Electrical Accident Prevention(2011)-An Toan Dien

PHNG NGA TAI NN IN

An ton in

Module ny cung cp thng tin v phng nga tai nn in, mi chng gm ni dung nguyn nhn gy ha hon chy n do h mch in, in git v do in.

1. C th hiu i sch phng nga tai nn in git do h mch in.

2. C th hiu i sch phng nga tai nn in git do chm vo b phn np in.

3. C th hiu nguyn nhn gy ha hon v i sch phng nga do tia la in.

Mc ch ca m-un

Mc ch ca vic hc

in git v i sch phng nga do h mch in ......................... 4 Nhng iu cn ghi nh

in git v i sch phng nga do chm vo b phn np in ................. 22

Nhng iu cn ghi nh

Nguyn nhn v i sch phng nga chy n ha hon do in .................. 30 Nhng iu cn ghi nh

Vn luyn tp theo m-un ................................................................................................ 44

Chng 1

Chng 2

Chng 3

PHNG NGA TAI NN IN

An ton in

4

in git v i sch phng nga do h mch in

C th hiu i sch phng nga tai nn in git do h mch in.

H mch in

Thng thng chng ta thng s dng t ng gi l h mch in nh t vong do in git hoc pht sinh ha hon do h mch in. Vy h mch in l g? Dng in b h mch d dng so snh nht l ging nh hin tng r r nc do h ng dn nc sinh hot. Di y l gii thch chi tit mt cch chuyn mn hn nh sau. (1) Dng in h mch

Dng in h mch l hin tng phng in (corona) v r r in hng ngy ra xung quanh do lng in tch t xung quanh. D nhin dng in ny rt yu, bnh thng khng th nhn thy, khng pht ra m thanh, nhng khi tri ma dng in h mch ny c th nghe c di cc my mc in t. Cui cng nh ngha dng in h mch l bao gm nh ngha h mch, khng th l nguyn nhn gy tai nn in git.

01

Chng 1

Chng 1_ in git v i sch phng nga do h mch in An ton in

5

Dng in b h mch

(2) Dng in gy tai nn do t ri

Dng in gy tai nn do t ri l dng in thot ra chung quanh t dy in hay b phn np in gy tai nn do tip xc hoc b hng cu dao ngt in. Chng ta phi ch v phng chng tai nn do dng in h mch.

Bi cnh pht sinh tai nn in git (1) Khng in ca c th ngi.

Mc nguy him do in git ty thuc vo mnh ca dng in i qua, theo nh lut Ohm th mc in p tip xc ty thuc vo sc khng in ca c th ngi. Sc khng in ca c th ngi xut hin t sc khng in da, bn trong c th, c th thay i theo mnh ca dng in. Theo bo co th tiu chun in p s dng khong 1,000, khi da trng thi kh th sc khng in tng ln gp 20 ln so vi mc ny, khi c th b t nc th sc khng in b gim gp 20 ln so vi mc ny.

02

u u u


PHNG NGA TAI NN IN

An ton in

6

Chng 1

Hnh v 1-1 Vng tun hon in ca c th ngi

Tr s trung bnh sc khng in ca c th ngi Hn Quc. A. Tay phi- tay tri khi kh : 35,102. B. Tay phi- tay tri khi t : 9,232. C. Tay tri- 2 bn chn kh c mang bt tt : 26,675. D. Tay phi- 2 bn chn trn t : 10,052.

Sc khng in ca c th ngi bnh thng. A. Kh nng khng in ca da bnh thng khong 2,500. B. Kh nng khng in ca bn trong c th 500. C. Kh nng khng in gia bn chn v giy 1,500. D. Kh nng khng in gia giy v mt t 700. E. Kh nng khng in ca ton b c th 5,000. C gi thuyt v gim n khong 500 do tng mt t ca da v s dn in ca c th nhng thc t khi da kh c mang giy kt qu o tay phi- chn tri th tr s khng in l v hn (). [theo Phn tch thng k tai nn in ca C quan an ton in Hn Quc tham kho s 13 nm 2004].

Sc khng in ca c th ngi theo tnh trng da. Thng thng khi da t so vi da kh theo kt qu th nghim ca Hip hi bo him ho hon M th khng nng khng in gim khong 1/10 v theo kt qu nghin cu khc kh nng khng in ca c th khi c ra m hi gim 1/12~1/20, khi da t gim 1/25. Tuy vy khi xem kt qu o ca i tng th nghim khi c mang giy so snh tay phi-tay tri khi kh v khi t th kh nng khng in ca c th gim khong 1/4~1/5. Khi i chn trn so sng gia tay v chn khi kh v t th t l gim kh nng khng in ca c th l khong 1/2.02~ 1/2.28.


7

Nu xem kt qu o tay phi-tay tri khi da kh th trung bnh o c 35,000. Theo kt qu nghin cu ca nc ngoi nu cho dng in AC 220V chy qua c th th gim khong 1/50 c th duy tr kh nng khng in khong 700.\

(2) Kh nng khng in ca mi trng chung quanh

Trng hp b in git a s t ng i ca dng in thng qua mi trng chung quanh gia c th ngi- mt t- my bin p, ty theo kh nng khng in ca mt t, nguyn nhn c quyt nh theo mnh ca tai nn. Nu quan st mt phn tnh trng giy ca ngi lao ng v mt t, mnh ca tai nn ty theo h c mang giy cch in v giy c kh hay khng. D nhin nu ngi lao ng khng mang giy cch in nhng mang giy th thao b t v nu mt t b thm t nc ma th kh nng khch in ca mt t gim cc k nhiu do khi tai nn xy ra kh nng gy t nn rt cao.

Hin tng in git

Hnh v 1-2 ng dn in i qua c th ngi khi b tai nn in git

Nu c th ngi tip xc vi dy in b trc v nh hnh v trn tuy dng in gi l I i qua dy in th dng in gy tai nn Ig i qua c th ngi. D nhin dng in Ig cng mnh th kh nng gy t nn cng cao, mnh dng in Ig c quyt nh ty theo dng in thng qua v kh nng khng in.

03


PHNG NGA TAI NN IN

An ton in

8

Chng 1

I = V/R v c lin quan vi V = IR Trc tin khi ngh n mnh ca dng in i qua, th dng in pin s dng trong gia nh 1.5V cc k nh nn khng gy nguy him. Nhng dng in i qua cng ln th mc nguy him cng cao, theo lut y t an ton cng nghip quy nh dng in 30V l dng in trong ranh gii an ton. Do phi lun d phng tai nn in git i vi dng in trn 30V. Hin ti chng ta s dng in th 220V nu so vi in th 110V s dng trc y th nguy him cao hn nhiu. Nhng nu chng ta s dng b bi khng x l an ton nguy him do dng in so vi in th 110V s dng trc y, nu s dng cu th hoc do thit k v thi cng s st s tr thnh nguyn nhn gy tai nn in git. Phn ng ca c th i vi in git Nu nghin cu dng in i qua c th ngi v kh nng khng in nh [Hnh 1-2] th t l t nn khi b in git cao nht khi mt t b t nc ma, c th t m hi, khng mang giy, vy thi k ny l khi no? Phn tch thi k pht sinh tai nn in git gy t vong cao nht l vo ma ma thng 7,8. [Nu dng in x thi gian] i qua c th ngi n mc no , do tc dng lm nng nn ni dng in i vo v ni dng in i ra s b bng, ni tng b ph hng hoc lm bin i huyt cu trong mu. c bit vn l do kch thch ca dng in lm pht sinh rung tm tht tim cn tr cung cp xy cho t bo, nu ko di vi pht s gy t vong. V nu b in git khi trn v tr cao. D cho dng in khng mnh khng gy mt tri gic nhng do b sc c cm gic t t gy tai nn ri xung t v c th b in git ln th 2 .Tiu chun IEC v nh hng ca dng in i qua c th ngi nh sau.

04


9

Hnh v 1-3 Phn ng ca c th i vi dng in (IEC 60479-1) Khu vc AC-1 : L khu vc khng c phn ng g ng k (dng in i qua yu).

Trng hp tr s mnh ca dng in i qua di mc gii hn, c th khng cm gic g l, nu tr s ny trn mc gii hn th s c cm gic b in git, tr s dng in c gi l yu l 2~5mA, bnh thng cng dng in s dng khong 0.5~1.0mA.

Khu vc AC-2 : L khu vc c th c cm gic t t, khng c phn ng nguy him (dng in c kh nng thot ra). Nu dng in thng qua vt qu mc gii hn cho php th c th c cm gic au do in git, c th chu ng c mc au ny, l dng in i qua khong 7~8mA cn trong gii hn khng gy nguy him cho tnh mng.

Khu vc AC-3 : Nu dng in i qua vt qu mc gii hn c kh nng thot ra khu vc (dng in gii hn gy t lit) khng pht sinh co rt c hoc kh th, khng gy rung tm tht tim, b phn ca c th c dng in i qua lm co rt c gy t lit thn kinh, lm cho c th khng th vn ng thoi mi c, sc lc c th ca bn thn khng th t thot ra khi khu vc nguy him c l do dng in (dng in mt chiu khong 60~90mA, dng in xoay chiu khong 10~15mA).

Khu vc AC-4 : Lnh vc c th xy ra rung tm tht tim (dng in gy rung tht) Dng in i qua trong c th vt qua gii hn dng in tch t trong c th th mt phn dng in s i qua tim, dng in bn ngoi c th tc ng thm vo tim, lm cho tim co bp bt thng, b phn iu khin tim b ri lon hoc b hng lm tim p bt thng, do rung tm tht bt thng gy cn tr tun hon mu, hin tng ny gi l rung tht, dng in lu hnh trong c th b ngt, nhp tim khng th hi phc tr li bnh thng.

Thi

gian

dn

g i

n i

qua(

pht

)

Cng dng in i qua (mA)


PHNG NGA TAI NN IN

An ton in

10

Chng 1

Nu tnh trng ny nh vy s t vong trong vng vi pht. Do a s tai nn t vong do dng in l do rung tm tht, thng thng tr s dng in v dng in i qua c th ngi gy rung tht nh sau :

Bng 1-1 Phn ng ca c th vi dng in quy cch.

Loi Phn ng ca c th Loi Dng in gy cm gic

b in git nh nht Cm gic t t 0.5~1[mA]

Dng in thot ra khi c th

Dng in mc gii hn cao nht c th cn ch kh nng thot khi ni tip xc ngun in. (au khng chu ng ni).

7~8[mA]

Dng in tch t trong c th

Dng in lm cho c th c cm gic b in git nhng khng kh nng thot khi ni tip xc ngun in (B co rt c).

10~15[mA]

Dng in gy rung tm tht

Mt chc nng tim, d c tch ri ra khi ngun in th cng t vong trong vi pht.

Nhng in hnh b in git do h mch in Ngi lm vic chung c mi xy, lp bng n b in git cht. Thi im pht sinh tai nn l ma h ang ma ma, nn nh b t nc ma khong 10cm. Nguyn nhn tai nn l ng dy in ni vi bng n b trc v, dng in b h mch ra ngoi, l do khng x tr an ton chng h mch, bn ngoi khng c lp dy thot in xung t (dy te).

Hnh v 1-1 Hin trng nn nh b t nc ma

05


11

Hnh v 1-2 Bng n b h mch in Hnh v 1-3 Du vt tia la

in u vo ca dy in i sch phng chng in git do h mch

Phng php gii quyt khi pht sinh tai nn h mch in (xt tia la in) ca dng in p thp lm nh phng php nhng phong php c hiu qu nht l cch lm nh sau :

(1) Gn dy thot in t thit b in xung t (dy te) phng nga nguy him in git do h mch, nn gn dy thot in xung t chc chn i vi nhng b phn tng ng nh sau. Bn ngoi v kim loi ca my mc dng c in, v ngoi bng kim loi v v

bc, bn st. C vi b phn nghi ng c th s tch t in tong s cht kim loi khng tch t

in b h mch ca my mc dng c in lp t c nh hoc lp vi h thng dy in c nh.

(2) Lp t cu dao ngt in h mch

Trong s my mc dng c loi di ng v loi cm tay c in p trn 150V cn phi lp t cu dao ngt in h mch dng phng chng in git do h mch, thit b ny phi thch hp vi quy cch ca dng in tng ng, cm ng tt, chc chn hot ng tt. Ni m t cht lng c tnh dn in cao nh nc. Ni c tnh dn in cao nh trn tm thp, khung thp. Ni c lp t ng dy in tm thi.

06


PHNG NGA TAI NN IN

An ton in

12

Chng 1

(3) S dng my mc dng c in ng quy cch, c kim tra. S dng sn phm bn lu v bo m tnh nng theo quy cch sn phm v sn phm c kim tra, i ngay hoc sa cha ngay nu my mc dng c in c kh nng ngt in km cht lng d gy ra tai nn in git.

(4) o khng ngt in.

D l my mc dng c in c trng thi tt, nu s dng lu ngy, kh nng ngt in c th b km i, c th b h mch, vic phi lm l o khng ngt in l phng php phn on bit c h mch hay khng.

Hnh v 1-3 Phn on theo kt qu o khng ngt in

Tr s o Tnh trng Tt 0 H mch

Tiu chun khng ngt in c nh gi tt ng dy in theo my mc, h thng dy in, thit b thp nht l 0.1M ~ cao nht l 0.4 M, thng thng my mc in p thp th trn 1M my mc in p cao l trn 5M. Dy dn in xung t o tnh trng khng ngt in nh ch gii trn l rt quan trng phng chng thot mch, nhng y khng th l cch phng nga hon ton chng in git. Bi v kt qu khng ngt in d cho khng trn tr s th iu g s xy ra khi pht sinh h mch bt thnh lnh? Do khng nn lc no cng ch o khng ngt in. V vy lp t dy dn in xung t (dy te) chnh l x l an ton d b. (1) Nguyn l dy dn in xung t

bo h h thng dy dn in xung t v nhn mng lin quan n h thng in lc v c bn cn tm hiu v dy dn in xung t c lin quan cht ch n phng nga in git.

07


13

Dy dn in xung t l dy khng c dng in i qua v l dy ni t v my mc dng c in thng xung t. Vy th lm th no dn in xung t bo h nhn mng? Xem v d nn sau khi s dng k hiu in v d in git.

Hnh v 1-4 ng i ca dng in h mch

ng dy dn xung t

Trng hp t vong do h mch ca bng n AC 220V, dng in i qua mnh bao nhiu? Dng in gy rung tm tht tim gy t vong l t 50~100mA, dy dn in xung t d c h mch, th phng php lm cho dng in yu i v ngn dng in i qua chnh l dy dn in xung t. Trng hp gn dy dn in xung t vo bn ngoi v bng n AC 220V nh [Hnh 1-5] c mc khng dn dn in xung t 100, mc khng ca h thng dn in xung t ca my bin p th 2 l 10, dng in tip xc l 220V, dng in i qua c th l 0.2A (220mA) khng th bo h c nhng nu dy dn in c mc khng dn dn in xung t t v my mc l 1, th in p tip xc tch ra l 20V, dng in i qua c th s cn 20mA th an ton.

B ngt mch

Dy tip a Dy in cc tip a

Dng in h mch I= in p tip xc e= IR=2x100=200V

Do dng in i qua c th ngi Hnh v 1-5 ng in in qua c th ngi khi c dy dn in xung t gn vo v my mc.


PHNG NGA TAI NN IN

An ton in

14

Chng 1

Chng ta c th bit rng vic lm gim in tr tip a bn ngoi ti ng in ny l iu kin cn thit ca cng trnh tip a. Phng php lm gim in tr tip a c phng php thng thng l chn su xung t cc tip a nh thanh tip a hay tm tip a v phng php chuyn nghip v c h thng hn mt cht l phng php phn nh v thi cng t giai on thit k nh mng tip a (Ground grid), chn su cc tip a hay cht lm gim in tr tip a hay nng cc tip a ln.

Dy tip a dng hi tip dng in h mch (tip a) Khi xy ra s c h mch cn ngt b ngt mch pha ngun khng cho dng in chy qua tc l pha ngun cn lp t dy tip a dng hi tip dng in h mch im trung tnh hay u kp dy tip a pha cun th cp my bin p. Dy tip a c cu to mch kn vi dy tip a c b tr cng vi dy din dng cung cp ngun in ging nh trongHnh 1-6, c s dng nhm mc ch ngt b bin i in, phn bit vi dy tip a c kt ni vi cc tip a trong t (dy in cc tip a). Dng in b s c h mch (dng in chm t) xy ra trong trng hp h mch thit b hay n in c gi tr khc nhau ty theo h thng nhng l gi tr vt khong vi chc n vi nghn Ampere. Dng in b s c ln ny c ngt ngay bi cc thit b bo v nh bng iu khin, cu dao t phn phi in, b ngt mch nn ngay c khi b h mch cng vn an ton. Ngha l dy tip a hi tip thc hin vai tr ny. Theo , gn y nhiu ngi c xu hng s dng nhiu loi dy cp c to bi 5 li dy tip a ngay c vi kiu 3 pha 4 dy.

(2) Tip a ca thit b in kiu di ng

Ai cng bit v iu quan trng ca vic tip a bn ngoi nhng nu kt ni phn bn ngoi vi cc tip a trong t bng dy in ca cc tip a ging nhHnh 1-6th thit b khng th di chuyn c, do n s ph hp vi thit b kiu c nh nhng s xy ra mt s vn i vi thit b kiu di ng.

Hnh v 1-6 Dy tip a dng hi tip dng in tip a

My bin p

in tr tip a in tr tip a

Thit b

in tr c th ngi


15

Tuy nhin phng php tip a bn ngoi ca thit b in kiu di ng l phng php ph bin v d dng nht, ngc li cng kh m bo nht. Thit b in kiu di ng phi tip t theo trnh t bn ngoi thit b-dy in kiu tip a- phch cm kiu tip a- cm kiu tip a- thanh tip a(hay mng tip a) do , dy tip a chuyn dng phi c b tr tch ring so vi dy in trn dy cp, hin nay chng ta s dng dy in kiu khng tip a vi loi dy 2 li hay cm v phch cm khng tip a. c bit chng ta dng cm v phch cm khng c cc tip a khin cho khng th duy tr c tnh lin tc ca dy tip a m b ngt qung.

Thit b ngt mch khi r in ni t

(1) nh ngha thit b ngt mch khi r in ni t Thit b ngt mch khi r in ni t l thit b ngt ngun in cung cp nhanh chng khi xy ra s c r in ni t, gip bo v c th khi s git in thng qua vic thit b bo v qu dng ca pha ngun in vn hnh vi dng in rt nh m chng ta khng cm nhn thy. Do nh mc thit b ngt mch khi r in ni t nhm bo v c th khi s git in l 30mA, 0.03 giy.

(2) Nhn bit bng nt kim tra (Test Button) Thit b ngt mch khi r in ni t nu phn loi v mt ch to th chng ta c th phn thnh loi vn hnh dng in v loi vn hnh in p, c phng php phn loi kiu in t v kiu my mc hoc phn loi theo nhy cm nhng nu chng ta phn loi theo kha cnh ngi s dng phng trnh in git th c nhng loi nh sau. Nt kim tra mu xanh

y l sn phm chuyn dng khi xy ra s c r in ni t nn rt cm c thit b bo v qu dng ring khi ct mch

Nt kim tra mu Dng bo v qu dng v bo v khi s c r in ni t nn khng cn lp t thit b bo v qu dng.

08


PHNG NGA TAI NN IN

An ton in

16

Chng 1

Hnh v 1-4 Cc loi thit b ngt mch khi r in ni t

Phn loi theo hnh dng

a. Loi thng dng Thit b ngt mch khi r in ni t s dng mt cch ph bin

Hnh v 1-5 Thit b ngt mch khi r in ni t kiu thng dng

b. Thit b ngt mch khi r in ni t kiu u ni dng cm

u ni c th cm vo trong ting Hn gi l phch cm/ cm do n li c phn loi thnh kiu phch cm, kiu cm, kiu b iu hp.

Hnh nh 1-6 Thit b ngt mch khi r

in ni t kiu cm Hnh nh 1-7

Kiu phch cm

Hnh nh 1-8 Kiu b iu hp


17

(3) Nguyn l vn hnh ca thit b ngt mch khi r in ni t Trng thi bnh thng

Ch c dng in ph ti mi chy qua my bin dng th t khng khin cho t trng xut hin ti my bin dng th t khng cn i ln nhau do chng ta khng th pht hin ra dng in h mch nn cun nh ca thit b ngt mch khng hot ng v th khng th ngt mch.

Hnh v 1-8 Trng thi bnh thng

Trng thi s c r in ni t

T trng do dng in ph ti cn i ln nhau nn chng ta khng pht hin ra nhng t trng do Ig dng in s c c pht hin trong my bin dng th t khng nn cun nh vn hnh v lm cho thit b ngt mch vn hnh.

Hnh v 1-9 Trng thi h mch

(4) Nhng iu cn ch khi s dng thit b ngt mch khi r in ni

t Thit b ngt mch khi r in ni t vn hnh bi dng in rt nh vi nhy dng in nh mc thng thng 30mA nn chng ta cn ch nhng hng mc sau.

Cun

My bin dngth t khng

Cun Pht hin

My bin dng th t khng


PHNG NGA TAI NN IN

An ton in

18

Chng 1

Cho d xy ra h in mt cch c bn trong b bin i hot ng theo phng thc khng tip a th dng in s c lin quan vn chy qua nn thit b ngt mch khi r in ni t khng hot ng.

Phi th bm nt kim tra ca thit b ngt mch khi r in ni t hn 1 ln 1 thng. Nu khng kim tra nh k c th xy ra trng hp thit b ngt mch khi r in ni t khng hot ng khi xy ra s c nn chng ta cn thc hin kim tra nh k hn 1 ln 1 thng.

C trng hp vn hnh sai do sng in t hay dng in r r. Thnh thong xy ra trng hp t nhin b st ngun trong khi ang s dng in thoi di ng hay b m gy ra s hn lon.

Tip a v thit b ngt mch khi r in ni t phng trnh tai nn in git, phng php thc hin hon chnh cng trnh tip a bn ngoi v phng php s dng thit b ngt mch khi r in ni t l nhng phng php hu hiu nht, nh vy chng ta cn la chn phng php no trong s 2 phng php tip a v thit b ngt mch khi r in ni t? Phng php l tng nht l hon thin cng trnh tip t bn ngoi duy tr gi tr in tr tip t mc rt thp v b sung thit b ngt mch khi r in ni t kiu b u ni dng cm ti nhng ni c nhiu hi m nh nc. Nhng ngc li, nu lp t thit b ngt mch khi r in ni t v lc b vic tip a th khng th c gi l i sch phng chng tai nn in git mt cch ng n. Trn thc t chng ta ch lp t thit b ngt mch khi r in ni t do thnh thong c trng hp t vong do in git khi b h mch. Cui cng, trong cc i sch phng chng tai nn in git do h mch th phng php tip a bn ngoi tt c xem l phng php tt nht v khi ny nhng iu chng ta cn lu l trc khi bt u thc hin cng trnh tip a chng ta cn thit k tip a mt cch ph hp, phi lp t trc cc tip a nh thanh tip a hay mng tip a. Nu chng ta thc hin khng cn thn th sau ny nu chng ta mun chun b phng n i ph, ging nh vic git nc b trn chng ta ch c th lp t cm kiu khng tip a v trng cy vo thit b ngt mch khi r in ni t.

09

Chng1

Nhng iu cn ghi nh trong chng ny

1.Phn ng ca c th i vi in git

Hnh v 1-3 Phn ng ca c th i vi dng in (IEC 60479-1)

2.Phn ng ca c th vi dng in quy cch

Loi Phn ng ca c th Loi Dng in gy cm gic b in git nh

nht Cm gic t t 0.5~1[mA]

Dng in thot ra khi c th

Dng in mc gii hn cao nht c th cn ch kh nng thot khi ni tip xc ngun in. (au khng chu ng ni).

7~8[mA]

Dng in tch t trong c th

Dng in lm cho c th c cm gic b in git nhng khng kh nng thot khi ni tip xc ngun in (B co rt c).

10~15[mA]

Dng in gy rung tm tht

Mt chc nng tim, d c tch ri ra khi ngun in th cng t vong trong vi pht.

Thi

gian

dn

g i

n i

qua

(mili

ph

t)

Cng dng in i qua (mA)

Chng1


3. i sch phng chng in git do h mch

(1) S dng sn phm c kim nh v quy cch. (2) o in tr cch in theo chu k kim tra s h mch. (3) Tip a bn ngoi phn kim loi ca cc thit b in. (4) S dng dy in c bc dy tip a ct mch khi b h mch. (5) S dng thit b ngt mch khi r in ni t kiu u ni dng cm. (4) Trng hp thao tc dy trn khng trong trng thi mt in cn lin lc vi

cng ty in yu cu thc hin nhng vic cn thit. (5) Khi thao tc lc mt in, ngi thao tc cn lin lc vi ngi ph trch ca

cng ty in. (6) Cn c ngi lp t v theo di bng hin th nguy him trn dy trn khng

v gim st vic thao tc.

Chng 2_ in git do tip xc vi phn ni in v phng php phng An ton in

21

C th tm hiu v hin tng b in git do tip xc vi phn ni in v cc phng php phng trnh s c ny.

in git do tip xc vi ng dy trn khng

Nhng trng hp b in git do tip xc vi ng dy trn khng ch yu xy ra ti nhng cng trnh xy dng v nguyn nhn quan trng ca nhng s c ny c k n nh sau: (1) Tip xc vi ng dy in trn khng khi ang s dng cc vt liu cng trnh c

kh nng nhim in nh ng thp, thp cn di. (2) Tip xc vi ng dy trn khng khi s dng trang thit b xy dng nh my

ng cc cu loi di ng.

Hnh v 2-1 V d b in git khi tip xc vi dy in trn khng

01

Chng 2 in git do tip xc vi

phn ni in v phngphp phng

in git do tip xc vi phn ni in v phng php phng

PHNG NGA TAI NN IN

Chng 2

An ton in

22

Phng php an ton khi thc hin cc cng vic c lin quan n ng dy trn khng (1) Lm vic an ton trong khu vc gn ng trn khng Lp k hoch phng thit hi do in git trc khi tin hnh cng vic. Lp t dng c bo v v cc thit b phng nga cch in trong trng hp dy

trn khng trong tnh trng dy ang c in chy qua. Vic lp t dng c phng h, thit b phng nga cch in phi c thc hin

theo phng php lp t thch hp v y l trang thit b s dng khi c in hot ng trong dy sau khi c cn b s dng dng c bo v cch in.

Trng hp lm vic trong tnh trng mt in ng dy trn khng, cn phi lin lc vi cng ty in lc yu cu x l cn thit.

Nu lm vic trong trng hp mt in th cn phi chc chn c s lin lc gia ngi thc hin v cn b ph trch ca cng ty in lc.

Lp t bin bo nguy him trn ng dy trn khng, c cn b gim st li gim st cng vic thc hin.

(2) Phng php lp t dng c phng h

Vic lp t dng c phng h cho nhng ng dy cao p trn khng trong trng thi in ang hot ng chnh l cng vic phi thc hin trong khi in cao p ang hot ng, v th ng dy ni in khng b h (d cc thit b phng h vn ang c hot ng) th khi tc nghip cn ch nhng ni dung di y: Cn b ph trch ch o cng vic phng h sau khi a ra cc ch th v phng

php v th t lp t trang thit b phng h i vi nhng cn b thc hin. Phi sa cha, x l tt cc dng c phng h c kh nng cch in v kim tra

xem c li, c b phn no b hng hc hay khng trc khi s dng. Cn b thc hin phi s dng dng c phng h cch in bo v c th ca

chnh bn than mnh v cn b ph trch quyt nh bt u cng vic sau khi kim tra tnh trng s dng ca cc dng c bo v ny.

Gii thch thut ng Dng c phng h, thit b phng nga cch in: Tm cch in,

lp bao ph cch in, ca v hng ro cch in dng chng in git c lp t ti nhng v tr ni in xut hin trong khi thc hin cng vic gn khu vc c s hot ng ca in cao p.

Dng c bo v cch in: M bo h, gng tay cao su, giy cao su .c chc nng cch in c ngi thc hin cng vic s dng chng in git.

Dng c dng lm vic khi in hot ng trong dy: thanh nng (hot stick), que vi cu dao c phn tip xc tay cm c lm bng nhng vt liu cch in, t c th thc hin gin tip cng vic khi tip xc vi nhng dy c in hot ng

Trang thit b dng lm vic khi in hot ng trong dy: xe t dng khi lm vic tip xc vi in, cu thang cch in, my ht bi cch in, bn cch in dng trong khi tip xc vi in . c s dng kim tra, sa cha nhng ng dy ni in.

02


23

Khi lm vic trn cao, cn phi lm thnh t 2 ngi, khng c lm c lp, ring r.

Phi s dng gin gio, gi hoc s dng trang thit b dng trong khi tip xc in hot ng v thao tc nghip v vi t th an ton.

Lp t dng c phng h cch in theo th t ln lt t ng dy ni in gn vi c th ngi, v khi tho d dng c cn phi thc hin theo trnh t ngc li, t ni xa vi c th ngi nht.

Ch gng tay cao su cch in khng b tn thng ti v tr li ln ca thit b u cui trong dy in v dy kt ni.

Phi c nh chc chn dy cao su dng c phng h cch in khng kh di chuyn hoc b ri ra trong khi ang tc nghip.

(3) Phng php phng trnh in git khi s dng trang thit b xy

dng nh cn cu Kim tra nhng vt khng cn thit, vt dng nguy him ti hin trng s dng

sn phm v phn cng cng vic vi cn b thc hin ti hin trng ri ln kt hoch tc nghip.

La chn ci bo dng s dng trang thit b. Ci bo phi c t ti v tr khng che khut tm mt v phi lm sao cho c th lin lc nhanh nht vi ngi li my.

Tm kin nhng phng tin s dng chng in git khi lm vic vi ng dy trn khng t thi im lp rp, chun b thit b. Phng tin chng in git phi c tip t on mch sau khi tnh in vi dy trn khng, v phi lp t dng c phng h vo ng dy trn khng trong trng hp cng vic tnh in gp kh khn.

Trng hp khng c cc iu kin nh trn, phi duy tr khong cch lm vic an ton nh sau. Khong cch lm vic an ton l khong cch cn phi cch ly t dy in n khng ch cc thit b nh my cu, m cn n vt c ti, cn trc (boom) dy thp (wire).

Trng hp vt c ti b ri ra hoc khi di chuyn trn tuyn ng khng bng phng, cn lu cn trc khng b vng ra.

Khng c bo qun vt liu bn di ng in trn khng.

Bng 2-1 Khong cch cch ly an ton (OSHA, NFPA 70E) in p Khong cch an ton22.9 kV 3m

154 kV 3.5m

345 kV 4.5m


PHNG NGA TAI NN IN

Chng 2

An ton in

24

Phng php an ton khi s dng trang thit b xy dng nh cn cu

(3) X l trong trng hp trang thit b xy dng nh cn cu tip

xc vi ng in trn khng Khi cn cu tip xc vi ng in trn khng, in p gn tng ng vi in p ca ng dy trn khng s b truyn vo my cu, v th ngi tip xc vi b phn cha kim loi ca my cu c th s gp phi mi nguy him v mt tnh mng. V vy ngoi ngi gp s c, th ngi li my cn phi lu nhng ni dung sau y khng gp phi tn hi cho bn thn mnh. Trng hp ng in trn khng b t v ri xung t, d dy in b ngt

nhng khng c ng gn hoc tip xc vi v tr dy ri v phi nhanh chng lin lc vi cng ty in lc.

Trng hp ngi trc tip tc nghip b in git vo my cu, khng c s trc tip vo ngi b in git m phi s dng tm bn kh, dy thng . di chuyn ngi b nn n v tr an ton ri tin hnh h hp nhn to.

D my cu tip xc vi ng dy trn khng nhng phn ln ngi li my u an ton, nn cn phi iu chnh my cu sao cho my ri khi v tr ng dy trn khng .

Trng hp dy in b t v qun vo my cu, ngi li my cn phi bnh tnh ngi yn ti v tr li v gi tinh thn.

Sau , ngi li xe ri khi v tr li, ch khng tip xc vi phn thn ca my cu, nhy ra khi my cu.

Ch khng b tip xc vi my cu khi nhy t khoang my ra ngoi ri thot ra hng ngc li vi my cu.

Kim tra nhng vt khng cn thit, vt dng nguy

him ti hin trng s dng sn phm v phn cng cng vic vi cn b thc hin ti hin trng v

ci bo phi c t ti v tr khng che khut tm mt c

th lin lc nhanh nht vi ngi li my.


25

Phng php an ton khi my cu tip xc ng in trn khng.

Tip xc v tr tip in khi ang tc nghip v in Hnh nh di y l v d v s c b in git khi ang sa phn dy cp hn b tn thng sau khi ngt ngun in bng cu dao ti t iu khin, nhng li c cn b khc n v khi ng li cu dao in. V d v s c xy ra khi ang tin hnh bo tr, kim tra nh trn rt khc vi trng hp b h in. V khng th gii quyt bng cch tip t hay ngt cu dao h in nn cn phi c bin php khc, v mt s bin php thng hay c ngh n nht l s dng cc cng c bo v nh gng tay cch in, giy cch in . Tuy nhin, c mt phng php hu hiu hn th, l quy nh p dng v phng php lp t cc trang thit b ng ngt, nhn mc k hiu c c s an ton khi lm vic ngay c trong Lut y t an ton cng nghip.

Hnh v 2-2 V d b in git khi ang lm vic v in

03

t dy


PHNG NGA TAI NN IN

Chng 2

An ton in

26

Phng php an ton khi lm vic v in Vic lp t thit b ng ngt, nhn mc k hiu c c s n ton trong khi lm vic lin quan n in nh trn c ngha l vic lp ra nhng quy nh, tiu chun v an ton lm vic v phi tun th n mt cch nghim ngt. Hu ht ti nhng khu vc lm vic u c nguyn tc v an ton lm vic ring. Tuy nhin c rt nhiu trng hp thc hin khng tt th tc, quy trnh lp t thit b ng ngt, nhn mc k hiu mt ni dung trng tm quan trng thuc ni dung nguyn tc ni trn, v th m nhng phng php an ton ny thc t cha c thc hin mt cch trit . Nguyn tc an ton lm vic l phi quy nh nhng quy trnh ring khc bit ty theo iu kin ca tng khu vc lm vic. Tuy nhin nguyn tc an ton c bn c th k n nh sau: Ngt ngun in. Trnh vic khi ng li ngun in (thit b ng ngt/ nhn mc k hiu, Lock Out/

Tag Out). Kim tra xem ni lm vic c in p hay khng. Tip t. Kim tra xem tt c mi quy trnh c c thc hin hp l hay khng. (1) Nhn mc k hiu

L du hiu cnh bo nguy him, cm thao tc, ch cho bit khng c khi ng my mc, thit b. Ghi r l do dn nhn, ngy thng thc hin, ngi thc hin ln nhn mc v khng c ti s dng li nhng nhn mc c lm bng giy hoc giy cc tng. Tuy nhin, nhn mc plastic th c th ti s dng sau khi thay i ni dung.

Hnh v 2-3 Lock Out/ Tag Out

04


27

(2) Thit b ng ngt L nhng trang thit b tng t nh kha hoc Blocking c chc nng ging kha c s dng thit b, my mc khng hot ng c. Thit b ny gip duy tr trng thi an ton my mc, thit b khng t b khi ng.

Hnh v 2-4 Thit b ng ngt ca cu dao mng li in (Minh ha 13)

Hnh v 2-5 Thit b ng ngt ca bnh quay tc ng bn ngoi ca cu dao mng in

Hnh v 2-6 Thit b ng ngt cng tc

Chng2


1. Phng php an ton lm vic i vi dy in trn

khng (1) Lp k hoch phng nga s c in git trc khi thc hin cng vic. (2) Lp t dng c phng h cch in trong tnh trng ng in trn khng c

in ang hot ng. (3) Dng c phng h cch in l dng c dng lm vic khi tip xc vi in

ang hot ng, sau khi s dng cc dng c bo v cch in, v vy cn phi tin hnh lp t theo phng php c quy nh.

(4) Trng hp lm vic vi ng in trn khng trong tnh trng mt in th cn phi lin lc vi cng ty in lc c th yu cu x l cn thit.

(5) Khi lm vic trong tnh trng mt in, cn phi c s lin lc thng xuyn gia k s thc hin v cn b ph trch ca cng ty in lc.

(6) Lp t bin bo nguy him ln ng in trn khng, c cn b gim st gim st cng vic.

2. Phng php an ton khi lm vic v in (1) Ngt ngun in. (2) Trnh vic khi ng li ngun in (thit b ng ngt/ nhn mc k hiu,

Lock Out/ Tag Out). (3) Kim tra xem ni lm vic c in p hay khng. (4) Tip t. (5) Kim tra xem tt c mi quy trnh c c thc hin hp l hay khng. Gii thch thut ng Dng c phng h, thit b phng nga cch in: Tm cch in, lp

bao ph cch in, ca v hng ro cch in dng chng in git c lp t ti nhng v tr ni in xut hin trong khi thc hin cng vic gn khu vc c s hot ng ca in cao p.

Dng c bo v cch in: M bo h, gng tay cao su, giy cao su .c chc nng cch in c ngi thc hin cng vic s dng chng in git.

Dng c dng lm vic khi in hot ng trong dy: thanh nng (hot stick), que vi cu dao c phn tip xc tay cm c lm bng nhng vt liu cch in, t c th thc hin gin tip cng vic khi tip xc vi nhng dy c in hot ng

Trang thit b dng lm vic khi in hot ng trong dy: xe t dng khi lm vic tip xc vi in, cu thang cch in, my ht bi cch in, bn cch in dng trong khi tip xc vi in . c s dng kim tra, sa cha nhng ng dy ni in

Chng 3_ Nguyn nhn v phng php phng chng chy n do in An ton in

29

Chng ta c th tm hiu v nguyn nhn v phng php phng chy n do in.

Ha hon t in

(1) Nguyn nhn gy ha hon do in V c bn, dng in c truyn i nh dy in cu to thnh bng mch, nn khi c mt ngun in qu ln i qua dy in hoc dng in chy ra ngoi khi dy in th c th gy pht sinh nhng s c nh ha hon hoc in git. Ni ngun in i ra khi dy in tc l ni n nhng hin tng nh h in, tia la in, cung la in. Ni dung v ngun pht la do in s c cp n mt cch chi tit pha di y.

(2) Ngun pht la in in qu ti

Khi in lu chy qua dy in s pht sinh nhit lng Joule (H=I2Rt), nu nhit pht sinh c bc x th s khng gy nguy him pht ha, nhng nu nhit b tch ly li th n s ln dn ln, v y s c th tr thnh nguyn nhn to ra ngun pht la. Ton b ngun dy in cn phi c quy nh dng in ti a c th chy trong dy mt cch an ton theo iu kin s dng v c tnh ca dy in . Ci ny c gi l dng in cho php ca dy in v khi dng in vt qu ch s ny, to ra mt dng in qu ln chy trong dy in th ngi ta gi l in qu ti.

01

Chng 3 Nguyn nhn v phng

php phng chng chy ndo in

PHNG NGA TAI NN IN

An ton in

30

Tm li, khi dng in vt qu mc cho php tip tc chy trong dy in, dy in b nng ln th s rt d gy nhit ha lp v bc ngoi (trng hp lp v bc ngoi dy in l nha tng hp th lp v bc ngoi s b mng dn i ri t), v cng c trng hp nu in qu ti tip tc b tng ln th nhit trong dy in s tng ln nhanh chng v gy pht ha. Theo kt qu th nghim th s pht sinh chnh lch ty theo nhit , a im, tuy nhin thng thng th i vi trng hp dy in bc vinyl cch in, khi dng in vt qu gp 2~3 ln th lp v bc bn ngoi s b bin hnh, bin cht, b t gy v nu dng in vt qu gp 5~6 ln th dy in s tr nn qu nng, sau s b tan chy.

on mch Khi lp v bc ngoi dy in b long ra hoc lp cch in ca thit b in b ph hng, khin cho hai si dy in b tip xc trc tip th dng in gp s c , hay cn gi l dng in on mch s chy v pha tip xc c in tr nh hn l pha thit b in c dng in kt ni vi dy in. Hin tng ny c gi l on mch (Short) v n s tc ng n im pht ha do s kt hp ca nhit cao v cung la (arc) pht sinh bi in on mch. V vn on mch ny, c th chia ra thnh hai loi l on mch hon ton v on mch khng hon ton nh di y. a. on mch hon ton

Khi hai si y in tip xc trc tip, gy t mch hon ton th s pht sinh nhit cao trong mt khong thi gian ngn, lm chy u ni dy v khi ny dng in on mch s l hng ngn ampere. Trong trng hp ny, nu lp t thit b aptomat v c hoc cu ch vi dung lng ph hp vo pha ngun in th s khin ngn dng in mt cch nhanh chng. Cn nu khng lp t thit b th s c th gy ra chy, n.

b. on mch khng hon ton Khi cch in gia hai dy in b km i nhiu th s c kh nng dng in cng ln s chy n v gy chy ti v tr lp v bc ngoi dy in hoc b mt ngoi ca vt cch in tip xc nhau. Lc ny, cung la s xut hin do s c on mch nh ti v tr lp v bc dy in u tin b hng v t hin tng cung la ny th lp v bc bn ngoi cch in s b km i, tc ng thnh im pht la.


31

on mch hon ton v khng hon ton

H in Theo ngha rng, h in l hin tng dng in khng i ng ng m chy ra khi ng dy ng, ging nh nc b thm ra ngoi. Ni mt cch c th th vt cch in ca lp v bc dy in hoc thit b in b pht nhit hoc dng in chy xung b mt t thng qua nhng vt cht kim loi, do vn h hngv mt my mc. Khi pht sinh ng dy b h in t phn sc in xung n t, nhit s c sinh ra do dng in h, vt cht cch in s b ph hy mt cch cc b v t trng thi h in s cng tr nn trm trng hn. Nu tip tc lm tng dng in h th lng nhit pht sinh s cng ln hn, t s gy ra im pht la. Thng thng, trong iu kin bt la tt th ch s ti thiu ca dng in h c th gy pht la l 0.3 ~ 0.5A. C nhiu trng hp c th pht la trong khong t vi n hng chc A ty theo iu kin xung quanh, c th ko di trong thi gian cn thit hoc t vi chc pht cho n hng thng. S nguy him ca hin tng h in khng ch l gy thit hi v mt con ngi do b in git m cn c th gy ha hon do in v phng trnh nguy c ha hon do in th cn phi quy nh khng c ch s dng in r r vt qu 1/2,000 dng in ti a.

on mch tng on mch tng phn l tnh trng cc lp dy in b t khng cng im trong lp v bc, hoc mt phn ca dy thp in cn li m cha hon ton t hn. Khi c dy in cha t hn trong dy cord th c th pht sinh nhng hin tng nh sau: a. Thit b in tt, m lin tc mi khi dy cord dch chuyn

Nu s kt ni gia cc dy in

c vn th trong mt lc no , dng in qu

ln chy qua, lm pht sinh cung la in hoc

lp v cch in b oxi ha nn s

gy chy n ch sao.

Trong trng hp on mch hon ton, hai on dy in tip xc trc

tip vi nhau th s gy chy do tia la bn ra, nhng cn

trng hp on mch khng hon ton th ti sao

li c th gy chy ch?

Nguyn nhn v phng php phng chng chy n do in

PHNG NGA TAI NN IN

An ton in

32

Chng 3

b. pha bn trong v pht ra m thanh nh. c. lp v bc bn ngoi ca phn on mch s pht sinh nhit v c mi l. Bi v on mch tng phn l on mch mang tnh cht vt l ch yu pht sinh trong dy cord, nn khi khong cch gia cc phn on mch ngn, lm cho dy cord mi khi dch chuyn th s gy hin tng ngt ri li ni, lm lin tc to ra cung la . Nu trng thi ny xy ra lin tc trong mt thi gian di th s dng in s bt u chy ti phn b carbon ha trong lp v bc cch in, t s dn ti hin tng on mch trong dy hoc mt phn ca dy in b on mch trc s b kt bm, lm cho dy cord b tng nhit qu mc mt cch cc b.

Cung la in Khi tt m bng mch in bng cng tc hoc khi cu ch b chy s gy pht sinh cung la in, c bit so vi khi tt bng mch in, th khi ngng s dng hoc so vi khi dng in xoay chiu th trong trng hp dng in mt chiu hin tng ny s cng trm trng hn v cung la in s d dng b sinh ra. Khi , nu trong iu kin d pht n nh c cc vt cht bt la xung quanh hoc c kh gas d chy th s to ra im pht la v c th gy ra chy, n.

Nhit ha cch in Vt cht cch in trong dy in hoc trong cc my mc thit b ch yu l c lm bng vt cht hu c, tuy nhin vt cht hu c thng b nhit ha sau mt thi gian di s dng, lm cho in tr cch in b yu i. c bit, vt cht cch in hu c nu tip tc b gia nhit trong iu kin nhit cao ti v tr m khng kh lu thng km th n s b oxi ha v bt u hnh thnh kh nng dn in. Nu c in p dn n y th hin tng xi ha s tip tc tng ln do s tng nhit ca dng in v cui cng, bn thn vt cht hu c s b chy hoc bt la vocht d chy xung quanh. Hin tng ny c gi l hin tng xi ha do nhit ha cch in.

Qu nhit phn tip xc Nu dng in chy trong trng thi vic tip xc khng din ra hon ton ti nhng vt cht dn in nh mt tip xc gia dy in v dy in, dy in v cm, b phn tip ni s b pht nhit do in tr tip xc v t y s c th tr thnh ngun pht la in. Ni mt cch chi tit th b phn pht nhit cc b nh th ny (phn tip xc s xy ra hin tng gin n ri co li lp i lp li mt cch lin tc, ng thi sinh ra hin tng xit ng mang tnh in v t y, phn pht nhit s tr nn sn si hn, in tr tip xc s tng ln mnh hn, dn ti trng thi nng v cui cng, s gy pht la ti nhng vt cht cch in xung quanh.

Tnh in Tnh in l hin tng sinh ra do ma st gia cc vt cht, v ln cng nh


33

cc tnh ca tnh in ph thuc vo dy in ma st (triboelectricity series. Trng hp tnh in chuyn thnh im pht la th s dn n vic phng la vo khu vc tnh in trong mi trng c nguy c chy, n cao. Ngoi ra, c th phn loi phng in hoa (corona, phng in chi (brush or strimmer, phng tia la in hoc phng in lin tc.... ph thuc theo hnh thi v cng pht quang.

(3) Phng php phng trnh chy, n do in S dng thit b in ng cch

Tt c cc thit b in u c ch tiu nh mc ring v in nh in p, in lu dng in, v cch thc s dng ca mi loi thit b theo u khc nhau. Cch s dng c bn nht l tun th theo ng ch tiu nh mc, ch sao cho thit b c ni vi ngun in ph hp v khng b pht sinh qu ti, phng thc khi ng cng phi c thc hin theo ng ni dung hng dn ca cng ty sn xut.

Bo v dng in qu ti Thit b in sau mt thi gian s dng s d b nhit ha do lo ha, t c th gy ra nhng s c khng th d on trc c. Vic kim tra, bo dng nh k l rt cn thit, tuy nhin do c s hn ch nn ty theo tng thit b in, cn phi la chn ph hp cc thit b bo v nh cu ch, p t mt, rle bo v ... lp t. i vi dy in, ngoi vic lp t thit b bo v bo v dy in th cn phi tun th ch tiu nh mc v dng in theo tiu chun dng in cho php ca dy, v ngoi ra, cn phi cho dng in chy trong dy ty theo ch tiu nh mc v nhit ca thit b u cui (terminal m dy in kt ni.

Chng chy n cho thit b in a im c s dng vt cht d chy cn phi c coi l khu vc c nguy c pht n v cn phi son tho v qun l biu phn loi. Khu vc c nguy c pht n c phn loi thnh loi , loi 1, loi 2 v phi s dng nhng thit b in c cu trc chng pht n ph hp theo tng loi nh di y.

Tng cng kim tra mi ngy, nh k Thit b s dng in c th gy pht sinh nhit ha hoc hng hc do cc nguyn nhn khc nhau ty thuc vo cch thc s dng thit b nh th no. Theo , cn phi kim tra nh k ti thiu t nht mt ngy 1 ln xem c vn g xy ra khng c th loi b trc nhng nguyn nhn c th gy ra chy, n.


PHNG NGA TAI NN IN

An ton in

34

Chng 3

Thit k v thi cng an ton, ph hp Trong cc nguyn nhn c th gy chy, n, c phng php qun l ngun pht la in mt cch hiu qu, tuy nhin phng php hu dng nht l vic la chn lp t thit b v dy in c cng sut trong giai on thit k, thi cng lp t thit b, my mc s dng in. V phi tin hnh thi cng theo ng quy nh an ton th mi c th ko di tui th v an ton cho sn phm. Theo , cn phi song song thc hin cc yu t nh an ton v thi cng ng cch trong giai on thit k.

Biu 3-1 Thit b in c cu trc chng chy n theo tng khu vc c nguy c chy n

Khu vc nguy him Cu trc thit b in c kh nng chng n Loi Cu trc chng pht n an ton (ia)

Loi 1

Cu trc chng pht n an ton (ia, ib) Cu trc chng n p sut trong (d) Cu trc chng n p sut (p) Cu trc chng n np in (q) Cu trc chng n dng vo (o) Cu trc chng n tng an ton (e) Cu trc chng n khun c (m)

Loi 2

Cu trc chng pht n an ton (ia, ib) Cu trc chng n p sut trong (d) Cu trc chng n p sut (p) Cu trc chng n np in (q) Cu trc chng n dng vo (o) Cu trc chng n tng an ton (e) Cu trc chng n khun c (m) Cu trc chng chy n khng bt la (n)

Tnh in (1) L lun v tnh in

Bn trong cc vt th u c electron t do di chuyn mt cch thoi mi gia cc phn t cu to nn vt cht v cc electron lin kt c kt ni vi nhau bi lc in t gia cc phn t . Nu c s thay i v ma st ti cc vt cht ny th electron t do s di chuyn, vt cht trung tnh in t s t cc tnh dng +, m - . Tm li, thng qua vic vt cht phng ra electron t do s c phn loi thnh cc tnh dng +, vt cht thu c eclectron t do s c phn loi thnh cc tnh m -, th tnh in s c sinh ra.

02


35

Lng in np ca mt electron rt nh vi khong 1.6 x 1-19 nhng s cc electron tng i nhiu nn ch cn tc ng bin i mt cht vo vt cht l c th to ra hng nghn V tnh in.

(2 ) To tnh in C th to thnh

Thng thng, tnh in c to thnh t vt th rn, nhng n cng c th c sinh ra t cht lng hoc cht kh. Ging nh hnh (3-1, khi hai vt th khc nhau tip xc vi nhau ri li c phn ly, th tnh in s c sinh ra ti b mt ca hai vt th , v c th chia 3 giai on: hnh thnh hai lp in mt tip xc, tng in th do s phn l ca hai lp in, tiu hy in tch c phn l. Hin tng in np pht sinh khi qu trnh 3 giai on ny lin tc sinh ra.

Phn ly do s tc dng ca my mc

Mt tip xc Mt tip xc

a. S di chuyn ca in tch do tip xc b. Hnh thnh 2 lp in c. To thnh tnh in do s phn ly Hnh v 3-1 To thnh tnh in do s tip xc phn ly

Nguyn nhn gy nh hng n s hnh thnh tnh in

a. c tnh ca vt th Ging nh v d v dy in ma st (triboelectricity series ca bng biu (3-2, kch thc v cc tnh ca tnh in pht sinh do loi hnh v s t hp ca 2 vt th tip xc, phn ly... s b chu nh hng.

b. Trng thi b mt ca vt th Hin tng pht sinh tnh in l hin tng xut hin ti phn b mt hoc mt ranh gii, v th trng thi b mt ca vt th s nh hng ln n s hnh thnh tnh in. Thng thng khi b mt sn si, th rp v khi tn ti hi nc, bi bn, cht xi ha trn b mt th s pht sinh tnh in s cng tng ln.

c. L lch ca vt th L lch pht sinh tnh in v np in ca vt th s gy nh hng n vic to tnh in ln b mt vt th ty theo s bin i tnh cht ca vt v trng thi np in. Thng thng s to thnh tnh in ny s rt ln trong ln u tin v s nh dn i do s lp i lp li v lin tc np in

Vt th A Vt th B Vt th A Vt th B Vt th A Vt th B


PHNG NGA TAI NN IN

An ton in

36

Chng 3

d. Din tch tip xc v p sut Din tch tip xc lin quan n phm vi to thnh tnh in, nn dn tch tip xc cng ln th s pht sinh tnh in cng tng. p sut tip xc nu ln th s pht sinh tnh in cng cng cao hn.

e. Tc phn ly Tc vt th c phn ly sau khi tip xc c quan h vi ngun nng lng c cp vo khi phn ly in tch, v th tc phn ly cng ln th s pht sinh tnh in cng tng. Khi kho st dng +, m - ca in vo trong hin tng tnh in, ty theo loi hnh vt cht i phng tip xc, phn ly th in tch dng hoc m s sinh ra. Nu lit k nhng cht ny ra xem th ging nh hnh (3-2 v ngi ta gi l dy in ma st (triboelectricity series.

(3 ) Cc hnh thc pht sinh tnh in Nhim in masat

in masat l hin tng tnh in pht sinh do s phn ly in tch do cc in th di chuyn bi masat khi vt th ging nh hnh (3-2 to thnh masat.

Nhim in phn tch in phn tch l hin tng pht sinh tnh in do s hnh thnh phn ly in np khi vt th b phn tch ra nh hnh 3-3.

Nhim in chuyn ng Nhim in chuyn ng l hin tng pht sinh in tnh khi lung cht lng chuyn ng thng qua ng ging nh trong hnh 3-4.

Nhim in phng Nhim in phng l hin tng pht sinh khi cc loi phn t, cht kh, cht lng ... phng ra ngoi thng qua nhng ng ng c din tch mt ct nh, ging nh hnh 3-5.

Vt rn trn xoay

Mng cch in in tch di ng

Di ng Phn ly in tch

Tia la in

ng

Thng

Cch in in k

Git Ming vi

Hnh v 3-2 Nhim in masat

Hnh v 3-3 Nhim in phn tch

Hnh v 3-4 Nhim in chuyn ng

Hnh v 3-5 Nhim in phng


37

V cc hin tng nhim tnh in nh trn th cn c nhim in rung (nhim in khuy, nhim in xung t, nhim in dn ....

(4 ) Phng php lm gim bt nhim in tnh Gim b mt tip xc

S nhim in tnh l hin tng b mt do nu lm gim bt b mt tip xc ca vt th rn c phn ly th s lm gim lng in tch b nhim. C th lm sn si, th rp mt cht b mt ca roller lm gim bt b mt ca cht i ng trong quy trnh phn ly.

nh hng ca tc phn ly Gim ti a tc phn ly ca vt th trong tm nhn ca b mt an ton trnh kh nng gy nguy him t tnh in. Khi tc phn ly t khong di 1m/s, nu in tr b mt ca vt th di 1G th hon ton bnh th ng, tuy nhin cc dng c cn bng tc cao (v d nh giy trong my in bo dng xoay ang hot ng cn phi c gi tr in tr thp hn.

H s di truyn (cch in Vic nhim in tnh trc tin l b chi phi ph thuc vo chc nng pht x (work function in t ca vt cht nhim in. Chnh v vy, phng php chc chn lm gim xu hng nhim in tnh l chn mt cht khng c s chnh lch ln nhau v chc nng pht x in t. Nhng cht c h s di truyn thp s nhim in v cc m, ngc li nhng cht c h s di truyn cao s nhim in v cc dng. Tm li, nh bng biu 3-2, khi cc vt cht cch xa nhau b phn ly th s pht sinh tnh in ln, v khi cc vt cht gn nhau b phn ly th s to ra lng tnh in nh.

Gim t l in tr b mt Kh nng duy nht c th lm gim nhim in tnh l lm gim in tr. Bi v in tch sinh ra trong qu trnh phn ly nhng vt th khng c tnh dn in c to ra theo t l in tr b mt ca vt th lin quan. Ty theo in tr ca vt th m mt phn in tch s i qua nhng vt tip t, chy xung t ri b trit tiu. Tip sau t l in tr b mt th t l in tr th tch cng nh hng n s nhim in tnh.

nh hng ca m trong khng kh in tr b mt c s khc nhau ln ty theo m trong khng kh. Tm li, m c coi l mt nguyn nhn quan trng trong trng hp iu kin th nghim, iu kin vn hnh ca thit b c s chnh lch ln. Mt phn ca m trong khng kh s c


PHNG NGA TAI NN IN

An ton in

38

Chng 3

hp th do vt cht cch in, ri to ra nh hng ti c tnh tnh in ca vt cht cch in.

(5) c tnh ca vt cht Dy in ma st

Hin tng tnh in b tch t li c gi l nhim in, tuy nhin ty theo c tnh ca vt cht m cc tnh nhim in c phn loi nh di y. Nu dy cng gim th khi pht sinh ma st gia hai vt cht, in tch cng ln. Tuy nhin, cng c trng hp khng hnh thnh dy in ma st do mi trng xung quanh hoc do trng thi b mt ca vt cht.

Bng 3-2 Dy in ma st Kim loi Bng si Cht t nhin Nha tng hp

(+) (+) (+) (+) Aming Tc ngi, lng th Knh Mica Len Nilong T nhn to

Ch Si t Bng Cotton ay G Da ngi Si thy tinh

Km Acetate Aluminum

Giy Crom

Cao su cng Thp ng Nikel Vng Cao su

Vinyl Bch kim

Polyester Acrylic Polyetilen

Polyvinyl clorua Celluloid

Cellophane Vinyl clorua PTFE

(-) (-) (-) (-)

Trong dy in masat bng trn, khi hai vt cht masat hoc phn tch th vt cht pha trn s nhim in theo chiu phn cc thng ng (+ (straight polarity, cn vt cht pha di s nhim in khng cc (- (non - polar. Lng nhim in ny cng ln khi v tr gia cc tng nhim tin cng xa nhau.


39

c tnh in c ca vt cht Hin tng nhim in ca vt cht chu nh hng theo mc in tch phng ra. Khi in tch b tch ly phng ra t t, vt cht nhim in s duy tr in p cao v ngi li, khi in tch b phng ra nhanh th s to ra dng in phng cng ln. Nu phn ly vt theo theo b mt phng in tch th c th phn loi thnh vt cht cch in, vt cht chng nhim in v cht dn.

Cht dn

Cht chng nhim in

Cht cch in

Hnh v 3-6 Phn loi in tr ca vt cht [ m] Cht dn: Kim loi, nc bin, carbon Cht chng nhim in: Bng t nhin, cotton, g Cht cch in: Plastic, cao su, bng tng hp

(6 ) Phng tnh in (Electrostatic Discharge

Tnh in l hin tng pht sinh do s ma st gia cc vt cht, do ln v cc tnh ca tnh in c quyt nh bi dy in ma st. Trng hp tnh in tc ng thnh im bt la, y s tr thnh nguyn nhn gy ra s phng tnh in trong bu khng kh c nguy c chy n, v ty theo hnh thi v cng ca s pht sng th thng thng c th phn loi thnh phng in corona, phng in blush, phng tia la in, phng in lin tc... Phng in hoa (phng in corona

L hin tng phng in c hnh thnh khi cht dn in (ng knh di 5mm c tch t vi in th cao hoc cht dn tip t c trong in trng cao, c nh sng yu v pht ra m thanh nh. S phng in ny thng khng gy bt la vi gas hoc hi nc do nng lng phng t v n khng c s lin quan vi ln nng lng c lu gi trong vt th nhim in.

Phng in chi (blush L hin tng sinh ra khi c lng nhim in cao gia cht dn c bn knh cong ln (ng knh trn 1mm hoc gia cht lng c t l dn in thp, mt loi


PHNG NGA TAI NN IN

An ton in

40

Chng 3

phng in corona hoc nng lng phng in c th t ti 4[mJ], do khi tip xc vi mi trng c nguy c pht n th n c th dn ti hin tng chy, n.

Phng tia la in S phng tia la in c hnh thnh gia cc cht dn c tip dn khi mt in tch b mt tch t qu ln, lm cho bn cch in hoc cht dn phn cc b nhim in. N c th gy pht sng v m thanh ln, dn ti s c chy, n khi tip xc vi mi trng c nguy c pht n.

Phng in lin tc S phng in lin tc l hin tng c hnh thnh ti b mt cht dn in trong trng hp bi bn c trong thng hay h cha in tch cao, trng hp cht tip t tip xc vo mt sau ca cht dn ph b nhim in theo tng lp mng nhim in nhiu. Ging nh trng hp phng tia la in, hin tng ny c th gy s c chy, n khi tip xc vi mi trng c nguy c pht n.

Hnh v 3-7 Cc loi phng in tnh (7 ) Phng php chng tnh in Tip t v ghp ni (bonding

Vt th c tnh dn in c th trc tip tip t hoc ghp ni vi vt th khc c tip t, t c th lm gim bt tnh trng tnh in. Thng cha ln, ng chn di t ... c xy dng trong t phi c tip t vi in tr rt nh bng cch tip t cc thit b in. V cc vt th di ng hay c th con ngi phi tip t vi 1 .

Tng m Trng hp m xung quanh qu cao, v d nh vo thi im ma ma, vt th nhim in s phng in tch lin tc v tnh in khng phi l vn lo ngi. Khi m tng i t trn 5%, vt cht s t c s cn bng vi trng thi hp th c mt lng hi nc y , v s c c kh nng dn in cho vic chng s tch t tnh in. Ngc li, nu di 3%, th vt th s b kh v c th tr thnh vt th cch in tt, t d hnh thnh s tch t tnh in.

Pht sng

Phtsng

Vt tip t Vt tip t

Vt nhim in

Vt nhim in

Tip cn

(a)Phng in hoa (b)Phng in chi (c)Phng tia la in (d)Phng in lin tc

Vt nhim in

Vt nhim in

Vt tip t Vt tip t


41

Tng tnh dn in Tnh tin rt d b tch t i vi vt th cch in, v vy c th lm gim bt hin tng tnh in bng cch tng kh nng dn in ca vt cht. Cc vt cht cch in ging nh PVC plastic d c tip t cng khng c hiu qu, do c th p dng phng php tng kh nng dn in bng cch ph gia thm carbon black. Trong trng hp l nhin liu th lng th c th s dng cht ph gia c tnh dn in.

Ion ha Tnh trng tnh in s c gim bt bi v khi thc hin ion ha bu khng kh xung quanh ca vt th b nhim in bng +, - th cho kt hp vi ion ca khng kh nu in tch b nhim in l + v ngc li, nu in tch l th kt hp vi ion + ca khng kh.

Chng3


1. Nguyn nhn ch yu v phng php chng ha hon

t in

(1) Nguyn nhn ch yu Dng in qu t on mch H in Tia la in

(2) Phng php S dng ng cc thit b, dng c in Bo v dng in

2. Thit b, dng c in c cu trc chng n ti v tr c nguy c pht n

Khu vc nguy him Cu trc thit b in c kh nng chng n

Loi Cu trc chng pht n an ton (ia)

Loi 1

Cu trc chng pht n an ton (ia,,, ib) Cu trc chng n p sut trong (d) Cu trc chng n p sut (p) Cu trc chng n np in (q) Cu trc chng n dng vo (o) Cu trc chng n tng an ton (e) Cu trc chng n khun c (m)

Loi 2

Cu trc chng pht n an ton (ia,,, ib) Cu trc chng n p sut trong (d) Cu trc chng n p sut (p) Cu trc chng n np in (q) Cu trc chng n dng vo (o) Cu trc chng n tng an ton (e) Cu trc chng n khun c (m) Cu trc chng chy n khng bt la (n)

3. Phng php chng tnh in

(1) Tip t v ni tip (2) Tng m (3) Tng kh nng dn in (4) Ion ha

Cu hi luyn tp An ton in

43

1. Khi xy ra s c b in git, dng in x thi gian gy ra hin tng rung tm tht i vi c th con ngi l bao nhiu? 1mA, .1 giy 1A, 1 giy 1A, .1 giy 1A, 1 giy

2. Khi dng c, my mc in b h in, nu o in tr cch in th ch s o c l

bao nhiu? 3. Hy gii thch mt cch s lc v mc ch lp t dy tip t. 4. Khi tc nghip ti gn ng dy 22,9kV khng lp t dng c bo v th khong

cch ti thiu cn phi cch ly l bao nhiu? 0.5m 1m 2m 3m

5. Sau y l nhng phng php chng thit hi in git do h in. Phng php

no l sai? S dng dy code c gn dy tip t o nh k in tr cch in

Gim bt tip t v lp t my chng h in S dng thit b, my mc in cch in hai ln 6. Thit b, dng c c cu trc chng n khng c s dng khu vc nguy him loi

1 l g? Cu trc chng n p sut trong Cu trc chng n khng bt la Cu trc chng n an ton Cu trc chng n dng vo 7. Phng php hn ch s pht sinh tnh in ph hp nht l g?

Thc hin tip t S dng vt liu plastic c in tr cao

Lm gim m Lm gim tnh dn in

Cu hi luyn tp

Vic sao chp, ti bn, ct b mt phn hay ton b gio trnh ny m khng c s ng ca Cng on an ton cng nghip Hn

Quc th c xem nh l xm phm quyn tc gi.

PHNG NGA TAI NN IN

Tc gi: Cheon Won Woo (Cng on An ton cng nghip & Y t Hn Quc) Bin tp: Phng d liu o to Ngy pht hnh: Thng 09 nm 2007 Ngy pht hnh li: Thng 10 nm 2011 Ngi pht hnh: Baek Heon Kee Ni pht hnh: Cng on An ton cng nghip & Y t Hn

Quc S 478 Munemiro, Bupyeonggu, TP. Incheon

PHNG NGA TAI NN IN

Electrical Accident Prevention(2011)-An Toan Dien

Documents

Transcript of Electrical Accident Prevention(2011)-An Toan Dien