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Grid impedance is one of the most important parameters for the satisfactory operation of variable frequency drive (VFD) and their interaction with other utilities connected to the same grid. In this research investigation a new approach to analytical evaluation and verification of grid impedance, and short circuit current is discussed. VFD under identical operating and loading conditions is connected to different grid capacities and configurations, being considered in this investigation. Grid impedance variation in terms of measured or estimated values, due to different grid connectivity affects the commutation of uncontrolled front-end rectifiers. This impacts the nonlinearity of input current wave shape, causing a significant change in current harmonics (THDi) and ripple current of DC link. This paper comprehensively investigates the reduction of DC capacitor lifetime and losses of DC inductor, and diode with various grid capacity and configurations under standard load conditions. High-frequency harmonics impact (2-9 kHz) on DC inductor losses is also analyzed. A VFD of 250 kW is considered for entire practical measurement including distortion effects and MATLAB simulation. This research may give a good insight into the sizing of VFD front-end devices. The reliability impact of VFD is also one of the important outcomes of this research.

Due to the stunning advancement of power electronics, DC power system is getting immense attention in the field of research. Protection and hereafter the protective devices for the DC power system application are two vital areas that need to be explored and developed further. Designing a protective device such as DC circuit breaker possesses a lot of challenges. The main challenge is to interrupt a current which does not have a natural zero crossing like AC current has. In addition, energy is stored in the network inductances during normal operation. Instantaneous current breaking is opposed by this stored energy during circuit breaker tripping, hence, all the DC circuit breaker topologies proposed in literature use snubber network, nonlinear resistor to dissipate this stored energy as heat during the current breaking operation. However, it is possible to store this energy momentarily and reuse it later by developing an improvised topology. In this paper, the prospects of energy recovery and reuse in a DC circuit breaker was studied and a new topology with regenerative current breaking capability had been proposed. This new topology can feed the stored energy of the network back into the same network after breaking the current and thus can improve the overall system efficiency.

The article proposes a mechanical DC circuit breaker (CB) based on a series LC circuit. It requires two switches (a fast disconnector and an AC circuit breaker), an inductor and a capacitor, and therefore the cost is expected to be low. A series LC circuit is analysed and it is concluded that fault current will always have natural zero-current crossings which enable use of simple AC CBs. The current commutation into a capacitor is investigated since this is important for successful operation. A number of analytical conditions are derived for the voltage stress across disconnector contacts which enable arc-less contact opening. Experimental results on a 900 V laboratory prototype LC DC CB illustrate successful DC fault clearing, with commutation of 130 A and peak DC current of 190 A. A detailed PSCAD model for 320 kV LC DC CB is developed and DC fault clearing is evaluated in order to understand the possible benefit for high-voltage direct current applications. Further comparisons with the commercialised hybrid DC CB and mechanical DC CB on 320 kV system illustrate some benefits in terms of performance and simplicity. The mechanical LC DC CB operates very fast because of early capacitor insertion, and this results in low peak current and energy dissipation.

This study presents a study on the time when the short-circuit fault current in an MV distribution network will cross the zero point in the presence of DC offset affected by the local synchronous and/or induction machines. The motivation of the study is to examine using thyristors to bypass a series compensator in the network while the subsequent turning-off of the thyristors depends on the zero-crossing of the current. One of the main uncertainties is the DC offset in the fault current due to the machines connected locally, which may defer the thyristor turning-off. This possibility has been examined in this study and the results demonstrate the parameters of the machines that have most influence on the time when the fault current will pass the zero point. It is shown that machines with higher unit ratings usually cause more delays in comparison with smaller units.

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.

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 gridconnected 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%. © 2022 by the authors. Licensee MDPI, Basel, Switzerland. Đại Học Lạc Hồng; Ministry of Higher Education, Egypt, MHE Funding: The study presented in this paper is funded in part by the Ministry of Higher Education in Egypt and in part by the Lac Hong University in Vietnam.

With the advantage of saving resources and high utilisation, DC transmission becomes the vital part of the sustainable development. However, due to the control strategies of grid-side inverter, the fault characteristics of the grid will change dramatically, which influences the reliability of grid protection. By establishing the model in PSCAD, the fault characteristics of the inverter was obtained and the effects on current protection was analysed here. The results reveal that the magnitude of fault current was directly influenced because of being connected with the inverter. The grid inverter can make a difference in selectivity and reliability of current protection. In order to solve this problem, the paper constructs the equivalent model of the inverter and attains the unique feature that the fault component impedance measured in the location of protection decreases with the increasing distance of fault location. According to the characteristics, a targeted fault component impedance protection is designed. The feasibility and effectiveness of this protection is verified by simulation in PSCAD model.

A wavelet-based electromagnetic time reversal method for locating faults in voltage source converter-high-voltage direct current (VSC-HVDC) transmission lines is proposed in this study. This principle, firstly, is to use wavelet decomposition to filter the 1-mode fault currents, which are recorded at ends of the transmission line. Secondly, the filtered currents are mirrored on time axes, which called time reversal. Thirdly, the time-reversed currents are set as current sources at ends of the lossless mirror lines. Through assuming a fault at each point of line, the assumed fault currents are calculated, and the RMS of fault current at actual fault location is maximal according to a strict scientific proof. Theoretically, the Wavelet-based Electromagnetic Time Reversal (WEMTR) method is robust against fault types and resistance. A multilevel converter-HVDC system is established in Power Systems Computer-Aided Design (PSCAD)/Electromagnetic Transients including DC (EMTDC) to verify the feasibility of the proposed method, and the transmission line is simulated by frequency independent phase model. The results show that, the fault location can be calculated exactly without high sampling rates.

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.

The present study is focussed on a comparative analysis of different meta-heuristic optimization approaches for directional overcurrent relay (DOCRs) coordination which has been discussed and presented in the literature. Further, to have a comparative analysis of the performance of the optimization methods discussed they have been tested on power system network of different sizes. To overcome such issues, this work proposed a simplex linear programming technique-based overcurrent relay method using general algebraic modelling system (GAMS). The execution of this work is done on the MATLAB 2018 a platform. Based on the obtained result the best meta-heuristic optimization method for mitigating the problem of relay coordination has been identified. Nevertheless, the operating time of the relay is high, so the fault is not corrected at a time. The developed model has been tested on test system of different sizes namely IEEE 9 bus and IEEE 14 bus system. The obtained values through series of simulation are compared with different methods for proving the proposed protection coordination scheme is more effective and efficient than others in terms of operating time and coordination time.

The 110 V lead-acid battery pack is widely used as the DC power supply for the load control of power plants. If the low-voltage DC circuit breaker (LVDCCB) at the DC side of its charging device cannot operate in time when the fault current is flowing in charging loop, there will be of harmfulness to the safety and the durability of the battery pack. The plasma theory is applied to analyse the arc mechanism based on the voltage, the current and the power waveform of LVDCCB when it breaking. Then, an arc extinction is developed by assembling an additional device to LVDCCB. The device, connected to the contacts of LVDCCB, includes an insulated-gate bipolar transistor series branch, an energy-absorbing branch, a transfer switches branch, and a drive circuit. The test shows that the break time of LVDCCB, assembled with the additional device, is significantly shortened than that of the original.

The presence of distributed generation (DG) in a power distribution network can cause difficulties in managing the voltage, power flow and fault level as the network was designed for supplying passive loads. This study focuses on the control of a back-to-back (B2B) voltage source converter operated as a synchronverter and a soft open point (SOP) between adjacent feeders to mitigate the voltage fluctuation caused by DG and to increase the reliability of the supply without increasing the fault level. Better reliability is achieved as the B2B converter can continue to supply the loads when a loss of mains occurs on one side. The proposed control of the two DC–AC converters, which also needs to regulate the DC link voltage and adapts the synchronverter algorithm to the new application requirements, so that events will cause minimum disruption. Simulation shows that the B2B-synchronverter is capable of regulating the load voltage under normal mains connected condition, and also limiting the fault current and supplying the loads within its rating during islanding, providing seamless transition to the islanded mode.

Direct current (DC) power systems are becoming very popular due to bettercontrol ability and equipment reliability thanks to the continuousdevelopment of power electronics. A DC circuit breaker (DCCB) used forcurrent interruption in a DC network is a major part of the system. It playsthe vital role of isolating networks during fault clearing as well as duringnormal load switching. Breaking the DC current is a major challenge as itdoes not have any natural zero crossing points like the AC current has. Inaddition, energy stored in the network inductances during normal operationopposes the instantaneous current breaking. Hence, all the conventional DCcircuit breaker topologies use lossy elements to dissipate this stored energyas heat during the current breaking operation. However, it is possible to storethis energy and reuse it later by developing an improvised topology. In thispaper, the prospects of energy recovery and reuse in DC circuit breakers havebeen studied, and a new topology with regenerative current breakingcapability has been proposed. This new topology can feed the stored energyof the network back into the same network after breaking the current and thuscan improve the overall system efficiency.

In this paper, series Flexible AC transmission systems (FACTS) devices like Thyristor control series capacitor (TCSC) and Static synchronous series compensator (SSSC) with designed control logic used to reduce the fault current located in LV distribution network at the LV busbar. The electrical distribution network in small and medium scale industries such as steel plants, process and power plants is through low voltage switchgear (LVS) fed from motor control centre (MCC) switchgear through step down transformer of 11kV or 33kV /415V. The designed switchgear in the LV side for these utilities usually is at 50kA. However, the process loads are continuously increasing and sustained with additional feeders with the existing switchgear. Consequently, the fault current at the busbar of the switchgear increases which may require the replacement of entire switchgear to the new design fault current. However, upgrading the existing switchgear is not an economical solution to the industries. Alternatively reducing the fault current at the busbar is feasible. Controller design implemented for reducing the short circuit current with series FACTS devices. A study carried on 800MW Thermal power plant Ash handling LVS in ETAP and Matlab. It is observed that the results are encouraging to use series FACTS devices effectively in the LVS.

A large increase in distributed generation integrated within power system networks has resulted in power quality challenges and in the need to resolve complex system faults. The monitoring of the real-time state of the power parameters of the transmission and distribution grid helps to control the stability and reliability of the grid. In such a scenario, having current monitoring equipment that is flexible and easy to install can always be of great help to reduce the price of energy monitoring and to increase the dependability of a smart grid. Advances in magnetic sensor research offer measurement system accuracy that is less complex to install and that can be obtained at a lower less cost. Tunneling magnetoresistive (TMR) sensors can be used to measure the AC current by sensing the magnetic field that is generated by the current-carrying conductor in a contactless manner. This paper illustrates the results of a thorough investigation of factors that can influence the performance of the TMR sensors that are used for the current phasor measurements of a single-phase AC current application, such as the effects of distance, harmonics, and conductor insulation.

The high energy density of new technology batteries, for example lithium-ion, comes with a downside; potentially extreme short-circuit current. This paper will describe the capability of a demonstrator for a new main battery for a submarine, the consequences of connecting it to the existing DC distribution system, and how the release of stored energy is to be controlled. A complication is that proprietary battery management systems will shut down on excessive current demand, but that behaviour is not consistent with the UPS support function of the battery or with making conventional fault clearance discrimination work in the extended network it serves. An innovative technique to meet the real-life use requirement will be described, giving an energy source with both power and responsibility.

One important problem in the operation of medium voltage networks is the detection of a single-line-to-ground fault in its incipient state, when the fault resistance values are very high. In a medium voltage (MV) distribution network with a neutral grounding resistor (NGR), one of the methods employed to discriminate a single line-to-ground fault is the use of an overcurrent relay with an operating characteristic adjusted according to the effective value of the current flowing through the limiting resistor. In case of a single line-to-ground fault with a high fault resistance value, the correct tripping settings of the protective relay require the precise computation of this current. In comparison to the assumptions made by the models from the literature—the three-phase voltage system of the medium voltage busbars is symmetrical and there are no active power losses in the network insulation—the model proposed in this paper considers the pre-fault zero-sequence voltage of the medium voltage busbars and the active power losses in the network insulation, which is necessary in certain fault conditions where the use of the former leads to unacceptable errors.

The requirements imposed on generator circuitbreakers greatly differ from the requirements imposed on other transmission and distribution circuit-breakers. Due to the location of installation between the generator and the associated step-up transformer, a generator circuit-breaker must meet high technical requirements with respect to rated normal currents, short-circuit currents, fault currents due to out-of-phase conditions and transient recovery voltages. The question whether the transient recovery voltage requirements laid down in IEEE Std C37.013-1997 (R2008) and in its amendment IEEE Std C37.013a-2007 are still adequate for the application of generator circuit-breakers in modern power stations is considered in the present work. In order to quantify the transient recovery voltage requirements for the application of generator circuit-breakers a comprehensive survey of different fault conditions occurring in several power stations has been performed. The fault transients’ simulations have been performed by means of the Electromagnetic Transients Program (EMTP).

This work presents a fault analysis simulation model of an IEEE 30 bus system in a distribution network. This work annalysed the effect of fault current and fault voltage in a distribution system. A circuit breaker was introduced into the system to neutralize the effect of the fault. The system was run on a PSCAD software and results were obtained. The system was monitored based on the start time and the end time of the fault and how well the circuit breaker reacts with those times. Fault occurred from 0.100 to 0.300 seconds before it was removed. At the time fault was not applied (i.e. from 0.00 to 0.100 and from 0.300 to 0.72), the circuit breaker was close and became open when fault was applied so as to cut off current flow through the line.The result obtained gave the disruption caused by the fault and the quick response of the circuit breaker in neutralizing it. Results gotten are based on when the circuit breaker is close and no fault is applied and when the circuit breaker is open due to fault. From this work, it was obtained that circuit breakers are very essential in system protection and reliability.

Metrology and Measurement Systems is an international journal, peer-reviewed, quarterly-published, launched in 1988; since 2001 it appears in English. The list of topics covered includes: theory and general principles of measurement; measurement of physical, chemical and biological quantities; medical measurements; sensors and transducers; measurement data acquisition; measurement signal transmission; processing and data analysis; measurement systems and embedded systems; design, manufacture and evaluation of instruments. Impact Factor for 2018: 1. 096 5-Year Impact Factor: 1.149 Contributions are invited on all aspects of the research, development and applications of the measurement science and technology. The list of topics covered includes: theory and general principles of measurement; measurement of physical, chemical and biological quantities; medical measurements; sensors and transducers; measurement data acquisition; measurement signal transmission; processing and data analysis; measurement systems and embedded systems; design, manufacture and evaluation of instruments., Verification of electrical safety in low-voltage power systems includes the measurement of earth fault loop impedance. This measurement is performed to verify the effectiveness of protection against indirect contact. The widespread classic methods and meters use a relatively high value of the measuring current (520) A, so that they are a source of nuisance tripping of residual current devices (RCDs). The meters dedicated to circuits with RCDs usually use an extremely low value of current (lower than 15 mA), which in many cases it is not acceptable in terms of the measurement accuracy. This paper presents a method of earth fault loop impedance measurement in 3-phase circuits, without nuisance tripping of RCDs – the concept of measurement, the meter structure and the experimental validation. The nuisance tripping is avoided in spite of the use of measuring current value many times higher than that of the rated residual current of RCDs. The main advantage of the proposed method is the possibility of creating values of measuring current in a very wide range, what is very important with regard to accuracy of the measurement.

The growth of intermittent distributed energy sources (DERs) in distribution grids is raising many new operational challenges for utilities. One major problem is the back feed power flows from DERs that complicate state estimation for practical problems, such as detection of lower level fault currents, that cause the poor accuracy of fault current identification for power system protection. Existing artificial intelligence (AI)-based methods, such as support vector machine (SVM), are unable to detect lower level faults especially from inverter-based DERs that offer limited fault currents. To solve this problem, a current tracing method (CTM) has been proposed to model the single distribution feeder as several independent parallel connected virtual lines that traces the detailed contribution of different current sources to the power line current. Moreover, for the first time, the enhanced current information is used as the expanded feature space of SVM to significantly improve fault current detection on the power line. The proposed method is shown to be sensitive to very low level fault currents which is validated through simulations.

In this paper, a flux-lock type superconducting fault current limiter (SFCL) using two triggered high-Tc superconducting (HTSC) elements was proposed and its fault current limiting characteristics according to short-circuit location were analyzed. The flux-lock type SFCL with two triggered HTSC elements consists of two parts. One is two magnetically coupled coils with serial connection. The other, which is connected in series with the second coil, is composed of two HTSC elements in parallel connected through the normal resistor. Since the amplitude of the fault current depends on the fault location in case the fault occurs in a power system, the suggested flux-lock type SFCL can perform the fault current limiting operation through the quench occurrences of one HTSC element or two HTSC elements according to the amplitudes of the fault current. In case a low fault current, the fault current can be limited by utilizing only one HTSC triggered element. On the other hand, a larger fault current can be limited by two HTSC triggered elements. The short-circuit tests for the proposed flux-lock type SFCL according to the fault location were carried out in a feeder line of a power distribution system and its effective limiting operations could be discussed through the analysis on the short- circuit.

In a conventional distribution system, protection algorithms are designed to operate on a unidirectional high fault-current level. In a microgrid, a fault current from distributed generation (DG) may bring about a relay malfunction because of the bidirectional and relatively small fault current. Therefore, the conventional protection scheme is not applicable to microgrids and a new protection method must be developed. In this paper, two protection coordination algorithms which can be applied for facility and secondary microgrids are proposed, respectively. The proposed protection algorithms eliminate faults not by the EMS signal but by directional relays. Moreover, this makes the algorithms flexible regardless of the types and numbers of DG. The proposed protection algorithms were simulated at the KEPCO RI Microgrid Demonstration Site.

This study analyzed the impact of varying the momentary cessation (MC) voltage level on the short circuit current of inverter-based resources (IBRs). To analyze the impact of the IBR MC function on the short circuit current, this paper proposes an advanced IBR model for fault current calculation to reflect its fault characteristics and a scheme for analyzing the influence of MC on the short circuit current. Based on the proposed methods, the authors conducted case studies using planning data from the Korea Electric Power Corporation (KEPCO). The influence of MC was investigated on the IBRs located at the southwest side of the KEPCO systems by screening the fault currents while varying the MC voltage. This paper demonstrates that the minimum MC voltage level needed for the fault current not to exceed the circuit breaker (CB) capacity can be proposed through analyzing the impact of MC voltage level on the short circuit current. The test results based on the proposed scheme showed that the short circuit current to power systems could not violate CB capacity if IBRs adjusted the MC voltage level higher than the lowest MC voltage level.

A short-circuit is a serious situation in a circuit. That is why the determination of the fault current during the operation of the IGBT requires suitable gestures in order to realise a better and reliable operation for the power converters. Thus, it is necessary to know the extreme operating limits for these devices since the use of the IGBT in power converters often subjects them to certain significant electric constraints such as, the short-circuit and the turn OFF on the inductive load. This paper presents then a means of protection for a safe and precise shutdown of the fault current in the device. This circuit allows the IGBT to operate without risks, and permits a reduction of the conduction losses in the device without compromising the characteristics of protection of the short-circuit.

The method of symmetrical components simplifies analysis of a three-phase network and provides information regarding the existance of a fault in the system. This concept is applied to a radial power system in the maritime sector. A fault analysis is performed for the main types of faults, applied in different locations of the network. The fault current is measured using the current transformers that are already present in the system as part of a time-inverse overcurrent protection. Simulation results show that the symmetrical components of the currents seen by these current transformers can be used to detect the electric fault. The method also provides an improved fault detection over the conventional overcurrent relays in some situations. All results are obtain using MATLAB/Simulink and are briefly discussed in this paper.

This paper presents the methodology of design of model-based sliding mode control (SMC) algorithms applied to power electronic dc-dc converters, which are part of the components of a solid-state low voltage dc breaker (SLVDB). The power converters used in the tested schemes of the SLVDB are the boost and sepic dc-dc converters. Accurate disconnection times, user-configured, are achieved with the proposed controllers, as well as a complete minimization of the transient recovery voltage (TRV) in the breaker terminals. Details of the performance of two SLVDB configurations are analyzed and compared in order to establish the best design comprising complexity vs. performance. MATLAB simulations support the results and provide a reasonable picture of the operation of the SLVDB. Montevideo

High voltage (HV) infrastructures market is growing due to the corresponding growth in industries and population. To ensure continuous and reliable electrical power supply, existing substation and transmission lines are being upgraded to accommodate the additional load requirements. These upgrades involve up-rating the existing transmission lines or the installation of new lines. To save on easement cost and reduce the environmental impacts, transmission lines are occupied the same easement or path. This parallel option introduces the risk of induced voltage which could reach an unsafe condition and jeopardize the safety of works and people. This paper analysis and highlight the hidden risk associated with two parallel transmission lines that connected the same high voltage substation. The theoretical study which is supported by the case study shows the high risk potential tempering with the OHEW on the isolated circuit while the other one is still energized

Distribution systems across most parts of the globe are highly radial in nature. As loads are gradually increased on a particular distribution system, a higher operating current state leading to increased fault current levels is attained. Hence, the relay co-ordination is disturbed and equipments such as feeders and circuit breakers need to be replaced with higher rating so that they can handle the new currents often leading to expensive retrofit costs. The use of fault current limiter (FCL) is proposed to mitigate the effects of high current levels on a distribution system. A comprehensive and up-to-date literature review of FCL technologies is presented. Detailed efforts of an in-house developed behavioral superconducting FCL model are delineated, including FCL control algorithm and its implementation in PSCAD®/EMTDC environment. Results from simulation studies are investigated and compared to an actual FCL commissioned by Z-energy to highlight the effectiveness of a generic model without having to access proprietary details. Extending those concepts, a solid-state and hybrid type of limiter is also modeled and it results discussed. Finally, an impact assessment is conducted on the distribution protection scheme, due to the FCL being inserted and subsequently operated in the distribution system. Master of Science

This paper describes the development of a solid-state fault current limiting and interrupting device (FCLID) suitable for low-voltage distribution networks. The main components of the FCLID are a bidirectional semiconductor switch that can disrupt the short-circuit current, and a voltage clamping element that helps to control the current and absorb the inductive energy stored in the network during current interruption. Using a hysteresis-type control algorithm, the short-circuit current can be constrained according to a predefined profile. Insulated-gate bipolar transistors and diodes are used to construct the semiconductor switch. Varistors are used as the voltage clamping element. An effective method is adopted to improve the current sharing between parallel varistors in order to provide the required capability of energy absorption. An overall protection scheme for the FCLID is described. A prototype FCLID for 230-V single-phase, or 400-V three-phase, applications is developed and tested. Analyses and experiments are carried out to define the stresses that the main components in the FCLID are subject to. The results show that the developed prototype is capable of limiting a 3-kA prospective short-circuit current to 120 A for a period of 0.8 s, without exceeding the thermal limits of the chosen switches and varistors

This paper analyses the impact of symmetrical and unsymmetrical voltage sags caused by distribution and transmission faults on the dynamic behaviour of small salient-pole synchronous machines connected to the MV grid, and proposes the modification of the protection settings to increase machine availability. As faults are considered, the voltage recovery is assumed to occur in a discrete way, in the fault current zeroes. The voltage sag effects include current and torque peaks, speed and load angle increase, and possible machine instability. Results from many cases are discussed, especially the positive-sequence voltage influence on machine stability. The study concludes that machine availability during unsymmetrical sags can be increased by modifying the undervoltage and overcurrent protection settings (the former should be based on the positive-sequence voltage instead of line-to-line voltages used in current settings).

One of the key features of Modular Multilevel Converters is the existence of inductors inside the branches that constitute each of their phases. These inductors, which may be coupled or non-coupled, authorize a certain independency in the control of the branch currents and contribute to the protection of the converter as well as the buses the latter is connected to. Through the analysis of the various current loops that are involved in this converter technology, the present paper aims to present a general parameter design method and proposes several criteria in order to analytically size these branch inductors. The possible use of coupled inductors is considered and compared with the use of non-coupled inductors. Finally, a numerical example as well as simulation results illustrate and confirm the validity of the proposed approach.