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Tng thch in t trong h thng ngun

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EMC (ELECTROMAGNETIC COMPATIBILITY) TNG THCH IN T TRONG H THNG NGUN SCHNEIDER ELECTRICVi tt c cc thit b s dng in, EMC phi c xem xt mt cch c th

ngay t giai on thit k ban u v nhng nguyn l, quy tc khc nhau tip tc c xuyn sut qu trnh sn xut v lp t thit b. iu ny c ngha rng tt c rt phc tp, t nhng k s v nhng kin trc s m thit k mt ta nh n nhng nh k thut thi cng dy in trong cc t thit b in, bao gm nhng chuyn gia thit k mng trong cc ta nh v nhng kp, i xy lp cc thit b, phi c quan tm n EMC Mt qui tc c chp nhn l "Sng ha bnh " cng vi s tn ti ca cc nhy ca thit b vi nhng nhiu lon in t trng (m thnh ra c xem xt nh l " i tng b nh hng ") dc theo thit b pht ra nhng s nhiu lon nh vy (trong nhng t khc, gi l " ngun " ca nhng s nhiu lon) Tp ti liu ny c bin son qua nhiu nm c kt kinh nghim ca Cng ty Schneider Electric, gii thiu nhng s nhiu lon thng gp v cung cp vi phng php thc hnh b p s nhiu lon .

Ni dung1. GII THIU 1.1 Tng thch in t - EMC - Nhng c trng v qui tc 1.2 Ngy nay, EMC l rt cn thit. 1.3 s phc tp ca l thuyt EMC 2. NGUN 2.1 Tm quan trng ca vic nhn dng h thng ngun 2.2 V d s nhiu lon vt dn in ca ngun lin tc trong in nng 2.3 V d bc x ca nhng nhiu lon ngun: ngn mch trong cc trm bin p MV v VHV 3. GHP NI 3.1 S khc nhau ca cc kiu ghp ang tn ti 3.2 Cc kiu trng chung hoc khc nhau lin quan ghp ni dy 3.3 Ghp tr khng chung 3.4 Cc kiu khc nhau ca vic ghp ni dy hoc bng xuyn cho 4. CC H HNG 4.1 Cc li thit b 4.2 Cch gii quyt vn 5. CI T 5.1 Ci t mt s h s quan trng trong ton b h thng EMC 5.2 Giai on thit k 5.3 Giai on ci t 5.4 V d thc hnh 6. TIU CHUN, KIM TRA THIT B V KIM TRA TON B 6.1 Tiu chun 6.2 Kim tra thit b 6.3 Kim tra 7. KT LUN Sinh vin thc hin: Trn Thanh Sn (T-VT 2006-2009) Trang 1

Tng thch in t trong h thng ngun Ti liu tham kho chnh:


1/ Gio trnh mn hc: Tng thch in t v sng in t trong cc h nh hng 2/ Cahier technique no. 149; EMC: electromagnetic compatibility of SCHNEIDER ELECTRIC Ti liu nghin cu: 1/ Introduction to Electromagnetic Compatibility; Second Edition CLAYTON R.PAUL Department of Electrical and Computer Engineering, School of Engineering, Mercer University, Macon, Georgia and Emeritus Professor of Electrical Engineering, University of Kentucky, Lexington, Kentucky A JOHN WILEY & SONS, INC. PUBLICATION 2/ Power Quality Application Guide Earthing & EMC Fundamentals of Electromagnetic Compatibility (EMC) of Copper Development Association

Sinh vin thc hin: Trn Thanh Sn (T-VT 2006-2009)

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Tng thch in t trong h thng ngun 1. GII THIU


1.1 Tng thch in t - EMC c trng v qui tc: EMC l mt c trng ca thit b hoc nhng h thng m t chng li nhng s pht x in t tng ng ca chng. Theo T Vng K Thut in Quc t (International Electrotechnical Vocabulary) IEV 161 -01-07, EMC l kh nng ca mt thit b hoc h thng lm chc nng tha mn trong mi trng in t trng ca n m khng cho nhng s nhiu lon in t qu qut lm quen vi bt c ci g trong mi trng . Ngy nay, EMC cng l mt qui tc c tp trung vo ci thin s ng tn ti ca thit b hoc nhng h thng m c th pht ra s nhiu lon in t v / hoc c cm ng ti chng. 1.2 Ngy nay, EMC rt cn thit Nhiu thit b v nhng h thng lun lun b l thuc ti s nhiu lon in t, v bt k thit b k thut in no, chnh n, t nhiu l mt my pht nhiu lon in t. Nhng s nhiu lon ny c pht sinh bng nhiu cch. Tuy nhin, nguyn nhn chnh gy ra chnh l nhng s bin i thnh lnh ca dng in hoc in p. Phn ln nhng s nhiu lon in chung nht (xem hnh 1) trong vng in t ca in p thp c tho lun trong "Cahier Technique "s 141". Cahier Technique "s 143 tho lun v nhng s nhiu lon pht sinh khi thit b hot ng ti mc in p chuyn mch l trung bnh. Lp Nng lng cao Tn s trung bnh Ngun gc - Chuyn mch ngun cng sut Nhng s st p - Nhng b ngn mch - Khi ng cc mt cng sut cao - Cc h thng vi bn dn cng sut iu ha - L h quang in - St nh trc tip hoc gin tip - B chuyn mch ca thit b iu khin Qu p - Ngt cc b ngn mch ca cc b bo v Hin tng phng in ca trng tnh Phng in tnh in in trong c th con ngi Hnh 1:Nhng nhiu lon chung nht Kiu

Tn s cao

Nhng s nhiu lon ny c th c truyn lan do s truyn dn dc theo nhng si dy cp hoc c bc x trong cc hnh thc sng in t. Nguyn nhn gy ra s nhiu lon c m t bng cc hin tng di y. Hai v d l giao thoa ca sng v tuyn v giao thoa vi nhng h thng iu khin v o lng gy ra bi nhng s pht x in t. Trong vi nm gn y, vi khuynh hng cng nhau lm cho EMC tr nn quan trng hn bao gi, l : * Nhng s nhiu lon ang tr nn mnh hn vi gi tr in p v dng in ngy cng tng . * Nhiu mch in t ang gia tng s dng cc b cm bin. Sinh vin thc hin: Trn Thanh Sn (T-VT 2006-2009) Trang 3



* Khong cch gia nhng mch cm ng (thng l in t ) v nhng mch gy nhiu (nh nhng mch cung cp ngun in) ang tr nn nh hn. Trong s pht trin ca nhng sn phm , nh h thng chuyn mch bo v Merlin Gerin (hnh 2), Schneider Electric thy trc nhu cu cn hiu bit v p dng nhng nguyn l EMC. Trong h thng thit b ng ngt v iu khin hin i, dng in thp v cao, b iu khin v cc b ngun in t, b bo v in t v nhng thit b cung cp in tt c c b tr tng i gn.

Hnh 2 : V d ng dng EMC : mc in p trung bnh panel SM6 cha mt cu dao in c thit k ngt b ngun (vi dng in hng trm ampe in p di hng chc kilvn), v mt chng trnh SEPAM iu khin, b theo di v bo v. T hp thit b hon thin phi c chc nng n nh di tt c mi trng hp. Do vy EMC l mt tiu chun c bn phi c xem xt trong tt c cc khu pht trin v sn xut sn phm, cng nh trong thi gian lp t v u ni dy. Hn na, by gi EMC bao gm mt trong nhng tiu chun v ang tr thnh mt yu cu hp php. Nhng kinh nghim v thnh tu ca Schneider Electric th khng gii hn i vi vic tha mn chc nng ca cc h thng in v/hoc in t trong mi trng in t thng thng ca n: v d, Merlin Gerin thit k v xy dng thit b c kh nng chng c nhng iu kin khc nghit nht nh s bc x in t pht sinh bi cc v n ht nhn cao . 1.3 L thuyt EMC th phc tp Bt k cng vic no lin quan n EMC dn n vic phn tch ba thnh phn sau: Sinh vin thc hin: Trn Thanh Sn (T-VT 2006-2009) Trang 4

Tng thch in t trong h thng ngun-


S gy nhiu ca my pht hoc ngun - Truyn lan hoc ghp ni - Thit b hoc h thng b nh hng hoc cc i tng b nh hng khc Ni mt cch chnh xc, ba thc th khng phi l c lp nhng tt c cc mc ch thc hnh u c gi thit ti. S phn tch l thuyt th kh khn bi v n lin quan n s truyn lan ca sng in t trng c m t bi mt tp hp phng trnh vi phn phc tp c gi l nhng phng trnh ca Maxwell. Ni chung, chng khng th c gii quyt nhng b mt gii php phn tch cho nhng thit b v nhng kch thc thc t. Thm ch vi nhng h thng my tnh mnh, gii php s thng rt kh thu c hiu qu. Trong thc t, nhng vn EMC phi c cp vi cc gi thit c n gin ha, vic s dng nhng m hnh v c bit l cc phng th nghim v a n cc phng php o. 2. NGUN NHIU 2.1 S quan trng ca vic nhn dng ngun Nhn dng v o th ngun th quan trng mt khi nm chc kiu ngun s xc nh nhng php o sau. - Gii hn ca nhng s nhiu lon pht sinh (E.g. trn mt cng tc, bng vic lp t mt mch cng hng n v RC song song vi ngun AC. Li dy, hoc mt it trn li dy ngun DC) - Trnh s ni cho (i.e. v mt vt l phn ra hai phn t khng tng thch cao) - Kh nhy nhng i tng b nh hng tim tng (e.g. s dng v cch ly) Cc tc nhn gy ra chnh: Bt k thit b hoc hin tng vt l /in pht ra s nhiu lon in t trng, hoc cc dy dn hoc bc x, gi l ngun nhiu. Nguyn nhn chnh gy ra s nhiu lon in t l s phn phi cc b ngun in, sng v tuyn, s phng in t v st nh - Phn phi ngun in, mt s ln s nhiu lon c to ra bi chc nng chuyn mch Trong vng in p thp, vic m nhng mch in cm nh nhng cun dy cng tc, nhng m t , nhng van cm ng t .v.v. pht sinh nhng xung in p rt cao (ln ti vi kV ngang qua nhng thit b u cui cun dy) m cha ng hi tn s cao (ti hng trm MHz). Trong vng in p cao hoc trung bnh, vic m v ng b ngt ni sn sinh nhng sng vi mt nhp rt nhanh (mt vi nan-giy). Nhng sng ny th c hi c bit ti nhng h thng trn nn b vi x l. - Sng v tuyn pht ra bi nhng h thng theo di t xa, iu khin t xa, truyn thng v tuyn, nhng my truyn hnh, nhng my b m .v.v. chnh l ngun gy ra s nhiu lon trong th t vi V/m. Ngy nay, tt c nhng my pht gy nhiu lon ny th ni chung ngy cng tng v d nh hng n thit b bi vy cn c cung cp ngy cng tng hiu qu bo v. - Mc np in ca c th con ngi : cho v d, mt ngi i b trn mt kiu thm trong mt kh hu kh v lnh c th c np ln trn ti hn 25 kV! Bt k tip xc vi sn phm thit b in t no u sn sinh mt s gii phng vi mt Sinh vin thc hin: Trn Thanh Sn (T-VT 2006-2009) Trang 5



thi gian rt nhanh (vi nan-giy) c np vo thit b bi s kt ni v bc x, pht sinh s nhiu lon chnh. Nhng c trng ca s nhiu lon Ngun c th c nh trc (E.g. my pht v tuyn) hoc khng c nh trc (e.g. n v hn h quang in). Tuy nhin ni chung chng c th c phn bit bi nhng c trng ca nhng s nhiu lon do chng sn sinh : - Ph - Dng sng thi gian ln hoc bao ph ca ph - Bin - Nng lng Ph, bng tn s b bao trm bi s nhiu lon c th rt hp, nh trng hp ca h thng in thoi di ng , hoc rt rng, nh nhng l h quang in. Nhng s nhiu lon kiu xung bao trm mt b rng ph c bit ln ti 100 MHz hoc hn (xem hnh 3). Ti loi cui cng ny phn ln thuc v ring ca ngun nh l: - S phng in ca trng tnh in - Chuyn mch r le, b ngt kt ni, cng tc, nhng chuyn mch v nhng cu dao in bn trong LV, MV v HV bng - St - Cc xung in t ht nhn (lnh vc c bit)

Hnh 3: Nhng v d v nhng c trng ph ca tn hiu nhiu Mt khi mc ca s ghp ni trc tip cn cn i ti tn s, EMC s dng min tn s m t c im s nhiu lon. Kiu trnh by ny ,cho mt tn hiu tun hon, th tng t nh mt chui Fourier (bao gm tng ca cc hi). Sinh vin thc hin: Trn Thanh Sn (T-VT 2006-2009) Trang 6



Dng sng m t nhng c trng ca s nhiu lon trong c thi gian v c th, cho v d, mt sng hnh sin tt dn hoc hm m gp i. N c biu th nh mt thi gian ln tr, mt tn s tng ng 0.35/tr hoc n gin l tn s nhiu lon cho tn hiu bng hp hoc nh mt bc sng c quan h vi tn s bi cng thc =c/f, trong c l tc ca nh sng (3 * 108 ms - 1). Bin l gi tr cc i ca tn hiu t n di dng in p (volt), lnh vc in (v/m ), etc. Nng lng l s nguyn ca mc nng lng tc thi trong c thi gian tn hiu nhiu ko di 2.2 V d ca mt ngun lin tc dn n s nhiu lon trong cc b ngun in t Trong cc b ngun in t, nhng ngun nhiu c bn hng ti l in p hn l nhng dng in tc thi. Nhng in p c th thay i hng trm vn thc t trong mt vi ns a dV/dts qu mc109 V/s.

Hnh 4: Ngun nhiu lon trong cc b ngun in t: K thut chuyn mch iu ch rng xung a) L thuyt b) M rng xung(m rng t); mt phn ca sng hnh sin khng tng xng khi n bao trm 20 ms; tr 2 to 3 tf (10 ns to 1 s) iu ch rng xung (PWM) (xem hnh 4), v d, pht sinh mt in p sng hnh sin t mt in p DC, vic in p thay i t 0 n Udc (660 V cho ngun ba pha) xut hin trong mt thi gian rt ngn, ns ti vi s ph thuc vo cng ngh c s dng. in p thay i nhanh chnh l ngun ca nhiu hin tng nhiu lon, phn ln s nghi vn da vo kinh nghim, pht sinh nhng dng chy xuyn qua bt k nhng in dung k sinh no. Dn n in dung k sinh Cp c tnh n, dng in tnh chung nh sau: ICM = Cp dV/dT. Vi nhng thi gian ln c cp sm hn, mt in dung k sinh 100 pF th pht sinh dng in ch chung ca vi trm mA. Dng nhiu ny s chy Sinh vin thc hin: Trn Thanh Sn (T-VT 2006-2009) Trang 7



xuyn qua dy dn tiu chun zr v c th sa i nhng tn hiu (d liu hoc nhng cu lnh), c chng ln nhy php o v quy ry thit b khc bi vic a tn hiu nhiu vo trong mng phn phi cng cng. Mt cch b tr hin tng ny, i.e. bo m EMC, tng thm thi gian ln in p. Tuy nhin mt gii php nh vy gia tng ng k s mt mt cc chuyn mch trong nhng tranzito, sn sinh nhit c hi. Cch khc lm gim bt nhng dng in ch chung c hiu qu khc gm c tng thm tr khng ch chung. Cho v d, khi ghp nhng thnh phn b ngun in t, c hai phng php sau th thng s dng : _ Ngt b tn nhit (khng kt ni in), (xem hnh 5), nu nhng qui tc an ton th cha b xm phm.

Hnh 5: in dung k sinh ca b tn nhit(thnh phn lm mt) c k n trong vic thit k UPS - Gim bt in dung k sinh gia thit b v b tn nhit s dng mt vt cch ly vi mt hng s cht in mi thp (xem hnh 6).

Hnh 6: Cc kiu cht cch ly c s dng khi lp cc thnh phn in t


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Trong lnh vc h thng UPS (ngun lin tc) chng hn, cc bin php phng nga trn lm khc i gia h thng " lm nhim " v mt h thng " sch ". Cho nhng h thng UPS, ch rng in t mc thp trong b o tnh phi c bo v chng li nhng s nhiu lon c to ra bi nhng mch in ngun ca chnh mnh. Tht cn thit hiu v iu khin hin tng ny gii hn nh hng ca s pht x c hiu qu v tit kim. Nhng ngun t thng xuyn hn khc tn ti nh st v chuyn mch t bin c th pht sinh dV/dts v dI/dts ln. S nhiu lon ny cng pht sinh bc x nhng trng. 2.3 V d ca ngun nhiu bc x : ng mch trong trm MV v VHV Mi trng trm, c bit trong nhng ng dng in p trung bnh v rt cao, c th cha ng nhng min c xung in t trng rt mnh. Nhng thao tc ng ngt nht nh c th pht sinh nhng in p cao hn nhiu gi tr danh nh trong mt thi gian rt ngn. Cho v d, khi mt chuyn mch 24kV c ng, hin tng nh la gy ra nhng s bin i in p hng chc KV trong mt vi ns. Phn ny s c bn lun chi tit hn trong "Cahier Technique no 153 :"SF6 Fluarc circuit breakers and MV motor protection" Nhng php o thc hin nhng phng th nghim Schneider cho thy trong thi gian chuyn mch 24 kV ng ngt, min hnh sin tt dn t n nhng gi tr nh 7.7 kV/M vi tn s 80 MHz khong cch 1 mt t t chuyn mch. Sc mnh ca min ny th qu ln khi so snh vi mt 1W cng sut pht ca my b m song cng m pht sinh 3 n 5 V/m o ti khong cch ca 1 mt. in p c truyn lan dc theo dy dn, nhng thanh gp, cp v dy trn. Tn s th phc tp, i.e do hin tng xy ra nhanh, nhng dy dn (c bit l nhng thanh gp) vn hnh nh anten v nh c trng lnh vc trng in t chng pht ra th ph thuc cao vo thit k ca nhng thng kim loi (vng phn chia con, t chuyn mch). Trong nhng trm in p rt cao c lp bc kim loi, trng in t th c bit mnh. V bc kim loi SF6 cch ly trm c hnh dng ng trc v bi vy n lun th hin tr khng c trng khng thay i. in p thay i nhanh bn trong kim loi c th ngn vic pht sinh hin tng sng ng; chng c to ra do xut hin phn x lc tr khng b thay i. Cng v thi gian ca hin tng cng c tng bi hiu ng ny. Mi trng in t vng in p trung bnh v rt cao yu cu nghin cu tng thch in t su hn thit k v lp t nhng h thng r le, nhng thit b iu khin v b kim tra. iu ny th c bit quan trng v phi thm vo bc x nhiu. (xem hnh 7)


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Hnh 7:3 v d thit b vi in t s c pht trin bi Schneider Electric c thit k y tng thch in t trng 1- A SEPAM c tch hp n v bo v v iu khin trong thit b MV 2- n v bo v v iu khin cho b ng ngt Masterpact 3- ANTIVA 66 iu khin tc 3 GHP NI 3.1 Tn ti nhiu kiu ghp ni khc nhau: S ghp ni ni n s lin kt, s chuyn i hoc truyn lan ca nhng s nhiu lon trng in t t my pht n i tng b nh hng. S ghp ni c biu din di dng h s ghp ni k, n v l dB (e.g 75dB), m c th nh gi nh hng truyn dn tn hiu nhiu lon t ni pht n i tng b nh hng .


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(k = 20 log A (received)/A (transmitted), vi A l cng ca tn hiu nhiu) H s k ch c nhiu ngha khi chuyn i s nhiu lon in t sang tn s, m thng l trng hp trong thc hnh. Ba kiu ghp ni ni ting c th c phn bit - Ghp ni trng vi dy theo kiu chung v kiu vi sai - Ghp ni tr khng chung - Ghp ni dy hoc xuyn cho theo kiu vi sai 3.2 Ghp ni trng vi dy theo kiu chung v kiu vi sai Vng trng in t c th kt ni vi bt k kiu cu trc nh dy no v pht sinh kiu chung (i vi t) hoc kiu vi sai (gia nhng dy) in p hoc, ni chung c hai trng hp. Kiu ghp ni ny c gi ghp ni trng vi dy v cng c bit nh hiu ng anten ca dy, rnh trong bng mch in, etc. Kiu ghp ni chung pht sinh nhng in p v dng in nhiu lon kiu chung. in p nhiu kiu chung (VCM) l in p m nh hng tt c cc cht dn sng. N c tham chiu ti v my hoc mass t (trong nhng h thng in bn tiu biu) : tt c kiu chung c c lp kim tra trong vic ng m in p thp bi vy c thc hin gia mass t v tt c cc pha. Dng in kiu chung (ICM) l dng in m chy xuyn qua tt c cc cht dn sng trong cng hng (Xem hnh 10). Dng in cm ng vo trong dy LV bi mt xung chp l dng in kiu chung.

Hnh 10: in p v dng kiu chung gia 2 rle ca phn in p thp trong t in p trung bnh - Ghp ni kiu vi sai ko in p v dng in vo v cm ng, v d, gia hai pha ca mt cu dao in hoc gia hai dy m truyn d liu cm ng ti linh kin in t. Nhng phng trnh m iu khin s ghp ni gia vng trng in t (tr khng ca mt sng bt k) v mt dy nh cu trc (c th cng bt k) th rt phc Sinh vin thc hin: Trn Thanh Sn (T-VT 2006-2009) Trang 11



tp. Trong a s cc trng hp chng khng th c phn tch m cng khng a ra s. D sao, n gin hn v a s cc kiu ghp ni chung c th c biu din phn tch : ghp ni gia thnh phn t tnh ca vng trng in t v vng ca vng A hnh thnh bi nhng dy dn (Xem hnh 11). Thnh phn t tnh H ca trng cm ng trong chui vng in p bng nhau : e = 0 A dH/dt Trong 0 = 4 10-7 H/m l thm thu trong chn khng

e = in p cm ng bi trng in t Hnh 11: V d ghp ni trng vi dy kiu vi sai Cho v d, trong mt trm in p trung bnh, mt vng (ca dy hoc cp) bao trm 100cm2 t 1m t t chuyn mch (xem hnh 12) v l xung kiu trng 5.5kVrms/m (php o trong phng th nghim) s pht sinh (bi s cm ng) mt chui in p 15 V.


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Hnh 12: V d ca vng t ca thnh phn in p thp trong t in p trung bnh 3.3 Ghp ni tr khng chung Nh tn gi , ghp ni tr khng chung l kt qu t mt tr khng c chia s bi hai hoc nhiu mch. Tr khng chung c th kt ni t, mng mass t , mng phn phi ngun, dng chung dy dn c mc ngun tn hiu thp etc.

Hnh 13: Cc i lng o bng khuych i thut ton s khng ng bi v dng nhiu trong mch A (phn cung cp ngun) cao to ra in p nhiu ti mch B (phn o) Mt v d cho thy nhng hiu ng ca kiu ghp ni ny (Xem hnh 13). Dng in nhiu trong mch A khong vi chc mA pht sinh nhng in p nhiu vi V trong mch B. Nu mch B s dng M nh l im tham chiu (c th l t), im Sinh vin thc hin: Trn Thanh Sn (T-VT 2006-2009) Trang 13



tham chiu c th thay i vi vn. iu ny chc chn nh hng n mch tch hp in t m lm vic vi nhng in p c cng ln. V d ch ra rng mt tr khng chung c th c hnh thnh bi mt dy c di vi mt v chung cho c hai mch A v B. S nhiu lon c ln Uc = Ia Zc trong + Ia l dng nhiu + Zc l tr khng chung (Xem hnh 14)

Hnh 14: S tr khng chung Ti nhng tn s thp tr khng chung th thng v cng nh. Cho v d, yu cu an ton khin mt ct ngang nh cho nhng cht dn PE, i.e dy mu xanh lc/nhum vng, ca nhng mng t ph thuc dng ngn mch sau . Tr khng ti 50 Hz gia hai im trong mng bi vy lun lun thp hn 1. 3.4 Ghp ni dy vi dy kiu Vi sai hoc xuyn cho S Xuyn cho l mt kiu ghp ni m ging vi s ghp ni trng vi dy. N c gi xuyn cho in dung hoc xuyn cho cm ng, ph thuc vo liu n gy ra s thay i dng in hoc in p. S thay i in p nhanh gia dy v mt t hoc gia hai dy (Xem hnh 15) pht sinh trng gn bn cnh, vi vi s xp x, th ch cha in trng.


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Hnh 15: S thay i nhanh in p V1 to ra mt trng m ti khong cch ngn c th c tnh hon ton l in trng v in p cm ng VN trong cu trc nh dy dn song song gi l xuyn cho in dung Trng ny c th kt ni vo trong cu trc tng t dy song song gi l s xuyn cho in dung. Tng t, s thay i dong in trong dy hoc cp pht sinh trng in t trng m xp x nh t trng. Trng c th ghp ni vo i dy v gy ra in p nhiu lon c gi s xuyn cho cm ng (Xem hnh 16).


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Hnh 16: Dng in thay i trong cp sinh ra trng in t m ti khong cch ngn ch cn l t trng v t trng cm ng hnh thnh vng gi l kiu kt ni xuyn cho cm ng in dung xuyn cho v cm ng xuyn cho tn ti mi khi nhng dy dn c nh tuyn song song hoc b tr gn nhau. S xuyn cho c th xut hin trong cp treo v nhng mng in v c bit gia nhng cp ngun mang nhng tn hiu nhiu lon tn s cao v i dy xon c s dng bi mng k thut s nh Batibus. S xuyn cho s mnh hn lu hn trn nhng ng dn song song, nh hn khong cch gia dy hoc nhng i dy v cao hn tn s ca nhng s nhiu lon. Cho v d, s dng k hiu trong hnh 15, h s ghp ni in p (xuyn cho in dung ) c th c biu th nh sau:

Trong V1: Ngun in p VN: in p cm ng nhiu lon bi ghp ni C12: in dung ghp ni gia hai dy t l vi chiu di dy v h s khong cch Log [1+(h/e)2] , h l khong cch gia hai dy ca 1 i dy v e l khong cch gia nhng i dy C20: in dung gia hai dy ca i dy b nhiu R: Tr khng ti ca i dy b nhiu Trong cng thc ny, iu kin u tin mu s thng l khng ng k nh c so snh ti iu kin hai. Vy th mt s xp x hp l l:

= 2f R C12 = R C12 c bit hn, hy xt hai i vi dy c ng knh 0.65mm chy song song 10 mt; nhng dy bn trong 1 i "b nh hng " l 1 cm v nhng cp l 2 cm v R=1 k. Cho mt tn hiu 1 MHz, h s ghp ni -22dB c tm thy, v vic tnh ton cho kt qu :VN V1 = 1 12

Trong thc tin, kiu ghp ni in dung v cm ng ny th gim ng k bi s dng ca nhng cp xon v nhng cp c che chn. 4 i tng b nh hng Bt k thit b no m c th b nh hng bi s nhiu lon c th th c xem nh mt " i tng b nh hng ". l kiu thit b cha mt vi: 4.1 H hng thit b: Nhng h hng thit b c chia thnh bn phm tr v c th : Sinh vin thc hin: Trn Thanh Sn (T-VT 2006-2009) Trang 16



- Khng i v c th o c - Ngu nhin v khng lp li, xut hin khi c nhng nhiu lon - Ngu nhin v khng lp li, cn li sau khi nhng nhiu lon bin mt - S h hng thit b (nhng thnh phn vt l b ph hy) Trn y m t c im trong thi gian ca li nhng khng phi l tnh nghim trng ca n. Tnh nghim trng ca mt li l vn ca chc nng hot ng. Nhng li bit c th c chp nhn c trong mt thi gian c hn nh s mt mt tm thi ca mt mn hnh; nhng ci khc c th khng chp nhn c nh nhng s trc trc thit b an ton. 4.2 Gii php vn Nhiu gii php vi iu kin lm sao thit b c xy dng tn ti cung cp s min tr c hiu qu ti nhng s nhiu lon in t vi chi phi thp. Nhng php o c phng nga c th dn n - Thit k tm bng mch (phn chia chc nng, cch trnh by ng mch, ni thng ni b) - La chn nhng thnh phn in t - La chn v thit k vt liu ph bo v - Kt ni t - Cch i dy Nhng s la chn ko theo nhiu qui tc khc nhau v cn phi c lm trong thi gian thit k d n trnh b sung chi ph m lun lun cao cho nhng s sa i sau khi thit k c hon thnh hoc khi no sn phm tn ti trn th trng. Tin hnh tt c nhng php o phng nga tun theo tiieu chun lc v k thut che chn thng c gii thiu tng thm kh nng bo v d hiu lc ca n cha c th thch. Nhng tm bng mch in Ngi thit k nhng tm mch in phi tun theo nhng quy tc nht nh lin quan n phn chia v sp t cc chc nng. Bt u vi s xp t thnh phn, c th gim bt nhng hiu ng ghp ni lin quan n s gn nhau ca linh kin. Cho v d, nhm li nhng phn t m cng thuc v phm tr mch (s, tng t, hoc nhng mch ngun) theo cm ng, gim bt s giao thoa. Hn na, cch trnh by ng i ca mch c mt hiu ng kch tnh v cm : cng mt s in thc hin nhng cch khc nhau dn n nhng mc min tr khc nhau. Cho v d, n mn cc tiu bn mch (Xem hnh 17) gim bt nhng hiu ng v nhy cm bc x.

Hnh 17: Trnh by mch in c th lm gim cm ng in t trng ca PCB Sinh vin thc hin: Trn Thanh Sn (T-VT 2006-2009) Trang 17



Nhng thit b in t Nhiu thnh phn sn sng cung cp s bo v c hiu qu chng li nh hng ca nhng s nhiu lon. Chn lc c nh hng mc nng lng ca mch bo v (mch ngun, iu khin v b kim tra, etc.) v kiu nhiu lon. Vy th, nhng s nhiu lon kiu chung trong mt mch in ngun, mt my bin th s c s dng nu nhng s nhiu lon tn s thp (< 1 kHz) v s dng b lc nu chng nhng tn s cao. Bng trong hnh 18 cho mt danh sch khng ton din ca nhng thit b bo v. Chng c nhng c trng khc nhau : b lc khng bo v chng li xung t bin, v mt b bo v xung t bin khng bo v chng li tn s cao ca nhng s nhiu lon. Kiu V d thit b ng dng Khong cch in cc B ngun, iu khin v gim st B van chng st - Phn lp t Chng xung t bin Mch hn ch Varistor - Mch in t Zener Diode Bin p Cun cm B ngun, iu khin v gim st Lc T in (Lp t v mch in t) B lc Li dy Dy m Che chn Cp che chn Truyn dn d liu m tn s cao Cht chn dng Hnh 18:Danh sch cc thit b bo v Che chn Vic bao bc thit b c cm bin trong mt vt liu che chn bo v chng li trng in t. c hiu qu, b dy ca vt liu che chn phi vt hn chiu su ca tn s nhiu lon (Xem hnh 19). Chng li s nhiu lon tn s cao hoc in trng, vt liu sn vecni c th hiu qu. Ch nhng v bc c thm thu cao c th chn ng t trng tn s thp.


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Hnh 19: Mn hnh din t hiu qu ca vt liu che chn Ni thng t Khi n thanh ni t, dng in tt lin tc gia cc b phn khc nhau th quan trng v cng. Chng phi c ni thng mt cch cn thn v chnh xc, v d nhng vng cng tc bo v dng sn v cng s dng dy ngn, rng bn ui sam ( gim tr khng ti cc tiu). i cp (bn cp) Cp che chn l mt m rng ca v bao dy dn t xung quanh nhng h thng c cm ng. Bi vy n c th kt ni ngn nht v c th chung quanh chu vi ca n bo v chng li s nhiu lon tn s cao. ng nh khi ghp ni gia mt trng in t v mt cu trc ging nh dy, l thuyt iu khin dy che chn rt phc tp v qu nhiu. Khi tt c qui tc thit k v sn xut c quan tm, h thng s c bo v mt cnh y nhng s nhiu lon in t trong mi trng n c xy dng. Tuy vy, s bo v ny ch c hiu lc bi nhng php o thc t m xc nh hiu lc ca k thut che chn khc nhau. Ti cng ty Schneider Electric, cho v d, nhng m hnh nguyn mu khc nhau nh nhng cu dao in c a ra kim tra quan trng tiu biu nhng s nhiu lon ln nht ti chng no chng khng ch c. Nhng cuc th tht khch quan s kim tra cc tc ng khng phi l tnh c v cu dao in m chnh xc vo thi gian i hi. Nhng tiu chun " Sn phm " by gi bao gm, cho v d : IEC 60947 - 2 tiu chun lin quan nhng cu dao in cng nghip, v IEC 61131 - 2 tiu chun lin quan chng trnh iu khin logic. 5 Lp t 5.1 Lp t l mt nhn t quan trng trong ton b h thng EMC Bng chng ca vic ny c th c tm thy trong NF C 15-100 (IEC 60364) nhng tiu chun chung lp t LV. Hai mc trc y cho thy rng s lp t


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ng mt vai tr quan trng trong EMC; iu ny th tht cho c hai pha thit k v cch trnh by v pha lp t thc t. 5.2 Pha thit k Trong khi khu thit k v cch trnh by l hai nhn t chnh iu khin EMC: S la chn thit b v xc nh v tng i ca h (Xem hnh 20).

Nhn t u tin lin quan s la chn c hai thnh phn pht ln nhng i tng b nh hng : mt mnh ca thit b c th pht sinh nhng s nhiu lon v/hoc d b nh hng. Cho v d, nu hai n v c chc nng gn ln nhau, chng phi : - Hoc kt hp phn pht m pht sinh nhng nhiu lon mc thp v mt "nguyn mu" i tng b nh hng. - Hoc kt hp mt my pht "Nguyn mu " m sinh ra mc n ha ca nhiu lon v i tng b nh hng c nhy thp. - Hoc dng tha hip gia gia hai thi cc. Nhn t th hai m ph thuc trc tip lin quan u tin n xc nh v tr ca thit b, c chn i vi nhng c trng ring l ca n, nhm tha mn nhng yu cu v EMC. Hin nhin rng s la chn ny phi tnh n chi ph ca thit b v lp t n. 5.3 Khu Lp t Cng vic lp t in v in t cn phi theo nhng nguyn tc c hng dn tho lun nhng mc trc y. Trong thc t, nhng cng tn ti nhiu kiu ghp ni khc nhau phi c nghin cu v tha mn nhng yu cu EMC. Cc k thut khc cn phi ng dng : - Mch in v v my/ni t phi c t trong mt li. - Mch in phi c phn ra v mt vt l . - Cch i dy phi ln k hoch cn thn . 5.4 Vi v d thc hnh B tr li cho mch in v v my/ ni t Sinh vin thc hin: Trn Thanh Sn (T-VT 2006-2009) Trang 20



Ngy nay, thit b c th d b nh hng t nhng mc nng lng rt thp. Mch in t ni thng vi nhau c nhy vi nhng tn s cao. Ghp ni tr khng chung thng xuyn xut hin v trnh n, tt nht lm cho h thng c ni t hoc chnh xc hn dng li t, l ch yu. iu ny l bc u tin trong vic cung cp s bo v chng li nhng vn nhiu lon. Trong mt mng phn phi ngun nh my, tt c cc dy bo v (PE) phi c ni vi nhau v ni ti cu trc kim loi c ch r bn trong NF C 15-100 (Xem hnh 21).

Hnh 21:Mng li cho mch in, v my v h thng t Tng t, bn trong thit b, tt c nn v nhng khung v phi c ni ti mt li nh h thng t c th bng cch ngn nht cch s dng tr khng thp (ti tn s cao), s ni dy ca mt t in l mt v d tiu biu : tt c cc nn phi th c ni cng nhau. C mt s thay i s c ghi ch y : phng php ko theo s ghp ni ca tt c cc nn ti mt im trung tm (cu hnh ngi sao), i khi s dng cho thit b cm ng in t tng t b nhiu tp 50 Hz, c thay th bi nhng li c hiu qu hn nhiu trong gim bt nhng s nhiu lon m nh hng nhng h thng s ngy nay, bo v cc rle v nhng h thng iu khin v b kim tra. Phn chia nhng mch in K thut ny gm c phn ra nhng ngun nng lng (thng l 50 hoc 60 Hz). Mc tiu s trnh giao thoa vi thit b cm ng gy ra nhng nhiu lon pht sinh bi nhng h thng khc ni ti cng b ngun . Nguyn l s to ra hai b ngun ring bit c c lp bi nhng tr khng th cao ti tn s ca s nhiu lon. Nhng my bin th (khng phi nhng t bin th) l nhng cht khng dn in c hiu qu, c bit nhng tn s thp: nhng my bin th MV/LV, cch ly nhng my bin th v bt k u vo lm ngng s nhiu lon in t. i khi cch ly mt b lc khng c yu cu loi tr nhng s nhiu lon tn s cao. Nu thit b c mch cm ng cng yu cu ngun khn cp, th n c th c cung cp bi b ngun UPS min l UPS yu cu cch ly bin p Thit k k phn i dy Nhng hiu ng ca ba c ch ghp ni c xem xt sm hn c th lm gim nu l trnh dy v cp tun th nhng quy tc sau : - Trong tt c cc h thng m khng th phn chia v mt vt l vi l do v mt kinh t, th dy, cp phi c nhm vi nhau theo tng loi. Nhng loi khc nhau cn i dy ring r :c bit, nhng cp ngun cn phi v mt bn vi nhng cp tn hiu (in thoi, iu khin v kim tra) (Hnh 22 ). Sinh vin thc hin: Trn Thanh Sn (T-VT 2006-2009) Trang 21



Hnh 22: V d mt cch i dy/ cp Nu c ch i cp hoc vi nhng mng in sn c, th nhng cp ngun c dng nhiu hn vi ampe ti 220 V cn phi c tch ring r vi cc loi cp tn hiu, hay ni cch khc, khong cch cc tiu t nht l 20 cm phi c gi gia loi. Bt k thnh phn chung no ca 2 loi ny phi c trnh. S mch in s dng cp tn hiu cn phi c, bt c u, c th i st dy 0V trnh s ghp ni tr khng chung. Phn ln nhng h thng truyn thng ng trc yu cu nhng cp dy d tr ch ring cho s trao i d liu. - Trong bt k trng hp no, ton b vng trn thnh hnh bi dy dn v s tr li ca n phi th thu nh. Trong s truyn d liu, nhng cp xon gim bt cm ng vi s ghp ni kiu vi sai - Nhng cp s dng cho php o v truyn d liu mc thp cn phi c che chn nu c th, v khi thiu nhng ch dn c bit t nh sn xut, vt liu che chn ca n cn phi c ni t. - Phi nh tuyn cp, nu tt c c th, c lm bng kim loi. Nhng mng in cn phi ni in chnh xc, e.g. ni vi nhau v cng nhau v ni ti li t. - Cc si cp cm ng nht (e.g. c s dng trong nhng php o) cn phi c t trong gc ca mng in ni chng c th c bo v cc i chng li s bc x in t. Vt liu che chn ca n, nu c, cn phi c ni ti mng in nhng khong bnh thng. Tt c cc k thut i dy ny, m c hiu qu trnh nhng vn EMC, ch lm tng chi ph khng ng k khi ng dng thi gian thit k hoc lp t. Nhng s ci tin v sau khi lp t khi thy s ghp ni in t qu mc th t hn nhiu. 6 Tiu chun, nhng phng tin o th v o th 6.1 Tiu chun Cc vn bn tiu chun iu chnh tnh tng thch in t ca nhng h thng c t lu. Nhng s iu chnh u tin c pht hnh bi CISPR, Comit International Spcial des Perturbations Radiolectriques (International Special Committee on Radio Interference). Nhng s iu chnh ny ch trong phm vi mc nng lng ti a c th chp nhn c c pht ra bi nhng kiu thit b khc nhau, ch yu bo v truyn dn v tuyn v s thu nhn. National Committees and the International Electrotechnical Commission (IEC ) pht hnh nhng tiu chun bao trm tt c cc kha cnh ca s pht x v cm ng EMC. Nhng tiu chun ca qun i v EMC c bin tp ti chui GAM EG 13 Php v chui MIL-STD Hoa k. S quan trng ngy cng tng ca EMC v s thng nht sp ti ca Chu u ang thay i phong cch nhng tiu chun thng dn. Sinh vin thc hin: Trn Thanh Sn (T-VT 2006-2009) Trang 22



The European Council xut bn Directive (reference 89/336/EC) vo thng 1989 v ti ny. N lin quan n vic hp nht lut EMC ca nhng nc thnh vin. The European Directive khng nhng gii hn tiu chun pht ra s nhiu lon nhng m cn t s min tr ti thiu i vi s nhiu lon ca trng in t. Directive lm tham kho cho nhng tiu chun m nh ngha mc nhiu lon cc i. Technical Committees c thit lp bi CENELEC, Comit Europen de Normalisation Electrotechnique (European Committee for Electrotechnical Standardization). Chng gp nht nhng tiu chun hin hu m tng ng vi The European Directive, The Technical Committee TC 210 t c s cho cng vic ca n trn thc t cng nghip. kim tra s pht x, nhng tiu chun c VDE 0871 v VDE 0875 thnh thong c tham kho. By gi nhng tiu chun c thay th bi nhng tiu chun EN 55011 v EN 55022 ca Chu u. Nhng tiu chun tham kho cho EMC by gi l series IEC 61000 (Trc y l IEC 1000). Trong cha ng vi phn, v d nh - 61000 - 1 : ng dng, nhng nh ngha - 61000 - 2 : Mi trng, nhng mc tng thch - 61000 - 3 : Nhng gii hn ca nhiu lon - 61000 - 4 : K thut o th - 61000 - 5 : Hng dn nguyn tc lp t v lm du - 61000 - 6 : Nhng tiu chun chung Phn 4 cha vi mc lin quan kim tra s min tr, bao gm : - 1 - Tng quan ca kim tra s min tr - 2 Hin tng phng in t - 3 - Bc x, nhng tn s v tuyn ca trng in t - 4 - Chuyn tip in nhanh/ n in - 5 - Xung t bin - 6 - Nhiu lon c dn > 9 kHz - 7 Sng hi - 8 Nng lng t trng - 9 - Xung t trng - 10 Dao ng t tt dn - 11 - lch in p, mt in ngn hn v bin thin in p - 12 - Sng dao ng - 13 Sng hi v sng hi trong - etc. Nhng tiu chun ny c chp nhn rng ri trong cng ng quc t v Schneider Electric a chng vo nhng sn phm. Mc sau m t chi tit hn nhng cuc th lin quan n nhng tiu chun ny. 6.2 Phng tin o th Nh c cp trc, xem xt s iu chnh, tiu chun ha nhng php o v th cng c thc hin. V nhng ng dng trong thng mi ca n,t lu Schneider Electric lm EMC l mt trong s phn lin quan chnh. Nhng lp t ln nh Lng Pharay c s dng t thp nin 70. Trong nhiu nm, Schneider Electric c hai phng th nghim EMC. Nhng trung tm ny s dng y nhng k nng v kin thc ca chng ta v y mnh s trao i thng tin. Chng cng ngh nhng dch v cho nhng khch hng bn ngoi. Nh vy vic o th nhng lnh vc ca cc ng dng EMC, vi : - Kim tra hin tng phng in t Sinh vin thc hin: Trn Thanh Sn (T-VT 2006-2009) Trang 23



- Kim tra s min tr bc x - Kim tra pht sinh bc x Trong khi vi mi php o khc, nhng php o tng thch in t c th cng lp li trong khng gian v thi gian, c ngha rng hai php o thc hin hai phng th nghim khc nhau phi c cng kt qu . Trong qui tc EMC, iu ny c ngha nhng phng tin ln yu cu u t ng k v mt chnh sch cht lng chnh xc. Chng trnh cht lng ti nhng phng th nghim EMC ca Schneider Electric th da vo cm nang cht lng v tp hp nhng th tc. Nhng th tc ny lin quan s hiu chnh v ghp ni hiu chnh nhng tiu chun c thm vo mi kiu php o. 6.3 Kim tra o th Hin tng phng in t Nhng bi test ny c thit k kim tra s min tr ca nhng tm bng mch, nhng thit b v h thng i vi hin tng phng in t. Hin tng phng in t l kt qu ca s tch ly bi con ngi, v d, i b trn sn nh c ph cht cch ly in. Khi con ngi chm vt dn in ni c tr khng vi t, v xy ra hin tng phng in t. Vi nghin cu ch ra rng dng sng l mt hm ca nhng c trng pha pht v ca nhng mch ko theo, khng nhng tham s khc nh s m tng i (xem hnh 23) hoc tc ti ni tip cn thn th, v d ca bn tay ca chng ta, etc.

Hnh 23: nh hng ca m tng i vi in p phng in t qua 3 loi vt liu sn Nghin cu ny hng dn tiu chun kim tra s phng in. Chng c thc hin vi mt sng tnh in m ng vai mt con ngi c nh trc nhng cu hnh (Xem hnh 24). Sinh vin thc hin: Trn Thanh Sn (T-VT 2006-2009) Trang 24



Hnh 24:Hin trng cuc th s phng in t theo tiu chun IEC 61000-4-2 S phng in c ng dng trn tt c cc b phn c th tip cn ca thit b kim tra, mi trng lc v s ln lp li kim tra chc chn rng thit b chng s phng in t. Nhng php o ny yu cu mt bn thch hp kim tra. Tt c cc cuc o th u c nh ngha bi tiu chun IEC 61000-4-2 vi nhng mc quan trng trong bng hnh 25.

Hnh 25: in p phng in t m tt c thit b tun theo tiu chun IEC 61000-4-2 Ch dn s min tr Kim tra s min tr c s dng kim tra s chng c ca thit b ti nhng s nhiu lon t nhng si cp thit b bn ngoi (u vo, u ra v ngun). Nh c cp trc, nhng s nhiu lon ny ph thuc vo kiu v nhng c trng lp t ca cp. Tn hiu trng in t hoc nhng xung c s dng trong nhng cuc th ny c nhng bin , dng sng, tn s, etc in hnh Nhng php o s nhiu lon thc hin trn nhiu v tr dn dt ti vic chn ra nm bi kim tra. - Cuc th u tin, c bao ph bi IEC 61000-4-4, m phng nhng s nhiu lon tiu biu c pht sinh bi thao tc ca iu khin s. Cuc th s dng nhng Sinh vin thc hin: Trn Thanh Sn (T-VT 2006-2009) Trang 25



v n. Tn s lp li v n l khong 3 Hz. Mi v n cha khong 100 trng thi chuyn tip mi 100 s. Mi trng thi chuyn tip c th ln n nh (5 ns) vi bin vi kV, ph thuc vo mc quan trng i hi (Xem hnh 26 v 27).

Hnh 26:Dng ca v n(a) v trng thi chuyn tip(b)

Hnh 27: Bng mc quan trng c nh ngha trong IEC 61000-4-4 Tt c cc cp c th ty thuc vo nhng trng thi chuyn tip nhanh. Kiu ghp ni s nhiu lon ny vo trong dy rt d dng e.g. s xuyn cho. N ch cn 1 si cp pht sinh s nhiu lon nh vy trong mt mng cp hoc dy gy nhiu tt Sinh vin thc hin: Trn Thanh Sn (T-VT 2006-2009) Trang 26



c cc cp khc chy dc theo n. S th bi vy phi bao hm tt c cc cp v dy: kiu kim tra chung c thc hin trn tt c cc dy vi s nhiu lon l nhn to (cp nhiu hn b ngun) v kim tra kiu vi sai v kiu chung trn nhng si cp ni ti nhng phn chnh. Nhng s nhiu lon c a vo trong cp o th hoc nh hng qua s ghp ni in dung (b ngun), hoc qua mt mng sng ghp ni gm hai kim loi c v bc bao nhng si cp th hai (Xem hnh 28).

Hnh 28: cm vi nhng trng thi chuyn tip nhanh, php o ca thit b iu khin chnh Lsis (61000-4-4) trong lng Faraday, bc nh ny din t pht sinh s nhiu lon c iu chnh bi ngi iu hnh, hp g cha mng sng ghp ni thit b iu khin chnh Lsis ni vi mng Batibus Thit b kim tra khng c cho thy mt s trc trc trong thi gian nh trc (khong 1 min). S th ny l thch ng nht vi s min tr thit b v nhng chuyn tip nhanh thng xuyn gp nht. - Cuc th th 2: th tiu biu l nhng hiu ng to ra bi nhng hin tng nh chp. N ng vai ch o nhng s nhiu lon xut hin trn nhng ng ngun LV sau khi st nh (tiu chun IEC 61000-4-5). Nhng s nhiu lon ny gm c nng lng c thay i : - Nhng xung in p 1.2/50 s, nu tr khng ca thit b kim tra l cao, vi bin c th t n vi kV. Kim tra in p c ch dn hnh 29

Hnh 29: Nhng mc quan trng nh ngha ti IEC 61000-4-5 (tr khng tng = 2) Sinh vin thc hin: Trn Thanh Sn (T-VT 2006-2009) Trang 27



- Dng xung 8/20 s nu tr khng thp, vi bin t n vi kA Thi gian ln ca kiu nhiu lon ny lu hn mt nghn ln, trong phm vi s, hn nhng s n ca chuyn tip nhanh (Xem hnh 26). Kiu s ghp ni xuyn cho th t thnh hnh hn bi vy v kiu th th hai ny ch p dng cho cp ni trc tip vi phn chnh. Cuc th th ba c thc hin ph hp vi IEC 61000-4-6. cp n nhng yu cu quan tm s min tr ca thit b ti s nhiu lon HF trn nhng si cp, trong phm vi 150 kHz ti 80 MHz (thm ch 230 MHz). Nhng ngun nhiu lon l trng in t c th gy p lc ton b chiu di ca nhng si cp ni ti thit b, v ngoi ra dng v p cm ng. Trong thi gian th, nhng s nhiu lon c ghp ti cp thng qua CouplingDecoupling Networks. (CDN) tr khng kiu chung bng 150 , i din tr khng in hnh ca hu ht cc si cp. Tuy nhin, n cn phi c ch dn trong thi gian, kim tra s nhiu lon, mc d trong thc t trng in t ghp ni ti tt c cc si cp c ni. iu ny cu thnh mt s khc nhau quan trng m khng th trnh c. Thc vy cuc th tr nn rt phc tp v t nu tn hiu HF b ghp ng thi ti tt c cc cp. Nu CDNs khng thch hp, v d khi dng cao qu, hy s dng mng sng ghp ni. Nhng nhiu lon HF gii thiu bi tiu chun IEC 61000-4-6 c nhng mc bng 1, 3 hoc 10 V. Bin ca n c iu ch 80 % bi mt sng sin 1 kHz. Trc khi th, tn hiu s c a vo thu c mc ng c c nh v lu tr, ri cung cp n nhng si cp ni ti thit b kim tra. - Cuc th th t gm c to ra s gin on nhanh v /hoc nghing in p trong cp ngun ca thit b kim tra. Tiu chun IEC 61000-4-11 l s tham kho c bn. Nhng s nhiu lon ny c gy ra bi nhng li trong nhng phn cung cp ch yu, s lp t hoc bi thay i thnh lnh trong ti. Hia hin tng ngu nhin ny c m t c im bi lch in p danh nh lch ca n. Mc nghing in p l 30, 60 hoc 100% ca in p danh nh. Khong thi gian thay i gia 0.5 v 50 chu k. - Cuc th (th) nm c ch o trong tha thun vi tiu chun IEC 61000-412, m nh ngha hai kiu sng : + sng sin tt dn (nh rung chung) m xut hin cch ly trn nhng si cp in p thp ca nhng hot ng chuyn mch trong mng cng cng hoc mng ring + sng dao ng tt dn xut hin trong dng ca v n. iu ni chung c tm thy trong nhng nh ga, nhng trm in, hoc thm ch lp t ti khu cng nghip ln, c bit thao tc b kt ni theo sau l s phng h quang in. Nhng in p v dng chuyn tip kt qu ca nhng thao tc ny xut hin trn nhng thanh gp v c m t c im bi mt tn s dao ng ph thuc vo ln v thi gian truyn lan. Tn s ny thay i gia 100 kHz v mt vi MHz khi m trm in p cao, v c th t n 10 MHz, hoc hn. Trong thi gian th, nhng sng b ghp ni vi cp qua mng Couplingdecoupling. Ph thuc vo phng php ghp, bin ca nhng s nhiu lon c th thay i gia 0.25 v 4 kV. Mt nh thit b c t ln mt cht khng dn in, trong khi sn ng hoc vt che chn c cch ly vi t khong 0.1m S Min tr chng li bc x s pht x Nhng cuc th min tr chng li bc x nhng s pht x c sp t bo m tha mn kh nng tr ca thit b vi trng in t. Sinh vin thc hin: Trn Thanh Sn (T-VT 2006-2009) Trang 28



Nhng cuc th ny t trong mi trng nhy cm c bit, Nhng phng tin trin khai v nhng kh nng yu cu bo m sn xut v ti sn xut nhng php o th rt cao. Mi trng ln cn phi "sch " v sng t do th bnh thng, t trng in t vi mc ln vi V/m thng xuyn v xung trng in t vi mc cao hn trong mi trng cng nghip. Do nhng cuc th ny c ch o trong Lng Pha-ra-y m nhng bc tng c bao trm bi vt liu hp th tn s cao. Nhng ci lng ny c gi l phng khng phn x khi tt c cc tng bao gm c sn nh c bao ph v bn phn x nu sn nh khng bao ph. Trong phng, nhng trng c pht ra bi nhng kiu antenna khc nhau ph thuc vo kiu trng, tn s v s phn cc khc nhau (Hnh 30). Antenna c iu khin bi mt my khuch i cng sut bng rng c kim sot bi mt my pht RF.

Hnh 30: Lng (phng) Faraday: Phng bn phn x v mt vi anten ca phng th nghim EMC ti cng ty Schneider Electric Trng c pht ra c hiu chnh bi nhng b cm bin ng hng bng rng (theo di cng trng). S trong hnh 31 din t ci t mt kiu th.


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Hnh 31: Cch ci t mt cuc th trong Lng Faraday. Php o thc hin 2 giai on 1- iu chnh trng vi mc tn s cho, khng c thit b th 2- Kim tra s min tr ca thit b th Nhng tiu chun nh ngha gii hn nhiu lon chp nhn c. T y, tiu chun IEC 61000-4-3 gii thiu kim tra trn bng tn 80MHz 2000MHz vi ba mc quan trng (1, 3, 10 V/m), v trn 800KHz 960MHz v 1.4GHz 2GHz vi bn mc quan trng :1, 3, 10 v 30 V/m. Nhng cuc th s min tr vi t trng ti nhng tn s chnh cng c ch o trong tha thun vi tiu chun IEC 61000-4-8. Nhng trng t tnh nh vy c pht sinh bi dng in lu thng trong si cp, hoc km thng thng hn khi gn thit b, nh t thng r t nhng my bin th. Nhng mc th trng khng i gia 1 v 100 A/m, nhng ngc li nhng trng ngn hn t 1 n 3s c dng 300 hoc 1000 A/m. Trng t tnh c thu c bi dng in lu thng trong mt cun dy cm ng. N c ng dng kim tra thit b theo phng php nhng, i.e. n c t ti trung tm ca cun dy. Cuc th ny ch cn tc ng ln nhng thnh phn nhy cm vi t tnh ca thit b(Mn hnh CRT, nhng b cm bin vi hiu ng. Nhng php o c chun ha xung trng in t cha tn ti. Trong lnh vc ny, Schneider Electric s dng nhng th tc ca chnh mnh kim tra thit b. Ch o s pht x Php o ch o s pht x xc nh s lng nhng s nhiu lon m thit b kim tra a vo trong tt c cc si cp ni ti n. S nhiu lon mnh ph thuc vo nhng c trng tn s cao ca ti ni ti n mt khi thit b kim tra l my pht trong trng hp ny (Xem hnh 32). kt qu php o thu c c th ti sn xut v c bit trnh nhng vn tr khng c trng ca mng, ch o nhng php o pht x c thc hin vi s gip ca Line Impedance Stabilizing Network (LISN). Mt my thu tn s cao c ni ti mng o nhng mc pht x ti mi tn s. Mc ca nhng nhiu lon a vo khng cn vt hn nhng gii hn c nh ngha trong nhng tiu chun. Nhng gii hn ny ph thuc vo loi cp v mi trng. th bn di (xem hnh 33) cho thy rng kt qu ca php o thc hin trn bng chuyn mch LV chnh v nhng mc nh ngha trong tiu chun EN 55 022 cho vic so snh. Sinh vin thc hin: Trn Thanh Sn (T-VT 2006-2009) Trang 30



Hnh 32: Cu hnh php o cho ch dn s pht x. EUT l my pht, tr khng ng dy n nh mng c np

Hnh 33:Php o s pht x tn s v tuyn t n v trung tm x l d liu ca bng chuyn mch chnh Bc x s pht x Php o bc x s pht x xc nh s lng mc nhiu lon pht ra bi mt thit b theo mu ca sng in t.


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Nh vi bi th s min tr bc x, kim tra bc x s pht x phi c thc hin vi s thiu vng ca sng bnh thng nh CB, v tuyn, etc. v khng c sa i bi nhng phn x t nhng i tng xung quanh. Hai iu kin ny th mu thun v y l l do cho s tn ti ca hai phng php th. Phng php u tin gm c t EUT trong mt trng t do ca nhng chng ngi vt bn trong mt chu vi cho. Mi trng th khng kim sot . Phng php th hai c thc hin trong Lng Pharay. Mi trng c th th iu khin hon ho. Nhng phng th nghim ca Schneider Electric s dng phng php th hai. N c li th nhng php o c th c t ng ha v cng dng thit b nh, t nhng php o mc pht x v min tr c th c thc hin cng v tr vi ch thay i ci t. Nh ch o s pht x, nhng mc pht x phi t hn gii hn t bi nhng thuyt minh hoc nhng tiu chun. o trng kiu xung Tiu chun ha nhng bi th c thc hin o nhng mc pht x hoc kim tra s min tr ca thit b hoc nhng h thng vi nhng kiu nhiu lon in t chung nht gp trong mi trng cng nghip. Tuy nhin, mi trng cho nhng thit b pht trin bi Schneider Electric c nhng c trng nht nh cha bao ph bi nhng tiu chun. V d, nhng th tc th EMC c bit cho thit b in p trung bnh cn cha tn ti. y l ti sao l Schneider Electric thc hin mt chui nhng php o hiu tt hn nhng s nhiu lon tiu biu m tn ti trong vng ln cn ca thit b m n sn xut, c bit chuyn mch in p thp, trung bnh v rt cao Trong pha th hai, bn trong nh kim tra s dng nhng h thng th c bit c pht trin. Chng cho php th tnh tng thch in t ca nhng thit b m khng phi tr li cc cuc kim tra qui m ln. Nhng s th ny l d ti sn xut v t tn km hn. Chng c thc hin sm trong thit k ti gin chi ph ca s bo v EMC. 7. Kt lun S dng in t trong mt s ln ng dng, v c bit trong thit b k thut in, gii thiu mt yu cu mi v quan trng : tnh tng thch in t (EMC). Hot ng tri chy trong nhng mi trng nhiu lon v thao tc m khng sn sinh nhng s nhiu lon th quan trng ti nhng yu cu cht lng sn phm. t c c hai mc ch ny, hin tng phc tp ko theo trong ngun, s ghp ni v nhng i tng b nh hng phi c hiu cn thn. Mt s nhng quy tc phi c i theo thit k, cng nghip ha v sn xut ca nhng sn phm. Nhng v tr v lp t c trng cng ng vai tr quan trng trong tnh tng thch in t. iu ny gii thch s quan trng ca vic xem xt cn thn v tr v cch trnh by ca nhng thnh phn ngun, nh tuyn cp, che chn ,etc. ngay t pha thit k ban u. D thit b lm tha mn EMC, mt thit k lp t tt c th m rng an ton tng thch. Ch nhng php o yu cu mt mc cao ca s thnh tho v thit b phc tp c th sn sinh nhng kt qu hp l xc nh s lng tnh tng thch in t ca thit b. Tun theo nhng tiu chun c cung cp s chc chn thit b s hot ng tha mn trong mi trng in t ca n. Sinh vin thc hin: Trn Thanh Sn (T-VT 2006-2009) Trang 32

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