A741, t C1 c U = 35 V , C = 0,47 F

Chn UC1max = UC2max = 10 V

y ta chn chu k phng np cho t l 10 ms

Thi gian np tn = 0,56 ms

Thi gian phng tp = 9,44 ms

Dng in np l: In =4R

E= iC

Gi tr in tch trn t l :

CC(t) = - 71

C t

Cdti0

= U -4R

Etp

Khi t = tp th Ut = 0 U =14CR

Etp ,(vi E = 12 V )

Thay s : 12 = 64

3

1047,0.

10.44,912

R

R4 = 10 ( k )

Chn it D3, D4 loi 1N 4009

Chn R6 = 10 k

3. Khu so snh.

Mch so snh thc hin hai tn hiu l in p iu khin c t

vo ca (+) ca OA3 v in p rng ca t vo ca (-) ca OA3.

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57/72

y ta chn OA3 loi 741

a. S nguyn l.

b. Dng in p.

c. Nguyn l hot ng :

Tn hiu rng ca c a vo ca (+) ca khuch i thut ton

c em so snh vi in p iu khin trn VR2 so snh ngc, khi no

tn hiu rng ca nh hn tn hiu iu khin th suy ra khuch i thut

ton mang phn dng, khi tn hiu RC ln hn tn hiu iu khin th

57

R7 OA3

E

U k

U5

U4

Uk

D

+E

-E


58/72

xung ra mang phn m -> u ra ca khu so snh c 1 xung c c

phn m phn dng qua iot D5 lc bt phn (-) i v xung ra ch cn

na (+) em xung ny trn vi xung chm khu to xung chm v a

ra ca BE ca T1,T2 khu khuch i

d. Tnh ton thng s khu so snh.

U0= Uk- Ur

Uk= E - UR8

Theo phn p ti im A ta c :

Uk= 228 .VRVRRE

+ -> dkUE

VR

VRR

=+

2

26

Uk theo l1 v chn = 7,610.3

2

3

2max ==cU v

Uk= 6,7 v chn E = -15 (v) -> Gi tr E = 15 v

24,21

2

8 =+=VR

R

U

E

dk

v -> R8=12,4 VR2

Chn VR2=10k th R8=12,4k

Chn R7= R8 + Rc

Rc=14 (k)

R8=4,5 k

R7=7,5k

4. Khu to xung chm.

a. S nguyn l b. Dng in p

58

Uchm

tC

2

R13

R11

R10

R12

OA4

D9

Uc

Ur

+

-

T1 T2


59/72

c. Nguyn l hot ng :

Khi a ngun nui +E,-E vo u ra ca khuch i thut

ton 0A4 c in p. Gi s Ua(+) qua R t C c np in 0A4. So snh

gia in p c t ly qua phn p qua R11,R12 t vo khuch i Uc

ln dn bng in p u ra so snh tri du Uc vi Ut.

Uc >Ut o du ln xung lin tip v Uc lc np lc phng trong

khu "to xung chm". mch iu khin u ra mc thm 1 Tranzitor

thun loi na (+) ca xung i ly na (-). Khi ngun E phng in

qua EC em trn vi xung ra ca khu so snh.

d. Tnh ton thng s v chn mch dao ng to xe dngkhuch i thut ton.

Ur=E

101211

0 .RRR

EU

+=

+=

12

11290

.21ln...2

R

RCRT

Chn R12=R11 = 10 k

->T1=T2

-> T = 2.R10C2ln(1+2)

-> T= 2,2.R10.C2

T=2,2.R10.C2 -> Chn t C2= 0,1F

Ly f=10kHz -> T = 43 1010.101 = (s) = 100.10-6 (s)

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60/72

= 100 (s)

R10= 5,410.45,010.1,0.2,210

.2,2

10 36

4

2

4

===

Ck

Chn T2 loi Tranzitor thun A564, R13 = 10 k

- U=50 (v)

- I = 100 mA

- = 10

Uk> URC th u ra ca OA3 l in p dng ( + )

Uk < URC th u ra ca OA3 l in p m ( - )

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61/72

5. Tnh khu khuch i xung v bin p xung

5.1- Tnh BAX

Theo phn tnh chn van ta chn Thyristor c:

Ug = 7 V

Ig = 300 mA

* Ta chn s b:

- Vt liu lm li st l thp Perit HM li c dng hnh tr c H =

50 A/m v B = 0,7 T, c khe h khng kh.

- T s my bin p xung chn m = 1,5

- in p th cp : U2 = Ug = 7 V

- in p s cp : U1 = m U2 = 1,5 7 = 10,5 V

- Dng in th cp: I2 = Ig = 600 mA

- Dng in s cp: I1 = mI

2

= 5,1600

= 400 mA

- rng xung : tx = 600s = 6 10-4 s

- Mc st bin xung : S = 0,15

Chn t thm khng kh 0 = 10-6 H/m

- t thm trung bnh tb ca li thp:

tb = HB

tb = 50107,0

6 = 1,4 104

H/m

Th tch li thp :

V =( ) 2

110

B

IUStxtb

61


62/72

V =( ) 2

464

7,0

400,05,1015,010610104,1 = 12 cm3

Chn Q = 2,25 (cm2)a = 1,5(cm) ,b = 1,5 (cm)h = 3 (cm)

K hiu li thp III 12 10

- Chn h s lp y K = 0,76

- S vng dy cun s cpBAX:

W1 =KQB

tUi

0 =

76,01025,27.0

105,104

4

= 870 vng

- S vng dy cun th cp BAX:

W2 =1

12

U

WU = 5,10

8707 = 580 vng

Chn J1 = J2 = 2 A/mm2

- Tit din dy s cp:

S1 =1

1

J

I=

2

10400 3= 0,2 mm

- ng knh dy s cp:

d1 =

14S =14,3

2,04 = 0,6 mm

- Tit din dy th cp:S2 =

2

2

J

I=

2

10600 3= 0,3 mm

ng knh dy th cp:

d2 =

24 S =14,3

3,04 = 0,6 mm

Thc t ta thng dng BAX bng vt liu ferit c kch thc v

ngoi v gng hnh tr l 30 x 25 (mm2) .

62


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5.2- Tnh chn khu khuch i xung

a. S nguyn l

b. Nguyn l hot ng

Khu khuch i xung lm nhim v khuch i tn hiu xung U7

im 7 thnh tn hiu cng c bin , rng v cng sut ln

kck m tranzito T1.

c. Cng thc tnh ton

Chn cc it D6 , D7 , D8 loi 2608 c cc thng s sau:

U = 220 V

I = 5 A

63

+ E2

R14D8

D6

T1

T2

R10

R11

D9

D10 D11

T1


64/72

Chn bng tranzito cng sut T2 loi HI 1061 c cc thng s sau:

UEC = 35 V

IEC = 5 A

= 100

Ta c : IEC T2 = I1BAX = 0,4 A

Tnh c dng IBT2 :

IBT2 = 2ECTI

= 102,0

= 40mA ( y ta chn = 10 )

IECT1 = IBT2 = 40 mA

* Tnh dng IBT1 : ( Vi T1 = 10 )

IBT1 = 11

T

ECTI

= 1020

= 4 mA

y ta chn tranzito T1 loi C828 c cc thng s sau:

UEC = 250 V

IEC = 350 mA ; = 100

* Tnh in tr R11

Thng thng st p trn tranzito l khong 0,6 V

Vy : R11 = 16,0

ECTI = 4,06,0

= 1,5

Chn cc in tr R10 =R14 = 10 k

B pht xung cho knh iu khin Thyristor T2 cng c thng s

tng t.

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65/72

S nguyn l mch iu khin

OA

OA

OA

OA

R

R

R

C

C

R

R

R

R

R

D

D

D

T

T

R

D

RR

R

D R D

R

R

R

R

D

RE

-E

E

DD

&

65


66/72

Dng in p

U~

0

2U

0

0U 3

U 1

4U

U 5

6U

0

0

0

0

2

0U

Uk

66


67/72

Nguyn l hot ng ca mch iu khin

Khi cp ngun xoay chiu vo pha s cp ca bin p ng pha dnn in p bn pha th cp s c chnh lu qua diot D 1, D2 to ra

in p ng pha a vo ca m ca khuch i thut ton OA1 v c

so snh vi in p U0 t vo ca dng OA1.

Khi in p ti cc im 1 v 2 ta c dng in p ti cc im

c trnh by trn bn v l U1, U2.

in p ng pha c a vo khu to in p rng ca (dng

khuch i thut ton OA2) to ra in p RC c xung in p ng b

vi in p ngun. Dng in p ra ca khu to in p RC l U3 .

- Sau in p RC c so snh vi in p iu khin nh

khuch i thut ton OA3, in p RC a vo ca dng ca OA3 cn

in p iu khin c a vo ca m ca OA3 vi nhim v l to ra

xung iu khin.

Nu Udk > URC . u ra ca OA3 ta nhn c xung m

Nu Uk < URC u ra ca OA3 ta nhn c xung dng

V in p o c u ra ca OA3 chnh l U4.Khu pht xung chm s dng khuch i thut ton OA4, nh s

phng np ca t C lp i lp li nhiu ln ta nhn c xung chm c tn

s f = 10 KHz. Khi ta c in p ti im 5 l U5.

67


68/72

Xung iu khin ( U4 ) v xung chm (U5) cng c a vo

phn t AND, sau c a ti khu khuch i xung qua in trhn ch R15 .

Lc ny xung iu khin l nhng xung dng (U6) c a n

s cp bin p xung s c cm ng sang pha th cp bin p xung c

cc tm tng ng m cc i t D8, D10 v a dng iu khin vo gia

cc iu khin catt ca (T .)

68


69/72

Kt lun

Qua 10 tun thc hin ti: Thit k b khi ng khi ng

cho ng c khng ng b 3 pha, em thy ti ny tht b ch cho

nhng sinh vin sp ra trng nh chng em, v thc t ng c khng

ng b l nhn t rt quan trng trong cng nghip, nghin cu v c

im ca n, v nhng phng php khi ng, phng php iu chnh

in p, tnh ton nhng phn t trong b khi ng thit k mch khi

ng ng c. iu s gip ch nhiu cho cng vic sau ny.

Tp n ny mc d cn nhiu hn ch, nhng trong qu trnhthc hin ti gip em t nh gi v hiu k hn v cc kin thc

chuyn mn, cng l kt qu ca nhiu nm hc tp cng vi s dy

d rt tn tnh ca cc thy c trong khoa, trong b mn THXNCN. Em

xin chn thnh cm n ti cc thy c v c bit l thy gio TS. V

Minh Chnh ch bo rt tn tnh em hon thnh quyn n ny.

Em xin chn thnh cm n.H Ni, ngy 21 thng 1 nm 2005

Sinh vin thc hin

Trn Th Phng Hin

69


70/72

Ti liu tham kho

1. Truyn ng in

Bi Quc Khnh Nguyn Vn Lin Nguyn Th Hin

2. in t cng sut

Nguyn Bnh

3. My in

V Gia Hanh Trn Khnh H - Phan T Th Nguyn Vn Su

4. in t cng sut

V Minh Chnh Phm Quc Hi Trn Trng Minh

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Mc lc

Li ni u

Chng I: Gii thiu chung v ng c khng ng b

I- Gii thiu chung.................................................................2II- Nguyn l lm vic ca ng c KB................................5

III- c tnh c bn ca ng c khng ng b....................9

IV - Cc phng php m my ca ng c KB..................13

V. Xy dng mch lc...........................................................19

Chng II: Gii thiu v tnh ton b bin i

I. Xung p xoay chiu 1 pha.................................................24

II- Xung p xoay chiu 3 pha...............................................31III. Dng in p - nguyn l lm vic.................................34

IV- Tnh chn v bo v van:................................................39

chng iii : thit k mch iu khin

I- S khi ca mch iu khin.......................................42

II- Cc nguyn tc iu khin.............................................43

III - Chc nng v nhng yu cu c bn i vi h thng

iu khin...................................................................................46

IV. Xy dng mch iu khin .............................................49

1. Khu ng pha ........................................................................................49

2. Khu to rng ca....................................................................................52

3. Khu so snh............................................................................................53

4. Khu to xung chm................................................................................55

5. Tnh khu khuch i xung v bin p xung............................................57

S nguyn l mch iu khin...........................................................................61Dng in p............................................................................................................62

Kt lun................................................................................................................................65

Ti liu tham kho................................................................................................................66

71


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* S mch lc:

K

khoi dong dong co

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