Conventional Protection Schemes Research Articles

AC Micro Grid Fault Analysis

Implementation of micro grid concept creates several issues to the existing protection scheme in the radial distribution network. Depending on the location and capacity of the distributed generators, the short-circuit current from the main grid and distributed generations causes variations in the fault current levels inside the micro grid. The changes cause effect of sympathetic tripping, blinding of protection, relay over-reaching, relay under-reaching and loss of selectivity of the overcurrent protection scheme. Such issues must be managed carefully to ensure full benefit from micro grid adaptation. Conventional protection schemes are unable to detect fault current levels common in micro grid. Several methods have been proposed in various research paper. Micro grid protection is substantial to provide reliable and continuous power supply to the customers. The main aim of proposed work is to detect the fault for fast restoration of the system back to the normal operation. The proposed protection scheme for micro grid uses intelligent electronics device for detecting the fault

A differential amplitude variation based pilot relaying scheme for microgrid integrated distribution system

Abstract The inclusion of inverter-interfaced distributed generating sources (IIDGS) in the active distribution network offers operational and protection constraints. Dynamic fault behavior of these DGS results in changes like the radial distribution systems. Thus, conventional protection schemes fail to discriminate the in-zone and out-zone faults. Hence, this manuscript describes a new protection scheme based on current variation at the relay location used to discriminate the internal and external faults. This technique requires phasor information of the current signals of both ends and adjacent lines using micro phasor measurement units (µPMUs). Using the current phasor information two components named internal and external are computed at the relay location which is called differential amplitude variation index (DAVI), used to identify the internal and external faults. A modified two-feeder radial distribution network and modified IEEE-13 bus test systems are modeled using EMTDC/PSCAD to validate the proposed strategy. Numerous disturbance cases have been simulated and the feasibility and applicability attributes of the suggested method are verified from the results.

A pilot protection method for the transmission line of wind farm-flexible DC system based on high-frequency inductance difference coefficients

Conventional protection schemes for wind farm-flexible flexible direct current (DC) system transmission lines are susceptible to malfunctions in external fault scenarios and exhibit limited immunity to fault resistance in internal fault scenarios. In the pursuit of enhancing pilot protection performance, a novel protection method based on high-frequency inductance difference coefficients is proposed. Firstly, the fault transient characteristics of both the wind farm and the flexible DC converter are analyzed, deriving their respective transient models. Subsequently, a high-frequency fault component network comprising inductive impedances is constructed. Then, a protection criterion based on high-frequency inductance difference coefficients is formulated. Finally, the proposed method is subjected to simulation tests on the RT-LAB platform. The results validate its capability to accurately identify the locations of internal and external faults, demonstrating robust immunity to fault resistance. Because it operates independently of synchronous information interaction, it functions rapidly.

Transformer faults identification via fuzzy logic approach

The need for a constant electricity supply is at an alarming rate especially in the 21st century due to the high rate of increase in industrialization across the globe. Conventional protection schemes such as differential relays, Buchholz relay, and other techniques such as genetic algorithms and artificial neural networks, do not match the precision and reliability needed for transformer fault indentification, due to their complexity in computation, tedious training system, time consumption, and need the of human experts. The method proposed in this research is the use of a fuzzy inference system in detecting potential faults in power system transformers. The faults in the transformer were observed and analyzed using a simulation system of MATLAB/Simulink software. The suggested approach ensures swift identification of faults as it relies on if-then rules and only uses current and voltage measurements with 100% independence toward the power flow direction, making it highly reliable and simple to implement compared to other techniques for transformer fault identification.

Adaptive harmonic-based protection coordination for inverter-dominated isolated microgrids considering N-1 contingency

Protection coordination is typically approached considering the main network configuration. Nevertheless, contingencies such as generator or line failures may disrupt power grids. Low fault currents in inverter-based isolated microgrids adversely impact the conventional overcurrent protection schemes. This paper proposes a sensitive and selective protection scheme for isolated microgrids using an adaptive third harmonic voltage generated by inverter-based distributed generators (IBDGs) and adapted to fault severity. The generated harmonic voltage results in a harmonic layer established during faults and is decoupled from the fundamental fault current, which is limited by IBDGs. Harmonic directional overcurrent relays sense the generated harmonic currents and voltages at the relay location to ensure optimal protection coordination (OPC). The OPC problem is formulated as a constrained nonlinear program to determine the optimal relays’ settings. The constraints are defined for the isolated configuration and each potential configuration resulting from an N-1 contingency. A radial microgrid that is part of a Canadian urban distribution network is used to ensure the successful operation of the proposed protection scheme. The results demonstrate the ability of the proposed scheme to protect isolated microgrids and preserve protection coordination without communication.

Enhanced Non-Communication-Based Protection Coordination and Advanced Verification Method Using Fault Impedance in Networked Distribution Systems

In recent years, the networked distribution system (NDS), which is normally connected to the distribution line (DL), was actively studied as the topology of the future distribution system for reasons such as improving supply reliability, improving line utilization, and increasing the capacity of distribution generators (DGs). However, the NDS creates new issues in terms of protection coordination because of its bidirectional power flow and fault current flow. The issues associated with conventional protection schemes in the NDS include malfunction of protective devices due to bi-directional fault currents and failure of protection coordination due to communication failures between protective devices. When applying a conventional protection method in the NDS, the protection schemes become complicated, and there is a risk of protection coordination failure due to communication failure between protective devices. To solve this problem, this paper proposes an effective and innovative non-communication-based protection algorithm for protection coordination in the NDS. The proposed protection algorithm utilizes fault impedance characteristics, which allow not only determination of whether a fault occurred, but also the ability to identify the exact fault point. Therefore, the proposed method is expected to be sustainably utilized and contribute to developing protection schemes and devices in various system topologies and scenarios in the future. Additionally, this paper addresses the overall concept of hardware-in-the-loop simulation (HILS) and directly verifies the proposed protection algorithm using HILS. Therefore, this study establishes a sustainable foundation for future research on protection coordination using HILS.

Communication-less adaptive directional overcurrent protection strategy considering islanded mode detection in active distribution networks

The integration of distributed energy resources (DERs) in electric distribution networks originates the Active Distribution Networks (ADNs). The presence of DERs introduces challenges to conventional protection schemes due to bidirectional power flows and variations in fault current magnitudes; furthermore, the connection and disconnection of DERs result in multiple ADN operating modes (OMs), deteriorating the effective operation of protective relays. Considering the above, this document presents an adaptive protection strategy to address the challenges related to the variable nature of the ADN operation. The main contribution of the proposed approach is accurate islanded mode detection without requiring communication links, enabling fault detection in all ADN operating modes. The protection strategy maintains directional overcurrent relays' coordination using local voltage and current measurements to continuously estimate the Thevenin equivalent, fault currents, and adaptive coefficients.Relay coordination is maintained through tests conducted on a modified IEEE 34-bus feeder, considering several OMs, fault types, and locations. A comparison between the proposed adaptive protection strategy and a conventional overcurrent scheme shows that relay operating time is better in 100% of the analysed cases for the former strategy. On the other hand, the maximum errors in the fault current estimation using the Thevenin equivalent parameters are between 0.05% to 2.6% for all of the analysed operating modes when compared with the true fault current magnitudes. Finally, the adequate results validate the potential of the proposed communication-less protection strategy for modern protective relaying applications.

CHALLENGES AND DESIGN ASPECTS OF MICROGRID CLUSTERING

With the growing penetration of distributed energy resources, the traditional microgrid concept is evolving into microgrid clustering, which decomposes the distribution system into interconnected microgrids to improve stability, reliability, and efficiency. Microgrid clusters coordinate power-sharing between microgrids and the main grid, effectively reducing problems such as voltage rise, harmonics, poor power factor, reverse power flow, and conventional protection scheme failures. However, there are challenges to overcome before adopting microgrid clustering, particularly in the design aspects. This paper critically reviews the challenges in the design of microgrid clustering, categorizing multi-microgrids into different architectures based on the interconnections' layout, evaluating reported control techniques in microgrid clustering, and presenting aspects of multi-microgrid protection. Possible areas of future research are highlighted to improve the operational aspects of microgrid clusters. Ref. 3, fig. 6, tables 2. Keywords: energy management; microgrid cluster; ring connection; power converter; protection; synchronization.

Adaptive Coordination of Relays in AC Microgrid Considering Operational and Topological Changes

Conventional protection schemes are vulnerable to varying changes in a microgrid with different types of distributed generators (DGs), which alter the fault current levels, leading to miscoordination of directional over-current relays (DOCRs). Due to limited storage in numeric relays, having one setting for each network scenario in the relays is infeasible. Also, schemes with one setting considering grid-connected mode (GCM) and islanded mode (IM) of operation with multiple scenarios may be infeasible for a microgrid with inverter-interfaced DGs due to low short-circuit level in IM. Thus, this article proposes an adaptive trip characteristics-based relay coordination scheme for a microgrid with different DGs, where two trip characteristics are assigned to each DOCR, one each for GCM and IM. Also, a novel framework for selecting the suitable trip characteristic is proposed. Hardware-in-loop simulations using Numerical Relay Development Environment for a meshed CIGRE microgrid, modified IEEE 34-bus distribution system, and comparison with previous works validate the proposed method's performance for various scenarios, such as the outage of a DG or line, variations in solar irradiation and wind speed, and network reconfiguration for different fault types during GCM and IM.

A protection scheme based on impedance for LV and MV lines in microgrids with high-impedance fault detection capability

Microgrid properties including bidirectional power flow in feeders, fault level decrease in the islanded mode, and intermittent nature of distributed generators (DGs) result in the malfunctioning of microgrid conventional protection schemes. In the present article, a protection scheme based on impedance is suggested for fault detection in LV and MV overhead and cable distribution lines in both grid-connected and islanded modes. To determine a fault detection index, new suggested equivalent circuits for doubly fed lines are applied. Relay location data and magnitude of positive sequence voltage of the other end of the line are used. It is simulated by PSCAD and MATLAB software in order to evaluate its performance and approve its validity. This scheme can detect even high-impedance faults in both grid connected and islanded modes in LV and MV overhead and cable distribution lines. In addition, it is robust against load and generation uncertainty and network reconfigurations. Low sampling rate and minimum data exchange are among the advantages of the proposed scheme.

Novel Adaptive Fault Detection Strategy in DC Microgrid Utilizing Statistical-Based Method

The DC microgrid emerges as a proficient solution for anonymously evolving DC loads and their accompanying applications. Overcurrent-based relaying schemes can't provide such systems with the desired sensitivity and selectivity. The differential scheme has become a prominent solution with an enriched data processing technique and advanced communication framework in real-grid scenarios. The faults may remain undetected with high fault impedance where the current direction doesn't change at fault inception in a differential scheme. The conventional local protection schemes result in limited performance with fixed relay settings. The threshold selection is multifaceted in various protection schemes and largely depends on system topology, leading to catastrophic failure with any system or operating conditions alteration. This article proposes an adaptive statistical Fano Factor tool-based scheme to detect and classify faults with enhanced sensor tolerance capability. The scheme utilizes the current data at line ends. The performance of the proposed method is tested under various operating scenarios, including instantaneous switching operations of sources or loads and an evolving case, where fault impedance varies during fault. The method is fast, effective with high impedance faults, and immune to system disturbances. Adaptability, robustness, sensitivity, and high efficacy are its strategic features even with different system topologies. The method's performance is tested using data obtained from PSCAD/EMTDC simulations for numerous cases.

Adaptive overcurrent protection scheme for distribution networks with connection of mobile energy storage devices

The increasing penetration of renewable energy sources in distribution networks has caused great challenges to the reliable operation of the conventional overcurrent protection schemes. In particularly, serious underreach and overreach problems of protection scope may occur under the ever growing application of mobile energy storage (MES) devices. To improve the adaptability to the connection of MES devices under distribution networks, this paper proposes an adaptive overcurrent protection scheme, which can avoid the unfavorable effects caused by infeed currents and out flowing currents. Firstly, the effects of MES device on the protection scope of the overcurrent protection strategy are investigated, considering the charging, discharging, and backup operation modes of MES device. Secondly, to adapt to the different operation modes, the equivalent impedance of MES device is calculated, and then it is introduced to determine the adaptive settings of fast current protection and time-critical fast current protection. Finally, the constructed adaptive overcurrent protection scheme can adapt to varied fault conditions, including different operation modes and output power of MES device, connection locations, fault locations, and fault types. Large amounts of simulation results show that the proposed adaptive overcurrent method can overcome the underreach and overreach problems of protection scope, demonstrating its good application prospects.

Compensated fault impedance estimation for distance-based protection in active distribution networks

Electric distribution networks are experiencing fast changes mainly due to the integration of distributed energy resources. These changes originate the active distribution networks, where several distributed energy resources are integrated, usually using power converters. In these active networks, the conventional control, operation, and protection schemes used in power systems are unsuitable, and as a consequence, new approaches must be proposed and tested. This paper analyses the distance relay performance in active distribution networks; as the main contribution, a communication-less compensation strategy is proposed to deal with the effects of fault resistance and the distributed energy resources’ infeed and remote currents. The obtained results demonstrate the excellent performance of the proposed compensation strategy aimed at determining the true value of the estimated positive sequence impedance. This compensation can be easily integrated into the software of conventional distance relays to overcome fault resistance, infeed, and remote current effects.

Reverse Blocking Over Current Busbar Protection Scheme Based on IEC 61850 Architecture

Substation Automation System (SAS) is currently in a matured state of technology that shall facilitate transformational changes from conventional protection scheme. IEC 61850 protocol is considered as the crux of digital SAS due to its multifunction features that include seamless communication, ability to integrate various intelligent electronic devices, potential for improved real-time condition monitoring, reliable protection, and control of critical electrical assets. Because the application of IEC 61850 in SAS is relatively new and has not fully implemented in many substations yet, further feasibility studies using multivendor equipment to assess its performance under different operating conditions is imperative. In this article, a practical reliable and efficient reverse blocking over current bus bar protection scheme based on IEC 61850 is implemented and tested. Also, a comparison of digital SAS and conventional protection scheme is presented to highlight the superiority of the former one. Experimental results attest the reliability and effectiveness of the proposed digital protection scheme along with the accuracy and security of transmitting data packets using sampled values and generic objective-oriented substation event communication protocols adopted by IEC 61850.

An IoT and Semi-Supervised Learning-Based Sensorless Technique for Panel Level Solar Photovoltaic Array Fault Diagnosis

The performance of solar photovoltaic (SPV) systems is significantly affected by faults in the SPV arrays. Changes in environmental conditions and nonlinear characteristics of solar cells make it challenging to identify faults by conventional protection schemes. Existing learning-based fault diagnosis approaches require voluminous data and sensors, making them costly and challenging to integrate with existing SPV systems. Moreover, the lack of panel-level monitoring in existing approaches renders them incapable of pinpointing the precise location of the faulty panel. To address these issues, this paper proposes a methodology for detecting faults, localizing the exact faulty panel, and accurately classifying faults in SPV arrays. The methodology involves a sensorless electronic circuit using a bipolar junction transistor and Zener diode for fault detection, an IoT-based web application for monitoring individual solar panels for fault localization, and a deep autoencoder-based semi-supervised learning module followed by a hybrid support vector machine and logistic regression for fault classification. The proposed methodology is a low-cost and less data-intensive solution that results in precise fault detection, exact faulty panel localization, and fault classification with an overall accuracy of 99.67%. The methodology is validated in a laboratory-scale real-time setup of a grid-connected SPV system under varying electrical and environmental conditions.

Harmonic Dual-Setting Directional Overcurrent Protection for Inverter-Based Islanded Microgrids

Limited fault currents in inverter-interfaced islanded microgrids impose immense challenges on conventional overcurrent protection schemes. This paper proposes a sensitive and selective protection scheme for islanded microgrids using a third harmonic voltage generated by inverter-interfaced distributed generators (IIDGs). The generated harmonic voltage results in a harmonic layer formed during short-circuit faults and is decoupled from the fundamental fault current, i.e., limited by IIDGs. Further, the generated harmonic voltage is adaptively adjusted based on fault severity to enhance protection sensitivity and obtain a universal set of relays’ settings. The proposed protection scheme utilizes harmonic directional overcurrent relays (HDOCRs) equipped with a dual-setting time-current-voltage setting that sense the generated harmonic voltages and currents at the relay location to ensure optimal protection coordination (OPC) of islanded microgrids. The OPC with the proposed dual-setting is formulated as a constrained nonlinear program to determine the optimal forward and reverse relays’ settings. The proposed scheme is tested on the Canadian benchmark urban distribution system and compared to the conventional protection scheme, which relies only on a single time-current-voltage trip characteristic. The results ensure the ability of the proposed scheme to protect islanded microgrids without communication and its capability to reduce relays’ operation times.

Six Phase Transmission Line Protection Using Bat Algorithm Tuned Stacked Sparse Autoencoder

Six-phase transmission lines have the capability to address the continually evolving power demand. It allows upgrading the power transfer capability of the prevailing three-phase double circuit line without major changes in the transmission corridors. However, the operational performance of any six-phase system is highly dependent on its protection scheme. The possibility of larger number of faults in six-phase system complicates the protection task. Furthermore, the harmonics intrusion arising because of nonlinear loading compromises the reliability of the conventional threshold-based protection schemes. In this regard, this article addresses the above-mentioned challenges by developing a protection scheme based on the hybrid frameworks of bat algorithm and stacked sparse autoencoder-deep neural network (SAE-DNN). To overcome the limitation of SAE-DNN regarding optimal selection of architecture and tuning parameters, the selection task has been formulated as an optimization problem and solved using Bat algorithm. The use of raw voltage and current signals as input to the SAE-DNN reduces the overall complexity of the protection scheme. The efficacy of the proposed scheme has been validated for all 120 types of faults under varying operating, loading and fault scenarios. Furthermore, the proposed scheme has been validated for practical settings by performing real-time simulations on OPAL-RT digital simulator.

Review of Methods for Addressing Challenging Issues in the Operation of Protection Devices in Microgrids with Voltages of up to 1 kV That Integrates Distributed Energy Resources

With the large-scale integration of distributed energy resources (DER) into passive distribution networks with voltages of up to 1 kV, these networks are being converted into microgrids. When the topology and operating conditions change, several challenging issues arise related to the functioning of the protection devices (PD) that are in operation. Most DERs, including renewable generators, are integrated into microgrids by means of inverters. In the event of short circuits (SC) in microgrids, these DERs provide a fault current contribution of no more than 1.2–2.0 Irated at the fault location. This makes it difficult to identify the fault location and to carry out the selective disconnection of the faulty element by means of conventional PDs. This article provides an overview of engineering solutions for improving conventional protection schemes that have been historically used in passive distribution networks, as well as for creating modern protection schemes based on innovative principles and new methods. The use of adaptive protections built on decentralized and centralized principles in most cases ensures the reliable protection of microgrids. Modern intelligent electronic devices (IEDs), where protection functions are implemented, rank higher with respect to their technical perfection in terms of reliability, sensitivity, selectivity, and speed performance. The use of multi-agent systems in the implementation of modern protection schemes requires the availability of broadband communication channels, which hinders their use because of the high cost. The combined use of fault current limiters (FCL) and energy storage systems (ESS) allows for the reliable operation of microgrid protections. The use of modern PDs ensures the reliable operation of DERs and power supply to consumers in microgrids, both in the case of grid-connected and islanded operation modes. Since there is no unified concept of designing protection schemes for microgrids with DERs, the choice of specific approaches to the design of protection schemes should be based on the results of a comparative technical and economic analysis of different options.

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.

Qualitative and Quantitative Evaluation of Overcurrent Protection in Active Distribution Systems

Greenhouse gas emissions are considered a global problem, which is why interest in implementing renewable distributed energy resources (DER) is increasing worldwide. However, despite the contributions to the reduction of fossil primary energy sources, the connection of DERs to power grids often gives rise to new problems in control, operation and protection systems that need to be analyzed and solved. The objective of this paper was to compare a conventional overcurrent protection scheme and several adaptive schemes for active distribution networks (ADN). The proposed methodology consisted of performing an analysis of the adaptive protection approaches for ADN. From this evaluation, the most relevant documents were classified according to the main requirements, contributions, and conclusions. Additionally, some of these proposals were tested with conventional overcurrent protection, using the ATP simulator and Python software. Finally, a quantitative and qualitative analysis of the proposed protection approaches was performed in order to identify limitations to be considered in future research work. The results obtained, when considering different faults and modes of operation of the DNA, showed that the conventional protection coordination approach is highly vulnerable to faults when DERs are connected, mainly due to the change in current magnitudes and direction. The adaptive schemes analyzed have adequate performance, however, several application issues need to be analyzed in the future.