Conventional Overcurrent Relays Research Articles

Innovative protection schemes through hardware-in-the-loop dynamic testing.

In microgrid environments, the behaviour of Distributed Generation (DG) during fault conditions varies significantly based on DG types and penetration levels. Conventional Overcurrent Relays (OCRs) with standard time-current characteristics may exhibit limitations during excessive fault scenarios, leading to OCR operating delays and mis-coordination within the microgrid. This study proposes a novel constraint on the maximum Current Multiplier Setting (CMS) and utilizes Water Cycle Algorithm (WCA) and Particle Swarm Optimization (PSO) techniques to optimize the Time Multiplier Setting (TMS). Comparative dynamic analysis through real-time validation shows that the non-standard OCR approach outperforms the standard IEC scheme across all grid operation modes with different type, size and location of DGs. For instance, under F1 conditions, the tripping time of OCR1 was reduced from 0.0226 seconds (IEC) to 0.000981 seconds (non-standard). HIL results further affirm the efficacy of the proposed scheme. The optimization process, implemented in MATLAB and validated using ATP/EMTP simulations and SIPROTEC 7SJ62 relays, demonstrates enhanced microgrid protection coordination, improving system reliability and performance.

An efficient protection scheme for microgrid using ROC of differential admittance angle

Advancement in converter control technology enables extensive integration of renewable energy sources (RES) in a grid or distribution network and operates as a single controllable entity constituting a microgrid (MG) to provide several benefits. Further intermittency of RES modified network topology; different operating modes of MG imposes protection challenges. The fault current level varies significantly with changes in operating conditions; thus, the conventional overcurrent relays cannot detect shunt faults (SFs) and high impedance faults (HIFs). This paper introduced an efficient protection scheme utilizing the Rate of Change (ROC) of the differential positive-sequence admittance angle (DPSAA) parameter and issued the trip signal (TS). The proposed scheme is compared with the existing scheme to evaluate the performance and efficacy of the proposed scheme. Furthermore, the proposed and existing schemes are tested and validated on the modified IEEE 13 Bus test system (BTS) in MATLAB R2021b /SIMULINK platform. The obtained test result reveals the proposed scheme's efficacy in detecting both SFs and HIFs.

Numerical Overcurrent Power Relay Enhancement Based on Integrated Discrete Wavelet Transform

As electrical power demands increases, the need for advanced protection relays has surged as a vital element in the power distribution system. That is, to ensure the continuity of power supply and eliminate abnormal faulty status, relays with different types and functions play a major role in electrical power system operation and protection as will. In the power system, current variation faults may accrue for many reasons, which may harm power system components, load, and jeopardize human safety. However, in now a day digital current relay, a large number of samples are collected and processed in order to continuously monitor and detect faults. This large amount of samples needs a bigger storage data real state and longer time to compile, optimization is needed to improve current relay reliability and accuracy with much fewer samples. Therefore, as this work aim toward optimizing the current relay, a substantial algorithm is needed for better current waveform analysis. As a result, the Wavelet transform algorithm with its wide spectrum feature of waveform analysis and decomposition process will be used as an enhancement tool. Using MATLAB/Simulink, a simulation, the unique characteristics of Wavelet transform (de-noising, mining, and decomposition) will be implemented into the modern numerical current relay to test the ability to advance fault detection based on less number of current waveform data. As this evaluation was compared with a typical conventional numerical overcurrent relay, a promising result in terms of less response time and compiling process was achieved.

Protection of DC Microgrids Based on Complex Power During Faults in On/Off-Grid Scenarios

The DC microgrid is an effective platform for integration of renewable energy sources, energy storage systems, and smart electronic loads. However, the integration of distributed generators can result weak fault currents with change in its direction during fault conditions, which lead to failure of conventional over-current relays with poor coordination. The above scenario may exhibits relay mal-operation and force the DC microgrid into blackout mode which is extremely undesirable. Thus, this paper proposes an complex power concept (real and imaginary), which can be extracted using Fast Fourier Transform (FFT) to construct the effective protection schemes for rapid short-circuit fault detection and fault isolation in a DC microgrid. To achieve fault isolation, solid-state DC circuit breakers are used in conjunction with proposed real and imaginary power, which is extracted from the total FFT power signal (i.e. by using bus voltage and line current). Further, the relay trip threshold value for real and imaginary power is also determined under various pole-pole (P-P) and pole-ground (P-G) fault scenarios in the DC microgrid. The proposed protection scheme is validated on simple and modified IEEE 9-bus DC microgrids under various P-P and P-G fault scenarios during On/Off-Grid modes through MATLAB/Simulink software. The simulation results reveal that the proposed protection scheme based on real and imaginary power has accurately identified the fault in the simulated DC microgrids. Thus, the proposed complex power based fault identification approach can be quite effective for protection of DC microgrids during On/Off-Grid scenarios.

Coordination of dual setting overcurrent relays in microgrid with optimally determined relay characteristics for dual operating modes

Fault current magnitude in a microgrid depends upon its mode of operation, namely, grid-connected mode or islanded mode. Depending on the type of fault in a given mode, separate protection schemes are generally employed. With the change in microgrid operating mode, the protection scheme needs to be modified which is uneconomical and time inefficient. In this paper, a novel optimal protection coordination scheme is proposed, one which enables a common optimal relay setting which is valid in both operating modes of the microgrid. In this context, a common optimal protection scheme is introduced for dual setting directional overcurrent relays (DOCRs) using a combination of various standard relay characteristics. Along with the two variables, i.e., time multiplier setting (TMS) and plug setting (PS) for conventional directional overcurrent relay, dual setting DOCRs are augmented with a third variable of relay characteristics identifier (RCI), which is responsible for selecting optimal relay characteristics from the standard relay characteristics according to the IEC-60255 standard. The relay coordination problem is formulated as a mixed-integer nonlinear programming (MINLP) problem, and the settings of relays are optimally determined using the genetic algorithm (GA) and the grey wolf optimization (GWO) algorithm. To validate the superiority of the proposed protection scheme, the distribution parts of the IEEE-14 and IEEE-30 bus benchmark systems are considered.

Improved Adaptive Protection Scheme Based Combined Centralized/Decentralized Communications for Power Systems Equipped With Distributed Generation

Recently, numerical relays with communication capabilities have been employed to provide adaptive solutions for Distributed Generations (DGs) protection issues. This paper presents an adaptive protection scheme based on centralized and decentralized communication to address DG protection problems. The proposed method uses two directional relays in each feeder, one at the beginning (called forward relay) and one at the end (called reverse relay). These relays can communicate with each other and the central unit. The centralized communication occurs between the central unit and the relays in the system when any relay’s status changes from connected to disconnected or vice versa. It aims to define the operation mode, islanding detection, and activate the relays settings to achieve proper coordination. Protective relays are coordinated using a Genetic Algorithm (GA) to optimize protection time. The optimization problem considers pick up current (Ipu), Time Multiplier Setting (TMS), Plug Setting Multiplier (PSM), and curve type. Decentralized communication, which occurs when any relay detects a fault, increases relays’ accuracy and speed of decision-making. This paper also proposes a novel method for detecting High Impedance Faults (HIF), a significant difficulty for protecting engineers as it draws a very low current that conventional overcurrent relays fail to detect in most cases. HIF is detected using wavelet transform, symlet 8, detail 2 (d2), and relay communication. On the IEC benchmark microgrid, the suggested algorithm is tested. ETAP is used for load flow analysis and short circuit analysis, whereas MATLAB is used for GA optimization, HIF modelling, and wavelet transform routines.

A Method Based on Only Currents for Determining Fault Direction in Radial Distribution Networks Integrated with Distributed Generations

Nowadays, more distributed generations (DGs) are connected to a radial distribution network, so conventional overcurrent relays cannot operate correctly when a fault occurs in the network. This study proposes a method to determine the fault direction in a three-phase distribution network integrated with DGs. The obtained pre-fault and fault currents are utilized to extract their phasors by the fast Fourier transform, and the phase angle difference between the positive-sequence components of the pre-fault and fault currents is used. Moreover, the method only uses the local current measurement to calculate and identify the phase angle change of the fault current without using the voltage measurement. Matlab/Simulink software is used to simulate the three-phase distribution network integrated with DGs. The faults with different resistances are assumed to occur at backward and forward fault locations. The simulation results show that the proposed method correctly determines the fault direction.

Design and implementation of an adaptive relay based on curve-fitting technique for micro-grid protection

Abstract The micro-grid should operate in a well controlled manner both during grid connected and islanded mode. Also, micro-grid equipped with conventional overcurrent relays has protection issues during faults due to the difference in fault currents when micro-grid operation changes from one mode to the other. This paper proposes suitable relaying scheme based on curve-fitting technique for micro-grids and performs well without using any extensive communication facility. A new algorithm is developed to create large number of fault data for fitting the curve. The fitness of curve is accessed by measuring the value of coefficient R-squared value (R 2). More number of polynomials is added to improve the value of R 2. Results show that the actual tripping time of the relay is very close to desired tripping time by introducing more number of polynomials. Efficiency of the proposed method is evaluated by comparing with conventional over current relay. The protection logic of the curve-fit relay has been implemented on a TMS32F28377S micro-controller based hardware. A laboratory based experimental setup has been established to test the operational performance of curve-fit relay for a five bus system.

Microgrid protection against high impedance faults with robustness to harmonic intrusion and weather intermittency

The high impedance faults (HIF) in microgrids are characterized by low magnitude fault current with inherent non-linearity and random behavior. The possible weather intermittency in PV integrated microgrids and the intrusion of harmonics due to power converters and non-linear loading, further reduce the fault current during HIF. The insignificant fault current does not allow detection of HIF by conventional overcurrent relays. In this regard, a reliable and robust protection scheme based on the combined framework of probabilistic modelling, least square and Adaline algorithm, sine cosine algorithm (SCA) and support vector machine (SVM), has been proposed to perform the tasks of mode detection, fault detection/classification and section identification during HIF in microgrid. The algorithm involves online extraction of harmonic components and stochastic modelling of intermittency in solar irradiance. The performance of the proposed scheme has been analysed in terms of robustness against harmonics intrusion and weather intermittency during HIF. The performance comparison of the proposed scheme with the decision tree (DT) and classical SVM based techniques reflects its effectiveness with improved immunity against harmonic intrusion and weather intermittency. Further, the proposed scheme has been validated using OPAL-RT digital simulator for evaluating its appropriateness in real-time settings.

Optimal Determination of Photovoltaic Penetration Level Considering Protection Coordination

Photovoltaic (PV) systems have been gaining popularity among distribution network engineers. The integration of these small-scale sources has a variety of benefits for the distribution network. One of the most important benefits is the power loss reduction. However, a high penetration level of PV systems may disrupt the protection coordination of conventional overcurrent relays of the distribution network, reducing the profit of the electricity distribution company (EDC) due to healthy feeder de-energization. This paper determines the optimal penetration level of PV systems in the distribution network considering both power loss reduction profit and protection miscoordination cost to maximize the profit of the EDC. The merits of the proposed methodology are verified through several case studies on a simulation model of the IEEE 33-bus test system in the Electrical Transient Analyzer Program (ETAP) environment considering the reliability data of the IEEE Roy Billinton Test System.

High-Impedance Fault Diagnosis: A Review

High-impedance faults (HIFs) represent one of the biggest challenges in power distribution networks. An HIF occurs when an electrical conductor unintentionally comes into contact with a highly resistive medium, resulting in a fault current lower than 75 amperes in medium-voltage circuits. Under such condition, the fault current is relatively close in value to the normal drawn ampere from the load, resulting in a condition of blindness towards HIFs by conventional overcurrent relays. This paper intends to review the literature related to the HIF phenomenon including models and characteristics. In this work, detection, classification, and location methodologies are reviewed. In addition, diagnosis techniques are categorized, evaluated, and compared with one another. Finally, disadvantages of current approaches and a look ahead to the future of fault diagnosis are discussed.

Implementation of Support-Vector-Machine-Based Relay Coordination Scheme for Distribution System With Renewables

During islanded mode, the fault current seen by the relay is less as compared to the system in a grid-connected mode. Due to this, the conventional overcurrent relay faces protection challenges, such as relay miscoordination, delayed operation, or failure (blinding) in relay operations. This article proposes a relaying scheme, which uses a support vector machine (SVM)-based classification approach to solve the protection issues. The algorithm integrates the merits of both the radial basis function (RBF) and the multiclass Cubic SVM classifier. The RBF classifier can identify the relay jurisdiction and helps prevent false tripping. The multiclass cubic classifier has been designed to find the SVM class with appropriate relay tripping time. Without using any extensive communication facility, the proposed scheme coordinates the relays and maintains the coordination time interval (CTI) within the desired limits. Irrespective of the mode of operation and configuration of the system, the tripping time and CTI value of the SVM relay is better as compared with the conventional overcurrent relay. The decision function of both classifiers is simplified and programmed in a 200-MHz 32-bit microcontroller. The prototype of the proposed relay is tested on a 400-V four-bus laboratory-type distribution system by creating faults at different locations. The results obtained indicate the ability of the proposed method to perform the real-time operation in a microcontroller-based hardware platform.

Impedance Angle-Based Differential Protection Scheme for Microgrid Feeders

The emerging trends in the microgrid development and the increasing penetration of distributed energy resources (DERs) in the distribution networks urge the modification in the existing conventional protection techniques. The integration of DERs changes the radial nature of the network, and thus, the schemes designed for such networks fail to operate for the microgrid system. Hence, a new fault detection technique is required for the microgrid system. In this article, a new fault detection scheme is developed for detecting the low-impedance faults (LIFs) as well as high-impedance faults (HIFs). The detection of HIFs is of major concern as these faults lead to a very low fault current value, which makes them undetectable by the conventional overcurrent relays. The proposed scheme uses the cumulative sum value of the differential negative-sequence impedance angle (DNSIA) as the fault detection parameter for generating the trip signal. The simulation results show that the proposed method effectively detects LIFs and HIFs accurately. The proposed scheme is independent of the type of faults, type of DGs, and the value of fault impedances. Furthermore, the proposed scheme also discriminates between the switching transients and faults effectively. The IEEE 13-bus test system is modeled and simulated on real time digital simulator (RTDS)/RSCAD platform. The method is further validated for the real-time implementation by developing the experimental setup for performing the control hardware-in-the-loop.

Smart overcurrent relay for operating in islanded and grid-connected modes of a micro-grid without needing communication systems

As the penetration of distributed generation resources in distribution networks increases, the need for designing micro-grids also increases. Micro-grids can operate in islanded and grid-connected modes. When a microgrid is connected to the main grid, it economically exchanges power with the upstream grid. However, in the islanded mode, the micro-grid can provide its own local demand. In addition to the technical and economic advantages due to the presence of micro-grids, there are some issues about the protection of distribution systems. The most important issue is the short circuit level in both islanded and grid-connected modes of operation. In this paper, a smart overcurrent relay is proposed that can adapt itself to the operation modes of a micro-grid. This relay detects the operation mode of the micro-grid using an adaptive algorithm. Two main features of the suggested adaptive method are the optimized accuracy and higher execution speed of the algorithm in determining the operation mode of the micro-grid. The optimal setting that is predefined in the relay is then activated based on the corresponding mode. The entire processing is performed in the relay itself by sampling the voltage and current of the relay line. Consequently, this relay can be installed and used in any location of a network without needing any communication infrastructure. Finally, the proposed method is implemented on a micro-grid. According to the numerical results, the coordination performance superiority of this smart relay over conventional overcurrent relays is proven.

Harmonic Directional Overcurrent Relay For Islanded Microgrids With Inverter-Based DGs

Conventional directional overcurrent relays (DOCRs) may fail to protect microgrids formed using inverter-based distributed generation (IBDG) units, as IBDGs have limited fault current contribution. Maloperation of DOCRs can be due to: 1) inability to distinguish load and fault currents; 2) incorrect fault direction identification; or 3) miscoordination of primary and backup DOCRs. This article proposes employing harmonic current injection capability of IBDGs to design a novel harmonic DOCR (HDOCR). In the proposed method, during fault conditions, each IBDG injects a harmonic current with an order different from the ones injected by its neighboring IBDGs. The magnitude of this current is modulated by an equivalent impedance that is locally computed at the terminals of each IBDG. New time-harmonic-current characteristic, directional element, and protection coordination optimization model are devised for the proposed HDOCRs. The proposed protection scheme is applicable to radial and ring microgrids with multiple IBDGs and does not require communication. Simulation studies in PSCAD/EMTDC verify the performance of the proposed scheme under various faults.

An Intelligent Adaptive Overcurrent Protection System for an Automated Microgrid in Islanded and Grid-Connected Operation Modes

As the penetration of distributed generation sources increases at the distribution level, the necessity of designing microgrids is highlighted. Microgrids can operate in either islanded (separated from the utility grid) or grid-connected mode. Apart from the technical and economic benefits of microgrids, they may cause some protection issues in distribution systems. The most important of these issues is the difference between the short circuit levels in islanded and grid-connected operation modes. In this paper, an intelligent overcurrent relay that can adapt to the microgrid operation mode is proposed; that is, the relay detects the microgrid operation mode by means of an adaptive algorithm. The proposed adaptive method optimizes the accuracy and speed of the algorithm for detecting the microgrid operation mode. Then, the optimal settings that have been already stored in the relay are activated according to the microgrid operation mode. All internal processes of the relay use the voltage and current sampled at the relay location. As a result, the relay can be used in all networks without communication infrastructures. Finally, the proposed method is implemented in a sample microgrid. The superiority of the intelligent relay performance over conventional overcurrent relays is shown by numerical results.

Differential Frequency Protection Scheme Based on Off-Nominal Frequency Injections for Inverter-Based Islanded Microgrids

Protection is considered one of the major challenges associated with the operation of islanded microgrids with high penetration of inverter-based distributed generation (IBDG). As stated in the IEEE Std. 1547.4, due to the limited injected fault current levels by IBDG, conventional overcurrent relays might not be capable of detecting and clearing faults. Thus, this paper proposes a novel protection strategy for inverter-based islanded microgrids which relies on injecting an off-nominal frequency, through the DG interface, during fault conditions. A differential protection scheme that is based on the differences in the current frequency components, measured at both ends of a feeder section, is proposed to detect and isolate faults. This paper also presents the structure and control logic of the proposed relay for differential protection. The proposed protection scheme is implemented and tested on a distribution system equipped with IBDG, modeled to operate in an islanded mode. Simulation results are presented to highlight the effectiveness of the proposed protection scheme in detecting and isolating faults for inverter-based islanded microgrids.

Microgrid protection under wind speed intermittency using extreme learning machine

Operation of wind turbine-based microgrids is characterized by increased intermittency due to the uncertainty in wind speed, which significantly affects the voltage-current profile. Conventional overcurrent relays based on prespecified threshold setting quite often are not able to detect faults under sporadic behavior of wind generators. With the aim of developing a protection scheme which is immune to the stochastic variation in wind speed under both grid-connected and islanding mode, a technique based on Discrete wavelet transform (DWT) and Extreme learning machine (ELM) has been proposed for mode detection, fault detection/classification and section identification. Uncertainty in wind speed has been modeled using Weibull distribution function and further incorporated in the protection modules. The proposed scheme has been validated using different statistical indices and compared with reported techniques for varying fault scenarios. Further, the effectiveness of the proposed scheme has also been validated for practical field applications by performing real-time simulations.

A Communication-Supported Comprehensive Protection Strategy for Converter-Interfaced Islanded Microgrids

The deployment of distributed generators (DGs) gives rise to several challenges for a microgrid or conventional distribution feeder, regarding control and protection issues. The major ones are: bi-directional flow of power, changes in fault current magnitude, and continuous changes in operational configuration due to both the plug-and-play of DGs and loads, and the intermittency of the renewable DGs. This issue is exacerbated when the microgrid contains several converter-interfaced DGs and operates in the islanded mode of operation. Hence, conventional protection strategies and relaying techniques will no longer be sufficient to protect islanded microgrids against network faults and disturbance conditions. This paper proposes a fast and reliable communication-supported protection strategy for ensuring the safe operation of converter-interfaced islanded microgrids. The strategy is implementable using commercially accessible microprocessor based digital relays, and is applicable for the protection of low voltage islanded microgrids. It provides backup protection to handle communication failures and malfunctions of protective devices. The paper also presents the detailed structural layout of the digital relay, which executes the proposed protection strategy. A number of improvements are proposed to find an alternative method for conventional overcurrent relays to reliably detect small-magnitude fault currents and high impedance faults, commonly encountered in converter-interfaced islanded microgrids. A simple and economical bus protection method is also proposed. Several simulations are conducted on a comprehensive model of a realistic operational industrial microgrid (Goldwind Smart Microgrid System) using PSCAD/EMTDC software environment—for different case studies and fault scenarios—to verify the effectiveness of the present strategy and its digital relay.

Analytical approach to modelling the interaction between power distribution systems and high impedance faults

High impedance faults (HIFs) and the associated electric arc is a topic of public safety and concern because fault currents are generally too small to be detected in a reliable way by conventional over-current relays. This study proposes an analytical model for analysing HIFs in power distribution systems. The proposed analytical model considers the complex interaction between a time-varying fault impedance, the power distribution line and an equivalent source impedance at the substation bus. Hence, this approach requires the joint solution of a partial differential equation and a single non-linear equation. The proposed methodology calculates the transient conductance, voltage and current at the substation bus, considering several contact surfaces and short circuit levels. The analytical model was validated by means of comparisons with measurements in a real distribution system, results published by other authors and computer simulations in electromagnetic transient programs. The obtained results show good agreement between the analytical model, measurements and computer simulations. A sensitivity analysis of the interaction of all the parameters associated to HIFs is also presented.