Search Results (65)

Background: Autologous serum eye drops (ASEDs) are produced without preservatives and need to be stored at 2–8 °C while in use. This study aims to analyze the behavior of specific bacteria and fungi in the case of contamination during the usage of single-day use ophtioles containing ASED. Methods: This is a prospective experimental study conducted at the Department of Ophthalmology, University Hospital of Zurich (USZ), and a regulatory-licensed, independent, external laboratory. The laboratory performed microbial testing on the ASEDs with 11 microorganisms in 100% concentration or 50% diluted using the original 2.5 mL ASED ophtioles provided by the Eye Bank of the Department of Ophthalmology, USZ. Storage took place at 2–8 °C and 20–25 °C. The acceptance criterion was the absence of microbial growth between opening (T0), 24 h afterwards (T24), and 48 h afterwards (T48). Results: The acceptance criteria were met for all microorganisms for 2–8 °C. For seven microorganisms, the acceptance criteria were met for 2–8 °C and 20–25 °C. For four microorganisms, the acceptance criteria were only met for 2–8 °C. Conclusions: No relevant growth was observed in any of the test strains from T0 to T24 and T48 at 2–8 °C, demonstrating the microbiological safety of reclosable single-day use ophtioles containing unpreserved ASEDs when stored at 2–8 °C. Full article

Pollution flashover accidents of transmission line insulators have a wide impact and low reclosing success rates, posing a serious threat to the safe and stable operation of the power grid. The existing pollution discharge and flashover models of insulator based on equivalent salt deposit density (ESDD) present significant differences from the actual situation. To address this issue, the conductivity of electrolyte solutions experiments is carried out in this paper, and the quantitative functional relationship between conductivity and concentration of typical components is obtained. On this basis, the concept of effective salt deposit density (SDD_e) is introduced to characterize the actual mass of pollution participating in surface conduction per unit area. A DC discharge dynamic model for polluted insulators is established and verified based on SDD_e combined with the discharge development process. Research results indicate that the average difference between the calculated flashover voltage and experimental value is less than 7%. The deviation of flashover voltage between the SDD_e basis model and measured salt deposit density (SDD_m) basis value increases with the increasing proportion of slightly soluble components. With the increase of insulator surface water adhesion, the flashover voltage obtained by the proposed model decreases while the corresponding SDD_m basis value remains constant. The effects of factors such as slightly soluble pollution and surface water adhesion are considered in the proposed model sufficiently. The application of the model based on SDD_e can improve the accuracy of the insulator discharge process and flashover voltage prediction, especially for the complex pollution area. During the generation and propagation of the arc, the leakage current under SDD_m is relatively higher and the pollution layer resistance is lower compared to that under SDD_e; the variations in the pollution layer resistance and leakage current with arc development under SDD_m do not adequately reflect the actual conditions. Full article

To address the reclosing failures in the distribution networks (DNs) with high penetration of distributed energy resources (DERs), this paper proposes a communication-free cooperative fault recovery control method based on staged active power injection of an energy storage (ES) system. First, during the initial phase of a fault, a back-electromotive force (b-EMF) suppression arc extinction control strategy was designed for the ES converter, promoting fault arc extinction. Subsequently, the ES switches to grid-forming (GFM) control, providing active power injection to the network following the circuit breaker (CB) tripping. A time-limited variable power control of ES converter is also designed to establish voltage characteristics for fault state detection. And a fault state criterion based on voltage relative entropy is designed, helping reliable reclosing. Simulation results demonstrate that the proposed method achieves coordination solely through local measurements without the need for real-time communication between ES and CB, and can shorten the recovery time of transient faults to hundreds of milliseconds. Full article

The ongoing decarbonisation of power systems is displacing synchronous generators (SGs) with converter-based plants, requiring a consistent assessment of grid-following inverters (GFLIs) and grid-forming inverters (GFMIs). Using an openly available four-bus root-mean-square (RMS) benchmark modelled in DIgSILENT PowerFactory, this work compares three generation configurations: (i) a single local SG connected at the point of common coupling; (ii) the same generator combined with a GFLI; and (iii) the generator combined with a GFMI. These configurations are evaluated under three disturbance scenarios: (1) a balanced load step, (2) an unbalanced double line-to-ground fault at low short-circuit ratio (SCR) with temporary islanding and single-shot auto-reclose, and (3) full islanding with under-frequency load shedding (UFLS), partial resynchronisation, and staged restoration. For the tested tuning ranges and within this RMS benchmark, the grid-forming configuration behaves as a low-impedance source at the point of common coupling in the phasor sense, yielding higher frequency nadirs during active-power disturbances and faster positive-sequence voltage recovery under weak and unbalanced conditions than the SG-only and SG+GFLI cases. During islanding, it supports selective UFLS, secure resynchronisation, and orderly load restoration. Rather than introducing new control theory, this work contributes a reproducible RMS benchmarking framework that integrates low-SCR operation, unbalance, and restoration sequences with a documented cross-technology tuning procedure. The findings indicate system-level improvements in frequency resilience and voltage recovery for the tested benchmark relative to the alternative configurations, while recognising that instantaneous device-level effects and broader generality will require electromagnetic-transient (EMT) or hybrid EMT/RMS validation in future work. Full article

Unplanned islanding and off-grid issues of photovoltaic (PV) power stations caused by tie-line faults have seriously undermined the power supply reliability and operational stability of PV plants. Furthermore, it takes a relatively long time to restore normal operation after an off-grid event, leading to substantial power losses. To address this problem, this paper proposes a tie-line fault ride-through control strategy based on the coordinated control of on-site energy storage units. After a fault on the tie-line occurs, the control mode of PV inverters is switched to achieve source–load balance, and the control mode of energy storage inverters is switched to VF control mode, which supports the stability of voltage and frequency in the islanded system. Subsequently, the strategy coordinates with the tie-line recloser device to perform synchronous checking and grid reconnection. Simulation results show that, for transient tie-line faults, the proposed method can achieve stable control of the islanded system and grid reconnection within 2 s after a fault on the tie-line occurs. It successfully realizes fault ride-through within the operation time limit of anti-islanding protection, effectively preventing the PV plant from disconnecting from the grid. Finally, a connection scheme for the control strategy of a typical PV plant is presented, providing technical reference for on-site engineering. Full article

Traditional fault phase selection methods are not easily adaptable to large-scale wind farms. This paper proposes a fault phase selection method based on transient voltage S-transform energy relative entropy (SERE) to realize adaptive reclosing of the circuit breaker on the wind farm outgoing line. According to the characteristics of the three-phase transient voltage fault component, the three-phase transient voltage after a fault is collected, and the fault component is calculated. The SERE of the three-phase voltage is calculated. The maximum and minimum entropy are determined, and the criterion is constructed to identify the fault phase. The simulation results show that the proposed method can identify the fault phase accurately and quickly. The method is less affected by fault location, fault type, initial fault phase angle, and wind speed. In particular, the method can also accurately identify the fault phase under a remote high-resistance fault. The results compared with those of the traditional methods show that the proposed method demonstrates its superiority under different transitions and wind speeds. Full article

A permanent fault identification scheme based on LCC signal injection for high-voltage direct current (HVDC) systems is proposed to avoid secondary damage when it recloses to a permanent fault. Firstly, using the fault control ability of LCC, the additional control strategy is applied to the trigger angle of LCC to realize signal injection. The frequency, duration, and amplitude of the injection signal are analyzed and determined, and a signal injection strategy based on LCC is proposed. Secondly, the differences in voltage after signal injection under different fault properties are analyzed under the distributed parameter model. There is a significant difference in the amplitude of the measured voltage at the local end and the calculated voltage at the remote end under different fault properties due to differences in line models. Finally, a normalized area differential is constructed based on the above amplitude difference to realize permanent fault identification. PSCAD/EMTDC simulation results show that the proposed scheme utilizes single end data and is not affected by data communication. There is no need to set a threshold through simulation, and it can reliably identify permanent faults under 400 Ω fault resistance and 40 dB noise. It is suitable for line lengths of 1500 km and below. Full article

Islanding detection remains a critical challenge for grid-connected distributed generation systems, as passive techniques suffer from inherent non-detection zones (NDZ), and active methods often degrade power quality. This paper introduces a hybrid detection strategy based on monitoring inherent grid harmonics via a Digital Lock-In Amplifier. By comparing real-time 5th and 7th harmonic amplitudes against their three-cycle-delayed values, the passive stage adaptively identifies potential islanding without fixed thresholds. Upon detecting significant relative variation, a brief injection of a non-characteristic 10th harmonic (limited to under 3% distortion for three line cycles) serves as active verification, ensuring robust discrimination between islanding and normal disturbances. Case studies demonstrate detection within 140 ms—faster than typical reclosing delays and well below the 2 s limit of IEEE std. 1547—while preserving current zero-crossings and enabling grid impedance estimation. The method’s resilience to grid disturbances and stiffness is validated through PSIM simulations and laboratory experiments, meeting IEEE 1547 and UL 1741 requirements. Comparative analysis shows superior accuracy and minimal power-quality impact relative to existing passive, active, and intelligent approaches. Full article

The distribution network line has the risk of an unsuccessful three-phase blind reclosing in permanent fault. Based on the response of the inverter of the distributed generation (DG) to the short-term low-frequency voltage disturbance to the line to be detected, this paper proposes a non-fault identification method for the distribution network before three-phase reclosing, based on model parameter identification. During the disturbance period, when there is no fault after the arc is extinguished, the detection line is three-phase symmetrical, and each phase-to-ground loop is its own loop resistance and inductance linear network, which is independent of the fault location, transition resistance and other factors. Furthermore, the R–L network without fault is used as the identification reference model, and the least squares algorithm is used to identify the resistance and inductance parameters of each phase loop of the detection line by using the voltage and current response information of the line side during the excitation period so as to identify the fault state. The non-fault criterion before three-phase reclosing, characterized by the difference between the calculated value of resistance and inductance and the corresponding actual value, is designed. Finally, PSCAD is used to build a distribution network with DG for verification, and simulations under different fault locations and transition resistances are carried out. The results show that when the line is in a non-fault state, the parameter identification results of the three phase-to-ground circuits are highly consistent with the true value; that is, the non-fault state is determined. When the fault continues, there is a large deviation between the parameter identification results of at least one phase-to-ground loop and the corresponding real value, which does not meet the condition of the non-fault criterion. The method in this paper is more sensitive than the detection method using response voltage. Moreover, it is not necessary to add additional disturbance sources, which is expected to improve the economy and feasibility of three-phase adaptive reclosing applications for distribution lines with a large number of DGs. Full article

Fault location in medium-voltage direct current (MVDC) systems is an essential yet underexplored area compared to high-voltage (HVDC) and low-voltage (LVDC) systems. MVDC systems, characterized by intermediate line lengths and fault resistances, as well as rapid fault clearance requirements, demand specialized solutions. This paper proposes a novel single-ended, offline fault location method based on controlled re-energizations after fault clearance. This approach employs a switched grounding resistor and a bypass connection through the current-limiting inductor to extract fault parameters from the discharge curves of two re-energization cycles. By analyzing the time constants derived from these curves, the method estimates fault location and resistance with high accuracy. The proposed method eliminates the need for additional active injection sources and circuit breaker modifications, ensuring seamless integration into existing MVDC infrastructure. Furthermore, the method avoids inter-terminal communication delays and sampling delays before fault clearance. Validation through electromagnetic transient simulations demonstrates fault location errors below 5% for fault resistances up to 50 Ω. Results show that the method performs better for faults farther from the active terminal, with the higher errors seen for short distances and elevated resistances. The proposed technique offers a robust and practical solution for post-fault location in DC lines. Full article

This paper delves into the critical issues of relay protection setting calculation in high-voltage power grids with large-scale integration of renewable energy sources, such as wind and solar power. By analyzing the topological structure of renewable energy systems, models of permanent magnet direct-drive wind turbines and photovoltaic power sources are established, with a particular focus on the short-circuit current characteristics of these renewable energy sources. Subsequently, a fault iterative method for short-circuit current calculation is proposed. This method effectively improves the accuracy of short-circuit current calculation by iteratively analyzing the fault region and considering the voltage-controlled current source characteristics of renewable energy sources. The paper also conducts in-depth research on various aspects of relay protection settings after the integration of renewable energy devices, including main transformer neutral grounding strategies, tie-line protection and reclosing principles, islanding prevention, and boundary backup protection management. By applying this method to a practical engineering case in G Province, China, the short-circuit current is calculated, and partial setting values are determined, demonstrating the ability of this method to enhance system safety and stability. This research provides valuable insights for operators of modern power systems. Full article

In active distribution networks (DNs), distributed energy resources (DERs) must be disconnected from the grid prior to automatic reclosing actions. Many scholars have proposed non-voltage checking reclosing methods, but a significant challenge arises; many substations lack line-side voltage transformers (LSVTs), making these schemes impractical. To address this, we introduce a time-limited adaptive automatic reclosing (TLAR) method that integrates DERs’ anti-islanding protection (AIP) with automatic reclosing. This method estimates the AIP action time using bus-side voltage measurements before the system-side protection (SSP) is tripped and adjusts the reclosing time accordingly to enhance power supply reliability. Simulations using PSCAD validate the method’s effectiveness. The TLAR method is well-suited for distribution lines without conditions for non-voltage checking, is cost-effective, easy to implement, and contributes to power system stability. Full article

This study analyzes recloser operation in the South Korean distribution system to propose effective operational strategies for improving safety and efficiency. This research is based on actual data, such as recloser operation data and fault statistics provided by the Ministry of the Interior and Safety and the Korea Electric Power Corporation, without the use of simulation tools or experiments. Key operational elements, such as reclosure counts, sequence settings, and high-current interruption features, were analyzed. First, an analysis of reclosure counts revealed that over 73% of faults were cleared after the first reclosure, and when the second reclosure was included, more than 90% were successfully restored. This finding suggests that reducing the number of reclosures from the standard three to one or two would not significantly impact fault restoration performance while simultaneously reducing arc generation, thereby improving safety. Additionally, a review of recloser sequence settings highlighted the fact that the traditional 2F2D (two fast, two delayed) sequence often led to frequent instantaneous tripping, increasing the risk of arc generation. The 1F1D (one fast, one delayed) sequence, which applies a delayed trip after an initial fast trip, offers a better fault-clearing performance and reduces the risk of arc generation. Lastly, an analysis of the high-current interruption feature suggested that enabling this function for faults with low reclosing success rates, particularly in cases of short-circuit faults, and setting an immediate trip threshold for fault currents exceeding 3 kA would enhance both safety and efficiency. This operational strategy was implemented in the South Korean distribution system over a three-year period, starting in 2021. While there was a 2.1% decrease in reclosure success rates, this strategy demonstrated that similar success levels could be maintained while reducing the number of reclosures, thus mitigating equipment damage risks and improving safety measures. The refined recloser operation plan derived from this study is expected to enhance the overall stability and reliability of distribution systems. Full article

The overhead line (OHL)–cable hybrid transmission line, which connects floating photovoltaic (PV) power plants, needs to be considered regarding whether to block reclosing operations or not. However, due to the weak-feed characteristics of PV inverters, existing methods are difficult to apply in this scenario. This paper proposes a criterion for fault section identification in the transmission lines of floating PV power plants based on traveling wave power and the zero-sequence impedance angle. Firstly, the fault current characteristics of photovoltaic inverters under dual-vector control are analyzed, and the applicability of the sequence component impedance directional criterion in this scenario is discussed. Then, the transmission, refraction, and reflection processes of traveling waves in OHL–cable hybrid lines are analyzed, and a traveling wave energy criterion is designed to determine the fault section. Finally, based on the scope of application of the zero-sequence impedance angle and traveling wave energy criterion, a fault section identification method for the hybrid lines of floating PV power plants is established. A deployment method for the proposed method, based on feeder terminal units (FTUs) at the connection points between the OHL and cable is proposed. This method identifies fault sections through traveling waves and zero-sequence impedance angles, which are unaffected by PV week feed characteristics, can be applied to all the AC fault types, and do not rely on multi-terminal synchronous sampling. The proposed method is verified on a 1MW PV system built in the PSCAD. Full article

The integration of new battery technologies has become a focal point for distribution utilities, driven by decreasing costs and the need for fast responsiveness. Transportable battery energy storage systems (TBESSs) offer additional flexibility, allowing connection at multiple substations or grid feed points. However, concerns remain regarding their impact on distribution systems (DSs), particularly on protection devices (PDs). This study addresses these concerns by investigating the influence of TBESSs on the protection systems of a real-world distribution network. Given the lack of studies in the current literature on this topic, this research aims to fill this gap by examining the potential effects of TBESS integration on PDs, such as reclosers and fuses, within a DS. Utilizing a model based on real data from a Brazilian utility, we conducted simulations to analyze the effects of TBESSs in both charging and discharging modes on the protection systems of three feeders. The methodology involved assessing variations in the operation times and coordination of PDs to determine if TBESS integration would necessitate adjustments to existing protection configurations. The results demonstrated that TBESS integration resulted in only minor variations in PD operating times, typically within hundredths of a second, indicating a negligible impact on protection performance. Consequently, no significant modifications to the protection system are required to accommodate TBESSs. These findings suggest that TBESSs can be seamlessly integrated into existing distribution networks, maintaining system reliability and operational integrity. This study provides valuable insights and a robust procedure for utilities to analyze the integration of TBESSs, supporting the effective deployment of modern energy storage solutions in DSs. Full article