Design of elementary switches for high power with minimal moving mass

Transcription

1 Design of elementary swithes for high power with minimal moving mass alter Holaus ETH Zürih, High Voltage Laoratory Physistrasse 3, CH-89 Zurih Switzerlan ABSTRACT For the use in hyri systems an for synhronous urrent interruption, ultra-fast swithes with high withstan voltage an high ontinuous urrent are require, ut they on t nee failities for fore ar ooling. This paper presents esigns for linearly an rotationally operate opening an losing swithes with a repulsion rive, that feature opening veloities of several m/s, requiring a rive energy of less than J. Base on the efinition of an elementary swith, the main imensions of these swithes suh as require ontat gap, ontat ross setion an minimal moving mass are estimate. A generally appliale equation to alulate the resulting opening veloity is given. As a result, rotational operation shows muh higher opening veloity than linear operation for the same esign parameters with goo agreement to measure values. KEY ORDS: Fast Swithes, Minimal mass, Repulsion rive, System protetion. INTRODUCTION Eletromehanial swithgear suh as iruit reaers, relays an ontators are state of the art for swithing in low, meium an high voltage systems []. They are ale to ope with the swithing emans require y stanars an toay are eonomially most attrative. The main rawa of iruit reaers in high voltage systems is, that its swithing priniple oes not feature a (fault) urrent limiting funtionality for two reasons: The rive system is to slow to at within ms The ar voltage annot e raise up to many V within several milliseons. Both prolems oul e overome, if using powersemionutor swithing evies, suh as GTO s or IGBT s. However, these evies are eonomially unattrative, eause the interrupting power of a single semionutor element is aroun 3 orers of magnitue lower ompare to high voltage iruit reaers (HVCB) as shown in Fig.. Therefore, thousans of these elements have to e operate simultaneously to replae one HVCB. Semionutor elements an operate in the highest power ratings ( M) only at a very short interrupting time of... µs ue to the losses generate uring swithing. The highest power ratings of eletromehanial swithes (> G) are possile at interrupting times of ms, whih is too slow for effetive fault urrent limitation in 5/6 Hz systems. Interrupting power per element [M] Minimal require operating time for effetive urrent limiting an syhronous reaing in 5/6 Hz iruits Integrate gate turn off thyristor Hyri systems High Voltage Ciruit Breaers Low voltage magnet last reaer Range of semionutor Range of eletro- swithes mehanial swithes.... Interruption time [ms] Fig. : Overview on interrupting power an swithing time of single semionutor elements an eletromehanial swithes. Reently, several puliations have shown how to use simple ut very fast swithes in hyri onepts to ahieve fault urrent limitation at meium-voltage levels []-[4]. The presente hyri systems show an interrupting power up to several M an require a mehanial opening swith in the ontinuous urrent path that ommutates the still inreasing (fault) urrent on a parallel path within several µs. Therefore, this swith has not to e esigne as a iruit reaer ut rather as a fast ommutation element. The mentione appliation in a hyri system requires fast swithes ut no ar ooling failities. Another appliation with the very same eman is the well-nown synhronous urrent interruption, where the neessarily fast swith is triggere to open shortly prior to urrent zero in an a iruit. Therefore, the goal of this paper is to present an isuss useful esigns for ultra-fast high power swithes that are showing opening veloities of several m/s ut are not equippe with fore ar ooling failities.. ELEMENTARY SITCHES Given the omprehensive nowlege on the esign an physis of moern high power swithing evies, it is highly unliely that a feasile an eonomial esign for high power swithgear an e foun without onsiering a major hange in the swithing approah. Therefore, the iea of using elementary swithes as high power swithes is isusse in the present paper: This wor was supporte y ABB Switzerlan Lt.

2 hat is an elementary swith? The swithing tas in toay s high power swithgear is mehanially performe y a rive- an ontat system ut the swithing ar eletrially performs it. Aoring to Fig., the swithing ar exist for several ms in the swith an the swith itself has to extinguish the ar at a urrent zero rossing. Therefore, when using this well woring priniple, to ope with the swithing ar has a major impat on swithgear esign. The situation is ifferent, if presuming an ultra-fast opening swith for fast ommutation or for synhronous urrent interruption, where the swithing ar exists for a very short time perio (several µs) only. There is no nee to esign a fast swith so to ope with an enuring highurrent ar. A high power swith, whih oes not onsier a esign impat of the ar at all, is terme an elementary swith in the present wor. Therefore, an elementary swith is a theoretial entity, whih serves as a asis to erive the very limits of inertia an opening veloity of power swithes. Anyhow, it will e shown in hapter 3, that, with the use of a repulsion rive, implementations are possile, whih are losely mathing the elementary swith esign. The main goal of the elementary swith esign is high opening veloity. Hene, the aelerate mass ( inertia) is to e minimize an the operating mehanism has to e ept as simple as possile. Both is ahieve, if the moving ontat part is the one an only moving part (MP) in the swith. This part in general an e move linearly or rotationally as shown in a priniple seth in Fig. a, with FC an FC eing the fixe ontats. a) Linear ) Rotational A FC m s v MP FC l Swithing Meium m rot MP FC v,ω A s + FC Fig. :Priniple esign of linearly an rotationally operate elementary swithes an the notations use throughout this wor. Per efinition, a swith is terme an elementary swith, if it only fulfills its elementary funtions. These are: ithstan the esign voltage if open Carry the esign urrent if lose Performing mehanial opening an losing operations. Note that aoring to the aove-mentione iea, ar ooling an extinguishing is not an elementary funtion, as it e.g. is the ase for a isonnetor. For the following theoretial onsierations on elementary swithes it is not reasonale to wor with rate values as given y stanars. Hene, the terms esign voltage an esign urrent are given to istinguish from rate values. A efinition for the esign values for elementary swithes is given as follows: The esign voltage U im is the reaown voltage of an elementary swith in the fully OPEN position. The esign urrent I im is the ontinuous thermal limiting urrent through the elementary swith in the CLOSE position. The average reaown fiel strength E is given y the ratio of U im over ontat gap s for a given swithing meium an pressure. The average ontat urrent ensity J is given y the ratio I im over the ross setion of the moving part A (see Fig. ). The average reaown fiel strength of the oil insulation material is terme E iso. These efinitions are use in the following setion for an estimation of the main imensions of suh swithes. Estimating the main imensions of elementary swithes A ieletri reaown mehanism is assume to alulate the minimum ontat gap in the open position for a given esign voltage U im. Therefore, the minimum ontat gap s in fully open position results from Eq. with the esign voltage U im, the average reaown fiel strength of the utilize swithing meium E, the pressure p of the swithing meium an a safety fator safe. U safe s im Eq. p E The safety fator safe is manatory, eause U im is efine aove as reaown voltage. As the ontat gap oes not show a homogeneous eletri fiel, E is unerstoo to e an average value, whih an e erive from fiel alulations or from experimental ata for a speifie geometry. Eq. gives the ross setion A of the moving part, where I im is the imensioning urrent an J is the average ontat urrent ensity appliale. Iim A l Eq. J Eq. presumes a homogenous istriution of urrent, what isregars the onstrition of a urrent path at the ontat points. Therefore, to apply Eq., the ontat fore, the numer of ontat points an the mass of the fixe ontats have to e hosen suffiiently high so that the thermal limit for the ontat region is not exeee for a urrent ensity equal or smaller than J. These assumptions are inlue in the efinition for J. Given the ontat gap s an its ross setion A, the minimum for the moving mass m of a linearly moving part is otaine y Eq. 3, whereas ρ is the mass ensity of the moving part. ρ safe m ρ A s U im I im Eq. 3 p E J hen using a rotationally operate swith aoring to Fig., the moving part remains in the ontat gap after a 9 turn. Consequently, the istane etween the fixe ontats has to e inrease to s +. Therefore, the moving mass of rotationally operate swithes m rot is (slightly) higher than at linear motion an shows more epeneny on the imensioning urrent, see Eq. 4.

3 mrot ρ A ( s safe ρ p E J + ) U im I im I + l J im Eq. 4 To show what values result for the moving mass, Fig. 3 gives m alulate (Eq. 3) as a funtion of U im I im for opper an aluminium an various fiel strengths. It an e seen, that using p E 5 V / m, e.g., air at ar an J A/mm whih oth are useful values the mass of a moving part out of aluminium is aroun m g/m. The values for m rot (Eq. 4) are nearly iential to m in the given range. mm [g]) Cu, 5 V/m 5 V/m 3 V/m V/m 4 V/m Aluminum safe.5 JUim*Iim [M] A/mm 5 5 U im I im [M]) 5 3 Fig. 3: Theoretial minimum for the moving mass in an elementary swith as a funtion of U im I im aoring to Eq. 3. The mass alulate in Eq. 3 an Eq. 4 only ontains the mass of the moving part itself, ase on the efinitions an the approximate imensioning formula given aove. Neither rive omponents (springs, hyrauli oil, valves, gear lever ) nor aitional mass for ontating, mounting or ontat oating is ontaine herein. All aitional funtional, - ieletri, -rive, -material, -ontat an aring requirements relate to high power swithes will a mass to this theoretial minimum. For this reasons, m an m rot are unerstoo to e the theoretially minimal (possile) moving mass. An elementary swith having a esign power U im I im as given in Fig. 3 is essentially not apale of interrupting this power. It is aleit assume, that this very small inertia m in omination with a repulsion rive leas to a high ontat separation veloity. It is then the high opening an losing veloity, whih is the ey parameter for suessful appliation. 3. DRIVE SYSTEM AND ENERGY The repulsion rive was foun to e est suitale to operate fast-ating swithes []. But most esigns for fast ating swithes equippe with a repulsion rive use separate parts for the ey-urrent loop an the ontat system an a mehanial linage in etween them. Only reently, a esign for a fast opening swith was presente in literature, whih uses the moving ontat rige as ey urrent loop at the same time [4]. This multiple use of the moving part allows swith esigns, where this part Synonyms are: Thomson rive, eletroynami rive stays the only moving part in the swith an therefore shows a minimal moving mass aoring to Eq. 3 an Eq. 4. Now, omining the iea of the elementary swith with a repulsion rive, where the ey urrent loop ats as moving ontat at the same time, results in a esign presente in Fig. 4. It shows the ross setion of an elementary swith with linear movement that is opene an lose y repulsion. A rief summary of an operation proess is given elow; see [] for a etaile isussion. Opening an losing elementary swithes y repulsion The ring-shape moving part MP is shown in the lose position. hen triggering the losing swith T, the rive apaitor C isharge through the opening rive oil. The rive urrent i together with the inue ey urrents in the moving part are generating a repulsion fore on MP, whih is then pushe upwars in a narrowing gap. The moving part is eelerate an arreste in the open position y frition on the narrowing walls. To lose this swith, the losing oil is energize the same way. The loa urrent is flowing in raial iretion aross the moving part. MP FC MP i T insulation i C FC... opening oil... losing oil U Fig. 4: Applying a repulsion rive for opening an losing a linearly operate elementary swith. Applying the repulsion rive to the asi geometry for elementary swithes with rotational operation (Fig. ) leas to another feasile esign. This esign for opening an losing elementary swithes with rotational movement is given in Fig. 5. Here, the moving part is of uois shape an its entre of rotation has to e fixe on oth ens. Opening an losing is ahieve aoringly y energizing the opening oil or the losing oil. The rive oils are woun elow the moving part on one sie an aove the moving part on the other sie of the axis of rotation. FC i T C U MP insulation i FC Fig. 5: Applying a repulsion rive for opening an losing a rotationally operate elementary swith. It is now to e isusse, whether the linear or the rotational priniple, whih has not yet een treate in literature, is etter suitale for ultra-fast swithes. This is first one y a omparison of the require rive energy.

4 The ineti energy of the moving part An elementary swith is efine to e OPEN if the istane etween fixe ontats an moving ontat is larger than the istane etween the fixe ontats. Thus, the opening gap x (on eah sie) has to e larger than half of the maximal ontat gap inrease y the thiness of the moving part as given y Eq. 5: s a) linear: x + Eq. 5 ) rotational α + sin s + Given an opening time t an the opening gap x alulate y Eq. 5, the neessary veloity v (ω if rotationally operate) for fully opening the ontats within t an e alulate using Eq. 6. This presumes that v respetively ω are onstant uring opening, whih is a goo approximation aoring to measurements an simulations on several esigns. x s a) v onst. + to to Eq. 6 ) ω α + sin onst. to t o s + The require opening veloity therefore is a funtion of the swith parameters s an an it is inversely proportional to the require opening time. Comining Eq. 3 an Eq. 6a leas to the ineti energy lin of linearly opene swithes as a funtion of the opening time, see Eq. 7. lin m v ρ s + l s t o Eq. 7 Therefore, the ineti energy lin strongly epens on l, an s, ut ontat length l an thiness are not separately etermine y Eq., whih gives possiilities for optimisation. For rotationally operate swithes, the moving part is approximate y a uoi an the moment of inertia J of uois. Thus, the ineti energy results from Eq. 8; mainly epening on ontat gap s an ontat thiness. rot J ρ l ω ( + ) ( s + ) ( s + ) + sin s + t o Eq. 8 For omparing linear or rotational operation, the ineti energy of oth priniples is to e ompare. Fig. 6 shows the asolute values of lin an rot (ompute using Eq. 7 an Eq. 8) as a funtion of the ontat istane s for an opening time of t o.5 ms while varying the ontat thiness. The ontat ross setion was hosen to A m, whih is suitale for urrents in the A-range lin, rot [J] Constants: Aluminum, t o.5 ms A m rot, 5 mm lin, 5 mm lin, 3mm rot, 3 mm lin, mm rot, mm s,[mm] s,[mm] lin, rot [J] lin, 5 mm lin, mm lin, 3mm rot, 5 mm rot, 3 mm rot, mm Fig. 6: Kineti energy of the moving part uring opening as a funtion of ontat istane s when opene within t.5 ms. Parameter is the thiness of the moving part, whih is of aluminum for oth linear an rotational operation. It an e rawn from Fig. 6, that the ineti energy of linearly moving ontats is notieale higher at high ontat gaps s, for all values of mass ensity an opening time. At small ontat gaps, there is small ifferene etween the ineti energy for linear an for rotational movement. The resulting values of ineti energy are within several J. Aluminum was hosen as ul material for the moving part as it shows high onutivity an low mass ensity. Using opper instea of aluminium for the moving part woul lea to three times higher energy values ue to higher mass ensity. Require rive energy for elementary swithes The values erive from Eq. 7 an Eq. 8 are giving the ineti energy of the moving part in motion. These have to e ivie y the rive effiieny whih is nown to e only aroun % for repulsion rives to get the require rive energy for the elementary swithes. From theoretial onsierations on repulsion rives foun in literature [5] an from measurements, the following epenene of rive effiieny η from esign parameters applie: η η U im δ e e E iso, η 8 % Eq. 9 inf inf δ is the sin epth of the ey urrents in the moving part an E iso is the reaown fiel for the rive oil insulation an η inf is the maximum rive effiieny. Comining Eq. 7 an Eq. 9 no leas to the require rive energy for linear movement Dlin Dlin η lin ρ l s η s + t C U Eq. Aoringly, the require rive energy for rotational movement Drot results to

5 Drot η ρ l rot ( + ) ( s + ) ( s + ) sin 4 + η t s + o Eq. One question to e answere y this erivation was, whether linear or rotational operation etter fits for ultrafast elementary swithes. The ratio of require rive energy Dlin / Drot for the same rive- an iruit parameters given in Fig. 7 shows, that using linear operation requires up to three times more rive energy. 3.5 Dlin / Drot ar 3 ar 5 ar ar Constants:.5 E 5 V/m l 3 mm mm J 4 A/mm I im 4 A U im [V] Fig. 7: Ratio of require rive energy of linear over rotational movement. Parameter is the pressure p of the swithing meium (see Eq. ). From this omparison it is onlue that aoring to rive energy requirements, rotational operation is superior to linear operation for most esigns. The lower the ieletri strength of the swithing meium an the higher the system voltage, the etter is rotational. A seon question arises from the a rive effiieny of the repulsion rive an the fat, that the rive energy is to e store in apaitors, whih itself have a low energy ensity: hat asolute values for the rive energy result for elementary swithes at higher voltage levels? Fig. 8 showing the require rive energy for imensioning voltage levels up to 5 V answers this question. The values erive for elementary swithes exponentially inrease with the esign voltage an are ompare to the rive energy of stanar iruit reaer, assuming U im eing omparale to the asi insulation level (BIL) in stanars. Fig. 8 shows, that a typial rive apaitor has to have a store energy of several J; for instane a isharge apaitor with C 5 µf, U 5 V, whih gives D 3 J. This apaitor has a volume of V 4.44 liter whih is reasonale an omparale to the require volume of the rive systems of stanar meium voltage iruit reaers. However, it is onlue for higher voltage levels that it maes soun sense to inrease the ieletri strength of the utilize swithing meium rather than rive energy. Inreasing the pressure p of the swithing meium or using one with higher ieletri strength, as e.g. SF 6, ahieves this. Dlin, Drot [J] For omparison: Drive energy for puffer-reaer (approx.) Self-last tehnology (approx.) Lin. ar Rot. ar Lin. 3 ar Rot. 3 ar Lin. 5 ar Rot. 5 ar U im [V] Fig. 8: Require rive energy as a funtion of imensioning voltage for linear un rotational movement. Parameter: E iso 5 V/mm, E.5 V/m, η inf 8%, mm, l 5 mm, t open ms, I im A. For omparison: Self-last: J/M, Puffer-reaer: 7 J/M from [6] 4. OPENING VELOCITY For the erivation of the main imensions of elementary swithes it was foun, that the ontinuous urrent efines the ontat ross setion A l ut not l an iniviually, see Fig. an Eq. aove. Therefore, there are possiilities for optimisation of the swith geometry, whih are isusse in the following. Opening veloity as a funtion of esign parameters As the vital harateristi of elementary swithes is fast operation, optimisation is arrie out for its opening veloity. Using the ineti energy Dlin from Eq., the minimal moving mass m from Eq. 3 an the rive effiieny given in Eq. 9, one an erive the opening veloity for linear operation as a funtion of swith esign an rive parameters as given in Eq.. U lin η im inf Dlin Eiso δ v, lin e e m Eq. ρ l s Aoringly, the opening veloities for rotational operation as a funtion of swith esign an rive parameters are given in Eq. 3. U 6 η ( + ) Drot s im inf Eiso δ v, rot e e ρ l ( + s ) + Eq. 3 ( ) Eq. an Eq. 3 are wiely appliale equations to alulate the opening veloity of elementary swithes as a funtion of swith esign, rive values an ontat material. These equations an e use as an optimisation tool for a qui he on the imensions for a speifi rating. Some speifi values alulate using Eq. an Eq. 3, for aluminium, magnesium an opper an the same rive energy for oth operating priniples Dlin Drot D J are given in Fig. 9. The veloity is at most 6 % higher if using aluminum or magnesium as ontat material instea of opper.

6 3 Sin epth opper 5 v [m/s] 5 Sin epth aluminum Sin epth magnesium Rotating, magnesium Rotating, aluminum Linear, magnesium Rotating, opper Linear, aluminum Constants: Linear, opper D J l. m Measure: linear, aluminum 5 η inf 8 % Measure: linear, opper s 7 mm f 3.5 Hz s i mm [mm] Fig. 9: Calulate opening veloity of elementary swithes with repulsion rive as a funtion of ontat thiness. Linearly- an rotationally operate swithes of Al, Mg an Cu are shown in omparison to measure values. From Fig. 9 it turns out, that the optimum ontat thiness to get highest veloity is in the range of some mm for all three materials. The opening veloity shows a flattish optimum at a thiness whih is little larger than the sin epth δ an thus epens on the rive frequeny f. In general, the optimal ontat thiness is within opt (.5 ) δ for linear an rotational movement; thus the optimum thiness if using opper is slightly smaller. In Fig. 9 also the measure opening veloities for mm of an implemente swith with the given parameters an equippe with a opper, respetively an aluminum moving ontat are given for. The measurements are in goo agreement with the alulate values. Comparison to measure values A omparison of the measure opening veloity of a rotationally operate swith to alulate values (Eq. 3) for a wie range of rive energy is given in Fig v [m/s] alulate using Eq measure values for a rotationally operate swith D [J] Fig. : Comparison of measure opening veloity with alulate values from Eq. 3 for a rotationally operate swith. An average opening veloity up to 5 m/s oul e measure on this rotationally operate swith, whih is a very high value. The omparison shows a very goo agreement etween measure an alulate values at high rive energy. At lower rive energy, what opes with lower opening veloity, the measure values are muh smaller than the alulate ones. This is suppose to originate from the ontat fore, whih ats as a retaration on the moving part. A onstant ontat fore eomes more effetive at low riving fores, i.e. at low rive energy. 5. CONCLUSIONS Base on the presumption that the esign voltage only etermines ontat gap an the esign urrent only etermines the ross setion of the moving part, a esign guieline for the so-alle elementary swithes with repulsion rive was given. The minimal moving mass of an elementary swith was alulate to e aroun g/m. The rive apaitor nees to store less than J energy for ontat veloities up to 5 m/s. The optimum thiness of the moving part is.5 times the sin epth for oth linear an rotational movement. ith regar to low rive energy an high ontat veloity, rotational operation tops linear operation an aluminum an magnesium are the most suitale materials for the moving part. As oth are worse ontat materials, they are to e oate with a suitale ontat material. A wiely appliale equation for alulating the opening veloity of elementary swithes as a funtion of swith esign, rive values an ontat material was given an the results show are in goo agreement with measure ata. This equation an e use as an optimization tool for a qui he on the imensions for a speifi rating. Possile appliations of ultra-fast swithes with the presente esign are in hyri systems for fault urrent limitation, for synhronous urrent interruption, for fast isonnetors or for fast losing swithes at meium voltage levels. The interruption apaility of suh swithes in these appliations is remarale an isusse in [] [4]. 6. REFERENCES [] M. Linmayer, Shaltgeräte: Grunlagen, Aufau, irungsweise (Springer Verlag, Berlin 987). [] M. Steurer, Ein hyries Shaltsystem für Mittelspannung zur stromegrenzenen Kurzshlussunterrehung (Thesis ETH Zürih, ). [3] M. Steurer, K. Fröhlih,. Holaus, K. Kaltenegger, A Novel Hyri Current Limiting Ciruit Breaer for Meium Voltage: Priniple an Test Results, Sumitte to: IEEE Transations on Power Systems. [4]. Holaus, K. Fröhlih, Ultra-Fast Swithes A New Element for Meium Voltage Fault Current Limiting Swithgear, Sumitte to: IEEE-PES inter Meeting, New Yor. [5] P. Zieve, High fore ensity ey urrent riven atuator. IEEE Transations on magnetis, 4, 988, [6] D.S. Johnson,. Hofauer, J. Steharth, Development of the type 45 PM self-last iruit reaer, 99 Dole Client Conferene, Boston 99.