Giáo trình cung cấp điện dùng cho các trường cao đẳng kỹ thuật

co cong suat dat tu vai ngan den hang van kVA, co vai tro quan trong doi vdi nen kinh te quoc dan phai dugc xep vao ho loai mot, khong dugc phep ngimg cung cap dien, cu the la tram bien

C L I E U

TS NGO HONG QUANG

Gido trinh

(Dung cho cac trirdng Cao dang ky thuat)

NHA XUAT bAn GlAO DUC VIET NAM

Cong ty Co phan sach Dai hoc - Day nghe - Nha xuat ban Giao due Viet Nam giCif quyen cong bo tac pham.

J l d ’i g j j & i t i i i e i i

M on hoc C u n g cap d ie n n am tro n g c h u d n g trin h d ao tao cua

nhi£u n g a n h dien: H e th o n g dien, Tif d o n g hoa, T hiet bi dien,

Do lu d n g , D ieu k h ien , Kinh te n a n g lu o n g , Su p h a m ky th u a t dien,

Moi ch u y en n g a n h lai bo tri th d i lu d n g hoc m o n C u n g cap d i in khac

nhau: 45, 60, 75, 90 tiet De d a p ling difOc ta t ca cac th d i lifOng tren, cuon giao trin h n a y dvfOc bien soan v6i n o i d u n g m d bao go m 10 chifOng v6i 110 tiet T uy theo tln h chat va m uc tieu d ao tao cua tCfng tru d n g , ttfng c h u y e n n g a n h , giao vien co the dd d a n g lua chon noi

d u n g gian g d a y th ich h o p

C h u n g toi b ien so an cu o n sach nay tren cO so k in h n g h iem giang day n h ieu n a m cho cac ch u y en n g a n h d ien he C ao d a n g va D ai hoc Giao trin h d u o c lien tuc h ieu chinh va cap n h a t cho p h u h d p v 6 i yeu c^u cua th u c te n g a n h dien P h in p h u luc c h u n g toi co' g an g su u tap

va dtfa vao n h u n g th ie t bi d ien h ien dai tien tien cua cac h a n g noi tien g tro n g va n g o a i n u 6 c d a n g chao b an tai thi tru d n g V iet N am

De d a p lin g v d i d o l tUOng la sinh vien he Cao d a n g , c h u n g toi co'

g an g tru y e n d a t n h u n g kien thuc cd b an n h a t va th ie t tliifc n h a t, vdi cach trin h bay d d n gian, dS h ieu va n h ieu vi d u m in h hoa C u o i m oi

c h u d n g d u a ra cac bai tap tu de d e n kho de siiih v ien tap d u d t, lam

q u e n d i n v d i co n g viec th ie t ke sau khi ra tru d n g

G iao trin h C u n g cap d ie n d u n g lam tai lieu g ian g d a y va hoc tap

tro n g cac trtfd n g cao d a n g ch u y en n g a n h dien, d o n g th d i c u n g co the

th am k h ao d e g ia n g d ay d he Dai hoc va T ru n g cap c h u y en n g h iep

N goai ra, h y v o n g c u n g g iu p ich cho cac ky su d a n g cong tac tro n g linh vuc th iet ke, xay lap cac cong trinh dien cong n g h iep va d a n dung

M3c d u tac gia d a ra t co g£ng tro n g cdng viec bi£n soan, n h tfn g cung cap d ien la giao trin h bao h a m n h ie u k ien thtfc ro n g v a p h u t tap, chfic chfin cu 6 n sach k h 6 n g tra n h khoi sai sot Tac gia r a t m o n g

n h a n d u d e y ki£n q u y b a u cua d o n g n g h ie p va b a n doc d e c u o n sach difdc h o a n th ien h d n tro n g n h u n g l i n tai b a n sau

M oi g o p y xin g u i ve C o n g ty Co p h £ n Sach D ai hoc - D ay nghe,

25 H a n T h u y en - H a Noi

r-f-i r • 9

Tac gia

C h ir a n g m a d a u

0.1 Liroi dien Viet Nam va lirai cung cap dien

Luai dien la mot tap hop bao gom dKdng day tai dien va tram bien dp

lam nhiem vu truyen tai va phan phoi nang luang dien tir cac nha may dien den cac ho tieu thu dien

Luai dien quoc gia co nhieu cap dien ap Su dung cap dien ap nao, a dau phu thuoc vao chidu dai va cong suat truyen tai Ludi dien Viet Nam hien co 8 cap dien ap: 0,4(kV), 6(kV), 10(kV), 22(kV), 35(kV), 110(kV), 220(kV) va 500(kV)

Co nhieu cach phan loai luai dien:

- Can cu vao tri so dien ap chia ra luai ha dp, luai trung dp, luai cao

dp va luai sieu cao dp.

- Can cu: vao quy mo cua luai dien chia ra luai khu vice va luai dia phuang.

Ngoai ra con nhung cach phan loai khac nhu phan loai luai dien theo vung mien lanh tho (luai dien mien BSc, luai dien mien Trung, luai dien mien Nam), phan theo cau true luoi (luai dien km, luai dien h a )

Bang 0.1 sau day chi ro chuc nang nhiem vu cung nhu quan he cua luai cung cap dien trong luai dien quoc gia Viet Nam

B ang 0.1 Li/di dien Viet Nam va ludi cung cap dien

Phan loai theo trj

Sieu cao ap Phan loai theo

chtic nSnq Ludi cung cap dien Ludi truyen tai

M6i loai luai dien co dac thu rieng, nguod ta phan chia ra cac loai de thuan tien cho viec thiet ke, quan ly, van hanh Tuy nhien can nha rang, dien nang la dang nang luang khac han vai cac dang nang luang khac, he thong dien bao gom ba khau: san xuat, truyen tai va phan phoi, la mot tong the thong nhat khong the tach rai Tir nhung thiet bi to lofn va quan trong nhu may phat dien, may bien ap den cac thiet bi tieu thu dien nho be nhu mot dong ca

dien trong xuang may, mot chiec bong den cua can ho gia dlnh deu nam trong

he thong dien Viet Nam M6i hanh vi ung xir cua phan tir nay, khau nay deu

co tac dung tuong h6 den phan tu khac, khau khac Can phai thiet ke, van hanh, quan ly timg phan tu, timg khau theo quy dinh chat che sao cho dam bao sir lam viec an toan, tin cay va kinh te cho toan bo he thong dien

0.2 Phan loai ludi cung cap dien

Nhu da noi a tren, luai cung cap dien la mot phan cua luoi dien Viet Nam

lam nhiem \oi phan phoi va cung cap dien true tiep cho cac ho tieu thu dien tir 35(kV) tra xuong, cu the la cap dien cho cac phu tai cua 5 cap dien ap: 0,4(kV), 6(kV), 10(kV), 22(kV), 35(kV)

Luai cung cap dien thucmg duac phan loai theo doi tuong sir dung dien: Ngudi ta chia ra: ludi dien cong nghiep, luai dien do thi, luai dien nong thon

Trong m6i loai luai tren deu co phan dien cap cho dan dung (can ho, ducmg pho, dich vu ) dugc goi la ludi dien dan dung hoac ludi dien anh sang sinli hoqt va co phan dien cap cho xuang may, nha may duac goi la ludi dien xi nghiep Cung con tuy theo so pha dugc su dung de cap dien, ngucfi ta chia ra

luai dien mot pha, luai dien hai pha, ludi dien 3 p h a

Sau day chung ta nghien curu ky han ve chuc nang cS'p dien cung nhu

sa do dac trung cho tumg loai ludi cu the

0.2.1 Lu&i dien cong nghiep

Luai dien cong nghiep lam nhiem vu cung cap dien cho khu cong nghiep, khu che xuat, xf nghiep, xuang m ay 6 do nguai ta su dung cac lo dien, cac dong co cong suat khac nhau vai cac cap dien ap khac nhau Cac dong ca may cong cu thuang dung dien ap 0,4(kV), vai may nghien, bang tai hoac may bam cong suat lan thi dung dien ap 6(kV) hoac 10(kV)

- Vai mot xuang may doc lap nhu xuang sua chua nong cu, xuang sua chua ca kill hoac mot phan xuang cua nha may ca nho chi dat mot vai chuc may cong cu (may tien, phay, m ai ) co cong suat su dung thuc te vai chuc

kW thi chi nen cap dien b^ng mot duang day ha ap tu tram bien ap phan phoi cong cong hoac tram bien ap phan phoi cua nha may Neu cong suat su dung len tai mot vai tram kW thi mdi nghi tdi phuang an dat cho cac xuang nay mot tram bien ap phan phoi rieng

1 Tu- BAPX

H inh 0.1 Lirdi dien ha ap phan xtfdng

1 B udng cap ha ap tC/ BAPX ve phan xifdng

2 Cac duong cap ha ap cap dien cho cac TDL, TCS

3 Cap ti/ TDL cap dien cho tC/ng may

- Vdi mot nha may co nho bao gom vai ba phan xuong vdi cong suat lOOOkVA trd lai, chi can dat mot tram bien ap chung cho toan nha may, tir day cap dien ha ap cho cac phan xuong Can luu y, de dam bao my quan cong nghiep va an toan, cac ducmg day cao, ha ap trong pham vi nha may nen su dung cap ngam

Cac xf nghiep co nho da phan thuoc ho loai ba, nghla la cho phep mat dien tam thdi (tru xf nghiep luyen kim), chi can mot nguon cung cap dien,

cu the la tram bien ap chi can dat mot may, cac ducmg day chi can di lo don

- Vdi cac nha may quy mo 1cm nhu nha may co khi trung quy mo, nha may det, nha may che tao may keo v.v co cong suat dat tu vai ngan den hang van kVA, co vai tro quan trong doi vdi nen kinh te quoc dan phai dugc xep vao ho loai mot, khong dugc phep ngimg cung cap dien, cu the la tram bien ap phai dat hai may, cac ducmg day phai dung lo kep O nhung nha may nay, do cong suat tai m6i phan xuong deu kha Ion tu vai tram den hang ngan kVA nen quy mo ludi cung cap dien cua nha may cung ldn theo, bao gom ca ludi trung ap va ludi ha ap Trong nha may phai dat mot tram phan phoi trung tam (TPPTT) hoac tram bien ap trung tam (TBATT) va nhieu tram bien ap phan phoi phan xudng (TBAPX) Vi day la nhung nha may quy mo ldn dugc xay dimg tren mot pham vi dat dai kha rong len toi hang chuc hecta nen TBATT hoac TPPTT can dugc dat tai trung tam phu tai cua nha may

0.2.2 Lu&i dien nong thon

Ho tieu thu dien d nong thon chu yeu la cac gia dinh song trong lang

xa, trudng hoc, tram xa, cac tram bofm tudi, tieu nude phuc vu cho san xuat nong nghiep Hau het cac ho tieu thu dien nay thuoc ho loai 3, nghla la cho phep mat dien tam thdi khi can thiet, chi can cap dien bang tram bien ap mot may va cac dudng day lo don Vdi cac tram bom quan trong cap huyen hoac cap tinh nen xep vao ho loai 1, dugc cap dien bang tram bien ap hai may va dudng day lo kep

Vdi ludi dien nong thon, co ba loai so do dac trung: so do cap dien cho mot thon (lang), so do cap dien cho mot xa va so do cap dien cho mot huyen

- Luai dien thon

C) Viet Nam, m6i thon (lang) thudng xay dung tach biet, cach nhau tren dudi mot km, vi the mdi thon phai dat mot tram bien ap phan phoi rieng M6i thon thudng nam tren chidu dai tir 800 den 1000 met; de dam bao chat lugng dien ap cho nhung nha d cuoi thon, can dat tram bien ap cua thon d tai

vi tri trung tam dudng true thon Dien tir tram bien ap phan chia ra hai nua dudng true, tir day re vao cac dudng dien xom ngo de cap cho cac ho dan Tat ca cac dudng dien true thon, ngo xom deu la dudng day tren khong

Hinh 0.5 Ltfdi dien cap cho m ot thon (lang)

B Tram bien ap cua thon TBA - 35(10)/0,4(kV)

1 B u ting day dien ha ap true thon

2 C ac hop cau dao ngo xom

3 D ifdng day dien ha ap ng5 xom

4 C ac cong ta dSt tren cot dien cap dien cho cac ho dan

- Luai dien xa

De cap dien cho xa, ngudi ta keo mot dudng dien trung ap (35 hoac 10(kV)) tu dudng dien lien xa ve trung tam xa Tu dudng dien true nay se keo tiep cac doan dudng day trung ap ve cac tram bien ap cua tung thon Tram bien ap cua thon co the lay dien true tiep tir dudng dien trung ap true cua xa, cung co the lay lien thong tu thon nay sang thon khac tuy theo dia hinh De tien cho viec van hanh, sua chua dudng dien cua xa khong anh hudng den ludi dien chung cua huyen, ngudi ta dat mot dao cach ly tai dau dudng day trung ap re ve xa

Hlnh 0.6 gidi thieu mot ludi dien cua xa gom 4 thon va mot tram bom dugc lay dien tir dudng true 10(kV) lien xa

H inh 0.6 Ludi dien cap dien cho m ot xa

1 Dao cach ly

2 D udng true 10(kV) cua xa

3 D udng 10(kV) re nhanh ve cac thon

4 Tram bien ap 10/0,4(kV) cua cac thon va tram bdm

- Lifdi dien huyen

Phu tai dien cua huyen chu yeu la cac xa, thi tran huyen Cung co the

co tram bam ldn hoac mot hai nha may che bien nong san nho le nam trong dia ban, tuy theo tfnh chat quan trong ma tram bam va nhung nha may nay can phai cap dien lien tuc bang dudng day lo kep hoac chi can cap bang dudng day lo dan

De cap dien cho huyen, ngudi ta xay dung mot tram bien ap trung gian 110/35(kV) hoac 110/10(kV) d trung tam, tir day di ra cac ducmg day trung

ap 10(kV) hoac 35(kV), m6i dudng day cap cho vai xa Neu co tram bam lcfn, can cap bang dudng day rieng

Hinh 0.7 Li/di cung cap dien m ot huyen

TBA Tram bien ap trung gian TBA TG -1 1 0 /3 5 (1 0)(kV) 1,2,3,4,5 Cac lo dufdng day trung ap cap dien ve xa

TB Tram bom ldn

• Cac tram bien ap phan phoi TBA - 35(10)/0,4(kV) Ranh gidi cac xa thj tran

(l)-» (X II) C ac xa trong huyen, (TT) Thj tran

0.2.3 Lu&i dien do thi

Phu tai dien cua do thi rat phuc tap, bao gom cac ho dan song tren

dudng pho, trong cac nha chung cu hoac biet thu rieng, cac ca quan hanh

chfnh, sieu thi, benh vien, trudng hoc, nha van phong, trien lam, khach san,

nha nghi, vudn hoa va cac cong trinh cong cong khac Ngoai ra con co cac phu tai cong nghiep nhtr xudng may, xf nghiep nam xen lan voi cac phu tai anh sang sinh hoat.

Phu tai dien do thi phong phu da dang dan toi ludi dien ha ap cung cap cho cac phu tai cung phong phu, da dang, nhung trong khuon kh6 han hep ve thdi luang cua giao trinh nen khong the gidi thieu het 6 day chi xin gidi thieu mot so so do ludi dien dac trung: So do ludi ha ap cung cap cho cac ho dan song tren dudng pho, so do ludi cung cap dien cho thi xa - thanh pho nho, so do ludi cung cap dien cho cac thanh pho ldn

- Ludi cung cap dien cho cac ho dan tren difong pho

De tranh phai dao dudng anh hudng den giao thong trong khi lap dat, sua chua cap ha ap, moi tram bien ap phan phoi cong cong chi cap dien cho mot phia mat pho Vdi nhung doan pho ngan 100, 200, 300m thi dat TBA d goc pho de cap dugc cho hai doan pho vuong goc ke nhau, vdi doan pho dai 500-^600m thi phai dat TBA d gitra doan pho, vdi nhung pho dai lien tuc tren 600m thi phai tang so tram bien ap sao cho ban kinh cap dien tir tram den

ho dan xa nhat khong qua 250-^300(m) nham dam bao chat lugng dien ap

Hinh 0.8 Phtfdng an cap dien ha ap cho do thj

a) Tram bien ap dat d goc pho; b) Tram bien ap dat d giCra pho

1 Tram bien ap; 2 Dudng true cap ha ap; 3 Ho dung dien

- Luai dien thi xa, thanh pho nho

Cap dien ap trung ap cap cho do thi la 22(kV) Ludi trung ap 22(kV) dugc cap tir cac tram bien ap 110/22(kV) De dam bao do tin cay, ludi trung

ap do thi dugc cau true thanh mach vong kin van hanh hd Mach vong cap trung ap nay se cung cap dien cho cac tram bien ap cong cong dat tren he pho (hinh 0.8) hoac cac tram bien ap cua khach san, sieu thi, benh vien, khu chung c u

Hinh 0.9 gidi thieu mot khu vuc do thi dugc cap dien tu hai tram bien

ap 110/22(kV) vdi 8 mach vong cap trung ap Tuy theo quy mo cua do thi,

so tram bien ap 110/22(kV) co the la 2,4,6,8

• • • • •

Hinh 0.9 Lirdi dien trung ap do thj

B,, B2 Tram bien ap trung gian 110/22(kV) - Cac mach vong cap trung ap

• C ac tram bien ap phan phoi 22/0,4(kV)

Nguyen tac cau true mot mach vong km van hanh ho cua lucri cap trung ap do thi dugc minh hoa tren hinh 0.10 Mach vong cap 22(kV) dugc cap dien tu hai phan doan thanh gop 22(kV) cua tram TBA van hanh doc lap (MC thudng md) Trong trudng hgp mach vong lam viec blnh thudng thi diem K md, m6i nua mach vong lam viec doc lap ca'p dien cho 4 tram bien

ap phan phoi Gia thiet xay ra su co tren doan cap noi giua hai tram B2 va B3, thiet bi dong cat tai 1 va 2 md ra tach phan cap bi su co ra khoi ludi d£ sua chua, diem K dong lai va tram B3, B4 tiep tuc dugc cap dien tu nua mach vong II sang Nhu vay, du bi su co tai bat ky doan cap nao thi mot vai tram bien ap chi mat dien tam thdi trong thdi gian thao tac

Hinh 0.10 So do nguyen ly mach v on g trung ap

- Lucri dien do thi lerti

Do thi co quy mo ldn nhat la cac thanh pho loai 1 nhu Thu do Ha Noi, Thanh pho Ho Q ii M inh Ngoai khu vuc noi thanh vai trieu dan vdi hang

ngan tram bien ap phan phoi, con ca vung ngoai o rong menh mong nhieu lang, xa, nhieu khu cong nghiep, khu che xuat, cum xf nghiep cung nhung tram bom ldn Dien tfch do thi loai nay len tdi vai ngan km2 va cong suat dien tieu thu cung len tdi vai ngan MW.

De cung cap dien cho nhung do thi ldn, thudng phai sir dung mot so mach vong vdi nhieu cap dien ap khac nhau

+ Mach vong 220(kV) n£m phfa ngoai cung vdi cac tram bien ap 220/110(kV) cap dien tir ludi dien quoc gia cho cac mach vong 110(kV) phfa trong

+ Mach vong 110/35,22,10(kV) cap dien cho khu vuc ngoai thanh, trong do cac dudng day cap dien ap 10,35(kV) thudng dugc cap cho cac lang

xa, cac tram bom ldn; dudng day cap 22(kV) cap dien cho cac khu che xuat, khu cong nghiep

+ Mach vong 110/22(kV) cap dien cho khu vuc noi do (hinh 0.9).+ Cuoi cung la cac mach vong cap 22(kV) cap dien cho cac tram bien

ap phan phoi 22/0,4(kV)

H inh 0.11 Li/di cung cap dien cho do thi ldn

1 Mach vong 220(kV), T Cac tram bien ap 2 20 /1 10(kV)

2 M ach vong 1 10(kV) ngoai thanh; B1 C ac tram bien ap 110/35,22,10(kV)

3 M ach vong 110(kV) noi thanh; B2 Cac tram bien ap 110/22(kV)

0.3 Nhurng yeu cau doi vdi luoi cung cap dien

Mot ludi cung cap dien d bat ky cap dien ap nao cap dien cho bat ky doi tuong su dung dien nao cung phai thoa man nhung yeu cau ve kinh te -

ky thuat Do la 4 yeu cau co ban sau day

0.3.1 Do tin cay cung cap dien

Do tin cay cung cap dien la miic dam bao cung cap dien lien tuc tuy thuoc vao tfnh chat cua ho tieu thu dien Trong viec tfnh toan lira chon phuong thuc cap dien, ngudi ta thudng chia ra 3 loai ho

Ho loai 1 la ho rat quan trong khong dugc phep ngiing cung cap dien,

neu de xay ra mat dien se d in den cac hau qua nghiem trgng:

- Lam mat an ninh chfnh tri, mat trat tu xa hoi Do la cac ho tieu thu: san bay, ben cang, khu quan su, dai phat thanh truyen hinh, khu ngoai giao doan, dai su: quan, nha ga, ben xe, true giao thong chfnh trong thanh pho

- Gay thiet hai ldn cho nen kinh te quoc dan Cac ho tieu thu thuoc loai nay gom co: khu che xuat, khu cong nghiep, dau khf, luyen kim, nha may co khf quy mo ldn, xi mang, dong tau bien, che bien hai san, cac tram bom nong nghiep ldn, tram bom cap nude cho do thi Nhung ho nay co vai tro rat quan trong trong nen kinh te quoc dan hoac san pham, gia tri chiem ti trong ldn, che bien hang xuat khau dem lai nguon ngoai te ldn, chong lu lut hoac cung cap mat hang thiet yeu cho ddi song

- Lam nguy hai den tinh mang con ngudi

Ho loai 2 bao gom cac xf nghiep che tao hang tieu dung (nhu xe dap,

banh keo, dudng sua, may m ac ) va thuong mai, dich vu (sieu thi, khach san ) Neu xay ra mat dien se gay thiet hai cho chfnh cac xf nghiep do nhu lan cong, gay thuf pham, phe pham, pha vd hgp dong cung cap nguyen lieu hoac san pham cho ban hang, lam giam sut doanh so va lai su at

Ho loai 3 la nhung ho khong quan trong cho phep mat dien khi can

thiet Do la cac ho anh sang sinh hoat do thi va nong thon

Can luu y rang, cach phan loai ho tieu thu nhu tren chi la tam thefi trong giai doan nen kinh te quoc dan con thap kem, sau nay khi nen kinh te phat trien se dam bao cung cap dien lien tuc cho tat ca cac ho tieu thu, nghia

la tat ca phai dugc coi la loai 1

Trong thuc te ngudi ta thuc hien cac phuong thuc cung cap dien tuong ung cho 3 loai ho nhu sau:

- Doi vdi ho tieu thu loai 1, dien dugc cap tu hai nguon —> dudng day

lo kep —» tram bien ap 2 may —> he thong thanh gop phan doan

- Doi vdi ho tieu thu loai 2, dien dugc cap tir mot nguon —> dudng day lo don —» tram bien ap 1 may —> he thong 1 thanh gop + may phat dien du phong.

- Doi vdi ho tieu thu loai 3, dien dugc cap tu 1 nguon —» dudng day lo

don —> tram bien ap 1 may —> he thong 1 thanh gop.

n

Hinh 0.12 Cac phtfdng thuTc cap dien

a) Cap dien cho ho loai 1; b) Cap dien cho ho loai 2; c) Cap dien cho ho loai 3

1 D udng day truyen tai; 2 Tram bien ap; 3 Thanh gop ha ap;

4 M ay phat dien du phong; 5 Bo ap to mat lien dong

Chu y: Cac ky hieu thiet bi dien xem d phan phu luc.

0.3.2 Chat litffng dien

Chat lugng dien dugc the hien d hai chi tieu: tan so va dien ap Mot phuong an cung cap dien co chat lugng tot la phuong an dam bao tri so cua tan so va dien ap luon nam trong pham vi cho phep

Tan so la chi tieu chung cua toan he thong dien, dieu chinh tri so nay tai moi thdi diem la nhiem vu cua co quan Trung tam Dieu do Quoc gia Viec dam bao cho tri so dien ap tai tat ca cac nut cua ludi trung ap va ha ap nam trong gidi han cho phep la nhiem vu cua ky su thiet ke va van hanh ludi cung cap dien

De dam bao su lam viec blnh thudng cua cac thiet bi dung dien (den, quat, tivi, tu lanh, dieu hoa, bep dien, binh nong lanh, cac dong co dien, ), yeu cau dien ap dat vao cuc cua chung khong dugc chenh lech qua 5% so vdi tri so dien ap dinh muc

Do chenh lech dien ap so vdi tri so dinh mtic goi la do lech dien dp, ky

hieu la 5U

Trong do: Udm - dien ap dinh mire cua luai dien (220V hoac 380V)

U - dien ap thuc te dat vao cuc cua thiet bi dung dien tai thdi die’m khao sat

Do lech dien ap thudng dugc tfnh theo phan tram so vdi tri so dien ap dinh muc:

U - U

(0.3)Yeu cau 18U% l< 5%Udm

Neu 8U > +5%UJm thiet bi dung dien se chay

Neu 8U < - 5%Udm thiet bi dung dien se lam viec khong tot: den khong du sang, thap qua den tuyp se khong sang, quat khong du gio, may bam nude khong khai dong dugc, may khau bo chi, cac may moc khac giam hieu suat hoac gay thu pham, phe pham v.v

Can phan biet khai niem do lech dien dp va khai niem ton that dien dp Ton that dien ap la dien ap rcri (hoac giang) tren luai dien, do chfnh la hieu

so dien ap diem dau va cuoi cua mot doan ducmg day hoac mot tuyen dudng day trong cung mot cap dien ap

Tren hinh 0.13a, gia thiet trudng hap dien ap dau nguon bang dinh muc, liic nay ton that dien ap tren duong day bang do lech dien ap tai diem 2

AU12 = u , - U2 = 5U2Nghia la ta co the cho phep ton that tren dudng day bang 5%Udm

AU12tp = 5%UdmTren hinh 0.13b dien ap nguon ldn hon dinh mire, khi do ve tri so ton that dien ap tren dudng day 12 bang tong tri so do lech dien ap tai 1 va 2

AU12 = 5U, + 8U2

V i du 1: Tai thdi diem khao sat, biet dien ap thanh gop ha ap cua tram

bien ap U, = 400 (V) va AU12 = 15(V) Hoi dien ap cuoi nguon U2 bang bao nhieu va do lech dien ap tai diem 2 bang bao nhieu?

Giai:

Dien ap tai diem cuoi nguon 2 la:

U2 = U, - AU12 = 400 - 15 = 385 (V)

Do lech dien ap tai diem 2 la:

5U2-= 5U2 - Udm = 385 - 380 = +5 (V)

5U2% = 385-380.100 = +i,32%

V i du 2: Tai thdi diem khao sat, dong ho von tai thanh cai ha ap tram bien

ap chi 390(V) Hoi ton that dien ap cho phep tren dudng day 12 la bao nhieu?

Giai:

Dien ap thap nhat cho phep tai diem cuoi nguon 2 la tri so ung vdi do lech 8U2= - 5%Udm, khi do:

U2 = Udm - 5%Udm = 380 - 0,05.380 = 361(V)Vay ton that dien ap cho phep tren dudng day 12 la:

dien ap tren dudng day la 5% trong trucJng hop van hanh binh thuong va

10% trong trucfng hop sir cd.

se dugc nghien cuu ky trong chuong 8 cua giao trinh nay

0.3.4 An toan

Khi thiet ke va lap dat cong trinh dien, van de an toan phai dugc dat len hang dau Do la an toan cho cac thiet bi dien, an toan cho can bo ky thuat van hanh, an toan cho cac cong trinh kien true va cu dan noi co luai dien di qua

Can nhd rang, ludi cung cap dien bao gom cap trung va ha ap di lln vdi dudng pho, xom lang, khu chung cu, xudng m ay Khi xay ra su co se gay chay no, khong nhung pha hoai cong trinh dien, gay mat dien ma con gay thiet hai cho nha cua, gay tai nan chet ngudi

Vi the, cong trinh dien can dugc thiet k e.lap dat, quan ly, van hanh va

su dung theo dung nhung quy dinh ky thuat nghiem ngat

Ngoai 4 chi tieu co ban tren ngudi ta con cd the quan tam den cac chi tieu khac nhu thuan tien cho van hanh, sua chua, d6 phat trien v v

0.4 Nhurng phan tu chfnh cua ludi cung cap dien va ky hieu tren ban ve

0.4.1 May bien dp va tram bien dp

May bien ap lam nhiem vu bien doi dien ap va truyen tai con2 suat

May bien ap bien doi dien ap tir thap len cao goi la may bien dp tang dp, ngugc lai thi goi la may bien dp giam dp Trong ludi cung cap dien chu yeu

dung may bien ap giam ap

Mot may bien ap co the lien he giua 2 hoac 3 cap dien ap May bien ap

lien he giua 2 cap bien ap goi la may bien dp hai cuon day (hoac hai day cuon), lien he giua 3 cap dien ap goi la may bien dp ba cuon day (hoac ba

day cuon)

Tram bien ap la nai dat may bien ap, mot tram co the dat mot, hai hoac nhieu may bien ap Ngoai may bien ap, trong tram con dat cac thiet bi dong cat (nhu may cat, dao cach ly) va nhiSu thiet bi khac (nhu bien dong, bien dien ap, chong set, noi d at ).

Can phan biet tram bien dp va tram phan phoi Train phan phoi khong

dat may bien ap vi khong lam nhiem vu bien doi dien ap, chi lam nhiem vu phan phoi dien nang cho cac ho tieu thu

u3

Hinh 0.14 Ky hieu may bien ap, tram bien ap, tram phan phoi

a) May bien ap hai cuon day; c) Tram bien ap: 1 Dau vao 2 Dau ra;

b) May bien ap ba cuon day; d) Tram phan phoi

Ngoai hinh ve, may bien ap con dugc ghi r5 cac thong so quan trong: ten loai may (hoac hang san xuat), cong suat may (kVA), dien ap ben cao, ben ha (kV) Loai may - SdmB(kVA) - U,/U2(kV)

Vi du:

TM -250-10/0,4: May bien ap dau ba pha, cong suat 250 (kVA) dien ap 10/0,4(kV) do Nga san xuat

3CA-1000-12/0.4: May bien ap giam ap 1000(kVA) dien ap 12/0,4(kV)

do Siemens san xuat

SCB8-630-10,5/0,4 (kV):May bien ap giam ap 630(kVA), dien ap 10,5/0,4(kV) do Trung Quoc san xuat

BA-500-22/0,4: May bien ap phan phoi 500(kVA) dien ap 22/0,4(kV)

do hang ABB san xuat

Chu y: Ngoai cac ky hieu chfnh thuc tren hinh 0.14, trong trudng hgp

dac biet nao do (vi du do khuon kho han hep cua ban ve), ngudi ta co the dung ky hieu rieng de mo ta may bien ap, tram bien ap, tram phan phoi (xem hinh 0.7, 0.9, 0.11), tuy nhien phai chu thich ro

0.4.2 Du&ng day truyen tdi dien

De truy6n tai dien ngudi ta su dung dudng day tren khong, dudng cap

va day boc cach dien

a) Ducmg day tren khong

Dudng day tren khong bao gom mot he thong cot dien dugc trai dai suot tuyen tren do co treo day din qua cac sur cach dien Vat lieu lam day din cua dudng day tren khong la nhom hoac nhom loi thep

Nhom la loai day nhe, d in dien tot nhung do ben khong ldn chi dugc dung d dudng day tren khong ha ap vdi khoang cot be tu 40 den 50m Dudng day tren khong trung ap vdi khoang cot 80 -f- 120m phai dung day d in la day nhom 15i thep, trong do nhom lam nhiem vu d in dien con thep lam tang do ben co Day nhom va day nhom loi thep dugc che tao tir nhieu sgi nho van xoln lai

Dong co kha nang din dien tot hon nhom nhung d lt va nang hon, chi dugc dung d nhung moi trudng dac biet co hoa chat an mon nhom

Day din cua dudng day tren khong con dugc ggi la day dan tran.

Tren ban ve cung cap dien, dudng day tren khong dugc ky hieu blng dudng thang net manh, tren do co ghi chu DDK va cap dien ap truyen tai.Vdi DDK trung ap va cao ap, vi luon tai dien 3 pha, nen khi ghi so hieu day din chi can ghi loai day va tiet dien day, khong can ghi ro so pha,

F - Tiet dien day pha (mm2)

F0 - tiet dien day trung tfnh (mm2)

Chu y, vdi DDK 3 pha 4 day thi:

Vdi DDK 2 pha 3 day hoac 1 pha 2 day thi:

Khi noi den tiet dien trong day din AC la chi ke phan tiet dien din dien tire la tiet dien cua phan nhom, khong ke phan loi thep.

Hinh 0.15 Cau tao day dan va ky hieu ODK

a), b) Day A va day AC cd nho, cd ldn 1), 2), 3) Cac ky hieu dtfdng day trung ap 4) + 8) Cac ky hieu dudng day ha ap 1,2,3 pha

Dudng day tren khong so vdi dudng cap thi re hon, tuy nhien lai thieu

my quan va an toan, vi the chi dung thuan tien d ludi trung, ha ap khu vuc nong thon va ludi cao ap Vdi ludi cung cap dien do thi, de dam bao my quan va an toan phai dung dudng day cap

b) Dudng day cap

So vdi day d in dudng day tren khong thi cap la loai day d in dac biet Vdi DDK cach dien giua cac day din pha la khong khf, thi vdi cap la chat cach dien cd kha nang cach dien cao hon rat nhieu so vdi khong khf, vi the loi cap cac pha cd the dat rat gan nhau lam giam nho kfch thudc cua cap, rat tien loi cho viec van chuyen, lip dat

De thuan tien cho viec sir dung, lip dat ngudi ta che tao nhieu chung loai cap Vdi ludi cao ap co cap 1 loi, vdi ludi trung ap co cap 1 loi, 3 loi Vdi ludi ha ap co cap 1 loi, 2 loi, 3 loi, 4 loi

Loi cap (hay con goi la ruot cap) dirge che tao tir nhom va dong Cap

loi nhom re hon, nhe hon nhimg kha nang tai dien kern hon, gay ton that dien nang ldn hon Cap loi dong nang hon, dat hon nhung kha nang tai dien cao hon, ton that dien nang nho hon, rat thich hgp vdi ludi cung cap dien do thi va xi nghiep

Ldp ngoai cung cua cap goi la vo cap Ngudi ta che tao nhieu loai cap

co vo khac nhau de sir dung d nhung moi trudng khac nhau: cap chiu nhiet (con goi la cap chong chay), cap chiu an mdn, cap chiu man, cap co dai thep chiu lire co hoc v.v

Cap dugc goi ten theo chat cach dien, cach dien cua cap lam blng nhua cach dien tong hgp PVC hoac XLPE Cap cach dien bang nhua PVC

goi la cap PVC, cap cach dien bang nhua XLPE goi la cap XLPE.

Khi thiet ke hoac mua cap can ghi rd loai cap, cap dien ap, vat lieu lam loi, so lugng loi, tiet dien loi, loai vo irng vdi moi trudng sir dung

Trong cac ban ve cung cap dien, cap dugc ky hieu bang mot ducmg

thang hai dau cd hai tam giac de trang (hai dau cap), dau cap lam nhiem vu

tach rieng cac loi cap ra de dau vao thiet bj dien khac Tren ky hieu cap phai ghi day du so lieu ve cap theo quy cach sau:

- Cap trung, cao ap: n chat cach dien (m.F)

Trong do:

n - so cap, neu = 1 thi khong can ghi, chat cach dien - ghi PVC hoac XLPE

m - so 15i cap

F - tiet dien loi cap (mm2)

- Cap ha ap: n cha't cach dien (mF + l.F 0)

Trong do:

n - so cap

m - so I5i pha

F - tiet dien loi pha (mm2)

F0 - tiet dien loi trung tinh (mm2)

1 Loi trung tinh

2 Lop boc cach dien

4 Lop boc cach dien

5 Lop boc thep

6 L6p boc PVC

7 Lop boc thep

8 Vo cap bang PVC Cap 0,4(kV) PVC (3x50 + 1x35) PVC (1x50+ 1x50) 2PVC (3x95 + 1x50)

2[3PVC (1x500) + 1PVC (1x300)]

C> -d

H inh 0.16 Cau tao cap va ky hieu cap tren ban ve

a) Cap ha ap 4 loi; b) Cap trung ap 3 loi

1 h - 5 Ky hieu cap trung ap lo ddn va kep khi dung cap 1 loi va 3 loi

6 h - 10 Ky hieu cap ha ap lo ddn va kep khi dung cap 1 loi va 4 loi

c) Day boc cach dien

Luai dien noi that trong cac can ho, trong lop hoc, sieu thi, benh vien,

co quan van phong deu dung day boc cach dien hoac cap Day boc cach dien dugc che tao phong phu ve chung loai, da dang ve m lu ma, mau sdc, rat

thuan tien cho lap dat dien noi that: co loai day 1 loi, 2 15i, co day loi dong, 15i nhom, co day 1 scfi, nhieu sod, co day cung, day mem De giam ton that ngudi ta thudng dung day dong.

Day boc cach dien thudng che tao cac cd sau:

M(2 x 1,5) - Day dong boc cach dien 2 loi, tiet dien 1,5 (mm2)

2M(1 x 4) - Hai day dong boc cach dien 1 loi, tiet dien 4 (mm2)

C h ircm g 1

XAC DiNH PHU TAI DIEN■ ■ ■1.1 Khai niem ve phu tai dien

M6i ho tieu thu dien (nha may, khu cong nghiep, nha chung cu, trudng

h oc ) deu cd nhu c£u su dung dien, nghla la deu doi hoi nganh dien cung

cap mot luang cong suat dien nhat dinh, lugng cong suat dien nay goi la phu tdi dien.

Phu tai dien la so lieu dau tien va quan trong nhat de tfnh toan, thiet ke

he thong cung cap dien Can cu vao so lieu nay ngudi ta tien hanh lua chon thiet bi dien, tfnh toan cac lugng ton that, lua chon phuong an cap dien toi uu, thiet lap che do van hanh

Viec xac dinh chfnh xac phu tai dien anh hudng ldn den cac chi tieu kinh te - ky thuat cua ludi cung cap dien sau nay Neu xac dinh phu tai dien qua ldn so vdi thuc te se d in den lua chon thiet bi dien qua ldn, lam tang von dau tu Neu xac dinh phu tai dien qua nho d in tdi lira chon thiet bi dien qua nho, khi van hanh se bi qua tai gay mat dien, nang hon co the gay chay no lam mat dien va pha hoai cong trinh dien

Xac dinh chfnh xac tri so phu tai dien dung nhu tri so phu tai thuc te su dung sau nay la rat kho, bdi vi phai xac dinh phu tai dien ngay trong giai doan du an dugc cap phep, ngudi thiet ke chi biet rat ft thong tin ve cac doi tugng sir dung dien sau nay Vf du, vdi khu che xuat, chi biet dien tfch va tfnh chat dac thu (cong nghiep nang hay nhe), vdi mot nha may thi chi biet san pham, san lugng; vdi nha chung cu chi biet so tang, so can ho, vdi trudng hoc chi biet so lap Tu lugng thong tin ft oi nay phai tfnh ra dugc phu tai dien de phuc vu cho cong tac thiet ke

Phu tai dien dung trong giai doan thiet ke tfnh toan ludi cung cap dien

goi la phu tdi tinh toan vdi dinh nghla: phu tai tfnh toan la phu tai cifc dai dai han khong thay doi theo thdi gian va tuong duong vdi phu tai thuc te ve hieu qua phat nhiet Tir dinh nghla tren nhan thay, dac trung quan trong d6

xac dinh phu tai tfnh toan la tri so cong suat cuc dai cua doi tugng su dung dien keo dai trong khoang thdi gian vai ba chuc phut trd len, vf du nhu cong

suat trung blnh cua ca mang tai ldn nhat doi vdi xf nghiep, cong suat trung binh tu 5 den 7 gid chieu doi vdi can ho gia dinh Tri so cong suat cuc dai nhung chi xay ra trong thdi gian rat ngan nhu dong dien md may cua dong

co khong dugc xac dinh la phu tai tfnh toan Dieu kien phu tai tfnh toan phai tuong duong vdi phu tai thuc te sau nay ve hieu qua phat nhiet, dam bao tfnh chfnh xac chap nhan dugc cua tri so phu tai tfnh toan

Cd nhieu phuong phap xac dinh phu tai tfnh toan, tat ca cac phuong phap nay deu la gan dung Su dung phuong phap nao phai can cu vao lugng thong tin thu nhan dugc Cang co nhieu thong tin ve doi tugng su dung dien sau nay thi cang chon dugc phuong phap chfnh xac hon

1.2 Xac dinh phu tai tfnh toan khu vuc cong nghiep

1.2.1 Xac dinh phu tdi tinh toan cho phan xuang

Co hai phuong phap xac dinh phu tai tfnh toan cho cac phan xuong trong xf nghiep hoac cho mot xudng san xuat nho le tuy thuoc vao thong tin thu nhan dugc

1.2.1a Xac dinh phu tdi tinh toan theo he so nhu can va cong suat dat

Trong giai doan xay dung nha xudng, cac ky su cong nghe cho biet cong suat dien can dat tai cac phan xudng va dien tfch phan xudng Tren ca

so hai thong tin nay, phu tai tfnh toan cua phan xudng dugc xac dinh theo cac cong thuc sau day:

Phu tdi dong luc (phu tai cac may) cua phan xudng xac dinh theo he

so nhu cau k^ va cong suat dat Pd

Trong do: D la dien tfch phan xudng, (m2)

Tuy theo yeu cau cua tung loai phan xudng ma lay tri so P0 thfch hgp

P0 = 10, .,1 5 , .,20 (W/m2)

Phu tai chieu sang tmh theo (1.3) la chieu sang chung, m6i may cong

cu (tien, phay, bao, khoan) con co den chieu sang cuc bo rieng Cac phan xudng may chi dugc chieu sang bang den sgi dot, neu chieu sang bang den tuyp se gay cho cong nhan hien tugng moi met, chong mat, hoa mdt, d in tdi tai nan lao dong, gay thu: pham, phe pham

Den sgi dot cd coscp = 1 —» tgcp = 0 —» Qcs = 0

Den tuyp cd coscp = 0,8 —» tgcp = 0,75 -> Qcs ^ 0 dugc dung trong cac phan xudng thiet ke, phong thf nghiem, nha hanh chfnh Vdi cac nha xudng nay, P0 dugc lay nhu sau:

- Xudng thiet ke, thf nghiem: P0 = 30(W/m2)

V i du 1.1 Phan xudng co khf so 2 cua nha may che tao may keo co

Pd = 2000 (kW), dien tfch 1250(m2) Yeu cau xac dinh phu tai tfnh toan

1.2.1b Xac dinh phu tdi tinh toan phan xudng theo he so cuc dai va cong suat trung binh

Phuong phap nay su dung khi da biet day du thong tin ve cac may cua phan xudng trong giai doan thiet ke chi tiet, do la: vi tri dat, cong suat tung may va che do lam viec cua tung loai may (dai han, ngan han, mot pha, ba pha )

Trinh tu xac djnh phu tai tmh toan cua phan xudng nhu sau:

1 Phan nhom phu tdi M6i phan xudng thudng dat 50 -j- 70 may moc

khac nhau Neu de nguyen tat ca so may moc nay thanh mot nhom va cap dien bang mot tu dong luc thi do tin cay thap va chat lugng dien nang cung kern De cap dien dugc tot ngudi ta thudng phan cac may trong phan xudng thanh vai nhom phu tai, m6i nhom khoang 8 h- 12 may roi dat cho m6i nhom mot tu dong luc, tir cac tu dong luc nay dien se theo dudng cap ngam cung ca'p cho timg may

Thudng chia nhom phu tai theo cac tieu chi sau:

- Bao gom cac may d gin nhau

- Cac may co cung che do lam viec

- Cong suat cac nhom may xap xi nhau

Viec phan chia cung chi la tuong doi bdi vi cac nhom kho ma dam bao chutin xac dong thdi ca 3 tieu chi tren

2 Xac dinh phu tdi tinh toan ticng nliom may Phu tai tfnh toan dong

luc cua m6i nhom xac dinh theo cong thiic:

Pjmi - cdng suat dinh muc cua may thu i (kW)

n - so may trong nhom

ksd - he so sir dung cua nhom may, tra s6 tay

Pib_ cong suat trung binh cua nhom may, (kW)

So thiet bi dung dien hieu qua la dai lugng gia tudng, ngudi ta dira vao

de tien tmh toan cho nhom thiet bj bat ky co cong suat khac nhau, co che do lam viec khac nhau

Dinh nghTa: nhq la so thiet bi co cong suat bang nhau co cung che do

lam viec va gay ra mot phu tai tmh toan dung bang phu tai tfnh toan do nhom thiet bi thuc te gay ra

- Xac dinh n, la so thiet bi co cong suat > cong suat cua thiet bi co

cong suat ldn nhat

- Xac dinh P, la tong cong suat cua n, thiet bi ke tren

- Tir n., P tra so tay dugc nhq,

- Xac dinh nhq theo bieu thuc

n h q = n n h q *

Ghi chu I: Phuong phap nay chi dung dugc vdi nhq * 4 Neu tfnh ra

n h q < 4 thi:

Hoac la tmh nhq theo (1.11);

Hoac la chia lai nhom phu tai;

Hoac la xac dinh gan dung phu tai tfnh toan cua nhom theo cong thuc:

P = I X Pdmi O l 2)1

Trong do: he so tai kti lay nhu sau:

kti = 0,9 vdi cac may lam viec 6 che do dai han

kti = 0,75 vdi cac may lam viec d che do ngan han lap lai

Ghi chu 2: Neu trong nhom co cac thiet bi lam viec mot pha hoac ngan

han - lap lai thi phai quy doi v6 dai han ba pha trudc khi xac dinh nhq

- Vdi thiet bi lam viec 1 pha dau vao dien ap pha (quat thong gio cong suat nho )

lTrong do:

m - so nhom phu tai

kdt - he so dong thdi, lay nhu sau:

m = 1, 2 —> kdl = 1

m = 3, 4, 5 —» kdl = 0,9 -h 0,95

m = 6, 7, 8, 9, 10 -> kdl = 0,8 -r 0,85

m = > 10 —> kdl = 0,7

4 Xac dinh phu tdi chieu sang cua phan xifdng

Phu tai chieu sang phan xudng cung xac dinh theo cong thuc (1.3), (1.4) cua muc 1.2.1a

5 Xac dinh phu tdi tinh toan toan phan xudng

Phu tai tmh toan cua phan xudng bao gom phu tai dong luc va chieu sang dugc xac dinh theo cac cong thuc (1.5), (1.6), (1.7)

V i du 1.2 Yeu cau xac dinh phu tai tfnh toan cho nhom thiet bi gom 3

quat thong gio, cong suat m6i chiec 12 (kW)

Giai:

VI nhom chi cd 3 thiet bi, phu tai tinh toan xac dinh theo cong thuc (1.12)

3

P = Z k tiPdmi 1

Vdi ku = 0,9 va coscp = 0,8 tfnh dugc

Pu = 3 0,9 12 = 32,4 (kW)Q„ = 32,4 tgcp = 32,4 0,75 = 24,3 (kVAr)

Su = a/ 32,42 + 24,32 = 40,5(kVA)

Vi du 1.3 Yeu cau xac dinh phu tai tfnh toan cua nhom may cong cu

co cac so lieu theo bang sau:

Can cu: vao so lieu trong bang moi tien hanh tmh toan nhq.

1 Thiet bi co cong suat ldn nhat la bien ap han 14,57 (kW), mot nira cong suat la 7,38 (kW), nhu vay co 4 thiet bi co cong suat Ion hon tri so nay

la bien ap han (1), may mai tho (2) va cau true (3)

Cuoi cung xac dinh dugc phu tai tmh toan cua nhom

1.2.2 Xac dinh phu tdi tinh toan nha may

1,2.2a Xac dinh phu tdi tinh toan nha may theo suat tieu hao dien nang tren dan vi san pham

Phuong phap nay sir dung trong giai doan du an kha thi, nghTa la viec xay dung nha may da dugc cap phep, thong tin duy nhat nhan dugc la san phcim va san lugng cua nha may Ngay thoi diem nay can xac dinh phu tai tfnh toan cua nha may de bao cho nganh dien biet de chuan bi nguon dien ca'p cho nha may khi nha may xay dung xong, bat dau di vao hoat dong.Phu tai tinh toan cua nha may xac dinh theo cong thuc:

m - san lugng (met/nam; tan/nam, chiec/nam )

a - suat dien nang tren don vi san phdm, nghla la dien nang can thiet

de san xuat 1 san pham (kWh/sp)

Tmax - thoi gian sir dung cong suat ldn nhat (h), tra phu luc

coscp - he so cong suat, tra phu luc

Vi du 1.4 Yeu cau xac dinh phu tai tfnh toan cho nha may det san

lugng 5 trieu vai mot nam, nha may da dugc ca'p phep xay dung va di vao san xuat sau 5 nam

Phu tai tfnh toan toan nha may xac dinh nhu sau:

n - so phan xudng trong nha may

kjj - he so dong thdi cuc dai cua cac phan xudng, la'y tri so theo muc 3

cua 1.2.1b

I-2.2c Bieu do phu tdi

Nhu da noi d chuong md dau, vdi nha may nho co phu tai tfnh toan 1000(kVA) trd lai thudng chi nen dat mot tram bien ap phan phoi chung cho toan nha may; con vdi nhung nha may quy mo ldn tu vai ngan den hang chuc ngan kVA can xay dung mot ludi trung ap vdi mot tram phan phoi trung tam (hoac bien ap trung tam) va nhieu tram bien ap phan xudng (xem hinh 0.3) De giup cho viec dinh hudng vach cac phuong an mang trung ap,

ta cin ve bieu do phu tai toan nha may

Bieu do phu tdi la mot vong tron cd tam trung vdi tam hinh hoc cua

phan ^udng, cd dien tich bang phu tai tinh toan cua phan xudng va dugc chia lam hai phan: phan gach cheo la phu tai dong luc, phan de trang la phu tai chieu sang vdi goc a° xac dinh theo bieu thuc:

(1 26) s^tt

Trong do: Scs, Su - phu tai chieu sang va phu tai tfnh toan cua phan xudng (kVA)

Ban kmh cua bieu do cung dugc xac dinh nhu sau:

ttR~ — Stt —> R —

Vi trong pham vi nha may co nhieu phan xudng, can phai can nhac khi

ve bieu do phu tai cac phan xudng vdi nhung vong tron hgp ly, nghia la khong nho qua kho quan sat nhung cung khong ldn qua lam chung trum phu len nhau Muon the, ngudi ta phai dua vao mot ty le xfch lay cung mot tri so vdi tat ca vong tron phu tai

Trong

do:-R - ban kmh cua vong tron phu tai timg phan xudng, (mm)

Slt - phu tai tinh toan cua tung phan xudng, (kVA)

m - ty le xich tu chon, (kVA/mm2)

Ben canh vong tron phu tai m6i phan xudng can dugc ghi r5 cac so lieu bang mot phan so: tir so la so thu tu cua phan xudng tren mat bang, m iu

so la S„(kVA) ciia phan xudng

Vi du 1.5 Phan xudng ca khf so 1 cua nha may che tao may keo co

Su = 2250 (kVA), trong do phu tai chieu sang Pcs = 36(kW) Yeu cau ve bi£u

do phu tai

Giai:

Vdi so lieu de bai cho, can cu: vao cac

cong thtic (1.26), (1.27), xac dinh dugc ban kmh

vong tron phu tai R va goc phu tai chieu sang a

vdi ty le xfch chon la m = 5(kVA/mm2)

V i du 1.6 Nha may co khf che tao bao gom 10 phan xudng Da xac

dinh dugc phu tai tfnh toan cua tung phan xudng, ket qua cho trong bang sau

PX sCfa chufa cd khf 18,62 120,52 125,38 168,71

Yeu cau:

1 Xac dinh phu tai tfnh toan toan nha may

2 Ve bieu do phu tai nha may

3 Dinh hudng xay dung mang cao ap nha may

Giai:

1 Phu tai tfnh toan toan nha may xac dinh theo cac cong thuc (1.22), (1.23), (1.24), (1.25)

La'y he so dong thdi bang 0,8 tfnh dirge:

10pnm = k d t Z Ptti =0,8.7303,34 = 5842,67 (kW)

PX sCfa chCfa cd khi 18,62 168,71 4,23 55,61

Tir day d6 dang ve dugc bieu do phu tai toan nha may:

168,;

10 84.12 CD

3 Nhin vao do thi phu tai nha may ta co nh^n xet: Phu tai phan bo tuong doi dong deu bao quanh vi tri trung tam nha may, trir ba phan xudng 1,

6, 10 phu tai tinh toan nho tren dudi 100(kVA), bay phan xudng con lai deu

co phu tai rat ldn tir gan mot ngan den gan hai ngan (kVA)

Tir nhan xet tren ta cd dinh hudng xay dung ludi dien cao ap ciia nha may nhu sau:

Dat 7 tram bien ap phan phoi cho 7 phan xudng co phu tai tfnh toan

ldn (goi la tram bien dp phan xitc/ng - TBAPX).

Ba phan xudng con lai 1, 6, 10 vi co phu tai qua nho, khong nen dat rieng m6i phan xudng mot tram bien ap, se khong kinh te; chi can cap dien

ha ap tir TBAPX lan can (hinh 1.3) hoac xay dung mot TBAPX chung cho ca

3 phan xudng (hinh 0.3)

Tai vi tri trung tam phu tai nha may M (vi tri chinh xac cua di6m M se xac dinh sau), dat mot tram phan phoi trung tam (TPPTT) hoac tram bien ap trung tam (TBATT) cd nhiem vu nhan dien tir tram bien ap trung gian (TBATG) quoc gia ve roi cap cho cac TBAPX cua nha may

1.3 Xac dinh phu tai tmh toan khu vuc nong thon

Ba loai ho tieu thu dien dien hinh cua khu vuc nong thon la ho gia dinh, trudng hoc va tram bom

1.3.1 Xac dinh phu tdi tinh toan cho tru&ng hoc

Trudng hoc d nong thon la trudng pho thong bao gom trudng tieu hoc, trung hoc co sd va trung hoc pho thong Tuy theo quy mo, m6i huyen co 1, 2, 3 trudng trung hoc pho thong, m6i xa deu cd trudng tieu va hoc trung hoc co sd.Dien dung trong cac trudng pho thong chu yeu de chieu sang va quat mat cho cac ldp hoc, cho phong giam hieu, phong giao vien va phong hop

1 Phu tdi tinh toan cua mot lap hoc

Vi den va quat dugc bo tri deu tren dien tfch ldp hoc, ngudi ta xac dinh

phu tdi tinh toan cua mot lap theo suat phu tai chieu sang tren don vi dien tfch.

Trong do:

Dl - dien tfch ldp hoc, vdi ldp hoc pho thong thudng cd

DL = 8 x 10 = 80m2P0 - suat phu tai chieu sang tren don vi dien tich (W/m2), thudng lay:

2 Phu tdi tinh toan khu van phdng

Tai khu van phong (phong giam hieu, phong giao vien, phong hop) dien dung thip sang, quat mat, dun nude, va cac may moc van phong