Search

Unique fault behaviors of renewable energy sources (RESs) may lead to the misoperation of traditional pilot protection. To cope with this issue, this article proposes a new pilot protection method using the improved Euclidean distance. For normal operation or external faults, the currents on both ends are completely opposite, so the Euclidean distance of current absolute values on both ends is equal to 0. However, it will be much larger than 0 for internal faults because transient currents on both ends will have a big difference at this time. Therefore, internal and external faults can be detected reliably. In order to facilitate the setting calculation, the Euclidean distance is normalized, and a stability factor is introduced to avoid invalid calculation results. The proposed method can be applied to different RES types and different fault ride through strategies. Meanwhile, it can withstand larger fault resistance and noise interference. Compared with other methods using the RES fault currents, this approach can operate correctly without any additional criteria when the circuit breaker recloses on a permanent fault or RESs output a low power. PSCAD simulation and real-time digital simulator experiment verify this method. [ABSTRACT FROM AUTHOR]

This article presents a new method for estimating the fault location in a voltage-source-converter-interfaced dc system. The proposed dc fault location estimation method evaluates the distance from the fault point to the dc line terminal by estimating the line inductance; hence, it is designated as $L$ location. Since the fault impedance usually only includes resistance, the proposed $L$ location is less affected by the variation of fault resistance. In addition, the ripple caused by the distributed capacitive discharge is excluded from the dc line current when the proposed $L$ location is applied in the dc system with the distributed-parameter transmission line. The cubic curve-fitting method is used to reconstruct the current signal based on the least squares method. The effectiveness of the proposed $L$ location is verified with an OPAL-RT-based multiterminal dc (MTDC) system and experimental point-to-point and MTDC systems. The comparison with the impedance estimation, the voltage-traveling-wave-based location, and the differential and directional protection substantiates the integral performance of the proposed method [ABSTRACT FROM AUTHOR]

This paper presents a general theoretical overview of a novel approach for the monitoring of the single phase-to-ground fault associated with power arc. Although several existing fault protection methods have been employed in order to resolve the power arcing faults associated with the single phase-to-ground faults, still ongoing research is trying to develop efficient methods that could help to suppress completely these dangerous power arcs from the systems. The operation of the protective relays and fuse systems is quite often questionable during recurrent failures in detecting the electric arcs as expected, especially during these arcs earlier events of formation. The most relevant reason causing these traditional faults protective switchgears seldom failures, limitations and drawbacks include essentially the varying amounts of resistance associated with these previously mentioned power arcs. Subsequently, the electric arcs related impedance and that of the power system tend to limit the arcing fault currents and voltages quantities at very low rates. Hence preventing the existing fault protective devices and switchgears to detect these arcs hazards, as long as the arcing fault related currents and voltages quantities are kept for a relatively long period of time below the nominal setting values of both the relays and the fuses systems. Subsequently, the entire power distribution system experiences the devastating effects of theses dangerous parasitic electric arcs hazards. However, in order to overcome the limitations, the disadvantages and the drawbacks of the above mentioned conventional fault protective devices, this paper divorces completely with the traditional practices in order to propose a radio measurement method. [ABSTRACT FROM AUTHOR]

Flexible direct current (dc) distribution networks are the development trend for the future distribution system. However, the protection and control of these networks are vulnerable to complicated dc faults, accurate fault analysis is required. In this article, we propose a three-stage transient fault analysis method to improve the accuracy of fault characteristic calculation for the voltage source converter based dc distribution network with multi distributed generators, which can unify and simplify the calculation process of different transient fault stages. An impedance parameter decoupling approach is proposed based on the dc line parameters, which can avoid the influence of the coupling impedance on fault response. The decoupled equivalent fault circuits are established for accurate fault analysis with flexibility and independence. In addition, a three-stage fault analysis is proposed, which is able to unify the calculation process. Finally, numerical simulations based on PSCAD/EMTDC have been carried out, which well demonstrates the effectiveness of the proposed impedance decoupling approach and the accuracy of the proposed method for fault analysis. Compared with the traditional fault analysis without decoupling, the proposed method stands out the conciseness and correctness. [ABSTRACT FROM AUTHOR]

Due to limited amplitude and controlled phase of current supplied by inverter-interfaced renewable power plants (IIRPPs), the IIRPP-side distance protection of lines connected to IIRPPs fails to detect the fault location accurately, so it may malfunction. The composite sequence network of a line connected to an IIRPP during asymmetrical faults is analyzed, and an adaptive distance protection based on the analytical model of additional impedance is proposed in this study. Based on open circuit property of negative-sequence network at the IIRPP-side, the equivalent impedance of power grid and current flowing through fault point are calculated in real-time using local measurements, which are substituted into the analytical model of additional impedance to calculate fault location. In the case of negative-sequence reactive current injection from IIRPPs during asymmetrical faults, the error of calculating fault point current from local measurements is analyzed and corrected to ensure reliability of the proposed protection. The proposed protection alleviates the effect of fault resistance in a system with weak sources. In addition, the proposed protection can adapt to different grid codes (GCs), the operation mode change of the power grid, and the capacity change of the IIRPP. PSCAD/EMTDC test results verify the effectiveness of the proposed protection. [ABSTRACT FROM AUTHOR]

Inverter-interfaced renewable energy sources (IIRESs) are typically controlled during fault conditions to meet fault ride-through (FRT) requirements, e.g., reactive current generation (RCG) requirements specified by grid codes (GCs). However, fault currents generated by inverters are different from the traditional sources, i.e., synchronous generators. Consequently, phase selection methods (PSMs) used by protection relays could suffer from erroneous fault type classification. This paper develops a dual current controller (DCC) that regulates the inverter's negative- and positive-sequence currents to simultaneously meet phase selection and RCG requirements. First, the negative-sequence-current angle is obtained based on the angles of both zero- and positive-sequence currents to enable a correct operation for phase selection. Then, the positive-sequence current angle is adjusted to reach a trade-off between RCG requirements and phase selection achieved by the negative-sequence current. Lastly, the reference currents of the IIRES are generated in the stationary frame without violating the inverter's current limits. The proposed DCC supports the grid voltage by meeting the RCG requirements and enhancing the grid reliability and resilience by enabling correct phase selection. Comprehensive time-domain and real-time simulation verify the precise operation of the proposed DCC under various fault conditions and GCs. [ABSTRACT FROM AUTHOR]

This article investigates the relationships between the pole-to-pole fault current and the topology in the bipolar voltage sourced converter (VSC)–high-voltage dc (HVdc) grid. Based on the improved high-frequency equivalent model, it is found that the pole-to-pole fault current value is significantly influenced by the grid topologies, which is different from the situation in symmetrical monopole dc grid. It is also found that only the adjacent converters and the subadjacent converters of the fault lines will impact the fault currents, while the other converters with longer electrical distances basically have negligible contribution to the fault current. According to above mechanism, the simplified index is also proposed in this article to evaluate the fault current level of dc grid efficiently when its topology varies. The proposed index can make evaluations by simple calculations between different topologies and avoid solving complex differential equations one by one when pole-to-pole fault occurs at different lines. Based on the practical evaluation index, the genetic algorithm is used to optimize the dc grid topology to limit the fault current level. Finally, the simulation verification is performed based on the six-terminal bipolar VSC–HVdc grids, and some suggestions on topology design are given. [ABSTRACT FROM AUTHOR]

Most of the available directional relaying schemes use the phase angle information of sequence components of voltage and current with a cycle or more as the decision time. Converter interfaced solar photovoltaic plants are subjected to follow grid codes, leading to significant voltage and current modulation compared to conventional synchronous machines based sources. This may result in malfunction of existing directional relaying. This paper presents a high-speed time-domain directional relaying method using only phase fault current for distribution systems in the presence of solar plant. The method proposes a fault direction discrimination function, and its sign provides the direction of fault. The proposed method is tested for various control options embedded in solar plant, fault parameters, and noisy signals in CIGRE 14-bus distribution system integrating solar plant. Results validate the ability of the proposed method to decide within one-fourth of a cycle following fault detection for both PV plant side as well as grid end. Comparative assessment reveals the superiority of the proposed current based direction relaying method over the existing technique. [ABSTRACT FROM AUTHOR]

Optimal protection coordination is usually solved for the original network topology with all lines, loads, and generation intact. However, power grids may experience contingencies due to transient events, e.g., generation or line outages. Low fault currents of inverter-interfaced distributed generators (IIDGs) necessitate a sensitive and reliable protection scheme. This paper proposes a protection scheme for islanded microgrids powered by droop-based IIDGs. The protection scheme utilizes virtual impedance-fault current limiters to limit IIDGs fault currents and achieve protection coordination. A two-stage method for optimal protection coordination (OPC) of directional overcurrent relays (DOCRs) is devised. In Stage I, relays short-circuit currents are calculated. Then, constraints on the operation times of primary and backup DOCRs are formulated for the islanded topology and each possible topology following an N-1 contingency. Lastly, in Stage II, the OPC problem is formulated as a constrained nonlinear programming problem and solved to obtain the optimal DOCRs settings. A radial test microgrid that is part of a Canadian urban distribution system is used to ensure the success of the proposed OPC method. [ABSTRACT FROM AUTHOR]

Power converters are essential for process optimization and electric drives control. However, the presence of both dc and ac currents in the same circuit makes the diagnosis and protection of this type of systems difficult. For this reason, a new ground fault location method for the controlled ac drive side of a dc–ac system is presented in this article. It is based on a grounding resistor placed at the midpoint of the dc bus, where its voltage is measured simultaneously with the ac drive side phase-neutral voltages.Applying a phasor operated equation, the faulty phase can be detected by angle comparison. Furthermore, an estimation of the fault location can be obtained. To verify the method, numerous simulations have been performed. The results show certain inaccuracies when the fault is close to the neutral of the system, which is inconvenient since the phasor equation requires precise values. In contrast, the ground arc resistance is not needed in the fault location process. The effectiveness of the method has been also corroborated through experimental tests on a 140 kW power converter, making the ground fault diagnosis in dc–ac systems practical and useful. [ABSTRACT FROM AUTHOR]

The multiplying factor (MF) is critical for the correct design, sizing, and selection of protection devices in a power system. This factor depends on the X/R ratio at the point of failure. The standards establish an equivalent MF for the X/R ratios for both three-phase and single-phase fault accordingly for engineering practices. However, X/R ratios for single-phase faults ignore how much from the total X/R ratio comes from the positive-sequence or zero-sequence X/R ratio. This research demonstrates that the total X/R ratio at the point of failure is not the only variable that affects how the multiplying factor changes. The results demonstrate with dynamic short-circuit simulations using EMTP-ATPDraw, which it is also necessary to establish the MF considering the differences of the X/R ratios of each sequence, respectively. To support the engineering designer in the correct selection of the protection device, this article proposes a methodology complementary to the standards, which allows establishing the multiplying factor using the X/R ratios of positive and zero sequence separately. The results show that both oversized and undersized design situations can occur when ignoring the zero sequence in particular scenarios. [ABSTRACT FROM AUTHOR]

Despite the substantial reliability and power quality improvements, the proliferation of distributed energy resources can introduce many protection complexities in distribution networks (DNs). This research article presents a comprehensive investigative analysis of the distributed generation (DG) impacts on the protection performance of the DN. Various protection coordination case studies have been analyzed under different operating conditions by varying the DG penetration level or the fault conditions to highlight the potential risks of the protection networks. The severity of the risks is evaluated by considering the DG locations, protection settings, and fault types/impedance parameters on a standardized IEEE 13 node test feeder in DIgSILENT Power Factory/MATLAB softwares. The subsequent protection hazards are examined for the mutual coordination of the overcurrent relays, auto-reclosers, and series fuses in DNs along with the differential protection issues for dc bus system. Furthermore, the impacts of DGs/PDs types are assessed on the nuisance tripping of the protection networks and results are reported. [ABSTRACT FROM AUTHOR]

Protection of microgrids at the Point of Interconnection (POI) is a challenging task. Particularly, single-line-to-ground (SLG) faults on interconnection lines are difficult to detect using the fault current detection relays if the microgrid is ungrounded at utility side of its interconnection transformer; such microgrid contributes very low fault current, which disappears once the utility feeder breaker opens. Other common schemes for protection of microgrid interconnection line against SLG faults include Direct Transfer Trip (DTT) and over-voltage relay (59G). The main challenges associated with these methods are installation and maintenance costs of high-speed communication system, sensitivity of relay settings, and delayed fault clearing time due to selectivity requirements. To address such concerns, this paper proposes the use of a distance relay at the microgrid/LV side of the interconnection transformer to provide protection against SLG faults on the interconnection line at the utility/HV side. The designed distance relay executes an enhanced apparent impedance calculation using residual voltage compensation to correctly detect the fault, properly measure the fault location, and timely isolate the fault. In this paper, various scenarios are analyzed using ASPEN and PSCAD simulation tools to demonstrate the effectiveness of the proposed method for protecting the microgrid interconnection line under different fault scenarios. [ABSTRACT FROM AUTHOR]

Rapid and accurate location of power distribution line faults is essential for power system reliability improvement. Based on the electromagnetic time reversal (EMTR), an improved expression of fault current considering the influence of both sides of the transverse branch in the reversed time was derived in this research. In the reversed time, the transient voltage signals were injected into both ends of the line and multiplied one signal by −1, as suggested in An et al.'s work, and an assumed impedance of the transverse branch was set to 1000 Ω. A new criterion of the mirrored minimum fault current signal energy was proposed to determine the fault location. In the direct time, by setting different ground fault impedances, the distribution of the fault current signal energy in the frequency domain was calculated. Furthermore, the time-domain simulation verification was performed in the power systems computer-aided design software. The results indicate that when the actual fault impedance was unknown, the accurate fault location of the distribution line can be achieved by the proposed EMTR-based method, and it is less affected by time synchronization. [ABSTRACT FROM AUTHOR]

Electrical faults, which can occur at all voltage levels in an electricity supply system, are a health and safety risk. Multi-branch distribution networks represent a significant ongoing challenge for fault detection, with the greatest challenge being high impedance fault (HIF) detection. To date, research has focused on higher voltage levels, and fault monitoring sensors have traditionally only been installed in limited locations within the higher voltage networks. The main contributions of this paper are to characterize a high impedance fault (HIF) involving a tree branch and to experimentally verify the feasibility of giant magneto-resistive (GMR) sensors, located distant from the overhead lines, for fault detection. In a purpose-built 400 V physical simulation test facility, we have collected current and magnetic field data during HIF involving a tree branch. We have identified new characteristics in the early stages of this fault type, which persist for a reasonable length of time but are only observable when suitable signal processing techniques are applied. New detection schemes will, therefore, need to be developed to detect such faults. GMR sensors were found to be suitable for observing the characteristics of HIF, validating their potential use for fault detection. [ABSTRACT FROM AUTHOR]

High Impedance Faults (HIFs) occur by the contact between an energized conductor and a high impedance surface. Due to the low fault current level, HIFs cannot be detected by conventional protection and there is no fully efficient solution to this problem. HIF detection methods often extract metrics using signal processing techniques, such as Fourier Transform, Wavelet Transform, Stockwell Transform, and Mathematical Morphology. However, these techniques are applied under specific conditions, which hinders comparative and critical analyses among them. Therefore, this paper presents a critical review of HIF detection methods based on the aforementioned techniques, and also shows a detailed investigation of the performance of the metrics commonly used with them. To do this efficiently, the authors proposed a set of assessment indices based on the ratio between the metrics’ characteristics and another one based on the repeating of the metrics features. The proposed indices revealed that some of these metrics fail to distinguish HIF from other typical occurrences in power distribution systems, and their performances are negatively affected by the fault location and by the existence of noise in the measurements. Additionally, the results showed a need to specify system conditions in which any HIF detection technique is valid. [ABSTRACT FROM AUTHOR]

To enhance the operating security and stability of the cross-linked polyethylene power cable based urban distribution network due to conventional cable joint (CCJ) faults, this paper presents a novel superconducting fault current limitation scheme by using a superconducting cable joint (SCJ). The basic principle, circuit modeling, conceptual design and distribution network integrated with the SCJ are presented in detail. The comparative study without and with the proposed SCJ scheme and comprehensive evaluation are carried out. The simulation results obtained under symmetrical and asymmetrical CCJ faults show that the harmful large fault grid currents can be limited effectively and the fault grid voltage can be well improved. Thus the high temperature electric arc in the fault location caused by CCJ faults can be safely controlled. And large area power failure in actual power system can be avoided. [ABSTRACT FROM AUTHOR]

DC fault protection is the bottleneck that restricts the development of modular multilevel converter based high voltage direct current (MMC-HVDC) system. Superconducting fault current limiters (SFCL) is an ideal protection device that can significantly limit short circuit current and enhance the fault tolerance ability of MMC-HVDC system. At present, several topologies of SFCLs have been proposed, but there is no systematical study of their current-limiting characteristics in MMC-HVDC. This paper studies the development process of DC short-circuit faults in MMC-HVDC system, and analyzes its demand for fault current limiting. Then, resistive type, saturated iron core type and hybrid type SFCL are modeled and their limiting effect of critical fault current under DC pole-to-pole fault is tested. By comparison, the current-limiting characteristics of three types of SFCL are concluded. Results show that resistive SFCL has best performance in steady state, while saturated iron core SFCL has best performance in transient state. The current-limiting characteristic of hybrid type SFCL is between the other two types. [ABSTRACT FROM AUTHOR]

A rapiddevelopment of the permanent magnetic synchronous generator (PMSG)-based offshore wind farm has been witnessed in the past decade. To prevent the offshore wind farms from being disconnected during a fault, many countries have proposed specification requirements for the fault ride-through (FRT). Traditional FRT scheme Chopper circuit for PMSG needs to consume all the mismatching energy and the impulse current is too high during the fault, which will even affect the safe of the PMSG. In this paper, the superconducting fault current limiter (SFCL) is applied to enhance the ability of the FRT in the PMSG-based offshore wind farm. In the proposed scheme, the resistive SFCL can reduce the energy consumption and improve the working performance of the Chopper circuit by absorbing the power of the grid-side converter (GCS) during the fault. An offshore wind farm model is built through PSCAD/EMTDC software. The comparison simulation results validate the feasibility of the proposed scheme. [ABSTRACT FROM AUTHOR]

Fault current-limiting dynamic voltage restorers (FCL-DVRs), also named as dual-functional DVRs, involving both the FCL and the voltage compensation (VC) function, have attracted more attention. However, in case of the FCL-DVR operating in VC mode, either the high capacity of storage system in the dc-link or the oversizing of power converter is needed, and in case of the FCL-DVR operating in FCL mode both the high dc-link voltage and the oversizing of power converter are needed. Thus, in order to overcome these drawbacks, an improved FCL-DVR, which consists of an LC filter coupled with series coupling capacitor (LCC) at the ac side, is proposed in this article. The improved FCL-DVR using energy-optimized control strategy can not only perform the dual functions well, but also achieve the capacity optimization of FCL-DVR key components. The operating principle and performance of the proposed FCL-DVR under FCL and VC mode are elaborated, respectively. The optimal design of LCC and selection of FCL branch are studied in detail to ensure high stability and reliability for the proposed FCL-DVR operating in both modes. The simulation and experimental results clearly validate the effectiveness of the proposed topology and method. [ABSTRACT FROM AUTHOR]

High speed trains supply is, nowadays, performed by 2 × 25 kV power systems. If a ground fault occurs, its location and correction are crucial to minimize downtime. One of the methods for locating ground faults in power systems is the impedance method. This was a good solution for 1 × 25 kV railways power systems, as the ratio between reactance and fault distance is linear. However, the use of autotransformers between the catenary, feeder and rails makes this ratio non-linear in 2 × 25 kV configuration. This work presents a novel ground fault location method for 2 × 25 kV power systems. The new method is based on the ratio of the currents of the autotransformers and the substation transformer. The main contribution, compared to previous methods developed, is that this new method is insensitive to the fault current variations produced by the network voltage fluctuations or by the main transformer tap changer position, among others for 2 × 25 kV power systems. The novel approach has been corroborated by numerous experimental tests in the laboratory and computer simulations, with satisfactory results. [ABSTRACT FROM AUTHOR]

The exclusive fault behaviors of MMC-HVDC stations bring great challenges to the correct operations of distance relays. This paper presents a new zone I distance relaying scheme that can accurately calculate fault distance in the case of integration of MMC-HVDC system. The two calculation formulas of fault distance are derived from mathematical perspective and geometrical relationship of impedances, respectively. Phase angle of fault current is the key to calculate fault distance. In power system without MMC-HVDC stations, the existing method for solving this phase angle is based on two premises, that is, the positive- and negative-sequence current distribution factors are equal and real numbers. However, owing to the integration of MMC-HVDC system, aforementioned premises are both not true. Consequently, the existing method cannot obtain accurate phase angle of fault current. To solve this problem, the three solutions corresponding to three different types of asymmetrical faults are provided. The proposed scheme has the advantages of satisfactory immunity against fault resistance, applicable to various asymmetrical faults, and performing well under rectifier as well as inverter modes. The performance of the proposed scheme is evaluated by simulation results in PSCAD/EMTDC and compared with prior-art schemes. [ABSTRACT FROM AUTHOR]

Directional, phase-selection, and distance elements of a relay are prone to misoperation in the presence of inverter-based resources (IBRs). To address these problems, modifications of relay elements as well as new control schemes for IBRs have been proposed in the literature. These methods focus mainly on addressing the misoperation of only one of the above relay elements. The available solutions that are based on a new control system focus only on the negative-sequence current loop. Thus, they work only for unbalanced faults. This paper proposes a comprehensive dual current control scheme for IBRs during all types of faults such that all of these relay elements operate correctly. The proposed method controls the IBR to operate as a voltage source behind a virtual impedance in the positive-sequence circuit, and a single impedance in the negative-sequence circuit, thereby emulating the phase angles of a synchronous generator's (SG's) fault current. The proposed method also maximizes the active, and reactive current generation of the IBR during faults, and emulates the incremental sequence current magnitudes of an SG. The proposed method does not require altering the relay elements. Moreover, correct operation of the relay elements is achieved regardless of the fault type, resistance, and location. The effectiveness of the proposed method is verified through not only simulation studies, but also hardware-in-the-loop testing of commercial relays. [ABSTRACT FROM AUTHOR]

Fault current limiters (FCLs) are promising fault current management measures and one of the most economical solutions to today's electric power systems challenges that could have potential for greater use in power systems. To achieve highest efficiency with lowest cost, several efforts have been proposed in literature to provide the optimal location, number, type, size, and parameters setting of FCL. In this article, the existing research works on FCL integration are reviewed from viewpoint of their used design variables, network structures, FCL types, constraints, protection devices, and objective functions. The main aim of this article is to provide a guide on the available FCL placement works, to aid electrical engineers and researchers. [ABSTRACT FROM AUTHOR]

Fault ride through compliance as imposed by the grid codes (GCs) prevents the inadvertent disconnection of the renewable plants from the network even during faults. Control algorithms applied in the converters associated with such plants modulate the fault characteristics significantly and result in malfunction of available fault type classifiers at times. In this article, an adaptive fault type classification technique is proposed for transmission network connecting converter-interfaced renewable plants. The method calculates sequence current angles in the faulted loop by determining pure-fault impedance of the plant at every instant during fault using local voltage and current data for fault type identification. The proposed method is tested for different fault situations on renewable integrated standard systems using PSCAD/EMTDC. The performance of the proposed method is found to be accurate in the presence of different types of renewable plants and complying different GC requirements. Comparative assessment reveals its superior performance. [ABSTRACT FROM AUTHOR]

The emerging trends in the microgrid development and the increasing penetration of distributed energy resources (DERs) in the distribution networks urge the modification in the existing conventional protection techniques. The integration of DERs changes the radial nature of the network, and thus, the schemes designed for such networks fail to operate for the microgrid system. Hence, a new fault detection technique is required for the microgrid system. In this article, a new fault detection scheme is developed for detecting the low-impedance faults (LIFs) as well as high-impedance faults (HIFs). The detection of HIFs is of major concern as these faults lead to a very low fault current value, which makes them undetectable by the conventional overcurrent relays. The proposed scheme uses the cumulative sum value of the differential negative-sequence impedance angle (DNSIA) as the fault detection parameter for generating the trip signal. The simulation results show that the proposed method effectively detects LIFs and HIFs accurately. The proposed scheme is independent of the type of faults, type of DGs, and the value of fault impedances. Furthermore, the proposed scheme also discriminates between the switching transients and faults effectively. The IEEE 13-bus test system is modeled and simulated on real time digital simulator (RTDS)/RSCAD platform. The method is further validated for the real-time implementation by developing the experimental setup for performing the control hardware-in-the-loop. [ABSTRACT FROM AUTHOR]

Methods and research for preventing utility-caused wildfires have significantly advanced in the past few decades, including development of criteria on reduction of energy release in an electrical fault to mitigate the probability of ignitions. Technologies to minimize energy release during electrical faults and achieve these ignition benefits are being applied at the substation level. However, the benefits can be targeted to a high-risk area by resonant grounding an isolation transformer on a distribution circuit. By doing this it is possible to reduce single line to ground fault current beyond the transformer to a level unlikely to ignite fires. This system was constructed and shown capable of reducing the power into a phase-to-ground fault by a factor of more than 10,000 and detect ground faults smaller than 0.5 A. This allowed it to meet the ignition criteria mandated for distribution network fire safety in the Australian state of Victoria. It was also tested for typical ignition scenarios such as downed phase conductors and phase conductors contacting with a tree branch. In all cases the probability of ignition was reduced by 90% or more. [ABSTRACT FROM AUTHOR]

This article presents the implementation and performance testing of a bus-differential protection for buses, which interconnect battery storage systems (BSSs). The proposed bus-differential protection is based on employing the α β 0 components of the apparent powers flowing in all branches of the protected bus. The α β 0 components of the apparent powers are employed due to their ability to accommodate changes in the power flow direction in the branches connected to the protected bus. The apparent powers are determined using the measured voltage and currents in all branches connected to the protected bus. The proposed α β 0-based bus-differential protection is implemented and tested for internal and external faults, which are created during the charging and discharging of BSSs. Test results demonstrate the ability of the proposed α β 0-based bus-differential protection to initiate fast, accurate, and reliable responses to internal and external faults in the protected bus. Observed response features of the proposed protection are found to have minor sensitivity to the mode of operation of the BSS (charging and discharging), fault location (internal and external), and/or fault type. [ABSTRACT FROM AUTHOR]

DC system protection is more challenging than that for AC system due to the rapid rate of rise of the fault current and absence of natural current zero-crossing in DC systems. Superconducting fault current limiter (SFCL) in DC systems is a promising technology to reduce the fault current level and the rate of rise of the fault current, and also SFCLs have no resistance during normal operation. In this paper, the behaviors of an SFCL coil are investigated under both low impedance and high impedance fault conditions in DC systems. In the low impedance fault condition system, the SFCL coil performs effective limitation of the fault current level under different prospective fault current levels. The application of SFCLs with limited inductance in the DC system can be a potential solution to effectively suppress the fault current under low impedance short-circuit faults. The SFCL coil under the high impedance fault condition can only limit the prospective fault current when it is much higher than the critical current of the coil. [ABSTRACT FROM AUTHOR]

Most industrial technologies are automated by sensitive electric parts such as programmable logic controllers(PLCs) and magnetic contactors which are required high power quality. The voltage sags occur in the non-faulted power distribution feeders during the fault duration. Therefore, voltage causes economic losses in the production process of various companies. To solve the fault current and the voltage sags, the superconducting fault current limiter (SFCL) is in the spotlight. The SFCL where was located on starting point of the feeder improves the reliability of the facility by reducing the fault current. In addition, it compensates the voltage sags on the bus-bar. In this paper, evaluating the voltage sags based on fault location in the power distribution system with the SFCL through PSCAD/EMTDC simulation. Next, the expected the voltage sags frequency is predicted by the reliability analysis technique of the power distribution system. The expected voltage sags frequency of the power distribution feeder is compared with before and after the application of the SFCL. [ABSTRACT FROM AUTHOR]

Recently, the development of the electric power industry has led to an increase in the fault current when a fault occurs. It is important to reduce the fault current, since fault currents exceeding the capacity of protective devices can result in large blackouts. In order to reduce the fault current, there is a method to separate the bus line of main substation. However, this method has the disadvantage of complicating the power system. Another method is to install a superconducting fault current limiter (SFCL). The SFCL has the advantage that the fault current can be quickly limited within 1/4 cycle immediately after the fault occurrence without affecting the power system since its impedance is zero in a normal time. However, the application of SFCL affects the operation of the over-current relay (OCR) due to the reduced fault current such as trip time delay. The trip time delay of OCR was reported to be suppressed by using SFCL's voltage component in previous studies. In this paper, the impedance compensation method was suggested to exclude the effect of SFCL on OCR. To prevent OCR from the influence of SFCL, the component that can exclude the impedance of SFCL was considered to be added to the characteristic formula of OCR. In addition, the effect of correcting this characteristic equation was analyzed by constructing a power distribution system using PSCAD / EMTDC. [ABSTRACT FROM AUTHOR]

Detection of the high impedance fault (HIF) in distribution systems is significant for power utilization safety. In addition to the low fault currents, traditional approaches are invalid to detect HIFs also due to the diverse characteristics, including the slight HIF nonlinearity during the weak arcing process, the distortion offset caused by the lag of heat dissipation, and the interference of background noise. This paper proposes a distortion-based algorithm to improve the reliability of HIF detection under various conditions. Firstly, the challenges brought by the diversity of HIF distortions are explained according to the field experiments in a 10 kV real-world distribution system. HIFs are classified into five types according to the distortions of their current waveforms. Secondly, a definition of interval slope is introduced to describe waveform distortions. The interval slope is extracted by combining methods of linear least square filtering (LLSF) and Grubbs-criterion-based robust local regression smoothing (Grubbs-RLRS), so that the distortions under different fault conditions can be uniformly described. Thirdly, an algorithm is proposed to judge the features presented by the interval slope, and distinguish from non-fault conditions. Finally, the reliability and security of the proposed algorithm are thoroughly analyzed with real-world HIFs and the simulated HIFs obtained in IEEE 34-bus and IEEE 123-bus systems. Results show the improvements of the proposed algorithm by the comparisons with other advanced algorithms. [ABSTRACT FROM AUTHOR]

The delayed operation of distance relays zone-2 element for the faults at the end of the line is excessive. It reduces the fault clearing speed and therefore, is one of the main factors that can endanger power system stability. This paper proposes an impedance-based scheme for discrimination between the last 20% of the line length faults and the adjacent line faults, which are covered by the relay zone-2. The suggested non-pilot scheme uses a modified fault location formula for the accelerated zone-2 operation of distance relays. The negative- and zero-sequence components of local signals are utilized to calculate the accurate fault location after the remote circuit breaker (CB) operation. The proposed algorithm is independent of fault resistance, power flow direction, pre-fault condition, and it can clearly distinguish internal faults from the adjacent line faults. Simulation results show that the proposed method can identify the remote CB operation and thus can accelerate the tripping of zone-2 within a very short time for different fault locations, fault types, fault resistances, and load angles. Also, accurate fault location has been achieved under all simulation conditions. [ABSTRACT FROM AUTHOR]

Large fault currents in a synchronous-based distributed generators (SBDG) can cause serious damage to the core and windings of the generator. This article proposes an adaptive grounding scheme to limit the ground-fault currents to a safe level. To do so, a high-impedance grounding configuration is designed to operate during the grid-connected mode to minimize damage to the generator during ground faults. An electronic switching mechanism is provided to identify the islanded mode of operation. This switching operation strategy will modify the grounding system to the low-impedance configuration during the islanded-mode of operation of the SBDG to ensure the steadfast operation of the overcurrent protection (OCP) relays to prevent the nuisance tripping by the protective devices. Furthermore, the schematic diagram of the proposed grounding configuration has been presented and discussed to ensure the safe decay of the generator field current during ground faults in the generator zone while the generator has been isolated from the grid. Simulation results for different test systems, including the IEEE 34-bus test system, validate the effectiveness of the proposed adaptive grounding scheme to ensure the steadfast operation of the inverse OCP and to limit the fault energy dissipation level inside the SBDG to a safe level by maintaining an appropriate grounding scheme during different operating modes. [ABSTRACT FROM AUTHOR]

This article focuses on the indeterminate protection challenge of the sensitivity deterioration (SD) (also known as protection blindness) of the overcurrent protection (OCP) devices due to the large-scale integration of distributed energy resources (DERs) in the unbalanced distribution networks (DNs). The protection blindness of the OCP has been demonstrated through novel mathematical formulations to quantify the percentage of the SD for different types of distributed generation (DG) units and for the varying DG penetration levels. Furthermore, this issue has been realistically analyzed for the different fault impedances and DG locations to examine its impact on the existing OCP system. A mitigation strategy has been proposed to overcome the SD issue of the OCP protective devices (PDs) for a steadfast operation of the OCP devices without requiring costly upgrades of the protection system. This protection blindness issue has been explored and the mitigation strategies have been tested for both synchronous and inverter-based DGs using the IEEE standardized test feeders. The proposed mitigation strategy has been validated in the IEEE 34-bus test system. The simulation results prove the effectiveness of the proposed mitigation strategy to restore the protection coordination and suitability to improve grid resilience. [ABSTRACT FROM AUTHOR]

Unlike conventional synchronous generators, the fault characteristics of inverter-based distributed generators (IBDGs) are mainly determined by the inverter control strategies. Their limited fault current contributions make the protection design of islanded microgrids (MGs) become a major challenge. This article focuses on the fault characteristics and protection scheme design of islanded MGs. First, the phase differences between the positive-sequence current fault components (PSC-FCs) at both terminals of fault line are analyzed under different network topologies and fault severities. It points out the phase characteristic differences between internal and external faults. Then, on basis of this to overcome the problems of the phase measurement error and protection setting, a waveform difference feature-based protection scheme is proposed. The protection criteria are formulated using the first peak sign and time information of PSC-FCs between both terminals of line, which are extracted by the mathematical morphology (MM) technology. Only relatively low bandwidth communication is required to achieve accurate fault identification. Finally, the simulation results on a 10-kV islanded MG model demonstrate that the proposed scheme can identify internal faults reliably in both looped and radial islanded MGs under different fault resistances and measurement noises. [ABSTRACT FROM AUTHOR]

This paper presents a new fast-acting backup protection strategy for future hybrid ac-dc distribution networks. By examining the impedance measured by a distance protection relay measuring from the “ac-side” of the network, a unique characteristic is established for faults occurring on the “dc-side” of an embedded medium-voltage dc (MVDC) link, interconnecting two 33 kV distribution network sections. Based on the identified impedance characteristic, appropriate settings are developed and deployed on a verified software model of a commercially available distance protection relay. To remain stable for ac-side faults, it is found that the tripping logic of the device must be altered to provide correct time grading between standard, ac, protection zones and the fast-acting dc region, which can identify faults on the dc system within 40 ms. An additional confirmatory check is also employed to reduce the likelihood of mal-operation. Trials on a test system derived from an actual distribution network, which employs distance protection, are shown to provide stable operation for both ac-side and dc-side pole-pole and pole-pole-ground faults. [ABSTRACT FROM AUTHOR]

This paper presents an innovative method for fault location in distribution networks based on classical circuit analyses. Two synchronized and few nonsynchronized pre- and during-fault voltages are required at few buses along with the impedancematrix. A new impedance matrix manipulation procedure is proposed so that the distribution system is investigated in partitions across multiple subsystems. This procedure allows the fault location process to be performed by solving systems of determined equations, making the method more technically accessible. The fault is located by analyzing the voltage sag at the terminal-bus of each subsystem separately. The proposed method is validated on the IEEE 33-bus, 12.66 kV distribution system with/without distributed generation (DG). Simulation results show the robustness and accuracy of the method under several pre- and during-fault scenarios and measurements errors. [ABSTRACT FROM AUTHOR]

Withstanding fault is a crucial technical challenge for inverter-based systems. Evolving grid codes require microgrids to possess fault ride-through (FRT) capabilities and support the grid voltage recovery. The traditional grid forming and grid feeding models lack such abilities. Consequently, this article enhanced these traditional models with droop control-virtual impedance and secondary power reference generation to form two models of a grid-supporting system. The first is a current source for grid feeding control, and the second is regulated as a voltage source for grid forming control. The result presents grid fault impact and FRT compliance in the proposed and traditional systems. Furthermore, the fault current curtailment and FRT improvement of the virtual impedances in the grid forming control were investigated within the MATLAB/Simulink environment. These proposed systems achieved FRT under a dynamic period and reverted to appropriate power delivery control under a static period. [ABSTRACT FROM AUTHOR]

Distribution lines are generally protected by overcurrent relays. With the integration of an inverter-interfaced solar photovoltaic (PV) plant having a current-limiting feature, the fault current seen by the relay on the PV side of that feeder becomes comparable to the load current. The conventional overcurrent relaying principle is not suitable for distribution line protection. Distance relay may be a viable option for protection of distribution lines connecting the solar PV plant. However, positive- and negative-sequence source impedances of the PV plant depend on an inverter controller, which results in limited performance of fixed setting distance relay. This article proposes an adaptive distance relay setting to protect distribution line connecting the PV plant, using prefault voltage and current data at the relaying point. The method calculates positive- and negative-sequence PV source impedances for boundary setting of distance relay at the PV side. The proposed trip boundary is modified adaptively with the change in prefault conditions of the PV plant. Performance of the proposed method is tested for different control strategies and operating capacities of the PV plant and variation in the grid source impedance on a 34-bus distribution system. Real-time application of the proposed method is validated in hardware-in-the-loop using OPAL-RT simulators with IEC 61850 as the communication protocol and found to be accurate. [ABSTRACT FROM AUTHOR]

Accurate fault calculation is vital for the parameter design and protection research of high-voltage DC (HVDC) grids. This paper proposes a general method to calculate short-circuit faults in HVDC grids, and the method is based on the premise that the modular multilevel converter (MMC) blocking and the current interruption have not occurred. The MMC is based on the average value model, and the MMC current source can reflect the impacts of the AC system and MMC control mode. The fault calculations based on variable and constant MMC current sources are presented. The numerical inversion of the Laplace transform is used to obtain the voltages and currents in the time domain. The proposed method has the following merits: 1) it can accurately calculate voltages and currents while considering the fault-generated traveling wave effect and impacts of the AC system and MMC control mode; 2) it is more time efficient than the electromagnetic transient simulation; and 3) it is applicable to HVDC grids with different configurations, such as symmetrical bipolar and asymmetrical monopolar. The proposed method is validated by comparisons with previous calculation methods and PSCAD/EMTDC simulation. [ABSTRACT FROM AUTHOR]

Inverter-Based Resources (IBRs), including Wind turbine generators (WTGs), exhibit substantially different negative-sequence fault current characteristics compared to synchronous generators (SGs). These differences may cause misoperation of customary negative-sequence-based protective elements set under the assumption of a conventional SG dominated power system. The amplitude of the negative-sequence fault current of a WTG is smaller than that of an SG. This may lead to misoperation of the negative-sequence overcurrent elements 50Q/51Q. Moreover, the angular relation of the negative-sequence current and voltage is different under WTGs, which may result in the misoperation of directional negative-sequence overcurrent element 67Q. This paper first studies the key differences between the WTGs and SG by comparing their equivalent negative-sequence impedances with SG's. Then, simulation case studies are presented showing the misoperation of 50Q and 67Q due to wind generation and the corresponding impact on communication-assisted protection and fault identification scheme (FID). The impact on directional element is also experimentally validated in a hardware-in-the-loop real-time simulation set up using a physical relay. Finally, the paper studies the impact of various factors such as WTG type (Type-III/Type-IV) and Type-IV WTG control scheme (coupled/decoupled sequence) to determine the key features that need to be considered in practical protection studies. The objective is to show potential protection misoperation issues, identify the cause, and propose potential solutions. [ABSTRACT FROM AUTHOR]

To meet the ultra-fast, selective, and reliable requirements of the DC fault protection, a protection scheme for modular multilevel converter based HVDC grids is proposed in this paper. The protection scheme is consisted of main protection, directional pilot protection, and faulty pole identification. The new fault directional criterion is achieved by employing the surge arriving time difference of line-mode backward traveling wave and line-mode forward traveling wave. This criterion is valid even when the fault current limiting reactors (FCLRs) are installed at the converter side of DC bus. The main protection without communication and complex computation relies on co-operation of the derivative of line-mode forward traveling wave and the directional criterion. The directional pilot protection by comparing the double end directional criteria can be used as a backup protection. The accumulation of zero-mode component is adopted to discriminate the faulty pole. Simulations have demonstrated that the proposed scheme is capable of identifying various types of faults with different fault resistances at different positions. The robustness analysis shows that the protection scheme presented is not sensitive to the FCLR size, noise environment, sampling frequency, and the operation of hybrid DC circuit breakers. [ABSTRACT FROM AUTHOR]

High impedance faults (HIFs) often draw too little current to activate conventional overcurrent protection, making the detection of a HIF event a difficult task. A practical and implementable solution to HIF detection and location is presented. In the proposed methodology, wavelet transform used for extracting features of HIFs signals and neural network used for HIF detection are used to develop a novel HIF detector called enhanced feeder terminal unit (FTU). The designed enhanced FTU is a high-performance HIF detector that is the retrofitting of the ready-made FTU with an embedded digital signal processor and a high-frequency current sensor. The enhanced FTU monitors the operation of distribution feeder system and sends a fault flag signal to feeder dispatch and control center when a HIF occurs. Based on the feeder automation mechanism, the HIF detection, isolation, and service restoration can be activated. Consequently, the power reliability can be significantly improved by reducing the outage area and repair time. The validation of the presented technique was evaluated through staged fault testing. Compared with the existing related research, the proposed enhanced FTU is available and feasible. [ABSTRACT FROM AUTHOR]

For the virtual synchronous generator, the voltage-controlled harmonic suppression method will seriously deteriorate the magnitude of inrush fault current in the moment of grid symmetrical fault, because the suppression effects of harmonic current and inrush fault current are mutually constrained from the perspective of its output impedance. For this issue, a harmonic current and inrush fault current coordinated suppression method is proposed to achieve both good results of harmonic current suppression in normal grid and inrush fault current limitation in fault grid, which mainly includes a passive branch, an active branch and an improved virtual synchronous generator (VSG) control. The passive branch is installed between the PCC and grid to introduce an additional voltage variable. Meanwhile, with the proper feed-forward of the PCC voltage and additional voltage, the active branch is used to increase the mid/high frequency impedance viewed from the grid fault point to VSG, and also decrease the harmonic impedance viewed from the PCC to VSG. Then, not only the transient inrush fault current is limited, but also the harmonic current introduced from the nonlinear load is mostly absorbed. Moreover, the improved VSG control is used to limit the steady-state fundamental frequency fault current. Therefore, the contradictory between harmonic current and inrush fault current suppression for VSG is well solved. Finally, the experiment results validate the proposed control method. [ABSTRACT FROM AUTHOR]

This article presents a new modified topology to cover both fault current limiter and dynamic voltage restorer functions in utilities. A new control pattern is proposed to minimize power loss during short circuits in downstream and compensate for voltage fluctuation effects on the grid. Power source will not experience any excess current conditions during fault current mode, which is a novelty of the proposed technique. Analysis is carried out for grid voltage unbalances and short-circuit faults and was verified through simulations. Finally, a scaled-down prototype is built to validate the feasibility and effectiveness of the proposed technique. [ABSTRACT FROM AUTHOR]

Integrating solar generation brings about unique challenges in power system protection. Previous studies have found inverter-based resources featuring distinct fault responses compared to conventional generators. The reduction in fault current magnitude and lack of negative and zero sequence currents can fundamentally impact the way that the power system is protected. This letter studies the negative-sequence current injection from transmission-connected solar farms. Using field recorded data, this letter reveals the negative-sequence current injection behaviors of solar farms by analyzing how inverters respond to faults. In addition, the paper studies how the negative-sequence current can impact negative-sequence directional elements used in protective relays. The response of protective relays’ is evaluated by replaying field events using actual relay settings applied on conventional systems. [ABSTRACT FROM AUTHOR]

A High Impedance Fault (HIF) in the power distribution systems remains mostly undetected by conventional protection schemes due to low fault currents. Apart from degrading the reliability of power supply to customers, HIF can impose a high cost on the utilities due to technical damages. The nonlinear and asymmetric nature of HIF makes its detection and identification very challenging. HIF signatures are in the form of minute-level distortions in the observable AC sinusoidal voltage and current waveforms but these signatures do not follow a clear pattern. In this paper, we present Advanced Distortion Detection Technique (ADDT), based on waveform analytics to distinguish and detect HIF. In addition, the ADDT analysis provides a fair assessment about the location and severity of HIF for efficient decision-making at the DSO level. ADDT is computationally lightweight and can be implemented in actual relays, hence it is enabled to provide an easy and cost-effective solution to HIF detection issues. ADDT robustness is tested in several simulation cases of interest using the IEEE-34 and IEEE-13 distribution test feeder systems in RTDS power system simulator. The test results successfully demonstrate the effectiveness and robustness of ADDT. [ABSTRACT FROM AUTHOR]

Hybrid AC/DC transmission grids require high-speed operation and high reliability for relay protection. Traditional derivative-based traveling wave protection methods have exposed the problems of low sensitivity and low reliability. In this paper, the fault traveling wave is analyzed considering the attenuation, distortion, and boundary effect of the DC transmission line as well as three converter types. The expressions of the fault initial traveling wave are derived and the conclusions show that 1) the expressions of the fault initial traveling wave at the end of the transmission line have the formation of a(1 − exp(−bt)); 2) the index of the exponential function in the fault initial traveling wave expression is related to the fault location, and is not affected by the fault impedance and line attenuation. Then a Levenberg–Marquart fitting method is proposed to fit the measured zero-mode fault current initial traveling wave and extract the index coefficients. Finally, a novel traveling wave protection method for DC transmission lines is proposed using the obtained index coefficients. The simulation results show that 1) the proposed protection method can complete fault identification within 1 ms, even with high fault impedance; 2) the proposed protection method has high robustness to the influence of the noise. [ABSTRACT FROM AUTHOR]