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A single-phase earth fault section location method based on fault component phase current in non-solidly earthed distribution networks is proposed. During a single-phase earth fault, the fault component currents of three phases obtained from the healthy lines and the sections at the back of the fault point are of the same amplitude and waveform, whereas those differ a lot in the sections between the fault point and the bus. On the basis of this characteristic, a fault section location method is put forward: earth fault detection devices are installed at every section, and each one measures and compares its three phase fault component currents independently, thus the sections between the fault point and the bus are identified, and the fault section location is achieved combining with the network topology. The detailed flow chart and criteria are also given. Simulation results prove the validity and reliability of the method proposed. This novel method requires only current signals, involves a simple principle and a bootstrap characteristic, and is expected in practical application in distribution networks. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

• Based on a control and protection coordination. • Taking into account the fault current limiting stage for the protection principle. • The amplitude distribution of injection signal is used to distinguish permanent fault. • Considering the fault impedance and distributed parameter model. • Less affected by the sampling rate and noise. To further improve the capability of fault identification for protection and adaptive reclosing, a fault identification scheme based on a control and protection coordination strategy for a hybrid multi-terminal HVDC system is proposed. The protection principle for fault isolation is constructed based on the difference of the polarity characteristic of fault current between the fault line and non-fault line in the uncontrolled fault stage and fault current limiting stage. In the adaptive reclosing stage, an active fault identification scheme based on the amplitude distribution law of the injection signal along the line is proposed. Intensive simulation studies prove the fault identification scheme can identify the fault area in various fault scenarios and identify permanent faults to carry out adaptive reclosing. [ABSTRACT FROM AUTHOR]

Abstract: An accurate fault location algorithm for parallel transmission lines, using fundamental frequency components of post-fault voltage and current measured at one terminal, is described in this paper. Parallel transmission lines can be decoupled into the common component net and differential component net. In differential component net, the current distributing coefficient is a function of fault distance, and the differential component current at the fault point can be expressed in terms of the current at the local terminal. Therefore, for asymmetrical faults, the phase fault current can also be expressed as a function of local terminal current and fault distance. With the fault boundary conditions for a given fault type, the fault location equations can then be derived. Based on distributed parameter line model, the proposed algorithm achieves superior locating accuracy, with mutual coupling between circuits, source impedance and fault resistance having very little influence on the locating accuracy. The performance of new algorithm is verified by computer simulation results for transposed and non-transposed lines. [Copyright &y& Elsevier]

Due to the special fault features of the inverter-interfaced system, traditional phase selectors exist adaptability problems. In this paper, a novel voltage phase selector based on a two-stage control strategy is proposed, which is not influenced by the special features of the converter. First, the fault features of the converter during fault ride through (FRT) operation are analyzed. Second, using the high controlled-ability of the converter, the control strategy is divided into two stages by adding disturbances to the power references of the control system at the second control stage. On this basis, a novel superimposed sequence network is defined as the subtraction of the compound sequence networks under the first and the second control stage. Then, the phase-angle differences of sequence voltages in the novel superimposed sequence network are analyzed, which are not influenced by the fault features of the converter and can be used to establish phase selection criteria. The simulation results show that the proposed phase selection scheme is immune to the fault features of the converter system, fault resistance, fault location and the operation modes of the remote end system. [ABSTRACT FROM AUTHOR]

• The proposed scheme is based on single terminal and independent of the DC boundary. • The proposed scheme used signal injection strategy needed for fault identification and improve reliability. • The proposed scheme is for the multi-terminal DC grid. • The proposed scheme is for fault isolation and system recovery stage. Effective fault identification scheme plays an important role in the fault isolation stage and system recovery stage of multi-terminal DC grid. Therefore, an active detection based single-end DC fault identification scheme is proposed to improve the reliability and sensitivity of fault identification. The control strategy is suggested of the generation of sinusoidal signals at different frequencies by the hybrid modular multilevel converters. Based on the blocking effect of the fault branch on the injection signal, by introducing the improved correlation discrimination algorithm, a single-end fault identification scheme is proposed by using the amplitude difference between the measured and calculated values of injection signals. The proposed scheme can be used for fault isolation and adaptive system recovery. Intensive simulation studies prove the improved sensitivity, and reliability of the proposed scheme for the full length of transmission line without relying on DC boundary. Moreover, the scheme can identify the permanent fault during the system recovery stage. [ABSTRACT FROM AUTHOR]

In view of the difficulties in coordination between reliability and sensitivity of conventional generator differential protection, this paper presents a novel generator differential protection scheme based on a new braking method. On the basis of the mathematical model of the field-circuit coupling method and the electrical network cascade characteristics, the stator windings were combined and decoupled by the improved six-sequence component method to eliminate electromagnetic coupling between winding coils. In accordance with the basic characteristics of longitudinal impedance, the function of sub-item discrimination was realized. Numerous simulations and the up-to-date dynamic experiments showed that the proposed method has good state discrimination ability and can effectively resist the influence of current transformer saturation. Thus, it has an excellent prospect for engineering promotion. [ABSTRACT FROM AUTHOR]

• An adaptive auto-reclosing scheme for converter-interfaced wind park. • Improved distance relaying algorithm, not influenced by high fault impedance and infeed/outfeed effect. • Active detection and independent judgements to realize the fault identification. • No additional equipment needed for active injection. The 110 kV single outgoing line powered by wind generation usually adopts tripolar tripping and three-phase auto-recloser. The electrical quantities of the single line attenuate quickly after fault tripping, which makes it difficult to identify fault properties during the dead time. Also, due to the high voltage or frequency protection, the converter-interfaced wind generation is prone to be blocked after tripolar tripping. The machine-side circuit breaker is then reclosed temporarily. A fast adaptive auto-reclosing scheme is proposed for three-phase tripping scenarios by injecting sinusoidal currents from interface converter to the faulty line. By re-activating pulse width modulation (PWM) for a very short time, the interface converter works as STATCOM to regulate the output voltage and then an active current injection is realized. Improved distance relaying algorithm is deduced in this injection scenario to locate the fault and achieve fault property identification. After the confirmation of arc extinction, the triggering control of interface converter will be re-activated and the circuit breaker will be reclosed to restore power transmission. The proposed fast three-phase reclosing scheme is validated in PSCAD/EMTDC and the simulation results show the accuracy of fault identification and short reclosing time. [ABSTRACT FROM AUTHOR]

• A fault location method is based on the single-frequency injection signal. • Parameter identification method is utilized to realize fault location. • Fault impedance and distributed parameters of lines are considered. • Fequency parameters of line and numerical differential error are considered. • Less affected by sampling rate and does not need additional devices. The traditional fault location methods on DC lines are facing many challenges such as low reliability and unsatisfied location accuracy. To ensure a more reliable fault recovery of DC line, a single-ended fault location method based on active detection is proposed for hybrid modular multilevel converter based high voltage DC transmission systems. The high controllability of hybrid MMC is utilized to activate the control strategy of injecting a sinusoidal signal. Furthermore, based on parameter identification and compensation methods for the distributed parameter model, the fault location equation with fault impedance parameters is formulated. Finally, the fault location can be identified under different fault scenarios. Simulation results verify the effectiveness and accuracy of the proposed active detection method. The proposed method can pinpoint the fault location with a lower sampling rate, its accuracy is not influenced by increasing of the line length and variation of the fault impedance. [ABSTRACT FROM AUTHOR]

High voltage dc grids are raised high-speed operation and high reliability requirement for relay protection. This article aims at proposing a protection scheme with high operation speed, high sensitivity, and high reliability. First, the symbolic expressions of the line-mode fault component traveling wave in case of the internal and external faults are derived, which consist of the traveling wave propagation term and the dc line boundary term. It is theoretically demonstrated that the index of the traveling wave propagation term in case of internal faults is greater than that for the external faults, and the index is independent of fault impedance. Second, the Levenberg–Marquardt algorithm is introduced to extract the index and an index-based nonunit protection method as well as the protection scheme is proposed. The proposed method is theoretically robust and independent of fault impedance and fault type. In the validation, the fitting results are indicated that the symbolic expressions are correct and the extracted indices are effective to characterize the location of the faults. Numerous fault cases of different fault distances, fault impedances, and fault types have demonstrated that the proposed protection scheme is of high sensitivity, high operation speed, and high reliability. [ABSTRACT FROM AUTHOR]

Most of the existing methods for harmonic analysis are from frequency‐domain perspective. In fact, the essential factor for generating harmonics is non‐linear characteristic or time‐varying property. Therefore, the harmonic generation mechanism and the harmonic source location method are investigated from the time domain perspective in this paper. Firstly, a general model of non‐harmonic sources is established. The non‐harmonic sources will match well with the proposed general model while the harmonic source will not. Then correlation coefficient that reflects compliance degree between each device and the general model is defined for distinguishing harmonic sources from non‐harmonic sources. On this basis, a novel time‐domain harmonic source location method is proposed. Numerous simulations and experiments have demonstrated that the proposed method has good performance under fluctuations, saturations, pre‐distortions, transient process, and resonances. The defined correlation coefficient can reflect non‐linearity/time‐varying degree of the harmonic source, which can be used for evaluating harmonic emission level of each harmonic source. On this basis, a simple harmonic responsibility division method is proposed, which is immune to possible fluctuations, pre‐distortions, saturations, resonances, and impedance variation. [ABSTRACT FROM AUTHOR]

At present, the MVDC distribution grid is developing rapidly and relay protection is the key technology to ensure stable operation. Therefore, this paper focuses on the fault line selection method. Firstly, the fault characteristics are analysed when a fault occurs in the line, and a novel single‐pole fault line selection method is proposed based on 0‐mode power. The polarity of current fault component measured at the terminal of each line is used to identify the internal and external faults. And the 0‐mode power is used to select the faulty line. Finally, to verify the correctness of the proposed method, a radial MVDC distribution grid is built in PSCAD to output fault data in different fault conditions, and the fault line selection algorithm is implemented in MATLAB. The simulation results show that the proposed method is fast, effective, reliable and it has a certain degree of tolerance to transition resistance with a strong anti‐data delay and anti‐interference ability. Moreover, the fault line selection method proposed in this paper can still correctly select the fault line in the case of serious faults such as multiple line faults, sudden removal of lines, and sudden changes in photovoltaic output power. [ABSTRACT FROM AUTHOR]

The multi-terminal hybrid LCC/MMC HVDC has been applied to overcome the simultaneous commutation failure problem caused by the multi-infeed LCC-HVDCs in the East China. The high-speed and selectivity line protection method is required for the multi-terminal hybrid HVDC system. In this paper, the reflection and refraction of the fault traveling waves at different kinds of line terminals are characterized by transfer functions. Then the fault voltage as well as its first peak time at different line terminals when different internal and external faults occur are derived respectively. The conclusion proves that the first peak time of line-mode fault component voltage (FPTV) for internal faults is smaller than that for external faults, which is independent of fault impedance and fault type as well. Therefore, a FPTV-based non-unit ultra-high-speed dc line protection method is proposed. The algorithm is implemented in the developed protection prototype and validated in the Kun-Liu-Long three-terminal hybrid HVDC RTDS test system. The test results show that the proposed method can fast and correctly identify line faults in the multi-terminal hybrid HVDC system, even with 500 Ω fault impedance. Comparing with the traveling wave protection method of ABB, the proposed method improves the sensitivity when high-impedance faults occur. [ABSTRACT FROM AUTHOR]

There exist problems of hard coordination and threshold setting as well as low sensitivity in overcurrent relay due to the bidirectional and small fault current when distributed generators are integrated into the distribution network. This paper introduces ferrite rings (FRs) to act as boundaries of distribution feeders, and a peak time of voltage traveling wave‐based protection is proposed. The characteristics of FRs are analyzed and their feasibility as line boundary is validated. The fault characteristics of internal and external faults are analyzed when FRs are installed at both ends of the protected feeder. The results show that the peak time of the voltage travelling wave of the internal fault is far smaller than that of the external faults. According to the difference, the fault detection method and the protection scheme are proposed. Simulations in PSCAD and experiment validate that the proposed protection principle can reliably distinguish between internal and external faults. Besides, the proposed protection scheme has higher sensitivity compared to ROCOV‐based protection. [ABSTRACT FROM AUTHOR]

• An active fault identification method for passive networks supplied by MMC-HVDC. • The active injection utilized for both adaptive single/three phase auto-reclosing scheme. • Application to single-circuit and multi-circuit transmission lines. • Repeated injections and extra independent assessments can be supplemented to prevent misjudgement. Modular multilevel converter (MMC) shows prominent advantages on supplying passive networks, which are usually classified by power supply shortage and relatively weak structure. In order to reduce the unnecessary outage time and improve the system stability, an adaptive ac auto-reclosing scheme for passive networks is proposed based on characteristic signal injection. Additional MMC controller is designed to inject the characteristic signals into the healthy line, which in turn induces corresponding signals to the faulty line. Then fault properties are assessed by the travelling wave based fault location method. Finally, an adaptive auto-reclosing scheme is proposed to shorten the reclosing time and avoid the second fault shock to a large extent. The proposed scheme could be applied for both single-circuit and multi-circuit transmission lines. The simulation results obtained from PSCAD/EMTDC verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The existing relay protections for line‐commutated converter (LCC)‐ultra high voltage DC (UHVDC) transmission lines are insufficient in protection sensitivity and operation speed. The travelling wavefront fault distance information can be used to improve protection performance, which has been used in protection of voltage source converter ‐high voltage DC (HVDC) transmission lines. The adaptability of travelling wavefront protection in LCC‐UHVDC transmission line is analyzed in this paper. First, the conditions that need to be met for the travelling wavefront protections to be able to effectively recognize faults are analyzed. Eight applicability conditions of wavefront protection are revealed from the perspective of travelling wavefront generation and practical application requirements. Then the degree of match between the applicability conditions and the conditions of LCC‐UHVDC system is analyzed as a basis for assessing the adaptability of travelling wavefront protection in the LCC‐UHVDC system. It is pointed out that the index coefficient‐based wavefront protections are not available for LCC‐UHVDC transmission lines since the hardware sampling rate of protection device is insufficient, while first peak time of transient voltage (FPTV)‐based wavefront protection is available for LCC‐UHVDC transmission lines if it has enough anti‐noise ability. Finally, an enhanced anti‐noise algorithm is proposed for the FPTV‐based travelling wavefront protection. The adaptability of the travelling wavefront protection is verified by hardware‐in‐the‐loop test and filed recording experimental data. [ABSTRACT FROM AUTHOR]

In order to improve the ability of the modular multi‐level converter to quickly clear and isolate faults in the multi‐terminal flexible DC grid, this paper analyzes the characteristics of current faults in the multi‐terminal flexible direct current grid, introduces the comprehensive distance of current fault waveform, and proposes a line protection method based on the similarity of current fault waveform. This protection method firstly uses Euclid Dynamic Time Warping (DTW) distance and entropy weight method to process electrical quantity signals, calculates the comprehensive distance of current fault waveform of two converter stations, and builds the protection criterion based on the similarity of current fault waveform. Then, the fault identification is realized by using the calculated comprehensive distance, and the fault pole identification is realized by using the ratio of comprehensive distance between positive and negative poles. Finally, PSCAD was used to build a simulation model to output the fault data under different fault conditions, and MATLAB was used to process the fault data to verify the protection algorithm. The simulation results show that the proposed method has good resistance to high resistance, and its rapidity and adaptability are further improved. Compared with other similarity methods, this method combines Euclidean DTW distance and entropy method to process the signal, realizes the fault pole identification, and can still operate correctly under the interference of 500 Ω transition resistance and 20 dB noise ratio. The research results will provide a theoretical basis for the safe and reliable operation of flexible DC power grid. [ABSTRACT FROM AUTHOR]

Single phase line‐broken (SPLB) fault is one kind of high impedance fault (HIF). When a SPLB fault occurs, there are four scenarios: SPLB fault with neither side conductors grounded (SPLB‐NSCG), with source side conductor grounded only (SPLB‐SSCG), with load side conductor grounded only (SPLB‐LSCG), with both side conductors grounded (SPLB‐BSCG). Traditional HIF detection methods using current or voltage characteristics have low sensitivity to SPLB fault. In this paper, voltage characteristics are analysed firstly in the cases of the first three scenarios of SPLB fault, respectively. Theoretical analysis finds that the voltage at both the sides of the disconnection point is significantly different. A high sensitive SPLB fault detection method based on differential voltage is proposed for radial distribution network with different data synchronization ability. Finally, SPLB fault location methods based on centralized intelligent mode feeder automation (FA) and intelligent distributed mode FA are proposed. Simulations based on PSCAD verify that the proposed SPLB fault detection method is feasible, highly sensitive and immune to the neutral grounded mode, fault scenarios and fault resistance. [ABSTRACT FROM AUTHOR]

• The waveform differences between the initial current forward traveling wave and the backward traveling wave are proven theoretically under internal and external faults. • The waveform similarity between the theoretically calculated curve and the fitted curve is introduced into the proposed method. • The proposed method does not require strict data synchronization and set setting values through simulation. • It can identify faults in situations with higher fault impedances, noise interference, and lower sampling frequency. The All-DC wind power generation system can effectively solve the harmonic resonance problem caused by large-scale wind power AC collection and transmission, gradually becoming a hot topic in future research. However, there are few studies on the relay protection of the All-DC wind power transmission systems. In the All-DC wind power systems, there are differences in topology, control strategies, fault characteristics, boundary characteristics, etc. At the same time, existing pilot protection has problems such as strict information synchronization requirements and selection of setting values through simulation. Therefore, the proposed pilot protection based on the similarity of the traveling wave between the quadratic fitting curve and the calculated curve for the All-DC wind power system transmission lines. Firstly, the difference of the 1-mode initial current waveform characteristics is analyzed in the time domain at both ends. Then, the least squares method is introduced to fit the differential curves of the current forward and backward traveling waves at two terminals. The differential characteristics of the differences between the fitted curve, the calculated curve, and the measured curve under the influence of internal and external errors are analyzed. Finally, the calculated value of traveling wave current during external metallicity fault is used as the standard. By comparing the fitting curve of current traveling waves and the difference in the calculation curve to distinguish internal faults from external faults. The simulation results show that the proposed protection principle can fault resistance of 2200 Ω and noise interference of 20 dB. In addition, the proposed method does not require strict data synchronization, higher sampling frequency, and setting value through simulation. [ABSTRACT FROM AUTHOR]

• The proposed ACLC fully utilizing the electrical quantities of the line to identify the fault area has achieved the selectivity of ACLC, preventing ACLC from expanding the scope of fault impact. • The proposed ACLC start-up threshold and control parameters are independent of the simulation. • The proposed ACLC presents a phased approach that satisfies both speed and selectivity. • The proposed ACLC can effectively limit the fault current and has certain adaptability to the fault type, fault resistance, and noise. The modular multilevel converters (MMC) based high-voltage direct-current (HVDC) grids have a fast rise rate and higher peak value of fault current. The active current limiting control (ACLC) of MMC can effectively reduce the breaking current of DC circuit breakers (DCCB) and reduce the requirement for rapid fault identification in the line protection. However, the current ACLC based on changing the MMC control strategy cannot meet the selectivity requirements. The lack of selectivity may lead to power transmission on non-faulty lines in a multi-terminal DC power grid, thus expanding the range of fault influence. Therefore, this paper proposed a selective and staged ACLC. Firstly, the starting range of ACLC is determined according to the selective requirement and purpose of ACLC in the flexible DC power grid. Secondly, a staged ACLC approach was proposed to balance the speed and selectivity of ACLC. In this approach, the single end and both terminals electrical quantities of the line are fully utilized as the starting criteria for staged ACLC, and corresponding ACLC principles are proposed. Finally, the AC side current and MMC bridge arm current under ACLC were analyzed, and an ACLC scheme was proposed in coordination with DC circuit breakers (DCCB) and fault identification. The simulation results show that the proposed ACLC guarantees the current limiting ability and the MMC does not block during the whole fault period, and has a certain adaptability to the fault type, fault resistance, and noise. [ABSTRACT FROM AUTHOR]

Abstract: This paper proposes a kind of new Individual Phase Impedance (IPI) and a novel pilot protection scheme for transmission line based on the IPI. The IPI is calculated by the ratio of the voltage difference of fault-superimposed component to the current difference of fault-superimposed component at both terminals of the protected line. The IPI has accurate mathematical expressions and reasonable physical definitions for various line models. The calculated result of IPI can be used to distinguish the internal faults from the external faults. When the IPI is identical to the value of line positive-sequence impedance, the external fault is detected; otherwise, the internal fault is detected if it differs from that value. The feature of the pilot protection scheme is that the inter-phase coupling relation and the distributed capacitance based on the three-phase line model are directly considered and included in the IPI expression. The novel pilot protection can be used for long distance HV transmission lines with some preeminent performances which are deficiency in the conventional directional comparison pilot protection and current differential protection. The test results obtained by EMTP simulation and from a laboratory model of a simplified real power system have demonstrated that the pilot protection is of high reliability and good adaptability. [Copyright &y& Elsevier]

• The research model is a hybrid three-terminal HVDC system model. • Wavelet threshold denoising and improved LMD algorithm are combined to calibrate the wave head. • A fault location method for hybrid three-terminal HVDC transmission line immune to wave velocity. To reduce the impact of traveling wave velocity, wave head recognition, and LMD (Local Mean Decomposition) end effect and mode mixing on location accuracy, this paper presents a fault location method based on improved LMD for hybrid three-terminal HVDC transmission lines, which is not affected by wave velocity. Firstly, the improved LMD is used to get the time when the fault traveling wave first arrives at the four measuring terminals. Then the fault branch is identified according to the ratio of the time of the fault traveling wave arriving at the measuring terminal. Finally, the equation is listed according to the principle of traveling wave location and the measurement equation which is not affected by the wave velocity is deduced. A hybrid three-terminal HVDC transmission system model is built by PSCAD to simulate various faults and output fault data under various fault conditions. MATLAB is used to process the fault data and verify the location algorithm. The simulation results show that the location method proposed in this paper is not affected by fault distances, fault types, infeed levels and transition resistances. In addition, it has higher accuracy than LMD based on CSI (Cubic Spline Interpolation) algorithm, wavelet packet location algorithm and double-ended location method of using wave velocity calculation. [ABSTRACT FROM AUTHOR]

In hybrid bipolar DC transmission systems with different types of converters at each pole, the transient high‐frequency component of the voltage signal under a single‐pole grounding fault and an inter‐pole fault is significantly different for internal and external faults because of smooth‐wave reactors on both sides of the DC line. Based on these characteristics, a single‐ended electrical quantity protection scheme based on transient energy is proposed. First, the voltage fault component is extracted and then processed by using a wavelet packet transform to obtain the transient energy in each frequency band. Second, the protection criterion is determined based on the ratio between low‐frequency energy and the sum of high‐frequency energy. After the setting principle is given, the influence of the protection scheme under high transition resistance is analysed. The protection scheme is implemented in MATLAB and tested based on fault data obtained from a hybrid bipolar HVDC transmission model built in PSCAD under different operating conditions. The effectiveness of the proposed protection method is verified by simulation tests under different fault types at different fault distances. The proposed method can provide strong tolerance to high transient resistance, accurately identify internal/external faults and automatically identify fault poles. [ABSTRACT FROM AUTHOR]

Abstract Traditionally, wind power and solar photovoltaic (PV) power generation is non-dispatchable and their normal operation relies on Maximum Power Point Tracking (MPPT) control. Therefore, it can be of highly disturbance to the system dispatch in particularly context of microgrids. To effectively fulfill dispatch command or market schedule, a novel cascading power sharing control (PSC) scheme is proposed to coordinate wind and solar PV power productions in microgrids while reducing the loss of renewable energy production involved. Considering different properties of wind and solar PV power generation systems, the discrepancies between dispatch command (market schedule) and actual renewable generation is firstly counterbalanced by adjusting wind power output via temperately storing or releasing kinetic energy of turbine rotors. Only when rotors of wind generator reach their limitations, should solar PVs begin to reduce their generation. The proposed PSC scheme is fully simulated in a microgrid with wind and solar PV, and the simulation results clearly indicate it can be more energy efficient than the traditional dispatch method while fulfilling the dispatch demand. Highlights • We focus on the power sharing control (PSC) in a microgrid with high penetration of renewables. • Energy production of wind generation (WG) and solar PV power generation is analyzed during PSC. • A novel cascading PSC scheme is proposed for fulfilling the dispatch order while reducing energy production loss. • The rotational mass of WG can be fully utilized for storing excessive energy and then released back when system needed. • The proposed scheme can be more energy-efficient than traditional one while fulfilling the dispatch demand. [ABSTRACT FROM AUTHOR]

• A reduced LCC model for DC fault analysis is proposed based Taylor expression, where the LCC-based rectifier with control effects is regarded as an equivalent RLC circuit. • By reserving only the high-frequency components of the Laplace fault circuit, the hybrid MTDC network is significantly reduced, and analytical expressions of the initial short-circuit current are derived. • A single-terminal DC fault detection scheme is designed for hybrid MTDC systems using the transient average of DC reactor voltage, which is steady and robust. The existence of various types of converters makes the fault characteristics of the hybrid multi-terminal DC (MTDC) system more complicated than the voltage source converter-based (VSC-based) MTDC system. A reduced line commutated converter (LCC) model for DC fault analysis is first proposed in this paper, where the LCC-based rectifier with control effects is regarded as an equivalent RLC circuit. By neglecting the resistive and capacitive components in the high-frequency domain, the original network analysis is significantly simplified to derive concise time-domain expressions of the initial DC fault current. On top of this, a single-terminal DC fault detection scheme using the transient average of DC reactor voltage is designed for the hybrid MTDC system. The thresholds for detecting faults on the LCC-connected and VSC-connected lines are calculated based on the derived fault current expressions, respectively. Simulation studies based on PSCAD/EMTDC have validated the proposed fault analysis model is accurate within the initial period after fault, while the proposed fault detection scheme for hybrid MTDC systems is fast, sensitive, and tolerant to high fault resistances. [ABSTRACT FROM AUTHOR]

The coupling of AC and DC power will impact the protective actions on the AC side and pose a threat to the stable operation of the interconnection system. Therefore, a new longitudinal protection method is proposed based on the comprehensive distance similarity of voltage waveforms. Initially, the measured voltage and current data are extracted to calculate the reference voltage, and the voltage waveform fitting is optimized. Subsequently, the Euclidean dynamic time warp (DTW) distance and entropy weight method are utilized to process the voltage waveform, enabling the calculation of its comprehensive distance similarity. This similarity is adopted to determine fault location. A hybrid DC multi-feed AC/DC interconnection system, incorporating a line commutated converter-voltage source converter (LCC-VSC) and a line commutated converter-modular multilevel converter (LCC-MMC), was established in PSCAD, and fault data were simulated and output. The effectiveness of the protection scheme was validated using MATLAB. Simulation results demonstrate that the proposed method can accurately distinguish between faults inside and outside a region. When compared to existing protection methods, it demonstrates superior performance in resisting transition resistance and noise interference, while also mitigating the impact of data asynchronicity. The speed and reliability of the method are further enhanced.

Knowledge of the molecular mechanisms of specific bacterial virulence factors can significantly contribute to antibacterial drug discovery. Helicobacter pylori is a Gram-negative microaerophilic bacterium that infects almost half of the world's population, leading to gastric disorders and even gastric cancer. H. pylori expresses a series of virulence factors in the host, among which high-temperature requirement A ( Hp HtrA) is a newly identified serine protease secreted by H. pylori. Hp HtrA cleaves the extracellular domain of the epithelial cell surface adhesion protein E-cadherin and disrupts gastric epithelial cell junctions, allowing H. pylori to access the intercellular space. Here we report the first crystal structure of Hp HtrA at 3.0 Å resolution. The structure revealed a new type of HtrA protease trimer stabilized by unique N-terminal domain swapping distinct from other known HtrA homologs. We further observed that truncation of the N terminus completely abrogates Hp HtrA trimer formation as well as protease activity. In the presence of unfolded substrate, Hp HtrA assembled into cage-like 12-mers or 24-mers. Combining crystallographic, biochemical, and mutagenic data, we propose a mechanistic model of how Hp HtrA recognizes and cleaves the well-folded E-cadherin substrate. Our study provides a fundamental basis for the development of anti- H. pylori agents by using a previously uncharacterized HtrA protease as a target., (© 2019 Zhang et al.)