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On the advance of SFCL: a comprehensive review

2019; Institution of Engineering and Technology; Volume: 13; Issue: 17 Linguagem: Inglês

10.1049/iet-gtd.2018.6842

1751-8695

Mohammad Reza Barzegar‐Bafrooei, Asghar Akbari Foroud, Jamal Dehghani Ashkezari, Mohsen Niasati,

Power Systems Fault Detection

IET Generation, Transmission & DistributionVolume 13, Issue 17 p. 3745-3759 Review ArticleFree Access On the advance of SFCL: a comprehensive review Mohammad Reza Barzegar-Bafrooei, Mohammad Reza Barzegar-Bafrooei Electrical and Computer Engineering Faculty, Semnan University, Semnan, IranSearch for more papers by this authorAsghar Akbari Foroud, Corresponding Author Asghar Akbari Foroud aakbari@semnan.ac.ir orcid.org/0000-0001-6902-8990 Electrical and Computer Engineering Faculty, Semnan University, Semnan, IranSearch for more papers by this authorJamal Dehghani Ashkezari, Jamal Dehghani Ashkezari Department of Electrical and Computer Engineering, Isfahan University of Technology, Isfahan, IranSearch for more papers by this authorMohsen Niasati, Mohsen Niasati Electrical and Computer Engineering Faculty, Semnan University, Semnan, IranSearch for more papers by this author Mohammad Reza Barzegar-Bafrooei, Mohammad Reza Barzegar-Bafrooei Electrical and Computer Engineering Faculty, Semnan University, Semnan, IranSearch for more papers by this authorAsghar Akbari Foroud, Corresponding Author Asghar Akbari Foroud aakbari@semnan.ac.ir orcid.org/0000-0001-6902-8990 Electrical and Computer Engineering Faculty, Semnan University, Semnan, IranSearch for more papers by this authorJamal Dehghani Ashkezari, Jamal Dehghani Ashkezari Department of Electrical and Computer Engineering, Isfahan University of Technology, Isfahan, IranSearch for more papers by this authorMohsen Niasati, Mohsen Niasati Electrical and Computer Engineering Faculty, Semnan University, Semnan, IranSearch for more papers by this author First published: 12 August 2019 https://doi.org/10.1049/iet-gtd.2018.6842Citations: 15AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Abstract This study aims to provide a comprehensive review of various superconducting fault current limiters (SFCLs) configurations. Regarding the applied technology, the different types of SFCLs are classified into three groups including quench-type SFCL, non-quench-type SFCL, and composite-type SFCL. Resistive-type SFCL, hybrid-type SFCL, magnetic-shielded iron-core-type SFCL, superconducting fault current limiting transformer, transformer-type SFCL, flux-lock-type SFCL, saturated iron-core-type SFCL, and resonance-type SFCL are some of the investigated structures. The structures are fully surveyed in terms of operating principle, technical feasibility, and recent advancements. The study is performed based on published information in papers, reports, and other available online documents. It is expected that this study provides a fundamental foundation for researchers and companies to become familiar with different types of SFCLs. It would be useful to help further studies about the development and the implementation of SFCL for real power systems. 1 Introduction As demand for electric energy continues to increase, many distributed generations (DGs) and new power plants are integrated into the power system. Moreover, the interest in the application of parallel transmission line to transmit the more power and the interconnection of networks to achieve high reliability is remarkably increasing. However, as a challenging issue in the existing power system, these activities lead to the escalation of the short-circuit level. As a consequence, the conventional protective equipment, which has already played the main role to protect the power system against fault current, are not able to perform their protective duties at a satisfactory level. Moreover, the enormous fault current has adverse effects on dynamic and thermal stresses on electrical equipment, transient overvoltage, and ageing of equipment [1]. To mitigate the fault current, various approaches have been introduced so far. The utilisation of the high rupturing capability fuses, the transformer with high short-circuit impedance, series reactors, and changing the configuration of power grids are the conventional techniques. However, the above-mentioned approaches are incapable to meet all requirements. Some of them are expensive and some others are not justifiable from the technical viewpoint for applying into different voltage levels [2]. Embedding the power system with fault current limiters (FCLs) is an alternative and effective solution to mitigate short-circuit level. FCL is an innovative power equipment, which is integrated into series with the power system. It has a low-voltage drop during normal conditions. However, it immediately limits the fault current after the appearance of the fault in the power system. Additionally, the application of FCLs improves the power quality, especially the magnitude of voltage sag [3]. It is possible to restore the coordination between protection equipment in the power system with high penetration of DGs by optimal placement of FCL [4, 5]. Finally, it can control low-voltage right through for wind systems [6, 7]. In the attempts to develop FCL with close to ideal attributes, academic researchers and companies offer the different configurations that are mostly classified into non-superconducting FCLs (NSFCLs) and SFCLs. NSFCLs are mainly developed based on liquid metals and semiconductor materials. In liquid metal FCLs, as their name implies, fault current limitation duty is achieved by the liquid metals such as mercury or gallium alloys [8]. In semiconductor based on FCL, which is named as solid-state FCLs (SSFCLs), the power semiconductor switches are implemented. For SSFCL technology, it can be found the various structures which are mainly reported in [9]. The variable reactor which works based on air gap variation is another type of NSFCLs [10]. Finally, superconducting materials are used to implement FCL. Owing to the significant discovery in the field of superconductors, SFCLs have attracted more attention within the researchers in the recent decade [11–18]. Moreover, the technical feasibility of SFCLs has been already confirmed with field tests. Similar to SSFCL, various topologies have been suggested for SFCL concept. Hence, the comprehensive survey of SFCL configurations, their operating principle, features, and drawbacks are essential. In relation to this subject, several works have been reported. Authors in [2, 14–17] particularly emphasise on some of the interesting structures in terms of the operating principle and commercial activities. The suggested structures for SFCL are briefly discussed in [18]. In [19], Badakhshan and Mousavi provide a review study associated with the flux-lock type of SFCLs. Although these works are well-described, however, all existing SFCL types up to publishing year and technical properties have not been investigated. As per the background, the main objective of this paper is to present a complete roadmap for future research related to SFCL technology. In this regard, this paper provides an up-to-date overview of research activities about this type of FCL. Various types of SFCLs are divided into three groups consisting of quench-type SFCL, non-quench-type SFCL and composite-type SFCL. Then, working principle of SFCLs introduced for each group, recent trends, their main features, and technical feasibility is discussed. 2 Requirement of SFCL Generally, the requirements for an ideal FCL are as follows: low-power loss during normal state, low-voltage drop during normal state, adequate fault current limitation capability for reductions of DC and AC components of fault current, the capability to withstand fault current up to the operation of conventional protective equipment, quick response time, short recovery time, the capability for multiple operations without human intervention, applicable for reclosing scheme, keep the current limitation behaviour without dependency on power system factors such as fault location, fault type, and fault resistance, no restriction for development in different burdens, no changing in the current limitation behaviour during the considered useful life, no undesirable operation for starting current of motors, transient currents of single-phase-to-ground faults, and inrush currents of transformers and capacitor banks, no dangerous overvoltage during operation, no adverse impact on existing protection schemes, small size and portable, and lightweight, low development and maintenance costs, low long-term cost, no harmful environmental effects, and no danger for operating personnel. In practise, the construction of an SFCL with all above-mentioned attributes is out of mind at the present time. However, an FCL should meet some key aspects to be acceptable for the modern power system in comparison with other solutions. The key aspects are as follows: Response time: Generally, the main objective of SFCL installation is to decrease the fault current as soon as possible. Indeed, SFCL should operate prior to the fault current reaches the first peak. Delay action for the operation of SFCL is only justifiable when the power system could withstand the harmful effect of the first peak of fault current. As will be mentioned later, most of the proposed structures for the development of SFCL have a good characteristic in terms of this point. Performance: As the prerequisite of an SFCL, it should enable to reduce the fault current components including DC and AC ones to consider value. Besides, the fault limitation period should be as long as responding to other protective devices. The power system factors especially fault type should not also affect this aspect. The compensation of voltage sag, the mitigation of electrical and thermal stresses, and enhancement of lifetime of other electrical equipment are the benefit offered by an SFCL with desirable performance. In the opinion of the authors, it is better that SFCL does not have the limitation function for low fault current. Two following benefits can be achieved; first, the conventional protective equipment can easily handle these fault currents and the power system remains safe. Second, SFCL ageing and maintenance cost decrease and consequently increasing of the lifetime. Recovery time: After the fault is cleared from SFCL, it should rapidly return to service without human intervention. The short recovery time period reduces the power supply interruption. This aspect is vital for reclosing scheme. Lifetime and maintenance: Similar to other equipment, SFCL needs for maintenance activities. Additionally, the lifetime is determined for it. The important point is that the above aspects should be close to the other electrical equipment in order to its application being justifiable. Cost: At the present time, the development cost of the SFCL is very expensive. Now, after designing an SFCL, it should be tested in laboratories to prevent unwanted failure. Then, the specified system should be designed to evaluate the performance of SFCL in real conditions. Finally, regarding the obtained experience and elimination of the possible faced issues in long-term operation, the reliable SFCL can be permanently installed in the power system. As mentioned, the above cost exists at the present time. By acquiring the experiences from prototypes and progress in research activities, it is expected that this cost significantly reduces in the future. However, the cost of employed components in the structure of SFCL and long-term operation costs are fixed. Generally, superconductors, cryogenic systems, high-voltage (HV) insulation devices, and other special components (if any) are the main components in all proposed configurations. Considering the cost of these components, the determinative part is the cryogenic system as the most expensive component [20]. The long-term cost also includes power loss and maintenance activities. As a general consequence, the fixed cost and life and maintenance cost of SFCL installation should be comparable with other existing technique to limit fault current. Indeed, the economic justification of SFCL installation should be elucidated. Weight and size: The weight of an SFCL should be light as much as possible to ground travelling. Furthermore, the space limitation can be an important issue in urban locations and indoor substations. Customer tends the compact design. Therefore, the SFCL design should be simple as much as possible. 3 Superconductivity and SFCL classifications Superconductivity is the state that the electric resistance of the materials (called superconductors) disappears. In this state, the current can flow through the superconductor with negligible power loss. This phenomenon happens when current density, temperature, and applied magnetic field intensity (H) in the superconductor are all below the critical values (Jc, Tc, and Hc, respectively). The critical values are not the same for different materials. In the case of one of the above quantities exceeds from critical value, the electric resistance of superconductor immediately returns and the superconductivity state destroys. This event is known as quench or transition. As the prerequisite for our study, the following descriptions are expressed about superconductors: In comparison to the conventional conductors, high-current density and low-power loss are achieved by superconductors. When the alternating current flows through the superconductor, the loss is not exactly zero. It has an AC loss. Superconducting materials can be categorised by two basic groups; low-temperature superconductor (LTS) and high-temperature superconductor (HTS). This classification is based on the critical temperature of superconductors. The critical temperature of LTS is near absolute zero; however, it is higher in the latter type. From the perspective of power system utilities, interest in HTS wires is more. Particularly, all SFCL configurations are developed based on high-temperature materials. Since LTS needs to be cooled using liquid helium to attain the superconductivity state, whereas liquid nitrogen is used in HTS. In terms of the magnetic property, superconducting materials can also be classified into Type I and Type II. Type I has one critical magnetic field intensity (Hc), whereas Type II is described by two critical magnetic field intensities (Hc1 and Hc2) as shown in Fig. 1a. Superconductivity state is achieved when H is below Hc1. For H above Hc2, superconductivity state completely destroys (called normal state). A mixed state or flux flow is also implied as H is within Hc1 and Hc2. In this state, the electric resistance of the superconductor is higher than superconductivity state. However, it is lower in comparison with the normal state. In the superconductivity state, a superconductor expels the weak magnetic field. The magnetic flux slightly penetrates into the superconductor surface (named as London penetration depth). Indeed, it acts as a magnetic shield, as shown in Fig. 1b. This phenomenon which is known as the Meissner effect can be used for fault current limitation concepts. It should be noted that the Meissner effect breaks down when H is above Hc (Type I) or Hc1 (Type II). Most of HTS materials are type II. Bismuth–strontium–calcium–copper-oxide (BSCCO) and yttrium–barium–copper-oxide (YBCO) as the first and second generations of high-temperature materials, along with magnesium diboride (MgB2) are used to develop SFCL and other superconducting equipment. With respect to the utilisation of silver, the development cost of BSCCO is high. The second generation currently has been attracted more attention in comparison with the first generation. The operating temperature of liquid nitrogen should be maintained between 65 and 80 K for first and second generations, whereas the desirable temperature range for MgB2 is between 20 and 30 K. The lower critical temperature and higher AC loss in comparison with YBCO and BSCCO have reduced its applications for AC utilities. However, MgB2 can be used for DC application as the cheaper superconductor. The modern superconductors employed in SFCL are mostly based on the BSCCO tube and tap, YBCO thin films, and YBCO-coated conductors. Fig. 1Open in figure viewerPowerPoint Superconductivity properties(a) Different states of Type II superconductor, (b) Meissner effect As per the background, the various types of SFCLs have been suggested. In general, SFCL configurations can be classified into three following categories [18]: Quench-type SFCL: In this type, the limitation action is performed when the superconductor transits and becomes resistive. To meet this purpose, the rise of temperature, magnetic field intensity, or current density from critical quantities are used to start quenching. Need for the recovery process after clearing fault current from the superconducting element is the major concern of this type. Non-quench-type SFCL: HTS element keeps its superconductivity state during all circumstances (normal and fault conditions) in this concept. Indeed, the main objective of the utilisation of superconductor instead of conventional conductors is the reduction of power loss. No recovery process related to HTS element is the astounding advantage of suggested structures for this concept. Composite-type SFCL: In this principle, the transition from superconductivity state to normal state depends on the type of fault. Hence, the superconductor may need recovery time. Currently, interest in this type is low and the suggested structures are only restricted to computer analysis and low-capacity laboratory models. In brief, Fig. 2 illustrates the classification of SFCLs and their subdivisions which will be discussed in the next sections. Fig. 2Open in figure viewerPowerPoint Classification of SFCL 4 Quench-type SFCL 4.1 Resistive-type SFCL Resistive-type SFCL (RSFCL) is known as the promising solution to solve the problem of rising the short-circuit level. RSFCL uses the superconductor as the main conductor to provide an unrestricted path to flow the line current under non-faulted conditions. During fault conditions, two principles including flux flow and typical types are viable to provide limitation function. After fault occurrence and rising the current density above the critical value, the superconductivity state disappears. Quench time depends on fault current magnitude and its rate of rising, but it is very short [21]. Anyway, flux-flow RSFCL refers to the case that the superconductor temperature is kept below the critical quantity and flux-flow resistance mitigates the fault current [22]. Consequently, the typical type is developed based on exceeding the temperature from critical value. Hence, the normal resistance performs the limitation duty. Both concepts have positive and negative points that should be considered in the design phase of RSFCL. Flux-flow RSFCL has less resistance in comparison with typical type for a specific amount of superconductor [23]. This means that at the same limitation percentage, HTS costs of flux-flow type are more than that of a typical type. Moreover, the flux-flow resistance strictly depends on the superconductor temperature, magnetic field, and the instantaneous value of current density [24]. On the other hand, applying the flux-flow type in power system reduces the concern about the recovery process if the fault is cleared in the appropriate time from HTS element [24]. Typical RSFCL encounters with the recovery issue. Relying on the fault duration, cooling system capacity, and fault current magnitude, a few seconds (even minutes) need to return the system in service after each operation. Hence, the coordination between different protective devices should be addressed before applying typical type (particularly in reclosing scheme). Moreover, two other problems related to typical RSFCL can be mentioned. Emerging the significant electric resistance in the shortest possible time may lead to produce excessive overvoltage across the RSFCL terminals. In addition, non-uniform heating conditions and hot spots may appear at the moment of quench [25]. The aforementioned problems can damage the superconductor and in turn fail the limitation function. These challenging issues can be controlled by incorporating a shunt impedance as illustrated in Fig. 3a. The shunt impedance can be implemented with resistive (RP) or inductive elements (LP) [26]. The concept also causes the major part of fault current commutates into the shunt impedance and limitation role is carried out by this impedance. Indeed, the HTS operates as the fault detection system. It should be noted that the hot spot protection is only achieved when the resistive element contacts with all over the length of the HTS [16]. In another type, the coil should be placed at the outside of the superconductor tube in a coaxial arrangement. It results in the transition occurrence in weakest points. In fact, the quenching process is accelerated and superconductor resistance rapidly rises. As a consequence, fault current mostly transfers to shunt branch in lower magnitude and hot spot problem decreases. Fig. 3Open in figure viewerPowerPoint RSFCL concept(a) Schematic representation of RSFCL incorporated with shunt impedance [16], (b) Matrix-type RSFCL [2] Finally, in three-phase applications, each phase of RSFCL operates independently. This sentence pursues this note that the quench time is slightly different for each phase during phase faults (particularly, three-phase-to-ground fault). As a drawback, a momentary phase unbalance is produced during the occurrence of three-phase-to-ground fault, which can cause the quench process start only in one or two phases of RSFCL [21]. Therefore, it is essential to evaluate the current limitation behaviour of RSFCL during the development step in different terms such as fault type, fault resistance, and fault distance [21, 27, 28]. HTS cryogenic system and HV insulation devices are the main components of RSFCL. The cryogenic system is very expensive in comparison with other parts. Regardless of the type of RSFCL, the superconductors should be maintained below critical temperature during normal operation. The total amount and length of superconductors strictly affect the cryogenic system capacity. Additionally, AC loss is an important issue in AC application of RSFCL. It could not be avoided by this loss. Therefore, the amount of AC loss should be considered in the size of cryogenic cooling equipment and even long-term operation cost. For the high voltage and current ratings, it can also be used as the matrix-like arrangement of RSFCL as shown in Fig. 3b [2]. The HTS elements are connected in series in order to achieve more limitation and then the arrangements are integrated in parallel to meet the high-current rating. For the protection of the superconductor against overheating and dangerous overvoltage, the shunt impedance is implemented across each segment. The current divider law determines how much current flows through each path. In ideal conditions, total current evenly divides between branches. Any unequal resistance between HTS elements leads to differing current distributions on the paths. Such a non-uniform distribution of current is harmful and can make the electrical stresses on the HTS element with the smallest resistance. At worst case, it can result in the cascade destruction of HTS elements, and consequently the complete destruction of SFCL may occur. Need for the high amount of superconducting materials, large volume and weight issues are the other negative features of matrix RSFCL. As an uncompleted project, superpower and several partners planned to develop this concept for the 138 kV transmission line, but it was cancelled. Nowadays, research and development activities in typical RSFCL with the utilisation of the different HTS materials are progressed. Since it meets the important criteria including effectiveness, compact design, fail-safe, autonomous, and fast response. Several successful prototypes of RSFCL have been installed in the live grid to the permanent application or evaluate the long-term operation. The majority of projects have been done for distribution systems (medium-voltage level). Therefore, it is expected that the application of RSFCL in distribution systems be commercialised sooner in comparison with transmission systems. Table 1 lists the main specifications of some of the recently performed projects [11, 17, 29–32]. As a new project, 220 kV RSFCL has been manufactured to install in Moscow, Russia [33]. According to the presented statements in [33], $4,000,000,000 will be the long-term saving for the Moscow city grid in the presence of this SFCL. Although the detailed costs of the completed projects in related RSFCL are not available now; however, the following information has been obtained from the literature: The considered budget for Ampacity project (HTS cable plus 12 kV/2.3 kA RSFCL) was about €13.5 million [29]. The total value of UK order for 12 kV/1.6 kA RSFCL 12 kV/1.05 kA including design, fabrication, and permanent installation is about €2.6 million [34]. The 13.8 kV/1 kA RSFCL was designed and constructed for installation in the US with the support of ∼$1.2 million of New York State Energy Research and Development Authority [31]. Table 1. Main specifications of RSFCL projects [11, 17, 30–32]a Ratings Installation country/location Year 115 kV/550 A Thailand/secondary side of transformer 2016 10 kV/815 A Germany/coupling the local generation 2016 9 kV/1 kA Italy/outgoing feeder 2016 12 kV/1.6 kA UK/bus-bar coupling 2015 12 kV/1.05 kA UK/bus-bar coupling 2015 12 kV/2.3 kA Germany/HTS cable protection 2014 13.8 kV/1 kA US/local grid protection and then neutral grounding resistor (NGR) 2013 9 kV/220 A Italy/outgoing feeder 2012 12 kV/400 A UK/bus-bar coupling 2012 12 kV/800 A Germany/outgoing feeder 2011 12 kV/100 A UK/bus-bar coupling 2009 a Some of the prototypes are now active and others have been N due to ending the considered operation period or technical problems. 4.2 Hybrid-type SFCL (HSFCL) family The term HSFCL refers to the principle that the HTS element is combined with the fast mechanical switch, circuit breaker (CB), or the power semiconductor switch to establish the limitation function. The superconductor mostly acts as the fault current commutation in this concept. The important objectives to develop HSFCL can be expressed as follows: The minimisation of required HTS material and in turn AC loss and cryogenic cooling capacity by reducing HTS limitation time. The minimisation of the development costs. The minimisation of required recovery time. The increase of the SFCL limitation time by transferring the current into another branch. The mitigation of technical issues about the application of HTS in HV by enduring the voltage stresses by the switch instead of the superconductor. Accordingly, interest in this concept is more and the many proposed structures can be found in the literature. Here, the important suggested structures are reviewed. 4.2.1 Developed HSFCL in South Korea Fig. 4a represents the primary structure of the introduced HSFCL by Korea Electric Power Research Institute (KEPRI) and LS Industrial Systems (LSISs) [35]. It utilises the combination of a fast mechanical switch including two contacts (main and auxiliary) and a driving coil, fast acting fuse, HTS element, and current limitation part (CLP) to fulfil the limitation duty. Similar to RSFCL, resistor and inductor can be used for CLP; however, these elements are placed at the outside of the cryogenic environment. The path of flowing normal state current is provided by HTS and normally closed (main) contact of the mechanical switch. After the appearance of a fault in the grid, the transition from superconductivity state to normal conducting state occurs and superconductor emerges the electric resistance. As a consequence, the major portion of the fault current transfers in the secondary path consisting of the driving coil in series with a parallel arrangement of CLP and fuse. No current flows through the auxiliary contact at this moment, since it is electrically open. The fault current causes the driving coil to produce the magnetic field and in turn the electromagnetic repulsion force. This force is sufficient to energise the fast switch. Therefore, the main and auxiliary contacts are quickly opened and closed, respectively. It should be noted that the amount of repulsive force depends on different factors such as the flowing current and HTS characteristics which are considered in the design step. Prior to arc extinction, the minor fault current passes through the HTS. Thereafter, the current entirely transfers to shunt branches. Moreover, after melting the fast acting fuse, CLP is responsible for moderating fault current. All the expressed steps take just a few milliseconds and the first peak of fault current is well-limited. The operation time of the fast switch is <2 ms in the 14 kV tested prototype [35]. Fig. 4Open in figure viewerPowerPoint Developed HSFCLs in South Korea(a) Primary configuration [35], (b) HSFCL with first half cycle limiting operation [36], (c) HSFCL with the first half cycle non-limiting operation [37] In this structure, the interesting point is that the HTS does not play the limitation duty role and only senses the occurrenc