1. MC LCChng 1 : Kin thc c bn in1 - 1 Nhng khi nim c bn trong mch in 41 - 2 Dng bt th in kim tra mch in 91 - 3 Cun dy c li st 121 - 4 in v t 141 - 5 Vt liu cch in 15Chng 2 : Nhng vn c bn ca h thng cp in2 - 1 Truyn ti in 172 - 2 Dy ci 222 - 3 in qung 302 - 4 Vn tip t im trung tnh 322 - 5 Cp in v thng tin 412 - 6 Nhng vn khc 43Chng 3 : Kh c in3 - 1 nh hng ca mi trng i vi kh c in 463 - 2 ng bc (lng) v v s 483 - 3 S sn sinh v dp tt h quang in 513 - 4 u tip xc 543 - 5 B ngt mch du 583 - 6 B ngt mch Hexafluoride lu hunh. B ngt mch khng kh. B ngt mchchn khng 653 - 7 Cng tc cch ly v cng tc cu dao 693 - 8 C cu thao tc v thao tc mch in 743 - 9 Cu ch 783 - 10 Cng tc khng kh t ng 863 - 11 Nam chm in 883 - 12 B tip xc 923 - 13 Rle 983 - 14 B in khng 1043 - 15 Thit b phng chng n in 108Chng 4 : My bin p4 - 1 Nguyn l chung ca my bin p 1124 - 2 Kt cu v cng ngh ca my bin p 1204 - 3 Phng php u dy my bin p 1334 - 4 o th my bin p 1394 - 5 Vn hnh my bin p 1444 - 6 B iu chnh in p v b h cm 152Chng 6 : ng c in khng ng b6 - 1 Nguyn l hot ng c bn ca ng c in khng ng b 1616 - 2 Kt cu ca mt in khng ng b 1716 - 3 Vn hnh mt in kiu lng sc 176 - Trang 1 -

2. 6 - 4 Khi ng v phanh hm mt in kiu lng 1826 - 5 Mt kiu vnh gp 1886 - 6 Mt mt pha 1936 - 7 Mt c gp chnh lu ba pha 1976 - 8 H hng v kim tra sa cha mt 198Chng 8 : Kt cu, cng ngh v nhng vn khc ca my in8 - 1 Kt cu ca my in 2038 - 2 Li st 2098 - 3 Cun dy 2118 - 4 trc 2188 - 5 B i chiu, vnh gp v chi in 2218 - 6 o kim my in 2238 - 7 Nhng vn khc 226Chng 9 . ng dy in lc9 - 1 Nhng vn chung ca ng dy in 2329 - 2 Dy dn 2369 - 3 ng dy mc trn khng , ngoi tri 2419 - 4 ng dy trong nh 2479 - 5 Kt cu cp in 2509 - 6 u ni cp in 2549 - 7 Lp t v vn hnh cp in 256Chng 10 : Tip t v an ton in10 - 1 Kin thc c bn phng in git 26210 - 2 Tip t v tip "khng" 26910 - 3 in tr tip t v an ton in 27410 - 4 Thit b tip t 27810 - 5 Bin php an ton 282Chng 11 : K thut chng st11 - 1 B thu li (B trnh st) 28511 - 2 Kim thu li, dy thu li v khe h thu li 29411 - 3 Chng st cho thit b in 29611 - 4 Chng st cho ng dy 29911 - 5 Chng st cho cng trnh kin trc 30411 - 6 Lp t dy tip t thu li v vn an ton 305Chng 12 : H s cng sut12 - 1 Dng t in nng cao h s cng sut 30812 - 2 Lp dt v vn hnh t in 310Chng 13 : Chiu sng13 - 1 n sng trng 31213 - 2 n hunh quang 31513 - 3 Cc ngun sng khc 321 - Trang 2 -

3. 13 - 4 Mch in chiu sng v vn hnh 323Chng 14 : c qui14 - 1 B tr bn cc c qui 32614 - 2 Dung dch in gii 32714 - 3 Np - phng in ca c qui 32814 - 4 Vn hnh c qui 330Chng 15 : Bo v bng rle v thit b t ng15 - 1 Bo v qu dng in 33215 - 2 Bo v vi sai v bo v chiu 33415 - 3 Bo v th t khng 33515 - 4 Ngun in thao tc 33715 - 5 Thit b t ng 339Chng 17 : K thut in t17 - 1 Linh kin in t 34217 - 2 Thirixto 34517 - 3 Vn hnh thit b thirixto 34817 - 4 Thit b thirixto xc pht v bo v 35017 - 5 Mch chnh lu 35317 - 6 Linh kin v thit b chnh lu khc 36217 - 7 n p ngun in 365Chng 18 : ng h in18 - 1 Kt cu v nguyn l ca ng h in 36718 - 2 S dng ng h in thng dng 37718 - 3 ng h vn nng 38518 - 4 ng h m ga m 39318 - 5 Cng t in v ng h cng sut 40018 - 6 ng h kp (dng gng km) 40718 - 7 Cu in 409Chng 19 : o th din19 - 1 o in 41019 - 2 Th nghim in 418Chng 20 : Nhng vn khc20 - 1 S b in kh 42820 - 2 u ni, hn ni v nhit in 43020 - 3 Xe in 43320 - 4 Linh tinh 435 - Trang 3 -

4. CHNG I KIN THC C BN IN 1 - 1 Nhng khi nim c bn trong mch in 1 - 1 - 1 (Tr v u chng, Tr v Mc lc) Hi: in xoay chiu bin i theo hnh sin, vy cng dng in v inp m chng ta thng ni ly g lm chun? p: Trong mch in xoay chiu, chng ta dng "Tr s hiu dng" lmchun o; bng cch tnh nhit lng m dng in xoay chiu - pht ra khi quain tr bng vi nhit lng m dng in mt chiu pht ra khi chy qua cngin tr, vi thi gian l nh nhau. Tr s ca dng in xoay chiu nh vy gi ltr s hiu dng. 1 - 1 - 2 (Tr v u chng, Tr v Mc lc) Hi: Sau khi mc song song mt pin kh 1.5V vi mt pin kh 1.2V ct mchngoi, mt lc sau pht hin in p cc pin 1.5V nhanh chng st xung, ti sao? p: Khi in th ca hai cc pinmc song song khng bng nhau, th gia haipin c dng in vng (hnh 1 - 1 - 2). Nuin th E1 cao hn E2, tuy ngt mchngoi, gia hai pin vn sinh ra dng invng: E1 E 2 Io = r01 r02 r01, r02 l in tr trong, khi dng in Io chy qua r01, r02 s lm tiu hao innng ca pin c in th cao hn, cho n khi in th El bng E2 th dng in vngIo s bng 0. Cho nn hai cc pin (hoc ACCU) c in th khc nhau khng th mc songsong vi nhau. 1 - 1 - 3 (Tr v u chng, Tr v Mc lc) Hi: Ti sao tr s c trn Ampe k tng ca mch in xoay chiu nhhn tng cc tr s c c trn Ampe k cc mch nhnh? p: Cng dng in c c trn Ampe k tng l tng vc t cng dng in cc mch nhnh, ch khi h s cng sut cc mch nhnh bng nhau, thtng vect cng dng in mi bng tng i s cng dng in cc mchnhnh. Trong thc t, h s cng sut ca cc mch nhnh khng bng nhau, cho nncng dng in c trn Ampe k tng lun lun nh hn tng cng dngin cc mch nhnh. 1 - 1 - 4 (Tr v u chng, Tr v Mc lc) Hi: Ti sao b in tr (dng gia nhit) loi 3 pha u hnh sao, khi t mtpha th dung lng ca n gim mt na? - Trang 4 -

5. p: Vi s u dy th hin hnh 1 - 1 - 4, nu cn 3 pha th dunglng ca n l: 2 3U 0 P = 3U I = r Khi t 1 pha (pha C), lc : Ic = 0 U 3U IA = IB = = 2r 2r 2 3U 3U Pt = PA + PB = UI A (hoc IB) = U = 2r 2r Pt 1 Do : = P 2 Cho nn khi t mt pha, dung lng gim xung cn mt na so vi 3pha. 1 - 1 - 5 (Tr v u chng, Tr v Mc lc) Hi: Th no l cng sut ton phn (biu kin)? Cng sut tc dng (hucng)? Cng sut phn khng (v cng)? p: o Tch tr s hu hiu ca in p v cng trong mch in gi l cng sut ton phn biu kin, tc S = UI. o Cng sut ton phn nhn vi Cosin ca gc lch pha gia cng v in p (tc h s cng sut) l cng sut tc dng (cng sut hu cng), tc P = UIcos. o Cng sut ton phn nhn vi sin ca gc lch pha gia cng v in p gi l cng sut phn khng (v cng), tc Q = UIsin. o Quan h gia 3 i lng l: S2 = P2 + Q2 hoc S = P 2 + Q2 1 - 1 - 6 (Tr v u chng, Tr v Mc lc) Hi: Khi s dng my hn ngn mch (hn bm im) hn thp l th dngin cc ng , nhng khi hn bc l ln ng l th khng th dng in ccng . Nguyn nhn ti sao? p: in tr sut ca thp l ln hn in cc ng nhiu, khi lm ngnmch do in tr ca thp l ti v tr hn ln hn nhiu so vi cc b phn khc camy hn im (tc I2R ca b phn thp l l ln nht), cho nn sinh nhit ln, nngchy cc b m lin kt vi nhau. Khi hn bc l vi ng l, in tr ti v tr hn lc ny thng nh hn incc. Kt qu b phn nng chy trc l in cc, khng th hn c. x lphi s dng kim loi c in tr ln nhng phi c nhit nng chy cao hocdng thi than graphit (nhit nng chy cao) lm in cc. Lc ny phng phphn l li dng nhit cao ca in cc h tr gia nhit, khin mt tip xcgia bc vi ng nng chy trc, nh th mi hn c. - Trang 5 -

6. 1- 1 - 7 (Tr v u chng, Tr v Mc lc) Hi: Gi thit in p ngun l 220V, nu c hai bng n 110V 25W v110V 100W, liu c th mc ni tip hai bng n ny vo mch in khng (dng in p 220V)? Sau khi mc nh vy th kt qu s ra sao? p: Khng c. Bng n khc cng sut th khng th mc ni tip, nuc mc th bng 25W s b chy. 25 25 Dng in nh mc ca bng n 25W l = 0.23A; in tr l: = 473 110 (0.23) 2 100 100 Dng in nh mc ca bng n 100W l = 0.91A ; in tr l: = 121 110 (0.91) 2 Khi hai bng n mc ni tip, u vi ngun 220V th dng in chy qua s l 220 khong = 0.37A . Cng dng in ny vt qu nhiu so vi dng 473 + 121 in nh mc ca bng 25W, do bng n ny s b chy (lc , in p hai u bng n 25W l khong 0.37 x 473 = 175V ch khng phi l 110V). 1 - 1 - 8 (Tr v u chng, Tr v Mc lc) Hi: Mt phn dy in tr ca b in tr b ngn mch, khi a ngunin vo, dy in tr b ngn mch khng nng, cn phn dy in tr khng bngn mch nng ln. Nhng vi mt cun dy qun trn li st b ngn mch mts vng, khi c dng xoay chiu chy qua, th cc vng dy b ngn mch li nnghn rt nhiu so vi cc vng dy khng b ngn mch. Vy l ti sao? p: Mt b phn b in tr b ngn mch, khi c in, dng in khngchy qua dy in tr b ngn mch cho nn khng nng. Cun y qun trn li st khi c b phn b ngn mch, tng ng nhcun th cp ca bin th t ngu b ngn mch. Lc ny cng dng in chyqua b phn b ngn mch ln gp nhiu ln so vi bnh thng, sinh ra nhit nng,lm tng nhit . 1 - 1 - 9 (Tr v u chng, Tr v Mc lc) Hi: Ti sao in tr xoay chiu v in tr mt chiu ca cng mt si dydn li khng ging nhau? p: Khi dng in xoay chiu thng qua dy dn, mt phn b dng introng tit din dy dn l khng ging nhau, cng gn tm dy dn th mt dngin cng nh, gn b mt dy dn th mt dng in tng i ln. Hintng ny gi l hiu ng b mt. Khi tn s cng cao, th hin tng ngy cng thhin r rng. Do kt qu ca hiu ng b mt ny m lm cho tit din hu hiuca dy dn gim, in tr tng. Khi dng in mt chiu thng qua dy dn, khngc hin tng ny, cho nn trn cng mt dy dn, in tr xoay chiu ln hn intr mt chiu. 1 - 1 - 10 (Tr v u chng, Tr v Mc lc) Hi: Khi qun cun in cm cao tn, ti sao phi dng dy nhiu si hocdy dn rng rut? - Trang 6 -

7. p: Khi qun cun cao tn, s dng dy dn nhiu si l nhm gim thiunh hng hiu ng b mt ca dng in xoay chiu tn s cao. S dng dy dnrng rut l nhm li dng y tit din hu hiu ca dy dn, tit kim kimloi mu. V vi cun dy cao tn (c dng in cao tn chy qua) th hiu qu cady dn rng rut cng ging nh dy dn c c cng ng knh ngoi. 1 - 1 - 11 (Tr v u chng, Tr v Mc lc) Hi: C mch in nh hnh 1-1-11. Khi cm mt list vo trong cun cm L, n tr nn ti li. Ti sao? p: Khi trong mch xoay chiu c u vi cun dy,dng in trong mch in khng ch c quyt nh biin tr trong bng n v in tr trn cun dy, m cn linquan n in cm L trong cun dy, L cng ln th dng in s cng nh, khi cmli st vo trong cun dy, L tr nn ln, v th bng n tr nn ti. 1 - 1 - 12 (Tr v u chng, Tr v Mc lc) Hi: Ti sao t in u vo mch in xoay chiu th c dng in chyqua,cn u vo mch in mt chiu th khng c dng in chy qua? p: Khi u t in vo mch in xoay chiu, do s thay i mang tnh chuk v chiu v ln ca in p xoay chiu, khin bn cc t in tin hnh np,phng in theo chu k. Dng in phng v np in ny chnh l dng in xoaychiu chy qua t in. Khi u t in vo mch in mt chiu, do chiu ca in p mt chiukhng thay i theo chu k, ch thi im u vo c dng in np nhng thigian rt ngn, np in xong s khng cn dng in chy qua. na, cho nn, dngin mt chiu khng th chy qua t in. 1 - 1 - 13 (Tr v u chng, Tr v Mc lc) Hi: Sau khi u ni tip hai t in c in p nh mc bng nhau nhngin dung khng bng nhau, phi chng c th t in p ngoi bng gp hai lnin p nh mc ca mi t in? p: Khng c gp i, v sau khi hai t u ni tip , s phn b in p bn t t l nghch vi in dung C, tc C cng nh th in p bn t ca n cngcao. Khi mc ni tip hai t in c dung lng khc nhau, nu in p ngoi gphai ln in p nh mc ca mt t in th t c C nh t s xy ra qu p. 1 - 1 - 14 (Tr v u chng, Tr v Mc lc) Hi: Hai t in Cl - C2, trong C1 l 16F 300V; C2 l 8 F 300V, uni tip chng vi nhau s ng ngun in mt chiu 550V, nhn thy t 8 F bnh thng. Ti sao? p: Khi ng dng t in u ni tip, th in p m n nhn c t lnghch vi in dung gi thit in p trn hai t Cl v C2 l U1 V U2 C1 .C 2 16.8 16 Tng dung lng: C = = = F C1 + C 2 16 + 8 3 - Trang 7 -

8. in lng trn cc t in: Q = CU = C2U2 C 16 / 3 U2 = U= x 550 = 367 V C2 8 Qua c th thy, t in c in dung nh th in p nhn c ln hngii hn chu p ca n, cho nn b nh thng. 1 - 1 - 15 (Tr v u chng, Tr v Mc lc) Hi: Khi hai cun dy khng c li st (c cng quy cch) ln lt u viin p mt chiu 220V v in p xoay chiu 220V, cun dy no nng nhanh hn.Ti sao? p: Cn c vo nh lut Jun ta c : nhit lng pht ra t l thun vi bnhphng cng dng in chy qua dy dn, t l thun vi in tr dy dn, t lthun vi thi gian gia nhit. Sau khi u vi in p mt chiu 220V, cng dng in trong cun dykhng c li st ch do in tr ca cun dy quyt nh. Cn khi cun dy khng cli st u vi in p xoay chiu 220V, cm khng ca cun dy s cn tr dngin xoay chiu chy qua, cng dng in do tr khng ca cun dy quytnh, cho nn cng dng in xoay chiu nh hn dng in mt chiu. V th,cun dy dn vi in p mt chiu s pht nhit nhanh hn cun dy u vi inp xoay chiu. 1- 1 - 16 (Tr v u chng, Tr v Mc lc) Hi: Cun dy in p ca cng tc in t xoay chiu, nu s vng qunkhng i m tng tit din dy dn th c th. gim tng nhit ca cun dy.Nhng vi cun dy mt chiu cng tng tit din dy dn nh vy, nhit litng cao. Ti sao? p: in khng ca cun dy xoay chiu ln hn in tr rt nhiu, nndng in trong cun dy hu nh khng chu nh hng ca in tr. Khi tit indy dn tng, in tr R gim, th cng dng in I hu nh khng thay i, tnhao I2R trn ng ca cun dy gim, cho nn nhit gim xung. Cng dngin ca cun dy mt chiu do in tr R quyt nh (khi in p khng i), khi Rgim, s tng ln ca I t l nghch vi R, tn hao I2R mt mt tng ln theo t lnghch vi bnh phng R, mt mt gim xung theo t l thun vi R, kt qu ltng ln theo t l nghch vi R, cho nn nhit li c tng ln. - Trang 8 -

9. 1 - 2 Dng bt th in kim tra mch in 1 - 2 - 1 (Tr v u chng, Tr v Mc lc) Hi: Bt th in ch c mt u chmvo vt dn in, ti san c th pht sng ? p: Kt cu bn trong ca bt th innh th hin hnh 1 - 2 - 1. B phn pht sng lbng n c hai cc. Bng n np kh neon, mtcc ni vi u khc ca bt th sau khi u nitip vi mt in tr c in tr ln. Khi in p gia hai cc ca bng n t ntr s nht nh, gia hai cc s pht sng, sng ca n t l thun vi in pgia hai cc. Khi in p gia vt mang in i vi t ln hn in p bt upht sng ca bng n, th khi chm mt u bt vo n, cn u kia qua ngi nivi t thnh mch kn, nn c th pht sng, tc dng ca in tr l hn ch dngin chy qua ngi nhm trnh in git nguy him. 1 - 2 - 2 (Tr v u chng, Tr v Mc lc) Hi: Lm th no dng bt th in c th phn bit in p 220V lin mt chiu hay xoay chiu? Lm sao c th phn bit cc m, cc dng cain mt chiu ? p: Khi bng neon ca bt th in thng in, ch c cc u vi cc m lpht sng. Khi th in xoay chiu, hai cc ca bng neon thay nhau lm cc m,cc dng cho nn c hai cc cng pht sng. Khi ni bt th in vo gia cc m,cc dng ca mch in mt chiu, trong bng neon ch c mt cc pht sng, ccpht sng l cc ni vi cc m ca ngun in, cc khng pht sng l cc ni vicc dng. 1 - 2 - 3 (Tr v u chng, Tr v Mc lc) Hi: Dng bt th in kim tra hai cc dng m ca my pht in mtchiu 110V, bng n u khng sng, nhng khi chm vi bt k u no caMgrm k trn 500V th u pht sng. Hai ci u khngtip t, ti sao ci sau c th pht sng? p: Mgrm k v my pht in tuy khng trc tiptip t, nhng u qua in tr cch in rt cao tipt. Nh hnh 1 - 2 - 3, A, B biu th cho hai cc, R1, R2 lin tr cch in ca hai cc i vi t. Nu Rl = R2 thhiu in th (tr s tuyt i) ca cc dng, m i vit bng nhau. Khi in p u l 110V, hiu in th cami cc i vi t ch c 55V, cha t ti in p phtsng ca bng n, cho nn khng sng. Khi in p u vt qu 500V, in thmi cc i vi t u vtqu in p pht sng ca bng n cho nn u pht sng. Nhng khi Rl v R2 chnhnhau rt xa, in th ca hai cc i vi t cng khng chnh nhau rt xa, lc mt cc ca in p 110V cng c th lm bng n pht sng, mt cc ca in p500V cng c th khng pht sng. - Trang 9 -

10. 1 - 2 - 4 (Tr v u chng, Tr v Mc lc) Hi: Dng bt th in kim tra u kim loi ca bngn, thng c th lm cho bng n neon pht sng, nhngdng vn k ph thng o li khng c in p. To sao? p: Hin tng trn y c th dng hnh 1 - 2 - 4 gii thch. im A biu th dy pha trong bng n, in trcch in ca n i vi kim loi trn ui n l Rl, in trcch in ca F i vi t G l R2, do dng in r gia A v VF l I1, st p gia FG l VFC = I1.R2 = R 2 , gi thit R1 + R 2 10U = 220V, R1 = 5, R2 = 10 th VFG = 220 = 147 V cho 5 + 10nn c th lm cho bng n neon sng. Nhng in tr ca vn k ph thng nhhn 0.1 dng n o in p gia F v G, tng ng vi vic mc song song 1 R FG = = 0.1mt in tr nh gia F v G, khin 1 1 (gi thit in tr ca + 10 0.1 0.1vn k l 0.1), th VFG = 220 = 4.3V nn khng thy c s c trn vn 5 + 0.1k ph thng. 1 - 2 - 5 (Tr v u chng, Tr v Mc lc) Hi: Nh th hin hnh 1 - 2 - 5a, khi dygia (trung tnh) ca mch in chiu sng b tdy, bng n b ngt, ti sao bt th in chm im F ca dy gia c th pht sng? Cn imG khng sng? Ti sao dng vn k o in p caim F i vi t li khng c? Hnh 1-2-5 p: Mch in tng ng ca tnh hung nh th hin hnh 1 - 2 - 5b. R1 l in tr cch in gia dy pha vi dy gia, R2 l tng in tr gia ngikhi vi bt in. Lc ny, in th ca im F do t s gia R1 vi R2 quyt nh. V 1 1 1 1d, khi R 2 = R 1 th UF = U = 55V; khi R 2 = R 1 th UF = U = 44V 3 4 4 5 - Trang 10 -

11. , cho nn bt in vn c th pht sng. im G trc tip ni vi t, in th can gn bng 0, cho nn bt in khng pht sng. Khi dng vn k o in p ca im F vi t, do in tr ca cun dy vn k nh hn R1 rt nhiu, UF hu nh bng 0, cho nn khng c s c. ngnhin, nu cch in gia dy pha vi dy gia rt km, tc tr s Rl rt nh th vn k cng c th c s c 1 - 2 - 6 (Tr v u chng, Tr v Mc lc) Hi: Dy trung tnh pha in p thp ca my bin th, c mang in, inp nghim c bng bt th in thy hn in p ca vt mang in thngthng. l do nguyn nhn g gy nn? p: tnh hung ny phn ln xy ra trng hp ni dng in cch nicung cp in tng i xa, ph ti ba pha qu khng cn bng, c bit l trnghp tit din dy trung tnh qu nh thng d xy ra nht. Nguyn nhn ch yuca n l cng dng in chy qua dy trung tnh qu ln, st p xy ra trndy trung tnh tng i ln. - Trang 11 -

12. 1 - 3 Cun dy c li st 1 - 3 - 1 (Tr v u chng, Tr v Mc lc) Hi Ti Sao trong cun cn tn s thp (thp dn), ni chung u c li st,cn trong cun cn cao tn li khng c li st? p: in khng ca cun cn c lin quan n in cm ca cun dy, min cm ca cun dy c lin quan n tnh cht ng t ca n. Nu ng tcacun dy l vt cht t tnh, th in cm tng ln. Sau khi cun cn qun ln list nh vy c th tit kim c nhiu kim loi mu (ng hoc nhm). Cun cn tn s thp ch nn s dng trong mch in di 100Hz. Do tnsthp nn dng phin thp Silic lm ng t s khng gy ra nhit cao do dngin xoy trong li st sinh ra. Cun cn cao tn do dng trong mch in cao tn, nn nu s dng li st,ssinh ra dng in xoy rt ln, lm tn tht nhiu nng lng, khin li st cnhit cao. Mt khc, in cm ca cun cn cao tn thng khng yu cu quln, cho nn ni chung cun cn cao tn khng dng li st. 1- 3 - 2 (Tr v u chng, Tr v Mc lc) Hi: Lc ht ca nam chm in sau khi li st c c nh c quytnh b tch ca cng dng in v s vng ca cun dy (I x W), th hi vingun in xoay chiu (mt chiu) th trong hai cun dy sau y, cun no c lcht ln hn, gi thit cun A l 500 vng, cun B l 1000 vng, cn li u hon tonkhc nhau? p: Khi vi ngun in mt chiu, lc ht gn nh bng nhau. V s vngca B tuy tng gp i, nhng in tr cnggn nh tng gp hai ln, dng in I gimi 1/2 cho nn IW gn nh khng thay i. Vi ngun in xoay chiu, lc htca cun dy c s vng t, ngc li, litng ln. Bi v cm khng t l thun viW2, cho nn tuy s vng ca B tng gp i,cm khng li tng ln gp 4 ln, v th,dng in gim cn 1/4, cho nn lc ht caB nh hn A khong 1/2 ln. 1 - 3 - 3 (Tr v u chng, Tr v Mc lc) Hi: Nh th hin hnh 1 - 3 - 3, hai cun dy honton ging nhau qun ln cng mt li st mch kn, t inp xoay chiu U ln hai u ca mt cun dy no (nt lintrong hnh) v u song song hai cun dy li vi nhau ri niVi U (nt t trong hnh), trong hai trng hp , dng inI ca mch in liu c bng nhau? p: Dng in I ca mch in bng nhau. - Trang 12 -

13. V dng in ny ch yu l dng in kch t, phn in th m t thngxoay chiu do n sinh ra cm ng trong cun dy, gn nh bng vi in p U bnngoi, ngc chiu nhau; vi s Vng ca cun y v tn s ca ngun in cnh, th ln ca phn in th s t l thun vi t thng; gi y in p ngoic nh, phn in th cng c nh, t thng cng c nh, cho nn trong hai tnhhung trn, t thng trong li st mch kn l bng nhau. Khi u song song, s vngca cun dy tng gp i, lm cho t thng bng nhau, dng in kch t chyqua mi cun dy phi gim 1/2, cho nn dng in I ca mch in vn khng i. - Trang 13 -

14. 1 - 4 in v t 1 - 4 - 1 (Tr v u chng, Tr v Mc lc) Hi: Dy ti in ti sao li rung v ku? p: Dy ci cng ca nh my in v trm bin in trong khi vn hnhb rung v ku, phn ln xy ra trong dy ci hai phin (hoc nhiu phin) cng pha.Bi v trong cc y ci cng pha, ln v chiu ca dngin chy qua l ging nhau (nh hnh 1 - 4 - 1): Khi c dngin chy qua, s sinh ra t trng quanh mi dy ci. Dotc dng tng h ca t trng v dng in trong dy cikhin hai si dy ci chu lc ht ln nhau, li v dng inchy qua dy ci l in xoay chiu 50Hz, trong mi nasng khi dng in bin i t "khng" n tr s ln nhtri li gim xung n tr s "khng", lc ht gia hai dyci cng bin i t "khng" n tr s ln nht ri ligim xung bng "khng". Nu phin in v cp gia kheh dy ci cp rt chc chn th tuy chu lc dy ci cng khng b rung. Nhng,thng thng trong qu trnh vn hnh, cp dy ci b r lng hoc khong cchcp dy qu xa (ni chung c 800-1000mm c mt cp) th di tc dng ca lc t,dy chnh s b rung 100 ln/giy, km theo c ting ku chi tai. Dy ci rung trong thi gian di khng nhng pht ra tp m chi tai m cn s lmcho kim loi dy ci b mi, nt v gy nn s c, cho nn cn nhanh chng loi trhin tng ny. 1- 4 - 2 (Tr v u chng, Tr v Mc lc) Hi: Mt thanh nam chm vnh cu v mt thanh st non, hnh dng hon tonging nhau (nh hnh 1 - 4 - 2), gi s khng da vo btc th g khc, c th nhanh chng on ra khng? p: Ly thanh A cho ht phn gia ca thanh B.Nu c ht, th thanh A l nam chm vnh cu, nu khnght th thanh A l st non. Bi v phn gia ca nam chmvnh cu khng th hin t tnh. V th, st non khng thht phn gia ca nam chm, nhng nam chm li c thht phn gia ca st non. 1- 4 - 3 (Tr v u chng, Tr v Mc lc) Hi: Mt thanh nam chm vnh cu nu ct lm i theong AB nh th hin hnh 1 - 4 - 3 th khi hai na gnnhau s c hin tng g xy ra? p: Sau khi thanh nam chm ct tch ra theo ng AB,thnh hai thanh nam chm, lc ny t cc cng tnh cnh nhau,gia hai thanh c lc y ln nhau khin chng khng th ghpli vi nhau c na. Trc khi chia tch ra, lc ht phn t ln hn lc t ynhau cho nn khngb y tch ra. - Trang 14 -

15. 1 - 5 Vt liu Cch in 1- 5 - 1 (Tr v u chng, Tr v Mc lc) Hi: Ti sao cch in trong ca thit b in cao p th s dng cch ingiy du, cn cch in ngoi li s dng cch in v c nh s cch in, thytinh v.v... p: Cch in trong phn ln dng cch in giy du c ch to bngcch chng xp giy cp in ri tm du, do x si c tc dng ngn cch trongdu, cn du li chn lp kn khe h trong giy, cho nn cng in hc rt cao,c bit l cng in hc tc thi; c th t trn 100kV/mm, tnh cng nghcng tng i tt, v th c s dng lm cht cch in trong rt nhiu thitb in cao p (nh t in, cp in, bin th, b h cm v.v...). Nhng cht v cnh s cch in, thy tinh v.v... do kh bin cht li t b nh hng ca thi titkh hu, m cng c hc li cao, li chu c phng in, v th c s dngrng ri lm cch in ngoi ca thit b in cao p. 1 - 5 - 2 (Tr v u chng, Tr v Mc lc) Hi: Ti sao in tr cch in gim theo s tng ln ca nhit ? p: Khi nhit tng cao, s chuyn ng ca phn t trong cht cch intng theo, in t trong phn t d thot ra do s va chm ln nhau gia cc phn tlm tng tnh nng dn in trong cht cch in; ng thi khi nhit tng cao ththnh phn nc trong cht cch in s bt u trng n, di ra, thnh dng sinh phn b gia hai cc, do trong nc c cha tp cht dn in, v th lm tngtnh nng in trong vt cht cch in. Tp cht cha trong nc v tp cht tnhkim, tnh axt cha trong cht cch in sau khi b nc phn gii s lm tng tnhnng dn in, do khi nhit tng cao, in tr cch in s gim thp. 1- 5 - 3 (Tr v u chng, Tr v Mc lc) Hi: dy cht cch in tng gp hai ln, phi chng cng chu pcng tng gp hai? p: Cht cch in tt v ng u (m ca rt mng) t trong in trngu th cng chu p ca n c t l thun vi dy. Nhng tuyt i a s vt liu cch in, do nhng nguyn nhn nh tnhkhng ng u v cht liu v s khc nhau v mc kh, c bit l, khi dytng ln nhit sinh ra do tn hao mi cht gy ra trong vt th cch in, khng thtn pht ton b n in cc hoc vo mi cht khc chung quanh, tp trung lptrong vt th cch in, lm nng vt cch in, d gy ra nh thng nhit. Do , dy tng gp i th cng chu p tng khng n gp i. 1 - 5 - 4 (Tr v u chng, Tr v Mc lc) Hi: Khi chn vt liu cch in cho t in, mong mun h s cch intng i r Ca vt liu phi ln mt cht, cn khi chn vt liu cch in cho cpin v my in th li yu cu r phi nh hn mt cht. Ti sao? p: Mi cht cch in c . tc dng cch in v c nh c hc i vith dn in vi in th khc nhau; nhng trong t in, mi cht cn c mt tc - Trang 15 -

16. dng quan trng na, l tng tr nng lng. i vi t in tm phng th indung ca n C= o. r.A/d, trong eo l h s cch in chn khng; r l h s cchin tng i ca mi cht; A l din tch bn cc; d l khong cch gia hai ccNu r ln, th in dung C s tng ln theo t l thun. V th, khi chn vt liucch in dng cho t in, mt mt phi ch cng in hc, mt khc mun r ln mt cht, nh vy c th gim th tch v trng lng cho n v dung lngca t in. Cht cch in dng cho cp in v my in khng c yu cu tngtr nng lng, mun tnh cc ha tng i yu, tc er tng i nh. i vicch in cho cp in, r nh cn c th gim thiu dng in np in khi cpin vn hnh. Ming rnh cun dy stato ca mt c khe h, nu r mi cht cchin th rn ca mt nh chnh lch vi .khng kh tng i nh th cng trng ca ming rnh hoc khe h cng tng i nh th c th nng cao in pnh thng. 1 - 5 - 5 (Tr v u chng, Tr v Mc lc) Hi: Trong khe h khng kh, thnh phn nc trong khng kh tng ln, inp nh thng tng cao, ti sao mi cht th rn b m th in p nh thng li stxung p: Trong khe h khng kh, nu m tng ln, thnh phn nc trongkhng kh d thu ht in t, hnh thnh ion m, do hnh trnh t do ca n rt ngnkhin in p nh thng tng cao. Mi cht cch in th rn sau khi ht m, do nc b thu ht vo bn tronghoc b mt mi cht n c th ha tan tp cht ion hoc lm in ly cht c cctnh mnh, hn na vi nh hng ca cc tp cht khc, tc dng in ly ca bnthn thnh phn nc tng mnh; do lm tng in ly mi cht th rn v tn haomi cht, dn n in p nh thng gim xung. i vi vt liu x si d htm th nh hng c bit ln, in p nh thng sau khi ht m lc thp nht cth ch bng vi phn trm lc kh ro; cho nn trong vn hnh cn ch chng m. 1 - 5 - 6 (Tr v u chng, Tr v Mc lc) Hi: Trong vt liu cch in cao p nu ln ln bt kh th trong vn hnhd lm hng ton b vt liu cch in. Ti sao? p: Trong vt liu cch in cao p, nu ln bt kh th s to thnh micht c lp, cng in trng ca n phn b U l nghch vi h s cch in.Do h s cch in ca bt kh nh, cng in trng ln, bt kh s in ly tdo trc khin ton b cng cch in gim, t lm hng tnh nng ca ton - Trang 16 -

17. CHNG II NHNG VN C BN CA H THNG CP IN 2-1 Truyn ti in 2 - 1 - 1 (Tr v u chng, Tr v Mc lc) Hi: Ti sao h thng in xoay chiu s dng sng hnh sin m khng sdng sng dng khc? p: Sau khi cc loi my in v thit b in t hp thnh h thng in,mun vn hnh bnh thng phi bo m h thng in c hnh (dng) sng thngnht nh vy thit k v ch to my in v thit b in mi c cn c chung. Biv,trn t C cng dng in i = C.du/dt (trong cng thc du/dt l biu sut) trnin cm L, in p u = L.di/dt (trong cng thc , di/dt l biu sut cng ); xtv ton hc, ch c hm s sin sau khi vi phn hoc tch phn th th (dng sng)ca hm s mi khng thay i. ng thi, trong mch in thng s c mt sin p v cng thm vo, duy chi c hm s sin khi cng thm vo dng sngmi khng pht sinh biu k d, cn bt c hnh sng no u khng c tnh chtny. 2 - 1 - 2 (Tr v u chng, Tr v Mc lc) Hi: Tn s lm vic ca in xoay chiu ti sao li nh l 50 hoc 60 chuk trong mi giy? p: Tn s ca in xoay chiu cao hay thp u c li v hi. Tn s caoc th gim thiu lng s dng ng v st dng trong my in v my binth,cho nn trng lng gim nh, gi thnh thp, s nhp nhy ca bng n dodng in thay i gy nn mt ngi cng khng d nhn thy. Song n s lmgim khng p ca ng dy ti in v thit b in tn hao nng lng tng ln,lm xu nng sut iu chnh v hiu sut ca in p. Tn s qu thp, s lm tng trng lng ca my in v bin th, gi thnhtng cao, s nhp nhy ca bng n cng d nhn thy, cho nn tn s lm vic quinh 50 hoc 60 chu k/giy l tng i hp l. 2 - 1 - 3 (Tr v u chng, Tr v Mc lc) Hi: Ti sao in p li in phi chn cc cp khc nhau ? p: Chn cp in p, ngoi vic tnh n li thp an ton cho ngis dng dng li in p thp ra, khi truyn ti phn phi in li c cngcng sut th in p cng cao, dng in cng nh, din tch tit din phn ti inca dy dn c th s dng cng nh, u t s gim tng ng. Nhng yu cui vi cch in th in p cng cao, u t v ct in, bin p, b ngt incng cng ln. Do i vi cng sut truyn ti v khong cch truyn ti nhtnh no th cn chn in p hp l nht. ng thi, vic chn in p inli phi tng hp xem xt ton din qui hoch trc mt v lu di ph ti inli v trnh k thut lc mi c th la chn thch hp. Cp in p chn qu - Trang 17 -

18. cao, th ph ti lu di ca ng dy khng , lng ph u t, chn qu thp thkhng lu li phi thay in p cp cao hn, cng khng kinh t. 2 - 1 - 4 (Tr v u chng, Tr v Mc lc) Hi: Thng nghe ni n in p ng dy 6 kil vn (kV) hoc 6.3 kilvn (kV), 6.6 kil vn (kV). Cch ni no ng? p: i vi cp in p ny, in p nh mc ca thit b in (nh ngc in, l in) l 6kV cn in p nh mc ca my pht in l 6.3kV. in pnh mc cun nguyn ca my bin p ging nh thit b dng in tc 6kV; inp nh mc ca cun ph cao hn ca thit b dng in 5%, tc 6.3kV. Khi tr sin p ngn mch ca bin p trn 8%, in p nh mc ca cun ph phi caohn ca thit b dng in 10%, tc 6.6kV. Theo qui nh, in p nh mc ca li in phi bng vi thit b dngin ca n, i vi in p cp ny m ni l 6kV. Cho nn ni, ng dy in p6kV l ng. 2 - 1 - 5 (Tr v u chng, Tr v Mc lc) Hi: St p v tn tht in p c g khc nhau? p: Trong mng in mt chiu, st p v tn tht in p l hon tonging nhau, nhng trong mng in xoay chiu, do v tr pha ca dng in v inp khc nhau, v quan h st p do in khng ca mch in gy ra nn hai khinim khc nhau. Hiu hnh hc ca in p hai u, u v cui ca ng dygi l st p; hiu i s in p hai u ca n gi l tn tht in p. Trong mngxoay chiu, tr s tuyt i ca st p ln hn tn tht in p. 2 - 1 - 6 (Tr v u chng, Tr v Mc lc) Hi: in p ca bung phn phi in p thp l 400V; st p ng dy tbung phn phi in n phn xng 32V. Nu h s cng sut ca phn xng l0.6 tr khng ca ng dy l in tr thun, th in p phn xng c phi l368V? p: Khng phi; m l 380V .Gi thit in p bung phn phi in l U1 ,st p ng dy l U in p phn xng l U 2 , . . . . cng dng in ph ti ca phn xng l I 2 . Quan h v tr pha gia chng vi nhau c th biu th nh hnh 2 - 1 - 6. V tr khng ca ng dy l in tr thun, cho nn U song song vi I 2 . Do h s cng sut ca ph ti phn . . . xng l 0.6 cho nn U phn gii thnh hai thnh phn 0.6 . . . U v 0.8 U (ng mnh trong hnh). T ta c : ( U 2 + 0.6 x 32) + (0.8 x 32) 2 2 .= 4002, gii ra. ta c U 2 = 380V. 2 - 1 - 7 (Tr v u chng, Tr v Mc lc) Hi: Ti sao my bin th dung lng ln hoc cu dao dn cao p s dngtrn ng dy ti in ba pha u dng ba pha to thnh? - Trang 18 -

19. p: Ngi ta thng dng ba ci mt pha m khng dng mt ci ba pha ldo: (1) th tch v trng lng qu ln, v mt vn chuyn phi chu s hn ch bikh nng ca phng tin vn ti hoc kch thc ca ng s, cu cng, nghm v.v... (2) Bin th hoc cu dao dn cao p d b ngi s dng ch cn chunb mt ci mt pha l c, so vi d b mt ci ba pha c th tit kim v mt ut rt ln. (3) Nu khng may b h hng th ch cn sa cha mt ci mt pha, tc sa cha s nhanh hn l sa cha thit b ba pha. 2 - 1 - 8 (Tr v u chng, Tr v Mc lc) Hi: Ti sao khi ti in trn khong cch xa th my bin th tng p uthnh - Y (tam gic - sao) bin th st p th u thnh Y - (sao - tam gic)? p: in p li ti in cng cao th hiu sut cng cng cao. My binth tng p u - Y, dy ra bn pha th cp thu c s l in p dy; t vis vng tng i t, s thu c in p tng i cao, nng cao c t l tng p.Cng cng l do my bin th h p u Y - , vi s vng ca cun dy bn scp khng nhiu c th t c ti l h p tng i ln. Ngoi ra, khi bn th cpca bin th tng p v bn s cp ca my bin th h p u kiu Y (hnh sao)u c th tip t, im trung tnh khin in p dy ti in i vi t l in p 1pha, bng in p dy; cng tc l h thp yu cu cch in ca ng dy, h 3gi thnh xy dng. 2 - 1 - 9 (Tr v u chng, Tr v Mc lc) Hi: Ti sao c mt s n v s dng in tch ring chiu sng v ng lcm khng dng chung mt my bin th ? p: Xt v mt gim thiu s lng thit b nu c chiu sng v ng lcdng chung mt bin th th s kinh t hn. Nhng, ph ti ca ng lc a phn lng c in, khi khi ng s lm st gim in p ngun mt cch r rt, v khiph ti ca ng lc thay i cng lm thay i in p ngun, nhng iu ulm cho sng ca n chiu sng mt n nh. phng nga hin tng ny,tch ring h thng in dng cho ng lc v h thng in dng cho nh sng ltt hn. 2 - 1 - 10 (Tr v u chng, Tr v Mc lc) Hi: Ti sao nhng my in quay trn khng th trc tip u vi phang dy thuc h "hai dy mt t"? p: Trong vn hnh ng dy trn khng h "hai dy mt t", c mt phathng xuyn tip t, v th in p pha khng tip t i vi t l in p dy.Nu u trc tip my in vo, th cch in ca n s phi vn hnh lu di diin p dy, iu ny l khng th c. V th, phi qua my bin th cch ly mic th u vo c. 2 - 1 - 11 (Tr v u chng, Tr v Mc lc) Hi: Trong mng phn phi in p thp h ba pha ba dy, liu c th pdng h "hai dy mt t" tit kim mt ng dy? - Trang 19 -

20. p: Khng c. Nguyn nhn l: (1) ch dy dn tip t s xut hin st p r rt khin in p pha tipt u c ph ti s rt thp; in p ba pha khng cn bng; tnh vn hnh caph ti tr nn xu. (2) Do in p ca pha i vi t l in p dy, cho nn khingi tip xc vi dy pha bt k no khng tip t th s rt nguy him. (3) Khiin p dy ca li in l 380V, khng th trc tip u ni vi ph ti chiusng. (4) Khi xy ra ngn mch gia dy dn pha tip t vi pha khng tip t, dodng in ngn mch b hn ch bi in tr tip t hai ch ca pha tip t,khng lm nng chy dy ch, nn s ko di qu trnh ngn mch. (5) Khichn in tr tip t tng i ln th phn vt tip t c th xut hin inp nguy him. 2 - 1 - 12 (Tr v u chng, Tr v Mc lc) Hi: Khi truyn ti in ba pha nngthn, ti sao c lc ch dng hai dy trn khng? p: nng thn, do ng dy ti indi m dy in thoi in tn khng nhiu, vth c th li dng t lm mt dy ti inba pha, nh th hin hnh 2 - 1 - 12, nhm titkim gi thnh lp t ng dy ti in(thng thng c th tit kim 25 - 30% vnu t ban u). Loi ng dy ti in tndng t lm mt dy pha thng gi l ng dy ti in ba pha h "hai dy mtt"; tuy c th tit kim nhng cng c nhc im, ch yu l: (1) nh hngtng i ln i vi ng dy thng tin. V th trong thnh ph khng c dng.(2) in p tip xc v in p vt ni tip t tng i ln, cho nn cn cbit ch an ton. (3) in p pha i vi t l in p dy ch khng phi in ppha, do khi trc tip dng vi ph ti ba pha, cch din ca ph ti i vi td b nh thng. 2 - 1 - 13 (Tr v u chng, Tr v Mc lc) Hi: H ba pha ba dy so vi h mt pha hai dy, tit kim c bao nhiudy? p: Gi thit tn hao trong in p dy v ng dy l nh nhau. Vy cngsut truyn ti ca mt pha v ba pha ln lt l: P = UI1 v P = 3 UI3 tc I1 = I3. 2 2 Tn hao ca hai ci bng nhau: PCU = 2. I1 R1 = 3. I3 .R3 Hoc R3 = 2R1. Trng lng ca dy t l thun vi s si dy, t l nghch vi in tr. 1 2 2 W1 R1 R 2 2R 1 4 = = 1 = = W3 2 1 3 R1 3 3 R 3 2R 1 1 Cho nn, c th tit kim c hoc 25%. 4 - Trang 20 -

21. 2 - 1 - 14 (Tr v u chng, Tr v Mc lc) Hi: Ti sao khi xy ra s c ngn mch mt ch no ca h thngin lc s lm cho h thng dao ng, thm ch phv c h thng? p: Nu xy ra ngn mch im D trnng dy gn nh my in A (xem hnh 2-1-14),in p dy chnh ca nh my A s st xung gnbng 0, mt ph ti, ng c khng kp iu chnhtng ng, tc quay ca t my nh my A tt stng cao. Lc ny, trn ng dy chnh ca nh myB vn cn in p cn li tng i cao, ph ti mt i khng nhiu, tc quayca my pht in tng tng i ln. Nh vy, t my ca hai nh my A, B sinh rachnh lch tc quay, nu thi gian ngn mch ko di tng i lu th t myca hai nh my s mt ng b, khin h thng dao ng thm ch b ph v. Vth nng cao tnh n nh vn hnh song song ca h thng, yu cu nhanh chngkhc phc s c ngn mch, phng nga m rng s c. - Trang 21 -

22. 2 - 2 Dy ci (Dy dn nh) 2 - 2 - 1 (Tr v u chng, Tr v Mc lc) Hi: Trong h thng 6 ~ 10 kV ca nh my pht in v trm bin in, tisao u s dng dy ci ch nht? p: Khi din tch tit din nh nhau, th chu vi y ci hnh ch nht lnhn hnh trn; tc b mt tn nhit ca thanh dn chnh hnh ch nht ln hn, do iu kin lm mt tt hn, ng thi, do nh hng ca hiu ng in tch tptrung b mt ca in xoay chiu, in tr ca dy chnh tit din hnh ch nht snh hn in tr tit din hnh trn, o khi din tch tit din v nhit phtnhit cho php ging nhau th dng in chy qua tit din hnh ch nht s lnhn. Cho nn, trong h thng 6 ~ 10kV ni chung u s dng dy ci ch nht, cntrn thit b phn phi in 35 kV v trn na, phng nga qung in tm,thng s dng dy ch hnh trn. 2 - 2 - 2 (Tr v u chng, Tr v Mc lc) Hi: Ti sao trong my in xoay chiu ni chung khng s dng dy cibng thp, nhng trong mt s mch in xoay chiu v mng in mt chiu lic s dng. p: in tr sut ca thp gp 6 ~ 8 ln ca ng; s dng trong mchin xoay chiu dung lng ln tt s gy nn tn tht in p v tiu hao innng. Mt khc tnh dn t ca thp tng i tt, d gy nn t tr v tn haodng xoy (Fuc) nn ni chung nhng mch in xoay chiu dung lng ln ukhng dng thp lm dy ci. Nhng cng c hc ca dy ci bng thp li cao,gi r, nn c th s dng trong mch in cao p xoay chiu dung lng nh nhb h cm in p bn cao p ca my bin th dng trong nh my in dunglng nh. Trong mch in mt chiu, do khng tn ti t tr v tn hao dngxoy, cho nn cng c dng y ci bng thp, nh thanh dn in mt chiu cabung c qui. 2 - 2 - 3 (Tr v u chng, Tr v Mc lc) Hi: Vi cng dng in rt ln, khi chn dy ci nn xem xt nh thno ? p: Khi chn dy ci khng nn s dng tit din qu ln. V cng dngin cho php ca n s gim theo s tng ln ca tit in, cng tc l s tng lnca dng in cho php khng t l thun vi s tng ln ca tit din dy ci. Vth, khi cng dng in mt pha vt qu dng in cho php ca mt tit dinln nht th thng s dng nhiu dy ghp song song. Dy ci trong mt pha, ni chung, khng qu hai dy. V khi s dy trong mipha tng ln, do lm ngui tr nn km, s gia tng ca ph ti cho php khng t lthun vi s dy, m gia tng tng i nh. Hn na, khi l xoay chiu hiu ngln cn rt ln. 2 - 2 - 4 (Tr v u chng, Tr v Mc lc) - Trang 22 -

23. Hi: Ti sao khi s dng ghp song song dy ci hnh ch nht, mi phakhng c qu 3 dy, cn dy dn chia tch th c th dng dy dn mm c 3 sitr ln? p: Khi dng in lm vic vt qu dng in cho php ca dy ci thmi pha c th dng hai hoc 3 dy ci hnh ch nht ghp song song c nh ln gicch in. c th ta nhit tt, gia cc dy phi gi khong cch bng dyca n, khng c chng ln nhau. Nhng s dy dn mi pha tng ln, th dngin cho php ca n b nh hng bi iu kin ta nhit tr nn km v hiu ngb mt, nn khng tng ln theo t l thun khi mi pha c 3 dy, dng in ca dygia chim khong 20% tng cng dng in, hai dy bn chim 40% mi dy.Do khng nn s dng mi pha qu ba dy ci ch nht. Cn dy dn chia tch donhiu si dy dn mm to thnh, do gia cng v lp rp tng i d, khng cnphi xp chng, c th xp rng gia, cho nn cho php s dng 4 si tr ln. 2 - 2 - 5 (Tr v u chng, Tr v Mc lc) Hi: Dy ci ba pha b tr ngang bng hoc thng ng th pha no chu scin ng ln nht? p: Cn c vo hin tng: chiu dngin ging nhau sinh ra lc ht, chiu dng inkhc nhau sinh ra lc y m xt th khi chiudng in hai pha hai bn ngc nhau th pha gia chu lc ln nht (xem hnh 2 - 2 - 5). Githit dng in trong ba pha l i xng v cn I1I 2bng th da vo cng thc F = 0 c th 2atnh c lc y m pha gia nhn c ln hn 1/4 so vi mi pha hai bn. 2 - 2 - 6 (Tr v u chng, Tr v Mc lc) Hi: Khi dy ci mt pha chia thnh vi dy lp ln cng v s, ti sao phitng thm m lt vo gia hai thanh dn gia v s ? p: Trong tnh hnh lc in ng m dy ci chu khng ch l lc giady ci khc pha m cn c lc tc dng ln nhau gia dy dn cng pha. V khongcch dy ci cng pha tng i gn, do lc in ng tng i ln. Tng thmm lt c th gim khong cch im chng , gim mmen ca lc in ng. 2 - 2 - 7 (Tr v u chng, Tr v Mc lc) Hi: Ti sao trong thit b phn phi in, ni chung u dng dy ci trn? p: Dy ci trn c cc u im sau y: iu kin ta nhit tt, dng incho php tng, lp rp d, sa cha n gin, gi thnh tng i thp cho nn. btk l thit b phn phi in trong phng hay ngoi tri, ni chung u s dngthanh dn trn. 2 - 2 - 8 (Tr v u chng, Tr v Mc lc) - Trang 23 -

24. Hi: Dy ci dng ai s dng trong thit b phn phi in, khi lp t chai cch: t ngang v t ng (xem hnh 2 - 2 - 8). Ti sao? p: Khi chn kch thc dy ci cn xt ti hai im: ( l ) Lu lng ti-Dy ci c th cho dng in m ph ti cn thit chy qua an ton. Nu chnqu nh, dy ci s nng do qu ti. (2) Cng c hc - thanh dn c ng lc chc ca dy ci chu c khi xy ra s c ngn mch, khng n ni lm hngthit b ca dy ci. Nhng tnh nng ca dy ci dng ai c tit din nh nhau, khi t ngang tng c ch khc nhau. Khi t ng, lu lng ti in tng i ln, nhng chc th chu c ng lc c hc tng i nh. Cn khi t ngang, lu lng tiin gim 5 - 8% so vi t ng, nhng c th chu c ng lc c gii tngi ln. Do , khi lp t dy chnh dng ai cn cn c vo tnh nng trn y quyt nh t ngang hay t ng. Nu cng sut rt ln, thng lp t cc phatrn di ch khng b tr trn cng mt phng ngang bng, v t ng dy ci lng ti in v cng c hc u tha mn. 2 - 2 - 9 (Tr v u chng, Tr v Mc lc) Hi: in p gia cc r (d) ng hp lu ng trong l in tng ithp. Nhng thng thng khong cch lp t gia chng rt xa, liu c th cn cvo yu cu cch in ni chung rt ngn khong cch? p: i vi vn khong cch gia cc dy ci cng dng in ln,ngoi vic xem xt khong cch, cch in gia cc dy ra, cn phi tnh n lcin ng do dng in sinh ra. Khi khong cch gia hai dy dn nh, th sc inng tng h s tng ln, c bit l l in trong thi gian nng chy, do nguynliu xung, nho trn, thng xy ra hin tng ngn mch. Lc , lc inng gia cc r ng hp lu rt ln. Nu khong cch chn khng chnh xc, sph hng b phn chng ca cc r ng hp lu. 2 - 2 - 10 (Tr v u chng, Tr v Mc lc) Hi: Ti sao bulng ni i ca dy ci khng th sit qu cht? p: Bulng sit qu cht th b phn dy ci di vng m b nn, tit dinca y ci gim. Trong vn hnh, dng in chy qua s pht nng, do h s n canhm hoc ng ln hn thp, y ci di vng m cng b nn thm khng thgin n t nhin, nu cng dng in trong dy ci gim nh, nhit gimthp, t l co rt ca dy ci ln hn bulng, th l hnh thnh khe b. Nh vy intr tip xc s ln, nhit tng cao, mt tip xc s b xy ha, khin in tr tipxc cng ln. Cui cng lm cho phn lin kt ca bulng xy ra hin tng qu - Trang 24 -

25. nng, nh hng an ton vn hnh. Ni chung, nhit thp, bulng nn sit chtmt cht, nhit cao, bulng nn sit lng mt cht. 2 - 2 - 11 (Tr v u chng, Tr v Mc lc) Hi: Kp vt dng c nh dy ci trn v s dy ci, ti sao sau khi sitcht li phi ni ra 2 - 3 vng, khng th vn qu cht ? p: Bi v trong vn hnh, dy ci tng nhit, c bit l dng in chy quakhi ngn mch, nhit tng tng i cao, dy ci b nng n ra. Nu kp vt vnqu cht, dy ci chnh khng cn ch gin n s sinh ng lc rt ln i vi vs, gy nn s c v hng v s. V th, khi lp rp, sau khi vn cht phi ni ra 2 -3 vng. 2 - 2 - 12 (Tr v u chng, Tr v Mc lc) Hi: Dy ci bng ng v bng thp, liu c th trc tip ni vi nhau bngbulng ? p: Khng c. V kim loi khc nhau ni vi nhau gia chng ch cn ckhe h th s gy nn n mn in ha do tc dng pin. Kt qu l lm tng in trtip xc, tng nhanh s n mn dy ci. phng nga n mn in ha, cn p dng hn ni hoc sau khi m thicdy ci ri mi lin kt bng bulng. 2 - 2 - 13 (Tr v u chng, Tr v Mc lc) Hi: Ti sao mt tip xc ca dy ci bng nhm khng cho php dng giynhm (vi nhm) gia cng phng bng? p: Thng thng dng da th gia cng phng mt tip xc ca dy cibng nhm. Khi khi lng cng vic ln c th tin hnh bng dao co hoc dythp (lp trn my phay). Bi v dng giy nhm (vi nhm) lm phng th ct vvn vi bm vo kim loi, khin in tr mt tip xc ca dy ci tng ln, d oxyha, pht nhit gy nn s c. 2 - 2 - 14 (Tr v u chng, Tr v Mc lc) Hi: Ti sao khi dng bulng ni dy ci t ngang, bulng phi x tdi ln? p: Ch yu l tin kim tra. Bi v khi x t di ln, khi dy chnh vbulng do h s n khng ging nhau hoc khi ngn mch, di tc dng ca lcin ng gy nn khe h khng kh gia dy ci, khin bulng tut xung, khi kimtra s nhanh chng v kp thi pht hin ra, khng m rng s c. ng thi, cchlp rp ny p, ngay ngn. 2 - 2 - 15 (Tr v u chng, Tr v Mc lc) Hi: ng bc xuyn tng c dng in 1500A tr ln chy qua, khi lp lntm thp ti sao li phi x mt ng khe ngang khong 3 mm trn ng ko ding knh ng bc trn tm thp (nh hnh 2 - 2 - 15)? p: Khi thp tm khng x rnh, do dng inxoay chiu chy qua ng bc, hnh thnh mch t khp kn - Trang 25 -

26. xoay chiu trn thp tm, sinh ra tiu hao t tr khin thp tm pht nng. S tnhao ny s tng mnh theo s tng ln ca dng in v do thp tm qu nng d lmlo ha cht in mi cch in ca ng bc, nh hng n tui th s dng. Saukhi thp tm x rnh, do c khe h, t thng trong thp tm gim r rt, t lmgim ng k s tn hao t tr. 2 - 2 - 16 (Tr v u chng, Tr v Mc lc) Hi: Ni thanh dn hnh ch nht nhiu thanh nh th hin hnh 2 - 2 16(a), (b), cch ni no tt hn? p: Phn ni ca mch in phi lm sao in tr tip xc cng nh cngtt nh vy tn hao do dng in chy qua phn ni sinh ra cng nh. Do ,phng php ni hnh (a) tng i tt. Bi v di plc n v din tch nht nh, din tch tip xc cng lnth in tr tip xc cng nh, tn hao do dng in chyqua sinh ra cng cng nh, tng dng in m phng phpni hnh (a) th hin chy qua ba mt tip xc, hnh(b) th hin ch chy qua mt mt tip xc .R rng intr tip xc ca ci trc nh, tn hao do dng in chy qua sinh ra cng nh. 2 - 2 - 17 (Tr v u chng, Tr v Mc lc) Hi: Hai vt kp cht trn ci cch in dy ci, ti sao thng mt cibng ng, mt ci bng thp? p: V chung quanh vt ti dn in sinh ra t trng, nu c hai vt ulm bng thp th tm kp trn di v hai vt s to thnh mch t kn c t trthp, tm kp v vt s pht nng bi tn tht t tr v dng xoy do t trng thayi gy nn. S dng mt vt bng ng s lm tng t tr ca mch t khin nkhng nng. C lc tng t tr cng c th s dng tm kp ng hoc nhm. 2 - 2 - 18 (Tr v u chng, Tr v Mc lc) Hi: Khi lp dy ci hnh ch nht ln v s, ti sao l khoan ca dy ci,ni chung u c hnh van? p: Khi dng in ph ti chy qua dy ci s lm dy ci nng n ra. Khidng in ph ti lun lun bin ng, do dy ci thng xuyn co gin. Nukhoan l thnh hnh van th khi dy ci co gin sthun tin cho n x dch t do theo hng dc,trnh c ng lc c hc tc dng ln v s. 2 - 2 - 19 (Tr v u chng, Tr v Mc lc) Hi: Ti sao khi di on thng cady ci qu di cn phi c ch ni co gin? p: Trn on thng dy ci bng nhmdi 15 mt v dy ci bng ng di 20 - 25 mt,nu c lp u ni co gin (xem hnh 2 - 2 - 19) th khi c dng ph ti chy qua, dyci b nng n ra s c ch co gin, khng n ni lm hng v s bi ng lc chc. u ni co gin lm t phin mng (0.1 ~ 0.4mm) bng vt liu ging vi dyci cn s lng bao nhiu th phi tng ng vi tit din dy ci. - Trang 26 -

27. 2 - 2 - 20 (Tr v u chng, Tr v Mc lc) Hi: Ch cong ca thanh dn xung t dy cicng ni vi thit b nn lm theo ng nt t hayng nt lin th hin hnh 2 - 2 - 20 ? Ti sao? p: B phn un cong ni t thanh dy ci vithit b phi c gng gn im ta nht, nh ngnt lin trong hnh. V rng nh vy dy dn xung sngn hn so vi ng nt t th hin s lm cho nglc c hc m dy ci phi chu khi xy ra s c ngnmch tng i nh. Nhng phi ch : theo qui nh,phn tip xc gia dy ci vi thit b phi ngoi 25mm sau on thng t chun cong. 2 - 2 - 21 (Tr v u chng, Tr v Mc lc) Hi: Ti sao khng trc tip ni u ni bng ng, nhm trong cc thit bin? p: Ly Hydro lm chun, cc kim loi u c th t in ha khc nhau.Th t in ha ca nhm nm trc Hydro, in th in cc tiu chun l -1.34V. Th t in ha ca ng sau Hydro, in th in cc tiu chun l +0.34V (Cu++) hoc 0.521V (Cu+). Nu ni ng vi nhm bng phng php c hcn gin, c bit l mi trng m thp v cha nhiu thy phn (trong khngkh lun cha thy phn nht nh v mt t mui v c c tnh ha tan), i u ning, nhm s nh mt i in cc ngm trong dung dch in gii, s hnh thnhpin c hiu in th l 0.34 (hoc 0.521) - ( - l.34) = 1.68 (hoc l.86)V. Di tcdng ca pin, nhm s nhanh chng mt ht in t nn b n mn, nh vy lm chou ni dn dn lng, gy nn in tr tip xc tng. Khi dng in chy qua, uni nng ln, nhit tng cao cn lm cho nhm bin dng do, cng lm tng intr tip xc ca phn u ni. C tun hon nh vy cho n khi u ni b chyhn. Do , u ni bng ng, nhm ca thit b in phi dng "u ni qu ng nhm" hn bng h quang li. 2 - 2 - 22 (Tr v u chng, Tr v Mc lc) Hi: Dy ci trn trong thit b phn phi in sao li phi sn mu? p: Ch yu dng th hin cng dng ca dy ci (dy ci in xoaychiu ba pha hoc dy ci in mt chiu), v tr pha ca dy ci xoay chiu v cctnh ca dy ci mt chiu. Trung Quc qui nh trong dy ci xoay chiu ba pha thpha A sn mu vng, pha B sn mu lc, pha C sn mu ; dy trung tnh sn mutm (dy khng tip t) hoc mu tm c vch ngang mu en (dy tip t); trongdy ci mt chiu, cc dng sn mu , cc m sn mu xanh lam. ng thi dychnh trn sau khi sn mu s lm tng kh nng bc x ta nhit, ci thin ciu kin ta nhit, cho nn c th tng lu lng ti so vi dy khng sn, v cth phng nga r mn dy chnh, c bit quan trng i vi dy ci bng thp. 2 - 2 - 23 (Tr v u chng, Tr v Mc lc) - Trang 27 -

28. Hi: Dy ci phn phi in t trong phng ni chung nn sn mu, ti saody ci phn phi in ngoi tri li khng sn mu? p: Do dy ci phn phi in ngoi tri phn ln dng dy cp (dy mctrn khng), khi nhit thay i, dy dn co gin rt r rt, nu b mt dy c snth s nhanh chng b ph hng. ng thi, do tc dng kh khng kh ngoi trirt ln, gp hn 4 - 6 ln so vi tc khng kh lm mt t nhin trong phng, chonn hnh thc ta nhit ch yu ca b mt dy ci phn phi in ngoi tri li lu. Sn mu khng th lm tng mt cch r rt kh nng ta nhit ca n. Chonn dy ci phn phi in ngoi tri ni chung u khng sn mu. - Trang 28 -

29. 2 - 2 - 24 (Tr v u chng, Tr v Mc lc) Hi: Ti sao dy ci bng st hoc nhm khng c sn trc tip sn binmu kim tra nhit vn hnh? p: l bi v thy ngn v bc cha trong sn bin mu c tc dng nmn tng i mnh i vi st hoc nhm. Nu trc khi sn khng sn mt lpsn bo v chng n mn th s lm hng dy ci do b n mn. 2 - 2 - 25 (Tr v u chng, Tr v Mc lc) Hi: ng vn dn in tt hn thic, ti sao li thng m thic lnu dy ng? p: l nhm phng nga ng b g to thnh lp "ng xanh" trongkhng kh m t, n lm tng in tr tip xc khin mt tip xc qu nng. Saukhi m mt lp thic ln b mt ng s c th phng nga xy ha ng, ngthi cht xy ha ca thic dn in tng i tt, khng dn n hin tng lmtng in tr tip xc lm mt tip xc qu nng. 2 - 2 - 26 (Tr v u chng, Tr v Mc lc) Hi: Ti sao dy ci cao p d b, khi bnh thng cng phi trng thic in? p: Trong khng kh cha lng hi nc nht nh, s bm vo dy ci vgi cch in lm gim cch in ca dy ci. Hi nc v bi than trong khngkh ng kt li vi nhau cng to thnh mch kn phng in. Khi dy ci trngthi mch in, hi nc c th bc hi, khng nh hng n cch in cady ci. Cho nn, dy ci ngng s dng thi gian lu, trc khi s dng phi o cch in ca dy ci. 2 - 2 - 27 (Tr v u chng, Tr v Mc lc) Hi: Thanh r hp lu s dng trong thit b phn phi in ti sao phi snmu? Lm sao cn c vo mu sc phn bit pha ca dng in? p: Ni chung, vic sn mu ca thanh r hp lu c ba mc ch: ( l ) nhn vin cng tc d phn bit. (2) Lm tng phn no lng nhit ta vo mitrng xung quanh. Do tng dng ph ti cho php ca thanh r. (3) C th chngr st.Vi in mt chiu, cc ng mu , cc m mu lam. in xoay chiu:pha A mu vng, pha B mu lc, pha C mu ; in xoay chiu mt pha: mu vngv mu . Thanh r hp lu trung tnh v thanh r hp lu cn bng mt chiu v xoaychiu khng tip t l mu tm, tip t l mu tm c vch ngang mu en. im ni t, im phn nhnh v im t u vi thit b th khng snmu. - Trang 29 -

30. 2 - 3 Vng quang in (phng in vng quang) 2 - 3 - 1 (Tr v u chng, Tr v Mc lc) Hi: Bui ti, trn ng dy ti in cao p c bit, ti sao c in qungmu lam thm? p: Quanh dy dn ng dy ti in cao p c in trng rt cao, ditc dng ca in trng mnh, lm cho khng kh quanh n ion ha sinh ra hintng phng in, gi l phng in qung tn (in qung). Nh vy, bui ti cth nhn thy qung nh sng mu lam thm. 2 - 3 - 2 (Tr v u chng, Tr v Mc lc) Hi: Ti sao trong trm bin in 220kV tr ln thng c ting phng in"tch tch"? p: l ting phng in qung. Tia v tr tia t ngoi trong khng trung,bc x ca nguyn t phng x di t u c quang t photon nng lng cao,c th bt in t trong cht kh ra, gi l quang ion ha. Khi in p trn dy dntng ln n tr s no , cng t trng b mt dy dn c th lm cho int do quang ion ha bn ngoi sinh ra s thu c ng nng trong khi chuyn ng.Nu ng nng ln hn nng lng ion ha ca phn t kh th in t c th lmcho phn t kh b va chm sinh ra ion ha va chm, di tc dng ca in trngmnh, in t do va chm sinh ra s thu c ng nng, sinh ra ion ha va chmmi, kt qu in t s tng ln nh tuyt l, ng thi pht ra ting "tch tch"? 2 - 3 - 3 (Tr v u chng, Tr v Mc lc) Hi: Ti sao ng dy ti in phi xt n vn in qung? Lm saophng nga in qung? p: in p cng cao cng d sinh ra in qung, cho nn dng dy tiin trn 35kV phi xt n in qung (phng in qung tn). in qung c baci hi sau: (1) Tn hao in nng. (2) Khi xy ra in qung, khng kh gn dy dns sinh ra hin tng ion ha, d gy rn v s, khi qu p, gia pha v pha d bxuyn thng. (3) S ion ha khng kh do in qung sinh ra d to ra cht xy haca nit v zn, kh zn c th lm xy ha kim loi, cht xy ha ca nit s hahp vi nc thnh axit nitric, c tc dng n mn ph hoi i vi kim loi. Tmli, bt k l v mt kinh t hay an ton, th tnh cht nguy hi ca in qung urt ln. Mun phng nga in qung th phi nng cao in p in qung ti hn,m in p in qung ti hn t l thun vi ng knh dy dn, t l thun vikhong cch gia cc dy dn; hiu qu tng tit din dy dn ln hn tng khongcch gia cc dy dn, m u t cng tng i t. 2 - 3 - 4 (Tr v u chng, Tr v Mc lc) Hi: Dy ci ca trm bin th cao p (nh 220kV) th tit din ca n lnhn nhiu so vi kt qu tnh ra da theo cng dng in lm vic lu di can. Ti sao? p: Chn tit din dy ci, khng nhng cn xt n cng dng inlm vic lu di cho php ln nht, m iu quan trng hn l phi xt iu kin - Trang 30 -

31. in p ti hn ca phng in qung tn. in qung khng ch lm tn tht mtphn in nng, m c khi dy dn xy ra in qung s lm cho khng kh gn ion ha, lm gim cch in, d gy nn chp rch v s hoc gia cc pha;trong phm vi in qung s sinh ra kh zn v axt nitric, c tc dng ph hoi ivi kim loi v cht cch in hu c. Ngoi ra, m thanh c bit do in qungsinh ra cng nh hng n s phn on ca nhn vin trm bin in i vi sc ca thit b. Tng ng knh ca dy dn c th nng cao in p ti hn cain qung. ng knh dy chnh ca trm bin in 220KV nn chn tng iln. 2 - 3 - 5 (Tr v u chng, Tr v Mc lc) Hi: Cng tc cao p 220 kV tr ln vn hnh vng cao nguyn d sinh rain qung hn hay vng ng bng? p: vng cao nguyn d sinh ra in qung hn, v kh p ca vng caonguyn thp, mt khng kh nh, khin in p khi u ca in qung xoaychiu ca cng tc cao p gim, v th hin tng in qung mnh hn nhiu vng ng bng, ngay c khi tri tnh ro cng c th nghe thy ting phng inqung tn tng i ln. Ban m, quanh vt mang in u sng. 2 - 3 - 6 (Tr v u chng, Tr v Mc lc) Hi: Ti sao trong thit b phn phi in, in p tng i thp (di15kV) thng thng s dng thanh hp dng hnh ch nht cn trong thit b phnphi in in p tng i cao (trn 35kV) li s dng thanh hp dng hnh trn? p: iu kin ta nhit ca thanh hp dng hnh ch nht tng i tt, cth cho php ph ti tng i ln, cho nn c gng chn dng (di 15kV). Nhngkhi in p tng i cao, nh cao hn 35kV do bc thang in th phn gcnhn qu cao, sinh ra in qung, khng th khng chuyn sang dng thanh hp dnghnh trn. in qung l hin tng phng in sinh ra sau khi bc thang ca in thqu cao. Lc , phn t khng kh b ion ha lm gim kh nng cch in ca khngkh, s sinh ra chp rch xuyn thng. ng thi, in qung to ra zn v cht xyha ca nit, s n mn kim loi v gim cch in. - Trang 31 -

32. 2 - 4 Vn tip t im trung tnh 2 - 4 - 1 (Tr v u chng, Tr v Mc lc) Hi: Ti sao h thng in 110 ~ 220kV l h thng tip t im trung tnhcn h thng in 3 - 35kV l h thng khng tip t im trung tnh? Cn hthng 380/220V li l h thng tip t im trung tnh? p: Trong h thng in cao p, mc cch in khi im trung tnh trctip tip t s gim thp hn khong 20% so vi khng tip t, m ngha kinht ca vic gim thp mc cch in th s khc nhau ty theo s khc nhau cain p nh mc. Trong h thng 110 - 220kV, gi thnh ch to bin th v thit bin, i khi t l thun vi in p th nghim (khi cho in p th nghim lnvt th nghim, khng b nh thng hoc chp rch cng khng c phng in ccb trong du). in 110 ~ 220kV nu p dng hnh thc im trung tnh trc tiptip t th gi ch to bin th v thit b in cng gim khong 20%, cho nn hthng cao p ny thng l h thng tip t. Nhng trong h thng 8 -35kV, u tcch in chim t l tng i nh, im trung tnh tip t khng c gi tr kinh tln m cn lm cho dng in ngn mch ca mi pha i vi t tng ln nhiu,cho nn u p dng hnh thc im trung tnh khng tip t. Cn nh h thng380/220V th do n l in p ca in sn xut sinh hot hng ngy ca mi ngi,im trung tnh ca 380V trc tip tip t s gim thp in th ca dy i vit, gim thiu nguy c in git. 2 - 4 - 2 (Tr v u chng, Tr v Mc lc) Hi: Trong h thng im trung tnh khng tip tt, ti sao c lc bt thin pht in mt pha no khng c in cn dy trung tnh c in? p: Lc ny, pha r in i vi t. Nu dng ng h vn nng os pht hin in p gia dy pha vi dy pha, gia dy pha vi dy trung tnh l bnhthng, nhng in p gia dy trung tnh vi t tng cao, gn 220V. in p capha r in i vi t gn bng 0, in p ca hai pha kia vi t gn bng 380V.Nu r in khng ng k, in tr i vi t ln, th hin tng ny khng rrt. 2 - 4 - 3 (Tr v u chng, Tr v Mc lc) Hi: Gia ng dy ti in i vi t tn ti indung trong h thng im trung tnh khng tip t, nu xy ramt pha tip t th s c bao nhiu dng in in dung chyqua im tip t? p: Sau khi hon i v tr y dy dn mc trnkhng th in dung mi pha i vi t gn bng nhau, tc C A =CB = CC .in p ngun i xng ba pha ln lt tc dng lnin dung mi pha, tng hp dng in in dung to ra bng 0. Nu pha C xy ratip t hon ton th in dung CC ca pha C i vi t b ngn mch, cn li CAv CB in p ba pha cng xy ra bin i,UA v UB t in p pha Uxg s tng lnn in p dy 3 Uxg .Do in p ba pha khng i xng, lc ny gc kp giavct UA v UB l 60o (nh hnh 2 - 4 - 3) dng in in dung ICA v ICB do chng tc - Trang 32 -

33. dng ln CA , CB sinh ra cng lch pha 60o, m ICA = ICB = ( 3 Uxg)/XC = ( 3 Uxg )/(l/ Co)= 3 CoUxg , tng vct ICB v ICA l vct IC = 3Uxg Co ,tc cng dngin chy vo im tip t gp 3 ln dng in in dung ca mi pha i vit. 2 - 4 - 4 (Tr v u chng, Tr v Mc lc) Hi: Khi cn c vo in p la chn thit b in, phi chng c linquan n h thng c hay khng tip t? p: C mt s thit b in phi cn c vo in p i vi t chn,tc cn c vo in p pha chn. Trong h thng tip t iu l ng. Nhngtrong h thng khng tip t th phi cn c vo in p dy chn v trong hthng khng tip t khi mt pha tip t m cu dao khng nhy th in p phai vi t cng pha khng s c s tng ln n in p dy (tip t tnh kimloi). 2 - 4 - 5 (Tr v u chng, Tr v Mc lc) Hi: Ti sao trong mng in tip t cng dng in nh th phi lpthit b gim st tnh hnh cch in i vi t, cn trong mng in tip t cng dng in ln li khng lp? p: Trong mng in tip t cng dng in nh im gia thng quatr khng ln tip t hoc khng tip t. Khi mt pha tip t, do dng in chyqua im s c tng i nh, a s khng th lm cho rle c ng tc bo vthit b. V th, s c s tn ti kh di, m vn c th tip tc lm vic rt lu.Nu khng sa cha kp thi, khng nhng d dn n tai nn in git m cn cth dn ti nh thng cch in gy s c ngn mch gia cc pha (v khi mt phatip t, in p hai pha kia i vi t s tng cao n gn in p gia cc pha). kp thi pht hin s c tip t, trong mng tip t dng in nh phi lpthit b chuyn gim st tnh hnh cch in i vi t. Trong mng in tip t cng dng in ln, im gia trc tip tipt hoc thng qua tr khng nh tip t, mt pha tip t s hnh thnh ngnmch, b rle bo v thit b ngt ring. V th, khng lp thit b gim st tnh hnhcch in i vi t. 2 - 4 - 6 (Tr v u chng, Tr v Mc lc) Hi: Tip t xy ra h quang c nguy hi g? p: Trong tip t mt pha, nguy him nht l tip t h quang gin on,bi v mng in mt mch dao ng c in cm in dung, s dp tt v chy lica h quang in theo s thay i ca chu k xoay chiu, s sinh ra hin tng quin p gp khong 4 ln in p pha. iu ny rt nguy him i vi thit b in,c bit l h thng 35kV tr ln, qu p c th vt qu kh nng cch in cathit b m gy ra s c. 2 - 4 - 7 (Tr v u chng, Tr v Mc lc) Hi: Ti sao trong h thng h ba pha bn dy khng cn thit b kim tracch in ? - Trang 33 -

34. p. Trong h thng h ba pha bn dy, im O ca bin p cp in in pthp, trc tip tip t. Nu trong ba pha c mt pha tip t th s sinh ra dng incng ln ca mt pha ngn mch tip t. Lc ny, cu ch tng i gnim xy ra s c trn ng dy cp in s nhanh chng chy t, khin dy cpin ca pha tip t ngt in, m khng nh hng n cc dy khc v h thng.V th, trong h thng ny ni chung khng cn v mt dy tip t m lp thit bkim tra cch in. 2 - 4 - 8 (Tr v u chng, Tr v Mc lc) Hi: Trong mng in im trung tnh khng tip t, lm sao cn c vong h gim st cch in phn on tnh hnh s c tip t ca mng in? p: Trong mng in im trung tnh khng tip t khi mt pha hon tontip t th tr s ch bo ca ng h gim st cch in ca n bng 0, cn hai phakhc s tng ln ln. Khi mt pha khng hon ton tip t tc tip t qua in trtng i ln th tr s ch bo ca pha tip t s thp hn khi bnh thng, cn haipha khc cao hn tr s bnh thng, in tr tip t cng ln th s thay i ca trs ch bo cng nh. Nu duy tr tip t th tr s ch bo ca ng h s khng thayi, nu tip t phn on th tr s ch bo ca n lc tng lc gim, c khi bnhthng. 2 - 4 - 9 (Tr v u chng, Tr v Mc lc) Hi: Khi dy ko trn khng cao p 10 kV xy ra s c mt dy t ri xungt, ti sao cng tc ngun cu dao khng phi ngt in? p: ng dy cp in 10 kV thuc h thng im trung tnh khng tipt Nu xy ra mt dy b t ri xung t th dng in chy qua im tip tch l dng in in dung, tr s ca n rt nh, ni chung ch c vi ampe. Dngin ny nh hn nhiu dng in ph ti ca n, do thit b rle bo v ungun in khng b tc ng, cng tc cu dao khng nhy ngt in. 2 - 4 - 10 (Tr v u chng, Tr v Mc lc) Hi: Ti sao thit b bo v dng in "khng", trn ng dy cc cpin 6 ~ 10kV khi lp b h cm dng in "0" tip t trn u y cp qua giab h cm thc hin tip t? p: Trong mng in tip t cng dng in nh, khi xy ra s ctip t mt pha, dng in s c va c th chy tr v theo v dn in ca cpin ng dy khng xy ra s c. Nu dy tip t trn u dy cp khng lunxuyn qua b h cm dng in O tip t, th dng in tip t khi c s c sc mt phn theo dy tip t t pha ngoi b h cm dng in th t O chy trli. V th, bo m ng tc tin cy ca thit b bo v dng in O ng dys c, phi xuyn dy tip t qua b h cm dng in O. 2 - 4 - 11 (Tr v u chng, Tr v Mc lc) Hi: C mt ng dy phn phi in ca mt trm ti tiu nng thnkh di. Ma ng, ph ti ca my bin th rt nh. C mt ln, ng dy bnngun ca my bin th (10kV, im trung tnh ca ng dy v bin th khng - Trang 34 -

35. tip t) xy ra t dy mt pha, nhng cha ri xung t, mt ca trm ti tiuu quay ngc. Ti sao? p: l hin tng do s cng hng nam chm in vi tn s lm vicgy nn thnh thong c gp trn ng dy. Khi ph ti ca my bin th rt nh,n nh mt in cm nam chm c in cm rt ln. Khi xy ra t dy mt pha.Cng tc ngun vn v tr ng, do im trung tnh bn ngun in 10kV v mybin th u khng tip t, m dy phn phi in th rt di, nn in dung ivi t ca cc on ca pha A b t tng i ln (hnh a), in dung i t Cny vi in cm L ca my bin th ngu hp thnh mng ni tip nh hnh (b).Sau khi pha A b t, hai pha B, C ni tip, hon ton i xng, im trung tnh cain p ba pha bn cao p ca my bin p trm ti tiu nh hnh(c) di chuyn nO (ng nt lin l vct in th khi dy cha t, ng nt t l vct inth sau khi dy t). Lc ny, E A = (3/2)EA.V in dng i vi t tng i ln, .pha A tuy t nhng vn c dng in in dung, m I vt trc E A 90o, in p . . . . . .trn in cm vt trc I 90o, nh hnh (d). U C , U L ngc chiu v U C - U L = EA . .nn chiu ca U L ngc vi E A c. Lc ny, th t pha bn cao p ca my bin pt ABC bin thnh ACB. Th t pha bn thp p cng thay i ngc litng ng khin cho ng c quay ngc. ng nhin, ip p ba pha lc ny skhng cn i xng, ng c khng th vn hnh bnh thng lu di c. 2 - 4 - 12 (Tr v u chng, Tr v Mc lc) Hi: Trong iu kin im trung tnh my pht in cch in i vi t, tisao in p dy ca my pht in cn bng, cn in p pha i vi t khng cnbng, ch gn bng? p: Trong iu kin im trung tnh ca my pht in cch in i vit in p dy o c l cn bng, UAB = UBC = UCA ,cn in p pha i vi t - Trang 35 -

36. khng cn bng, ch gn bng nhau, l bnh thng. Do im trung tnh ca mypht in i vi t l cch in, cho nn ip p pha ca cc pha my pht in .khng bng in p ca cc pha i vi t. Nu in p pha A i vi t U AO . .bng tng vct in p pha A U A vi in p in dung ca pha A i vi t U AD . . .tc U AO = U A + U AD .Bi v iu kin l cch in v v tr lp t ca cc cundy pha khc nhau. Cho nn s phn b in dung cun dy cc pha i vi tkhng ging nhau, do din p o c ca cc pha i vi t khc nhau. Mypht in khng ging nhau th mc khng cn bng ca in p pha i vi tcng khng nh nhau. Hin tng ny l bnh thng. 2 - 4 - 13 (Tr v u chng, Tr v Mc lc) Hi: B h cm in p s dng trong h thng in thng thng c thnhn thy pha B trong cun th cp u hnh sao (U) th tip t, cn im trung tmli khng tip t. Ti sao? p: Bi v h thng in cn li dng in p th cp ca b h cm inp thc hin lm vic song song ng thi ca h thng. Mt trong cc iu kinu tin ca song song l th t pha ca cc h thng song song phi thng nht. Vth, trc tin phi tm mt si dy dn chung (t) lm mt pha trong ca chng(gi thit pha B). Trong ba pha A, B, C ca cc h thng in c mt pha xc nh(tc pha B l pha chung) th hai pha A v C cn li c th li dng bng th t pha xc nh. Cho nn, cun dy th cp u hnh sao U ca b h cm in p yucu em pha B tip t ch khng cn im trung tm tip t. 2 - 4 - 14 (Tr v u chng, Tr v Mc lc) Hi: My bin th m im trung tnh ba pha khng tip t th c th oc in p i vi t khng? p: Cc pha cc my bin th i vi t khng phicch in tuyt i, i vi t u c dng in r rt nh,nh vy tng ng nh em ba pha qua in tr cao uthnh hnh sao U (nh hnh 2 - 4 - 14), im trung tnh l t (v)khi in tr cch in ca ba pha bng nhau, in p cc phai vi t l in p pha, khi in tr cch in khng bngnhau, th in p i vi t ca pha in tr nh s nh. Nhng thng thng,dng vn k ch c th o c ip p thp nh, thm ch o khng c in p. l v in tr ca vn k nh hn nhiu so vi in tr cch in khin gia phavi t hu nh ngn mch, do o khng c st p. in tr trong ca vnk cng ln th in p o c cng cao, dng bt th in th c th thy rtr. 2 - 4 - 15 (Tr v u chng, Tr v Mc lc) Hi: Trong h thng im trung tnh khng tip t, khi vn k gim st cchin ca dy ci ch bo in p hai pha bnh thng cn mt pha gim r rt. y ldo s c g? p: Khi vn hnh bnh thng, ch bo ba pha ca vn k gim st cchin dy ci phi c bn bng nhau. Khi ch bo in p ca hai pha bnh thng, - Trang 36 -

37. cn in p mt pha gim r rt l thuc s c cu ch in p thp mt pha chyt. V d, pha C chy t th in p i vi t ca pha A, B bnh thng, nhngin p pha C st gim r rt, cn khong 30 ~ 50% in p pha, in p gia phaAC v BC cng c st gim. l v mch in p ba pha cn u nhiu ph ti gia dy, nh vn k ng h o in v.v... Lc ny, vn k pha C v ph ti ugia pha AC, BC ni tip nhau nn c s phn p nht nh, ln ca phn p ny tl nghch vi ln ca tr khng ph ti gia cc pha. 2 - 4 - 16 (Tr v u chng, Tr v Mc lc) Hi: Trong h thng im trung tnh tip t, ti sao c mt s im trungtnh my bin p khng tip t p: Ch yu l hn ch dng in ngn mch mt pha. Mc ch l: (1)Lm cho cng dng in ngn mch ca mt pha khng ln hn dng inngn mnh ba pha, v khi chn thit b u cn c vo cng dng in ngnmch ba pha hiu chnh, nhm phng h hng. (2) Khng ch cng dngin ngn mch mt pha v s phn b trong h thng, p ng yu cu bo v tht O. (3) Gim thiu s gy nhiu ca dng in ngn mch mt pha khng ixng vi h thng thng tin. 2 - 4 - 7 (Tr v u chng, Tr v Mc lc) Hi: Th no l cun dy kh h quang? Trong tnh hnh no th phi lpcun dy kh h quang? p: Cun dy kh h quang l mt cun dy m in tr rt nh, cm khngrt ln, qun trn li st, c u trn im trung tnh ca bin th hoc my phtin. Bnh thng, dng in khng chy qua cun dy kh h quang, nhng khimt pha tip t. Cun dy di in p pha, dng in chy qua ch tip t ldng in in cm ca cun dy v dng in din dung, hai ci lch pha 180 o, chonn b sung nhau, tc khng c dng in chy qua ch tip t, loi tr c s ctip t tc th, do ch b hng khng pht ra h quang gin on nn khng dnn hu qu nguy him. Trong cc tnh hnh sau, im trung tnh ca bin th phi thng qua cun dykh h quang tip t: 1 - Trong li in 20 ~ 60kV, khi dng in tip t ln hn 10A. 2 - Trong li in 6 ~ 10kV khi dng in tip t ln hn 30A. My pht in trc tip ni vi mng in 3 - 10KV, nu s c tip t ctnh cht lu di, my pht in phi vn hnh vi s c tip t th khi dng intip t ln hn 5A, cn phi lp cun dy kh h quang. 2 - 4 - 18 (Tr v u chng, Tr v Mc lc) Hi: Ti sao cun dy dp h quang phi lp phn tn nhiu ch trn mngin lc? V li khng nn lp trm bin in u cui do mng in n cungcp in? p: Cun dy dp h quang phi lp phn tn nhm trnh ch xy ra sc hoc khi cp in kim tra sa cha s gy nn nhiu cun dy dp h quangphi ra khi vn hnh. Trm bin in u cui cho mch in n cp in khngnn lp cun dy dp h quang, v sau khi mch in ny nhy cu cao, cun dy - Trang 37 -

38. dp h quang ca trm bin in s ra khi vn hnh. Bi vy, khng nn p dngphng php u mc trn, l nhm phng nga dung lng cun dy dp hquang khng m khng th tha mn yu cu b dng in in dung. 2 - 4 - 19 (Tr v u chng, Tr v Mc lc) Hi: Ti sao cun dy dp h quang trong h thng cp in c th kh hquang? p: Trong h thng m im trung tnh khng tip t, mi pha u tn tiin dung i vi t, nu khi h thng xy ra mt pha tip t, dng in indung IC chy qua im tip t vt qu tr s qui nh (h thng 35kV l 10A),dng intip t s hnh thnh h quang lc tt lc chy c tnh chu k im s c. Dotrong mng in c in cm v in dung, s hnh thnh mng dao ng, sinh raqu in p tr s ca n c th t ti gp 2.5 ~ 3 ln in p pha, lm hng thitb. Nu lp mt cun cm L (xem hnh 2 - 4 - 19 (a)) trn im trung tnh u hnhsao cun dy cao p my bin th, khi h thng xy ra mt pha tip t th imtrung tnh c in p lch pha Uo tc dng ln L, sinh ra dng in in cm IL chyqua im tip t. Vct ca IC v IL ngc nhau (xem hnh (b)). Khi L di tc dngca Uo khin IL chy qua n bng vi tr s IC th s c tc dng b tr. Thng qua btr, im tip t c th trnh c hnh thnh h quang mang tnh gin on. Bi vcun cm ny c tc dng kh h quang, nn gi l cun dy kh h quang. 2 - 4 - 20 (Tr v u chng, Tr v Mc lc) Hi: Ti sao cun dy kh h quang u trn im trung tnh bn Y camy bin th c cun dy u m khng nn u trn im trung tnh my bin thc mch t t do n Y/Y. p: Cun dy kh h quang l ph ti c tnh cht th t O ca mng in,c lp trn thit b c tr khng th t O tng i nh mi pht huy c y tc dng ca n. Tr khng th t O ca my bin th m cun dy u tam gic() tng i nh. i vi my bin th m cun dy u Y/ v Y/Y/ lc t hado dng in b tr chy qua cun dy pha hnh sao sinh ra b trit tiu bi lc t hado cun dy cng mt li st sinh ra cho nn tr khng th t O ca my bin thloi ny tng i nh. My bin th u Y/Y c mch kn t t do (ging nh mybin th ba pha u Y/Y do ba bin th mt pha to thnh) v tr khng th t khngqu ln, cun dy kh h quang khng th pht huy ht tc dng nn khng dng. - Trang 38 -

39. 2 - 4 - 21 (Tr v u chng, Tr v Mc lc) Hi: Mng phn phi in 3 - 10kV im trung tnh khng tip t, khi dngin in dung i vi t ln hn 30A, yu cu phi lp cun dy kh h quang,i vi my pht in in p l 3 - 10kV, khi dng in in dung i vi t lnhn 5A phi lp cun dy kh h quang, ti sao? p: Mng phn phi in 3 - 10kV im trung tnh khng tip t, khi xyra mt pha tip t th dng in tip t ca n l dng in in dung. Khi dngin tip t tng i nh th h quang tip t s t ct, nhng khi ln hn 30Ath h quang in khng th t tt na, thng km theo h quang gin on sinh raqu in p khong gp 3 ln ton pha. Ngoi ra, do dng in tip t tng iln, kch thc v phm vi tc ng ca h quang cng ln di tc dng ca gi,sc nhit v lc in ng nn h quang dao ng ko di, thng gy nn ngnmch nhiu pha, dn n mt in. Do , khi dng in in dung i vi tca mng phn phi in 3 - 10kV im trung tnh khng tip t ln hn 30A thphi lp cun dy kh h quang b tr, nhm gim dng in tip t, c li chodp kh h quang. Khi cun dy bn trong my pht in c s c mt dy tip t, nu tip tcvn hnh khi cn s c th c th gy chy li st stato. Cho nn, nu cn my phtin vn hnh mt thi gian khi vn cn s c mt pha trong my tip t th dngin in dung nht nh phi nh hn 5A, nu ln hn 5A th phi lp cun dykh h quang im trung tnh b tr, nhm gim dng in tip t, ph hngmy pht in. 2 - 4 - 22 (Tr v u chng, Tr v Mc lc) Hi: Ti sao khng th lp cu ch dy trung tnh trong mch in h bapha bn dy? p: Khi in th ba pha ca my pht in cn bng m ph ti mi phakhng bng nhau (ph ti mi pha ca my pht in thng khng bng nhau), lc trong dy trung tnh gia c dng in, nu dy trung tnh lp cu ch m b t,cng dng in dy trung tnh gia bng 0, nh vy dng in cc pha s binng do li gy nn bin ng in p pha, lm cho lch pha in p ba pha rtln, in p mt pha no c th vt tr s nh mc ca n lm chy bng n. 2 - 4 - 23 (Tr v u chng, Tr v Mc lc) Hi: n chiu sng do h 3 pha 4 dy cp in, t nhin sng khng bnhthng, c ci rt sng, c ci rt ti, nu tng gim s lng n mt pha no thu lm thay i sng ca tt c cc n, nhng lc , in p dy gia 3 phagn nh bng nhau. Ti sao? p: Trong ng dy cp in h 3 pha 4 dy, sau khi ct tch dy trung tnh,in p cc pha ca ba pha s mt thng bng theo s mt thng bng ca ph ti.Ly ph ti ca hai pha lm v d (nh hnh 2 - 4 - 23), gi thit trong pha A, pha Bu c mt s n chiu sng cng sut nhnhau. Khi bnh thng, ng cng tc ca btc bng n no, in p hai u ca bng nu l 220V. Nu y trung tnh t ch x,lc ny in p a vo gia A, B l 380V. Khi - Trang 39 -

40. mi pha A, pha B u bt s bng n bng nhau (tc bt s cng tc) th in pa n mi bng n l 190V. Khi s bng n bt trn pha A ln hn s bng ntrn pha B th in tr ng tr RA < RB, in p u ca n pha B ln hn in pu ca n pha A. Nu s n pha B khng thay i, th cng vi vic tng s npha A, sng ca n pha B cng sng, cn sng ca n pha A cng ti. Khinghim trng, n pha B c th b chy dy tc do in p qu cao. Cng l do , trong h 3 pha 4 dy, dy trung tnh b t s xut hin hintng ging nh vy, pha nhiu bng n c bit ti, pha t n c bit sng. 2 - 4 - 24 (Tr v u chng, Tr v Mc lc) Hi: Ti sao di ging khai thc than nghim cm tip t im trung tnhh thng cung cp in? p: Do di ging rt m t, nu dy trung tnh tip t, th khi khngmay tip xc vi dy dn ca pha no , con ngi s c kh nng nguy him ntnh mng. ng thi, khi dy trung tnh tip t, cng dng in ngn mchmt pha tip t tng i cao, d dn n chy v n kh m tan. bo m anton hm m nn nghim cm tip t dy trung tnh di ging khai thc than. 2 - 4 - 25 (Tr v u chng, Tr v Mc lc) Hi: u dy ca mt my bin th phn phi in (380/220V) nh hnh 2 -4 - 25. Nu dy trung tnh b t, liu bng n Dl, D2 c sng khng ? Dl hay D2 snghn? p: Nu dy trung tnh t th mch inbin thnh hai bng n mc ni tip vi nhau riu vo in p 380V, do bng n vn sng,nhng sng khc vi khi cha t. Bng n Dlvn c cng sut tng i ln hn nn in tr nhhn, do st p trn Dl nh hn (in p gia haicc ca bng n khng n 220V) cho nn sngtng i ti, cn bng n D2 cng sut tng i nh nn in tr ln, do inp hai u ca n ln hn 220V, nn sng hn nhng lu n s b chy. - Trang 40 -

41. 2 - 5 Cp in v thng tin 2 - 5 - 1 (Tr v u chng, Tr v Mc lc) Hi: Mng in lc ca nhiu nc c ni p dng thng tin ti ba, c nili p dng thng tin vi ba. Mi loi c c im g? p: Thng tin ti ba l dng dy ti in cao th ca chnh mng in lc truyn dn thng tin. N l sng cao tn chuyn tn hiu ngn ng thnh tn hiuin, ti trn sng in ngun theo tn s lm vic, truyn dn theo truyn ti incc. N c cc u im: cng c hc cao, bo dng tin li, u t tit kim.Nhc im ca n l bng tn thng tin hp, tn s s dng cht khi ng dyxy ra s c thng gin on thng tin, cht lng thng tin km, thng thng chc th m n tuyn, ch thch hp vi mng in lc dung lng tng i nh. Thng tin vi ba l mt trong cc loi thng tin v tuyn, bc sng di mtmt, s truyn b vi ba tng t nh s truyn b sng nh sng, bc sng pht xca n ch c th truyn b theo ng thng. V qu t l hnh cu, khong cchtruyn b sng vi ba khong 50km, nu mun thng tin vi ba c khong cch xa hnth phi c cch 50km t thm mt trm trung chuyn vi ba. Trm trung chuynnhn tn hiu ca trm pha trc, qua khuch i ri truyn tip n trm k tip,c th truyn b, sau cng truyn b tn hiu n on cui, hon thnh nhim vthng tin. Thng tin vi ba l da vo sng khng gian truyn b nn vic truyn brt n nh, cht lng thng tin tt, tin cy cao, bng tn thng tin rng (2 11kHz) dung lng ln, thng c th truyn 2700 ng thoi. Cng vi s tngln ca dung lng li in, cc mng in ln sau ny s tng bc dng thngtin vi ba thay cho thng tin ti ba. 2 - 5 - 2 (Tr v u chng, Tr v Mc lc) Hi: Ti sao ng dy in cao p phi bo m duy tr khong cch cnthit i vi ng dy thng tin? p: nh hng (v mt thng thoi v an ton) ca ng dy in lc ivi ng dy thng tin ph thuc rt ln vo hnh thc tip t ca im trung tnhtrong h thng in lc cp in p mng in, chiu di song song. Khi bnhthng, in p v cng dng in ca ng dy ti in ba pha l cn bng;nh hng cm ng in t i vi dy thng tin tng i nh. Nhng, nukhong cch qu gn th do khong cch gia ng dy thng tin i vi ng dyti in ba pha khng u nhau, s gy nhiu in t i vi dy thng tin, nhhng cht lng thng thoi. Nu dng in ba pha khng cn bng th nh hngi vi dy thng tin cng ln. c bit l khi trn ng dy in lc im trungtnh trc tip tip t m xy ra s c mt pha tip t th dng in ngn mch rtln. T trng do n sinh ra s to ra th in ng cm ng rt ln trn ng dythng tin song song vi n, uy hip s an ton i vi nhn vin thng tin v thit b,nu l dy thng tin ng st th c th gy nn ng tc nhm tn hiu ng st.Do , gia ng dy thng tin vi ng dy truyn ti in phi bo mkhong cch cn thit. 2 - 5 - 3 (Tr v u chng, Tr v Mc lc) - Trang 41 -

42. Hi: Ti sao tin hnh hon v dy dn ba pha ca ng dy ti in cao pc th gim thiu s gy nhiu i vi ng dy thng tin? p: Dy dn ba pha ti in cao p thngxp ngang bng, thng ng hoc tam gic khngu b tr l khng i xng. . Khi ng dy tiin gn hoc song song vi ng dy thng tin,tng giao kt t ca cc pha giao nhau vi ngdy thng tin khng phi bng khng, t c thcm ng ra in p gy nhiu trn ng dy thng tin, nh hng thng tin v nguyhim n s an ton ca ngi v thit b. Nu lun lu thay i v tr ca dy dnba pha ng dy ti in trn ct in nh th hin trong hnh, trong ln thay i vtr th nht, dy dn cc pha ln lt chim gi cc v tr hnh hc A, B, C nh vytng giao kt t cc pha giao nhau vi ng dy thng tin s gn bng 0, nn c thci thin hoc loi tr gy nhiu i vi ng dy thng tin. 2 - 5 - 4 (Tr v u chng, Tr v Mc lc) Hi: Ti sao hin nay, nh my in hoc trm bin in dung lng tngi ln a phn p dng iu khin bng in yu? p: Nh my in hoc trm bin in dung lng tng i ln th itng iu khin, o c nhiu, nu dng in yu vi in p mt chiu 220Vhoc 110V v in p xoay chiu 100V, dng in 5A iu khin ngun in thth tch thit b iu khin v cc ng h o u tng i ln, cp in dng chy ni tng i to, bung iu khin cng phi rng ln. Nu i sang dngin yu vi in p mt chiu tng i thp (hin nay a s dng 6V, 12V, 24Vhoc 48V) v din xoay chiu 50V (hoc 100V) v dng in 0.5A (hoc 1A) iu khin ngun in th c th dng cp in tit din nh, thit b iu khin vng h o c nh, nh vy c th tit kim kim loi mu, gim s mn iu khinv thu nh c din tch phng iu khin. p dng iu khin bng mng inyu cn tin do vic thc hin t ng ha, phi hp d dng vi my tnh, thit bo. V th, ni chung khi khong cch iu khin tng i xa, i tng iukhin tng i nhiu, a phn p dng iu khin bng mng in yu. - Trang 42 -

43. 2 - 6 Nhng vn khc 2 - 6 - 1 (Tr v u chng, Tr v Mc lc) Hi: Ti sao khi chn thit b in khng ch phi xem xt in p, cng m cn phi xem xt n nh ng thi? p: in p, cng dng in l ch ph ti m thit b in c th chuc trong tnh hnh bnh thng, mt khi xy ra ngn mch th ng lc gia cc phart ln, ng lc ny ph thuc vo ln ca dng in ngn mch h thng, nukhi xy ra ngn mch, thit b in chu khng ni ng lc gia cc pha th thit bny khng th vn hnh an ton. Vi th phi xt n n nh trng thi ng(ng thi). 2 - 6 - 2 (Tr v u chng, Tr v Mc lc) Hi: Ma ng, trn thit b in ng vn bng, c nh hng g khng? p: Theo kinh nghim, tnh nng cch in ca bng khi mi ng tng icao, nhng sau mt lc, do b mt dnh bi, bt than, s lm gim tnh nng cchin. Cn phi tm cch loi b, nu khng s xy ra s c. 2 - 6 - 3 (Tr v u chng, Tr v Mc lc) Hi: n ch bo trn t cng tc cao p l 110V, nu mc n ch bo vongun 110V, ti sao phi mc ni tip mt in tr? p: Theo qui nh chung, bng n 110V, u vo ngun