Hybrid Superconducting Fault Current Limiter Research Articles

Optimal placement and sizing of hybrid superconducting fault current limiter for protection coordination restoration of the distribution networks in the presence of simultaneous distributed generation

This paper presents the placement and sizing of the hybrid superconducting fault current limiters (SFCLs) to restore the protection coordination of the distribution system with the synchronous distributed generations (SDGs). Therefore, the normalized objective function considers minimizing the size of the hybrid SFCLs and the total operation time of overcurrent relays (OCRs) for two primary and backup protection models in the fault conditions. This function is selected to achieve the optimal protection coordination (OPC) for the distribution network with SDGs considering low installation cost for SFCLs. Constraints include limits of coordination time interval (CTI), protection coordination restoration (PCR), size of the switches coupled with OCRs, setting parameters of OCRs, and size of the SFCL, and equations concerning the calculation of the fault current flowing through OCRs. This scheme has a nonlinear programming (NLP) framework. Also, the hybrid differential equations (DE) and crow search algorithm (CSA) are utilized to obtain the reliable optimal solution. Finally, the scheme is applied to the standard distribution network, so that the numerical results obtained from various case studies confirm the capability of the suggested strategy in improving the protection coordination of the distribution system with SDGs using the optimal size and location of SFCLs.

Novel Design of a Hybrid Superconducting Fault Current Limiter with Controlled Solid-State Device

Fault current limiters are essential devices used to protect the power system and its equipment against high levels of fault current, which are growing up due to the increase of new power sources. This paper proposes a novel design of a Hybrid Superconducting Fault Current Limiter (Hybrid SFCL), which is composed basically by thyristors in series with a superconducting element. This branch is connected in parallel to an air-core reactor, which improves limitation and ensures the safe operation of the superconductor element. Another advantage of this topology is the use of the voltage drop in the superconductor as an input parameter to the controller. This voltage is used to detect the fault, which avoids the need for a current sensor and, consequently, reduces the manufacturing costs. In this work, the PSCAD/EMTDC software was employed to modeling the Hybrid SFCL and the 2G superconducting tape, which was modeled considering the thermal-electrical analysis. The results show that the fault current is efficiently limited, and the developed controller strategy has shown a relatively good performance. Furthermore, the proposed system guarantees a fast recovery time, in the order of 500 ms, which is a good advantage when compared to the conventional resistive SFCL.

Sustained Coordination of Devices in a Two-Layer Protection Scheme for DGs-Integrated Distribution Network Considering System Dynamics

Distribution networks are usually protected by directional overcurrent relays (DOCRs). Besides, autoreclosers and fuses can be used for protecting lateral feeders to minimize power cuts. Coordinated operation of protection device must be maintained to ensure optimal fault isolation. Typically, steady-state fault current and static protective device characteristics are used to determine optimal settings of devices such that coordinated operation is verified. Sine fault current is not a steady signal and protection devices have dynamic behaviors, the conventionally-determined settings of devices can lead to loss of coordination jeopardizing system reliability. In this paper, a two-layer protection scheme is proposed for a distribution network with distributed generators (DGs). The first layer has DOCRs to protect main feeders. The second has autoreclosers and fuses to protect lateral feeders. Optimal settings of devices are determined to achieve both local-layer and inter-layer coordination of devices by constrained nonlinear optimization. Full dynamic models of every component and transient data of fault current are considered. Furthermore, to sustain coordination under DGs, a hybrid superconducting fault current limiter (HSFCL) with high temperature superconducting resistive element is connected in series to each DG. Dynamic modeling-based HSFCL cost minimization is searched by multi-objective optimization. The approach is applied to two distribution networks and simulation results are analyzed.

New Hybrid Superconducting Fault Current Limiter For Primary Distribution Systems (Dept.E)

In this paper, a new hybrid fault current limiter is proposed for primary distribution systems. It incorporates a high temperature superconducting element in parallel with other two branches. The first is an inductive impedance to share the fault current with. The second branch is a gate-turn off thyristor switch controlled to operate the device in either of two modes: the main mode and the stand-by mode. For the main mode, it controls the temperature of the superconducting element and protects it against damaging excessive heating. Instead, in the stand-by mode, it keeps the device applicable without that superconducting element. The design, control and operation of the device is addressed. Its performance in 11 kV distribution systems with DG is investigated. The effect of fault location and fault incidence angle on the device behavior are explored.

Experimental investigation of current limiting characteristics for a novel hybrid superconducting fault current limiter (SFCL) with biased magnetic field

High temperature superconducting fault current limiter (SFCL) is widely considered as an effective protection for power system when the short-circuit fault currents occur. This paper proposes a novel design of a hybrid SFCL with biased magnetic field which has two-stage current limiting characteristics. This kind of SFCL limits the short current using non-inductive superconducting coil at the first stage, and then by the double-split reactor at the second stage, usually 10 ms later. The advantage of this type of SFCL is saving the amount of superconducting tapes, and it is especially attractive in large current and high voltage occasions. A prototype hybrid SFCL with biased magnetic field is designed and constructed in China Electric Power Research Institute (CEPRI) using YBCO coated conductor. A high speed Data Acquisition (DAQ) System based on LABVIEW is established to monitor and control the SFCL. The current limiting ratios for this prototype SFCL have been investigated experimentally under the operating temperature of 77 K. The experimental results show that the current limiting ratio reaches to 89.66% which validates the design and proves the potential application of this hybrid SFCL.

THE ANALYSIS ON HYBRID SUPERCONDUCTING FAULT CURRENT LIMITER (SFCL) USAGE TO LIMIT SHORT CIRCUIT FAULT CURRENT OF 20 KV ELECTRIC POWER DISTRIBUTION IN SENGKALING SUBSTATION

Abstract —The occurrence of fault in electrical power system operation is inevitable. The causes of fault in electrical power transmission and distribution system for instances are lighting strikes on transmission canal, tree collapses, or short circuit inter-phases to the ground. In order to protect the equipment and the whole electrical system in Sengkaling Substation and to reduce the short circuit fault current quickly within timeframe of ½ cycle, it requires Superconducting Fault Current Limiter (SFCL) which is going to be placed on the bus that comes close to a critical point. The designing and analysis on the system of before and after hybrid SCFL installment utilize PSCAD software. The simulation result obtained by installing hybrid SFCL in incoming bus 2 (20 kV) was that hybrid SFCL was able to reduce short circuit fault current in ½ initial cycle with L-G fault of 16.77 kA changed to 5.9 kA, L-L-G fault of 35.38 kA changed to 9.15 kA, L-L-L-G fault of 38.36 kA changed to 9.8 kA, and L-L fault of 28.89 kA changed to 4.35 kA. The average percentage of short circuit fault current that was reduced by hybrid SFCL was 74.12%.

Design and Evaluation of a Novel Non-Inductive Unit for a High Temperature Superconducting Fault Current Limiter (SFCL) with Bias Magnetic Field

The level of the fault current is enlarged against the capacity of conventional circuit breaks in some urban power grids with the rapid increase of power load. Thus, a high-temperature superconducting fault current limiter (HT SFCL) has been suggested to provide effective and reliable protection of power devices against fault currents. This paper deals with the design of a prototype hybrid SFCL, which is integrated by a double-split reactor with asymmetric noninductively wound copper windings and a noninductive HTS magnet in series to one branch of the reactor. There is a fast switch in series to the magnet as well. The role of non-inductive magnet is for reducing the fault current in the first swing and the double-split reactor further decreases the fault current. The noninductive HTS unit is designed based on the magneto-thermal coupled model. A noninductive superconducting unit prototype is constructed using a YBCO-coated conductor and is immersed in the liquid nitrogen. A high-speed Data Acquisition System of National Instruments based on LABVIEW is built. The critical current and current impact performance for this prototype under the operating temperature of 77 K are investigated experimentally. The experimental results validate the current limiting effectiveness of the noninductive unit for the SFCL with bias magnetic field.

Appropriate Protection Scheme for DC Grid Based on the Half Bridge Modular Multilevel Converter System

The half bridge (HB) modular multilevel converter (MMC) technology is considered a breakthrough to mitigate the shortcomings of the conventional voltage source converter (VSC) in high-voltage direct-current (HVDC) grid application. However, interruption of the DC fault is still a challenge due to fast di/dt and extremely high levels of DC fault current. The fault interruption using a DC circuit breaker (DCCB) causes enormous energy dissipation and voltage stress across the DCCB. Therefore, the use of a fault current limiter is essential, and the superconducting fault current limiter (SFCL) is the most promising choice. Past literature has focused on the operating characteristics of DCCB or limiting characteristics of the SFCL. However, there is little understanding about the fault interruption and system recovery characteristics considering both DCCB and SFCL. In this paper, we have presented a comparative study on fault interruption and system recovery characteristics considering three types of fault limiting devices in combination with circuit breaker. The transient analyses of AC and DC system have been performed, to suggest the most preferable protection scheme. It has been concluded that, amongst the three fault limiting devices, the Hybrid SFCL in combination with circuit breaker, delivers the most desirable performance in terms of interruption time, recovery time, energy dissipation and voltage transients.

Magneto-Thermal Coupling Design and Performance Investigation of a Novel Hybrid Superconducting Fault Current Limiter (SFCL) With Bias Magnetic Field Based on MATLAB/SIMULINK

Energy demand is growing rapidly worldwide, and sustainable solutions are required to improve the energy supply. The new devices like high-temperature superconducting fault current limiters (SFCLs) are popular in recent years. They use the electrical properties of high-temperature superconductivity to instantaneously protect power grids against short circuits and thereby prevent costly outages. They can not only reduce the capacity of the circuit breaker but also lower the cost of line construction. They have become much promising for application in a high-voltage transmission line. A novel hybrid SFCL with a bias magnetic field is proposed by combining a reactor with double-split symmetrical windings and a non-inductive high-temperature superconducting (HTS) magnet, which is in series to one branch of the reactor. An electro-magnetic model of the reactor and a magneto-thermal coupling model of the non-inductive HTS element have been built, and the simulation model of this SFCL is developed in MATLAB/SIMULINK. Its performance is investigated through the simulation considering a serious short-circuit fault and is compared to the performance without SFCL. The results validated the effectiveness of this kind of hybrid SFCL.

Performance evaluation of distance relay in the presence of hybrid SFCL

This study presents a detailed analysis about the impact of hybrid superconducting fault current limiter (HSFCL) on distance relay performance through the analytical and simulation techniques. For assessments, two possible installation locations for HSFCL (before or after potential transformer (PT)) are considered here which has not been evaluated in the literature so far. Moreover, the impact of action time of fast mechanical switch implemented in the HSFCL structure on impedance trajectory and trip time is investigated. The obtained results show the adverse impact of HSFCL on distance relay performance in all cases. Specially, for forward faults, the worst case happens when HSFCL is installed at the downstream of PT. Using quadrilateral characteristic instead of mho can improve the performance of distance relay; however, this way does not fulfil the enough security and sensitivity under different conditions. Therefore, two approaches are proposed to overcome these challenging situations: (i) modifying trip region of distance relay with respect to the HSFCL impedance and (ii) the new impedance calculation procedure. The significant aspect of the proposed solutions compared with the existing techniques is that the accuracy of distance relay is improved without using additional hardware to provide information from HSFCL.

Cryogenic cooling system for a 154 kV/ 2 kA superconducting fault current limiter

A cryogenic cooling system is designed for a 154 kV/ 2 kA three-phase hybrid type superconducting fault current limiter (SFCL). The superconducting modules of the SFCL have the operating condition of 71 K at 500 kPa. The total heat load of the SFCL including the cooling system is estimated at 9.6 kW. The cooling system of the closed loop is configured to meet the operating condition, depending on cooling methods of forced flow cooling and re-liquefaction cooling. The cooling system is composed of three cryostats with superconducting modules, cryocoolers, liquid nitrogen circulation pumps, a subcooler and a pressure builder. The basic cooling concept is to circulate liquid nitrogen between three SFCL cryostats and the cryocooler, while maintaining the operating pressure. The design criterion for the cooling system is based on the operation results of the cooling system for a 154 kV/ 2 kA single-phase hybrid SFCL. The specifications of system components including the piping system are determined according to the design criterion.

Calculation of current limiting reactance of hybrid SFCL for low voltage ride-through capability enhancement in DFIG wind farms

This paper presents a new approach for the low voltage ride-through capability enhancement of doubly-fed induction generator (DFIG) wind farms using a hybrid superconducting fault current limiter (SFCL) of the first peak current limiting type, which has the advantage of a fast recovery time. A design for the hybrid SFCL, focusing on current limiting reactor (CLR) reactance calculation, is proposed in this paper to determine an appropriate value for the CLR reactance that satisfies the grid code requirements of the DFIG wind turbines. High-temperature superconductors (HTS) such as Bi-2212, YBCO, Bi-2223, Ti-2223, and Hg-1223 are investigated for use in the hybrid SFCL. The recovery time and first peak current reduction effectiveness are the criteria for selecting the HTS. In the proposed method, a during-fault voltage from the grid code requirement is used as an input parameter to compute the reactance of the CLR. Based on the results of the base-case simulations conducted on the DIgSILENT PowerFactory software, the Bi-2223 HTS with the first peak of fault current less than 4.5 kA and recovery time of 2.5 s is selected for adoption in the hybrid SFCL. The calculated results of the proposed method are compared with the simulation results of the hybrid SFCL, in terms of the DFIG wind turbine fault ride-through capability enhancement, to demonstrate that the performance of the proposed method satisfies the grid code requirements.

Cooling performance test of the superconducting fault current limiter

The superconducting fault current limiter (SFCL) is an electrical power system device that detects the fault current automatically and limits the magnitude of the current below a certain safety level. The SFCL module does not have any electrical resistance below the critical temperature, which facilitates lossless power transmission in the electric power system. Once given the fault current, however, the superconducting conductor exhibits extremely high electrical resistance, and the magnitude of the current is accordingly limited to a low value. Therefore, SFCL should be maintained at a temperature below the critical temperature, which justifies the cryogenic cooling system as a mandatory component. This report is a study which reported on the cooling system for the 154 kV-class hybrid SFCL owned by Korea Electric Power Corporation (KEPCO). Using the cryocooler, the temperature of liquid nitrogen (LN2) was lowered to 71 K. The cryostat was pressurized to 5 bars to improve the dielectric strength of nitrogen and suppress nitrogen bubble foaming during operation of SFCL. The SFCL module was immersed in the liquid nitrogen of the cryostat to maintain the superconducting state. The performance test results of the key components such as cryocooler, LN2 circulation pump, cold box, and pressure builder are shown in this paper.

Study on Fault Current Limiting Characteristics of an SFCL Using Magnetic Coupling of Two Coils With Mechanical Switch Driven by Electromagnetic Repulsion Force

In this paper, the superconducting fault current limiter (SFCL) using magnetic coupling of two coils with mechanical switch, which the extra driving coil to drive it unlike the previous hybrid SFCL was not required, was suggested. The operational principle of the suggested SFCL using magnetic coupling of two coils with the mechanical switch is basically the same as one without mechanical switch, except that the mechanical switch is driven by the electromagnetic repulsion force generated by the magnetic flux between two coils comprising the SFCL. With the operation of the mechanical switch, the fault current flowing through the SFCL using magnetic coupling of two coils can be commutated from the magnetically coupled two coils into the coil operated as the current limiting reactor (CLR) immediately after the fault occurs, which is contributed to the fault current limiting operation of this SFCL. To verify the operation of the suggested SFCL, the mechanical switch with electromagnetic contact comprised of the fixed and the moving parts, which were located just above open iron core wound by two parallel connected coils, was designed and fabricated. With the fabricated mechanical switch, the short-circuit tests of the SFCL with the suggested mechanical switch were carried out. Through the analysis on the results of the short-circuit tests, the current limiting characteristics of the suggested SFCL with the mechanical switch could be confirmed to be improved effectively with the reduction of the power burden of the high- TC superconducting (HTSC) element comprising the SFCL.

A hybrid superconducting fault current limiter for enhancing transient stability in Korean power systems

Additional power generation sites have been limited in Korea, despite the fact load demands are gradually increasing. In order to meet these increasing demands, Korea’s power system company has begun constructing new generators at existing sites. Thus, multi-unit plants can create problems in terms of transient stability when a large disturbance occurs. This paper proposes a hybrid superconducting fault current limiter (SFCL) application to enhance the transient stability of multi-unit power plants. SFCLs reduce fault currents, and limitation currents decrease the imbalance of the mechanical and electrical torque of the generators, resulting in an improvement in transient stability.

Empirical Modeling of Cryogenic System for Hybrid SFCL Using Support Vector Regression

The hybrid superconducting fault current limiter (SFCL) is now at the stage of practical use in a power grid in Korea. A cryogenic cooling system was designed, fabricated, and successfully tested for a prototype of 22.9 kV/630 A SFCL. The operation scheme of cryogenic system has been investigated in preparation for temporary loss of cryocooler power in hybrid SFCL (in Kim et al., IEEE Trans. Appl. Supercond. 21(3):1284–1287, 2011). In this paper, we investigated the empirical modeling of cryogenic cooling system for SFCL using principal components and auto-associative support vector regression (PCSVR) for the prediction and fault detection of the cryogenic cooling system. For empirical model, data were acquired during a blackout test of cryogenic cooling system. Blackout times of the test were 1 hour and 4 hours at two operation current levels. Three set of data were used for training and optimization of the model and the rest set of data was used for verification. Signals for the model are temperatures measured at copper band and cold head of cryocooler, system pressure and liquid temperatures measured at two locations in liquid-nitrogen pool. For optimization of the SVR parameters, the response surface method (RSM) and particle swarm optimization (PSO) were adopted in this paper. After developing the empirical model we analyzed the accuracy of the model. Also, these results were compared with that of auto-associative neural networks (AANN). RSM and PSO gave almost the same optimum point. PCSVR showed much better performance than AANN in accuracy aspects. Moreover, this model can be used for the prognosis of cryogenic cooling system for SFCL.

Design and Tests of Prototype Hybrid Superconducting Fault Current Limiter With Fast Switch

This paper deals with design and operating tests of prototype hybrid superconducting fault current limiter (SFCL) which is series connected non-inductive solenoid resistive coil and asymmetric non-inductively wound coils. The role of resistive SFCL is for reducing the fault current in the first swing. Moreover, resistive SFCL can reduce a load of dielectric strength in hybrid SFCL. Two kinds of high temperature superconductor (HTS) wires were used to fabricate asymmetric HTS coil. These HTS wires had different quench characteristics such as different critical current and n-value. Unbalanced current distribution between two HTS wires in the asymmetric HTS coil during the fault should occur. Thus, the asymmetric HTS coil generates impedance and repulsive force from magnetic flux. The finite element method was performed to calculate maximum repulsive force. From experimental tests and FEM simulation results, proper combination of HTS wires and configuration of asymmetric HTS coil with fast switch were determined to increase maximum repulsive force. Also, the prototype hybrid SFCL with fast switch was fabricated and performed.

Dynamic Characteristics of a 22.9 kV Hybrid SFCL for Short-Circuit Test Considering a Simple Coordination of Protection System in Distribution Networks

This paper presents the results of short-circuit tests with a 22.9 kV hybrid superconducting fault current limiter (SFCL) on the KEPCO test grid. The hybrid SFCL we used for the test had suffered from lots of field tests including a long term operation and it is still in working order. We have already proved that the SFCL showed high reliability as well as feasibility through a long term operation and short-circuit tests performed before. In this paper, we tried to study a dynamic characteristics of the same SFCL on the distribution power grid through short-circuit tests with a circuit breaker and a reclosing relay. An artificial fault generator (AFG) was used to generate fault currents in the KEPCO power test center. The two objectives of the tests are (1) verifying a precise reaction of the SFCL to reclosing operation and (2) a study for protection coordination with SFCL. The test results showed that the SFCL worked precisely with a fast recovery of the superconducting elements when we applied a one-time reclosing operation with the interval of 0.6 second. We also suggested a proper manipulation of the coordination of the protection system in distribution networks with the SFCL in the paper.

초전도소자의 저항변화에 따른 반주기내 한류형 하이브리드 초전도 전류제한기의 전류제한 특성 분석

Abstract - The fault current has been increasing due to expansive substation facilities for meeting the increase of demand. To limit increasing fault current in a power system, among methods the superconducting fault current limiter (SFCL) has been considered to be adopted in the power grid. However, in case of adopting SFCL in the power system, most of SFCLs need to solve problems such as recovery, cost. With efforts to solve those problems, the novel fault current limiting device which is called hybrid SFCL is developed. To apply the hybrid SFCL, it has to be needed to analyze application possibility and itself operation characteristics. In this paper, the fault current limiting and operation characteristics of hybrid SFCL with first half cycle the limiting operation in case of various resistances of superconducting element were analyzed through experiment.Key Words : Hybrid SFCL, Fault current, Superconducting fault current limiter*정 회 원 : 숭실대학교 공대 전기공학과 박사과정** 펠로우 회원 : 숭실대학교 공대 전기공학과 교수*** 정 회 원 : 한국전기안전공사․공박† 교신저자, 정회원 : 숭실대학교 공대 전기공학과 교수E-mail : superlsh73@ssu.ac.kr 접수일자 : 2011년 1월 14일 최종완료 : 2011년 9월 8일

반주기 이후 동작 하이브리드 초전도 전류제한기와 보호기기 협조 분석

The fault current has increased due to the large power demand in power distribution system and network distribution system. To protect the power system effectively from the increased fault current, the superconducting fault current limiter (SFCL) has been notified. However, the conventional SFCL has some problems such as cost, operation, recovery, loss. To solve some problems, the hybrid superconducting fault current limiter using the fast switch was proposed. However, hybrid SFCL also has a problem that is protection coordination in power distribution system with hybrid SFCL. In this paper, the fault current limiting characteristics of hybrid SFCL with first half cycle non-limiting operation according to the fault angle, the resistance of superconducting element, and the magnitude of Current Limit Resistor (CLR) which are the components of hybrid SFCL were analyzed through the experiments.