Fault Current Reduction Research Articles

Study on Application of Superconducting Fault Current Limiter Considering Risk of Circuit Breaker Short-Circuit Capacity in a Loop Network System

This paper suggests an application method for a superconducting fault current limiter (SFCL) using an evaluation index to estimate the risk regarding the short-circuit capacity of the circuit breaker (CB). Recently, power distribution systems have become more complex to ensure that supply continuously keeps pace with the growth of demand. However, the mesh or loop network power systems suffer from a problem in which the fault current exceeds the short-circuit capacity of the CBs when a fault occurs. Most case studies on the application of the SFCL have focused on its development and performance in limiting fault current. In this study, an analysis of the application method of an SFCL considering the risk of the CB’s short-circuit capacitor was carried out in situations when a fault occurs in a loop network power system, where each line connected with the fault point carries a different current that is above or below the short-circuit capacitor of the CB. A loop network power system using PSCAD/EMTDC was modeled to investigate the risk ratio of the CB and the effect of the SFCL on the reduction of fault current through various case studies. Through the risk evaluations of the simulation results, the estimation of the risk ratio is adequate to apply the SFCL and demonstrate the fault current limiting effect.

Analysis of the Operation Characteristics of the Flux Offset-Type Fault Current Limiter for Reinforcing the Safety of an Electric System

In this paper, a flux offset-type fault current limiter was proposed as a new means of reducing fault currents. The flux offset-type fault current limiter is a device that is integrated into the fault current technology, to which the flux offset principle of a transformer is applied, and is combined with a transformer and a fast switch. To secure the operation reliability of a flux offset-type fault current limiter, a simulation system was constructed to analyze its operation characteristics by generating a single line-to-ground fault and a triple line-to-line fault. According to the test results, the system performed stably without any impedance, because the primary and secondary winding fluxes of the transformer offset each other at normal times. However, when a fault current event occurred, because the fast switch was activated to limit the fault current by opening the secondary windings of the transfer within an average of 9.5 ms, which is shorter than the operation time of the existing electric circuit breakers by 3–5 cycles, the system is likely to perform protective coordination with circuit breakers in the future. In addition, the application of this current limiter could keep the fault current limit ratio to about 96 %.

FDM based multi-objective optimal sitting and design of TC-FLSFCL for study of distribution system reliability

An approach for optimal placement of flux-lock type SFCL with tap changer (TC-FLSFCL) and adjustment of tap changer related to it is used in this paper by debating the reduction of fault current and enhancement of reliability in a distribution network connected with distributed generation (DG). Recently, various superconducting fault current limiters (SFCL) have been developed in the field of power system. Especially, through researches, SFCLs have been put to practical use in distribution network as well as in the transmission network. TC-FLSFCL is a flexible SFCL that it has some preference than previous SFCLs. In this type of SFCL the current limiting characteristics are improved and the fault current limiting level during a fault period can be adjusted by controlling the current in the third winding, which also made the magnetic field applied to the high-Tc superconducting (HTSC) element. Three objective functions based on reliability index, reduction of fault current and the number of installed TC-FLSFCL are systematized and a nonlinear time-varying evolution (NTVE) based multi-objective particle swarm optimization (MOPSO) style is then formed in searching for the best location and tuning of tap changer of TC-FLSFCL to meet the fitness requirements. A decision-making procedure based on fuzzy decision making (FDM) is used for finding the best compromise solution from the set of Pareto-solutions obtained through MOPSO-NTVE. In a distribution network, Bus 4 of Roy Billinton test system (RBTS), comparative analysis of the results obtained from application of the resistive SFCL (RSFCL) and TC-FLSFCL is presented. The results show that optimal placement of TC-FLSFCL than RSFCL can improve reliability index and fault current reduction index with less number.

Study Of Superconducting Fault Current Limiter (SFCL) Technology For Optimal Power Plant Performance and Grid Expansion

This paper presents the application of Superconducting fault current limiters (SFCL) for smart grids in order to reduce possible effect of abnormal fault current. Increased demand results in increased generation capacity in power systems which has lead to increased fault current. At present several conventional protective devices are installed to reduce fault currents in electrical power systems. Predominantly used is circuit breaker which gets tripped off after two to three cycles of fault current by over-current protection relay. Thus they have a response delay of initial two to three cycles before getting activated. SFCL is an innovative electrical equipment which is capable of reducing fault current within first cycle itself and thus providing improved transient stability. In this paper the performance of SFCL for a three phase system is tested using simulink tool and the results are analyzed during both presence and absence of SFCL.

Optimal Placement of Superconducting Fault Current Limiters (SFCLs) for Protection of an Electric Power System with Distributed Generations (DGs)

Power flow patterns and fault current levels are influenced by the introduction of distributed generations (DGs) in an electric power system. In particular, the change in the fault current levels caused by DG installation may require a change in the coordination of relays to prevent their misoperation. When DGs are installed in an electric power system, superconducting fault current limiters (SFCLs) can be used to help reduce the fault currents within the breaking capacity of the protective devices. In this paper, multiple criteria such as the number of SFCLs, fault current reduction, and the total operating time of the relays are considered in order to determine the optimal placement of SFCLs for protection of an electric power system with DGs, and a scenario optimization based approach is used to solve the multi-criteria SFCL placement problem. Numerical simulations are also carried out to demonstrate the effectiveness of the proposed approach.

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.

Determining the location of superconducting fault current limiter considering distribution reliability

As electric power demand of customers is constantly increasing, more bulk power systems are needed for installation in a network. The amount of distributed resources has increased considerably in distribution networks by meeting the demand for renewable energies, highly efficient facilities and a deregulated electricity market. These networks have become more and more complex as mesh network for improving system reliability and flexibility of network operation. This increasing complexity has resulted in an increase in fault currents that exceed a circuit breaker capacity. In order to solve this problem, replacing breaker, changing operation mode of system and rectifying transformer parameters can be taken into account. However, the superconducting fault current limiter (SFCL) is economically one of the most promising power apparatus. This study proposes a methodology for determining the location of SFCL by considering the reduction of fault current by device type and the improvement of reliability by customer type according to the location of SFCL in a distribution network connected with distributed generation (DG). With case studies on the method of determining location for SFCL applied to a radial network and a mesh network, respectively, the authors prove that the proposed method is feasible.

Reliability Evaluation of Distribution Network With DG Considering the Reliability of Protective Devices Affected by SFCL

This paper proposes a reliability model for a superconducting fault current limiter (SFCL), which is a new alternative in limiting the fault current recently increasing in a network. An evaluation technique for distribution reliability that uses the improved failure rate of all protective devices in a network, depending on the location of the SFCL, is also proposed. As a result, it is expected that the SFCL makes the reliability of adjacent equipment on an existing network improve, and these changes are analyzed. In addition, in order to apply the effect of the intermittent output of renewable-energy sources, distribution reliability indices were redefined in this paper. Case studies verify that the SFCL is effective in reducing fault currents and improving distribution reliability. These effects are analyzed with respect to the location of the SFCL in a case study system.

Superconducting fault current limiter application in a power-dense marine electrical system

Power-dense, low-voltage marine electrical systems have the potential for extremely high fault currents. Superconducting fault current limiters (SFCLs) have been of interest for many years and offer an effective method for reducing fault currents. This is very attractive in a marine vessel in terms of the benefits arising from reductions in switchgear rating (and consequently size, weight and cost) and damage at the point of fault. However, there are a number of issues that must be considered prior to installation of any SFCL device(s), particularly in the context of marine applications. Accordingly, this study analyses several such issues, including: location and resistance sizing of SFCLs; the potential effects of an SFCL on system voltage, power and frequency; and practical application issues such as the potential impact of transients such as transformer inrush. Simulations based upon an actual vessel are used to illustrate discussions and support assertions. It is shown that SFCLs, even with relatively small impedances, are highly effective at reducing prospective fault currents; the impact that higher resistance values has on fault current reduction and maintaining the system voltage for other non-faulted elements of the system is also presented and it is shown that higher resistance values are desirable in many cases. It is demonstrated that the exact nature of the SFCL application will depend significantly on the vessel's electrical topology, the fault current contribution of each of the generators, and the properties of the SFCL device, such as size, weight, critical current value and recovery time.

Optimum fault current limiter placement with search space reduction technique

A fault occurring in power networks normally results in a large short-circuit current flow in the system, which may exceed the rating of existing circuit breakers and can damage system equipments. Because of 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 utilisation of fault current limiters (FCLs) in power systems could provide an effective way to suppress fault currents. In a loop transmission or distribution system, the advantages would greatly depend on the number and locations of FCL installations. The authors propose a method to determine the optimum number and locations for FCL placement in terms of installing smallest FCLs circuit parameters to restrain short-circuit currents under circuit breakers' interrupting ratings. In the proposed approach, the sensitivity factor, defined as the reduction of bus fault currents because of a given variation in the branch parameter, is derived and used to choose better candidates for active FCL installations. The search space for FCL installations can be reduced by using the proposed sensitivity factor calculation; therefore the computational efficiency and accuracy can be improved. A genetic-algorithm-based method is then designed to include the sensitivity information in searching for the best locations and parameters of FCLs. The test results demonstrate the efficiency and accuracy of the proposed method.

Superconducting Fault Current Limiter Design Using Parallel-Connected YBCO Thin Films

Superconducting fault current limiters (SFCLs) are able to reduce fault currents to an acceptable value, reducing potential mechanical and thermal damage to power system apparatus and allowing more flexibility in power system design and operation. The device can also help avoid replacing circuit breakers whose capacity has been exceeded. Due to limitations in current YBCO thin film manufacturing processes, it is not easy to obtain one large thin film that satisfies the specifications for high voltage and large current applications. The combination of standardized thin films has merit to reduce costs and maintain device quality, and it is necessary to connect these thin films in different series and parallel configurations in order to meet these specifications. In this paper, the design of a resistive type SFCL using parallel-connected YBCO thin films is discussed, including the role of a parallel resistor and the influence of individual thin film characteristics, based on both theory and experimental results.

Experimental study on an SFCL using series-connected YBCO thin films

Superconducting Fault Current Limiters (SFCLs) are able to reduce fault currents to an acceptable value, reducing potential mechanical and thermal damage and allowing more flexibility in an electric power system's design. Due to limitations in current YBCO thin film manufacturing techniques, it is necessary to connect a number of thin films in different series and parallel configurations in order to realise a practical SFCL for electric power system applications. The amount of resistance generated (i.e. the degree of current limitation), the characteristics of the S-N transition, and the time at which they operate is different depending on their comparative characteristics. However, it is desirable for series-connected thin films to have an operating time difference as small as possible to avoid placing an excess burden on certain thin films. The role of a parallel resistance, along with the influence of thin film characteristics, such as critical current (Ic), are discussed in regards to the design of SFCLs using YBCO thin films.

Solução do problema de superação de disjuntores pela alocação ótima de dispositivos limitadores de corrente de curto-circuito utilizando algoritmos genéticos

Este artigo apresenta uma metodologia para auxiliar nos estudos de limitação de correntes de curto-circuito em sistemas elétricos com problemas de superação de disjuntores, através da alocação ótima de dispositivos limitadores. O problema de otimização é solucionado aplicando-se Algoritmos Genéticos e levando em consideração os requisitos de custo mínimo, alocação de um número mínimo de dispositivos e a máxima redução da corrente de curto-circuito. A detecção da superação do disjuntor é feita pela análise tanto da corrente de curto-circuito que o disjuntor deve interromper como também da relação X/R do sistema. O modelo computacional desenvolvido utiliza de modo integrado o programa ANAFAS do CEPEL, mantendo a compatibilidade com as bases de dados utilizadas em estudos de curto-circuito no setor elétrico brasileiro. Os resultados obtidos com o sistema IEEE14 e com um sistema real brasileiro de grande porte comprovam a robustez do modelo, apresentando soluções que satisfazem às restrições com custo de investimento reduzido para todos os cenários analisados.

Effective limitation of line fault currents by means of the series-connected VSC-based facts devices

In this paper, the nearly instantaneous response of the series-connected VSC-based FACTS controllers when used to limit possible fault currents in a compensated line, will be presented. The effectiveness of both FACTS controllers (SSSC and UPFC) towards this system condition was investigated exploring the series voltage effect upon the line. Moreover, it will be shown that the UPFC shunt converter can also contribute to the reduction of such fault currents. The short-circuit current limitation strategy presented herein showed that aside of the power flow control and voltage support commonly carried out by the SSSC and the UPFC, they could also perform this additional functionality, thus offering a useful tool for the protection of the line in which these devices are installed.

Efficient reduction of fault current through the grounding grid of a substation supplied by an overhead line

AbstractThe paper presents a directly applicable and reasonably accurate method for the evaluation of the effects of the counterpoise, the measure for the reduction of the fault current through the substation grounding grid. Under practical conditions the magnitude of the current diverted from a substation grounding grid by the counterpoise conductor is a very complex function of the self and mutual impedances of overhead and underground conductors, substation grounding impedance, transmission line towers resistance, proximity effect between the grounding grid and the counterpoise conductor, as well as on many other factors of lower order. Therefore certain idealizations and simplification of the real physical model were indispensable to develop the mathematical model presented here. The obtained expressions are mostly based on the general equations of a line represented by its lumped parameters and the general equations of uniform ladder circuits. Copyright © 2006 John Wiley & Sons, Ltd.

Integration of fault current limiters on power systems for voltage quality improvement

Abstract Voltage sags and the associated phase angle jumps are resulting in numerous production outages due to the tripping of adjustable speed drives and sensitive process controls. In order to eliminate the enormous economic losses associated with these outages, utilities are actively looking for possible sag mitigation solutions. This paper focuses on the proper selection and design of suitable solid-state Fault Current Limiter configurations for application on the power systems to mitigate voltage sags in term of voltage magnitudes and phase angle jumps. Sensitivity analysis was also performed to determine the effects of varying FCL parameters on its performance in term of voltage supporting capability, phase angle jump reduction and fault current reduction.

Efficient reduction of fault current through the grounding grid of substation supplied by cable line

The paper presents an analytical procedure suitable for the determination of the part of the ground fault current emanating from the substation grounding grid in the conditions when a particular measure has been taken to reduce it. The practical realization of this measure can be simply described as burying one bare copper wire of a certain length in the same trench as the cable feeding line. In the case of an overhead feeding line, the similar measure is denoted in the expert literature as the "counterpoise". The presented method enables a quick and, for practical purposes, sufficiently accurate evaluation of the copper wire length providing the maximum possible reduction of the substation grid current. The conveniences of the method result from the simplicity of the formulae for the determination of the realized grid current reduction at the effective copper wire length.

The analysis of the fault currents according to core saturation and fault angles in an inductive high-Tc superconducting fault current limiter

In this paper, we investigate the fault currents in an inductive high-Tc superconducting fault current limiter (SFCL). The currents can cause serious damage to the reliability and stability of the power system. To analyze the transient fault characteristics of the SFCL, we fabricated an inductive high-Tc SFCL and tested it under different fault conditions. To simulate a fault condition, a fault angle controller was connected to a load. As the firing angle of the triac in the fault angle controller was controlled, various angles of the fault instant can be selected. An important parameter for the design and the fabrication of the SFCL is the reduction of the fault currents. If abnormally high currents due to low impedance of SFCL do not occur in the network with SFCL, the currents flowing under fault conditions can be limited to a desired value within one cycle. The fault current reduction depends on saturation, normal zone propagation velocity, turns ratio, and the fault angle (the instant of the fault occurrence within a cycle).

Principles of fault current limitation by a resonant LC circuit

The reduction of fault current is one of the oldest problems of power systems engineering. Fault current reduction permits the interconnection of large networks without replacing circuit breakers, improves transient stability, and reduces the cost of equipment. The paper investigates the reduction of fault current by the insertion of a resonant LC circuit into the transmission line. The device consists of a capacitor and a thyristor-switched inductance, tuned to the supply frequency. The thyristor switches are operated at zero-current-crossing to eliminate the generation of harmonics. The system operation is analysed using analytic methods and transient simulation techniques. A parametric study determines the effect of components and network parameters on the current limiter operation. Design methods and component selection criteria are developed. The results demonstrate that the device can reduce both transient and steady-state fault current significantly. It can be built with commercially available components. The significant operation improvement is expected to justify the cost of the new device.

145-kV Current Limiting Device - Design, Construction and Factory Test

The development of a current- limiting device (CLD) designed to reduce fault currents on a 145-kV transmission line is discussed. This CLD system consists of an electronic sensor that predicts the magnitude of a fault during the first 400 , is of its evolution, a fast switching system that opens in approximately 1 ms, and a large energy-absorbing resistor that is inserted into the line to limit the fault current when the switch opens. The prototype hardware performed successfully in the field during staged fault tests.