REAL EFFICIENCY OF INTELLIGENT SWITCHING OF HIGH VOLTAGE CIRCUIT-BREAKERS

Transcription

1 U.P.B. Sci. Bull., Series C, Vol. 72, Iss. 1, 2010 ISSN x REAL EFFICIENCY OF INTELLIGENT SWITCHING OF HIGH VOLTAGE CIRCUIT-BREAKERS Florin MUNTEANU 1, Ciprin NEMEŞ 2 Comutre inteligentă se referă l extindere comutării controlte în situţii noi printe cre se numără regimurile de scurtcircuit. Unul dintre cele mi importnte specte este cel legt de utilizre întrerupătorelor moderne, ultrrpide cre declnşeză îninte c un din componentele curentului de defect, component continuă, să tingă vlore zero. Având l bză rezulttele cercetărilor efectute de utori în implementre comutării inteligente, l înlt tensiune şi în czuri de defect, lucrre re drept subiect detliere vntjelor rele le cestei reltive noi tehnologii în sistemele electroenergetice. Printre ceste, cele mi importnte sunt meliorre clităţii energiei electrice c urmre limitării suprtensiunilor şi suprcurenţilor ce însoţesc comutările clsice mi les în condiţii de scurtcircuit şi reducere costurilor cu mentennţă. The concept of intelligent switching mens extending the existing controlled switching chrcteristics to new situtions from which the cse of fults is the most importnt. One of the min spect is relted to modern high speed circuit-brekers which re opening before the d.c. component of the short-circuit current is closed to zero. Bsed on uthors min reserch results in implementtion of intelligent switching of high voltge circuit-brekers in cse of fults, the pper dels with the rel dvntges nd efficiency of this reltive new technology in power systems. Between min positive results of this new technology there is mjor power qulity improvement s much s the overvoltges nd overlods re strongly diminished. Keywords: intelligent switching, stress mitigtion, circuit-brekers 1. Introduction Controlled switching is one of severl terminologies pplied to the principle of coordinting the instnt of opening or closing of circuit with specific trget point on n ssocited voltge or current wveform. Other common terminologies pplied include synchronized switching, point-on-wve switching. This technology ws progressively developed, during lst decdes, not only from theoreticl spects [1], [2], stte-of-rt sttisticl reviews [3], but lso from prcticl pplictions [4], [5]. 1 Deprtment of Power Engineering, Gheorghe Aschi Technicl University of Işi, Romni 2 Deprtment of Power Engineering, Gheorghe Aschi Technicl University of Işi, Romni

2 174 Florin Muntenu, Ciprin Nemeş All, or most of the electronic devices llowing for controlled switching re especilly recommended for norml stedy-stte, or so-clled conventionl, switching nd not in cse of fults s tble 1 shows ccording to [3]. 2. Models nd techniques for intelligent switching in cse of fults 2.1 Pötl nd Fröhlich method bsed on sfe points The most recent published method for synchronized fult interruption found ws n pproch developed by Pöltl nd Fröhlich, in 2003 [2]. This pproch proposed novel scheme whereby the synchroniztion trget is not directly bsed on future current zero, but rther on chosen periodiclly occurring instnt on the fult current, known to lwys precede current zero, referred to s sfe point. The uthors proposed set of different sfe points for different switching cses; symmetricl, shifted nd symmetricl fult currents. These re illustrted in fig. 1 nd fig. 2. Tble 1 Results of worldwide survey of controlled switching pplictions instlled between [3] Controlled component nd switching type Percent form the totl of 2500 pplictions Energising / de-energising of shunt cpcitors 64% Energising / de-energising of shunt rectors 17% Energising / de-energising of power trnsformers 17% Energising / de-energising of lines 2% Combined controlled opening nd closing of threepole operted mechniclly stggered 7% circuit-brekers Fult current b b b t Fig.1 Controlled switching method, in cse of n infinite power source, bsed on sfe points : ) symmetricl; b) shifted [7]

3 Rel efficiency of intelligent switching of high voltge circuit-brekers 175 Fult current b b b t Fig.2 Controlled switching method, in cse of finite power source, bsed on symmetricl () nd symmetricl (b) sfe points [2] 2.2 Richrd Thoms method bsed on LMS lgorithms As opposed to the sfe point pproch, the scheme proposed by Richrd Thoms [6] is bsed on predicting future current zero behvior nd synchronizing the tripping commnd to the circuit breker with respect to the erliest vible, predicted current zero(s) ccordingly. Contrry to the idel circuit breker with ner zero rcing time implied by the concepts mentioned by Gerszonowicz nd Grzon, the uthor hs focused on potentil ppliction to existing modern SF6 circuit breker designs, for which certin minimum rcing time behvior hs been, or could be, estblished from conventionl type testing. The proposed controlled switching lgorithm is bsed on determintion of the chrcteristic prmeters of the instntneous single-phse fult current model described by eqution: t / τ t / τ i f ( t) = I F [sin( ωt + α ϕ) sin( α ϕ)] e + I PFα e (1) where, t = time; I F = pek stedy stte fult current mgnitude; I PFα = the instntneous pre-fult current mgnitude t fult initition; ω = power system ngulr frequency; α = fult initition ngle with respect to driving source single-phse voltge; tn (ϕ ) = ωl/r; L = source-to-fult series inductnce nd R = source-tofult series resistnce; τ = L/R = time constnt of the exponentilly decying symmetricl component(s).

4 176 Florin Muntenu, Ciprin Nemeş The key unknown prmeters to be determined in eqution include I F, α, ϕ ndτ. It is cler tht ϕ nd τ re relted through L, R nd ω. For the short time trnsient durtions tht the prmeters must be clculted it is ssumed tht the power system frequency is constnt. Vrious methods could be pplied to try nd scertin the unknown chrcteristic prmeters. Some investigtion ws mde of the possible use of discrete derivtives of the smpled current in order to predict future zero crossing behvior, but such methods re inherently noise sensitive. Wht hs been selected nd exmined in most detil in Thoms pper hs been method bsed on lest men squre regression nlysis. Advntges of LMS methods include: flexibility to dt window sizes; tolernce to noise; reltively strightforwrd mthemtics. Potentil disdvntges of LMS methods include: processing burden proportionl to squre of dt window size; ssumption of linerity in the dt - (strictly this is non-liner regression problem); vibility of the chosen regression model with respect to rnge of possible fult behviors; mngement of exponentil terms. 2.3 This pper uthors method bsed on fult type detection nd normlistion of the d.c. component of fult current The uthors of the present ppers elborted new method to nticipte the first zero crossing of fult current. Essentilly it is bsed on qulittive (without ny clcultion due to extremely necessry speed of type of fult detection) evlution of the initil vlues of d.c. components (I dc, I dcb, I dcc ) [7]. The result is hybrid rely shown in fig.3 where the inputs re the initil vlues of the bove mentioned d.c., nd the negtive (i - ) nd zero (i 0 ) sequence components of short-circuit current. The output is the short-circuit type ccording to the qulittive reltions presented in [8]. For exmple, b-c mens line to line type fult.

5 Rel efficiency of intelligent switching of high voltge circuit-brekers 177 I dc Σ three phse fult vlidtion -b-c Σ I dcb b-c I dcc Σ i - i 0 Σ -g b-c-g Fig.3 The principle of hybrid structured rely for fult type detection After this, it is esier to nticipte the first zero crossing nd even it will be the cse of zero crossing missing. The reltion describing the fult current on phse, in the simplified cse of n infinite power source cse, is given by: i k = I sin( ωt + α ϕ) + [ I sin( α ϕ) I sin( α ϕ )] e (2) F PFα where the nottions re the sme like in eq. (1) excepting the pre-fult power fctor defined by ϕ nd φ k = rctg (ωl k /R k ) = rctg (X k /R k ) for the fulted circuit. The most importnt observtion is relted to this vrible, ϕ which ws not included in the eq. (1) for correct nlysis. One of the most importnt problems relted to the fult current first zero crossing nticiption is to evlute the number of mesurements on the totl fult current wve to optimize the durtion ccurcy rtio nd, consequently, to be in time with switching commnd. The uthor s studies [8] conducted to the correct nswer nd conclusions. According to the nottions in fig 4, the key elements of the method to solve the bove mentioned problems re: F k t τ

6 178 Florin Muntenu, Ciprin Nemeş - Δtd, time intervl for mechnicl breker opening; - tn, necessry time intervl for dt cquisition relted to the c.c. fult component with view to ccurtely nticipte his evolution for intelligent switch; - tr, rel time estimted for the fult current first zero crossing on tht phse. Zero time is the fult initition moment. According to fig.4, the restriction for intelligent breker switching, neglecting the time for fult initition detection is: tn + Δtd tr (3) i k.c. component decy d.c. component decy t tn tr Δtd Fig. 4. The key elements to ccurtely nticipte the first zero crossing in the cse of the intelligent fult interruption Considering the possible necessry time intervl for fult initition detection, eqution (3) becomes: ti + tn + Δtd tr Continuous fult current component evolution nticiption nd the time of the first time zero crossing of the totl fult current re bsed on the clcultion of the prmeters of the d.c. component, given by where is the initil vlue of i nd k kt i = e ; k < 0 (4)

7 Rel efficiency of intelligent switching of high voltge circuit-brekers 179 The norml equtions system, s the lgebr theory demonstrtes, llows clculting prmeters nd k is s it follows: n n logii = t i i= 1 i= 1 n n n 2 = + ti logii t i ( ti ) log i= 1 i= 1 i= 1 (5) Solving eqution (5) cn be done in n ccurte nd rpid mnner so, the minimum mesurements number (n) for sufficient given ccurcy hs to be estblished to clculte nd k [9]. 3. The rel efficiency of the intelligent switching The generl benefits of controlled switching re relted not only to the involved circuit-breker but lso to the network components nd to the qulity of delivered energy. Limittion of trnsients is one of the most importnt benefits of controlled switching s presented in tble 2. Tble 2 Techniques for switching trnsients mitigtion Method Benefits Desvntges Constnt inductce Resistnce preinsertion Inductnce preinserţion Synchronous circuit-breker Esy to instll nd use Current limittion Short time insertion before switching No losses Short time insertion before switching No losses Better solution compred to constnt inductnce Effective trnsients mitigtion during opening nd closing Reduced circuit-breker wering Energy losses nd noisy Expensive Reltive complicte Low relibility Techniclly complicted Low relibility The specific benefits re relted to the switched component. A typicl exmple is the shunt cpcitor for which the detils re included in tble 3. -

8 180 Florin Muntenu, Ciprin Nemeş Tble 3 The benefits for controlled switching of shunt cpcitor bnks Appliction Closing Opening Optiml trnsient limittion U : 2.0 p.u. I : miniml inrush current U : better thn rted circuitbreker restrike probbility Other potentil benefits Longer breker life Longer breker life Optiml control trgeting principles Zero-voltge cross breker 1/4-1/3 cycle rcing time For shunt rector bnks, the similr dvntges re presented in tble 4. Tble 4 The benefits for controlled switching of shunt rector bnks Appliction Closing Opening Optiml trnsient limittion U : 1.2 p.u. I : miniml dc inrush current U : void reignitions Minimise chopping overvoltges Other potentil benefits Longer breker life Longer breker life Reduced stress of rector insultion Optiml control trgeting principles According to rector configurtion 1/4-1/3 cycle rcing time The primry focus for controlled switching of power trnsformers is normlly on energiztion control in order to minimize current inrush trnsients nd their effects. The similr purpose is in the cse of power lines energiztion. Figs. 5 nd 6 show clerly these rel effects for every phse:, b nd c [8] I [A] 1500 I [A] t [ms] ) b) t [ms] Fig. 5. Phse inrush currents on every phse during the energiztion of 400/220 kv, 400 MWA power trnsformer: norml switching, worst cse () nd perfect controlled switching (b)

9 Rel efficiency of intelligent switching of high voltge circuit-brekers 181 I [A] 200 I [A] t [ms ] t [ms] ) b) Fig.6. Phse currents on every phse during the energiztion of 220 kv power line: norml switching, worst cse () nd perfect controlled switching (b) 4. Conclusions This pper focuses on the methods principles of controlled switching. The uthors method ws implemented in high voltge power sttion for controlling 220 kv trnsmission line in cse of fults inclusive. According to the type of switch (opening or closing) nd the type of component (cpcitor bnk, rector bnk, power trnsformer, power line, etc.) the rel dvntges of intelligent controlled switching re very effective control of switching surges for different pplictions, better power qulity, nd reduced stress of power system components, lower mintennce costs for circuit-brekers. R E F E R E N C E S [1] Pöltl A., Fröhlich K., A New Algorithm Enbling Controlled Short Circuit Interruption, IEEE Trns. Power Delivery, Vol. 18, No. 3, pp , July 2003 [2] Pöltl A., Fröhlich K., Two New Methods for Very Fst Fult Type Detection by Mens of Prmeter Fitting nd Artificil Neurl Networks, IEEE Trns. Power Delivery, Vol. 14, No. 4, pp , Oct [3] *** CIGRE Tsk Force of Study Committee 13 Controlled switching - A stte-of-thert-survey. ELECTRA review nr. 163, December 1995, pg [4] *** ABB, Controlled Switching with Switchsync, Presenttion mnul. Edition [5] *** MITSUBISHI ELECTRIC, Advnced monitoring nd digitl technologies. Documenttion I-0334 BL [6] R. Thoms, Controlled switching of high voltge SF 6 circuit-brekers for fult interruption. Licentite of Engineering Thesis. Goterborg, Sweden, ISSN

10 182 Florin Muntenu, Ciprin Nemeş [7] Fl. Muntenu, M. Adm, D. Ivs, C. Nemes, Aprte si comutri inteligente in sistemele electroenergetice. Ed. Venus, Isi, ISBN [8] F. Muntenu, EMTP Methods nd Algorithms for Intelligent Switching. EEUG Conference, Dresden, Germny.