Superconducting Fault Research Articles

On the Reclose Operation of Superconducting Fault Current Controller for Smart Power Grid With Increasing DG

At present, the operation of protection coordination in a complex and uncertain power distribution system is satisfied through the use of a recloser and fuse. Due to the increased adoption of renewable energy resources, distributed energy resources as well as expanded electric transportation and dynamic demand response technologies in the power industry confront significant challenges during grid operations. As a result, protection coordination may be broken due to an increase in the current level in a power system. In general, once the protection is well coordinated by a fault current controller (FCC), the previously installed recloser on the existing power distribution system becomes useless because the FCC plays the role of the recloser. In this work, we propose an operating strategy of protection coordination for the FCC, which is capable of replacing the recloser in an environment where various types of distributed generation are introduced simultaneously due to the proliferating demand of renewable energy sources. Specifically, the suggested method based on PSCAD/EMTDC is investigated.

Experimental and Numerical Study of Co-ordination of Resistive-Type Superconductor Fault Current Limiter and Relay Protection

Superconducting fault current limiter (SFCL) has become one of the most ideal current limiting devices to solve the problem of increasing short-circuit current in high-voltage power grid. This paper presents a resistive-type SFCL model developed using simulation software PSCAD/EMTDC. After being verified by finite-element model and experimental results, the model is used to study the impact of SFCLs on the power grid and the co-ordination between SFCL and relay protections in 10 kV distribution network. A series of simulations are carried out to find appropriate parameters of SFCL model to cooperate with relay protection devices. The final result in this paper could provide important quantitative basis of parameters for SFCL to be applied in a real power system.

Methods of Improving Superconductive Fault Current Limiting Devices in Power Engineering

Superconducting fault current limiter is a fundamentally new type of device that has no direct analogue among the traditional electrical equipments. The basis of most of its variety, subject to intensive research in the world, is based on the principle of transition-temperature superconductors in the resistive (normal) condition when the current extended, flowing through the superconducting fault current limiter, above defined value. The problem of scaling on superconducting power of current-limiting transformer-type device has been investigated. Opportunities of increasing nominal power of such device based on experiments and calculations have been proposed.DOI: http://dx.doi.org/10.5755/j01.eee.19.3.1441

A Resistive-Type Modular Superconducting Fault Current Limiter Fabricated With Stainless-Steel-Stabilized YBCO Tapes

A resistive-type superconductor fault current limiter (SFCL) is experimentally studied with stainless-steel-stabilized 12-mm-wide YBCO tapes. The SFCL is assembled with six noninductive modules, each rated for 120 V, 100 A. The module has several YBCO tapes connected in series that are arranged such that the flow of current in one tape is in the opposite direction from its neighboring tapes. The modules can be connected for different SFCL configurations with series and parallel combinations. In this paper, the SFCL is assembled in two configurations and is tested for continuous, overload, and short-circuit currents. The first configuration is assembled to evaluate current carrying performance in parallel connected modules at 600 A. The second configuration is assembled for short-circuit performance of two series-three parallel connected modules at 240 V, 300 A. The evaluated data will be useful to develop higher rating SFCL with modular construction.

Concept and Viability of High Temperature Superconductor Fault Current Limiter for Power Systems Protection

In today’s technological era, electrical energy is one of the most vital forms of energy and is needed directly or indirectly in almost every field. As load gradually increases on a particular power system network, a higher operating current state leading to increased fault current level is attained. It is not possible to change the rating of the equipment and devices in the system or circuits to accommodate the increasing fault currents. Integration of High Temperature Superconductor Fault Current Limiter (HTSFCL) in power system network will provide instantaneous (sub cycle) current limitation abilities, which mitigates the effects and the buildup of fault currents in the power system network .The devices in electronic and electrical circuits are sensitive to disturbance and any disturbance or fault may damage the device permanently so that it must be replaced. The cost of equipment like circuit breakers and transformers in power grid are very expensive. Moreover, replacing damaged equipment is a time and labour consuming process, which also affects the reliability of power systems. It is not possible to completely eliminate the faults but it is possible to limit the current during fault in order to save the equipment and devices in the circuits or systems. One of the solutions to this age longed problem is the application of a current limiting device in the system. This paper is centered on the concepts and viability of High Temperature fault current limiters for power systems protection. The demonstration of this High Temperature Superconductor Fault Current Limiter (HTSFCL) in power systems has been explained and simulated using MATLAB tool. The results of the simulation with and without the fault are shown

Impact of smart subtransmission level fault current mitigation solutions on service reliability

Superconductive fault current limiters and substation automation systems are two major smart grid technologies that can be directly or indirectly used for mitigation of high fault current levels at subtransmission systems. In comparison to the other conventional fault current mitigation solutions, it is expected that these solutions have much less negative impacts on the service reliability. This paper aims to quantitatively evaluate how these smart fault current mitigation solutions may affect the major attributes of the service reliability. Sustained interruptions, momentary interruptions and voltage sags are considered as major events that might appear in the electricity service of the customers due to a typical short circuit fault on the subtransmission systems. A typical Finnish subtransmission system is utilized in this paper for directing the quantitative reliability case studies. The study results show that in addition to the fault current mitigation aspects of the targeted solutions, their possible impacts on the service reliability should also be taken into account.

Study on a New Setting Method of Distance Relay with Superconducting Fault Current Limiter Adapt in the Grid

Considerable attention is given towards developing Superconducting fault current limiter (SFCL) due to increasing short circuit levels in transmission lines, which itself imposes further changes on the measured impendence at the relaying point and causes significant impact on the lines’ relay protection, especially on the distance protection as the single-phase grounding fault occurs. In this paper, resistive superconducting fault current limiter connected to the grid is studied as the model to analysis how SFCL affects the grounded short-circuit impedance relay’s setting, then an new setting method of distance protection for the SFCL-equipped line is proposed. Finally, a power system model is built to analysis the theory by PSCAD / EMTDC simulation software. The results show that in the condition of using the impedance relays’ new setting method, impedance measurement error is greatly reduced, SFCL and line distance protection can work in coordination with each other properly.

Development of a 220 kV/300 MVA superconductive fault current limiter

After we developed a saturated iron core type 35 kV/90 MVA superconductive fault current limiter and installed the device in a transmission network at Puji substation of China Southern Power Grid for live-grid operation in 2007, we continued our efforts in advancing this technology. A 220 kV/300 MVA device has been designed, manufactured and factory tested. This device differs from the 35 kV device in its form of electrical insulation even though the two devices have the same working principle and similar core structure. Improvements in the dc magnetization circuit and the cryogenic system were also achieved. This 220 kV/300 MVA superconductive fault current limiter has been installed and has passed all field tests at Shigezhuang substation in Tianjin, China. Trial operation is underway. This paper introduces the major design parameters, key functional specifications and some testing results of the device.

Tests and Simulations of Different YBCO Tapes for FCL

The superconducting (SC) fault current limiter (FCL) is very effective to enhance the security and the power quality of electrical grids, two real demands today. This explains the great interest throughout the world. The YBCO tape characteristics are very important for the FCL. They play a part in the design itself (length and section) and in the behavior especially under low prospective current faults. These certainly are the most severe operation conditions for SC tapes, which inevitably show some inhomogeneities along their length. The three phases clear short-circuit, a rather rare event in fact, does not represent the most severe requirement for the SC element. We have tested different YBCO coated conductors in variable voltage conditions. Modeling has shown that these easy experimental conditions lead to the same results compared to variable prospective fault currents. The SC tapes present very different behaviors. Numerical simulations complete these experiments. The influence of the silver thickness is studied especially in terms of electric field under limitation and of conductor inhomogeneity consequences for low prospective currents. Temperature excursions in the lowest Ic part of the tape are investigated. A compromise should be found between the design (minimum volume) and a safe behavior.

Experimental Tests on a Superconducting Fault Current Limiter Using Three-Strand $\hbox{MgB}_{2}$ Wire

Magnesium diboride (MgB2) in simple round wire form has shown significant potential to be a low-cost resistive superconducting fault current limiter (SFCL). The commercial exploitation of MgB2 SFCLs for typical distribution network voltages requires a considerable scale-up of the current-carrying capability of MgB2 wire. The two obvious options to achieve this are to increase the wire size and use multifilament wire and/or use multiple wire strands. This paper assesses the current capacity for multi-strand wire and presents results of initial tests on a three-strand MgB2 demonstrator SFCL coil. Three strands of monofilament MgB2 wire were braided together to form a single multi- strand wire. The wire was fabricated, wound on a ceramic former and heat treated by Hyper Tech Research, Inc. One of the key performance aspects of this type of wire arrangement is ensuring each strand of wire carries the same current. This paper demonstrates the potential for increasing the current capacity of SFCL using multi-strand MgB2 wire to that required for distribution network levels. The paper includes a detailed analysis of the results and the implications for the practical design of commercial SFCLs.

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.

Design and Tests of Coreless Inductive Superconducting Fault Current Limiter

In this work, we report on the design and tests results of a coreless inductive SFCL with a 600 A rated current for MV distribution system. The fault current limiter comprises of 4 identical units immersed in liquid nitrogen bath. Each unit consists of 3 windings. The primary and secondary windings made of 2G HTS tape SF12050 are magnetically coupled with the primary Cu winding. The high magnetic coupling between superconducting primary and secondary windings gives a low voltage drop on the limiter at nominal current. The presented solution reduces the size and the weight of the device. Tests performed at high power test facility prove the limiting capability of the coreless inductive SFCL.

A Study on the Direct Stability Analysis of Multi-Machine Power System With Resistive SFCL

This paper describes a method for analyzing the direct stability of a multi-machine system that consists of three machines and one resistive superconductive fault current limiter (SFCL). The resistive SFCL, which affects the transient stability of a multi-machine power system, must be taken into account. In order to evaluate the transient stability in the power system, a direct stability analysis that has rapid prediction stability is used. Although the equal-area criterion method is useful in determining the stability as a transient stability evaluation method, the method is only applicable to a one-machine system connected to an infinite bus or to a two-machine system. Therefore, the transient energy function (TEF) should be constructed. Using the TEF, the effect of the SFCL in the multi-machine system can be identified by increasing the critical clearing time.

Improvement in operational characteristics of KEPCO’s line-commutation-type superconducting hybrid fault current limiter

A 22.9kV class hybrid fault current limiter (FCL) developed by Korea Electric Power Corporation and LS Industrial Systems in 2006 operates using the line commutation mechanism and begins to limit the fault current after the first half-cycle. The first peak of the fault current is available for protective coordination in the power system. However, it also produces a large electromagnetic force and imposes a huge stress on power facilities such as the main transformer and gas-insulated switchgear. In this study, we improved the operational characteristics of the hybrid FCL in order to reduce the first peak of the fault current. While maintaining the structure of the hybrid FCL system, we developed a superconducting module that detects and limits the fault current during the first half-cycle. To maintain the protective coordination capacity, the hybrid FCL was designed to reduce the first peak value of the fault current by up to approximately 30%. The superconducting module was also designed to produce a minimum AC loss, generating a small, uniform magnetic field distribution during normal operation. Performance tests confirmed that when applied to the hybrid FCL, the superconducting module showed successful current limiting operation without any damage.

Comparative Analysis of Various Superconducting and Non-Superconducting Fault Current Limiting Devices Designed for Operation in a 110kV/100 MW Power Network

Abstract As it is known one of the most promising fault current limiting (FCL) devices for high-power electric networks can be the so-called transformer type superconducting fault current limiter (SFCL) with the primary winding connected to the load in series and the secondary one shortened by a fast-acting circuit-breaker. These devices when made of conventional materials can be very large and expensive – e.g., for a 100 MW circuit under protection the total mass of copper winding conductors can exceed 15 tons and the heat losses in a normal operating mode can be more than 200 kW. Therefore, using of high-temperature superconductors (HTSC) can be a solution which can sufficiently improve the mass, geometrical and operational characteristics of an FCL. Unlike other superconducting AC devices, the magnetic field in SFCL does not exceed 0.1 – 0.2 T what allows using HTSC windings even at a comparatively high level of AC losses existing nowadays. In this paper is performed a comparative analysis of various designs of SCFL with the non-superconducting FCL. It has been shown that the former have a mass by an order of magnitude lower than the latter and the rate of lowering of heat losses in a normal operating mode is the same. The equalization of costs of both designs is expected to be reached within the nearest 3 – 5 five years.

Prospective of Applications of Superconducting Fault Current Limiters in Chinese Power Grids

China is home to the world's second largest electric power industry, and has plans to modernize its power network into a robust and efficient grid. Short-circuit fault current control becomes increasingly important to the power grid modernization process. Superconducting fault current limiters (SFCLs) may contribute significantly to the solution to the fault current problem. This paper discusses the demands and challenges in the application of SFCLs to Chinese power grids, from the perspective of the present situation and taking into consideration future developments of the electric power industry. Technical and economical comparisons with conventional fault current control technologies are presented

Manufacture and test of the dc superconducting coil for a 220kV/300MVA SFCL

A 220 kV/300MVA saturated iron-core superconductive fault current limiter (SI-SFCL) had been manufactured and factory test had been completed by September 2011. The superconducting coil was wounded using 17 km BSCCO tapes. The height of the coil is about 0.9m, the OD is 2.08m, and the total magnetizing is about 176000 ampere-turns. The fundamental section of the coil is the 45 superconducting double-pancakes, which are divided into five groups. In each group, the pancakes are connected in series, while these five groups are connected in parallel to form the whole coil. In this way, the current could self-adjust within the groups, thus the critical current of the coil can be optimized. This configuration also allows us to arrange the pancakes with different Ics into appropriate positions as the magnetic field distribution of the coil is considered. In real operation, the magnetization and demagnetization are the most important working states of the magnetization circuit. As we know, there is massive energy stored in the iron core, while the time spent on either charging or discharging the iron core by the superconducting coil is required as short as possible in order to be compatible with the grid's relay settings. Thus high-speed and controllable energy charging and releasing mechanism is introduced to the system. This article introduces the manufacture, the key specifications and the magnetization and demagnetization test results of the superconducting coil for the 220 kV/300MVA SFCL.

Superconducting Fault Current Limiting Cable (SFCLC) with Current Limitation and Recovery Function

We have proposed a Superconducting Fault Current Limiting Cable (SFCLC), which is an HTS cable with fault current limitation function. SFCLC will transmit the bulk power with low loss in steady state, and also limit the fault current during the fault condition, and recover into the superconducting state after the fault clearance. Using a numerical model, we investigated the current limitation and recovery characteristics of SFCLC for different voltage and current levels, and cable lengths. We verified the feasible conditions and performance of SFCLC with the current limitation and recovery function.

Finite element modeling of a superconducting fault current limiter

This paper summarizes the work done to show finite element modeling results on a high temperature superconductor fault current limiter (FCL). The paper also gives the small mock-up design of the matrix FCL and its finite element model (FEM). It also discusses the limitations of the FEM and explains how the results from the FEM compare with the experimental data derived for the configuration. A 3-dimensional FEM has been used because of the structure of the real geometry, which does not show any plane or axisymmetric features.

Design of ReBaCuO-coated conductors for FCL

The superconducting (SC) fault current limiter (FCL) improves the security and the powerquality of electric networks; these are the two essential demands of today. The device mustfulfil several requirements in normal and fault operations, and must operate under a varietyof conditions. Low prospective current faults represent the most severe conditions. Properdesign of the ReBaCuO-coated conductor is essential for safe and optimized operations.The design of the superconducting conductor is mainly based on thermal criteria.The minimum superconducting conductor volume is given by its enthalpy andthe limited current through the SC conductor. The superconducting quantitiesplay only a small role in the design. A high resistivity conductor reduces theReBaCuO volume. Of other considerations to be taken into account, the quenchhomogeneity is one of the most important for resistive FCLs. The coated conductorarchitecture and design can help to reduce the consequences of quench inhomogeneityalong the conductor. The presented arguments, for a high limited current forcingthe conductor to quench uniformly and for a moderate conductor resistivity toreduce the temperature differences, are supported by experiments carried oututilizing two rather different coated conductors in various limiting conditions.