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Fractional slot concentric winding (FSCW) machine features with short end winding, high torque density and good fault tolerance. However, this type of machine suffers from abundant MMF harmonics which causes high iron loss and partial saturation, etc. Hence, majority of the FSCW adopts surface-mounted PM (SPM) rotor which have large effective airgap to minimize the influence of the MMF harmonics while the interior PM (IPM) rotor is rarely used. The SPM rotor tends to induce high PM flux linkage and cause large fault current when experiencing a short-circuit failure. As a result, this paper presents a triple 3-phase FSCW-IPM for fault-tolerant applications. The triple 3-phase windings facilitate the uninterrupted fault tolerant operation, the more even distributed windings also induce a more sinusoidal MMF which enables the application of IPM rotor. The IPM rotor reduces the PM usage while reluctance torque can be explored to compensate the PM torque reduction which improves the machine fault tolerance. As a result, the proposed machine owns good performance and excellent fault tolerance. The machine is investigated by electromagnetic and thermal finite element analysis and prototyping tests. Both findings confirm that the proposed triple 3-phase FSCW-IPM is a competitive solution for high reliability application. [ABSTRACT FROM AUTHOR]

With rapid development of high voltage direct current (HVDC) grids, hybrid circuit breakers (HCBs) have gained more attentions, due to their great ability for fault current interruption in HVDC grids. This paper proposes a novel low-cost HCB based on the coupled inductor, to be utilized in HVDC applications. To realize high current breaking capability with low cost, a coupled inductor in combination with the bridge-type circuit is utilized in the breaker branch. The bridge-type circuit is constructed by the series connection of a not pre-charged capacitor, thyristor, and diodes to provide bidirectional breaking ability. After an interruption, the capacitor in the breaker branch can be discharged quickly to guarantee that the proposed HCB is available for the next interruption. Detailed analysis and design equations are also provided to describe the operation of proposed HCB. The proposed HCB is simulated in Matlab/Simulink and simulations are used to analyze the performance of the HCB under the different conditions. Moreover, the proposed DCCB topology is validated using prototype experiments. [ABSTRACT FROM AUTHOR]

Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In modern railway traffic systems, direct current (DC) electrification is a prevalent choice, with numerous traction networks adopting a variety of voltage levels to accommodate varying load current dynamics. These dynamics are influenced by passenger density, aggregate demand for electrical power, headways, and frequency of locomotive operations. Load currents are prone to surges during periods of dense traffic and transient phases such as acceleration, deceleration, and the start–stop sequences of trains. Such surges hold the potential to precipitate fault currents within the traction system, which are similar to those engendered by external anomalies. Conventional protection systems, such as the Détection Défaut Ligne’—French for ’Line Fault Detection), may not always effectively identify remote faults or prolonged overcurrent situations. These scenarios necessitate an advancement beyond the traditional fault detection methodologies, which primarily rely on fixed thresholds and may not account for the dynamic nature of the railway system’s electrical load. This paper addresses the limitations inherent in the existing DDL protection mechanisms by focusing on the feeder attributes specific to the DC Traction System. In pursuit of this objective, we introduce an innovative adaptive current DDL algorithm to refine the rigid threshold paradigm inherent in the conventional approach. To facilitate a pragmatic assessment, the Rapid Rail network of Malaysia serves as a reference for emulating the railway’s electrical system. This comprehensive analysis yields insights that are potentially useful for safety protocols in DC electrified railroad traffic systems.

Decaying DC offset frequently emerges as a major issue in power systems, especially under fault conditions. This leads to a distortion in the current waveform associated with the fault, which could significantly challenge protective and control mechanisms, possibly leading to their malfunction or breakdown. These decaying DC components (DDCs) complicate the extraction of critical parameters such as the current magnitude and phase angle of the fundamental frequency component from fault signals, which is crucial for the accurate operation of protective relays. Discrete Fourier Transform (DFT)-based algorithms are frequently used for phasor estimation, but their accuracy suffers when confronted with decaying DC components (DDCs) in power system fault currents. The low sampling rate further exacerbates the inaccuracy of DFT-based estimations, leading to inaccurate fault detection by protective relays. This paper comprehensively reviews three innovative methods that leverage the Multiple Delayed Signal Cancellation (MDSC) filter to overcome these limitations. The MDSC-based phasor estimation effectively attenuates the DDC component, enabling precise and rapid phasor estimation, benefiting from its higher sampling rate, and enhancing accuracy in relaying applications. The theoretical foundations of each method are analyzed, with an emphasis on their unique advantages and potential applications in digital relaying and power system protection. This review provides valuable insights into the latest advancements in DDC elimination, offering a pathway to more reliable and efficient fault analysis in power systems. Numerical and simulation tests unequivocally demonstrated the effectiveness of the proposed approach by showcasing its superior performance compared to four other phasor estimation methods. The proposed methods demonstrated exceptional performance in conditions plagued by multiple DDCs, harmonics, noise, and off-nominal frequencies, achieving fast and precise phasor estimation.

This paper presents the impact of adding single-phase photovoltaic systems on the fault current of short-circuit faults in asymmetric 400 V low-voltage feeders. This study also attempts to investigate the impact of various parameters on the fault current, such as the penetration coefficient of photovoltaic systems, the impact of downstream or upstream fault on the system installation location, and distance of photovoltaic systems and fault location. Simulations were carried out in the DIgSILENT software. The results show that the fault current will be more different when using photovoltaic systems and that difference is sometimes incremental and sometimes decremental. Therefore, if the penetration coefficient of the system is high, it will sometimes have a significant impact on the protection system. [ABSTRACT FROM AUTHOR]

Dc microgrids (MG) have drawn more attention due to the demand for renewable energy sources, energy storage devices in distributed generation, and the separation of DC loads requiring more power converters. This system needed protection DC circuit breakers (DCCB) that could quickly isolate the faults in the system. These devices must be as small and light as possible but should only produce low power loss during the ON state. The impedance source DC circuit breaker was introduced as an improved structure (SSCB) which provided automatic turns off without needing external command due to its natural commutation operation principle. In addition, it had many advantages such as faster response, simpler control design, restricted fault current magnitude, which makes the system more fault-resilient, the fault current will not affect the source or the SCR, coordination of cascaded breakers is automatic, and convenience for protection with power converters. This paper presents different impedance source DC circuit breakers such as ZCB, ΓCB, TCB, and YCB. It will show their benefits and drawbacks, which could be used as a helping guide while choosing which type of impedance source DC circuit breakers is suitable for a specific application. General Statement: The Impedance source circuit breakers are developed from the solid-state DC circuit breakers. They had been preferred over the traditional types of DCCB in protection systems because of their various advantages, such as the fastest response that could isolate the fault in microseconds, automatically isolated without needing external control or sensing elements, and so forth. This paper is the first review paper on the different kinds of Impedance source circuit breakers. It also presents different impedance source DC circuit breakers such as ZCB, ΓCB, TCB, and YCB. Moreover, showing their benefits and drawbacks. So, it provided a helping guide when choosing an impedance source DC circuit breaker suitable for a specific application or as a reference guide for additional research or topological enhancements. [ABSTRACT FROM AUTHOR]

Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

[Introduction] With the rapid development of AC/DC distribution networks and distributed generation technology, the role of DC microgrids in distribution networks is becoming increasingly important and will become an important component of future distribution networks. Due to the small coverage area and low line impedance of the DC microgrid, when an inter pole short circuit fault occurs, the fault current increases rapidly and has a large amplitude, which can reach more than 10 times the rated working current. This makes it difficult to set the protection of DC microgrids and requires high equipment selection, which restricts the rapid development of DC microgrids. [Method] In response to the above issues, taking the DC microgrid as the research object, starting from the working principle of inter pole faults in the DC microgrid, the fault characteristics on the DC side of the DC microgrid were analyzed. In response to the shortcomings of existing main current limiting methods, a voltage controllable fault current controller was proposed to achieve precise control of fault current. The simulation model of DC microgrid and fault current controller was built for simulation verification. [Result] The simulation results show that the fault current controller can significantly reduce the fault current and achieve precise control of the fault current, making the system controllable before and after the fault without locking the protection. During steady-state operation, the fault current controller can also assist the VSC (Voltage Source Converter) in further stabilizing the DC bus voltage. [Conclusion] To cooperate with the normal operation of the relay protection device and avoid VSC triggering overcurrent protection blocking, it is recommended to set the fault current control range between 1~2 pu.

Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Microgrids of varying sizes and applications are regarded as a key feature of modernizing the power system. With modern technologies, sources of renewable energy are paving the way in microgrid power systems through various converter topologies. However, distortion is caused by harmonics in an electrical system for which many strategies aimed to reduce harmonics in the power system, but they failed to detect harmonics induced by high impedance defects. Also, the occurrence of distortion in power and current discrepancy leads to stability issues of the converter. Hence this research addresses these problems through a novel Harmonic Response Technique using a Packet wavelet transform based high impedance fault diagnosis which determines the distorted current waveforms leading to harmonic energy levels. Furthermore, to minimize the fault current distortion, a Feedback controlled fault current limiting Converter is employed which regulates the system by utilizing a shunt active power filter in a fault current limiter. Moreover, power discrepancy in transition is balanced by accepting a novel Balanced Phase Transition Technique which determines the energy consumption over the current demand period using reactive power & a load factor of the converter using triangular functions which ensure a balanced load phase angle and helps in a smooth transition between phases. Thus the adopted techniques are simulated in the Simulink platform and the consequences depicted a good level of effectiveness in response, balance, and control of the suggested system. [ABSTRACT FROM AUTHOR]

Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Due to the demand for eco-friendly energy, distributed energy resources (DERs) using renewable energy have increased. The increase in DER has caused the power system to become more complex and caused problems in the protection system. Typical problems include an increase in fault current and a problem that causes malfunction of the overcurrent relay (OCR). If the fault current increases and exceeds the capacity of the existing protection devices, it may lead to a large blackout. The most effective way to limit the fault current is to install a superconducting current limiter (SFCL). The installation of SFCL and system penetration of DER both affect OCR operating characteristics. In this paper, a simulated power distribution system is constructed and OCR malfunctions caused by DER penetration and SFCL installation are analyzed. [ABSTRACT FROM AUTHOR]

Copyright of Southern Energy Construction is the property of Southern Energy Construction Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The fault characteristics of direct current (DC) grids can be analyzed by addressing the grid damping characteristics. However,the frequency-dependent characteristics of the transmission line parameters are usually ignored in the conventional grid impedance modeling methods,which cannot accurately reflect the grid damping characteristics. To compare and analyze the fault currents characteristics of the DC grids with cables and overhead lines,an impedance model of DC grid considering the frequency-dependent characteristics of the transmission line parameters based on vector fitting is proposed in this paper. Then,the proposed model is applied to compare and analyze the fault current features including time delays,initial rising rates and amplitudes of the DC grids with cables and overhead lines. Meanwhile,the impacts of the DC grids key parameters on the fault current characteristics of the two DC grids are investigated. Compared with the sweeping results of the frequency-dependent line model,the proposed model performs well in reflecting the damping characteristic of the DC grid,where the root square error is less than 0.6,informing that the proposed model is much more accurate than the simplified model. Finally,the simulation is conducted in a symmetrical monopolar two-terminal DC grid with pole-to-pole fault. The simulation results show that the fault current rising rate of the DC grid with cables is 24.96% higher than that of the DC grid with overhead lines when the arm inductance is increased,which validates that the fault currents of the DC grids with cables are more sensitive to the inductive key parameters than the DC grids with overhead lines.

In order to enhance the security of ±800 kV High-Voltage DC (HVDC) system, it is needed to consider and analyze the grounding mode of the neutral point of converter transformer. Different neutral grounding modes have different inhibitory effects on the current of transmission lines when faults occur, and also produce different overvoltages at the neutral point. Therefore, this paper first analyzes the influence of converter transformer on fault current and neutral point voltage in three cases of ungrounded, direct grounding and via small reactance grounding. Through the analysis, it is known that the neutral grounding via small reactance is the most suitable for the HVDC transmission system. Then the model of ±800 kV bipolar HVDC transmission system is built in PSCAD/ EMTDC simulation software and analyzed under two typical conditions of grounding overvoltage and breaking overvoltage. By comparing several cases of converter transformer neutral point grounding directly, via 5Ω, 10Ω, 17Ω, 20Ω and 25Ω reactance grounding, it is found that grounding via small reactance can effectively suppress fault current. However, with the increase of the resistance value, the inhibitory effect will gradually weaken and cause the increase of the neutral point overvoltage.

Many modern limiting methods have been developed for power systems in recent years. Resistive superconductor fault current limiter (R-SFCL), one of the modern limiting methods, has advantages such as small size and low cost. R-SFCL, which theoretically transmits energy without loss in normal operation, becomes high resistance in case of fault and reduces fault current level. However, R-SFCL, which rapidly increases its resistance during a fault, cannot immediately switch to superconductivity after the fault. During this period, which is called the recovery time, R-SFCL causes unwanted voltage drops and power losses under normal operating conditions. Therefore, recovery time is an important design parameter that should be kept short. With the bypass breaker proposed in this study, the recovery time was shortened, and voltage stability was improved. In addition, the system's reliability is increased by providing breakers' controls from two different points instead of a single point. This method is a hybrid system where limiting and protection elements are combined in one system. Modeling and simulations were performed in MATLAB/Simulink. [ABSTRACT FROM AUTHOR]

By increasing load demands and extending power networks to respond to customers' needs, the complexity and integration of power systems have been boosted, increasing the system's short circuit current level, which may threaten the network's reliability. Over the years, some approaches have been proposed to deal with this issue. Proper examples are reconfiguring networks, increasing circuit breakers (CBs) capacity, and implementing fault current limiters (FCLs). Reconfiguration and increasing CB rating have applied exorbitant costs to the system, and in some cases, it may be infeasible. Hence, FCLs can play a pivotal role in the mitigation of the fault current level, but the effectiveness of FCLs depends on the numbers and impedance of FCLs. In this paper, a novel and multi-objective approach is presented to optimize three objective functions simultaneously: decreasing the short circuit level, increasing the systems reliability level, and minimizing the costs of FCL installation. The adaptive penalty factor and Pareto-based multi-objective evolutionary algorithm based on decomposition are used to optimize the objectives mentioned above. Numerical and graphical results of optimization studies in MATLAB software on the IEEE RTS 24-Bus system confirm the proposed method's competence. [ABSTRACT FROM AUTHOR]

For the problem of fault isolation and power flow control in DC grid, this paper proposes a DC power flow controllable multi-port DC circuit breaker. Under the normal operation, this breaker has the function of DC power flow regulation, which is used to regulate the power flow on DC lines. After the DC system fails, this breaker is equivalent to the hybrid DC breaker, which is used to cut off the fault current and isolate the fault line. In the paper, the steady-state power flow regulation mechanism and transient current interrupting mechanism of the breaker are described in detail. Finally, a meshed DC grid is built in PSCAD/ EMTDC simulation platform. The simulation results show that the proposed topology has good performance in power flow control and current interrupting.

A hybrid sliding mode controller is proposed for rapid earth fault current limiters (REFCLs) used in resonant grounded power distribution networks to self‐extinguish powerline bushfires where the concepts of the proportional integral (PI) action and nonsingular fast terminal sliding surface (NFTSS) are combined together to utilize the benefits of both schemes. A hybrid sliding surface is designed for obtaining the control input so that the fault current compensation is achieved by the residual current compensation (RCC) inverter used within a REFCL to a value that the fire does not ignite. The inclusion of an integral action along with the NFTSS helps to significantly reduce the chattering effect. Furthermore, a continuous function is introduced within the proposed scheme to replace the discontinuous signum function. The switches for the RCC inverter are controlled by deriving control actions from the Lyapunov stability theory applied on the hybrid PI‐NFTSS. The performance of the proposed controller is compared with a nonsingular fast terminal sliding mode controller. For this reason, this paper also includes the design process of nonsingular fast terminal sliding mode controller which is designed using only the NFTSS. Simulations under different scenarios having different fault resistances clearly depict the superiority of the proposed scheme over the nonsingular fast terminal sliding mode controller and an existing integral sliding mode controller in terms of maintaining transient responses. [ABSTRACT FROM AUTHOR]

The full-cycle discrete Fourier transform (FCDFT) is commonly used to estimate phasors in numerical relays because of its immunity to harmonics and accurate identification of a decaying dc component (DDC) in a fault current. For fast protection of power systems, it is necessary to speed up the phasor estimation by using a data window below one cycle. The conventional least squares (LS) methods below one cycle approximate the DDC as the first several terms of the Taylor series expansion, which degrades the phasor-estimation accuracy. This paper proposes an LS method that uses Fourier analysis for approximation of the DDC to speed up phasor estimation without accuracy degradation. The phasor-estimation accuracy of the proposed method is investigated for the data-window length in simulations using synthetic data of fault currents containing DDC, harmonics, and measurement noise. The phasor-estimation speed is also investigated with respect to the delay of the antialiasing filter in the numerical relay. The proposed method is compared with the conventional LS and FCDFT methods in simulations using synthetic fault-current data. The feasibility of the proposed method is demonstrated through the phasor estimation of simulated transmission-line faults. [ABSTRACT FROM AUTHOR]

The paper proposes three new algorithms for estimation of the fundamental phasor in a power system, based on the removal of exponentially decaying DC components (DDCs). These components, as well as high-order harmonics and noise components, have a considerable effect on the accuracy and speed of convergence in numerical and digital relays speed of the protection relay operation. A discrete Fourier transform based approach with a modified Prony method was used to calculate and remove the unwanted effect of DDCs in a time interval slightly longer than the period of the fundamental harmonics. The use of an FIR notch filter leads to an algorithm that offers the possibility to estimate the parameters of unwanted DDCs in a simpler and analytically more precise way, thus facilitating their program implementation. The first two algorithms offer the ability to easily adjust the response speed detection time. This flexibility of the algorithms provides a compromise in terms of response speed and expected reliability and security of fault detection. In the third algorithm developed based on the application of the Least Error Squares method, new analytical expressions for estimating the parameters of the processed current signal are derived. The developed algorithms have low numerical and computational complexity, while maintaining their high performances even in conditions of a very strong noise signal. The simulation results for different test signals demonstrate high precision in the estimation of fundamental phasor of the proposed algorithms. [ABSTRACT FROM AUTHOR]

In bushfire-prone regions, powerline faults, notably single line-to-ground (SLG) faults, are significant contributors to wildfires. In order to promptly mitigate conflagration risks and reduce fault currents from SLG faults, the resonant grounded (RG) technique is implemented. Nevertheless, the literature has not reported a comprehensive derivation of SLG faults using this grounding method. The dynamic phasors method is used in this study to extract fault current characteristics, which are subject to substantial variations under various operating conditions, including harmonics, fault impedance variations, and the compensation levels necessary for resonance. The behavior of fault currents resulting from SLG faults is analyzed in this work by first deriving the fault current under RG conditions, accounting for leakage parameters, and subsequently incorporating harmonic components. The simulation results unequivocally demonstrate that the fault current retains a residual component, even under ideal resonance conditions, and that the ground fault neutralizer does not suppress this residual fault current. The analysis presented indicates that it is imperative to exercise caution when selecting the resonant grounding approach. Further, this method can be employed to extract the remaining fault current component, which is not explicitly accounted for, in order to identify faulty feeders in nonlinear high impedance fault scenarios. • A detailed derivation process for the SLG fault current in an RGPDN. • An evidence about the presence of harmonics in the fault current during the fault. • The necessity of utilizing the RCC inverter for fault compensations. • Revealing different components of the fault current in an RGPDN. [ABSTRACT FROM AUTHOR]

The National Society of Electricity and Gas of Algeria (SONELGAZ) is interconnecting the national power grid with the isolated power grids in the south of the country. One such grid is the Pole In Salah-AdrarTimimoune (PIAT). It is an exceptional power grid of considerable installed renewable energy sources values. The paper investigates the short-circuit phenomenon in the PIAT. The share of the renewable sources in the PIAT fault current is studied, and the difference between fault currents with and with-no integration of renewable sources are studied in order to find out if the protection parameters need to be changed in the case of the absence of renewable sources. Also, to interconnect the PIAT with other power grids, the PIAT short-circuit power is studied at different short-circuit points in the current situation and after the planned increase in the PV installed power. It is shown that the actual installed renewable sources contribute to the fault current with less than 10 % regardless of the fault position. Increasing the installed power by 300 % would increase the short-circuit power with less than 10 %. A method is suggested to determine the power grid short-circuit power using the short-circuit admittance instead of the impedance. [ABSTRACT FROM AUTHOR]

Low currents and voltage levels in a microgrid system make the fault detection by the conventional methods, very difficult. Due to ground faults voltage level drops to a very low level and thus, it becomes even more difficult to detect in case of a microgrid system. In this paper, a method of fault location identification and discrimination of fault type has been proposed. IEEE standard 14 bus microgrid system has been considered for this purpose. Faults are made to occur in two specific load buses and the outgoing currents of two generator buses were analysed in different conditions. S-Transformation is performed on the generator bus outgoing currents and kurtosis of the S-Transformation matrices has been calculated. An algorithm has been proposed for the detection of fault type and location. It has also been verified with different unknown cases. The simulation is carried out on the IEEE standard 14 bus system using MATLAB. The method presented here may be useful for the design of better protection schemes for such systems. [ABSTRACT FROM AUTHOR]

The contribution current of an inverter-interfaced distributed generator unit during a fault is one of the significant challenges for two modes: grid-connected and isolated AC microgrid. For this challenge, this article is aimed to study two methods of fault current calculation for two modes: grid-connected and isolated microgrids. These methods include a virtual equivalent impedance and a proposed method. The proposed method is a new technique for calculating the fault current contribution depending on the droop control of inverter-interfaced DG. The proposed method can control the contribution short-circuit current of DG within its limit (2 p.u.) where it is dependent on the voltage value of the DG bus to calculate the short circuit current of DG by using the control criterion. Static security risk and load shedding are calculated after fault clearance using an operation scenario in which the distribution system will be divided into small subsystems and is then grid-connected and isolated due to the removal of the faulted bus by protection devices. The proposed technique is applied to a standard IEEE 33-bus distribution network with five DGs. The results show that the contribution current of inverter-interfaced DG during the fault has more effects than the fault current of the nearest faulted bus to the DG bus. The proposed technique improves the calculated fault current value by about 30% for the grid-connected microgrid and by about 50% for the isolated microgrid from its value of the virtual impedance method. The static security risk is improved after load shedding. The static security risk improved by about 0.025%. [ABSTRACT FROM AUTHOR]

Distributed energy resources (DERs), recently introduced into distribution systems, are mainly inverter-based distributed generations (IBDGs), which have different short-circuit behaviors from conventional synchronous-based distributed generations (SBDGs). Hence, this study presents a comprehensive analysis of the short-circuit behaviors of distribution systems with IBDGs, based on sequence networks and superposition, from the perspectives of interconnected transformers, and observes the flow of zero-sequence fault currents with different transformer topologies. Moreover, two- and three-winding transformers with various bank connection types and groundings are investigated. It was concluded that the transformer topology and its grounding influence the fault current contribution in zero-sequence networks, and the high penetration of IBDGs alters the fault current magnitude and phase angles. [ABSTRACT FROM AUTHOR]

Today, there is a significant increase in electricity consumption with population growth, expansion of residential areas and industrial areas, and the development of technology. Parallel to this, with the increase in production capacity, high current levels caused by faults in the system for various reasons create dangerous situations for the system and the elements in the system. Limitation of fault currents provides protection of the system and system elements from the compelling thermal, dynamic and electromagnetic effects of these currents. In this study, the structure and working principle of Resistive Superconducting Fault Current Limiters (R-SFCL), which is one of the modern fault current limiting methods, are investigated. In addition, the real data obtained by performing the R-SFCL design in the laboratory environment and performing the faults in the created experimental system, and the simulation results performed with MATLAB/Simulink are compared. [ABSTRACT FROM AUTHOR]

The two main challenges of medium voltage direct current (MVDC) distribution network are the flexible control of power flow (PF) and fault protection. In this paper, the power flow controller (PFC) is introduced to regulate the PF and inhibit the fault current during the DC fault. The coordination strategy of series-parallel PFC (SP-PFC) and hybrid DC circuit breaker (DCCB) is proposed. By regulating the polarity and magnitude of SP-PFC output voltage during the fault, the rising speed of fault current can be suppressed so as to reduce the breaking current of hybrid DCCB. The access mode of SP-PFC to the MVDC distribution network and its topology are analyzed, and the coordination strategy between SP-PFC and hybrid DCCB is investigated. Moreover, the emergency control and bypass control strategies of SP-PFC are developed. On this basis, the mathematical model of SP-PFC in different fault stages is derived. With the equivalent model of SP-PFC, the fault current of the MVDC distribution network can be calculated accurately. A simulation model of the MVDC distribution network containing SP-PFC is established in MATLAB/Simulink. The fault current calculation result is compared with the simulation result, and the effectiveness of the proposed coordination strategy is verified.

Due to load growth and various load types within the service territory, utilities need to enhance the utilization of substations. In any case, towards the coordinated substation design, the utilization of the transformers’ most total capacity cannot be reduced just because there is a lack of proper coordination between transmission and distribution systems. The transmission and distribution systems’ stability and safe operability must be investigated in a coordinated substation. The critical issues are the asymmetric fault currents on the high voltage and arc-related safety issues on the distribution switchgear at different dynamic loading scenarios. We found that when one 138 kV transmission line and two transformers are energized, with increased dynamic loading, from 40% and above, the substation, as a whole, gets gradually more stressed. Because of the highest amount of fault currents on the 138 kV bus, to avoid CT saturation, we need to consider that three transmission lines are connected, and all three transformers are running at 100% dynamic loading. At this value of dynamic loading, in the 13.2 kV switchgear, the incident energy is 2 cal/cm2, and the arc flash boundary is four feet, which ensures that all workers need to wear the proper arc-rated clothes to work on any de-energized cubicle of the switchgear.

Utility encounters situations like when one out of two power transformers in the substation requires maintenance and only one transformer remains in operation. To meet the load requirements of a maximum number of customers, if not all, the only transformer needs to be overloaded. Due to various load types within the service territory, utilities need to understand the customers' maximum dynamic loading amount to overload a transformer in an emergency. We propose the iteration process with real-world substation data, which considers the concept of a coordinated substation for optimal power flow. We found to what extent the only 138 kV//13.8 kV, 30/40/50 MVA transformer can be safely overloaded beyond its nameplate's maximum rating for a minimum time. Within that time, the utility personnel can work on the substation yard and switchgear room safely and comfortably to bring back the other transformer in operation. We found from the perspective of power flow that with increased dynamic loading, transformer secondary current increases. Therefore, under the maximum dynamic loading condition, we should calculate the asymmetric fault current on the 13.2 kV switchgear bus to select the suitable CTs and develop a protection scheme accordingly.

In this paper, a new approach to an optimized overcurrent protection in a distributed real city grid is presented. A superconducting fault current limiter (SFCL) can be used for solving overcurrent problems. The most important overcurrent problem in the grid are the short circuit currents, especially in high voltage lines. Therefore, many devices connected to the grid could be damaged. In spite of the protection advantages of the SFCLs, using them for all connection nodes of the grid is an expensive and complicated solution. If the optimal points of the grid to use the SFCL are decided, the most appropriate number of SFCL can be used. A 2.026 MW powered distributed real city grid application is realized in Sincan providence in Ankara City. Also, the distribution line is 0.4 kV and the transmission line is 34.5 kV. Besides, the distributed grid is fed by two generators and two renewable energy sources which are a wind turbine and a solar power plant. Electricity consuming parts of the grid are greenhouses, loads and electrical transmission/distribution/customer lines. In order to analyse the grid, two options are simulated. Firstly, any resistive type superconducting fault current limiters (RSFCL) have been used for short-circuit protection. Results of the first option are not acceptable according to overcurrent standards. The second option is that RSFCLs are used at the optimal points of the grid. Optimal nodes are founded by the genetic algorithm. When the RSFCL is positioned at the determined optimal points, the fault current in some busbars has been obtained 82.78% less.

With the increased demand for permanent magnet synchronous machines (PMSMs) in various industrial fields, interturn short fault (ITSF) diagnosis of PMSMs is under the limelight. In particular, to prevent accidents caused by PMSM malfunctions, it is difficult and greatly necessary to diagnose slight ITSF, which is a stage before the ITSF becomes severe. In this paper, we propose a novel fault indicator based on the magnitude and phase of the current. The proposed fault indicator was developed using analysis of positive-sequence current (PSC) and negative-sequence current (NSC), which means the degree of the asymmetry of the three-phase currents by ITSF. According to the analysis, as ITSF increases, the phase difference between PSC and NSC decreases and the magnitude of NSC increases. Therefore, the novel fault indicator is suggested as a product of the cosine value of the phase indicator and the magnitude indicator. The magnitude indicator is the magnitude of NSC, and the phase indicator means the phase difference between the PSC and the NSC. The suggested fault indicator diagnoses the degree of ITSF as well as slight ITSFs under various conditions by only measured three-phase currents. Experimental results demonstrate the effectiveness of our proposed method under various torque and speeds. [ABSTRACT FROM AUTHOR]

This paper proposes a simulation model to calculate short-circuit fault currents in a DC light rail system with a wayside energy storage device. The simulation model was built in MATLAB/Simulink using the electrical information required to define a comprehensive DC traction power rail system. The short-circuit fault current results obtained from the simulation model were compared with hand calculation results obtained using EN 50123-1 guidance. The relative error was 1.02%, which validates the model. A case study was carried out for a 1500 V DC light rail system. In the case study, a method was proposed to assess the DC protection and the withstand and breaking capacity of the DC circuit breakers for maximum current and distant faults. A traction power modeling simulation was conducted for the 1500 V DC light rail system to calculate the maximum load current in the analyzed electrical sections. It is concluded that the proposed simulation model and fault methodology can be used for DC protection settings calculations and DC circuit breaker rating analysis. [ABSTRACT FROM AUTHOR]

The increasing permeation of the distributed generators in the power system brings great challenges for fault diagnosis, especially for the distribution networks with ungrounded neutral or grounded by Peterson coil as the fault current is limited and easily affected by the noises and interferences. A single phase‐to‐ground fault section identification method is proposed based on feature extraction of the synchronous waveforms and the calculation of the eigenvalues for the time‐sequenced features. First, several fault features are defined and extracted from the synchronous current waveforms obtained by the fault recorders. Then, the topology related fault feature matrix is constructed using the time‐series features obtained from different measurement sites, and the eigenvalues of the matrix are calculated based on the random matrix theory. Lastly, using the distribution characteristics of the eigenvalues, improved K‐means clustering algorithm is utilised in classifying the fault cases and identifying the faulty sections. The effectiveness of the proposed scheme is verified by IEEE 34 nodes test system and a multi‐feeder distribution network.