TCXDVN 46-2007 - Chong Set Cho Cong Trinh Xay Dung - Huong Dan Thiet Ke_ Kiem Tra Va Bao Tri He Thong

TCXDVN TIU CHUN XY DNG VIT NAM

TCXDVN 46 : 2007

CHNG ST CHO CNG TRNH XY DNG - HNG DN THIT K, KIM TRA V BO TR H

THNG

Protection of Structures Against Lightning - Guide for design, inspection and maintenance

H Ni - 2007

www.vatlieuxaydung.org.vn

Li ni u

TCXDVN 46: 2007 do B Xy dng ban hnh theo Quyt nh s : ................................. ngy......thng.......nm 2007.

Tiu chun ny thay th TCXD 46:1984 "Chng st cho cc cng trnh xy dng - Tiu chun thit k, thi cng"


MC LC

1 Phm vi p dng ............................................................................................................... 1

2 Ti liu vin dn ................................................................................................................ 1

3 Thut ng v nh ngha ................................................................................................... 1

4 Quy nh chung ................................................................................................................. 3

5 Chc nng ca h thng thu v dn st ........................................................................... 3

6 Vt liu v kch thc ....................................................................................................... 3

7 S cn thit ca vic phng chng st ............................................................................. 7

8 Vng bo v .................................................................................................................... 13

9 Cc lu khi thit k h thng chng st ....................................................................... 18

10 Cc b phn c bn ca h thng chng st .......................................................... 19

11 B phn thu st ........................................................................................................ 19

12 Dy xung ................................................................................................................ 29

13 Mng ni t ............................................................................................................ 38

14 Cc ni t ............................................................................................................... 39

15 Kim loi trong hoc trn cng trnh. ...................................................................... 41

16 Kt cu cao trn 20 m .............................................................................................. 48

17 Cng trnh c mi che rt d chy ........................................................................... 52

18 Nh cha cc vt c kh nng gy n hoc rt d chy ......................................... 52

19 Nh ....................................................................................................................... 57

20 Hng ro .................................................................................................................. 57

21 Cy v cc kt cu gn cy ..................................................................................... 59

22 Cc cng trnh c ng ten v tuyn truyn thanh v truyn hnh ............................. 60

23 Cc kt cu khc ...................................................................................................... 61

24 S n mn ............................................................................................................... 66

25 Lp dng kt cu ..................................................................................................... 67

26 Dy in trn cao ..................................................................................................... 67

27 Kim tra .................................................................................................................... 68

28 o c ...................................................................................................................... 68

29 Lu tr h s ........................................................................................................... 68

30 Bo tr ....................................................................................................................... 69

Ph lc A Cc kha cnh k thut ca hin tng st .......................................................... 68

Ph lc B Gii thch mt s iu khon ca tiu chun ........................................................ 71


Ph lc C Hng dn chung i vi vic chng st cho thit b in trong v trn cng trnh .............................................................................................................................................. 77

Ph lc D Mt s v d tnh ton ......................................................................................... 111

Ph lc E S liu v mt st Vit Nam ....................................................................... 114


1

TIU CHUN XY DNG VIT NAM TCXDVN 46:2007

Chng st cho cng trnh xy dng - Hng dn thit k, kim tra v bo tr h thng

Protection of Structures Against Lightning - Guide for design, inspection and maintenance

1 Phm vi p dng 1.1 Tiu chun ny thay th tiu chun TCXD 46-1984.

1.2 Tiu chun ny a ra nhng ch dn thit k, kim tra v bo tr h thng chng st cho cc cng trnh xy dng. Tiu chun ny cng a ra nhng ch dn cho vic chng st i vi cc trng hp c bit nh kho cha cht n, nhng cng trnh tm nh cn cu, khn i bng kt cu khung thp, v cc ch dn chng st cho cc h thng lu tr d liu in t.

1.3 Tiu chun ny khng p dng cho cc cng trnh khai thc du, kh trn bin, cc cng trnh c bit hay p dng cc cng ngh chng st khc.

2 Ti liu vin dn TCXD 25:1991 t ng dy dn in trong nh v cng trnh cng cng. Tiu chun thit k.

TCXD 161:1987 Thm d in trong xy dng.

TCVN 4756:1989 Quy phm ni t v ni khng cc thit b in.

BS 7430:1998 Code of Practice for Earthing.

BS 923-2: 1980 Guide on high-voltage testing techniques.

BS 5698-1 Guide to pulse techniques and apparatus - Part 1: Pulse terms and definitions.

UL 1449:1985 Standard for Safety for Transient Voltage Surge Suppressors

ITU-T K.12 (2000) Characteristics of gas discharge tubes for the protection of telecommunications installations.

3 Thut ng v nh ngha 3.1 H thng chng st: Ton b h thng dy dn c s dng bo v mt cng trnh khi tc ng ca st nh.

3.2 B phn thu st: Mt b phn ca h thng chng st nhm mc ch thu ht st nh vo n.

3.3 Mng ni t: Mt b phn ca h thng chng st nhm mc ch tiu tn dng in st xung t.


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3.4 Dy xung: Dy dn ni b phn thu st v mng ni t.

3.5 Cc ni t: B phn hoc nhm cc b phn dn in c tip xc vi t v c th truyn dng in st xung t.

3.6 Cc ni t mch vng: Cc ni t to ra mt vng khp kn xung quanh cng trnh di hoc trn b mt t, hoc pha di hoc ngay trong mng ca cng trnh.

3.7 Cc ni t tham chiu: Cc ni t c th tch hon ton khi mng ni t dng vo mc ch o c kim tra.

3.8 in cm t cm: c trng ca dy dn hoc mch to ra trng in t ngc khi c dng in thay i truyn qua chng.

in cm t cm ca mt dy dn hoc mch to ra th in ng c tnh t cng thc:

dtdiLV =

Trong :

V l trng in t ngc tnh bng vn (V);

L l in cm t cm tnh bng Henri (H);

dtdi

l tc thay i dng tnh bng Ampe trn giy (A/s).

3.9 in cm tng h: c trng ca mch mt in p c to ra trong mt vng kn bi mt dng in thay i trong mt dy dn c lp.

in cm tng h ca mt vng kn to ra mt in p t cm c tnh nh sau:

dtdiMV =

Trong :

V l in p t cm trong vng kn tnh bng vn (V);

M l in cm tng h tnh bng Henri (H);

dtdi

l tc thay i dng trong mt dy dn c lp tnh bng Ampe trn giy (A/s).

3.10 in cm truyn dn: c trng ca mch mt in p c to ra trong mt vng kn bi mt dng in thay i trong mt mch khc m mt phn ca n nm trong vng kn.

in cm truyn dn ca mt vng kn to ra mt in p t cm c tnh nh sau:

dtdiMV T=

Trong :

V l in p t cm trong vng kn tnh bng vn (V);

MT l in cm truyn dn tnh bng Henri (H);

dtdi l tc thay i dng trong mt mch khc tnh bng Ampe trn giy (A/s).


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3.11 Vng bo v: Th tch m trong mt dy dn st to ra kh nng chng st nh thng bng cch thu ht st nh vo n.

4 Quy nh chung 4.1 Cc hng dn trong tiu chun ny mang tnh tng qut, khi p dng vo mt h thng chng st c th cn xem xt ti cc iu kin thc t lin quan n h thng . Trong nhng trng hp c bit kh khn th cn tham kho kin ca cc chuyn gia.

4.2 Trc khi tin hnh thit k chi tit mt h thng chng st, cn phi quyt nh xem cng trnh c cn chng st hay khng, nu cn th phi xem xt iu g c bit c lin quan n cng trnh (xem mc 7 v 8).

4.3 Cn kim tra cng trnh hoc nu cng trnh cha xy dng th kim tra h s bn v v thuyt minh k thut theo cc yu cu v phng chng st c quy nh tiu chun ny.

4.4 i vi nhng cng trnh khng c cc chi tit bng kim loi ph hp th cn phi c bit quan tm ti vic b tr tt c cc b phn ca h thng chng st sao cho va p ng yu cu chng st va khng lm nh hng n thm m ca cng trnh.

4.5 i vi cc cng trnh xy dng c a phn kt cu bng kim loi th nn s dng cc b phn bng kim loi trong h thng chng st lm tng s lng cc b phn dn st. Nh th va tit kim kinh ph cho h thng chng st li khng lm nh hng n thm m ca cng trnh. Tuy nhin cn lu rng khi st nh vo phn kim loi nh vy, c bit phn kim loi c bao ph, c th ph hu cc lp bn ngoi phn kim loi; i vi khi xy c ct thp c th gy khi xy. C th gim thiu, m khng loi tr c hon ton, ri ro trn bng gii php s dng h thng chng st c c nh trn b mt cng trnh.

4.6 Nhng kt cu kim loi thng c s dng nh mt b phn trong h thng chng st gm c khung thp, ct thp trong b tng, cc chi tit kim loi ca mi, ray v sinh ca s trong nh cao tng.

4.7 Ton b cng trnh phi c bo v bng mt h thng chng st kt ni hon chnh vi nhau, khng c b phn no ca cng trnh c tch ra bo v ring.

5 Chc nng ca h thng chng st Chc nng ca h thng thu v dn st l thu ht st nh vo n ri chuyn dng in do st to ra xung t mt cch an ton, trnh st nh vo cc phn kt cu khc cn c bo v ca cng trnh. Phm vi thu st ca mt h thng thu v dn st khng c nh nhng c th coi l mt hm ca mc tiu tn dng in st. Bi vy phm vi thu st l mt i lng thng k.

Mt khc, phm vi thu st t b nh hng bi cch cu to h thng thu v dn st, cho nn s sp t theo chiu ngang v chiu thng ng l tng ng nhau. Do khng nht thit phi s dng cc u thu nhn hoc chp nhn, ngoi tr vic l cn thit v mt thc tin.

6 Vt liu v kch thc 6.1 Vt liu

Tt c vt liu ch to cc b phn khc nhau ca mt h thng chng st cn tun theo tiu chun TCVN 47561.

1 p dng phin bn hin hnh i vi cc tiu chun trch dn khng km nm ban hnh.


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Khi la chn vt liu, cn xem xt nguy c b n mn bao gm n mn in ho. i vi vic bo v dy dn, cn ch lp bo v chng li s n mn trong mi trng khc nghit, v d:

a) Ph dy dn bng ch dy t nht 2mm trn nh ng khi. Bc ch c hai u v ti cc im ni

b) Nu c th th b phn thu st nn trn, nu khng c th dng lp PVC mng 1mm bc trong trng hp cn chng g (c bit i vi nhm).

Cc mi ni trong c th c din tch mt ct bng khong mt na mi ni ngoi (xem 12.10.2). Cc mi ni mm do c th c s dng nhng cn tun theo tiu chun TCXD 25:1991.

6.2 Kch thc

Kch thc ca cc b phn hp thnh trong mt h thng chng st cn m bo cc yu cu nu trong Bng 1 v Bng 2. dy ca cc tm kim loi s dng trn mi nh v to thnh mt phn ca h thng chng st cn m bo yu cu trong Bng 3.

Bng 1. Vt liu, cu to v din tch tit din ti thiu ca kim thu st, dy dn st, dy xung v thanh chn di t

Vt liu Cu to Din tch tit din ti thiua Ghi ch

ng

Dy dt c 50 mm chiu dy ti thiu 2 mm

Dy trn ce 50 mm ng knh 8 mm

Cp 50 mm ng knh ti thiu ca mi si 1,7 mm

Dy trn cf,g 200 mm ng knh 16 mm

ng ph thicb


Dy trn ce 50 mm ng knh 8 mm



Nhm


Dy trn c 50 mm ng knh 8 mm


Hp kim nhm

Dy dt c 50 mm chiu dy ti thiu 2,5 mm



Dy trn cf 200 mm ng knh 16 mm

Thp m kmc

Dy dt c 50 mm chiu dy ti thiu 2,5 mm




Thp khng gd Dy dt c h 50 mm chiu dy ti thiu 2 mm


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Vt liu Cu to Din tch tit din ti thiua Ghi ch

Dy trn ch 50 mm ng knh 8 mm


Dy trn cf,g 200 mm ng knh 16 mm a Sai s cho php: - 3 %. b Nhng nng hoc ph in, chiu dy lp ph ti thiu l 1 micron. c Lp ph phi nhn, lin tc v khng c vt sn vi chiu dy danh nh l 50 microns. d Chromium 16 %; Nickel 8 %; Carbon 0,07 %. e 50 mm (ng knh 8 mm) c th gim xung 28 mm (ng knh 6 mm) trong mt s trng hp khng yu cu sc bn c hc cao. Trong trng hp cn lu gim khong cch gia cc im c nh. f Ch p dng cho kim thu st. Trng hp ng sut pht sinh do ti trng nh gi gy ra khng ln th c th s dng kim thu st di ti a ti 1m ng knh 10mm g Ch p dng cho thanh cm xung t. h Nu phi quan tm c bit ti vn c v nhit th cc gi tr trn cn tng ln 78 mm (ng knh 10 mm) i vi dy trn c v 75 mm (dy ti thiu 3 mm) i vi thanh dt c.

Bng 2. Vt liu, cu to v kch thc ti thiu ca cc ni t

Vt liu Cu to Kch thc ti thiua

Ghi ch Cc ni t Dy ni t Tm ni t

ng

Cpb 50 mm2 ng knh ti thiu ca mi si 1,7 mm

Dy trn cb 50 mm2 ng knh 8 mm

Dy dt c b 50 mm2 chiu dy ti thiu 2 mm

Dy trn c ng knh 15 mm

ng ng knh 20 mm chiu dy thnh ng ti thiu 2 mm

Tm c 500 mm x 500 mm chiu dy ti thiu 2 mm

Tm mt co 600 mm x 600 mm tit din 25 mm x 2 mm

Thp

Dy trn c m kmc

ng knh 16 mmd

ng knh 10 mm

ng m kmc ng knh 25 mmd chiu dy thnh ng ti thiu 2 mm

Dy dt c m kmc 90 mm

2 chiu dy ti thiu 3 mm

Tm c m kmc

500 mm x 500 mm chiu dy ti thiu 3 mm

Tm mt co m kmc

600 mm x 600 mm tit din 30 mm x 3 mm


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Vt liu Cu to Kch thc ti thiua

Ghi ch Cc ni t Dy ni t Tm ni t

Dy trn c m ngce

ng knh 14 mm

m ng 99,9 % ng, dy ti thiu 250 microns

Dy trn c khng mf

ng knh 10 mm

Dy dt c trn hoc m kmf,g

75 mm2 chiu dy ti thiu 3 mm

Cp m kmf,g 70 mm

2 ng knh ti thiu ca mi si 1,7 mm

Thp ng m kmc

50 mm x50 mm x 3 mm

Thp khng g

Dy trn c ng knh 16 mm ng knh 10 mm

Dy dt c 100 mm chiu dy ti thiu 2 mm a Sai s cho php: - 3 %. b C th ph bng thic. c Lp ph phi nhn, lin tc v khng c vt sn vi chiu dy danh nh l 50 microns i vi vt liu trn v 70 microns i vi vt liu dt. d Chn ng cn c tin trc khi m km. e ng cn c lin kt vi li thp. f Ch cho php khi hon ton chn trong b tng. g Ch cho php khi c lin kt tt ti cc im cch nhau khng qu 5m vi ct thp nhng b phn mng c tip xc vi t

Bng 3. dy ti thiu ca tm kim loi s dng lp mi nh v to thnh mt phn ca h thng chng st.

Vt liu dy ti thiu (mm)

Thp m 0,5

Thp khng g 0,4

ng 0,3

Nhm v Km 0,7

Ch 2,0

GHI CH: Cc s liu trong bng ny l hp l khi mi nh l mt phn ca h thng chng st. Tuy nhin vn c nguy c tm kim loi b nh thng i vi cc c st nh thng.


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7 S cn thit ca vic phng chng st 7.1 Nguyn tc chung

Cc cng trnh c nguy c chy n cao nh nh my sn xut thuc n, kho cha nhin liu cn s bo v cao nht khi cc nguy c b st nh. Chi tit cho vic bo v cc cng trnh ny c cho trong mc 18.

i vi cc cng trnh khc, tiu chun v phng chng st c cp n trong tiu chun ny l p ng v cu hi duy nht c t ra l c cn chng st hay khng.

Trong nhiu trng hp, s cn thit phi chng st l rt r rng, v d:

a) Ni t hp ng ngi;

b) Ni cn phi bo v cc dch v cng cng thit yu;

c) Ni m quanh khu vc thng xuyn xy ra st nh;

d) Ni c cc kt cu rt cao hoc ng n c mt mnh;

e) Ni c cc cng trnh c gi tr vn ho hoc lch s;

f) Ni c cha cc loi vt liu d chy hoc n.

Tuy nhin, trong rt nhiu trng hp khc th khng d quyt nh. Trong cc trng hp cn tham kho 7.2; 7.3; 7.4; 7.5; v 7.6 v nhiu yu t nh hng n xc sut st nh v cc phn tch v hu qu ca n.

Tuy nhin mt s yu t khng th nh gi c v chng c th bao trm ln tt c cc yu t khc. V d nh, yu cu khng xy ra cc nguy c c th trnh c i vi cuc sng ca con ngi hoc l vic tt c mi ngi sng trong to nh lun cm thy an ton c th quyt nh cu hi theo hng cn c h thng chng st, mc d thng thng th iu ny l khng cn thit.

Khng c bt c hng dn c th no cho nhng vn nh vy nhng c th tin hnh nh gi cn c vo xc sut st nh vo cng trnh v nhng yu t sau:

1) Cng nng ca to nh.

2) Tnh cht ca vic xy dng to nh .

3) Gi tr ca vt th trong to nh hoc nhng hu qu do st nh gy ra.

4) V tr to nh.

5) Chiu cao cng trnh.

7.2 Xc nh xc sut st nh vo cng trnh

Xc sut ca mt cng trnh hoc mt kt cu b st nh trong bt k mt nm no l tch ca mt st phng xung t v din tch thu st hu dng ca kt cu. Mt st phng xung t, Ng, l s ln st phng xung mt t trn 1km2 trong mt nm. Gi tr Ng thay i rt ln. c tnh gi tr Ng trung bnh nm c tnh ton bng quan st trong rt nhiu nm cho cc vng trn th gii c cho trong Bng 4 v Hnh 1. Bn mt st nh trung bnh trong nm Vit Nam c cho Hnh 2. S liu v mt st nh trung bnh trong nm ti cc trm kh tng Vit Nam c cho ph lc E ca tiu chun ny.

Cc mc ng mc c s dng trn bn Hnh 2 dao ng t 1,4 n 13,7. Khi p dng gi tr mt st phng xung t cho mt v tr khng nm trn ng ng mc tnh ton nn ly gi tr ln hn gia cc gi tr ng ng mc ln cn n. V d v tr nm gia hai ng ng mc c gi tr l 5,7 v 8,2 th ly gi tr mt st phng xung t l 8,2 ln/km2/nm; v tr nm gia hai ng


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ng mc c gi tr l 8,2 v 10,9 th ly gi tr mt st phng xung t l 10,9 ln/km2/nm; v tr nm vng c gi tr > 13,7 th ly gi tr mt st phng xung t l 16,7 ln/km2/nm. C th tham kho ph lc E v mt st phng xung t cho cc a danh c lp trn c s bn mt st (Hnh 2) v khuyn co mc ny.

Din tch thu st hu dng ca mt kt cu l din tch mt bng ca cc cng trnh ko di trn tt c cc hng c tnh n chiu cao ca n. Cnh ca din tch thu st hu dng c m rng ra t cnh ca kt cu mt khong bng chiu cao ca kt cu ti im tnh chiu cao. Bi vy, i vi mt to nh hnh ch nht n gin c chiu di L, chiu rng W, chiu cao H (n v tnh l m), th din tch thu st hu dng c di (L+2H) m v chiu rng (W+2H) m vi 4 gc trn to bi ng trn c bn knh l H. Nh vy din tch thu st hu dng Ac (m2) s l (xem Hnh 3 v v d Ph lc D):

Ac = LW+2LH+2WP+ H2 (1) Xc sut st nh vo cng trnh trong mt nm, p c tnh nh sau:

p = Ac x Ng x 10-6 (2)

Bng 4. Mi quan h gia s ngy c st nh trong 1 nm v s ln st nh trn 1 km2/nm

S ngy c st nh

trong nm

S ln st nh trn km2 trong nm

Trung bnh Khong gii hn

5 0,2 0,1 n 0,5

10 0,5 0,15 n 1,0

20 1,1 0,3 n 3,0

30 1,9 0,6 n 5,0

40 2,8 0,8 n 8,0

50 3,7 1,2 n 10,0

60 4,7 1,8 n 12,0

80 6,9 3,0 n 17,0

100 9,2 4,0 n 20,0

7.3 Xc sut st nh cho php

Xc sut st nh cho php c ly bng 10-5 trong mt nm.

7.4 Xc sut st nh tng hp

Sau khi thit lp c gi tr ca p, l s v st c kh nng nh vo cng trnh trong mt nm, tnh xc sut st nh tng hp bng cch nhn p vi cc h s iu chnh c cho cc bng t Bng 5 n Bng 9. Nu xc sut st nh tng hp ny ln hn xc sut st nh cho php p0 = 10-5 trong mt nm th cn phi b tr h thng chng st.


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Hnh 1. Bn s ngy c st nh trong nm trn ton th gii


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Hnh 2. Hnh 2


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7.5 Cc h s iu chnh:

Bng 5 n Bng 9 lit k cc h s iu chnh t A n E biu th mc quan trng hoc mc ri ro tng i trong mi trng hp.

Bng 5. Bng tra gi tr h s A (theo dng cng trnh)

Dng cng trnh Gi tr h s A

Nh v cng trnh vi kch thc thng thng 0,3

Nh v cng trnh vi kch thc thng thng v c b phn nh cao hn xung quanh

0,7

Nh my, xng sn xut, phng th nghim 1,0

Cng s, khch sn, nh chung c 1,2

Ni tp trung ng ngi nh hi trng, nh ht, bo tng, siu th ln, bu in, nh ga, bn xe, sn bay, sn vn ng.

1,3

Trng hc, bnh vin, nh tr mu gio 1,7

Bng 6. Bng tra gi tr h s B (theo dng kt cu cng trnh)

Dng kt cu cng trnh Gi tr h s B

Khung thp hoc b tng ct thp c mi kim loi 0,1

Khung thp c mi khng phi bng kim loi (*) 0,2

B tng ct thp c mi khng phi bng kim loi 0,4

Th xy c mi khng phi bng kim loi hoc tranh tre na l 1,0

Khung g c mi khng phi bng kim loi hoc tranh tre na l 1,4

Th xy, khung g c mi bng kim loi 1,7

Cc cng trnh c mi bng tranh tre na l 2,0

CH THCH: *) Cc kt cu c b phn kim loi trn nc mi v c tnh dn in lin tc xung t th khng cn theo bng ny

Bng 7. Bng tra gi tr h s C (theo cng nng s dng)

Dng cng nng s dng Gi tr h s C

Nh , cng s, nh my, xng sn xut khng cha cc vt qu him hoc c bit d b hu hoi (*)

0,3

Khu cng nghip, nng nghip c cha cc th c bit d b hu hoi (*)

0,8

Trm in, trm kh t, in thoi, i pht thanh 1,0


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Khu cng nghip then cht, cng trnh di tch lch s, bo tng, to nh trng by tc phm ngh thut hoc cng trnh c cha cc th c bit d b hu hoi (*)

1,3

Trng hc, bnh vin, nh tr mu gio, ni tp trung ng ngi 1,7

CH THCH: *) D b hu hoi do chy hoc hu qu ca ho hon

Bng 8. Bng tra gi tr h s D (theo mc cch ly)

Mc cch ly Gi tr h s D

Cng trnh xy dng trong khu vc c nhiu cng trnh khc hoc c nhiu cy xanh vi chiu cao tng ng hoc ln hn

0,4

Cng trnh xy dng trong khu vc c t cng trnh khc hoc cy xanh c chiu cao tng ng

1,0

Cng trnh xy dng hon ton cch ly hoc cch xa t nht hai ln chiu cao ca cc cng trnh hay cy xanh hin hu trong khu vc

2,0

Bng 9. Bng tra gi tr h s E (theo dng a hnh)

Dng a hnh xy dng Gi tr h s E

Vng ng bng, trung du 0,3

Vng i 1,0

Vng ni cao t 300 mt n 900 mt 1,3

Vng ni cao trn 900 mt 1,7

Bng 7 lit k cc h s iu chnh k n thit hi v gi tr ca cc i tng bn trong cng trnh hoc hu qu dy chuyn. Thit hi v gi tr cc i tng bn trong cng trnh l kh r rng; cn thut ng hu qu dy chuyn c ng khng nhng k n thit hi vt cht i vi hng ho v ca ci m c nhng kha cnh v s ngt qung ca cc dch v thit yu, c bit l trong cc bnh vin.

Ri ro i vi cuc sng thng thng l rt nh nhng nu mt to nh b st nh trng, ho hon hay s hong lon c th xy ra mt cch t pht. Bi vy nn thc hin tt c cc bin php c th c gim thiu cc tc ng ny, c bit cc tc ng i vi ngi gi, tr em v ngi m yu.

i vi cc to nh s dng vo nhiu mc ch khc nhau, nn p dng h s A cho trng hp nghim trng nht.

7.6 Din gii xc sut st nh tng hp

Phng php xc sut trong tiu chun ny nhm mc ch hng dn cho cc trng hp kh quyt nh. Nu kt qu tnh c nh hn 10-5 (1 trong 100.000) kh nhiu th nhiu kh nng khng cn n h thng chng st; nu nh kt qu ln hn 10-5, v d nh 10-4 (1 trong 10.000) th cn c cc l do xc ng lm c s cho vic quyt nh khng lm h thng chng st.


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Khi c cho l cc hu qu dy chuyn s l nh v nh hng ca mt c st nh s ch gy h hi rt nh i vi kt cu ca cng trnh, c th s l tit kim nu khng u t lm h thng chng st v chp nhn ri ro . Tuy nhin ngay c vic quyt nh nh vy cng cn phi tnh ton bit c mc ri ro .

Cc kt cu cng rt a dng v d c s dng phng php nh gi no i na cng c th cho cc kt qu khng bnh thng v nhng ngi s phi quyt nh liu s bo v l cn thit hay khng c th s phi s dng kinh nghim v s phn on ca mnh. Ly v d nh, mt ngi nh kt cu khung thp c th c nhn nh l c xc sut st nh thp, tuy nhin vic thm h thng chng st v ni t s nng cao kh nng chng st rt nhiu nn chi ph lp t thm h thng ny c th c xem l hp l.

i vi cc ng khi bng gch hoc b tng, kt qu tnh xc sut st nh tng hp c th thp. Tuy nhin nu chng ng mt mnh hoc vn cao hn cc kt cu xung quanh hn 4,5m th cn phi chng st cho d xc sut st nh c gi tr no i na. Nhng ng khi nh vy s khng p dng c phng php xc sut st nh tng hp. Tng t nh vy, cc kt cu cha cht n hay d chy cn c xem xt thm cc yu t khc na (xem mc 18 v 8.3 ).

V d v vic tnh ton xc xut st nh tng hp quyt nh c cn b tr h thng chng st hay khng c cho ph lc D.

8 Vng bo v 8.1 Khi nim

Khi nim vng bo v c hiu mt cch n gin l th tch m trong gii hn cc b phn chng st to ra mt s bo v chng li cc c phng in trc tip bng vic thu cc tia st vo cc b phn chng st .

Kch thc v hnh dng ca vng bo v thay i theo chiu cao ca ngi nh hoc chiu cao ca cc thit b thu st thng ng. Ni chung i vi cc cng trnh khng cao qu 20m, vng bo v ca cc b phn thu dn st thng ng t di mt t ln c xc nh l th tch to bi mt hnh nn vi nh ca n nm nh b phn thu st v y nm di mt t. Vng bo v ca cc b phn thu st ngang c xc nh bi khng gian to bi hnh nn c nh nm trn dy thu st ngang chy t im u n im cui. i vi nhng kt cu cao hn 20m, vic xc nh vng bo v nh trn c th khng p dng c, v cn phi c thm cc thit b chng st lp t theo cch thc nh trong Hnh 4 (xem thm mc 16) chng li cc c st nh vo pha bn cnh cng trnh.

8.2 Gc bo v

i vi cc kt cu khng vt qu 20m v chiu cao, gc gia cnh ca hnh nn vi phng thng ng ti nh ca hnh nn gi l gc bo v (Hnh 5). ln ca gc bo v khng th xc nh c mt cch chnh xc v n ph thuc vo ln ca c st nh v s hin din trong vng bo v cc vt th c kh nng dn in v chng c th to nn cc ng ni t c lp vi h thng chng st. Tt c nhng g c th khng nh l kh nng bo v ca h thng chng st s tng ln khi gc bo v gim i. i vi cc kt cu cao hn 20m, gc bo v ca bt k mt b phn dn st no cao ti 20m cng s tng t nh i vi cc b phn thu dn st ca cc kt cu thp hn 20m. Tuy nhin cng trnh cao hn 20m c kh nng b st nh vo pha bn cnh, bi vy cn xc nh th tch c bo v theo phng php hnh cu ln (xem B.5).

i vi cc mc ch thc hnh nhm cung cp mt mc chng st chp nhn c cho mt kt cu thng thng cao ti 20m hoc cho phn kt cu di 20m i vi kt cu cao hn, gc bo v ca bt c mt b phn ring no ca li thu st, thu st ng hay nm ngang, c quy nh l 45o

(xem Hnh 5.a v Hnh 5.b). Gia 2 hay nhiu hn b phn thu st thng ng t cch nhau khng


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qu 2 ln chiu cao ca chng th gc bo v tng ng c th t ti 60o so vi phng thng ng (xem Hnh 5.c). i vi mi bng, din tch gia cc dy dn song song c coi l c chng st nu b phn thu st c b tr theo 11.1 v 11.2. i vi cc kt cu c yu cu chng st cao hn th khuyn co p dng cc gc bo v khc (xem mc 18).

8.3 Cc cng trnh rt d b nguy him do st nh

i vi cc cng trnh rt d b nguy him do st nh, v d c cha cht chy n, th cn p dng tt c cc gii php chng st c th c, mc d ch l phng chng cc v st nh rt him khi xy ra trong vng bo v c nh ngha nh 8.1 v 8.2. Xem chi tit mc 18 v vic gim din tch bo v v cc bin php c bit khc cho cc cng trnh ny.


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Hnh 3. Mt s dng cng trnh v din tch thu st

Mu B tr chung Din tch thu st v phng php tnh

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

Tt c cc kch thc u tnh theo n v l mt

A c =14 x 50 + 2(15 x 50)

+ 2(15 x 14) + x 15 A c = 3 327 m

A c =15 x 40 + 2(21 x 40)

+ 2(21x 15) + x 21 A c = 4 296 m

A c = x 14 + 2(14 x 30) A c = 1 456 m

A c =7 x 8 + 2(6 x 7) + x 9 + 10 (xp x) cho vng t enA c = 405 m

A c = x 40 A c = 5 027 m

A c = 12 x 55 + 2(18 x 55) +2(18 x 12) + x 18 A c = 4 090 m

A c =25 x 60 + 25 x 30 +6 x 60 + 6 x 50 + 6 x 25 + 6 x 25 + 6 x 30 + 6 x 24 +5/4 x x 6 A c = 3 675 m

A c =20 x 30 + 2(4 x 30)

+ 2(4 x 20) + x 4 + 20 (xp x) cho vng ten A c = 1 070 m


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Hnh 4. H thng chng st cho ng khi xy gch

M gang c

Ni t

(a) ng khi ng knh nh nhhn 1,5m v cao di 20m

GHI CH: Hnh ny khng p dng cho ng khi BTCT s dng ct thp lm dy xung

(b) ng khi bng gch cao 60m

K hiu: 1. Kim thu

2. Thanh kp

3. ng ni 4. Dy xung 5. Dy dn ngang

6. im o 7. Cc ni t 8. Kp ni ch A

9. ng bc cc nit

10. Kp dy dn GHI CH: Khongcch im c nhxem bng A.1

11.Vng ai 12. Chp gang thay vngai 11 13. Kp ti nt giao nhau


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Hnh 5. Xc nh gc v phm vi bo v hiu qu ca kim thu st

a) Dy dn ng b) Dy dn ngang

Mt bng vng bo v ti ct nn Mt bng vng bo v ti ct nn

c) Bn dy dn ng vi cc gc bo v v vng bo v kt hp

K hiu:

VC: Dy dn ng

HC: Dy dn ngang

ZP: Vng bo v

GL: Ct nn Mt bng vng bo v ti ct nn


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9 Cc lu khi thit k h thng chng st 9.1 Quy nh chung

Trc v trong c qu trnh thit k, n v thit k cn trao i, tho lun v thng nht v phng n vi cc b phn lin quan, c th theo 9.2; 9.3; 9.4 v 9.5.

9.2 Kin trc

Nhng s liu sau y cn c xc nh mt cch c th:

a) Cc tuyn i ca ton b dy dn st;

b) Khu vc i dy v cc cc ni t;

c) Chng loi vt t dn st;

d) Bin php c nh cc chi tit ca h thng chng st vo cng trnh, c bit nu n nh hng ti vn chng thm cho cng trnh;

e) Chng loi vt liu chnh ca cng trnh, c bit l phn kt cu kim loi lin tc nh cc ct, ct thp;

f) a cht cng trnh ni xy dng v gii php x l nn mng cng trnh;

g) Cc chi tit ca ton b cc ng ng kim loi, h thng thot nc ma, h thng cu thang trong v ngoi cng trnh c th cn hn u ni vi h thng chng st;

h) Cc h thng ngm khc c th lm mt n nh cho h thng ni t;

i) Cc chi tit ca ton b h thng trang thit b k thut lp t trong cng trnh c th cn hn u ni vi h thng chng st.

9.3 H thng k thut cng cng

Tho thun vi cc c quan qun l h thng k thut ngoi nh v vic u ni gia cc h thng k thut ngoi nh (cp in, cp nc, thot nc, thng tin, tn hiu) vi h thng chng st ca cng trnh.

9.4 Lp t h thng pht thanh, truyn hnh

Cc cng trnh pht sng ca i pht thanh, truyn hnh phi c tho thun v vic u ni gia phn thp thu pht sng vi h thng chng st.

9.5 Cc nh thu xy dng

Cn tho thun, thng nht c nhng vn lin quan sau y:

a) Chng loi, v tr, s lng thit b chnh do nh thu xy dng cung cp;

b) Nhng ph kin no ca phn h thng chng st do nh thu xy dng lp t;

c) V tr ca b phn dy dn st nm ngm di cng trnh;

d) Nhng b phn no ca h thng chng st s phi c s dng ngay t trong qu trnh thi cng xy dng cng trnh. Chng hn nh h thng ni t ca cng trnh c th c s dng ni t cho cn cu thp, vn thng, cc ng ray, dn gio v cc b phn tng t trong qu trnh xy dng;

e) i vi cc kt cu khung thp, s lng v v tr ca cc ct thp v bin php x l mi ni vi h thng ni t;

f) i vi cc cng trnh c s dng mi che bng kim loi nh mt b phn ca h thng chng st th phi thng nht gii php u ni vi h thng dn st v ni t;


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g) V tr v c im ca cc cng trnh k thut ni vi cng trnh trn hoc di mt t nh h thng ng st, ng ray cn cu, h thng cp treo, h thng mng dy cp in, ct thu pht sng pht thanh truyn hnh, ng khi, ng ng kim loi, v.v

h) V tr, s lng cc ct c, cc phng k thut trn mi (nh: phng my ca cu thang my, thng gi, iu ho..), b nc trn mi, v cc phn nh cao khc;

i) Gii php xy dng cho tng v mi, nhm mc ch xc nh phng php ph hp c nh dy dn st, c bit lu n vn bo v cng trnh khi tc ng ca kh hu;

j) Vic a dy dn st xuyn qua cc lp chng thm. B tr cc l lun dy xung qua kt cu, tng mi, g trn,.v.v;

k) Cc bin php lin kt vi ct thp, kt cu thp hoc cc chi tit kim loi;

l) Cc bin php bo v h thng khi b h hng do tc ng c, l, ho;

m) Cc iu kin c th o c, kim tra h thng;

n) Vic cp nht h s bn v v h thng chng st cho cng trnh.

10 Cc b phn c bn ca h thng chng st Cc b phn c bn ca h thng chng st bao gm:

a) B phn thu st

b) B phn dy xung

c) Cc loi mi ni

d) im kim tra o c

e) B phn dy dn ni t

f) B phn cc ni t

Cc chi tit c nh v chi tit im o kim tra in hnh ca h thng dy dn c th hin trn Hnh 6, Hnh 7 v Hnh 8.

11 B phn thu st 11.1 Cc nguyn tc c bn

B phn thu st c th l cc kim thu st hoc li thu st hoc kt hp c hai (xem minh ho ti cc hnh t Hnh 9 n Hnh 14).

Khong cch t bt k b phn no ca mi n b phn thu st nm ngang khng nn ln hn 5 mt (xem thm Ghi ch 1 v Ghi ch 2 trong Hnh 10). i vi nhng dng mi bng c din tch ln thng s dng li thu st khu 10 mt x 20 mt. i vi nhng mi c nhiu nc, nu khong cch S gia hai nc ln hn 10 + 2H, trong H l cao ca nc (tt c c tnh bng n v mt) th phi b sung thm cc dy thu st (xem Hnh 11).

i vi nhng cng trnh b tng ct thp, b phn thu st c th c u ni vo h ct thp ca cng trnh ti nhng v tr thch ng vi s lng dy xung cn thit theo tnh ton.

Tt c cc b phn bng kim loi nm ngay trn mi hoc cao hn b mt ca mi u c ni t nh mt phn ca b phn thu st (xem minh ho ti Hnh 4, Hnh 6 v tham kho Hnh 15).

Lp ph nh tng, nh mi v lan can bng kim loi (xem mc 9), li bng kim loi sn thng nn c tn dng lm mt phn ca b phn thu st (xem Hnh 4, Hnh 6 v Hnh 16).


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11.2 Cc dng cu to b phn thu st

11.2.1 Nguyn tc chung

Cc dng cu to b phn thu st thng dng nht c minh ho ti cc hnh t Hnh 9 n Hnh 14. Phm vi ng dng ca tng dng thu st c ch dn ti 11.2.2; 11.2.3; 11.2.4; 11.2.5 v 11.2.6. Vic s dng b phn thu st dng no l tu thuc vo kin trc v kt cu cng nh v tr xy dng ca tng cng trnh.

11.2.2 Kim thu st n

Hnh 5 (a) minh ho kim thu st n v phm vi bo v. Hnh 5(c) minh ho dng thu st kt hp 4 kim thu st gia tng phm vi bo v nh th hin ti hnh v mt bng bo v.

11.2.3 Dy thu st, li thu st cho nh mi bng

Hnh 5 (b) minh ho b tr dy thu st vin theo chu vi mi ca cng trnh dng khi ch nht v mt bng, mt ct phm vi bo v. Hnh 9 minh ho cch b tr b phn chng st in hnh i vi cc cng trnh mi bng din tch ln (xem 11.1). Thng thng s dng li thu st cho cc cng trnh dng ny nhm gim tc ng ca hiu ng lan truyn st.

11.2.4 Cng trnh c mt bng rng v hnh khi phc tp

i vi cc cng trnh bao gm nhiu khi trong c c phn cao tng v thp tng, nh minh ho ti Hnh 13, h thng chng st s bao gm y cc b phn: thu st, dy xung v tip a. Khi thit k h thng chng st cho phn thp tng cn b qua s hin din ca phn cao tng. Li tip a v cc mi u ni c s dng theo dng thng dng (xem Hnh 6, 12.9, 12.10, mc 13, v cc ph lc B.1; B.2; v B.5).

Hnh 10 minh ho cng trnh gm nhiu khi c mi bng vi cc cao khc nhau. Bo v cc khi bng h thng li thu st vin xung quanh chu vi mi v xung quanh phn mi bn trong ti v tr c cc khi nh cao ln (xem Ghi ch 1 ti Hnh 10). Tt c cc b phn ca h thng chng st phi c u ni vi nhau theo quy nh 4.7 (xem Hnh 14 v Hnh 30)

GHI CH: Trn Hnh 14 b phn dy thu st xung quanh chn phn cao tng c s dng u ni li thu st vi dy xung ca phn cao tng. Trn thc t th khu vc ny nm trong phm vi bo v, ni cch khc l bnh thng th khng cn b tr dy thu st.

Hnh 11 minh ho cc dng mi c din tch ln. Dy thu st c b tr trn mi c u ni vi nhau c hai u mp mi. Nu mi rng hn 20 mt th cn b sung thm dy thu st ngang bo m khong cch gia hai dy thu st khng ln hn 20 mt.

i vi cc cng trnh c cao trn 20 mt th cn phi p dng phng php hnh cu ln - (xem Ph lc B v Hnh B.1) xc nh v tr lp t b phn thu st (tr trng hp cng trnh c kt cu khung thp).

11.2.5 i vi cc cng trnh mi ngi

i vi cc cng trnh c mi khng dn in, dy dn st c th b tr di hoc tt nht l b tr trn mi ngi. Mc d vic lp t dy dn st di mi ngi c li l n gin v gim c nguy c n mn, nhng tt hn l lp t dc theo b nc ca mi ngi. Trng hp ny c u im l gim thiu nhiu hn nguy hi i vi mi ngi do dy thu st trc tip v cng tc kim tra cng d dng, thun tin hn.


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K hiu: 1. lan can 2. Lin kt vi ct thp 3. Lin kt vi nh tng 4. Mi ni phi kim loi (b phn csn)

Mi ni cc kim loi

lan can thp

Chi tit s 4

th hin 1 thanh ct thpmang tnh minh ho

Lin kt vikt cu thp

Hnh 6. Lan can, lp ph nh tng bng kim loi v ct thp c s dng lm kim thu st v dy xung

Dy dn st b tr di mi ngi ch c s dng ch yu trong trng hp mi c dy nh hoc c t ngay di lp ph bn trn mi, v khong cch gia cc dy dn khng ln hn 10m.

Kt cu BTCT cmi v tng mikhng dn in

Mi thpm km

Lin kt vi trntreo kim loi

Kt cu BTCT,mi dn in


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i vi cng trnh dng nh th hoc dng kin trc, kt cu tng t th x l nh cng trnh c bit. Phn thp cao hon ton khng tnh n trong qu trnh thit k h thng chng st cho cc hng mc thp hn ca cng trnh.

11.2.6 i vi cc cng trnh n gin c cha cc cht d gy chy n

Hnh 17 minh ho gii php b tr h thng chng st ch yu c s dng i vi cc cng trnh n gin, c cha cc cht d gy chy n. H thng bo v chnh bao gm hai kim thu st ni vi nhau bng mt dy thu st. Phm vi bo v c th hin trn mt bng, mt ct trong hnh v, ng thi th hin nh hng ca vng ca dy thu st ngang (xem 18.2.1).

Hnh 7. im o kim tra

Ghi ch: Ph lp chng g cho tt c cc nt v lin kt


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Hnh 8. Cc kiu kim thu st in hnh


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Hnh 9. Thu st cho mi bng

a) Mt ng th hin gc bo v

b) Mt bng th hin vng bo v ti ct nn

Ln nht 10m

c) B tr tng th

K hiu:

ZP: Vng bo v

HC: Dy dn ngang

Ln nht 10m


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Hnh 10. Thu st cho mi bng c nhiu cao khc nhau

Ni dy xung v dy dn ngang tng mithp

GHI CH 1: Cn b tr li thu st dc chu vibao ngoi mi v khng c im no mi cch n qu 5m tr b phn thp cho php cch xathm 1m trn mi chiu cao chnh mi

Chu vi = 24+24+12+12 = 72m S dy xung cn thit = 72/20 = 4

GHI CH 2: Khng cn li thu st ngang tng mi quanh ging tri; vng bo v cgc 600 to ra bi 2 dy thu ngang i vi ktcu di 20m. Khng p dng cho kt cucao hn 20m

Hnh chiu B

Mt ct A-A


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Hnh 11. Thu st cho mi c din tch ln v nhiu nc

GHI CH 1: Nu S>10+2H cn b sung dy thu st dc nh khong cch gia cc dythu st khng vt qu 10m GHI CH 2: Nu chiu di mi vt qu 20m cn b sung cc dy dn ngang GHI CH 3: Cc hnh v trn khng th hin cc dy xung


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Hnh 12. Thu st v dy xung c che y cho nh mi dc vi chiu cao di 20 mt

1. Cc mi c gc dc ln t 45 tr lnch yu cu dy thu st nc

2. Cc mi c dim mi cch b nc cha n 5m

Cc kch thc tnh theo mt GHI CH: Cc v d trn minh ho cho nhiu loi mi c kch thc khc nhau. Khi thit k li thu st mi cn tun th nguyn tc: - Khng b phn no ca mi cch dy thu st qu 5m - Cn m bo khong cch ln nht l 20x10m

a) B phn thu st v dy xung

Dy xung

Li thu st

Gc dc


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b) Cc dy thu st nm di tm lp

Hnh 12.Thu st v dy xung c che y cho nh mi dc vi chiu cao di 20 mt (tip)

Hnh 13. Thu st v dy xung cho cng trnh mi bng

Hnh 14. Thu st cho cng trnh c thp cao dn in

Dy dn hocrim mi dnin

Dy dn trn vinmi, c c nhdi tm lp nhhnh bn

Kim thu st

Dy dnngang

K hiu:

GHI CH: Cc dy dn ngang cn c lin kt ti cc v tr giao nhau

GHI CH: Thu st cho kt cu BTCT hay kt cu thp cao cn m bo: a) li thu nm ngang b tr theo 10m x 20m b) lin kt vi kt cu thp ti cc gc vi khong cch 20m dc chu vi v chn phn nh cao trn mi thp 1 on 0,5m

Li 10x20m

----- Dy dn i chm

Kim thu st (kim trn khng sn bc, cao 0,3m) hoc tm kim loi


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Hnh 15. Thu st cho cng trnh c cha cc cht d gy chy n

12 Dy xung 12.1 Khi nim chung.

Chc nng ca dy xung l to ra mt nhnh c in tr thp t b phn thu st xung cc ni t sao cho dng in st c dn xung t mt cch an ton.

Tiu chun ny bao hm c vic s dng dy xung theo nhiu kiu bao gm cch s dng thp dt, thp trn, ct thp v tr kt cu thp... Bt c b phn kt cu cng trnh no dn in tt u c th lm dy xung v c kt ni mt cch thch hp vi b phn thu st v ni t. Ni chung, cng s dng nhiu dy xung cng gim c ri ro do hin tng lan truyn st v cc hin tng khng mong mun khc. Tng t, cc dy dn ln lm gim ri ro do hin tng lan truyn st, c bit nu c bc cch in. Tuy nhin, c tnh ca h thng dy xung ng trc c lp bc c s khc bit khng ng k v bt c phng din no vi cc dy dn c kch thc tng th nh nhau v c cch in nh nhau. S dng cc dy dn c lp bc khng lm gim i s lng ca cc dy xung c kin ngh tiu chun ny.

Trong thc t, ty thuc vo dng ca cng trnh, thng thng cn c cc dy xung t song song, mt s hoc ton b nhng dy xung c th l mt phn ca kt cu cng trnh . V d, mt khung thp hoc kt cu b tng ct thp c th khng cn cc dy xung v bn thn ci khung to ra mt mng li gm nhiu nhnh xung t mt cch hiu qu, ngc li mt kt cu c lm

Thu st miLn nht 5m

Thu st mi

Ln nht 10m

* th hin lin kt vo kt cuthp mi

GHI CH: Khng th hin dy xung trong hnh v ny

(in hnh)


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hon ton t cc vt liu khng dn in st s cn cc dy xung b tr theo kch thc v dng ca kt cu .

Tm li, h thng dy xung khi c th thc hin c th nn dn thng t b phn thu st n mng li ni t v t i xng xung quanh cc tng bao ca cng trnh bt u t cc gc. Trong mi trng hp, cn phi lu n hin tng lan truyn st (xem 12.5).

Hnh 16. Kp u ni b phn thu st cho mi bng trong trng hp mi kim loi c s dng lm mt b phn ca h thng chng st

12.2 B tr dy xung.

B tr dy xung cho nhiu dng cng trnh, c hoc khng c khung thp, c th hin trn Hnh 18.

Trong cc cng trnh c chiu cao ln, khung thp hoc ct thp trong b tng phi c lin kt vi nhau v tham gia vo s tiu tn dng in st cng vi cc ng thng ng v cc chi tit tng t, chng nn c lin kt phn trn cng v phn di cng. Thit k ca h thng chng st do s bao gm cc ct lin tc hoc cc tr thng ng c b tr ph hp vi 12.3. Vi cc cng trnh c khung thp hoc cc cng trnh btng ct thp khng cn thit phi b tr cc dy xung ring r.

Hnh 18a) minh ha mt cng trnh c khung thp. Theo khng cn b tr thm cc dy xung nhng cn ni t ph hp vi tiu chun ny. Hnh 18b) th hin cch b tr dy xung trong trng hp mi ua 3 cnh. Hnh 18c) th hin cch b tr trong trng hp phng khiu v hoc b bi c khu ph tr.

Hnh 18d), Hnh 18e), Hnh 18f) v Hnh 18g) th hin cc cng trnh c hnh dng m c th b tr tt c cc dy xung c nh cc bc tng bao. Cn phi thn trng khi la chn khong cch cc

Lin kt bulng2M8

Dy dn st

X g

Thp

Dm

GHI CH: Chiu dy nh nht khi s dng tm lp kim loi lm mt b phn ca h thngchng st l: - Thp m km 0,5mm - ng 0,3mm - Nhm, km 0,7mm - Ch 2,0 mm


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dy xung ph hp trnh khu vc ra vo, lu n yu cu trnh in p bc nguy him trn b mt t (tham kho thm Hnh 19).

12.3 S lng khuyn co

V tr v khong cch cc dy xung trong cng trnh ln thng ph thuc vo kin trc. Tuy nhin, nn b tr mt dy xung vi khong cch gia cc dy l 20m hoc nh hn theo chu vi cao mi hoc cao nn. Cng trnh c chiu cao trn 20m phi b tr cc dy cch nhau 10m hoc nh hn.

12.4 Nhng cng trnh cao kh thc hin vic o kim tra.

Vi cng trnh c chiu cao ln, iu kin kim tra v o c l kh, cn phi c bin php o kim tra tnh lin tc ca h thng. Cn t nht hai dy xung cho cng tc o c (xem Hnh 4).

12.5 B tr ng dn xung

Dy xung cn phi i theo li thng nht c th c gia li thu st v mng ni t. Khi s dng nhiu hn mt dy xung th cc dy xung cn c sp xp cng u cng tt xung quanh tng bao ca cng trnh, bt u t cc gc (xem Hnh 18), ty thuc vo kin trc v kh nng thi cng.

Trong vic quyt nh tuyn xung, cn phi cn nhc n vic lin kt dy xung vi cc chi tit thp trong cng trnh, v d nh cc tr, ct thp v bt c chi tit kim loi lin tc v c nh ca cng trnh c kh nng lin kt c.

Cc bc tng bao quanh sn chi v ging tri c th c s dng gn cc dy xung nhng khng c s dng vch lng thang my (xem 15.3.10). Cc sn c tng bao c 20m phi c trang b mt dy xung. Tuy nhin, nn c t nht hai dy xung v b tr i xng.

12.6 S dng ct thp trong kt cu btng

12.6.1 Nguyn tc chung

Cc chi tit c th cn c quyt nh giai on thit k, trc khi thi cng cng trnh (xem 9.5).

12.6.2 Tnh dn in lin tc

Cc thanh ct thp kim loi ca kt cu btng ct thp c ti ch i khi c hn, trng hp hin nhin l n to ra kh nng truyn in lin tc. Thng thng chng c ni buc vi nhau bi cc dy ni kim loi cc im giao nhau. Mc d vy, khng k n nhng mi lin kt tnh c t nhin ca kim loi, th mt s lng rt ln ca cc thanh v cc mi giao nhau thi cng nh vy cng l m bo tch nh cng ca dng in st ra thnh nhiu nhnh tiu tn song song. Kinh nghim ch ra rng kt cu r rng c th tn dng nh l mt b phn trong h thng chng st.

Tuy nhin, cn lu cc vn sau :

a) Phi m bo tip xc gia cc ct thp, v d bng cch c nh chng bng dy buc;

b) Cn phi ni ct thp ng vi nhau v ct thp ng vi ct thp ngang.

12.6.3 B tng ng lc trc

Cc dy dn st khng c kt ni vi cc ct, dm hay ging btng ct thp ng lc trc v thp ng lc trc khng c lin kt v do khng c tnh dn in lin tc.

12.6.4 B tng c sn

Trong trng hp cc ct, dm hay tr bng b tng ct thp c sn th ct thp c th c s dng nh l dy dn nu cc on ct thp cc cu kin ring bit c gn kt vi nhau v m bo tnh dn in lin tc.


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Hnh 17. B phn thu st v vng bo v cho cng trnh n gin c cha cht d chy n.

c) Vng c bo v GHI CH: trnh hin tng lan truyn st, khong cch ti thiu gia cngtrnh v dy dn/ ct chng l 2m hoc theo 15.2 (ly khong cch ln nht)

Vng c bo v ti v tr ct Vng c bo v ti v tr vng nht ca dy thu st

Cc ni t

Cng trnh c bo v

a) Mt ng

b) Mt bng

Cng trnh c bo v

Ti thiu 2m

Dy thu st dng treo

Ct

Ti thiu2m

Ti thiu 2m

Dy thu st dng treo

K hiu


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Hnh 18. Cc cch b tr dy xung (dy b tr thm bn ngoi hay s dng b phn dn in ca cng trnh) cho cc dng cng trnh cao

Mi ua

Phng khiu v

Ct chu lc Ct chu lc dn in s dng lm dy xung v ni t Dy xung v ni t bn ngoi

GHI CH 1: Dy xung c th l mt b phn ca kt cu hoc thanh trn, thanh dt b tr mt ngoi cngtrnh GHI CH 2:i vi kt cu cao hn 20m, dy xung t cch nhau khng qu 10 m mt chic

K hiu


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Hnh 19. Chnh lch in p mt t gn ct , thp, tr c cc ni t nhiu cc n gin

12.7 Tuyn i bn trong

Khi kh nng b tr tuyn dy xung pha bn ngoi l khng kh thi hoc l khng thch hp (xem 12.8.3), cc dy xung c th c b tr vo trong mt ng rng bng vt liu phi kim loi, khng chy v c ko thng xung t (xem Hnh 20).

Bt c rnh c che kn, mng thit b, ng hoc mng cp chy sut chiu cao cng trnh khng cha si dy cp no u c th c s dng cho mc ch ny.

Chnh in th i vitrng hp khng c ccni t vng

in th Vs thp khic cc cc tip vnggim th

Bc cch in phng ngi tipxc vi kt cu

Cc ni t vng c ngknh v su chn khcnhau kim sot chnhlch in p

t 4x1.5m n 4.5mph thuc vo v tr

Chnh in th i vitrng hp c cc ni tvng

khng c bin phpcn bng in th

Na mt bng btr cc ni t

5 vng li c lin kt vo cc ni t


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12.8 Un gc nhn v nhnh vng

12.8.1 iu kin thc t khng phi lc no cng cho php cc tuyn i theo con ng thng nht. Tuy c th chp nhn un gc nhn ti mt s v tr, v d nh ti cc g mi, nhng cn lu cc nhnh vng trong dy dn c th lm in cm cao gim xung nhanh lm cho vic tiu tn dng in st c th xy ra pha h ca nhnh vng. V c bn, ri ro c th xut hin khi chiu di ca dy dn to ra nhnh vng vt qu 8 ln chiu rng phn h ca mch (Xem Hnh 21).

12.8.2 Khi khng th trnh c nhnh vng di, v d nh trong trng hp tng lan can, tng mi, cc dy dn phi c sp t sao cho khong cch ca phn h nhnh vng p ng c nguyn tc a ra 12.8.1. Cch lm khc l to l qua cc tng lan can cc dy dn c th xuyn qua d dng.

12.8.3 Ti cc cng trnh c cc sn trn ua ra, cn xt ti nguy c lan truyn st t dy xung bn ngoi n ngi ng di phn nh ra. Cc dy xung phi theo mt tuyn bn trong, ph hp vi 12.7, nu kch thc ca phn nh ra c th gy nguy c v lan truyn st cho ngi hoc nu khong cch cc dy xung ln hn 20m.

Ri ro vi ngi l khng th chp nhn nu chiu cao h ca phn nh ra nh hn 3m. Vi phn nh ra c chiu cao ln hn hoc bng 3m th chiu rng w ca phn nh ra phi nh hoc bng (tnh theo m) gi tr tnh theo biu thc:

w 15(0,9h-2,5) (3)

nu cc dy xung i theo tuyn bn ngoi.

Cch xc nh h v w ca phn nh ra c minh ha Hnh 21d.

12.9 Lin kt trnh hin tng lan truyn st

Bt c chi tit kim loi trong hoc l mt phn ca kt cu hoc bt c thit b cng trnh c cc thnh phn kim loi c thit k hoc ngu nhin tip xc vi t nn phi c cch ly hoc lin kt vi dy xung (Xem mc 17). Tuy nhin, tr phi cc tnh ton 15.2 v cc yu cu B.2 ch ra rng cn phi lin kt th nhng th c tip xc vi h thng chng st, trc tip hoc khng trc tip, thng qua cc lin kt kim loi vi kim loi chc chn v tin cy th khng cn cc dy dn lin kt thm.

Ch dn chung tng t cng p dng cho ton b cc chi tit kim loi ln h ni hoc khng ni vi t.

GHI CH: Trong phm vi vn ny, chi tit c coi l ln khi c kch thc mt cnh bt k ln hn 2m.

C th b qua cc chi tit nh nh cc bn l ca, gi mng bng kim loi hay ct thp ca cc dm nh n c.

12.10 Lin kt

12.10.1 Quy nh chung

Hu ht cc phn ca h thng chng st c thit k sao cho c th lp va vo trong mt bng chung. Tuy nhin cc lin kt c s dng kt ni cc b phn lm t kim loi c cc hnh dng v thnh phn khc nhau do khng th c mt dng chun. Do tnh a dng trong s dng ca chng v cc nguy c n mn nn cn phi ch ti cc b phn kim loi ca chng, v d nh phn kt ni v cc b phn c kt ni.

12.10.2 Cc yu cu v c v in.

Mt lin kt phi hiu qu c v c v in v c bo v trnh n mn v xm thc trong mi trng lm vic.


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Cc chi tit kim loi bn ngoi trn kt cu hoc l mt phn ca kt cu c th phi tiu tn ton b dng in do st nh vo n v do lin kt ca cc chi tit vi h thng chng st phi c tit din khng nh hn tit din ca dy dn chnh. Ngc li, cc chi tit kim loi bn trong khng d b h hi v lin kt ca n ngoi chc nng cn bng in p th nhiu lm cng ch ti mt phn cng dng in st. Do cc lin kt bn trong c th c tit din nh hn tit din cc dy dn chnh.

12.10.3 D tr cho vic lin kt cc thit b tng lai

i vi mi cng trnh, ti mi ct sn cn phi d tr cho vic lin kt my mc thit b trong tng lai vi h thng chng st, v d nh lin kt vi thit b kim loi cp gas, nc, h thng thot nc hoc cc thit b khc tng t. Cc kt cu li in, in thoi hoc ng dy khc trn cao khng nn lin kt vi h thng chng st m khng c s cho php ca nh chc trch c thm quyn.

Hnh 20. Dy xung trong ng dn b tr bn trong

12.10.4 Cc mi ni

Bt k mi ni khc vi mi ni hn u th hin s gin on trong h thng dn in v nhy cm vi s thay i v h hng. Cho nn, h thng chng st cng t mi ni cng tt.

Cc mi ni phi hiu qu c v mt c v in, v d nh kp, vt, bu lng,cht, inh tn hoc hn. Vi mi ni chng, khong chng ln ca mi kiu dy dn phi khng nh hn 20mm. B mt tip xc trc ht phi c lm sch v sau ngn chn hin tng xy ho bng ha cht chng r thch hp. Mi ni gia hai kim loi khc nhau phi c lm sch bng cc cht khc nhau vi mi kiu vt liu.

Tt c cc mi ni phi c bo v n mn v xm thc do mi trng v phi c din tip xc thch hp. Kim tra nh k s thun tin do s dng cc lp sn bo v bng:

a) sn ph c gc ho du;

b) sn ph cao su bng phng php phun;

c) sn ph khng co nhit.

Vt liu s dng lm ai c v bulng phi ph hp vi cc tiu chun hin hnh v bu lng v ai c. bt bulng thanh dt, cn t nht l 2 bulng M8 hoc mt bulng M10. Vi cc mi ni inh tn, cn phi s dng t nht 4 inh tn c ng knh 5mm.

Bulng lin kt cc thanh dt vi tm kim loi c chiu dy nh hn 2mm cn phi c ming m vi din tch khng nh hn 10cm v phi s dng khng t hn 2 bulng M8.

12.10.5 Cc im o kim tra.

Mi dy xung phi b tr mt im o kim tra v tr thun tin cho vic o c nhng khng qu l liu, d b tc ng khng mong mun.

Cn t cc bng ch v tr, s lng v kiu ca cc cc ni t trn mi im kim tra.

GHI CH: Cn tham kho cc quy nh c lin quan v ng dn kn chng chy mi sn


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Hnh 21. Cc nhnh vng

Dy xung bn ngoi

Dy xung bn trong

c) Phng php lun dy xungqua tng mi chp nhn c d) ng i ca dy xung i vi nh c tng trn ua ra

Vt qu 8d Ti a 8d

a) B tr chp nhn c b) B tr khng chp nhn c


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13 Mng ni t GHI CH: Thng tin thm v mng ni t c trnh by B.1.

13.1 in tr ni t

Cc ni t phi c kt ni vi mi dy xung. Mi cc phi c in tr (o bng ) khng vt qu 10 nhn vi s cc ni t c b tr (xem 12.3). Tt c mng ni t nn c in tr ni t tng hp khng vt qu 10 v khng k n bt k mt lin kt no vi cc thit b khc.

in tr ni t trc v sau khi hon thnh cc lin kt cn c o v ghi chp li v s dng trong mi t o kim tra sau (xem 13.4 v mc 28).

Nu in tr ca ton b h thng chng st vt qu 10 , c th gim gi tr bng cch ko di hoc thm vo cc in cc hoc bng cch lin kt cc cc ni t ring r ca cc dy xung vi mt dy dn c t su t nht 0,6m di mt t, i khi c gi l cc ni t mch vng (xem Hnh 22). Cc cc ni t mch vng nn c b tr bn di cc thit b u vo cng trnh.

Vic chn cc cc ni t mch vng nh trn c xem nh mt phn khng tch ri ca mng ni t v phi c xt n khi nh gi gi tr in tr ni t tng th ca h thng c lp t.

Trong kt cu khung thp, cc cu kin ca khung thp thng c lin kt chc chn m bo c th s dng nh cc dy xung. Phn thp nht ca kt cu nn c ni t mt cch tha ng, vi cc dy xung c b tr tun theo cc yu cu 12.3. Trong hu ht cc trng hp, cc mng ca cng trnh s c in tr ni t thp ph hp m khng cn cc cc ni t khc, c bit nu mng ca cng trnh bao gm c cc cc c ct thp. Vic o in tr ni t ca cc mng va mi hon thnh s quyt nh liu bn thn mng m bo cha hay c cn thm cc cc ni t (xem B.1.6). Trong cc cng trnh hin c, vic o in tr ni t ca mng i khi bt kh thi v do phi tm kim gii php ni t khc nh trnh by mc 14. Nu ch s dng mng ni t, cn c cc bin php ni tng cu kin thng ng ca kt cu thp vi nn t to bi ct thp trong mng b tng.

13.2 Tm quan trng ca vic lm gim in tr ni t

Vic lm gim gi tr in tr ni t xung di 10 to thun li cho vic gim chnh lch in th xung quanh cc cc ni t khi tiu tn dng in st. N c th lm gim nguy c lan truyn st vo kim loi trong hoc trn cng trnh (xem 12.9).

13.3 Mng ni t chung cho mi thit b

Nn s dng mng ni t chung cho h thng chng st v mi thit b khc. Mng ni t cn ph hp vi nhng xut trong tiu chun ny v cng cn tun theo cc quy nh p dng cho cc thit b c lin quan. in tr ni t trong trng hp ny cn c gi tr thp nht p ng bt c thit b ring l no.

13.4 Cch ly h thng cc ni t o kim tra

Cc cc ni t cn p ng yu cu cch ly v nn b tr mt cc ni t tham chiu (xem 3.7) phc v cho mc ch o kim tra.

Khi kt cu thp trong cng trnh c s dng lm dy xung, cn b tr cc im o c kim tra tnh lin tc v in tr thp ca kt cu thp. iu ny c bit quan trng vi cc thnh phn khng l ra ca kt cu. Cc ni t tham chiu l cn thit cho vic o kim tra .

13.5 Cng trnh trn nn

Cc kt cu ng trn nn nn c trang b cc ni t mch vng chy theo ng ng mc ca nn. Nn ph t ln trn nu c th. Cc ni t ny nn c lp t bn di phn mng ca cng trnh mi. Nu khng p dng c cc iu trn th nn s dng t nht 2 thanh in cc dt


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hoc cc ni t to ra bng cch khoan v lp h bng vt liu dn in nh bentonite hay b tng dn in hoc ximng ch to vi ct liu cacbonat ha dng ht cp phi thay cho ct hay ct liu thng thng. ng knh ca h khng nn nh hn 75mm. Bi than cc hay tro bay khng nn s dng lm vt liu lp bi tnh ph hy dn ca chng.

14 Cc ni t GHI CH : Thng tin thm v cc ni t c cho B.1.

14.1 Quy nh chung

Trc khi bt u qu trnh thit k, cn quyt nh v kiu ca cc ni t thch hp nht vi tnh cht t nhin ca t thu c theo th nghim l khoan.

Cc cc ni t gm c cc thanh kim loi trn, dt, cc ng hoc kt hp cc loi trn hoc l cc b phn ni t t nhin nh cc hay mng ca cng trnh (xem B.1.4 v B.1.6).

14.2 iu kin t

14.2.1 Quy nh chung

Khi s dng cc thanh ni t, tr nn , chng nn c ng vo lp t khng phi t p, t lp hoc l loi t d b kh (theo ma hay do nhit ta ra t cc thit b, nh my).

14.2.2 Cc ni t c lp bc s dng bn trong cc kt cu dng b cha

Khi cc cc ni t i qua mt kt cu dng b cha nn p dng bin php bc kn nh minh ha Hnh 23.

14.3 Thanh ni t

14.3.1 V tr

Khi s dng cc thanh ni t, chng nn c ng vo t ngay bn di cng trnh v cng gn dy xung cng tt. Thi cng cc thanh ni t xa cng trnh thng l khng cn thit v khng kinh t (xem Hnh 24). Khi cc iu kin v t l thun li cho vic s dng cc thanh ng song song vi nhau, s gim bt in tr ni t l nh khi khong cch gia cc thanh nh hn chiu di ng vo t.

14.3.2 o in tr ni t trong qu trnh lp t

Trong qu trnh ng cc thanh vo t, nn tin hnh o in tr ni t. Lm nh vy s bit c trng thi khng cn phi gim tip in tr na, c bit khi ng cc thanh di.

14.3.3 Kt ni vi mng ni t

im kt ni vi mng ni t phi c kh nng di di v d dng tip cn c t trn mt t thun tin cho vic kim tra, o c v bo dng h thng chng st. Nu nm di mt t, im kt ni nn c t trong mt ci h hoc cng c xy dng cho mc ch kim tra. Tuy nhin, c th chp nhn cc b tr n gin trong mt s trng hp v d nh lp h thng nh, mng ni t su hn bnh thng hoc cc trng hp khc ph thuc vo iu kin hin trng (xem B.1.2).

14.4 Cc thanh dt

14.4.1 V tr v hnh dng

Khi s dng cc thanh dt, li hay bn, c th chn chng bn di cng trnh hoc trong cc rnh su khng chu nh hng ca ma kh hn hoc cc hot ng nng nghip.

Cc thanh dt nn c b tr hng tm t im kt ni vi dy xung, s lng v chiu di ca chng c xc nh sao cho c c in tr ni t cn thit.


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GH

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Nu cc hn ch v khng gian i hi s dng cch b tr song song hoc dng li, nn b tr nh Hnh 24 vi khong cch gia cc thanh song song khng nn nh hn 3m.

14.4.2 n mn

Khng cho php bi than cc tip xc vi cc in cc bc ng do tnh cht n mn nguy him ca chng. Khng nn nhi mui vo t xung quanh cc cc ni t.

15 Kim loi trong hoc trn cng trnh. GHI CH: Cc thng tin thm v kim loi trong hoc trn cng trnh c cho B.2

15.1 Khi nim chung

Khi st nh vo mng thu st, in th ca mng thu st vi t tng ln v, tr khi c bin php phng nga thch hp, s phng in c th xy ra theo cc ng khc nhau xung t thng qua hiu ng lan truyn st vo cc chi tit kim loi khc trong cng trnh.

C 2 bin php phng nga hiu ng lan truyn st, l:

a) Cch ly

b) Lin kt

Bin php cch ly yu cu khong cch ly ln gia h thng chng st v cc chi tit kim loi khc trong cng trnh. im hn ch chnh ca bin php cch ly nm ch rt kh to ra v duy tr khong cch ly an ton cn thit v bo m rng cc chi tit kim loi c cch ly khng kt ni vi t, v d nh thng qua nc hoc cc hnh thc khc.

Nhn chung, lin kt l bin php thng c s dng hn.


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Hnh 22.

Hnh 23. V d v cc ni t c lp bc c s dng trong kt cu b cha

B tng

B tng tphan

B tng

B tng tphan


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Hnh 24. Mng ni t: b tr cc cc ni t

Dy xung

Dy xung

Thanh ni t

Thanh ni t

Thanh ni t

Mt bng b tr cho cc dy song song (nt lin m) hoc dng li (nt t) (a) Cc ni t dng dy dt (b) Cc ni t n hoc a cc GHI CH 1: Khi phn mng ni t cn thit phi chy gn hoc di ng i, phn nn c chnsu khng di 0,6m tnh t mt t. GHI CH 2: in th mt t c th gim bng cch chn thanh hoc dy thp su hn.

im kim tra dy dn st

Dy dn st bnngoi

im kim tra

Ko di cho thch hp

Thanh ni t

Mt ct v hnh chiu cng trnh

Mp nh

Mp nh

Mt bng b tr cho dy dt n chia i bi dydn xung

Thp dt


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Hnh 25. ng cong xc nh xc sut ln nht dng in trong tia st t t s p/p0

Phm vi c trng ca dng in st

X

c s

ut s

t

nh

Xc

su

t chp

nh

n

Dng in st (kA)


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Hnh 26. in cm truyn trong mch n gin

15.2 c lng khong cch ly chng lan truyn st

15.2.1 Khi nim chung

Khong cch ly cn thit chng lan truyn st ph thuc vo in p duy tr bi h thng chng st so vi t, in p ny li ph thuc vo cng dng in st. Trnh t nh gi khong cch ly cn thit c trnh by cc phn 15.2.2, 15.2.3 v 15.2.4 di y.

GHI CH: L thuyt v thc nghim ch ra rng cc trng in t l nh nhau i vi mt dy xung c che chn v mt h thng thng c kch thc tng t. Dy dn c che chn c bt li l in th gia dy dn bn trong v dy dn bn ngoi c che chn c th ln ti hng trm kilvn n mc gy ra lan truyn st. im bt li khc na l dy dn bn trong khng tip cn c kim tra.

15.2.2 Xc nh dng in pht sinh

xc nh dng in do st nh xung cn tin hnh theo cc bc sau:

- c lng xc sut st nh vo cng trnh p (xem 7.2).

- Chia xc sut c lng, p cho xc sut st nh cho php p0 (xem 7.3).

- S dng Hnh 26 xc nh c dng in c cng ln nht c kh nng pht sinh.

Dy xung

Lin kt ng kim loi, cp in,ng thng hihoc cc chi tit kim loi khc

a)

b) 5.3twre

+=


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15.2.3 in p duy tr bi h thng chng st

in p ny c 2 thnh phn: mt l tch ca dng in v in tr ni t v thnh phn khc l tch ca bin thin dng in vi in cm t cm ca dy dn st. Trng hp nguy him nht, tng ca hai tch ny s cho gi tr in p cn s dng trong tnh ton.

15.2.4 Quan h gia in p phng in v khong cch.

Hnh 27 minh ho quan h gia in p phng in trong khng kh, qua b mt th xy v qua vt nt trong khi xy gch vi khong cch. in p phng in i vi mt khong cch cho trc c xc nh t Hnh 27 so snh vi kt qu tnh ton in cm. V d tnh ton quyt nh c cn lin kt cc chi tit kim loi vo h thng chng st hay khng c th hin ph lc D.

15.2.5 Tnh ton in cm pht sinh gia mt dy dn st v cc chi tit kim loi d b nh hng bi hiu ng lan truyn st.

Mc d cho n nay thut ng in cm t cm c s dng cho vic tnh ton in p cm ng, trn thc t in p cm ng c sinh ra trong mt mch kn to bi chnh dy xung v cc chi tit kim loi khc. Do ni chnh xc hn in p cm ng s t l vi hiu ca in cm t cm (L) tr i in cm tng h (M) gia dy dn st vi cc chi tit kim loi. Hiu s ny c gi l in cm truyn dn (MT) v c dng thay th cho in cm t cm trong vic tnh ton in p cm ng. in cm truyn dn c th c tnh theo phng trnh (4).

Cho mt dy dn st ng c tit din trn bn knh r (m), cch cc b phn kim loi thng ng khc mt on l S (m), trong S l khong cch gia tm ca 2 dy dn nh Hnh 26a) v l l chiu cao ca mch, in cm truyn MT (o bng micro henry) c tnh theo phng trnh:

MT=0,46 x l x log 10Sr

(4)

Vi nhng dy xung khng c tit din trn th phi dng bn knh hiu dng re (Xem Hnh 26b). V d vi dy c tit din ngang l 25mm x 3 mm, re (m) c tnh theo phng trnh di y:

re= 5,3tw +

(5)

=5,3

003,0025,0 +

=0,008

Tuy nhin cch tnh MT khng b nh hng bi hnh dng tit din ngang ca ng kim loi hay cc chi tit kim loi khc. Khi tnh c MT th in cm VL (kilovol) pht sinh trong mch minh ho Hnh 26a c tnh theo phng trnh (6):

VL=axm

didt

x TMn

(6)

Trong max

didt

l bin thin ln nht ca dng in (kA/s) ngha l 200 kA/s (xem ph lc A.1)

n l s lng dy xung cng chu dng in do st truyn vo.

Khi c nhiu dy xung th khong cch S t dy c st n dy xung gn nht cn phi c s dng tnh ton.

V d khi s dng phng trnh (6) nu S=1m, l = 5m v n = 4;


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VL =200 x 5,3

)008,0/1(log546,0 10x

VL=240 V

T Hnh 27, khong cch t im cao nht ca mch (c th mt nhnh ngoi ca mng li) n dy xung s phi nh n 0,4m ti mt v tr nht nh to ra nguy c phng in. Mt nhnh ngoi gn n nh vy phi c lin kt vi dy dn xung cho an ton.

Vi cng trnh c mt bng dng ch nht hoc hnh vung c hn 4 dy xung, dy xung gc s chu mt in p ln hn mc trung bnh ca tng dng in (i) (ngha l > i/n), do h s 30 % phi c tnh thm vo in p pht sinh gn dy dn . Ngc li, vng gia ca cng trnh c rt nhiu dy xung (cch xa dy xung nm gc) gi tr di/dt l thp hn gi tr c a ra bi s lng dy xung khong 30 % v nguy c lan truyn st l tng i t, vi gi thit rng cc thit b c lin kt sao cho in tr ca t khng to ra s chnh lch in th.

15.3 Tnh hung cn thit phi lin kt

(xem thm ph lc B.2)

15.3.1 Khi lin kt cc chi tit kim loi lin k vi h thng chng st, cn phi cn nhc k v cc tc ng c th xy ra ca cc lin kt i vi cc chi tit kim loi c bo v ca-tt. Cn lu ti cc khuyn co t 15.3.2 n 15.3.10.

15.3.2 Vi cc cng trnh c kim loi dn in lin tc (v d nh mi, tng, sn,v bc hoc tng bao kim loi) nhng chi tit kim loi ny c th c s dng nh mt b phn trong h thng chng st vi iu kin s lng v cch b tr ca chi tit kim loi to ra n ph hp vi vic s dng, nh trong khuyn co mc 11, 12, 13 v 14.

15.3.3 Vi cng trnh n gin ch l mt khung kim loi lin tc,th khng cn phi c b phn thu st hay dy xung. Khung iu kin m bo tnh lin tc v mt c hc v dn in.

15.3.4 Mt kt cu BTCT hoc mt kt cu khung BTCT c th c in tr ni t ca bn thn chng kh nh c th lm phng tin bo v st nh. Nu cc mi ni c a ra bn ngoi im cao nht ca ct thp trong lc xy dng th vic kim tra c th c tin hnh xc minh iu ny khi hon thnh cng trnh (xem Hnh 6).

Nu in tr ni t ca khung thp ca cng trnh hoc ct thp trong kt cu b tng ct thp m bo th cn lp t mt b phn thu st ngang trn im cao nht v lin kt vi khung thp hoc ct thp.

GHI CH: Trong trng hp c bit ca thp lm lnh nc thng khng lp b phn thu st.

Khi khng th kim tra theo cch thng thng th nn s dng vt liu chng r lin kt vi thp hoc ct thp v nn a ra ngoi kt ni vi b phn thu st. Cn trang b b sung dy xung v b phn thu st nu khi kim tra in tr ni t ca bn thn cng trnh khng tha mn (xem 13.1).

15.3.5 Khi cng trnh c cc chi tit kim loi khng th lin kt vo mng c tnh dn in lin tc v n khng hoc khng th c trang b h thng ni t bn ngoi, th s tn ti ca n c th c b qua. Mi nguy him do cc chi tit kim loi c th gim thiu bng cch cch ly hon ton cc chi tit kim loi vi h thng chng st, phng n x l cn tham kho cc khuyn co 15.2.

15.3.6 Khi b phn mi cng trnh c kim loi che ph hon ton hoc mt phn th cn phi thn trng khi lin kt n vi h thng chng st.

15.3.7 Trong bt c kt cu no, kim loi gn vi mt ngoi hoc nh ra khi tng hay mi m c khong cch ly n h thng chng st l khng v khng thch hp s dng nh mt phn ca


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h thng th cn gn cng trc tip cng tt vi h thng chng st. Nu c chi tit kim loi no chy gn vi b phn thu st, v d nh ng ng nc chy n b cha nc trn mi, dy cp, cc ng ng, mng xi, ng dn nc ma v cu thang, v nu cc chi tit ny chy gn nh song song vi dy xung hoc lin kt vi n, n phi c lin kt cc im cui nhng khng thp hn im kim tra. Nu cc chi tit ny khng lin tc th mi phn ca n phi c lin kt vi h thng chng st, khi c cc khong khng cho php th s tn ti ca cc chi tit kim loi c th b qua.

Hnh 27. ng quan h in p phng in theo khong cch

Khong cch (m)

i

n p

ph

ng

in

(kV)

Trong khng kh

Qua vt nt cath xy


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15.3.8 Khi kim loi trong cng trnh nh khung chung trong nh th, tng bao, cc thit b my mc m n c kt ni hoc tip xc vi ng ng nc hoc cc thit b c cp in m bn thn n ni t phi c lin kt n dy xung gn nht bng ng i cng trc tip cng tt.

15.3.9 Kim loi i vo hoc i ra cng trnh dng c v bc hoc ng dn in, gas, nc, nc ma, hi nc, kh nn hoc cc thit b khc phi c lin kt cng trc tip cng tt n cc ni t. im kt ni phi c lm ti v tr m cc thit b i ra hoc vo cng trnh. Cc bc thang phi c x l tng t.

Khi cc chi tit kim loi dng l mt phn ca thit b cha ra khong cch ly (xem 15.2), n phi c lin kt vi phn gn nht ca h thng chng st im cao nht ca thit b v vi cc khong cch khng vt qu 20m.

Do cc thit k h thng chng st rt a dng nn khng c khuyn co chnh xc no c a ra. Tuy nhin, cn phi lu rng c th c vn khi cc ng ng hoc cp c bc cch nhit hoc cch in.Vi trng hp nh vy, mi lin kt phi c thc hin im gn nht ni m phn kim loi ca ng hoc cp c l ra. Mi lin kt sau phi c ni vi h thng ni t bn ngoi cng trnh cng thng cng tt.

iu ny rt c th c p dng trong cng trnh bit lp m cc thit b c kt ni vi nhau.Tuy nhin khi cng trnh bao quanh bi cc chi tit bng thp gm mt lot cc chi tit dng ng ni vi nhau th bn thn n rt c th tr thnh mt im thch hp ni t. i vi h thng cp in, vic ng dng cp kt hp ni t (CNE) l c vn v vic ngt dy trung tnh c th gy dng ti ngc t in cc ni t. iu c th gy nguy him cho bt c ai ngt mch in cc ni t o th nghim.

H thng kt ni in hnh c th hin trong Hnh 28. Quy tc chung l mi h thng cn c nh gi v u im ca n v c tho lun vi cc bn c lin quan quyt nh phng n ph hp.

15.3.10 Khi lp t thang my, kt cu kim loi lin tc bao gm c ray dn hng phi c kt ni vi h thng chng st im cao nht v im thp nht ca b phn lp.

Khi ct thp hoc cc chi tit kt cu kim loi to thnh mt b phn ca h thng chng st, th vic kt ni cc chi tit kim loi ny l cn thit.

Khi kh c th tn dng c ct thp hoc kt cu kim loi ca cng trnh th h thng thang my cn c lin kt vi h thng an ton in ni t c im cao nht v thp nht. Trong mi trng hp, cn lin kt im ni t ca bng in gn nht.

16 Kt cu cao trn 20 m GHI CH: C th xem thm thng tin v cc kt cu cao trong B.2 v B.5.

16.1 Cc kt cu khng dn in

Trn cc kt cu khng dn in, nn c t nht 2 dy xung t cch u nhau v m bo rng, khi s dng phng php hnh cu ln (xem B.5), b phn thu st s to ra vng bo v mong mun. Trn cc ng khi, dy xung nn ni vi chp kim loi ca ng khi hoc vi mt dy dn quanh nh ca ng khi.

16.2 Cc kt cu dn in

C th p dng cc quy nh 15.3.4 cho nhng kt cu cao dn in, nhng ti nhng v tr cn cc dy xung nn ni t nht 2 dy dn v t cch nhau khng qu 10m quanh chu vi.


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Hnh 28. S lin kt cc thit b (gas, nc v in)

16.3 Thp v chp nh th

Thc t chng minh st c th nh vo pha di im cao nht ca cc kt cu cao, do nn s dng t nht hai dy dn cho tt c cc ta thp v ngn thp nh th.

i vi cc kt cu khng dn in, nn thit k mt li thu st (xem mc 14) xung quanh tng bao ca mt ta thp; v cng nn bao gm trong h thng c ct c v bt k nhng im nh ra no khc trn tng mi. Mi v tr cn li ca nh th nn c bo v theo tiu chun ny v ph hp vi nh, mi hin v cc dy xung, cc mng ni t v b phn ng p bo v st. Cc dy xung khng nn gn bn trong (xem Hnh 29).

Cc mi nh bng kim loi c th c s dng nh cc li thu st (xem Bng 4 v Hnh 16).

17 Cng trnh c mi che rt d chy 17.1 Cc b phn thu st

Vi cng trnh c mi che bng rm, tranh, cy, c hoc cc vt liu c kh nng d chy cao, c th treo b phn thu st tch khi mi mt on t nht 0,3 m trn b phn khng dn in v khng chy hoc cc b phn thu st c th t trn mt thanh g cng dt c rng ti thiu l 75 mm. Vi mng dy c to ra bo v mi che bng rm r v cc mi nh c lp theo cch tng t chng li cc cn gi v by chim, mng khng nn kt ni vi h thng chng st.

17.2 Dy dn v cc ghp ni

Vi cc dy dn hoc cc ghp ni buc phi xuyn qua vt liu lm mi, nn b tr vo trong cc ng khng dn in v khng chy.

Nc Cp in

Mng ni t ca hthng chng st

Cc ng ng thit b

im o c

t trong ng ivi tng hai lp

Dy xung bn ngoi

Vt cch in B phn ni t chnh

Gas


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Hnh 29. Thp v chp nh th

Dy dn ng lin kt vinhau bn trong tng mi

Dy dt gn votng mi

i vi mi kim loi c th khng cn dy dn K hiu 1. Dy thu st 2. Dy xung 3. Lin kt gi thanh ng 4.Dy thu st ngang

5. Dy ng 6. Dy nc mi 7. Dy vin mi 8. im o kim tra

9. Cc ni t 10. Ni t ca h thng in 11. Lin kt vi khung chung 12. Dy dn quanh chu vi

GHI CH 1: li thu st nn c kch thc 10m x 20m. Khong cch cc dy xung xung quanh chu vi nn l 20m i vi kt cu thp hn 20m, l 10m i vi kt cu cao 20m tr ln. Dy dn ngang nn cch nhau 20m tnh t mi tr xung. GHI CH 2: Mi kim loi c th s dng lm b phn thu st


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18 Nh cha cc vt c kh nng gy n hoc rt d chy 18.1 Quy nh chung

Nhng vn pht sinh trong quy nh v cc h thng chng st cho cc kt cu c cha vt gy n hoc rt d chy tt nht nn gii quyt bng cch hi kin cc chuyn gia thng tho v lut hoc cc quy nh ca chnh ph v cc quy phm thc hnh.

C th chp nhn mt ri ro nht nh nu cc vt liu nguy him c bo qun mt cch nghim ngt, nh trong phng th nghim hoc kho cha nh, hoc ti ni kt cu c t v tr tch bit hoc c thit k c bit hn ch nhng nh hng ca thm ha c th xy ra. Trng hp cc vt liu nguy him khng b h ra m c che kn hon ton trong thng bng kim loi c dy thch hp th ngoi tr phi m bo ni t thch hp, c th khng cn b tr h thng chng st. Trong cc trng hp khc, mi nguy him ti sinh mng v ti sn c th i hi phi p dng tt c cc bin php c th c bo v tc ng ca st nh. xut cho cc trng hp ny c trnh by trong 18.2 v c th p dng cho cc kt cu cc cht rn, cht lng, gas, hi nc hoc bi d n hoc rt d chy c ch to, cha ng, s dng, hoc cc cht kh, hi hoc bi d chy n c th tch t li.

18.2 Cc phng php bo v chng st nh

18.2.1 B phn thu st dng treo

Li thu st nn c treo cao thch hp trn vng cn bo v. Nu ch dng mt dy dn t nm ngang, gc bo v chp nhn c khng nn qu 30o (xem Hnh 17).

Nu s dng hai hay nhiu dy dn nm ngang song song nhau, gc bo v thch hp c th ln ti 45o trong khng gian c bao quanh bi cc dy dn, nhng khng vt qu 30o bn ngoi khng gian (xem Hnh 30). cao ca dy dn nm ngang nn la chn theo cc gi trong 15.2 (xem Hnh 30); trong trng hp cn cha chc chn, nn tham kho kin chuyn gia. B phn ca li thu st nn c ni t mt cch ph hp.

C th dng cch khc i vi nhng ni chi ph cho phng php trn l khng hp l v khng c cc ri ro lin quan ti dng st nh vo b mt ca kt cu cn c bo v, c th chn la mt trong hai cch lp t sau y:

a) B phn thu st dng treo nh th hin trn Hnh 30 nhng cc gc bo v l 45o thay v 30o, v 60o thay v 45o;

b) Mt li dy dn nm ngang vi mi mt li 10 m x 5 m hoc nh hn ty theo mc ri ro, c c nh trn mi ca kt cu (xem Hnh 15).

GHI CH: Mi kt cu ring bit c bo v theo cc cch ny nn c ni vi s dy xung v cc b phn ni t gp i so vi xut 12.3.

18.2.2 Cc dy dn ng

Mt kt cu hoc nhm cc kt cu c kch thc ngang nh c th c bo v bng mt hoc nhiu dy dn st ng. Nu s dng mt dy xung, gc bo v tnh ton khng nn qu 30o.

Nu s dng hai hay nhiu dy xung, gc bo v c th l 45o trong khng gian b gii hn bi cc dy dn, nhng khng nn qu 30o bn ngoi khng gian . Minh ha v phng php bo v ny c th hin trn Hnh 31.


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18.2.3 Cc kt cu b chn mt phn hay ton b di t

18.2.3.1 Kt cu b chn mt phn di t nn c bo v theo cch tng t nh i vi kt cu trn mt t.

18.2.3.2 Nu kt cu hon ton nm di mt t v khng c kt ni vi bt k thit b no trn mt t c th c bo v nh mt li thu st nh trong 18.2.1a), cng vi mng ni t ca n l hon chnh. Kh nng chn xung in ca t c th c tnh n khi xc nh mc ri ro ca vic pht tia la in t h thng bo v ti kt cu c bo v, bao gm cc b phn ph tr ca n. Ti ni su chn lp l thch hp, li thu st c th c thay th bng mng cc thanh ni t dt c sp xp trn b mt theo li khuyn ca chuyn gia. nhng ni chp nhn phng php ny, nn b qua cc xut ghp ni cho kim loi, hoc cc dy dn kim loi a vo kt cu (xem 18.2.4, 18.2.5 v 18.2.6).

18.2.4 Cc cc ni t mch vng

Cc cc ni t ca mi h thng chng st nn c ni vi nhau bng mt cc ni t mch vng. Cc ni t mch vng ny nn c chn su t nht 0,6 m tr khi c nhng l do khc, nh cn lin kt cc vt th khc ti n, hoc l ra trong trng hp cn o kim tra. Cc cc ni t mch vng ca cc kt cu k nhau nn c ni vi nhau.

18.2.5 Kim loi trn hoc trong kt cu (xem B.2)

18.2.5.1 Tt c kim loi chnh to ra cc b phn ca kt cu, bao gm ct thp bng kim loi v cc b phn ph tr bng kim loi c tnh lin tc, nn c ghp cng nhau v ni vi h thng chng st. Cc kt ni nh vy nn c lm t nht ti 2 ni (xem Hnh 15) v bt c ni no c th, nn t cch u nhau khng qu 10 m quanh chu vi ca kt cu.

18.2.5.2 Cc chi tit kim loi bn trong kt cu nn c gn vi h thng chng st (xem 12.9).

18.2.5.3 Vic s dng kho bng thp chuyn dng ni hn cha cc cht n tr nn kh ph bin. i vi cc kho nh th, vic bo v st thch hp c thc hin bng cch ni t kt cu t nht hai im.


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Hnh 30. B phn thu st c hai dy thu st treo ngang v vng bo v cho kt cu c cha cht n hoc cht rt d chy

Xem ghi ch 2

Cc ni t vng

Cng trnh c bo v

Cc ni t

a)Mt ng

Dy thu st treo ngang

Ni t vng Dy thu st treo ngang

b) Mt bng

K hiu Vng bo v v trnh dy Vng bo v v trdy vng nht

Xem ghi ch2

Xem ghi ch 2

Cng trnh cbo v

Cng trnh cbo v

Ct

Dy thu st treo ngang

Xem ghi ch 2

c) Mt ng u hi th hin vng bo v GHI CH 1: Khi dng hai dy thu ngang tr ln, c th dng gc bo v 45o cho khng gian bao bi dy.Ch khc gii hn gc bo v l 30o. GHI CH 2: trnh hin tng phng in gia dy thu v cng trnh, khong cch ly ti thiu phi l 2mhoc theo 15.2 tu theo gi tr no ln hn. Khong cch ly ti thiu phi c m bo v tr vng nhttrong mi iu kin.


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Hnh 31. Cc kim thu st ng ca nh kho cha cht n

18.2.6 Dy dn in vo cng trnh

18.2.6.1 Cc dy dn in vo cng trnh d chy n nn a vo trong ng kim loi. V bc kim loi ny cn c lin tc v in trong ton kt cu; nn c ni t ti im u vo trong kt cu bn pha h thng dch v ca ngi dng v c gn trc tip ti h thng chng st (xem Hnh 28). Nn c s tha thun gia cc bn lin quan khi u ni.

18.2.6.2 Ti ni cc dy dn in ni vi mt ng dy cung cp in trn cao, nn chn mt on cp kim loi hoc bc kim loi c chiu di 15 m c chn su vo gia ng dy trn cao v im ni vo kt cu (xem Hnh 32). Nn ch ti cc quy nh c lin quan (xem mc 24). Vic thc hin iu ny mt cch chun xc l quan trng, cn c s thng nht ca cc bn c lin quan.

GHI CH: St nh c th gy xung in ln trn cc ng dy cp in bn trn. Do , nn c b phn hm xung in ti nhng ni cc ng dy cp in bn trn ni vi cp chn di t. iu ny s cho php phn ln dng in do st gy ra c truyn vo t ti mt khong cch an ton so vi kt cu.

H

Cng trnh c bo v

Ct

im kim tra

Cc ni t

a) Mt ng

b) Mt bng

Ti thiu 2m


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18.2.7 Cc ng ng, lan can, ni vo cng trnh

Cc ng dn bng kim loi, dy thp, lan can, ng ray tu ha hoc cc bin hng dn khng lin kt thng in vi t m ni vi cng trnh cha vt d chy, n, cn c gn vi h thng chng st. Cc vt ny nn c ni t ti im u vo bn ngoi kt cu v ti 2 im xa hn, mt im cch xa 75 m v im kia cch 75 m tip theo. Vic ni t cc lan can nn c thc hin ti cc im sau:

- im i vo hoc i ra khi kt cu;

- Cch xa im i vo hoc ra 75 m; ngha l hng vo trong nu l kt cu ngm hoc hng ra ngoi nu trn mt t;

- Cch xa im i vo hoc ra 150 m hoc bn ngoi kt cu trong trng hp nm pha trn mt t;

- Cc im cch nhau 75 m khi lp t di mt t;

Cc yu cu ny cng p dng cho cc tuyn b mt trn c s dng cn trc hoc cu trc lu ng (xem 15.3.9).

Hnh 32. Bo v c bit chng qu dng do st gy ra trong ngun in cp vo nh c cha cht n hoc cht rt d chy

B phn chnxung in

Hp in tng

Dy ni t

Ni vo cc nit mch vng

Cp di 15m chn gia ngdy in trn cao v cng trnh

Ni vo cc ni t mch vng


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18.2.8 ng hoc hm vo cng trnh

i vi cng trnh ngm hoc cc h o di mt t c tip cn bng ng hoc hm vo cn tun theo cc gi 18.2.7 v vic ni t b sung ti cc khong cch khng qu 75 m, cng nh bn ngoi kt cu.

18.2.9 Cc hng ro, tng chn

Cc chi tit thng ng bng kim loi, cc b phn v dy kim loi ca tt c cc hng ro v tng chn trong phm vi 2m ca kt cu nn c ni theo cch to ra mt kt ni kim loi lin tc gia chng v h thng chng st (xem mc 20).

18.2.10 Cc l thng hi

gim thiu nguy c st nh thng, cc l thng hi ca bt k cc thng cha c nh no bao gm bnh gas hoc cht lng d chy, v cc l thng kh hoc ng khi t cc nh my ch bin sinh ra hi hoc bi d chy, nu c th, nn c t trong vng bo v ca h thng chng st. Do iu ny khng hon ton ngn chn s pht chy, cc l thng hi cn c bo v trnh s lan chy bng vic s dng cc vt chn la, cc thit b lc kh tr hoc cc phng tin thch hp khc.

18.2.11 Mi nguy him t cc b phn cao trn hoc gn cc kt cu d b st nh

Khng nn trang b cc b phn cao nh chp thp, ct c hoc cc dy anten v tuyn cho cc kt cu d b st nh hoc b tr chng trong phm vi 50 m quanh kt cu. Khong cch ly cng p dng i vi vic trng cy mi, nhng cc kt cu gn cy c nn c x l ph hp vi cc khuyn co mc 21.

18.2.12 o kim tra an ton

Vic o kim tra nn c thc hin ph hp vi khuyn co mc 28 v thit b o c phi thuc loi an ton i vi tng trng hp nguy him c th.

19 Nh Cc quy nh ca tiu chun ny c th p dng cho nh . Vic chng st cho cc ta nh c cc anten v tuyn truyn hnh v truyn thanh c nu chi tit hn mc 22. Ti ni c h thng chng st, gi cch x l i vi cc ng ng thng hi bng kim loi c minh ha trn Hnh 33.

20 Hng ro 20.1 Bn cht ca mi nguy him

Nu st nh vo mt hng ro kim loi ko di, on gia im b st nh v im ni t gn nht s tng ngay lp tc n mt in th cao tng i so vi in th ca t. Con ngi hoc vt nui gn, hoc tip xc vi hng ro ti thi im st nh vo hng ro c th b nguy him. Do , cn ni hng ro ti t thng qua cc in cc t ti cc on sao cho c th tiu st mt cch hiu qu nht.

V l tng, nn ngt s lin tc ca hng ro bng cch to khe h c m cht cch ly dc chiu di ca hng ro bi iu ny gip hn ch nh hng ca st nh ti cc on ring bit. Tuy nhin, cc hng ro ch yu dng cho cc l do an ninh, vic a ra cc khe cch ly s lm ny sinh cc vn khc.

Khuyn co i vi hng ro dng cho cc mc ch c th c nu trong 20.2 v 20.3.


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Hnh 33. Bo v st nh cho cc thit b trong nh

ng thng hi ng ten tivi Kim thu st ng

Lin kt vo thnh ng kim loi

a) Nh bng vt liu khng dn in c ngten tivitrn mi v b phn k thut lin kt vi dy xung

ng thng hic ni t

b) Cc ni t vng cho nh bng vtliu khng dn in xy trn nn

Cc ni t vng

Ct ngten TV ni t v hthng mng lin kt vi dy xung

Mt bng th hin h thng chng st inhnh c) Nh xy bng c ct ngten TV

c lin kt ni t v h thng mng linkt vi dy xung

d) Cng trnh ln bit lp


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20.2 Bo v vt nui trn cnh ng

20.2.1 Thng tin chung

Thit hi v vt nui khi c st nh trong cc cn ma dng ch yu l do cc by n t hp di gc cy trn cc cnh ng trng hoc quanh cc hng ro bng kim loi khng c ni t nn b dng in st phng vo ln git cht chng.

Do bn cht ca vic nui th vt nui trn cnh ng nn khng th loi tr hon ton mi nguy him, nhng nu mun gim mi nguy him ny th nn thc hin cc bin php phng nga trong 20.2.2 v 20.2.3.

20.2.2 Ni t

Vi cc hng ro c xy dng bng cc cc kim loi thng ng v cc dy kim loi dn in lin tc, v d dy thp gai, cc dy c ko cng hoc dy xch, mi on dy lin tc cn c ni vi cc ct ng bng kim loi t ti cc khang u nhau. Trong trng hp s dng cc ct bng g hoc b tng, nn ni cc on dy vi cc cc ni t, v d cc cc ng xung t.

nhng ni t thng xuyn b t, khong cch gia cc ch ni khng nn qu 150 m v nn gim xung 75 m ni t kh.

20.2.3 Cc khe h cch in

Hng ro kim loi khng nn di lin tc m chia thnh cc on khng qu 300 m bng cch chn cc cng bng g hoc cc khe h c rng t 600 mm tr ln, c khp kn nh cc on vt liu khng dn in.

GHI CH: Khng nn s dng dy xch bc bng vt liu do ni kn cc khe h trn.

Ni t cho hng ro ti khe h trn nn b tr cch cc cnh ca khe h t nht l 8 m v mi pha.

20.3 Hng ro bao quanh cc kt cu c cha cht lng hoc kh d chy

20.3.1 Ni t cc hng ro hon ton bng kim loi

i vi hng ro bao quanh cc v tr nguy him lm hon ton bng kim loi thng khng c vn g xy ra v cc hng ro c th c ni t nh miu t trong 20.2.2 nhng ti cc khong cch nhau khng qu 75 m.

20.3.2 Ni t cc hng ro c bc bng vt liu do

Cc lp ph bng vt liu c tc dng bo v tc ng ca thi tit v vic ngt lp bc ni t cho phn kim loi s tng nguy c n mn, do khng c khuyn khch p dng.

Tuy nhin, loi hng ro ny thng thng c mt li dy thp gai trn cao. Do nn ni t li thp gai ny ti cc khong khng qu 75 m to thnh b phn thu st bo v hng ro.

20.3.3 Cc khe cch in

Cc hng ro ch yu dng cho mc ch an ninh nn cc khe cch in c kh nng vi phm cc yu cu an ninh, do khng c khuyn khch p dng.

21 Cy v cc kt cu gn cy GHI CH: Cc thng tin thm v cy v kt cu gn cy c th xem trong B.3.

Ch cn bo v cy trnh tc ng ca st nh trong trng hp c bit cn gi gn ci cy v l do lch s, thc vt hc v mi trng hoc cc ngha tng t khc. Trong cc trng hp ny,

nn thc hin nh sau:


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a) Dy xung chnh chy t phn cao nht ca nhnh chnh ca cy ti cc ni t v dy cn c bo v khi cc ph hng c hc mt t.

b) Nn cp thm cc dy dn nhnh ni ti dy dn chnh cho cc nhnh cy ln.

c) Cc dy dn nn c bn v bc li. Tng din tch mt ct ngang khng nn nh hn 50 mm2 i vi ng v nhm. Cc kch thc khng c cho c th v iu s gy phin toi cho vic la chn gii php dy, nhng iu quan trng l cc dy dn phi c tnh mm do.

d) Khi gn cc dy dn nn tnh n s pht trin t nhin ca cy v s ung a ca cy do cc cn gi gy ra.

e) Ni t nn bao gm 2 cc c ng vo t hai pha i din v gn vi thn ca cy. Nn chn mt cc ni t mch vng bao quanh cc r cy v ni vi cc cc bng hai dy dn hng tm. Ni t v in tr ni t nn p ng cc iu mc 13.

f) Khi hai hay nhiu cy gn nhau v c kh nng cc cc ni t mch vng bao quanh ca chng giao nhau, nn s dng mt cc ni t mch vng chung c ni thch hp vi cc cc chn di t bao quanh tt c cc gc cy.

g) Khi mt cy bit lp gn mt kt cu, c cao khng vt qu cao ca kt cu th khng cn chng st cho cy ny. Nu cy cao hn kt cu, khong cch ly sau y gia kt cu v phn cao nht ca cy c th c xem l m bo an ton:

- i vi cc kt cu thng, khong cch ly bng mt na chiu cao ca kt cu;

- i vi cc kt cu cha cc vt d n hoc kh nng chy cao, khong cch ly bng chiu cao ca kt cu;

Nu cc khong cch ly ny khng c m bo, cn xem xt ti cc mc ri ro lin quan. gim ri ro ti mc ti thiu m vn gi li cy, kt cu cn c bo v ph hp vi cc khuyn co ca tiu chun ny v b phn thu st hoc dy xung nn c sp xp sao cho c th i gn ti b phn gn nht ca cy.

GH CH: Khi mt cy khng c chng st, lung in do st nh vo cy c th truyn qua khong cch hng chc mt, dc hoc di b mt t, tm mt vt dn in tt, v d ng nc hoc gas, cp in hoc b mt t bo v st ca mt ta nh.

22 Cc cng trnh c ng ten v tuyn truyn thanh v truyn hnh 22.1 Cc ng ten bn trong cng trnh c chng st

Vi cc cng trnh c chng st ph hp vi cc quy nh ca tiu chun ny, c th lp thm cc ng ten v tuyn truyn thanh v truyn hnh trong nh m khng cn c thm bin php phng chng khc, min l khong trng gia h thng anten, bao gm dy thu v dy dn xung, v h thng chng st bn ngoi ph hp vi cc gi tr c cho trong mc 15.

22.2 Cc anten bn ngoi cng trnh c chng st

Vi cc cng trnh c chng st ph hp vi cc quy nh ca tiu chun ny, c th lp cc ng ten v tuyn truyn thanh v truyn hnh bn ngoi m khng cn c bin php chng st b sung nu mi phn ca h thng ng ten, bao gm cc b phn chu lc bng kim loi, trong vng bo v ca h thng chng st. cc v tr khng p ng iu kin ny, cn c bin php chng st m bo rng st c th truyn xung mt t m khng gy nguy him cho kt cu v ngi s dng kt cu nh sau:


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i vi h thng ng ten c lp trc tip ln kt cu c chng st, lung in do st nh gy ra c tiu tn bng cch ni kt cu gi ng ten vi h thng chng st ti im gn nht c th ti c bn di v tr lp t

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TCXDVN 46-2007 - Chong Set Cho Cong Trinh Xay Dung - Huong Dan Thiet Ke_ Kiem Tra Va Bao Tri He Thong