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CHNG ST: NGUYN NHN - GII PHP CHNG ST - THIT B CHNG ST

A. NGUYN NHN HNH THNH ST1/ Nguyn nhn hnh thnh st :

Trong nhng nm qua, c mi khi ma ma n, ngoi vic chun b cc bin php phngchng bo lt chng ta cnphi quan tm n mt hin tng thin nhin khc c tc hi nghimtrng n c s vt cht v con ngi - l dng st. C th hiu nm na rng st l s phng

in gia m my dng v mt im no trn mt t khi in trng kh quyn t n m tgi tr ti hn. Vit Nam thuc vng kh hu nhit i nn dng in st thng rt ln khong30kA, do nu mt cng trnh no b st nh th phn kin trc ca cng trnh c th bph v do nh hng ca p sut v nhit pht tn cao, cc thit b in trong cng trnh cth b hng do trng in t ca dng st cm ng v con ngi c th b tn thng nu gnim phng in st. Trong thc t xy ra nhiu trng hp mt cn phng in st lmcho hng chc ngi b thng v cht (xy ra x Hip Thnh - Bc Liu) cn nhng v st lmcht ngi hng nm th xy ra lin tc khp ni nht l cc vng trng im nh i Ru, BuSm, Bo Vinh ....thuc Huyn Long Khnh -ng Nai, cc x vng su thuc Huync Linh,Hm Tn - Bnh Thun, hoc mt s x thuc cc tnh ng bng sng Cu Long, ngay tiTpHCM nm no cng xy ra vi trng hp t vong do phng in st.

C ch hnh thnh mt cn st ni chung kh phc tp, c nhiu cng trnh nghin cu vqu trnh nhim in ca mt m my dng cng nh c ch pht trin ca tia st hng xungt, ngoi ra cng cn nhiu vn khc lin quan n st v chng ti mong rng s c dpc trnh by chi tit hn trong cc bi bo khc, y chng ti ch xin cp n mt githuyt ph bin nht gii thch nguyn nhn to dng st nh sau :

Dng l hin tng kh quyn lin quan vi s pht trin mnh m ca i lu nhit vcc nhiu ng kh quyn, n thng xy ra vo ma h l thi im m strao i nhit giamt t v khng kh rt ln. Nhng lung khng kh nng mang theo hi nc bay ln n mt cao no y v ngui dn, lc hi nc to thnh nhng git nc nh hay gi l tinh thbng chng tch t trong khng gian di dng nhng m my. Tri t cng b nng th khng

kh nng cng bay ln cao hn, my cng dy hn n mt lc no th cc tinh th bng trongmy s ln dn v ri xung thnh ma. My cng dy th mu ca n cng en hn. S vachm ca cc lung kh nng i ln v cc tinh th bng i xung trong m my s lm xut hincc in tch m ta gi l m my b phn cc in hay m my tch in. Cc phn t in tchm c khi lng ln nnnm di y m my cn cc phn t in tch dng nh hn nnb y ln phn trn ca m my.

Nh vy trong bn thn m my hnh thnh mt in trng cc b ca mt lngcc in v di tc dng ca in trng cc b ny cc phn t s di chuyn nhanh hn, intch c to ra nhiu hn v in trng cng mnh hn. Qu trnh ny tip din cho n lcin trng t gi tr ti hn v gy ra phng in ni b trong m my m ta gi l chp.

Ngoi ra khong khng gian bn di m my thng c mt lp in tch dng gi lin tch khng gian v vy gia phn y m my mang in m v lp in tch dng ny lihnh thnh mt in trng ring v chnh in trng ny lm pht sinh mt tia st ban u gil dng tin odi chuyn xung t vi tc khong 150km/s. Trong qutrnh pht trin xungt, dng tin o mang theo mt in th rt ln s ion ho lp khng kh trn ng i ca n,ni no c cch in khng kh yu th dng tin o s pht trin v hng v vy ta thydng tia st i xung khng phi l ng thng m thng c dng ngon ngoo, phn nhnh.Ngoi ra do hiu ng cm ng in nn phn mt t nm bn di m my dng s mang mtlng in dng. Lng in ny s phn b trn cc vt c kh nng dn in nh nh ca,cy ci, cng trnh, tr in, thp anten......, vt no dn in cng tt th in tch phn b trn vt cng ln v in trng ca n cng mnh so vi cc vt xung quanh. V vy, khi dng tinopht trin xung gn mt t th n s chn vt c in trng mnh nht nh vo m tagi l phng in st, ni tip xc ca chng gi l knh st. y l thi im trao i in tchgia m my v mt t c gi l giai on trung ho in tch, dng in trong knh st lcny rt ln c th n 200kA nn b nng ln rtmnh khong 20.000oC v do ta thy n sngchi ln (cng c gi l chp). Di tc dng ca nhit ny, lp khng kh chung quanh

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knh st b gin nmnh gy ra ting n ln m ta gi l sm. Do nh sng c vn tc ln hngtriu ln so vi m thanh nn ta thy nh chp trc ri sau mt lc mi nghe thy ting sm.

2/ Mt s bin php phng trnh st thng dng v hiu qu : y chng ta cn phn bit cc loi st khc nhau nh st nh trc tip, st nh gintip, st cm ng.- St nh trc tip l st nh thng vo nh ca cng trnh hoc nh vo bn nc kim

loi hay tr anten nm trn cng trnh ,nh vo cy ci, nh vo ngi ang di chuyn khiang c dng .....y l loi st nguy him nht v n c th gy thit hi nng n cho cng trnhhoc gy cht ngi.

- St nh gin tip l st nh vo ng dy in thoi, ng dy ti in cao thhoc h th mt ni no ri theo ng dy truyn vo cng trnh lm h hng thit b inang s dng. Chng ta thng thy hin tng bng n, in thoi, TV, t lnh .... b chy hocngi ang gi in thoi b in git mnh sau mt cn dng st tt c l do nh hng ca loi

st ny.- St cm ng bao gm cm ng tnh in v cm ng in t. St cm ng tnh in

thng ch nguy him cho cc cng trnh c cha cht d chy n nh xng du, kh t do tcng ca phng in th cp cn st cm ng in t ch nguy him i vi cc thit b hin idng cc linh kin in t nhy vi xung in trong cc cng trnh bu in, vin thng, phtthanh truyn hnh.

Mt h thng chng st hon chnh phi th hin y cc ni dung chng st ni trn,tuy nhin i vi a s cc h gia nh ngi ta thng ch quan tm n vic chng st nhtrc tip.

C nhiu bin php k thut phng chng st nhng cho ti nay th cha c mt thit bhoc h thng chng st no t c hiu qu tuyt i. Mt m hnh chng st thng dng c cng nhn l c hiu qu trong mt phm vi gii hn nht nh vn cn c s dng rngri nhiu ni trn th gii l h thng dng kim thu st c in Franklin vn chng minhkh nng bo v vi mt tin cy cho php tn ti hng trm nm qua. Kim thu st Franklinl mt thanh kim loi c u nhn di khong 3m c lp ti ni cao nht trong khu vc cn bo

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v, n hot ng theo nguyn l phng in i m, ngha l trong in trng kh quy n ca dngbo, kim thu st ny s lin tc nh in tch vo vng khng gian do quanh u kim thu st sc in trng cc b mnh so vi cc im xung quanh v hnh thnh mt tia la in mi (dngmi) nn n d dng thu ht dng st tin o t my i xung, dng in st ny s truyn tkim qua h thng dy dn i xung t v tn nhanh trong t nh bi tip a tn st. Nh vyh thng chng st s to ra mt phm vi an ton cho cng trnh m n bo v . Tuy nhin trongthc t vn c hin tng st nh vo cng trnh c h thng chng st m ngi ta gi lst nh vng, do m bo an ton chng ta khng nn t lp ly h thng chng st mphi nh n chuyn vin k thut tnh ton thit k sao cho h thng m bo cc thng s k

thut nh phm vi bo v, in tr tn st, kh nng st nh vng, kh nng phng in th cp....., c nh th th h thng chng st mi hon thnh tt nhim v ca n. Trong trng hpngc li th chnh h thng l nguyn nhn dn n cc tai hocho cng trnh v nhngngi sng trong cng trnh .

3/ La chn u thu st :Theo tin b ca khoa hc k thut, ngi ta nghin cu ch to cc loi kim thu st

tch cc (thay cho loi kim thu st c in th ng nu trn) ch ng bt st khng cho nnh vo cng trnh cn bo v. Hin trn th trng Vit Nam c gn mt chc loi kim ch ngca cc nc khc nhau nh M, Php, Uc, .....

Cc loi kim thu st ny hot ng da trn cc nguyn l lm vic khc nhau nhng nichung c th chia lm hai loi chnh :a/ Loi phng in sm: l cc loi kim thu st c c tnh pht ra dng mi kh sm khi intrng kh quyn cha t n tr s ti hn ngha l n ch ng n bt dng phng in st mt im no trong khng gian cch xa cng trnh m n bo v. Chng ta c th hnh dung lkhi hot ng th kim thu st nh c ko di ra mt on gp hng chc ln chiu di thc cachng, on ny c gi l cao o ca kim thu st v nh th chng c phm vi bo v lnhn rt nhiu so vi kim thu st c in cng mt cao.

b/ Loi phn tn in tch: l cc loi kim thu st c c tnh to ra mt lp in tch khng gianmang in dng trong vngkh quyn nm bn trn u kim da trn nguyn l phng in

im . Trng tnh in my dng cng mnh th dng phng in cng mnh v lp in tchkhng gian cng nhiu, n tc dng nh mt mn chn tnh in lm cho in trng gia mmy dng v t yu i ngha l loi b nguy c phng in st.

Ngoi ra cn mt dng kt hp ca hai loi trn to thnh mt h thng chng st khcgi l loi phng in tr hon. Loi ny c u im lm tng phm vi bo v nhng li rt tn kmso vi hai loi trn.

Trong gn 20 nm qua, chng ti nghin cu c tnh k thut ca trn 20 loi kim thust khc nhau gm c nhng loi cha c mt th trng Vit Nam v cng thit k thi cnghng trm h thng chng st cho nhiu chng loi cng trnh khc nhau, ni chung v nguyn llm vic th chng c hiu qu cao hn nhiu so vi loi kim thu st c in v mi loi c nhng

u khuyt im khc nhau. Hn na, do cc loi kim thu st ch ng ch mi pht trin mnh tiVit Nam trong vng 5 nm tr li nn phi cn c thm thi gian theo di v nh gi xem loikim no t yu cu v cht lng, bn v hiu qu trong vic bo v cng trnh trong iukin kh hu nhit i nh nc ta, ngoi ra gi c cng l mt yu t cn quan tm v chngkhng ph hp lm i vi a s cc h gia nh mun lp mt h thng chng st ring cho nhca mnh.

Tm li nh trnh by trn, mt h thng chng st ngoi kim thu st cn c phn dnst v bi tip a tn dng st trong t m y l cc phn khng d dng lp t nht l i vinh ca cng trnh thuc cc khu th . Dy dn st c tc dng chuyn ti dng st xung td dng, n phi chu c nhit pht nng cc b khng b bin dng . Bi tip a cnhim v tn nhanh dng st trong t trnh in p cao tn ti trn h thng chng st tc l

phng trnh hin tng phng in th cp v nh hng ca in p bc, l cc yu tnguy him c th lm h hng cng trnh v gy cht ngi. Do ta thy rng mt khi h thngchng st khng t cht lng k thut th tht l tai ho cho chng ta khi c st nh vo cngtrnh. V vy nu cc bn c yu cu lp t h thng chng st th c th lin h vi chng ti c hng dn c th bng cch da vo c im thc t ti cng trnh ca bn nh in trsut t, c tnh a l ca vng, v tr lp t v cu trc bi tip a, khong cch an ton trong

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khng kh v trong t ...... hu t c mt h thng chng st pht huy ht kh nng cachng trong vic bo v an ton cho cng trnh v nhng ngi sng trong cng trnh .

Ngun: Phn Vin Nghin Cu Khoa Hc

B. GII PHP H THNG CHNG ST

PHN LOI CC DNG CHNG ST

A/ CHNG ST NH THNG :1. Chng st nh thng bng cng ngh kim c in .Cu hnh ca loi ny gm c 3 phn :a) Cc u kim thu st:

Thng lm bng thp m ng , ng thau choc bng inox. La chn chiu di ca kimcn ph thuc vo cu trc ca cng trnh cn c bo v .b) Dy dn st:

Dng dn dng st t cc u kim thu n h thng tip t. Thng lm bng ng l hoccp ng trn, tit din ca dy dn c quy nh theo tiu chn quc t ( NFC 17 102 ca Php) t 50mm2 n 75mm2.

c) H thng tip t:Dng tn dng in st trong t.Cu hnh ca h thng tip t ny gm :- Cc cc tip t: thng di t 2,4 mt n 3 mt . ng knhngoi thng l 14 16mm .

c chn thng ng & cch mt t t 0,5 n 1 mt . Khong cch cc vi cc t 3 n 15mt .

- Dy tip t: thng l cp ng trn c tit din t 50 n 75mm2 dng lin kt cc cctip t ny li vi nhau . Cp ny nm m di mt t t 0,5 n 1 mt .

- c sit cp hoc mi hn ho nhit CADWELD: dng lin kt dy tip t & cc cc tipt vi nhau.

2. Chng st nh thng bng cng ngh tiu tn m my in tch khng cho hnh thnhtia tin o st (dissipation array system).

Cng ngh ny hin nay Vit Nam rt t s dng v gi thnh cao, ch c ng dng vomt s cng trnh cn thit.

Cc hng sn xut nh: LEC USA, LIGHTNING PREVECTION SYSTEM USA .Cu hnh ca loi ny gm c3 phn:

a) Cc u pht ion dng:Thng lm bng thp m ng hoc bng inox . Cc u phtion dng c dng qu cu nhiu gai, dng ci d nhiu gai , hoc dng cnh di nhiu gai

b) Dy dn st:Dng dn dng ion dng t mt t i ln cc thit b pht ion dng .Thng lm bng cp ng trn, tit din ca dy dn c quy nh theo tiu chn quc t ( nfc

17 102 ca php ) t 50mm2 n 75mm2 .c) H thng tip t:Dng tn dng in st trong t. Cu hnh ca h thng tip t nygm:

- Cc cc tip t:thng di t 2,4 mt n 3 mt . ng knh ngoi thng l 14 16mm.c chn thng ng & cch mt t t 0,5 n 1 mt . Khong cch gia cc vi cc t 3 n15 mt .

- Dy tip t :thng l cp ng trn c tit din t 50 n 75mm2 dng lin kt cc cctip t ny li vi nhau. Cp ny nm m di mt t t 0,5 n 1 mt . Yu cu dy cp tipt ny phi c ni thnh mt mch vng kn trc khi ni vi dy dn st.

- c sit cp hoc mi hn ho nhitcadweld:dng lin kt dy tip t & cc cc tip tvi nhau.

3. Chng st nh thng bng cng ngh pht tia tin osm (Early Streamer Emission) .Cc hng sn xut : INDELEC PHP, SATELIT PHP, HELITA PHP, POUYET PHP,PARATONNORRES PHP, ERICO C. INGESCO TY BAN NHA.Cu hnh ca loi ny gm c 3 phn :

a) u thuli: Dng pht tia tin oi ln thu ht st v n. u thuli c gn trn tr c cao trung bnh l 5 mt so vi nh ca cng trnh cn c bo v.

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b) Dy d n st:Dng dn dng st t u thuli n h thng tip t . Thng lm bngng l hoc cp ng trn, tit din ca dy dn c quy nh theo tiu chn quc t (nfc 17102 ca php) t 50mm2 n 75mm2.

c) H thng tip t: Dng tn dng in st trong t. Cu hnh ca h thng tip t nygm:

- Cc cc tip t: thng di t 2,4 mt n 3 mt. ng knh ngoi thng l 14 16mm.c chn thng ng & cch mt t t 0,5 n 1 mt . Khong cch cc vi cc t3 n 15mt.

- Dy tip t: thng l cp ng trn c tit din t 50 n 75mm2 dng lin kt cc cc

tip t ny li vi nhau. Cp ny nm m di mt t t 0,5 n 1 mt.- c sit cp hoc mi hn ho nhitcadweld: dng lin kt dy tip t & cc cc tip t

vi nhau.B/ CHNG ST LAN TRUYN :I. Chng st lan truyn cho trm bin p 1000v (1kv) :1. Dng chng st Van La (Lightning Arrester)lp ti u ng dy vo trm bin p ctxung in st xung t.

- Dng chng st van s cp ( gi l thit b ct st ngun 3 pha hoc 1 pha ), lp song song vingun in ct gim xung in st ln xung t. Cu hnh ca loi ny gm c 3 phn :

a) Van ct st:Dng ct x xung in st lan truyn trn li h th xung t , trc khin c th theo ngun in i vo ph ti .

b) Dy dn st:Dng dn dng st t imnt mng n van ct st & t van ct st nh thng tip t .

c) H thng tip t :Dng tn dng in st trong t . Cu hnh ca h thng tip t nygm :

-Cc cc tip t: thng di t 2,4 mt n 3 mt . ng knh ngoi thng l 14 16mm .c chn thng ng & cch mt t t 0,5 n 1 mt . Khong cch cc vi cc t 3 n 15mt .

- Dy tip t: thng l cp ng trn c tit din t 50 n 75mm2 dng lin kt cc cctip t ny li vi nhau . Cp ny nm m di mt t t 0,5 n 1 mt .

- Oc sit cp hoc mi hn ho nhit CADWELD : dng lin kt dy tip t & cc cc tip

t vi nhau.d) Cu to ca van ct st :Van ct st c ch to t xt kim loi (metal oxide varristormov) thng l xt km . c im ca loi vt liu ny l ch c th dn in in p cao &s tr thnh vt cch in in p thp , in p cng cao th dng in thng mch cng lnv in p cng gim th dng thng mch cng gim v z r ( cn gi l khi in tr phi tuyn)

e) Nguyn l lm vic ca van ct st :Khi st nh trc tip vo ng dy in h th 3pha 220/380vac50hz , hoc st nh vo cc vng ln cn ri cm ng vo ng dy h thri lan truyn vo van ct st trc khi n n ph ti ( cc thit b dng in ) . Xung in st nyc bin in p ln lm cho in tr phi tuyn ca van ct st ngngdn , lc ny n s mmch cho dng in st i qua n xung t . Khi xung in st gim thp n di gi tr inp ngngca van ct st th in tr phi tuyn ca van ct st s tng nhanh ngt dng ct

xung st .

2. Dng thit b ct lc st(thng l lp ni tip vi ph ti) va ct xung in st , va lcc cc loi sng hi , cc nhiutn s cao ca st :

a) Cu hnh: loi ny gm c 3 phn :

Thit b ct lc st: Dng ct x xung in st lan truyn trn li h th xung t &lc cc sng hi cc nhiutn s cao trc khi chng c th theo ngun in i vo ph ti.Dy dn st : Dng dn dng st t thit b ct lc st st n h thng tip t .H thng tip t :Dng tn dng in st trong t . Cu hnh ca h thng tipt

ny gm :- Cc cc tip t: thng di t 2,4 mt n 3 mt . ng knh ngoi thng l 14 16mm . c chn thng ng & cch mt t t 0,5 n 1 mt . Khong cch cc vi cct 3 n 15 mt .- Dy tip t: thng l cp ng trn c tit din t 50 n 75mm2 dng lin kt cccc tip t ny li vi nhau . Cp ny nm m di mt t t 0,5 n 1 mt .

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- c sit cp hoc mi hn ho nhit cadweld : dng lin kt dy tip t & cc cc tipt vi nhau.

b) Cu to ca thit bct lc stthng bao gm :Van ct st s cp (nm pha trc)- B lc sng hi & nhiu(nm gia)- Van ct st th cp (nm pha sau)

Van ct st s cp & th cp c ch to t xt kim loi (metal oxide varristor mov)thng l xt km. c im ca loi vt liu ny l ch c th dn in in p cao & s tr

thnh vt cch in in p thp , in p cng cao th dng in thng mch cng ln v inp cng gim th dng thng mch cng gim v z r ( cn gi l khi in tr phi tuyn).

B lc sng hi c cu to t cun khng in l & cc t lc c , cun khn l c lp ni tipvi mch in cn t lc c th lp song song vi mch in (nm pha sau cun khng in l).

c) Nguyn l lm vic ca thit bct lc st:Khi st nh trc tip vo ng dy in hth 3 pha 220/380vac 50hz , hoc st nh vo cc vng ln cn ri cm ng vo ng dyh th ri lan truyn vo thit b ct lc st trc khi n n ph ti ( cc thit b dng in ) .Xung in st ny c bin in p ln lm cho in tr phi tuyn ca van ct st s cpngngdn , lc ny n s m mch cho dng in st i qua n xung t . Tip theo blc l c c tc dng lm gim thp bin xung st v tch b cc thnh phn sng hi , nhiutn s cao . Xung in st cn st vi bin thp khi ra khi b lc l c th s b van ct st thcp ct thm mt ln na. Khi xung in st gim thp n di gi tr in p ngngca vanct st th in tr phi tuyn ca vanct st s tng nhanh ngt dng ct xung st .

II. Chng st lan truyn cho li in h th 3 pha 220/380v 50/60hz :1. Dng chng st Van s cp( gi l thit b ct st ngun 3 pha hoc 1 pha ), lp song songvi ngun in ct gim xung in st ln xung t .

* U IM :- Khng b gii hn dng ti nn cng lc c th

Bov c nhiu thit b dng in .- V y ch l thit b ct st s cp nn thng gi thnh thp .

* NHC IM :- Ch ct hu ht cc xung ln m khng lc c cc thnh phn tn s cao ca st , nh ccsng hi , cc loi nhiu . . .Cc hng c th p ng tt nh : TPS C , OBOC , MCG USA, ERICO C ,TERCEL C .

2. Dng thit b ct lc st(thng l lp ni tip vi ph ti) va ct xung in st , va lcc cc loi sng hi ca st .

* U IM :- Bo v a cp cho ph ti ( gm ct st s cp , lc , ct st th cp ) , do c an ton cao.

* NHC IM :- V c ch to bo v a cp nn gi thnh cao .- V lp ni tip nn b gii hn vi mt dng in nht nh .- Cc hng p ng tt nh : TPS C , OBOC , ERICO C , TERCEL C .

3. Chng st lan truyn cho ng dy thng tin :

1. Chng st lan truyn cho ng dy in thoi lp trn phin Krone 10 i dy : tutheo mcin p tn hiu , tn s lm vic , tc ng truyn s la chn cc thit b bo v khc nhau .Cc hng c th p ng nh : TPS C, ERICO C, TERCEL C .2. Chng st lan truyntrn ng dy ni mng my tnh cp RJ45 : c nhiu hng la chnnh APC USA , ATLENTIC USA , ERICO C , TPS C.3. Chng st lan truyntrn ng dy cp ng trc 75W : c nhiu hng la chn nh

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ERICO C , TPS C , OBOC .

Thanh ThnhTheo http://kythuat.tech.officelive.com