ITSI Transactions on Electrical and Electronics Engineering (ITSI-TEEE)
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Superconducting Fault Current Limiter in DC Systems with MLI Fed to IM
1Rama Rao P .V .V., 2M.Swathi
1,2Dept. of EEE, Shri Vishnu Engineering College 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 20 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 a16KA fault current within 2 ms[5]. While rated voltage is 320Kv.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. This resistive type 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 deministration, 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
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 step- down 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 20 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 1750A.when the transformer provides 20VAC
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 20 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 20 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 [10]. Many models for SFCL have been designed as resistortype, reactor-type, and transformer- type etc. In this paper a resistive-type SFCL is modeled using Simulink.
Quench and recovery characteristics are designed on the basis of [9]. Where Rm is the maximum resistance of the SFCL in the quenching state, Tsc is the time constant of the SFCL during transition from the superconducting state to the normal state. Furthermore, t0 is the time to start the quenching. Finally, t1and t2 are the first and second recovery times, respectively.
Superconducting fault current limiters (SFCL)
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 auto- recovery.
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 zeroloss conductors when carrying high current is necessary.
B. Types of SCFCL 1. 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 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 TYPEII conductors, which have highly resistive
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substrates. Their feasibility is being studied and tested in many different countries.
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.
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
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 used to obtain variable speed. Recently, power 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
4. MAT LAB SIMULATION RESULTS
Fig.4: Simulation circuit of proposed system without
SFCL
4.1.SIMULATION MODEL OF SFCL IN DC SYSTEM
Fig .5 : Figure shows the sfcl in dc system Resistive
SFCL Diagram
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=0.7s. Simulations are carried out with the short fault happened at t=0.8s(t=0s at the beginning of the simulation), and the fault will be cleared at t=1.0s.the total simulation time is 200ms.
short circuit currents with and without sfcl is shown in fig.5
Fig.7: Short circuit current, voltage without SFCL
Fig.8.: Raising edge of Short circuit current without
SFCL
Fig.9. Short circuit current, voltage level proposed
system
Fig.10: Raising edge of short circuit current proposed
system
SIMULTION DIGRAM OF SFCL WITH MOTOR DRIVE
Fig.11: Simulink diagram of SFCL with motor drive
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Fig.12.Simulation result for armature current, speed,
torque with MLI fed to IM
The short circuit current in fig.10 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 50% 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.
V. CONCLUSION
Super conducting fault current limiter is one of the most ideal current limiting device to the system and electrical equipments. A dc SFCL have 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. In order to determine the SFCL in neighboring AC and DC. 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’s 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. Volume l26, no.11, page no. 3225-3230, Nov, 2013.
[2] G. F .Tang “Multiple–terminal DC power grid technology” presented at the fragrant hill science .meeting, Beijing, china, Sep-27-29, 2012.
[3] L. Ye and L. Lin, “Study of superconducting fault current limiter for system integration of wind farms” IEEE Transaction. Applied.
Superconductivity, volume.15, page No 2027- 2030 June 2015.
[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 Transaction. Applied. Superconductivity, volume 23, no.3, p.5602504, June. 2013.
[5] L. Xiao, s. Dai, L. Lin, Z. Zhang, and J. Zhang
“HTS power technology for future DC power grid” IEEE Transaction. Application.
Superconductivity, volume. 23. No.3, p.5401506, June. 2013.
[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, 2004 Page no.1459-1463.
[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 1-6.
[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 Transaction . Applied.
Superconductivity. Volume 20, No.3. Page no 1233-1237, june.2010.
[9] E.Thuriesetal “Toward the superconducting fault current limiter”, IEEE Transaction. Power delivery. Volume 6, Page no.801-808, April.1991.
[10] L. Ye, L. Lin, and K. P. Juengst, “Application studies of superconducting fault current limiter in electric power systems” IEEE Transaction.
Applied. Superconductivity, volume.12, no.1, March 2002
