Fault Current Level Research Articles

A multi-objective optimization of FCL and DOCR settings to mitigate distributed generations impacts on distribution networks

Despite providing increased reliability and power quality in meeting the load demand, the integration of DGs has imposed challenges on the protection system. High penetration of DGs changes the overall network impedance and increases the fault current level in the network. Consequently, some buses are exposed to critical conditions, violate the circuit breakers (CB) handling capacity, and affect the existing relay coordination settings. To mitigate these adverse impacts, fault current limiters (FCL) can be a potential solution to minimize the short circuit current within permissible switchgear-rated limits. Due to its expensive cost, it is crucial to ensure the optimal FCL placement and sizing, and at the same time maintain the effectiveness of the protection performance during various network operation states. This research formulates FCL and directional overcurrent relay (DOCR) settings as a combined protection coordination scheme optimized by a multi-objective hybrid optimization technique. The proposed formulation aims to determine the minimal FCL sizing with minimum investment cost to satisfy the relay coordination constraints at high fault-level buses, irrespective of DG locations and network operating state. User-defined relay characteristics (UDC) are employed to intensify the DOCR coordination performance and obtain minimum operating time, where the conventional inverse relay constants (A&B) are optimized with (TSM & Ipu). The combined UDC relay settings and FCL problem formulation solution attained by MO-hybrid optimization can lessen the escalated electromagnetic stresses, costly switchgear replacement, and relay maloperation. The performance of the proposed technique is assessed by implementing it on the radial (IEEE-33 Bus) and meshed (IEEE 30-Bus) DNs with optimized FCL sizing and relay settings. The optimal results demonstrate the effectiveness of the proposed technique in maintaining the relay coordination performance in the presence of DGs and FCL under an ON/OFF grid connection.

An advanced control and protection integration scheme for microgrids

The increasing trend in integrating intermittent distributed energy resources (DERs) into AC microgrids presents operational challenges in stability and protection. In islanded microgrids with power electronic interfaces, protection poses a major challenge due to the reduced level of short circuit currents resulting from inverter output capabilities. However, traditional protection schemes that are utilized in distribution systems are no longer appropriate to protect the microgrid in the presence of different levels of fault currents. This paper develops an integrated control and protection framework based on state observer and fault current limiter (FCL) devices. The state observer has been developed to detect and identify the faults that occur within multiple protection zones. In addition, controlled switches, consisting of FCLs, have been utilized to limit the fault currents and provide rapid switching during the faults, thereby improving system reliability. An adaptive control and protection integration scheme proposed in this paper has been applied to islanded microgrid configuration and is demonstrated to be an effective means to protect the system and maintain the voltage and frequency within an acceptable range with the capability of power continuity during both transient and persistent faults.

Optimal settings of multiple inverter-based distributed generation for restoring coordination of DOCRs in mesh distribution networks

Integrating the inverter-based distributed generation (IBDGs) into distribution systems has a great impact on coordinating directional overcurrent relays (DOCRs). The IBDGs shifts the fault current level leading to relay time grading errors and incorrect order of operations. For mitigating this problem, this paper proposes a method building on the versatility of IBDGs controls. The proper settings of IBDGs current magnitude and angle restore the fault current level and the corresponding DOCRs operating times. The settings of IBDGs are formulated as a non-linear optimization problem to maintain the operating times of individual DOCRs within a narrow band after IBDGs integration. Also, the settings of IBDGs are optimized in the presence of dispersed synchronous generators (DSGs). The optimal sizing and siting for IBDGs are determined according to DSGs position. The interior-point algorithm is employed to find the optimal IBDGs settings. Applications are carried out on two meshed networks: the 33 kV 30-node distribution system and the 15-bus test system. The proposed settings are insensitive to fault locations. For IBDGs outages, less than 2% of the relay pairs are sensitive to these outages. The proposed approach introduces a zero-cost strategy for mitigating the IBDGs impact and preserving the protection coordination without re-setting DOCRs.

Short-circuit constrained distribution network reconfiguration considering closed-loop operation

This paper presents a novel scenario-based stochastic mixed-integer second-order cone programming model to solve the problem of optimal reconfiguration of distribution systems with renewable energy sources considering short-circuit constraints. The proposed formulation minimizes technical losses by modifying the statuses of sectionalizing and tie switches, allowing the operation of distribution networks with radial and closed-loop topologies. Since the formation of loops could impact fault current levels, short-circuit constraints are considered in the problem formulation. Numerical experiments are carried out using an 84-node system and the results demonstrate the effectiveness of the proposed formulation to reduce technical losses notably when a closed-loop operation is allowed. Additionally, it is verified that short-circuit constraints prevent the adoption of network configurations with high short-circuit values.

A Coordination Scheme for a Combined Protection System Considering Dynamic Behavior and Wind DGs Fault Ride-Through Constraints

• A proposed design of a hierarchical protection scheme is presented. • Protective devices are optimally coordinated based on fault current transients. • Hybrid superconducting fault current limiters are optimally allocated to keep coordination under synchronous and inverter-based wind DGs. • Ride-through capability of wind DGs is integrated into the fault current limiter sizing problem. • Changes of network topology and variation of detected fault current are considered. A combined protection system has multiple types of devices such as directional overcurrent relays, reclosers, and fuses to protect distinct areas in a DG-incorporated network. An approach for setting all protective devices to realize complete coordination of adjacent ones taking transient responses into account is presented. The participation of synchronous generator-based and/or inverter-based wind DGs can degrade protection coordination. So, a scheme for sustaining coordination by optimal hybrid superconducting fault current limiters is proposed. The scheme can cope with variation of network topology; and handles the change of fault current level perceived by the protection device under a given topology. Moreover, instead of the conventional steady-state models, more realistic dynamic models of relays, reclosers, DGs, and fault current limiter are used. As a serious operation problem, undesired tripping of wind DGs under fault condition can occur due to the sag of terminal voltage below certain limits defined by national and international standards. Therefore, the proposed scheme prevents this undesired tripping of wind DGs by integrating its ride-through capability constraints into the fault current limiter allocation problem. The proposed approach is applied to the IEEE 9-bus and 30-bus systems. Results confirm the efficacy of the proposed method.

Alpha Harris Hawks Optimization based Overcurrent Relay Coordination with Hybrid Time-Current-Voltage Characteristics Considering the Grid-Connected Distributed Generation

The conventional protection schemes may lead towards the inadvertent operation of the protection devices with the increased penetration of renewable energy sources based distributed generation (RES-DG) in distribution networks (DN). The miscoordination and the malfunctioning of directional overcurrent relays (DOCR) may occur due to significant change in the fault current level (FCL) and the change in the network topology form the radial to ring topology caused by the RES-DG. Optimization algorithms (OA) and modification in relay characteristics were mostly used to tackle the DOCR miscoordination problem. However, in this paper, a fast and an accurate protection coordination scheme is proposed to eliminate the DOCR miscoordination and to reduce the overall operation time of DOCRs by employing an advance optimization algorithm along with an innovative modification in the relay characteristics. In the first step, time-current characteristics (TCC) of the conventional DOCR are modified to a hybrid time-current-voltage (TCV) characteristics by including the effect of the fault voltage in the relay characteristics equation. Thereafter, the performance of conventional Harris Hawk’s optimization (HHO) is enhanced with an improvement in the exploration strength of the HHO by an adaptive mutation-selection of the alpha hawks during each iteration named as alpha-HHO (α-HHO). The protection coordination problem is formulated as a non-linear constrained optimization problem. The proposed protection scheme is evaluated on the IEEE-8 bus meshed DN. The standard IEEE-8 bus test system is modified by integrating multiple squirrel cage induction generators and PV-based RES-DGs at optimal bus locations. Detailed numerical studies are carried out with the help of simulations to show the performance of the proposed scheme. The results are compared with the existing protection schemes reported in recent literature. The investigation results show that the highest reduction in overall relay operating time with zero mis-coordination is achieved with the proposed scheme.

A novel current-limiting method for MMC-HVDC by coordinating virtual impedance control and fault current limiter

The modular multilevel converter (MMC) topology is very suitable for high voltage direct current (HVDC) system to achieve feasible power control, favorable black start capability as well as long-distance power transmission. This paper proposes a novel current-limiting method based on the coordination of virtual impedance control (VIC) and resistive fault current limiter (R-FCL) for MMC-HVDC, and it aims to effectively decrease the DC fault current level and assist the DC circuit breaker (DCCB) to remove the fault reliably and smoothly. Firstly, the MMC-HVDC’s topology and control strategy are expounded, and the modeling method of the VIC and the R-FCL is presented. According to the DC fault evolution, the time sequence coordination scheme of the VIC and the R-FCL for the MMC-HVDC is put forward. Then, considering the introduction of the proposed current-limiting method, the fault characteristics of the MMC-HVDC are theoretically deduced, and the capacity design of the VIC and the R-FCL is conducted. Using MATLAB, a typical ±320 kV MMC-HVDC system with VIC, R-FCL, and DCCB is built, and comparative simulations are performed. The results indicate the proposed approach can strongly limit the DC fault current within the acceptable range, and reduce the electrical stress and thermal stress in the MMC and DCCB. The proposed approach possesses better techno-economics than the R-FCL alone to solve the DC fault problem, and a more efficient protection of the MMC-HVDC is realized.

A signed correlation index-based differential protection scheme for inverter-based islanded microgrids

The different fault characteristics of the inverter-based distributed generation (IBDG) units make the protection of the inverter-based islanded microgrids (IBIMGs) a formidable task. According to IEEE Std 1547.4, the limited fault current levels associated with the IBIMGs may result in misleading decisions of the traditional protective relays during fault occurrence. In this paper, a new differential protection scheme for the IBIMGs is introduced based on the signed correlation technique. The proposed scheme is formulated based on the signs of the instantaneous phase currents at both line ends instead of the current magnitudes. In addition, a signed correlation index is defined to measure the similarity between the signs of the instantaneous phase currents at both line ends employing only a time window of half-cycle. Moreover, a fault detection index is introduced to discriminate the internal faults from other events. In order to validate the proposed scheme, the 9-bus IBIMG and the modified IEEE 33-bus system are simulated on the PSCAD/EMTDC platform, and several scenarios are conducted, including load switching, outage of IBDG units, external bus faults, and internal faults. The obtained results emphasize that the proposed scheme operates correctly considering all types of faults, different fault resistances and inception angles, as well as measurement and synchronization errors.

Mitigating low fault current in microgrids through renewables-battery hybrid units

One of the major problems with inverter-based distributed generation (IBDG) compared to synchronous generators, is the little fault current contribution during fault condition in islanded mode of operation. Particularly, the increased penetration of IBDGs such as renewable energy sources (RES) into the microgrid (MG) has a substantial impact, as it would lower the fault current level; such diminished fault current induces mal-trip and fail to trip of protective relays causing problems in fault detection and isolation and consequently degrades the MG protection. To tackle this issue, this paper proposes an adaptive protection scheme that considers RES, Battery Energy Storage System (BESS), Hybrid units in the MG. The proposed scheme applies an internal cooperation strategy between RES and BESS to ensure reliable output power. Then, a power flow-based fault analysis is performed to determine the fault current paths. A fault current zone (FCZ) is formed out of the IBDGs that are found to be on the observed fault current paths and an optimal residual capacity is determined for the BESS units within FCZ; the optimization is formulated as a nonlinear program for maximizing the residual capacity of the BESS unit. Validation of the proposed scheme is carried out through simulation of the IEEE 33 bus systems. The simulation results confirm the effectiveness of the proposed protection scheme and its superiority to competing approaches in the literature.

Improved Recovery Time and Voltage Stability for Resistive Superconductor Fault Current Limiters

Fault current levels occurring in power systems force the breaking capacities of the breakers. In the power system elements, the generator, transformer, cables, etc., are exposed to the dangerous effects of fault current until the breaker clears the fault. Various limiting methods have been developed to eliminate this adverse situation in recent years. One of these methods is Superconducting Fault Current Limiters (SFCL). With the discovery of High-Temperature Superconductors (HTS), SFCL's Resistive type has become more popular. Resistive SFCL (R-SFCL), based on the non-linear resistance property of superconducting materials, limits the fault within the first half period. However, it cannot provide such a fast response after the fault. The time required to regain the superconducting state after the fault is the recovery time. For R-SFCL manufacturers, recovery time is a design parameter that must be kept short. This study examines limiting performance, recovery time, and voltage stability with the dynamic model created using MATLAB/Simulink. With the shunt breaker method proposed in the study, the recovery time was shortened, and the voltage stability improved.

Practical Fault Current Level Evaluation and Limiting Method of Bipolar HVdc Grid Based on Topology Optimization

This article investigates the relationships between the pole-to-pole fault current and the topology in the bipolar voltage sourced converter (VSC)–high-voltage dc (HVdc) grid. Based on the improved high-frequency equivalent model, it is found that the pole-to-pole fault current value is significantly influenced by the grid topologies, which is different from the situation in symmetrical monopole dc grid. It is also found that only the adjacent converters and the subadjacent converters of the fault lines will impact the fault currents, while the other converters with longer electrical distances basically have negligible contribution to the fault current. According to above mechanism, the simplified index is also proposed in this article to evaluate the fault current level of dc grid efficiently when its topology varies. The proposed index can make evaluations by simple calculations between different topologies and avoid solving complex differential equations one by one when pole-to-pole fault occurs at different lines. Based on the practical evaluation index, the genetic algorithm is used to optimize the dc grid topology to limit the fault current level. Finally, the simulation verification is performed based on the six-terminal bipolar VSC–HVdc grids, and some suggestions on topology design are given.

A Robust Protection Scheme for Multimicrogrids Using Fault Current Limiter

The operation of multimicrogrids (MMGs) can cause significant impact on power system network, especially changes in level and direction of fault current. The fault current level may exceed rating of existing directional overcurrent relays (DOCRs) that lead to sympathetic tripping or fail to trip DOCRs in the network. It is expensive and extremely challenging to upgrade or replace the existing DOCRs in the network. If not properly addressed, this issue may hinder the deployment of MMGs in to the network. Hence, this article proposes a robust protection scheme for DOCRs coordination in MMGs without replacing existing DOCRs in network. First, the proposed scheme calculates optimal settings of DOCRs in all stand-alone microgrids of MMG during islanded mode. Then, optimal values of fault current limiters are obtained using calculated optimal settings. The main advantage of proposed scheme is that it provides one set of DOCRs settings valid for all operating modes of MMG. In this work, the DOCRs coordination problem is formulated as nonlinear problem and solved using proposed hybrid approach symbiotic organisms search (SOS) and nonlinear programming (NLP). The initial solution is determined by SOS and final solution is obtained using NLP. Further, the proposed scheme is examined during gird connected and islanded modes in two different configurations (series and parallel) of MMG, which are not stated in previous literature. Finally, simulation results are validated using numerical relay and real time digital simulator, which are interfaced through voltage and current amplifier to execute hardware-in-loop test bed.

Efficient Smart Grid Fault-Identification Approach with Photovoltaic- Distributed Generators Based on Monitoring of Current/Voltage Signals

A Smart grid fault-identification is a critical aspect of the protection relaying system with the integration of renewable energy based on photovoltaic-distributed generators. With increasing the distributed generators usage in smart grids, the conventional relaying techniques suffer from maloperation owing to the risk of changing fault current levels. Therefore, in this paper, a discrete wavelet transform (DWT) and the statistical cross-alienation coefficients-based method is proposed to detect and classify different types of faults considering the dynamic response of photovoltaic. The proposed protection scheme does not require any extra-measuring systems as it relied on the one-ended measurements that are installed at PV-feeder over a moving window, which are available due to the use of advanced measuring facilities in smart grids. This opens the doors to transferring real-time data from / to protective relays, and then these datasets are processed for discriminating among various internal fault classes and external and healthy conditions. Intensive simulation studies are executed using PSCAD/EMTDC platform along with the validation of the proposed scheme. The 300 kW PV panel is connected to grid though a boost converter and Voltage Source Inverter. Results unveil that the application of alienation concept and differential faulty energy method for approximation coefficients-based DWT for voltage and current signals show a better performance in terms of accuracy and computational burden.

Limitation Analysis of 1st and 2nd Generation Superconductors used in Resistive Superconductor Fault Current Limiters

Fault currents in power systems force valuable power system elements thermally, dynamically, and electromagnetically until the arc disappears. Installation elements that can withstand fault currents or damage existing components require a high cost. Installing components that withstand fault currents and the damage of fault currents to existing components are costly. Resistive Superconducting Fault Current Limiter (R-SFCL), one of the modern limiting methods, increases the safety and sustainability of the system by eliminating these risks. In this study, a dynamic model was created in MATLAB/Simulink for 1G and 2G HTS used in R-SFCL, and their response to single phase-to-ground fault was observed. According to the simulation results, the most advantageous HTS type for R-SFCL was determined. The fault current level, limitation rate, resistance and temperature values, and response times were compared in terms of limiting performance.

Modelling and Simulation of Fault Current Limiter in Single and Three Phase Line for Compensating Voltage Sag a Review

A high potential fault current levels in power grid is not a new approach, and should eventually exceed, the limitation of short-circuit-current would be existed protection devices. Different to pricey system upgrades of protection devices, Fault Current Limiters (FCL’s) gives an additional cost efficient solutions to forestall recent protection devices and different instrumentality on the system from being broken by excessive fault currents. Evaluation of short circuit faults may usually the origin of voltage sags at a purpose of common coupling point (PCC) during a power network, the extent of the voltage sag is proportional to the short current level, reducing the fault current level at intervals the networks will scale back voltage sags throughout faults and defend sensitive loads that are interfaced to a similar PCC. The planned structure prevents voltage sag and counter balance the phase-angle of the PCC once fault prevalence. As a result, different feeders which are interlinked to the sub-station PCC can have attentive power quality. During this paper a high performance 3-phase fault current electrical model is planned. A Matlab/Simulink model is developed and simulation results are conferred.

Performance Analysis of Overcurrent Protection in a Digital Substation with Process Bus

The digitization of electrical substations brings great challenges for the commissioning of electrical protections, and interoperability tests must be performed with different equipment. Therefore, this work evaluates the response time of an electrical protection relay operating with sampled values in a digital substation with a process bus. A test scheme is proposed to emulate the process bus based on analyzing the main components in a digital substation with multi-vendor device interoperability. In addition, the delay times of the protection relay with the process bus are measured, considering interoperable infrastructure as a fundamental factor in the system performance. The results are compared with the response times of a conventional relay that operates with analog signals to identify the impact of the digitalization of signals in electrical substations with a process bus. Each relay has an instantaneous overcurrent function adjusted to operate with the same pickup currents at different fault current levels. The results show that tripping times are admissible for the operation of the protection relays, considering three-time measuring points in the test scheme. The time delays found are related to high data traffic in the communication network and the traffic saturation according to the time measuring point. Other delays related to processing SVs in an MU do not represent a risk for the protection scheme. For the industry, the methods presented in the research are useful for configuring and testing electrical substations with different equipment and topologies. In addition, the results presented here seek to generate confidence in companies and engineering teams when migrating to systems with digital substations.

Fault Classification in a DG Connected Power System using Artificial Neural Network

Distributed generation is playing an important role in power system to meet the increased load demand. Integration of Distributed Generator (DG) to grid leads to various issues of protection and control of power system structure. The effect of the distributed generators to the grid is changes the fault current level, which makes the fault analysis more complex. From the different fault issues occurs in a distributed generator integrated power system, classification of fault remains as one of the most vital issue even after years of in-depth research. This paper emphasis on the classification of faults in DG penetrated power system using Artificial Neural Network (ANN). Because researchers are attempting to detect and diagnose these faults as soon as possible in order to avoid financial losses, this work aims to investigate the sort of fault that happened in the hybrid system. This paper proposed artificial neural network based approaches for fault disturbances in a microgrid made up of wind turbine generators, fuel cells, and diesel generator. The voltage signal is retrieved at the point of common coupling (PCC). The extracted data are used for training and testing purpose. Artificial neural network technique is utilized for the classification of fault in the simulated model. Furthermore, performance indices (PIs) such as standard deviation and skewness are calculated for reduction of data size and better accuracy. Both the fault and parameters are varied to check the usefulness of the proposed method. Finally, the results are discussed and compared with different DG penetration.

A Novel Method for Real Time Protection of DC Microgrid Using Cumulative Summation and Wavelet Transform

DC microgrid is a compact framework comprising interconnected nearby sources and loads. The renewable energy source used in DC microgrids being intermittent leads to the change in the power availability as well as the fault current levels. In such situations, detecting and clearing the faults is very important to protect the DC microgrid without compromising on fault clearing time and interruption of the load. This paper proposes a hybrid Cumulative Sum (CumSum) and Wavelet transform-based approach to detect the fault. The CumSum value raises the amplitude by averaging the fault current. Wavelet transforms obtain important fault current features by decomposing the current signal. The hybrid method of CumSum and Wavelet analysis proposed here enables the detection of the fault and differentiates the fault condition from sudden load variation. Additionally, it helps to recognize the location of the fault by the wavelet energy difference. The proposed scheme is tested with a developed ring-type low voltage DC (LVDC) microgrid hardware model under various fault conditions. The scheme is implemented using TMS320F28069 digital signal processors (DSP) of Texas Instruments. The hardware results are validated using MATLAB simulation. The proposed method performance is also compared with the existing methods used for DC microgrid protection. The outcome shows that the proposed method has a high accuracy of 98.72%, selectivity of 96.08%, and reliability of 99.01%. The execution time required by the proposed method is also less.

Distributed generation adverse impact on the distribution networks protection and its mitigation.

Integration of Distributed Generation (DG) generates problems for the protection of Distribution Networks (DNs) in power systems. When DG is integrated into a power distribution system (DS), the radial nature of the network is altered and the power starts to flow in a reverse direction. In addition to the reverse flow of power, the DG upsurges the fault current level and affects the existing time intermission coordination of the protective overcurrent relay. This study proposes a reverse power relay (RPR) and Fault Current Limiter (FCL) to mitigate the fault current level and reverse power flow in a Distribution Network (DN) by the use of DG. The FCL works only as a unidirectional fault current limiter (UFCL) by restricting the flow of fault current that occurs in the main grid (MG) of the DG. However, FCLs can protect the flow of fault currents from the MG by affecting the operational flexibility and reliability of the DG. To overcome the flow of fault current of the DG, this study proposes RPR to monitor the power flow to the DG. Collectively the study focuses on the protection of radial DS by using RPR and UFCL. The analysis and the modeling were conducted on the 15KV DN of the radial feeder in Debre Markos DN. The 3Φ fault analysis (which is more severe than others) was performed to validate the protection capability of the mitigation techniques which were proposed in this study.

Review on Compensating Voltage Sag in Single Phase and Three Phase Lines Using Fault Current Limiter

A high potential fault current levels in power grid is not a new approach, and should eventually exceed, the limitation of short-circuit-current would be existed protection devices. Different to pricey system upgrades of protection devices, Fault Current Limiters (FCL’s) gives an additional cost efficient solutions to forestall recent protection devices and different instrumentality on the system from being broken by excessive fault currents. Evaluation of short circuit faults may usually the origin of voltage sags at a purpose of common coupling point (PCC) during a power network, the extent of the voltage sag is proportional to the short current level, reducing the fault current level at intervals the networks will scale back voltage sags throughout faults and defend sensitive loads that are interfaced to a similar PCC. The planned structure prevents voltage sag and counter balance the phase-angle of the PCC once fault prevalence. As a result, different feeders which are interlinked to the sub-station PCC can have attentive power quality. During this paper a high performance 3-phase fault current electrical model is planned. A Matlab/Simulink model is developed and simulation results are conferred.