Short-circuit Current Limitation Research Articles

The Identification of Microstructural Changes in High-Temperature Superconducting Tapes for Superconducting Fault Current Limiters

HTS 2G tapes used in Superconducting Fault Current Limiters (SFCLs) have properties that allow for the effective limitation of short-circuit currents; however, due to the specificity of the device operation, they should be characterized by the high stability of the parameters when repeatedly leaving the superconducting state. During the operation of SFCLs, a situation may occur in which the parameters of the HTS tapes used will change several times as a result of the action of short-circuit currents that exceed the critical current IC of the superconductor of the tape used. This paper presents the results of microstructural tests of 2G HTS tapes intended for SFCLs, subjected to surge currents corresponding to prospective short-circuit currents with values higher than their critical currents IC and for which IC changes were observed. The HTS tapes were examined using a JEOL 7600F field emission scanning electron microscope (SEM), and their chemical composition was analyzed using Energy-Dispersive X-ray Spectroscopy (EDS). The test results indicate the possibility of micro-damage in the form of cracks in the superconductor layer, as well as the interruption of the buffer layers and the oxidation of the silver layers. The analysis of the chemical composition of the HTS tape layers may indicate the occurrence of diffusion processes.

On the Solution to Optimal Topology Adjustment in Long-Term Power System Operation with Explicit Short-Circuit Current Limitation Constraints

To restrict the excessive short-circuit current (SCC), this letter proposes an SCC-constrained optimal topology adjustment model considering the N-1 security criterion. Topology adjustment, including transmission switching (TS), bus sectionalization (BS), lines operating out of breaker bay (LOB) and commitment status of units (CU), has nonlinear relationships with SCC and is difficult to express explicitly. In this letter, an explicit formulation of SCC considering topology adjustment is proposed based on the equation of admittance matrix and nodal self-impedance, which is further recast as a mixed-integer linear programming (MILP) model. In addition, the N-1 security criterion is included for avoiding jeopardizing system security by topology adjustment. Numerical case studies validate the effectiveness and advantages of the proposed model in SCC restriction.

Inexpensive short-circuit current limiter and switching device based on one commutation circuit for a three-phase system

The escalating levels of fault currents resulting from short circuits, particularly in the context of distribution generators, have presented a critical need for the widespread implementation of fault current limiters (FCLs) in power systems. Despite their evident advantages, the extensive adoption of FCLs has been hindered by the high production costs associated with these devices. To address this challenge, a comprehensive study was conducted to develop a cost-effective FCL tailored specifically for three-phase power systems. This paper proposes a novel approach based on a single commutation circuit for the FCL and offers detailed insights into the construction of the FCL circuit, with a particular focus on efficient current interruption. Additionally, the study comprehensively discusses the logic controller and measurement system employed in conjunction with the proposed FCL, ensuring precise fault detection and rapid response to disturbances within the power grid. The integration of an artificial zero-crossing circuit within the FCL design further enhances its capability to limit short-circuit currents proactively, even before the occurrence of the first peak, thereby bolstering overall system reliability and stability. The study's significant contribution lies in achieving cost-effectiveness through the simplicity of the FCL's design, eliminating the need for extensive upgrades to various network components.

Model predictive control for solid state transformer

The solid-state transformer (SST) is being presented as a technology that enables the construction of new power systems due to its many advantages. These benefits include reduced weight and volume compared to traditional transformers, power factor compensation, accurate output voltage regulation, harmonic mitigation, short-circuit current limitation, and voltage dip immunity, under certain conditions. Unlike other studies that only demonstrated the effectiveness of Model Predictive Control (MPC) in individual parts of the SST, this study shows the control of an entire SST using the MPC strategy. The performance of the SST during power system transients is evaluated to showcase the features of the SST by predictive control.

Study of Electromagnetic and Thermal Transients in a High-temperature Superconducting Transformer during a Short Circuit

Today, high-temperature superconducting (HTS) current limiters and transformers allow to limit the surge short circuit current during failure without negatively affecting on the power grid complex at the normal operation mode. However, the transition of a superconductor to a resistive state at the moment of current limitation can cause significant heat generation, which can destroy the transformer windings. The research goal is to provide optimal technical characteristics of the HTS transformer to achieve effective short circuit current limitation and prevent thermal breakdown of its windings. To achieve this goal, a mathematical model of a HTS transformer was developed. The presented method considers the material type and geometry of the superconducting tape, the critical parameters of the superconductor (current and temperature), the parameters of the cryogenic liquid, dependence of the resistance and heat capacity of the HTS tape layers on temperature. The simulation model was created in the Matlab/Simulink software. The most important result is the possibility of obtaining optimal electrical and thermal parameters of the HTS transformer windings during the short circuit current limitation, as well as ensuring the thermal stability of the superconducting tape at the quench moment. The obtained results are significant in the design and operation of HTS transformers. For efficient and safe operation in the current-limiting mode, it is necessary to take into account heat generation on the transformer windings. It is important for the superconductor returning to the superconducting state without causing significant overheating of the windings.

Critical Current Degradation in HTS Tapes for Superconducting Fault Current Limiter under Repeated Overcurrent

Superconducting fault current limiters (SFCL) can be an alternative to conventional devices limiting short-circuit currents in power systems. SFCL use high-temperature superconducting tapes of the second generation (HTS 2G) in SFCL, which, after reaching the characteristic critical current of the tape, go into the resistive state (quenching), limiting the short-circuit current. The critical current determines the moment of activation of the SFCL. Therefore, its value should not change during the operation of the device due to repeated limitation of short-circuit currents. The constancy of the critical current is a prerequisite for proper cooperation with the power system protection devices. Multiple quenching can cause microdamage in the superconducting layers responsible for lowering of the value of the critical current of the HTS tapes. The article presents the research results on the degradation processes of 2G HTS tapes intended for the construction of SFCL due to the action of prospective short-circuit currents with values exceeding the critical current of the tested tapes. The decrease in the value of the critical current of the HTS tape as a result of multiple transitions to the resistive state was investigated. The amount of energy emitted during the test current pulse of 0.2 s duration was determined. The limitation values of the voltage drop on the tape, which does not cause accelerated degradation processes, were defined. The microstructural tests of cross-sections of new HTS tapes subjected to prospective short-circuit currents were performed.

Methodology for determining the parameters of high-temperature superconducting power transformers with current limiting function

<span lang="EN-US">This paper substantiates a new adaptive method for determining parameters of high-temperature superconducting power transformers with current limiting function. The main focus is the design of current-limiting superconducting windings in the light of new restrictions on current density, magnetic induction, critical current and critical temperature. The presented method considers the nature of alternating current (AC) losses in a superconductor under nominal operating conditions, features of the dielectric medium (liquid nitrogen), as well as the reduced values of the short-circuit voltage (0.5 to 1.5%). The main design features of high-temperature superconducting (HTS) transformers are specified, and a prototype of a three-phase HTS transformer of 63 kVA with a short-circuit current limiting function is developed. It is shown that HTS units have some advantages over conventional transformers: a 90 to 95% active losses reduction, short-circuit current limitation function, explosion and fire safety, a 60% reduction in weight and size, and increased efficiency (up to 99.8%). Experimental studies confirm that the short-circuit current limitation function is safe and efficient. It is demonstrated that during the short-circuit current limitation, significant heat flows occur on the windings, which should not exceed the critical value above which the superconductor could not return to the superconducting state by itself.</span>

Backup protection method based on multi-interval information in low voltage distribution network of high proportion of renewable energy system

With the large number of renewable energy power sources such as wind power and photovoltaic power connected to the grid, the power system is becoming more electronic. The fault characteristics of renewable energy power sources and synchronous generators are obviously different, mainly manifested as the characteristics of short circuit current amplitude limitation and frequency offset, etc. The traditional protection based on the fault characteristics of synchronous generators may have adaptability problems. For a high proportion of renewable energy system, the short circuit current in the low voltage distribution network is greatly affected by the operation state of the renewable energy power sources after the short circuit fault occurs, which leads to the difficulty of the traditional three-stage overcurrent protection setting and coordination. In order to ensure the safe and stable operation of the system, this paper proposes a new backup protection method for low voltage distribution network. This method uses the information of the electric parameters on the high voltage side and low voltage side of the transformer. Firstly, the modulus sum of the voltage sampling value, the equivalent distance between the fault point and the protection installation place, and the modulus sum of the current sampling value are calculated. Secondly, the direction is judged by the criterion of the voltage direction element and the criterion of the distance protection element based on the multi-interval information. Finally, the maximum current branch of the low voltage distribution network is selected as the fault branch by the overcurrent element based on multi-interval information, so as to trigger the circuit breaker trip and isolate the fault. The low voltage distribution network model of the high proportion of renewable energy system is built on the PSCAD/EMTDC electromagnetic simulation platform. The simulation results show that the proposed protection method can reliably achieve fault removal by using multi-interval information, and has strong adaptability to the high proportion of renewable energy system.

Research on Efficiency of New Self-driven Fault Current Limiter Based on the Improved Genetic Algorithm

To study the current limiting characteristics and system efficiency of the new fault short-circuit current limiter, an equivalent geometric model based on the rectangular guide rail, an algorithm analysis model of electromagnetic drive equation and a self-driven process is established. The effect of the geometric size and skin effect of the current limiter on the current limiting characteristics and system efficiency of the current limiter is analyzed. At the same time, the two goals of the initial time of current limiting and system efficiency are considered, and the important parameters of the new fault limiter are optimized by the improved genetic algorithm. The results show that the cross-sectional area of the rectangular guide and the width of the metal slider have a comprehensive effect on the performance. The algorithm model can optimize and analyze the target in a shorter time and a smaller algebra, which provides the theoretical basis and technical support for improving the current limiting characteristics and system efficiency of the new current limiter.

Using the Stiffness Indicators of 110 and 220 kV Electric Network Nodes to Estimate Short-Circuit Currents

The topical problem of evaluation, analysis and limitation of short-circuit currents in electrical networks by simple and accessible methods without resorting to rather complex conventional calculations is addressed. The article suggests a new procedure for estimating short-circuit currents at network nodes based on their stiffness degree determined by the values of electric power system (EPS) configuration generalized parameters. The node balance admittance defined as the difference between the nodal admittance matrix diagonal and non-diagonal elements is used as the node stiffness indicator. The problem solution adequacy is confirmed by examples of constructing stochastic models for estimating short-circuit currents at the 110 kV networks nodes in the regional EPS and 220 kV nodes in the Moscow power system. The obtained stochastic models feature high values of correlation coefficients. This opens the possibility to determine (predict) average and interval values of short-circuit currents at network nodes, as well as the probability of their going beyond the established boundaries, which is important for short-circuit current limitation measures, including enhancement of the EPS configuration reliability.

Optimal Transmission Switching for Short-Circuit Current Limitation Based on Deep Reinforcement Learning

The gradual expansion of power transmission networks leads to an increase in short-circuit current (SCC), which has an impact on the secure operation of transmission networks when the SCC exceeds the interrupting capacity of the circuit breakers. In this regard, optimal transmission switching (OTS) is proposed to reduce the short-circuit current while maximizing the loadability with respect to voltage stability. However, the OTS model is a complex combinatorial optimization problem with binary decision variables. To address this problem, this paper employs the deep Q-network (DQN)-based RL algorithm to solve the OTS problem. Case studies on the IEEE 30-bus system and 118-bus system are presented to demonstrate the effectiveness of the proposed method. The numerical results show that the DQN-based agent can select the effective branches at each step and reduce the SCC after implementing the OTS strategies.

Brief Analysis of the Short-circuit Current Limit Measure of A Domestic Steel Plant

Brief Analysis of the Short-circuit Current Limit Measure of A Domestic Steel Plant

Optimum Short Circuit Current Limiter Deployment Using Immune-PSO Algorithm

The optimum of short circuit current limiter deployment (SCCLD) is a 0-1 mixed integer programming problem. It is non-continuous, non-convex and nonlinear. Ordinary mathematic optimization can hardly solve it. In this paper, the sensitivity factor was defined to choose better candidates for active current-limiting measure installations as to reduce bus fault currents. And the integrated measures deployment is solved by a discrete particle swarm optimization algorithm with immune (IA-DPSO). The results of IEEE 39-bus system in New England are provided to validate the possible applications of the proposed method.

Первое в энергосистеме России токоограничивающее устройство на основе высокотемпературной сверхпроводимости

Superconducting fault current limiter (SFCL) is an innovative method for reducing the level of short-circuit currents in high-voltage electrical networks. This reduces the number of points of separation of the electrical network in conditions of short-circuit current limitation and thereby increases the network capacity and reliability of power supply to consumers. At the same time, the development of such devices poses new challenges for power engineers related to the integration of this equipment into the existing power system. The article discusses the process of implementation and pilot operation of the SFCT 220 kV pilot project (produced by CJSC “SuperOx”) at the 220/20 kV “Mnevniki” high-voltage substation in Moscow. The project required an extensive set of scientific studies and tests to confirm the characteristics of new devices and the possibility of their use in Russian power systems, the use of digital modeling technologies to test the operability of relay protection devices, as well as the development of new methodological documents for calculating the short-circuit current and relay protection parameters. As a result of the work, SFCT was switched on at the 220/20 kV “Mnevniki” substation at the end of 2019. The subsequent operation of the SFCT in 2019-2020 fully confirmed the declared characteristics of the device and the correctness of the selected technical solutions. The article is devoted to the features of the process of integrating a new device into the existing power system, the main technical solutions, the results of testing and operation of the device, as well as possible prospects for the development of SFCT technology.

Fault steady-state analysis method for the AC system with LCC-HVDC infeed

Fault steady-state analysis method can help to analyze the variation law of electrical quantities, clarify the fault characteristics, and provide the basis of power system design, protection scheme formulation, short-circuit current limitation and electrical equipment selection. Existing methods of fault steady-state analysis for alternating current (AC) system with line-commutated converter (LCC) high voltage direct current (HVDC) infeed are not suitable for high-severity AC system faults and existing equivalent models of LCC-HVDC system are inaccurate under asymmetrical AC system fault. Hence, a more accurate method is proposed in this paper. First, according to the relationship between the injected current of LCC-HVDC system and the fault phase voltage of commutation bus, equivalent models of the LCC-HVDC system under symmetrical fault and asymmetrical fault of AC system are established respectively. Based on the equivalent models of LCC-HVDC system and the fault sequence network of AC system, a fault steady-state analysis method for AC system with LCC-HVDC infeed is proposed. The proposed method is validated on CIGRE Benchmark HVDC model using PSCAD/EMTDC software. The results show that the proposed method is accurate and suitable for faults of different severities in AC system with LCC-HVDC infeed.

SHORT CIRCUIT CURRENT CONTROL DEVICE TO INCREASE THE EFFICIENCY OF POWER SUPPLY SYSTEMS

Amid growing levels of short-circuit currents, issues related to increasing the efficiency of methods and means of limiting short-circuit currents are central in the context of development of Ukraine’s energy sector. A key factor here is intensifying pace of decreasing electricity losses in power supply production systems (PSPS), which could be achieved through implementation of new and improved efficiency of existing methods and means of limiting short circuit currents. The scientific and practical relevance of improving the functioning of credit limit short – circuit (short circuit), formulated the goal and objectives of research. As a solution proposed research and the way to manage complex limitation of short circuit currents in electricity supply production systems under the reactor – controlled shunt. The algorithm of the system reactor – controlled shunt. For the first time the schemes cause – effect relationships occurrence of short – circuit currents – Figure Ysikavy according to ISO 9004. The proposed method of limiting short circuit currents in the PSPS and the suite for its implementation under the controlled shunt reactor scheme fully compensates for all the disadvantages that occur when limiting short circuit currents in the PSPS under the unregulated shunt reactor scheme. It should also be noted that the limitation of short circuit currents in the PSPS under the controlled shunt reactor scheme has certain advantages over other means of limiting short circuit currents.

Dual Operation Mode of a Transformerless H-Bridge Inverter in Low-Voltage Microgrid

This paper presents the bilateral operation of a transformer-less H-bridge inverter as a power flow controller and fault current limiter in low-voltage distribution network. A novel control strategy has been developed to initiate and activate the H-bridge inverter to control the power flow at point of common coupling (PCC). On the other hand, the H-bridge inverter operation like a short-circuit current limiter during grid disturbance event and its smooth reinsertion after fault clearance have also been clarified. Besides, an island mode control strategy incorporating synchronization controller, and proper coordination with flip flops have been implemented in order to synchronize the microgrid with the main grid before reclosing the circuit breaker. The results confirm: The effectiveness and feasibility of the novel control methodology in activating the real power flow; the inverter capability of minimizing the short-circuit current during fault and the successful resynchronization of the microgrid voltage source inverter (VSI) and the H-bridge inverter to the main grid.

Analysis of design features of inductive electromagnetic current limiter

The design circuits of an electromagnetic short-circuit current limiter of inductive type with movable armature and moving core are considered. A comparative analysis of the design features of the electromagnetic current limiter with copper or superconducting winding is carried out. The operation principle of the electromagnetic short-circuit current limiter of inductive type with copper or superconducting winding is considered. The peculiarities of operation modes of the electromagnetic short-circuit current limiter of inductive type with copper or superconducting winding are analyzed. Using results of the mathematical modeling of the magnetic system of the electromagnetic short-circuit current limiter by the Finite Element Method in the FEMM software environment, the character of the distribution of the magnetic flux density in the nominal mode and in the current limiting mode is determined, which allows to determine the parameters of the current limiter and design features. In accordance with the design features of the electromagnetic short-circuit current limiter of inductive type, the sequence of calculation of the basic parameters of the magnetic system, taking into account the voltage drop factor, is given. The basic equations of the electric equilibrium of the voltage drop of the electromagnetic short-circuit current limiter of inductive type for nominal mode and short-circuit conditions are given. The use of the design circuit of the electromagnetic short-circuit current limiter with superconducting winding can provide energy-saving in nominal mode. The use of high-temperature superconducting wire due to increased critical parameters will ensure preservation of the superconducting state of the winding in short-circuit mode.

Reducing Short Circuit Level in 400 kV Iraqi Grid System by Using FACTS Device

Electrical power systems are different in their sizes because of their amount of generation power stations, substations, transmission lines and loads. Therefore, these factors may impact on short circuit levels values. Capacity of power stations and dummy transmission lines in Extra high voltage grid (400kV) of the Iraqi Electrical power grids cause high short circuit levels values such that exceed both rating of the peak and breaking capacity of switchgear equipment's. Reduction of short-circuit levels by using Fast-acting Flexible Alternating Current Transmission Systems (FACTS) types devices in power grids maintain the operation of power grids with acceptable value of short circuit levels for their electrical equipment's and preventing cascading event outages which may lead to blackouts. This paper mainly studies strategies on how to add Short Circuit Current Limiter (SCCL) device by determining its number, value and location of connection in power grids by programing with (PSS™E version 30.3 Package Program). IEEE 25-bus system is used for testing the adding series SCCL at power transmission lines method procedure. The results of adding series SCCL with power transmission lines give significant reducing short circuit levels for the stations have highest short circuit levels in order to prevent the blackouts of overall power grid.

LVRT Performance Enhancement of DFIG-Based Wind Farms by Capacitive Bridge-Type Fault Current Limiter

Low voltage ride-through (LVRT) is one of the main requirements of the new grid codes for integration of wind farms (WFs) to power system. In this paper, to enhance the LVRT capability of doubly-fed induction generator (DFIG)-based WFs, a capacitive bridge-type fault current limiter (CBFCL) is proposed. The CBFCL is based on the conventional inductive bridge-type fault current limiter (IBFCL), in which the limiting impedance (LI) of the IBFCL is adapted according to WFs requirement to provide the reactive power needed of WFs after fault clearance. The WF has been modeled based on an equivalent aggregated DFIG. To check the effectiveness of the CBFCL, its performance is compared with the IBFCL. The PSCAD/EMTDC simulation results show that the CBFCL is an effective and novel solution for LVRT augmentation and short circuit current limitation of WFs. Also, it was found that the CBFCL is more competent to satisfy the LVRT requirements than the IBFCL.