Superconducting Fault Current Limiter in DC Systems with MLI Fed to IM

Transcription

1 Superconducting Fault Current Limiter in DC Systems with MLI Fed to IM 1 Rama Rao P.V.V., 2 M.Swathi 1,2 Shri Vishnu Engineering for Women, Bhimavaram, India Abstract: In this paper, an application of superconducting fault current limiter (SFCL) is proposed to limit the fault current that occurs in power system, SFCL is a device that uses superconductors to instantaneously limit or reduce unanticipated electrical surges that may occur on utility distribution and transmission networks. Due to the difficulty in power network reinforcement and the interconnection of more distributed generations, fault current level has become a serious problem in transmission and distribution system operations. The utilization of fault current limiters (FCLs) in power system provides an effective way to suppress fault currents and result in considerable saving in the investment of high capacity circuit breakers is felt. In this work, a resistive type SFCL model was implemented by integrating Simulink and Sim Power System blocks in Matlab. The designed SFCL model could be easily utilized for determining an impedance level of SFCL according to the fault-current-limitation requirements of various kinds of the DC system. In this paper SFCL in dc systems implemented, and it is used in motor drive to reduce the fault current. I. INTRODUCTION The utilization of SFCL in power system provide them most effective way to limit the fault current and results inconsiderable saving from not having to utilize high capacity circuit breakers. With Superconducting fault current limiters (SFCLs) utilize superconducting materials to limit the current directly or to supply a DC bias current that affects the level of magnetization of a saturable iron core. Being many SFCL design concepts are being evaluated for commercial expectations, improvements in superconducting materials over the last 2 years have driven the technology [4]. Case in point, the discovery of high-temperature superconductivity (HTS) in 1986 drastically improved the potential for economic operation of many superconducting devices. Based on the previous works, this paper presents feasibility analysis results of positioning of the SFCL and its effects on reducing fault current in DC system. Superconducting fault current limiter is ones of the most ideal current device to protect the system and electrical equipments. DC power systems are widely adopted because flexible position arrangement, low maintenance cost and fast transient capability. High power DC system has been utilized as isolated power system in many applications [1-2]. Due to high power capacity, reliable and safety performance, fault protection and tolerance are usually required. In DC grids, the fault current has no zero crossing point as ac current does. So it s difficult open the over current fault transmission line. So use sfcl to reduce the fault current. In recent years HVDC transmission constantly developed china. Multiple transmission lines have been built in china [7-9] increase of power system capacity and the development of transmission technique, the short circuit current will reach the peak current which ranges between kilo amperes and tens of kilo amperes within several milliseconds at present using circuit breakers to cut off the fault current is applied in the dc system to ensure the whole system safety. In recently the dc breaker developed by ABB can cut off a16 ka fault current within 2 ms [5]. While rated voltage is 32 kv SFCL could bring a solution to interruption of the fault current in dc net works. Most of the SFCL prototypes up to now have been designed for ac systems. This paper introduces a DC SFCL prototype. These resistive types SFCL designed and constructed by shanghai Jiao Tong University. the prototype will be applied in an isolated dc network as an Ingrid demonstrations to prove the current limiting ability of SFCL in dc systems [4].In real grid demonstration, the utilities require the SFCL to provide good current limiting performance. So the hts tapes chosen based on their characteristics. Then simulations are carried out to optimize the limiting effect and determine the SFCL parameters. So the series of experiments conduct to prove the SFCL has good current limiting ability. This paper focuses on a factor for resistive type SFCL, which is useful to improve the reliability of the system, with the transient stability study based on the equal area criterion, the performances of the proposed SFCL to reduce the level of fault currents. In this SFCL used in induction machine get good results. This paper proposed a new configuration of SFCL in Multilevel Inverter fed to motor drive and Simulation results given and explained. The simulation results to SFCL have good current limiting ability in dc systems ISSN (Print): , Volume-4 Issue-5,

2 II. HIGH TEMPERATURE SUPERCONDUCTOR TAPES TESTS A high power dc short circuit test platform is built to verify the limiting effect of the second generation (2G) high temperature superconductor (HTS) tapes in dc power systems. The platform is composed of a stepdown transformer, an uncontrolled rectifier bridge and a short-circuit control circuit, as shown in Fig. 1. The system voltage is provided by an isolated transformer. The low voltage level is good for the safety of the test system, so the test is conducted when the voltage is 2 VAC. So the dc voltage behind the rectifier bridge is about 28 V. Without the superconducting limiting module, the normal and short circuit current respectively 6.7 A and 175A.when the transformer provides 2VAC Fig 1.Over all test platform Superconducting limiting module of two types of HTS tapes, respectively produced by the Physics Department of Shanghai Jiao Tong University (SJTU) and American Superconductor Corporation (AMSC), are applied to the dc system to prove the current limiting ability of superconducting materials. Short circuit test with the limiting module are conducted when the transformer supplies 2 VAC. The circuit current is obtained by testing the voltage of the line resistor. Short circuit current and the resistance of the superconducting limiting module in 2 VAC systems are simulated. III. BASICS OF SFCL Superconducting fault current limiter is a promising technique to limit fault current in power system. Normally non-linear characteristic of superconductor is used in SFCL to limit fault current. In a normal operating condition SFCL has no influence on the system due to the virtually zero resistance below its critical current in superconductors. But when system goes to abnormal condition due to the occurrence of a fault, current exceeds the critical value of superconductors resulting in the SFCL to go resistive state. This capability of SFCL to go off a finite resistive value state from zero resistance can be used to limit fault current. Different types of SFCLs have been developed until now [1]. Many models for SFCL have been designed as resistor-type, reactor-type, and transformertype etc. In this paper a resistive-type SFCL is modeled using Simulink. Quench and recovery characteristics are designed on the basis of [9]. Where R m is the maximum resistance of the SFCL in the quenching state, T sc is the time constant of the SFCL during transition from the superconducting state to the normal state. Furthermore, t is the time to start the quenching. Finally, t1and t2 are the first and second recovery times, respectively. Upper conductors are widely adopted in FCL topologies, mostly because they offer superior performance by presenting negligible normal operation impedance, when the temperature and magnetic field on them are below critical values (Tc and Hc). Besides, superconductors can also provide inherent fast current limiting characteristics and repetitive operation with autorecovery. 3.1 Characteristics of SCFCL Superconductivity When refrigerated below the critical temperature Tc, the superconductors have very low resistivity (almost zero to DC current), which means low conduction copper losses. Quenching: The resistance of the superconductor will increase rapidly when large current flows through it and drives the material beyond its critical temperature. In this case, the superconductor coil will quench the current with substantial amount of impedance presented in the circuit. Many SCFCL technologies take advantage of one or both of the above characteristics. For example, the resistive type and magnetic assisted resistive type SCFCL s utilize the superconductivity in normal operations, while the quenching characteristic is used to limit the fault current in these FCL types. On the other hand, in some topologies, such as in saturated-core FCL s and bridge-type FCL s, superconductors are sometimes used only as zero-loss conductors when carrying high current is necessary. 3.2 Types of SCFCL a. Resistive type Resistive superconductor FCLs use the quenching effect of superconducting materials. It is the simplest form of SCFCL. Figure 2 demonstrates the principle topology of a resistive type SCFCL device. Fig.2. Resistive type superconductor FCL The main current carrier SC is a low inductance superconductor. Shunt resistor R is necessary to suppress hot-spot and overvoltage on the superconductor during quenching transients. Figure 3 illustrates an example configuration of the resistive type SCFCL ISSN (Print): , Volume-4 Issue-5,

3 elements. Because of the low resistance of the silver substrate of TYPE-I superconductors, large number of elements are required to achieve the desired current limitation goal. This increases both the material costs and the operation AC losses, in that more superconducting materials are subject to carrying AC current. Hence, this configuration is suitable for the TYPE-II conductors, which have highly resistive substrates. Their feasibility is being studied and tested in many different countries. b. Magnetic assisted resistive type As implied by its name, the magnetic assisted resistive SCFCL works similar in principle to the resistive SCFCL described above. A copper coil is connected in parallel with the superconductor elements. Also, this shunt coil is physically wrapped around elements. During normal operation, the superconductor carries all the normal operation current and presents little impedance to the power network. Under fault, the resistance of the shunt coil has the same function as the shunt resistor in the resistive type SCFCL, bypassing the fault current and preventing hot-spots caused by inhomogeneous quenching of the superconductor. electronics and control systems have matured to allow these components to be used for motor control in place of mechanical gears. These electronics not only control the motor s speed, but can improve the motor s dynamic and steady state characteristics. Adjustable speed ac machine system is equipped with an adjustable frequency drive that is a power electronic device for speed control of an electric machine. It controls the speed of the electric machine by converting the fixed voltage and frequency to adjustable values on the machine side. High power induction motor drives using classical three phase converters have the disadvantages of poor voltage and current qualities. To improve these values, the switching frequency has to be raised which causes additional switching losses. Another possibility is to put a motor input filter between the converter and motor, which causes additional weight. This modified configuration of multilevel inverter method can be applied to higher level converters. As the number of level increases, the synthesized output waveform adds more steps, producing a staircase waveform V. MAT LAB SIMULATION RESULTS Fig.3. Schematic of magnetic assisted resistive type SCFCL Other than this, a voltage drop caused by the initial quench is seen by the shunt copper coil, and builds up a magnetic field inside the coil. This magnetic field effectively accelerates the quenching process of the superconductor, since the superconductors critical temperature reduces substantially when exposed to external magnetic fields (as shown in Figure 2.4). This type of SCFCL applies to the TYPE-I superconductor enabling it with performance improvements such as faster and more homogeneous quenching process. IV. MULTILEVEL INVERTER FED TO MOTOR DRIVE Fig.4: Simulation circuit of proposed system without SFCL 4.1. SIMULATION MODEL OF SFCL IN DC SYSTEM DC motors have been used during the last century in industries for variable speed control applications, because its flux and torque can be controlled easily changing the field and armature currents respectively. Furthermore, four quadrant operation of induction motor was also achieved. An induction motor being rugged, reliable, and relatively inexpensive makes it more preferable in most of the industrial drives. They are mainly used for constant speed applications because of unavailability of the variable-frequency supply voltage. But many applications are in need of variable speed operations. In early times, mechanical gear systems were Fig.5 SFCL in DC system used to obtain variable speed. Recently, power ISSN (Print): , Volume-4 Issue-5,

4 torque speed voltage(v) current Voltage(v) voltage(v) voltage International Journal of Advance Electrical and Electronics Engineering (IJAEEE) Fig 6: Resistive SFCL 4.6. MODELING AND SIMULATION The SFCL model is used in the system to simulate its impact on the dc network. Considering the limiting effect and the co operation with other electrical equipments, the shunt resistor in parallel t with the superconductors to adjust the limited current and to avoid the over voltages. The DC is stable at t =.7s. Simulations are carried out with the short fault happened at t =.8s (t = s at the beginning of the simulation), and the fault will be cleared at t = 1.s. The total simulation time is 2ms. Short circuit currents with and without SFCL is shown in fig Fig.9. Short circuit current, voltage level proposed system Fig.1. Raising edge of short circuit current proposed system SIMULTION DIGRAM OF SFCL WITH MOTOR DRIVE Fig.7 Short circuit current, voltage without SFCL Fig.11. Simulink diagram of SFCL with motor drive Fig.8. Raising edge of Short circuit current without SFCL Fig.12. Simulation result for current, speed, torque with MLI fed to IM ISSN (Print): , Volume-4 Issue-5,

5 The short circuit current in fig.1 are damped oscillation curves because of the large inductance and large capacitor behind the rectifier bridge used to stabilize the dc current and voltage from fig to observed that the short circuit current significantly limited by SFCL. Response time of sfcl is about 1.5ms.the peak value of the fault current is limited about 5% of the fault current without SFCL in 2ms.the simulation results show SFCL has the current limiting ability in the real isolated dc net work and will provide important reference for field test in Ingrid demonstrations. VI. CONCLUSION Super conducting fault current limiter is one of the most ideal current limiting device to the system and electrical equipments. A dc SFCL has been introduced in this paper. This paper presented feasibility analysis results of positioning of the SFCL and its effects on reducing fault current in DC systems. AC and DC SFCL models were designed to perform for the worst case faults with the different SFCL arrangements. From the simulation results, the optimal strategic installation placement of SFCLs in power systems simulation are performed to research impact of SFCL on a real dc systems, and determine the SFCL parameters suitable for this network. It is application of HVDC in future. In this paper SFCL used in induction asynchronous (induction) machine. It does also reduce the fault current. REFERENCES [1] Y. Chen, S. Li, J. Sheg, Z. Jin, Z. Hong, and J. Gu Experimental and numerical study of coordination of resistive type superconducting fault current limiter and relay protection J. superconductivity, Novel magazine, Vol. l26, no.11, page no , Nov [2] G. F.Tang Multiple terminal DC power grid technology presented at the fragrant hill science.meeting, Beijing, china, Sep-27-29, 212. [3] L. Ye and L. Lin, Study of superconducting fault current limiter for system integration of wind farms, IEEE Transactions on Applied Superconductivity, Vol. 15, page No June 215. [4] L. Martini, M. Bocchi, M. Ascade, A.Valzasina, V. Rossi, C. Ravetta and G. Angel Live grid installation and field testing of the first Italian superconducting fault current limiter, IEEE Transactions on Applied Superconductivity, Vol. 23, no.3, p.56254, June 213. [5] L. Xiao, s. Dai, L. Lin, Z. Zhang, and J. Zhang HTS power technology for future DC power grid IEEE Transactions on Applied Superconductivity, Vol. 23. No.3, p.54156, June [6] Y. Huang and Z. Xu study on the pure dc transmission from the west to east in proc. IEEE power Engineering Society General meeting, 24, Page no [7] H. Haung, Xu, W. Wang, and C. Wang Transient stability analysis of shanghai power grid with multiple HVDC links in proc. lnt. POWERCON system Technology, Page No [8] O. B. Hyun, H. R. Kim, J. Sim, Y. H. Chun, K. B. Park,B. W.Lee and I.S.Oh, 6.6 Resistive superconducting fault current limiter based on YBCO films IEEE Transactions on Applied Superconductivity, Vol. 2, No. 3, Page no , June.21. [9] E.Thuriesetal Toward the superconducting fault current limiter, IEEE Transactions on Power delivery, Vol. 6, Page no , April [1] L. Ye, L. Lin, and K. P. Juengst, Application studies of superconducting fault current limiter in electric power systems IEEE Transactions on Applied Superconductivity, Vol.12, No.1, March 22. ISSN (Print): , Volume-4 Issue-5,