Magnitude Of Short Circuit Current Research Articles

Evaluation of Over Current Relay Settings Optimization for Multi-infeed DG-connected-grid

Increasing the short-circuit current magnitude and bidirectional flow in a multi-infeed DG-connected grid have significant impacts on protection systems based on over-current relays (OCRs). An adaptive protection scheme based on defining the optimal setting of a directional OCR (DOCR) has recently been introduced as a solution for mis-coordination and false tripping issues associated with DG penetration increase. In this paper, this approach is highlighted, and its performance in different operating modes of the DG-connected grid is evaluated. Genetic algorithm (GA), and gray wolf optimization (GWO) have been used to provide optimized values of the time multiplier setting (TMS) of the DOCR scheme. Different faults at different locations with different DG locations and sizes are studied. The international electrotechnical commission (IEC) micro-grid benchmark and different DG units are modeled with MATLAB Simulink and ETAP software to carry out and test all these operating modes and evaluate this scheme. The ability of this scheme to maintain the coordination between the forward and reverse main and backup relays for each fault location is focused on in this study.

Necessity of Protective Coordination Systems According to Battery Capacity

As the capacity of lithium-based batteries rapidly is increasing, the number of applications using them is continuously increasing. However, this leads to the risk of fire and explosion, and thus, the number of accidents is increasing. To analyze the magnitude of short circuit currents according to the battery capacity and external circuit impedance and the necessity of protective coordination, this study conducted experiments using cylindrical batteries with capacities of 800, 2200, 3000, and 5000 mAh and cables with an impedance of 0.1<i>Ω</i>/m. Results indicated that as the battery capacity increased, the short circuit current increased and circuit-opening time decreased. However, as the circuit impedance increased, the short circuit current decreased and circuit-opening time increased. Based on these results, we reviewed protective systems applied to batteries and analyzed their problems. For protective systems designed considering the maximum short circuit current, if the state of charge is low or the impedance is high at the point of short circuit, the protective system does not operate when short circuit occurs, thus failing to block the circuit and potentially leading to fire. Therefore, while designing protective systems, it is appropriate to use multiple circuit breakers and fuses, considering the short circuit current according to the battery capacity and circuit impedance to enable protective coordination between devices.

Selectivity Problem in Adaptive Overcurrent Protection for Microgrid With Inverter-Based Distributed Generators (IBDG): Theoretical Investigation and HIL Verification

The advancements in smart grid technologies had brought forth the prospect of self-healing distribution grid through intentional islanding, aided by the steadily rising penetration of inverter-based distributed generations (IBDGs). Adaptive protection is the key enabler for this resilient grid architecture. For cost-effectiveness, overcurrent relays (OCRs) with adaptive features had been proposed, often with the sensitivity problem due to low short-circuit current magnitude from the IBDG taken into consideration and largely addressed. However, apart from this widely discussed sensitivity problem, there is an underlying issue on selectivity of the OCR which is frequently disregarded when designing an adaptive overcurrent protection scheme for IBDG dominated microgrid. This selectivity problem is mainly caused by the current diversion to load during fault, which is often disregarded when performing OCR grading for a conventional grid. In this paper, this selectivity problem of the OCR is discussed in depth through a comparative study of conventional grid and a modern IBDG dominated grid. The coordination time interval margin violations problems are demonstrated through theoretical calculations and real-time hardware-in-the-loop experiments. This research aims to provide better insights into the selectivity problem as a step towards achieving a cost-effective yet reliable overcurrent-based adaptive protection for IBDG dominated microgrid.

Adaptive fuzzy directional bat algorithm for the optimal coordination of protection systems based on directional overcurrent relays

Despite bringing several benefits to modern power systems, distributed generation (DG) and microgrids cause a significant impact on the operation of power distribution networks, especially with regard to the protection system. The topological evolution of power distribution networks comprising DG units and the islanding capacity of microgrids have lead to significant changes in the magnitudes of short-circuit currents, consequently affecting the reliability of protection systems in terms of loss of selectivity (false tripping and/or sympathetic tripping), sensitivity (blind protection), and dynamic response (delayed trip). In this new scenario, the adoption of smart protection systems capable of incorporating advanced control and protection mechanisms is of paramount importance for ensuring the automatic reconfiguration and restoration of the power grid when undesirable phenomena like faults occur. Considering this scenario, this work proposes a novel metaheuristic called adaptive fuzzy directional bat algorithm (AFDBA), which can calculate optimal settings for directional overcurrent relays (DOCRs) in any power grid topology without the need for tuning the initial parameters. The technique is applied to three case studies, that is, the 3-bus, 9-bus, and 30-bus test systems. The algorithm performance is compared with that of genetic algorithm (GA), particle swarm optimization (PSO), differential evolution (DE), bat algorithm (BA), and directional bat algorithm (DBA). The results evidence that the proposed approach has high convergence speed, high robustness, and acceptable computational burden, while providing the proper coordination of protection systems.

Generic approach to calculation of short circuit currents in power transformers

Power transformer in service is exposed to various voltage and current stresses. The ability to withstand short circuit is an essential requirement for power transformers. There are different types of short circuit: single - phase to earth, double - phase with or without simultaneous earth fault and three - phase short circuit. These various short circuit conditions result in different stress conditions for the windings. Mesh analysis and symmetrical components are the two methods most commonly used for determining the magnitude of short circuit currents. In this paper, both methods will be presented with results compared on a real-case transformer. Also, a generic scheme using the symmetrical components approach is designed in order to standardize the short-circuit currents calculation for all power transformer types and to reduce the time required for obtaining results.

Experimental analysis of saturated core fault current limiter performance at different fault inception angles with varying DC bias

Economic growth has exponentially increased the power demand resulting in bulk power systems. The distributed generations are also integrating into the grid network to retrieve the benefits of the locally available generating resources. Also, the high-reliability expectations of supply systems lead to the interconnection of power networks. All these modern characteristics escalated the magnitude of short circuit currents in the grids. The security from these currents, therefore, challenged the power network protection systems. The deployment of the scalable and reliable Fault Current Limiter (FCL) technology can enhance the service span of existing components in the power industry. The Saturated Core Fault Current Limiter (SCFCL) can be a commercially viable solution to this problem. This paper reports the test performance of a scaled-down, compact, novel, copper-coils-based SCFCL model. The steady-state and transient-state behavior have been characterized in terms of saturation levels and the fault inception angles. The importance of DC bias selection in the optimum current limiting performance of the device is demonstrated in the results. The results also exhibit that the fault inception at the peak of voltage causes the most asymmetric transient during the current limiting process. Also, the heuristic design methodology based on extensive experimental work has been proposed, taking into account an application of optimum DC bias.

Influence Mechanism and Suppression Control of the MMC on Short-Circuit Current Under AC Faults

Modular multilevel converter based high voltage direct current (MMC-HVDC) transmission systems may increase the short-circuit current and affect the AC fault clearing of circuit breakers. To address this issue, this paper analyzes the influence of the MMC on the short-circuit current when a symmetrical or asymmetrical fault occurs in the AC system. Firstly, the influence mechanism of the MMC on the short-circuit current under symmetrical AC faults is studied. It is found that the short-circuit current magnitude at the fault point is mainly affected by the $q$ -axis output current of the MMC. For the single-phase line-ground fault, the three-sequence equivalent circuit of the MMC is analyzed, and the calculation method of the three-sequence short-circuit current is presented. It is observed that the negative- and zero-sequence currents at the valve side of the MMC are both zero, and the positive-sequence current is determined by MMC operating conditions. Besides, the short-circuit current magnitude under the single-phase line-ground fault is also mainly related to the $q$ -axis output current of the MMC. Based on these results, an additional controller is proposed to reduce the short-circuit current under the symmetrical and asymmetrical faults. Finally, the effectiveness of the proposed mechanism and suppression control is verified by PSCAD/EMTDC simulations.

Accounting power supply schemes for traction substations in the calculation of short circuits in the AC traction network

When calculating short-circuit currents in the AC traction network, it is assumed that each of the traction substations receives power from uncoupled external power supply sources with known resistances. In some cases, especially when powering a group of traction substations from a high-voltage power line of a longitudinal power supply, the external power supply system affects not only the magnitude of short-circuit currents, but also their redistribution between adjacent traction substations of the interstation area where this circuit is considered. Such unrecorded redistribution can have a negative effect on short circuit protection. The article considers the equivalent circuit of the traction network, taking into account resistance of the external power supply system. Particular attention is paid to the fact that in replacement circuits of direct and negative sequence value of reduced resistance of one phase of a multiwinding transformer, calculated from the short circuit voltage, does not depend on the connection scheme of its windings. It is noted that in some cases it is difficult to obtain a complete scheme of an external power supply system. Considering that the short circuit in the traction network for the external power supply system is remote, it is proposed taking into account the reference network or traction substations as power sources, from which high-voltage transmission lines power the traction substations. Resistance of the supporting substations as power sources must takes into account connected equivalent power system.Such equivalenting should be carried out by known values of currents or short-circuit powers at the inputs of the reference substation or, if such information is not available, by the rated values of the switched-off currents or powers of the switches of high-voltage line connections.The following power schemes for traction substations are considered: each from its own supporting substation, which is part of an electrically uncoupled external power supply system; from the double-circuit high-voltage line of longitudinal power supply when it is powered from different supporting substations; from the supporting network substation, the traction substation receives power from two lines, and from this the traction substations receive power from two lines in a circle pattern.These three common cases cover all the most common power schemes for traction substations. For each of them formulas are given to determine the resulting equivalent resistance of the external power supply circuit, which should be taken into account in the replacement circuit of the traction network.

Developing three‐dimensional‐phase surface‐based wide area protection centre in a smart grid with renewable resources

The complexity of interconnection modern power systems has made them more subject to wide area disturbances that have contributed to several failures of system protection that operate as a standalone and with the multi-zones operation. The high penetration of doubly-fed-induction-generator wind farms in power grid has a negative impact on the operation of the modern system protection while the sensing components of the current signals decay rapidly due to the high crowbar resistance during fault events. Such cases can drop the relays that operate in standalone mode and depend on the current magnitude only. Standalone relays are not a proper solution for the future of protecting large-scale interconnected grid. Wide area monitoring has been developed to enhance the protection schemes but unfortunately it is limited to backup protection application and also work in standalone mode. More than 70% of the wide area disturbances are caused by relay mal-operation due to protection settings and miss-coordination. The concept of the idea does not depend on the short-circuit current magnitude and operates as one-zone. The developed idea is based on describing the dynamic operation of the lines before and after the faults using differential-equations. The differential equations are solved through orbits movement in a phase-diagram.

Topology Evaluation of a Slotless High-Speed Electrical Machine with Stator Core Made of an Amorphous Alloy for the Aerospace Industry

The paper presents the experimental research of different slotless high-speed electrical machine topologies for integration into the auxiliary power unit gearless. It was shown that the 6-poles and 8-poles with the concentrated windings and the wound stator core are the most effective for aerospace industry. Based on the experimental and computer research of different slotless high-speed electrical machine topologies. It was found that for use in the gearless auxiliary power unit of modern and perspective aircrafts, the use of the 6-poles and 8-poles slotless high-speed electrical machines with concentrated windings and wound stator core is the most effective. This topology allows providing the sufficient rigidity of the slotless high-speed electrical machine stator core, the minimum length of the frontal part and the minimum weight and size parameters of the slotless high-speed electrical machine at the maximum efficiency. In addition, in this case, the slotless high-speed electrical machine windings have a high inductance, which leads to limit the magnitude of short circuit currents.

MINIMIZING THE SHORT CIRCUIT CURRENT AND OVER-VOLTAGE IN A POWER DISTRIBUTION SYSTEM BY USING SFCL IN THE PRESENCE OF DISTRIBUTED GENERATION

The insertion of distributed generation systems into power distribution system raises the fault current and over-voltage magnitude under fault condition. Application of SFCL will helps to avoid the situation. SFCL is the combination of air-core type transformer and pulse width modulation inverter. By regulating converter output current, the mmf in air-core transformer is changed to produce high SFCL equivalent impedance during abnormal condition. This will limit short circuit current magnitude. In this paper the effect of SFCL can be analyzed using simulation model and mathematical derivation. The performance of the SFCL on short circuit current and over-voltage magnitude limiting characteristics can be analyzed when distributed generators are connected at different locations. The short circuit current and overvoltage limiting characteristics of SFCL is simulated in MATLAB software. The results from simulation model shows that SFCL plays an important role in minimizing the over-voltage magnitude and short circuit currents during abnormal conditions.

Comparative Analysis of European and American Standards for Maximum Fault Current Calculations on Medium Voltage Mine Power Networks

Continuous work of mine supplying electrical power networks is a prerequisite to ensure the continuity of the mining process and the safety of its crew. The choice of the appropriate method for calculating short-circuit currents is therefore particularly important in terms of both economic and safety considerations. The methods used are always a compromise between the accuracy of obtained results, computational complexity and availability of data necessary for calculations. The study compares the two most common standards for calculating maximum short-circuit currents - IEC and ANSI/IEEE. The study presents the most important interrelationships that describe the characteristic magnitudes of short-circuit currents for IEC standard and for the ANSI/IEEE standard. This comparison has been done on the basis of novel calculations performed on a typical MV mine network. The results of the calculations showed a high contiguity of the results despite the different methodological assumptions for rotating machines modelling and for determining the equivalent value of resistance and reactance of the network where the fault occurred, and the extent of assumed simplifications. DOI: http://dx.doi.org/10.5755/j01.eie.22.2.7733

Dynamic thermoelectricity in uniform bipolar semiconductor

The theory of the dynamic thermoelectric effect has been developed. The effect lies in an electric current flowing in a closed circuit that consists of a uniform bipolar semiconductor, in which a non-uniform temperature distribution in the form of the traveling wave is created. The calculations are performed for the one-dimensional model in the quasi-neutrality approximation. It was shown that the direct thermoelectric current prevails, despite the periodicity of the thermal excitation, the circuit homogeneity and the lack of rectifier properties of the semiconductor system. Several physical reasons underlining the dynamic thermoelectric effect are found. One of them is similar to the Dember photoelectric effect, its contribution to the current flowing is determined by the difference in the electron and hole mobilities, and is completely independent of the carrier Seebeck coefficients. The dependence of the thermoelectric short circuit current magnitude on the semiconductor parameters, as well as on the temperature wave amplitude, length and velocity is studied. It is shown that the magnitude of the thermoelectric current is proportional to the square of the temperature wave amplitude. The dependence of the thermoelectric short circuit current on the temperature wave length and velocity is the nonmonotonic function. The optimum values for the temperature wave length and velocity, at which the dynamic thermoelectric effect is the greatest, have been deduced. It is found that the thermoelectric short circuit current changes its direction with decreasing the temperature wave length under certain conditions. The prospects for the possible applications of the dynamic thermoelectric effect are also discussed.

A Brief Review of Super-excitation Schemes in Short-circuit Generators

Most short circuit generators have static excitation systems to supply field current to the rotor circuit. All synchronous alternators suffer a reduction in the terminal voltage due to high armature reaction which is a result of the extremely high magnitude short-circuit currents. The reduction in terminal voltage will lead to a corresponding reduction in the stator current magnitude. The short-circuit generators are expected to maintain a constant magnitude of current for specified duration to complete the tests as per corresponding standards. Hence the short-circuit generators invariably make use of super-excitation to maintain the required magnitude of short-circuit currents for specified duration. During circuit breaker testing, it is required to maintain the recovery voltage at pre-fault levels. This requires significant over excitation of the machine. This paper presents a brief review of the methodology and algorithm of super-excitation schemesadopted in short circuit testing along with actual data recorded at the High Power Laboratory at CPRI, Bangalore.

Data mining approach to fault detection for isolated inverter‐based microgrids

This study investigates the problem of fault protection in a microgrid containing inverter-based distributed generators (IBDGs). Owing to the low magnitude of short circuit currents generated by IBDGs, traditional protection techniques which relay on current (fuses and overcurrent relays) may fail to protect such networks. This study addresses the problem of finding suitable features derived from local electrical measurements that can be used by statistical classifiers to better discriminate fault events from normal network events. Given a series of simple electrical features, a study of feature selection and data mining techniques is conducted in the context of fault detection in isolated microgrids with IBDGs. Two statistical classifiers are compared and implemented in this framework: Naive Bayes and decision trees. The proposed approach is tested on a facility scale microgrid consisting of three IBDGs.

Electric Arc Hazards

This article aims to analyse the electric arc exposure hazards to human health and to develop proposals for improvement of safe operation of electric equipment in organizations. The study is carried out on the situation in the field of regulatory documents governing the safe operation of electric equipment; moreover, recommendations are also given. It is concluded that the standard IEC 61482-1-2 (LVS EN 61482- 1-2) is adapted in the Republic of Latvia, which puts forward the requirements to protective clothing against electric arc exposure, but this standard only takes into account the spectrum of partially served electric devices. It is, therefore, necessary to introduce the international standard IEC 61482-1-1, which takes into account the actual short-circuit current magnitude and environmental layout of electric devices.

Methods to Determine Overhead Ground Wire Sizes in Distribution Systems

This paper presents an approach to analyze the overhead ground wire (OHGW) sizes in distribution system focus on the i2t of line to ground fault current. For line to ground fault, the fault current and duration time when fault take place as well as the relay operating time have been concerned. The Line Type 1, OHGW not connected to the neutral of substation power transformer, give the short circuit current magnitude which is less than the current from Line Type 2, OHGW connected to the neutral of substaion power transformer. So the Line Type 1 gives the smaller OHGW sizes than Line Type 2. To find the suitable OHGW sizes, the fault current magnitude, the duration time when fault take place and the relay operating time have to be considered. For the short circuit current is not greater than 3 kA, the 25 mm2 can be used. For the short circuit current is not greater than 7 kA, the 35 mm2 should be used for distance of 500 m from the substation, 25 mm2 for line beyond that location should be used. For the short circuit current is not greater than 12 kA, the 50 mm2 should be used for 500 m from substation, 35 mm2 should be used between 500 m-3 km and 25 mm2 for line beyond that location should be used.

Effects of power and hydrogen in the discharge on the photovoltaic properties of sputtered amorphous silicon

The photovoltaic properties of amorphous silicon films produced by reactive sputtering have been investigated as a function of power level and hydrogen concentration in the discharge. We find that raising the power in the discharge leads to films with better bulk properties but poorer surface properties. Increasing the hydrogen concentration in the discharge affects the photovoltaic properties of the films by increasing the optical gap of the film and simultaneously decreasing the density of states in the middle of the gap. Because of this dual role of hydrogen, films with optical gaps of 1.7–1.85 eV are capable of generating the same magnitude of short circuit current in sunlight. However, the large gap material is capable of providing a higher open circuit voltage and therefore results in solar cells with better overall performance.

Plasma Density Measurements Using a Double Langmuir Probe in a Prototype Vaccuum ARC Fault Current Limiter

Electric power systems could benefit from a device that would limit the magnitude of short-circuit current. A switched resistor fault current limiter requires a commutating switch capable of interrupting current without the benefit of a natural current zero. The unstable diffuse plasma discharge between electrodes in a cylindrical geometry might be capable of such a task but the phenomena involved in this discharge is not completely understood. To develop a detailed model of this unstable discharge, measurements of the plasma density as a function of position and time were made using a double probe. A maximum density of 5 x 1020 m-3 was measured 90 mm from the cathode of this diffuse copper vapor discharge in vacuum.

Influence of Short-Circuit Currents on HV and EHV Strain Bus Design

Methods are presented to design strain bus for short-circuit currents up to 100 kA rms for new 230 and 500 kV substations and to uprate existing substations. Mechanical, electrical and arc-thermal effects of short-circuit currents on strain-bus systems as they are affected by various design parameters are discussed. These parameters include span length, number and lengths of subspons, bundle-conductor spacing, short-circuit current magnitude and duration. New techniques to reduce short-circuit effects on strain-bus systems for minimum service disruption and cost include the use of polymeric insulated phase-phase spacers, small bundle-conductor spacing, insulation coordination and bay-by-bay analysis of forces on the supporting structures.