Chng M u: tnh hnh ging st vit nam v s nh hng ti li in

n tt nghip : tnh ton thit k chng st cho ng dy v trm bin p 110/22Kv

Li m u

H thng in l mt h thng quan trng ca h thng nng lng Vit Nam v khng th thiu c trc cng cuc hin i ho, cng nghip ho t nc. Do ngun in thng t xa ni tiu th in nng nn phi chuyn qua cc trm bin p tng hoc gim in p. i vi nc ta l nc c kh hu nhit i gi ma, m h thng in li ko di t Bc vo Nam do phi i qua nhiu vng kh hu khc nhau c bit l nhng ni c m cao, mt ging st nhiu. Thit hi do st gy ra cho ngnh in v nn kinh t quc dn l rt ln.

V vy chng ta phi u t vo nghin cu, tm ra nhng gii php chng st nh vo cc nh my, trm bin p, ng dy gim n mc ti thiu thit hi do st gy ra cho nn kinh t. Vi yu cu nh vy, n thit k ca em gm bn thuyt minh ny v km theo bn v thit k v bo v chng st cho trm bin p 110/22/0,4KV v ng dy 110KV.

Do thi gian c hn nn vic thit k ca em khng trnh khi nhng sai st, em mong c s ch bo gip ca cc thy c gio b mn h thng in..

Mt ln na em xin chn thnh cm n!

Sinh vin thit k

Chng m u

------o0o-----

tnh hnh ging st vit nam v nh hng ca n ti li in

V

ic nghin cu ging st v bin php chng st c lch s lu di cng vi s pht trin ca ngnh in. Ngy nay ngi ta tm ra c cc phng php, nhng h thng thit b v k thut cao phng st nh mt cch hu hiu v an ton.

Tuy nhin mt , thi gian xy ra st nh khng th d on c trc nn vic nghin cu chng st l rt quan trng c bit l ngnh in .

I - Tnh hnh ging st vit nam.

- Theo ti KC - 03 - 07 vin Nng Lng, trong mt nm s ngy st nh mim Bc khong t 70 - 100 ngy v s ln c ging t 150 - 300 ln. Vng c ging nhiu nht trn min Bc l khu vc: Mng Ci, Tin Yn (Qung Ninh) hng nm c t 100 - 110 ngy ging st, thng 7 - 8 c th c n 25 ngy ging trn mt thng.

- Mt s vng c a hnh chuyn tip gia cc vng ni v vng ng bng, s ln ging cng n 200 ln/ 1 nm, vi s ngy cng n 100 ngy/nm. Ni t ging nht l Qung Bnh, hng nm ch c khong 80 ngy ging. Xt v din bin ca ma ging trong nm, ma ging khng hon ton ng nht gia cc vng. Ni chung mim Bc ma ging tp trung t thng 4 n thng 9, min Ty Bc tp trung khong t thng 5 n thng 8 trong nm.

- Trn vng duyn hi Trung B pha Bc n Qung Ngi l khu vc tng i nhiu ging trong thng 4 n thng 8 s ngy ging xp x 10 ngy/thng. Thng nhiu nht l thng 5 c th t 12 n 15 ngy. Nhng ngy u ma v cui ma ch c 2 n 5 ngy/ thng.

- T Bnh nh tr vo l khu vc t ging nht thng ch c vo thng 5 vi s ngy xp x bng 10 ngy (Tuy ho: 10 ngy; Nha Trang 8 ngy; Phan Thit: 13 ngy), cn cc thng khc ca ma ng ch quan st c t 5 n 7 ngy ging st.

- Min Nam cng c kh nhiu ging hng nm quan st c t 40 - 50 ngy tu tng ni. Khu vc nhiu nht l ng bng Nam B, s ngy ging st c th ln ti 120 n 140 ngy. Ma ng Nam B t thng 4 n thng 11 s ngy ging trung bnh 10 ngy/thng cn t thng 5 n thng 10 c khong trn 20 ngy ging ( Si Gn: 22 ngy; H Tin: 28 ngy)

- Ty Nguyn ma dng thng ch c t cc thng 4,5 v thng 9. Thng cc i (thng 5) trung bnh quan st c 15 ngy ging v Ty Nguyn trung bnh s nga ging t 10 - 12 ngy(Ply cu: 17 ngy; Kon Tum: 14 ngy, Lt: 10 ngy) cn cc thng khc ca Ma ng trung bnh c t 5 n 7 ngy/thng.

- Qua s liu kho st ta thy rng trung bnh ging st 3 min Bc - Trung - Nam, nhng vng ln cn li c mt tng i ging nhau. Kt qu nghin cu ngi ta lp c bn - phn vng st Vit Nam (cc thng s cho trong bng 1-1).

Bng 1-1:

VngNgy ging trung bnh (ngy/nm)Gi ging trung bnh(h/nm)Mt st trung bnhThng ging cc i

ngBngven bin Mim Bc81,1215,66,478

Min ni trung du Bc B.61,6219,16,337

Cao nguyn MinTrung47,6216,213,315,8

Ven bin MinTrung40,095,23,555,8

ng Bng Min Nam60,189,325,375,9

- T cc s liu v ngy gi ging, s lng o lng nghin cu thc hin qua cc giai on c th tnh ton a ra cc s liu d kin v mt phng in xung cc khu vc (s liu d bo trong bng 1-2 ).

Bng 1-2:

S ngy dngng bng ven binMin ni trung du Bc BCao nguyn min trungVen bin min trungng bng Min Nam

20 ( 402,43 ( 4,682,1 ( 4,21,2 ( 2,41,22 ( 2,441,26 ( 2,52

40 ( 604,68 ( 7,924,2 ( 6,32,4 ( 3,62,44 ( 3,652,52 ( 3,78

60 ( 807,92 ( 9,826,3 ( 8,43,6 ( 4,83,65 ( 4,873,78 ( 5,06

80 ( 1009,82 ( 12,158,4 ( 10,54,8 ( 6,04,87 ( 6,095,06 ( 6,3

100 ( 12012,15(14,5810,5 ( 12,66,0 ( 7,26,09 ( 7,316,3 ( 7,76

II. S nh hng ca ging st ti h thng in:

- Vit Nam, trong khun kh ti cp nh nc KC - 03 - 07 lp t cc thit b ghi st v b ghi tng hp trn cc ng dy ti in trong nhiu nm lin tc, kt qu thu thp tnh hnh s c li in 220 KV min Bc t nm 1987 n nm 1992 c ghi trong bng 3.

- Trong tng hp s c vnh cu ca ng dy trn khng 220 KV Ph Li - H ng, nguyn nhn do st l 8/11 chim 72,7%. S d ly kt qu s c ca ng dy Ph Li - H ng lm kt qu chung cho s c li nh Min Bc v y l ng dy quan trng ca Min Bc v s c ng dy ny nh hng rt ln n tnh hnh truyn ti in nng trn li in. Ngoi ra theo ti nghin cu khoa hc - nghin cu gii php k thut hon thin h thng chng st bo v li in trung p ca Vin Nng Lng tp trung thng k, phn bit tnh hnh s c li in 35 n 110 KV ca Min Bc ni chung v li in quc gia ni ring t nm 1976 n nm 1982. Kt qu thng k c th hin bng 1- 3.

Bng 1- 3:

NmDi 220 KVng dy Ph Li - H ng

Tng sVnh cuTng sVnh cuDo st

1987

1988

1989

1990

1991

19922

5

24

25

30

191

2

3

4

2

12

5

6

2

3

41

2

2

1

1

41

1

1

1

1

3

Tng s1051622118

- T thng k ny cho ta thy rng: Tng s c do st gy ra i vi ng dy trung p l ln hn tng s ca ng dy cao p, nhng tc hi ca n mang li i vi h thng in l rt ln. S ln s c li in 35KV chim t l kh ln n 54%.

Bng 1- 4:

Nm theo diCp in p KVTng chiu di ng dy (Km)Sut s c (ln /100Km)

Tng sDo st

1979110

351050

34008,5

11,51,85

6,00

1980110

351100

34006,8

10,71,46

5,40

1981110

351150

38005,6

7,72,50

1,20

1982110

353300

112006,9

10,82,50

5,10

*Kt lun: Qua nghin c tnh hnh ging st Vit Nam v nhng thit hi do s gy ra cho li in l rt ln nn vic m bo chng st cho ng dy in v trm bin p l rt cn thit nhm gim n mc thp nht s c ct in ng dy. V vy vic u t nghin cu chng st l rt quan trng nng cao tin cy cung cp in v trong vn hnh li in quc gia.

chng i

------o0o-----

tnh ton trng st nh trctip vo trm bin p

T

rong h thng in (HT), trm bin p (TBA) ng vai tr quan trng. N quyt nh rt ln v tin cy cung cp in ca ton HT v mt yu t quan trng dn n s mt n nh ca HT trong nhiu yu t l do sng st qu in p truyn vo trm t ng dy v do st nh trc tip vo trm.

- Qua thng k, ngi ta thy s ln s c ca HT do b st nh chim t l rt ln so vi cc trng hp khc. V vy vic tnh ton bo v TBA do st nh h n mc ti thiu l mt nhim v ht sc quan trng v cn thit. Khi b st nh vo trm, cc thit b in s b h hng v c th dn n vic cung cp in b ngng ton b , ng thi c th lm nh hng trc tip n qu trnh sn xut in nng v cc ngnh kinh t khc.

- m bo chng st nh trc tip vo trm cn dng cc ct thu st v dy chng st. Cc ct thu st ny c th c t c lp hoc trong iu kin cho php ta vn dng chiu cao ca cc ct, x ct n chiu sng. Ring ct c lp thng tn km hn v kinh t nn ch dng khi khng th tn dng c chiu cao ca cc ct, x...

- Nu t cc ct thu st trn cc kt cu ca trm phn phi ngoi tri v dng dy chng st bo v cho don dy dn ni t s cui cng ca trm n ct u tin ca ng dy th chng s c ni t chung vi h thng ni t chung ca trm v tng ln nh ny cn tu thuc vo thng s ca dng in st v in tr ni t xung kch ca h thng. Khi in p ny vt qu gii hn cho php th c th gy nn nguy him cho cc thit b in, do vy ch trong iu kin cho php mi c t ct thu st trn cc cng trnh trong trm hoc dy chng st trong trm.

- Khi thit k bo v chng st nh trc tip vo trm bin p, ngoi cc yu cu v k thut cn phi ch n vn kinh t v vn m thut.

I. cc yu cu k thut:

- Vi mc ch gim vn u t khi thit k bo v chng st nh trc tip vo trm bin p ngoi tri, ngi ta thng b tr ct trn cc cao c sn nh ct, x... i vi trm 110KV do c mc cch nh cao nn cc ct thu st c th t trc tip trn cc kt cu ca trm. Cc tr ca cc kt cu trn c t cc ct thu st phi l ngn nht sao cho dng in st (Is) khuych tn vo t theo 3 ( 4 thanh ci ca h thng ni t.

- i vi trm 22KV khi b tr ct thu st trc tip trn x th phi tng cng cch in n cp 110KV, do vy s c tn tht v kinh t. Khi dng ct thu st c lp th phi ch n khong cch gia cc ct thu st ti cc b phn ca trm trnh kh nng phng in t ct n cc thit b bo v. Khi dng ct n chiu sng lm gi cho ct thu st th phi cho dy dn in n bng n vo ng ch v chn di t.

- m bo cho c gii v chng n mn kim loi cn phi theo ng quy nh v cc loi vt liu, tit din dy khi dng trn mt t v di t.

II. gii thiu s lc v thit k trm 110/22KV:

-Trm c kch thc: 60 x 100m2 -Tng din tch trm: 6000m2 - Chiu cao ln nht cn c bo v pha 110KV l 11m pha 22KV l 8m

- Trong trm c 2 my bin p 110/22KV, c 2 l ng dy 110KV i vo v 5 l ng dy 22KV i ra.

- Trn cc l 110KV c dy chng st nn cc thit b ca trm nm di on ng dy vo trm n x n dy u c bo v nn ta thit k chng st cho pha 110KV c th khng cn tnh n phm vi ny.

- Trong phn thit k ny ta a ra cc phng n b tr ct thu st bo v trm bin p ngoi tri theo cc yu cu k thut, m thut v kinh t sau chn phng n hp l tnh ton.

III - Phm vi bo v ca ct Thu st:

1. Phm vi bo v ca mt ct thu st (H1-1):

- Bn knh bo v cho cao hx l:

Trong : h - L cao ca ct.

hx - L c cao cn bo v.

h - hx = ha - L chiu cao hiu dng ca ct.

Nu th

th

- Nu chiu cao ca ct h > 30m th ta phi k n h s iu chnh ngha l:

(vi P l h s hiu chnh)

2. Phm vi bo v ca hai ct v nhiu ct thu st :

- Nu hai ct c chiu cao bng nhau: gi s 2 ct cch nhau mt khong l a.

+ Nu a = 7h th bt k im no trn mt t gia hai ct s c bo v an ton.

+ Nu a = 7h th ct bo v c cao l c xc nh t h).

+ Ta xem h0 nh cao mt ct v tnh phm vi bo v cho cao hx

+ Khi ct thu st c h> 30 th

Hnh 1-2

-Nu hai ct c cao khc nhau:

Hnh 1 - 3

- Nu c nhiu ct: Ta phi xc nh cho tng nhm ct gn nhau (3 hay 4 ct) phi hp bo v thu st sao cho nh cc ct cng nm trn mt ng trn ngoi tip, cc ct to thnh mt tam gic hoc a gic th phn bn trong s c bo v hon ton nu:

Trong : D - ng knh ng trn ngoi tip a gic do cc ct to thnh.

h L chiu cao ca cc ct thu st.

hx - L chiu cao ca vt cn bo v.

Hnh 1- 4

IV. Khong cch an ton trong khng kh v t.

- Khong cch an ton trong khng kh SK.

- Bin in c xung (Dmax) trong trng hp chung xc nh theo cng thc:

Trong : Imax - Dng in st tnh ton (KA)

RXK - in tr xung kch ca b phn ni t (R)

L - cm ng ca dy dn t b phn ni t n im kho st cn gi l h s in cm.

- Khi ta thay Imax = 150 KA; bn cch in ca khng kh l 500KV/m v vi th ta s c cng thc tnh ton dng xc nh khong cch an ton cho php ca khng kh nh sau:

- Khong cch an ton trong t S

- Tiu chun khong cch an ton S c xc nh bng biu thc sau:

S= a.RxkTrong :

a- H s ph thuc tr s dng in st chn trong tnh ton vi Imax = 150 th a = 0,5.

Rxk- Tr s in tr tn xung kch ca dng in st i qua b phn ni t

Hnh 1- 5

V. trnh t tnh ton chng st nh trc tip.

1 - B tr cc ct thu st :

2 - Xc nh chiu cao hiu dng ca ct :

- Tm ng knh D ca ng trn ngoi tip a gic i qua nh thu ct st sao cho din tch a gic c bo v cho hx, p dng ton trm. Ta phi tnh cao L ca ct thu st: h = hx + ha.

3- Kim tra kh nng bo v i vi vt nm ngoi phm vi ct thu st bo v:

- Tnh bn knh bo v ca mt ct thu st.

- Tnh bn knh ca khu vc bo v gia 2 ct thu st v tnh bn knh r0x m h0 bo v c.

- V khu vc bo v theo kch thc tnh c.

4. Kim tra li ton b:

- Kim tra li ton b bn v thit k nu c cao x no m cn bo v cn nm ngoi bn knh bo v ro x th cn phi xem xt li thit k: tng cao ct hoc b tr thm ct sao cho cc cao cn c bo v phi nm trong phm vi bo v ca cc ct thu st.

VI. la chn phng n b tr ct:

1. Phng n 1: B tr 10 ct thu st trong c 2 ct thu st t thm 2 u ca x n dy u trm cn 8 ct dng c lp

a. Xt cc cp ct:

- Cc cp ct 1 - 2 -10 ta c:

Do to thnh mt tam gic vung nn:

vi hx =11m cho nn chiu cao ca cc ct l : 11+3,88=14,88(m)

Vy ta chn chiu cao cc ct l 19 (m)

Cc ct 2 - 3 - 10:

Do cc ct ny to thnh mt tam gic thng nn.

Vi hh = 11m chiu cao ca cc ct thu st l 11+5,15 = 16,15 (m)

Vy ta chn chiu cao ct l 19 (m).

- Cc ct 3 -4 -10.

Ta c

Do cc ct to thnh mt tam gic thng nn:

Vi hx = 11m ta c chiu cao ca cc ct l : 11+7,02 = 18,02(m)

Vy ta chn chiu cao ct l 19 (m)

- Cc ct 4-5-9-10:

Do cc ct to thnh hnh ch nht nn:

Chiu cao ca cc ct thu st vi hx = 11m l 11+ 7,94 = 18,94m

Vy ta chn chiu cao ca cc ct l :19(m).

- Cc ct 5 - 6 -7:

Do cc ct to thnh mt tam gic vung nn:

Vi hx = 8m chiu cao ca cc ct l: 8+ 5,41=13,41(m)

Vy ta chn chiu cao ca cc ct l : 16 (m)

- Cc ct 5 - 7 - 9:

Do cc ct to thnh mt tam gic nn ta c:

Vi hx = 8m chiu cao ca cc ct l: 8+ 7,09 = 15,09(m)

Vy ta chn chiu co ca cc ct l: 16(m)

-Cc ct 7 - 8 -9:

Do to thnh tam gic thng nn:

Vi hx = 8m cho nn chiu cao ca cc ct thu st l 8+5,41=13,41(m). Vy ta chn chiu cao ca cc ct l: 16(m).

* Vy ta xc nh c:

+Cc ct 1-2-3 -4 -10 cao l 19 m

+Cc ct 5 - 6 -7 - 8 -9 cao l: 16m.

b. Xt cc cp ct bao quanh trm:

- Cp ct 1 -2:

+ Bn knh bo v ca mi ct cao 19m l:

EMBED Equation.3 v

=

+Phm vi bo v gia hai ct l:

v

=

- Cp ct 2-3:

+ Bn knh bo v ca mi ct cao 19m l 7,88 (m)

+Phm vi bo v gia hai ct l:

v

- Cp ct 3-4:

+ Bn knh bo v ca mi ct cao 19m l 7,88m

+Phm vi bo v gia 2 ct l:

v:

- Cp ct 4-5:

+ Bn knh bo v ca ct 4 l 7,88m

Bn knh bo v ca ct 5 l:

V:

+ Phm vi bo v gia 2 ct: v 2 ct c cao khc nhau nn bn knh bo v ca ct 5 vi cao hx = 16(m) l:

V:

V:

-Cp ct 5-6:

+ Bn knh bo v ca ct 5,6 l 3,75 (m)

+ Phm vi bo v gia hai ct:

v

-Cp ct 6-7:

+ Bn knh bo v ca mi ct cao 16m l: 3,75 (m)

+ Phm vi bo v gia hai ct:

V

-Cp ct 7-8:

+ Bn knh bo v ca ct cao 16m l 3,75(m)

+ Phm vi bo v gia hai ct:

V:

- Cp ct 8- 9:

+Bn knh bo v ca cc ct cao 16m l 3,75(m)

+Phm vi bo v gia hai ct l:

-Cp ct 9 -10

+ Bn knh bo v ca ct 9 cao 16m l 3,75m.

Bn knh bo v ca 10 ct cao 19m l 7,88m

+Phm vi bo v gia 2 ct: V 2 ct c cao khc nhau nn bn knh bo v ca ct 10 vi cao h h =16m l:

V:

V:

-Cp ct 10 -1:

+ Bn knh bo v ca mi ct cao 19m l 7,88(m)

+ Phm vi bo v gia 2 ct:

V:

*T cc s liu tnh ton trn ta c bng sau:Bng 1-6

STTCc cp cthx(m)ho(m)rox(m)

11-21117,866,17

22-31116,143,84

33-411142,25

44-5812,043,06

55-6811,292,47

66-78123

77-88123

88-9811,282,46

99-10812,043,06

1010-11114,712,78

- T bng s liu trn ta v phm vi bo v ca cc ct thu st (theo s b tr ct thu st)

2 - Phng n 2: B tr 12 ct thu st trong 2 ct t trn x n u trm, ct cn li t c lp.

a. Xt cc cp ct:

- Cp ct 1 - 2 - 11

Do cc ct to thnh mt tam gic vung nn:

Vi hx = 11m chiu cao ca cc ct l: 11+ 3,88 = 14,88 (m)

Vy ta chn chiu cao ca cc ct l 18 (m)

- Cc ct 2 -3 -11:

Do cc ct to thnh mt tam gic cho nn:

Vi hx = 11m chiu cao ca cc ct l: 11+ 5,15 = 16,15(m).Vy chn chiu cao ca cc ct l 18(m)

- Cc ct 3 -11- 12:

Do cc ct to thnh tam gic thng nn:

Vi hx = 11m th chiu cao ca cc ct l: 11+ 5,45 = 16,45(m). Vy ta chn chiu cao ca cc ct l18 (m)

- Cc ct 3 - 4 -12:

Do cc ct to thnh tam gic thng nn:

Vi hx = 11m th chiu cao ca cc ct l: 11+ 6,1 = 17,1 (m). Vy ta chn chiu cao ca cc ct l: 18(m)

- Cc ct 4 -5 -12:

Do cc ct to thnh tam gic thng nn ta c:

Vi hx = 11m chiu cao ca cc ct l: 11+6,48 = 17,48 (m)

Vy ta chn chiu cao cc ct l 18 (m)

- Cc ct: 5 -6 -12:

Do cc ct to thnh tam gic thng nn ta c:

Vi hx = 8m chiu cao ca cc ct l: 11+4,57 =15,57 (m)

Vy ta chn chiu cao cc ct l: 18 (m)

- Cc ct 10 -11-12:

Do cc ct to thnh tam gic cn nn:

Vi hx = 11m chiu cao ca cc ct l: 11+4,57 =15,57(m). Vy ta chn chiu cao ca cc ct l 18(m)

-Cc ct 6 -7 - 8:

Do cc ct to thnh tam gic vung nn:

Vi hx = 8 m chiu cao ca cc ct l: 8+5,41= 13,41m

Vy ta chn chiu cao ca cc ct l 16 (m)

- Cc ct 6 -8 -10:

Do cc ct to thnh tam gic thng nn:

Vi hx = 8m th chiu cao ca cc ct l: 8+7,09 = 15,09(m)

Vy ta chn chiu cao ca cc ct l 16(m)

- Cc ct 8 -9 - 10:

Do cc ct to thnh tam gic vung nn:

Vi hx =8(m) th chiu cao ca cc ct l 8+5,41=13,41(m)

Vy ta chn chiu cao ca cc ct l 16(m)

* Vy ta xc nh c:

+ cc ct 1 - 2 -3 -4 - 5 - 11 - 12 cao 18 (m)

+ cc ct 6 - 7 - 8 -9 - 10 cao16 (m)

b. Xt cc cp ct bao quanh trm:

-Cp ct 1 - 2:

+ Bn knh bo v ca mi ct cao 18 (m)

V:

+ Phm vi bo v gia 2 ct :

V:

-Cp ct 2 -3:

+ Bn knh bo v ca ct cao 18 m vi hx = 11m l 6,38m .

+ Phm vi bo v gia hai ct

V:

- Cp ct 3 - 4:

+ Bn knh bo v ca ct cao 18m vi hx = 11m l 6,38 (m)

+ Phm vi bo v ca 2 ct

V

- Cp ct 4 - 5:

+ Bn knh bo v ca ct 4 cao h = 18m l 6,38m

+Phm vi bo v gia 2 ct:

V

- Cp ct 5 - 6:

+ Bn knh bo v ca ct 5 cao 14m v hx= 8m l 6,38(m)

Bn knh bo v ca Ct 6 cao 16 m l:

V:

+ Phm vi bo v ca 2 ct: V 2 ct c cao khc nhau nn bn knh bo v ca ct 5 cao hx = 16(m) l: V

V:

V:

Cp ct 6-7:

+ Bn knh bo v ca ct cao 16m l 9 (m)

+ Phm vi bo v gia hai ct:

V

-Cp ct 7- 8:

+ Bn knh bo v ca ct cao 16m l 9 (m)

+ Phm vi bo v gia hai ct.

V

-Cp ct 8 -9:

+ Bn knh bo v ca ct cao 16m l 9 (m)

+ Phm vi bo v gia hai ct.

V

-Cp ct 9 -10:

+ Bn knh bo v ca ct cao 16m l 9m

+ Phm vi bo v ca 2 ct:

V

-Cp ct 10 -11:

+ Bn knh bo v ca ct 11 cao 18m l 6,38 (m).

Bn knh bo v ca ct 10 cao 16m l 9 (m).

+ Phm vi bo v gia 2 ct: v 2 ct c cao khc nhau cho nn bn knh bo v ct 11 vi cao hx = h10 = 16m l:

v

v

-Cp ct 11-1:

+ Bn knh bo v ca ct cao18m l 6,38m

+Phm vi bo v gia hai ct:

V

* T nhng s liu tnh ton trn ta c bng tng kt sau y:

Bng 1-8STTCc cp cth0 (m)hx = (m)r0x (m)

11 - 216,86114,39

22 - 315,14113,11

33 - 414112,25

44 - 513,71112,03

55 - 611,9382,95

66 - 711,2882,46

77 - 81283

88- 91283

99 - 1011,2882,46

1010 -1111,9382,95

1111-113,71112,03

T bng s liu trn ta v c phm vi bo v ca cc ct thu st (theo s b tr ct thu st)

* So snh 2 phng n:

+ V mt k thut th c 2 phng n u m bo thit k bo v trm

+ V mt kinh t th phng n 1 kinh t hn v phng n 1 ch phi dng 10 ct trong c 8 ct c lp so vi phng n 2 l phi dng ti 12 ct trong c ti 10 ct phi dng c lp.

Do vy ta chn phng n 1 thit k thi cng bo v trm bin p 110/22KV.

Chng II

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tnh ton ni t cho ton trm

N

him v ca ni t l tn dng in xung t m bo an ton cho vt cn ni c tr s b. Trong HT ngi ta chia lm 3 loi ni nh sau:

- Ni t lm vic: Nhim v l m bo cho s lm vic bnh thng ca thit b theo ch c quy nh sn. Loi ni t ny gm ni t im trung tnh MBA o lng v ca khng dng trong b ngang trn cc ng dy ti in.

- Ni t an ton (ni t bo v): c nhim v m bo an ton cho ngi v thit b khi cch in b h hng tc l ni t mi b phn kim loi bnh thng khng mang in nh: v MBA, my ct, cc gi kim loi... khi cch in h hng trn cc b phn ny s xut hin in nh th nhng do c ni t nn gi c mc in th thp m bo an ton cho ngi v thit b khi tip xc vi nhng b phn ny.

- Ni t chng st: Mc ch l nhm m bo tn dng in st vo trong t khi c st nh xung ct thu st hoc trn ng dy. Do s hn ch c dng in st ti cc thit b in cn c bo v.

- trm bin p v nguyn tc phi thit k tch ri 2 h thng ni t l ni t lm vic v ni t chng st. phng khi c dng ngn mch ln hay dng in st i vo h thng ni t lm vic ln hay nh s khng gy nn in th cao trn h thng ni t an ton.

- Trong thc t cng vic ny rt kh thc hin c v nhiu l do nn ngi ta thng ch dng mt h thng ni t chung thc hin c 2 nhim v. V l nn h thng ni t chung l phi m bo yu cu ca c 2 loi ni t, ngha l phi c in tr ni t nh hn hoc bng in tr ni t nh nht ca mt trong hai h thng ni t k trn.

- Cc yu t cn chung cho h thng ni t.

+ B phn ni t c tr s in tr ni t cng nh th s thc hin c cng tt nhim vu tn dng in st trong t v in th trn cc thit b c ni t mc n nh. Tuy nhin vic gim in tr ni t s lm cho chi ph v u t xy dng tng ln nhiu (do s lng kim loi tng). Do cn phi c quy nh tiu chun tr s cho php ca in tr ni t.

* Vi cc thit b in ni t trc tip th in tr ni t yu cu l R

* Vi cc thit b c im trung bnh tnh ni t trc tip th in tr ni t yu cu l (nu h thng ni t ch dng cho cc thit b cao p)

* Vi h thng c im trung tnh cch in v h thng ni t cho c thit b cao p v h p th in tr yu cu l: (nhng R ch c Dng in I tu theo mi trng hp c tr s khc nhau.

+ i vi ni t an ton th in tr c chn sao cho cc gi tr in p bc v in p tip xc trong mi trng hp u phi khng vt qu tr s cho php.

+ Ngoi vic m bo tr s in tr ni t quy nh v gim in tr ni t ca h thng ni t cn cn phi ch n vic ci thin s phn b in th trn ton b din tch trm.

- H s ma: Ta bit rng t l mt mi trng phc tp khng ng nht v kt cu v thnh phn m ch yu l do kh hu. Do vy thit k h thng ni t cn tp trung v ch n tr s ln nht v tr s tnh ton in tr sut ca t c th c trong cc ma.

K l h s ma

(0: in tr sut c theo ma

- Phng php ni t: Theo chc nng ngi ta phn lm nhiu loi. H thng ni t bao gm cc in cc trong t lm gim in tr ni t theo tiu chun ca tng loi ni t. Cc in cc thng l cc thanh di nm ngang hoc cc thng ng in p bc nh. Khi tnh ton ta phn ra lm cc loi ni t t nhin v ni t nhn to.

Ni t t nhin l s dng cc ni t c sn nh dy chng st, ct thu st, cc kt cu kim loi ca cng trnh cc ng ng nc. Cn ni t nhn to nhm mc ch tho mn cc yu cu ni t ca cc cng trnh khi ni t t nhin khng m bo c.

- Cc tham s nh hng n ni t :

+ nh hng ca kch thc hnh hc

+ nh hng ca cc b tr in cc.

+ nh hng ca tr s in tr t.

+ Hin tng phng in xung kch: Khi c dng xt i vo in cc ni t, th gy ra mt in trng ln trn b mt in cc v trong t. in trng t n gii hn th xy ra qu trnh phng in trong t. Cc tia la in phng in pht trin xung quanh in cc to ra vng h quang, cc ni t xem nh l to ra v in tr ni t gim, in tr ni t c tnh bng cng thc:

Vi l h s xung knh.

Tnh ton ni t cho trm c thit k: trm thit k l trm 110/22KV ta tch ra lm 2 phn: 110KV v 22KV thit k.

I. Tnh ton ni t an ton : 1. Ni t an ton cho trm 110KV:

Phn trm 110KV l mng in c trung tnh trc tip ni t nn yu cu ca ni tan ton l . in tr ni t gm 2 phn. in tr ni t t nhin ( trm 110KV s dng l dy chng st v ct chng st) v in tr ni t nhn to yu cu

a- Tnh ton in tr ni t t nhin:

Trm c thit k c dy chng st dng bo v ng dy c ko vo n x n dy ca trm nn phn in tr ni t t nhin l in tr ca h thng dy chng st ct v n c tnh theo cng thc:

Trong : + Rcs lin tr ca dy chng st ( ta dng loi C- 70 c in tr trn mt n v di l )

+ Rc l in tr ni t ca ct

vi n- s l ng dy

b- H thng ni t nhn to ca ni t an ton:

H thng ni t an ton ta s dng mch vng hnh ch nht c kch thch nh sau:

Hnh 2-1

Mch vng c chn di phn in tch trm 110KV su 0,8m. Phn mch vng ny cch tng ro 5m.

Ta chn loi thp dp 50 x 1mm = b = 50 mm = 0,05 m lm mch vng.

Ta c:

L- Chu vi mch vng L = ( 50+60).2 = 220 m

t- chn su ca mch vng t = 0,8 m.

d- ng knh quy i ca thanh dt

K- H s ph thuc t l tra bng ta c K = 5,64.

vi

Ta thy cho nn ta ta phi ng cc dc theo mch vng gim in tr ca h thng ni t. Ta ng cc cc dc theo mch vng c 3m mt cc v mi cc di 3m c ng knh l 40mm v nh vy s cc l ( cc).

in tr tn ca h thng ni t c tnh nh sau:

Tra bng ta c:

tho mn.

Vy in tr ni t ca h thng l:

Nh vy tho mn iu kin

2- Ni t an ton cho trm 22KV:

H thng ni t an ton ta s dng mch vng hnh ch nht c kch thc nh sau:

Hnh 2-2

Mch vng c chn di phn din tch trm 22KV c su 0,8m phn mch vng ny c cch tng ro 5m

Ta chn loi thp dp 50 x 1mm = b = 50mm = 0,05m lm mch vng. Ta c:

Trong : L - Chu vi mch vng: L= (30+50) 2 = 160(m)

t - chn su ca mch vng t = 0,8m

d - ng knh quy i ca thnh dp

K - h s ph thuc t l Tra bng ta c K = 6,05

EMBED Equation.3 vi Kmt = 1,6

EMBED Equation.3 Nh vy cho nn m bo yu cu m khng phi ng cc.

II. tnh ton ni t chng st cho trm:

1. M u:

Khi c dng in i vo b phn ni t nu tc bin thin ca dng in theo thi gian rt ln th trong thi gian u in cm s ngn cn khng cho dng in i ti cc phn cui ca in cc, khin cho in p phn b khng u, sau mt thi gian nh hng in cm mt dn v in p s phn b u hn.

Thi gian ca qu trnh qu ni trn ph thuc vo hng s thi gian:(T l t trng vi in cm tng L .1 v in dn gl ca in cc)

T biu thc trn cho thy khi dng in tn trong t l dng mt chiu hoc xoay chiu tn s cng nghip nh hng ca L khng ng k v bt k hnh thc ni t no (thng ng hoc nm ngang) cng u biu th biir tr s in tr tn.

Khi dng in tn trong t l dng in st tham s biu th bi ni t tu thuc vo tng quan hng s thi gian T v thi gian u sng in. Khi T