Non-Superconducting Fault Current Limiter

Transcription

1 Proceeings o the 5th WEA International Conerence on Applications o Electrical Engineering, Prague, Czech Republic, March -, 6 (pp-7) Non-uperconucting Fault Current Limiter A. CHARMIN*, M. TARAFDAR HAQUE, M. ABAPOUR Islamic Aza University, Ahar Branch* Departement o Power Engineering, University o Tabriz Faculty o Electrical an Computer Engineering, Tabriz IRAN Abstract Many types o superconucting ault current limiters (FCLs) are propose but consiering their high technology an consierable cost it is not possible using these evices commercially, yet. This paper eals with presentation the esigning ormulas an characteristics or near zero resistance copper DC reactor type FCL. The evice is series with istribution line an it uses a single copper coil with a ioe brige without any other control circuits. The simplicity to be built an its low cost are the main avantageous o analyze system. The results show that the power loss is a very small percentage o protecte loa power. The analytical an simulation results are presente an the overall operation is compare with superconuctor FCLs. Keywors Fault current limiter, Non-superconucting Introuction By growth o interconnections in electrical systems the short circuit capacity increases. This not only aects the reliability o system but also it coul result in amaging, egraation, mechanical orces, extra heating an electrical stresses o power apparatus. On the other han, the increasing eman o electric energy makes these problems more important in uture. The FCLs are useul evices or limiting the ault currents an avoiing upgraing o switchgears uring system expansion. An ieal FCL shoul have the ollowing characteristics []: (a) zero resistance/impeance at normal operation (b) no power loss in normal operation an ault cases (c) large impeance in ault conitions () quick appearance o impeance when ault occurs (e) ast recovery to normal state ater ault removal () reliable current limitation at eine ault current (g) goo reliability (h) low cost Dierent structures are propose or FCLs such as resistive, screening, saturate core an inuctive types but superconucting inuctive evices have attracte more attention [-3]. This is ue to this act that it is possible achieving to many o abovementione ieal eatures o FCLs by these evices. The common power circuit topology o inuctive FCLs coul be ivie into two categories as ollows: a) AC reactor type b) DC reactor type The AC reactor type FCL makes use o a parallel resonant circuit that connecte in series with line an it poses high resonant impeance uring ault conition. A ast soli state switch inserts an inuctance in parallel with a capacitor uring ault conition. The capacitor remains in circuit or reucing the inuctive reactance o line even in normal operation o system. Unortunately, resonant type FCLs generates transient voltages that coul cause in transient oscillations with series L-C circuit orme by power actor correction capacitors an customer step own transormers. This gives rise to unwante voltage magniication o customer voltages []. The DC reactor type FCL uses a ioe brige to rectiying the system current that passes through a superconucting inuctor. The inuctor coul be a saturate or linear inuctance [5, 6]. The ioebrige an DC reactor connect in series with istribution or transmission line irectly or by a current transormer. The inuctive FCL coul have a three-phase or single-phase structure but, in both cases usually it has only one superconucting DC reactor [7]. As mentione beore, using superconuctors is because o their no-loss uring normal an ault conitions. Unortunately, ue to high technology an cost o these evices those are not commercially available. There are many attempts to realize using

2 Proceeings o the 5th WEA International Conerence on Applications o Electrical Engineering, Prague, Czech Republic, March -, 6 (pp-7) superconucting coils or example in high temperature but most o propose methos results in more complicate technology an cost. On the other han, it is interesting to analytical analysis an comparison o using near zero resistance copper coils with superconuctors in FCL structure. Obviously, using copper coils or making FCLs is very easy an initial cost woul be much lower than superconuctors. But, there will be power losses uring normal an ault conitions using copper coils so we shoul pay or power loss cost. This paper eals with analytical analysis o DC reactor type superconuctor an non-superconuctor type FCLs. Designing ormulas an useul characteristics are use to compare the mentione FCLs. Ours stuies show that power losses o near zero resistance copper coils which have enough copper cross section area, have less than % power loss o their protecte loas power. On the han, it woul be interesting to present new methos or recovery o generate heat by copper coil FCLs or example to warming up o their cooling water. It seems, using copper coil FCLs coul be a suitable way or less-evelope countries especially those with low electrical energy cost such as mile-east area. Power Circuit Topology Fig. shows the power circuit topology o analyze copper coil DC reactor type FCL. The utility voltage is a sinusoial waveorm with angular requency ω, an rms value, an its impeance consists o series connection o resistor r s, an inuctor L s. There is a switchgear W, that coul isconnect the utility rom loa ater a small time elay ater ault current occur that shoul be etermine by protection relay setting time. The propose FCL consists o a ioe-brige that rectiies the system current that passes through a copper coil DC reactor. The system has no control circuit. The resistance o DC reactor is moele with a small series resistor R while its inuctance is shown by L in Fig.. By choosing appropriate value or inuctor L, it is possible to achieve an almost DC current with small ripple i, that results in short circuit o inuctance L uring normal operation o system. Obviously, increasing the inuctance o L, results in ecreasing the ripple currents o i an the DC reactor will have almost no eect on normal operation o system. Existence o R woul result in power losses an voltage rop which they coul be ecrease by increasing the cross section area o copper coil. AC v v v ( t) =. in( wt) v v Fig.. Power circuit topology o analyze FCL There woul be a orwar voltage rop across rectiier ioes v, too. The loa is assume to be a R-L loa with r L an L L as its resistor an inuctor, respectively. During ault conition, the ault current increases an this time varying current passes through DC reactor that increases voltage rop an ecreases the ault current magnitue. In this way, the power rating o switchgear coul be etermine or lower ault current magnitue. The ault current will pass through DC reactor or only some millisecons ue to the operation o switchgear. 3 Circuit Analysis Fig. shows the line an FCL current waveorms in circuit normal operation case. The line current is a sinusoial waveorm while the reactor current i, is a rectiie current. The reactor current is perioic with time interval between t to t 3. The circuit has two moes o operation a ollows: (a) Charging moe (b) Discharging moe Dio D Current Line Current Dio D Current Reactor Current Fig.. The Line an FCL current waveorms in normal circuit operation case

3 Proceeings o the 5th WEA International Conerence on Applications o Electrical Engineering, Prague, Czech Republic, March -, 6 (pp-7) Charging moe begins at t an it continues until t. At t the ioes D an D3 turns ON an DC reactor connects in series with utility. Eq. () shows the system current ormula in charging moe [6]. ( r L)( tt ) i( t) = e i sin( ωt + r + sin( ωt z r Where: () il ( t) = i ( t) = i( t) r = r + rl + r L = L + LL + L v is the orwar voltage rop o the ioes that is assume to be constant i = i( ) t z = r + ( Lω) tan ϕ = Lω r. It is interesting to notice that the current waveorm in charging moe is not sinusoial ue to transient o insertion o DC reactor. Obviously, the resistance o DC reactor is not so important in this subject because it is much more less than sum o line an loa resistors. o, using inuctive FCLs woul result in istortion o line current. Discharging moe begins at t an it continuous until t 3. At t=t, ue to changing the irection o current through L, the polarity o its voltage v L (t), changes an between t to t its magnitue begins to increase. It is possible to write eq. () at t=t in which v L (t) equals v r (t) with opposite polarity an the ioes D an D turns ON because o their orwar biasing. [ vl ( t = [ v v Where ) + vr ( t ( t ) + v )] = [ v( t) + v ( t )] = 3 ( t )] () i ( t ) t ) = L (3) t L ( During ischarging moe, the inuctor current ree-wheels through the ioes D3-D an D-D. The line current il lows both the upper an lower ioes o rectiier brige. Eq. () an Eq. (5) show the line current an DC reactor current ormula uring ischarging moe, respectively. ( ) ( r L)( tt ) i t = e i sin( ωt + sin( ωt ϕ ) () L z r L t t ( t) = ( )( ) e i (5) r r i Where: r = r + r L L = L + L L i = i( ). t + The inuctor current ecreases because o resistor r an ioe orwar resistors. o, the superconucting coil current will ecrease in slower rate because o existence o only rectiier ioes resistors. The current o D an D3 which are similar, ecreases in ischarging moe because o ecreasing the line current. At t=t 3 the current o these ioes reaches to zero an they turn OFF naturally. On the other han, the current o D an D which are similar, increases uring ischarging moe. At t=t 3, the current through these ioes begins to increase the current o DC reactor, so the charging moe begins again. Obviously, the sum o currents o ioes in each ioe-brige arm is equal with line current, instantaneously. Ripple Current Eq. () an eq. (5) show the charging an ischarging current ormulas o DC reactor, respectively. Obviously, these currents consist o a DC value in aition to a ripple current. Existence o ripple current, results in voltage rop across L uring normal system operation case. o, it is appropriate to ecrease the ripple currents as much as possible. Eq. (6) is use or einition o DC value o inuctor current, I DC : i I DC r, p p = i Max (6) Where i Max stans or the maximum current o reactor an it is equal with i an ir, p p stans or the peak to peak o ac ripple current o reactor an it is equal with ( i i3). Eq. (7) shows the ormula o DC value o inuctor current. I r T T DC imax ( ) L L (7) The ir p p, coul be obtaine using eq. (8) as ollows: T r imax i r( p. p) ( + ) (8) L

4 Proceeings o the 5th WEA International Conerence on Applications o Electrical Engineering, Prague, Czech Republic, March -, 6 (pp-7) Where T is ( t3 t ) an it equals (ms) or power requency o 5 Hz. By consiering the inuctor resistor r equal with zero it is possible getting eq. s (9) an () which show the DC value an the peak to peak o ac ripple current o a superconucting FCL, respectively [6]. I T DC imax L (9) T ir( p. p) () L Comparison o eq. (8) with eq. () shows that existence o resistance in copper coil FCL woul result in increasing o ir, p p through inuctor. On the other han, increasing o L coul ecrease the ir, p p in aition to increasing o DC value o current through inuctor. Fig. s (3) an () show the variations o ir, p p versus DC reactor inuctance or ierent values o line current an inuctor resistance. Consiering these igures, it seems 5A A A 7 3A 5A 7A Peak to peak o ripple current in DC reactor (A) Fig. 3. The Peak to peak o ripple current in DC reactor (A) Fig r =.5 (ohm) DC reactor inuctance (H) ir, p p vs. the variations o L or ierent values o line current r= r=.5 r=.75 r=.5 i L =7 (A) DC reactor inuctance (H) ir, p p vs. the variations o L or ierent values o inuctor resistance choosing the DC reactor inuctance near to. (H) woul result in acceptable value o i r, p p. 5 Power Losses The main objective or using superconuctors in FCLs is their zero resistance an no power loss in normal operation case as well as ault conition. Eq. () shows the magnitue o DC power losses in reactor consiering this act that ir, p p is very small compare with I DC as ollows: r T T P c = r I DC = r imax ( ) () L L Fig. s (5) an (6) show DC power losses variations versus DC reactor inuctance where its resistor an line current is as the parameter o curves. This igures show that the power loss in resistance o reactor is less % o its protecte loa power. DC power losses in reactor (W) r=.5 r= DC reactor inuctance (H) r=.75 r=. Fig. 5. DC power losses vs. DC reactor inuctance or ierent values o reactors resistance DC power losses in reactor (W) A A A 3A 5A 7A DC reactor inuctance (H) i L =7 (A) r =.5 (ohm) Fig. 6. DC power losses vs. DC reactor inuctance or ierent values o line current

5 Proceeings o the 5th WEA International Conerence on Applications o Electrical Engineering, Prague, Czech Republic, March -, 6 (pp-7) DC store energy in reactor A A A 3A 5A 7A r =.5 (ohm) 3 Dio D Current Dio D Current Line Current Dc Reactor Current DC reactor inuctance (H) Fig. 8. line an FCL currents uring a ault conition Fig. 7. torage energy in inuctor vs. ierent values o L The energy store in inuctor can be obtaine using eq. (). Fig. (7) show the storage energy value versus ierent values o L. This igure shows that the store energy is a unction o L in almost linear orm. r T T W DC = L imax ( ) () L L 7 imulation Results During ault conition, the line current increases because the ault impeance z = r +jωl is substitute to loa impeance z L. The power circuit topology o Fig. is use or analyzing the ault conition. The simulation parameters are as ollows: z L = 9.+jω. z s =.+jω. z =.+jω. v s (t) =3.8 in(3t) v = 3 r =. L =. (kv) (v) (H) Fig. (8) shows the line an FCL currents uring a ault conition. The ault occurs at t=t an the loa current begins to increase. As is shown in this igure, beore ault conition, the current through inuctor is a almost ripple ree DC current. The prouce voltage across L in ault conition has resulte in limiting the ault current as well as istortion o its waveorm. At t=t 5 a charging moe begins an the line current reaches the inuctor current. The operation o FCL has resulte in ault current limiting between t 5 to t 6. At t=t 6 a ischarging moe starts an it continuous until t=t 7. The current equation in charging moe, between t 5 to t 6 is shown by eq. (3) as ollows: ( r L)( tt ) i ( t) = e 5 i5 sin( ωt5 + r + sin( ωt z r Where: r = r + r + r L = L + L + L z = r + ( Lω) i 5 = i( t 5 ) (3) Eq. () an (5) shows the loa an inuctor currents uring ischarging moe, respectively. ( ) ( r L)( t t 6 ) il t = e i6 sin( ωt6 + sin( ωt ϕ ) () z r L t t ( t) = ( e )( 6 ) i6 (5) r r i Where, i = i ) 6 ( t 6 + Consiering the resistance o DC reactor ha not so important eect on FCL operation but, Fig. (9) is use to magniy the ierence between superconuctor an copper coil FCL. This igure shows that existence o resistor ha resulte in spee up the ischarging o L that has not signiicant eect on FCL operation. Fig. () shows the line an FCL currents ater removal o a ault current. The ault has been eliminate at t=t 8. This igure shows that the DC reactor current that has been raise to a high value

6 Proceeings o the 5th WEA International Conerence on Applications o Electrical Engineering, Prague, Czech Republic, March -, 6 (pp-7) Reactor Current with Resistance Reactor Current without Resistance Fig. 9. Magniie charging/ischarging moes or superconucting an copper coil FCLs Dio D Current Dio D Current Line Current Dc Reactor Current Fig.. Operation o copper coil FCL ater ault conition uring ault conition, is ecreasing graually to its normal state value. The simulation results show there is not consierable ierence between superconucting an copper coil FCLs in limiting the ault current magnitues. I the maximum permitte ault time consiere to be equal with t = t 8 t then it is possible writing eq. (6) as allows: L ri8 D + t8 t = ln (6) r ri + Where; D r = r + r + r an D = / π Using this equation, it is possible calculate the esire value o L using eq. (7). L = ri ln ri 8 rkt D + + D L L (7) 8 Conclusion The analytical analysis an esigning characteristics or DC reactor "superconuctor" an "copper coil" type FCLs presente. The overall operation o mentione FCLs in normal an ault cases stuie, careully. The results show the power loss o copper coil FCL is less than % o its protecte loa power. On the other han, the simulation results show that there is not signiicant ierence between superconuctor an copper coil FCLs operation in limiting the ault currents magnitue. It seems, the lower initial cost an simpler technology or builing an using the copper coil FCLs in aition to the possibility or recovering o its heat energy coul make this kin o FCLs a goo alternative or more researches in this iel. 8 Reerences [] M. Yamaguchi,. Fukui, T. atoh, Y. Kaburaki; T. Horikawa, T. Honjo, Perormance o DC Reactor Type Fault Current Llimiter Using High Temperature uperconucting Coil, Applie uperconuctivity, IEEE Trans., ol. 9, Issue, Part, June 999, pp [] C.. Chang an P. C. Loh, Integration o Fault Current Limiters on Power ystems or oltage Quality Improvement, Journal o cience, Electric Power ystems Research, ol. 57, Issue, 5 March, pp [3] M. Ahme, G. Putrus, L. Ran, Power Quality Improvement Using a oli-state Fault Current Limiter, Trans. an Dist. Con. an Exhibition : Asia Paciic. IEEE/PE ol., 6-, Oct., pp [] C.. Chang, P. C. Loh, Designs ynthesis o Resonant Fault Current Limiter or oltage ag Mitigation an Current Limitation, Power Eng. ociety Winter Meeting,. IEEE ol., 3-7, Jan., pp [5] H. Tsutomu,. Khosru Mohamma, N. Massanori, M. Itsuya an N. Taketsune, Proposal o aturate DC Reactor Type uperconucting Fault Current Limiter (FCL), Intl. Journal o cience, Cryogenics, ol., Issue 7, July, pp [6] T. Hoshino, K. M. alim, A. Kawasaki, I. Muta, T. Nakamura, M. Yamaa, Design o 6.6 k, a aturate DC Reactor Type uperconucting Fault Current Limiter Applie uperconuctivity, IEEE Trans. on uperconuctivity, Issue, Part, June 3, pp. -5. [7] L. Eung Ro; L. eungje; L. Chanjoo;. Ho-Jun; B. Duck Kweon; K. Ho Min; Y. Yong-oo; K. Tae Kuk, Test o DC Reactor Type Fault Current Limiter Using ME Magnet or Optimal Design, Applie uperconuctivity, IEEE Trans. ol., Issue, March, pp