Australian Journal of Basic an Applie Sciences, 7(): 76-8, 13 ISSN 1991-8178 Design an Application of Fault Current Limiter in Iran Power System Utility M. Najafi, M. Hoseynpoor Department of Electrical Engineering, Bushehr Branch, Islamic Aza University, Bushehr, Iran. Abstract: Rectifier type fault current limiter is one of well known fault current limiters, because of using superconuctor in the structure of rectifier type FCL, using this type is limite to research projects an laboratory applications. In this paper we have been stuying on rectifier type fault current limiter using copper coil. Such reactor consists of copper coils an is applicable in Iran power system utility. The coil is connecte to the DC link of the brige circuit. The DC reactor effect of the current limiter has been stuie. This type of FCL is similar to the brige type SFCL but a copper DC ironcore reactor is use instea of superconucting reactor. The simplicity to be built an its low cost are the main avantageous of analyze system. The results show that the power loss is a very small percentage of protecte loa power. Key wors: Fault Current Limiter, Power Losses, Voltage isturbance, fault Current INTRODUCTION Electric power system esigners often face fault-current problems when expaning existing buses. Larger transformers result in higher fault-uty levels, forcing the replacement of existing buswork an switchgear not rate for the new fault uty. Alternatively, the existing bus can be broken an serve by two or more smaller transformers. Another alternative is use of a single, large, high-impeance transformer, resulting in egrae voltage regulation for all the customers on the bus. The classic traeoff between fault control, bus capacity, an system stiffness has persiste for ecaes (Bouslama-Bouaballah, S., et al., 1). Since a large fault current mechanically an thermally amages electric equipments in the system, it is esirable to incorporate a fault current limiter in the system. There are many types of fault current limiters: current limiting reactors, power fuses, current limiting wires an superconucting fault current limiters (SFCLs). Of the fault current limiters, SFCLs exhibit the best current limiting performance because (1) current limiting reactors, fuses an wires cause substantial power loss uring normal operation in the power system while SFCLs o not; () power fuses must be replace by han after their operation while SFCLs are recovere automatically; (3) current limiting wires have limite lifetime. SFCLs operate from the properties inherent to superconuctors (Hyo-Sang Choi, et al., 1; Boening, H.J., D.A. Paice, 1983). Superconucting fault current limiter (SFCL) using rectifier brige circuit is well known. As mentione before, using superconuctors is because of their no-loss uring normal an fault conitions. Unfortunately, ue to high technology an cost of these evices those are not commercially available. There are many attempts to realize using superconucting coils for example in high temperature but most of propose methos results in more complicate technology an cost. On the other han, it is interesting to analytical analysis an comparison of using near zero resistance copper coils with superconuctors in FCL structure (Ishigohka, T., A. Ninomiya et al., ; Uea, T., M. Morita et al., 1993). Obviously, using copper coils for making FCLs is very easy an initial cost woul be much lower than superconuctors. But, there will be power losses uring normal an fault conitions using copper coils so we shoul pay for power loss cost. This paper eals with analytical analysis of DC reactor type superconuctor an non-superconuctor type FCLs. Designing formulas an useful characteristics are use to compare the mentione FCLs. Ours stuies show that power losses of near zero resistance copper coils which have enough copper cross section area, have less than 1% power loss of their protecte loas power. On the han, it woul be interesting to present new methos for recovery of generate heat by copper coil FCLs for example to warming up of their cooling water. It seems, using copper coil FCLs coul be a suitable way for less-evelope countries especially those with low electrical energy cost such as mile-east area.. Circuit Topology: The power circuit of the propose fault current limiter (FCL) is shown in Fig. 1. In this case, a simple ioe Brige is use. This brige consists of four ioes D1-D4. L is the inuctance of coil. The positive half cycle of current flows through D1 an D3 an the negative half cycle through D an D4. The higher value of inuctance prouces almost a DC current through the inuctor coil. It keeps the ioes continuously conucting. Again, the higher inuctance effectively reuces the fault current. On the other han, the loa increasing effect is expecte to be worse at higher value of the inuctance. Corresponing Author: M. Najafi, M. Hoseynpoor, Department of Electrical Engineering, Bushehr Branch, Islamic Aza University, Bushehr, Iran. 75
Aust. J. Basic & Appl. Sci., 7(): 75-8, 13 v( t) V. Sin( wt) Fig. 1: Power circuit topology of analyze FCL 3. Ripple Current: Fig. shows the line an FCL current waveforms in normal operation case of the circuit. The line current is a sinusoial waveform while the reactor current i, is a rectifie current. The reactor current is perioic with time interval between t to t 3. The circuit has two moes of operation as follows: (a) Charging moe (b) Discharging moe Charging moe begins at t an it continues until t. At t the ioes D1 an D3 turns ON an DC reactor connects in series with utility. Eq. (1) shows the system current formula in charging moe. ( rl)( tt ) V VDF it () e i sin( t ) z r V VDF sin( t ) z r (1) Where: i ( t) i ( t) i( t) L S r r r r L L S L L L L v DF is the forwar voltage rop of the ioes that is assume to be constant i i( ) t z r ( L) tan L r. Line Current Reactor Current Fig. : The Line an FCL current waveforms in normal operation case of circuit 76
Aust. J. Basic & Appl. Sci., 7(): 75-8, 13 It is interesting to notice that the current waveform in charging moe is not sinusoial ue to transient of insertion of DC reactor. Obviously, the resistance of DC reactor is not so important in this subject because it is much more less than sum of line an loa resistors. So, using inuctive FCLs woul result in istortion of line current. Discharging moe begins at t an it continuous until t 3. At t=t 1, ue to changing the irection of current through L, the polarity of its voltage v L (t), changes an between t 1 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 D4 turns ON because of their forwar biasing. [ vl ( t) vr ( t)] [ vdf1( t) vdf 4( t)] [ vdf ( t) vdf3( t)] () v L Where i ( t) ( t) L (3) t During ischarging moe, the inuctor current free-wheels through the ioes D3-D an D4-D1. The line current il flows both the upper an lower ioes of rectifier brige. Eq. (4) an Eq. (5) show the line current an DC reactor current formula uring ischarging moe, respectively. ( rl)( tt) V V il () t e i sin( t ) sin( t ) (4) z z ( r L )( t t) () VDF V i DF t e i (5) r r Where: r r S r L L L S L L i i( ). t Eq. (1) an eq. (5) show the charging an ischarging current formulas of DC reactor, respectively. Obviously, these currents consist of a DC value in aition to a ripple current. Existence of ripple current, results in voltage rop across L uring normal system operation case. So, it is appropriate to ecrease the ripple currents as much as possible. Eq. (6) is use for efinition of DC value of inuctor current, I DC : ir, p p I DC i Max (6) Where i Max stans for the maximum current of reactor an it is equal with i 1 an ir, p p stans for the peak to peak of ac ripple current of reactor an it is equal with ( i1 i3). Eq. (7) shows the formula of DC value of inuctor current. r T VDFT I DC imax (1 ) (7) 4L L i The ir p p, coul be obtaine using eq. (8) as follows: T r imax ( V ) (8) L r( p. p) DF Where T is ( t3 t ) an it equals 1 (ms) for power frequency of 5 Hz. By consiering the inuctor resistor r equal with zero it is possible getting eq. s (9) an (1) which show the DC value an the peak to peak of ac ripple current of a superconucting FCL, respectively. VDFT I DC imax L (9) i T r( p. p) VDF (1) L 77
Aust. J. Basic & Appl. Sci., 7(): 75-8, 13 Comparison of eq. (8) with eq. (1) shows that existence of resistance in copper coil FCL woul result in increasing of ir, p p through inuctor. On the other han, increasing of L coul ecrease the ir, p p in aition to increasing of DC value of current through inuctor. 4. Power Losses: The main objective for using superconuctors in FCLs is their zero resistance an no power loss in normal operation case as well as fault conition. Eq. (11) shows the magnitue of DC power losses in reactor consiering this fact that I as follows: ir, p p is very small compare with DC r T VDFT P c r I DC r imax (1 ) (11) 4L L 5. Simulation Results: During fault conition, the line current increases because the fault impeance z f = r f +jl f is substitute to loa impeance z L. The power circuit topology of Fig. 1 is use for analyzing the fault conition. The simulation parameters are as follows: z L = 9.4+j. () z s = +j.1 () z f = +j () v s (t) =3.81 Sin(314t) (kv) = 3 r = () L =.1 (v) (H) Fig. (3) an (4) show the variations of ir, p p versus DC reactor inuctance for ifferent values of line current an inuctor resistance. Consiering these figures, it seems choosing the DC reactor inuctance near to. (H) woul result in acceptable value of ir, p p. Peak to peak of ripple current in DC reactor (A) 7 6 5 4 3 1.3 5A 1A A 3A 5A 7A r =.5 (ohm).4.6.7.9.11.1.14.15.17.19 Fig. 3: The DC reactor inuctance (H) ir, p p vs. the variations of L for ifferent values of line current 78
Aust. J. Basic & Appl. Sci., 7(): 75-8, 13 Peak to peak of ripple current in DC reactor (A) 8 7 6 5 4 3 1 r= r=.5 r=.75 r=.15 i L =7 (A).3.4.6.7.9.11.1.14.15.17.19 Fig. 4: DC reactor inuctance (H) ir, p p vs. the variations of L for ifferent values of inuctor resistance. Fig. (5) an (6) show DC power losses variations versus DC reactor inuctance where its resistor an line current is as the parameter of curves. This figures show that the power loss in resistance of reactor is less 1% of its protecte loa power. 7 6 r=.5 r=.15 r=.75 r= DC power losses in reactor (W) 5 4 3 1 i L =7 (A)..4.5.7.8.9.11.1.14.15.16.18.19 DC reactor inuctance (H) Fig. 5: DC power losses vs. DC reactor inuctance for ifferent values of reactors resistance DC power losses in reactor (W) 14 1 1 8 6 4.5 5A 1A A 3A 5A 7A.4.55.7.85.1.115 DC reactor inuctance (H) r =.5 (ohm).13.145.16.175.19 Fig. 6: DC power losses vs. DC reactor inuctance for ifferent values of line current 79
Aust. J. Basic & Appl. Sci., 7(): 75-8, 13 The energy store in inuctor can be obtaine using eq. (1). Fig. (7) show the storage energy value versus ifferent values of L. This figure shows that the store energy is a function of L in almost linear form. 1 r T VDFT W DC L imax (1 ) (1) 4L L DC store energy in reactor 6 5 4 3 1 5A 1A A 3A 5A 7A r =.5 (ohm).3.4.6.8.1.11.13.15.16.18. DC reactor inuctance (H) Fig. 7: Storage energy in inuctor vs. ifferent values of L Conclusion: The analytical analysis an esigning characteristics for DC reactor "superconuctor" an "copper coil" type FCLs presente. The overall operation of mentione FCLs in normal an fault cases stuie, carefully. The results show the power loss of copper coil FCL is less than 1% of its protecte loa power. On the other han, the simulation results show that there is not significant ifference between superconuctor an copper coil FCLs operation in limiting the fault currents magnitue. It seems, the lower initial cost an simpler technology for builing an using the copper coil FCLs in aition to the possibility for recovering of its heat energy coul make this kin of FCLs a goo alternative for more researches in this fiel. ACKNOWLEDGMENT This research paper has been financially supporte by the office of vice chancellor for research of Islamic Aza University, Bushehr Branch. REFERENCES Boening, H.J., D.A. Paice, 1983. Fault current limiter using superconucting coil, IEEE Trans. Magn., 19(3): 151-153. Bouslama-Bouaballah, S., M. Tagina, A. Fault Detection an Isolation Fuzzy System Optimize by Genetic Algorithms an Simulate Annealing, 1. International Review of Moelling an Simulations (IREMOS), 3(): 1-18. Hyo-Sang Choi, Hye-Rim Kim, Ok-Bae Hyun, 1. Operating properties of superconucting fault current limiters base on YBCO thin films, Cryogenics, 41(3): 163-167. Ishigohka, T., A. Ninomiya et al.,. Fabrication an test of cryogenic fault current limiter combining semiconuctors an DC reactor, Proc. IPEC, pp: 155-158. Uea, T., M. Morita et al., 1993. Soli-state current limiter for power istribution system, IEEE Trans. Power Delivery, 8(4): 1796181. 8