Numerical Relays Research Articles

Design of adaptive protection coordination scheme using SVM for an AC microgrid

Microgrids have gathered a significant amount of attention within the past decade and becoming an essential asset in the energy industry. The ability to integrate sustainable renewable energy generation into the distribution network is one of the main reasons for microgrids' popularity. Besides technical advantages, renewable energy sources integration with the grid poses many technical challenges. Due to randomness in generation and different modes of operation, integrating renewable energy sources into power systems will be challenging. Reliable operation of renewable energy sources integrated microgrids even when faults occur, requires an adaptive protection scheme and relay coordination. In order to tackle those issues, this paper developed an adaptive protection coordination scheme using numerical overcurrent relays and support vector machines with a particle swarm optimization approach. Renewable energy sources based on microgrids use power electronics systems that require relays to operate in milliseconds, and the power system will be safe. particle swarm optimization's program execution time exceeds the primary relays. The machine learning algorithm is faster in computation time. This article proposes a method, particle swarm optimization, to estimate the optimum relay operating time. The machine learning model having a support vector machine is proposed to estimate the relay operating time. The proposed research is developed and tested on an IEEE12BUS and IEEE35BUS system. The support vector machine -based on adaptive protection coordination schemes estimates the operating time of directional overcurrent relays, with a lesser program execution time and a low percentage error rate. The derived result defined that the proposed approach is well-suitable for real-time applications of an AC microgrid system.

Testing the Influence of the Quality of the Supply Voltage on the Performance of a Numerical Relay

To ensure consistent reliability and proper operation, protective relay equipment must be evaluated and tested. This paper presents the requirements for testing the ac and d.c. auxiliary power supply of protective relays and the test results. The test severity levels, test set-up, test procedures and test report are presented according to the IEC60255-11 Ed.2.0. A numerical relay commonly found in the power distribution systems is used for testing. The tests are carried out to determine the ability of the relay to withstand a variety of disturbances as specified in the international standard.

The Implementation of the Low Voltage Ride-Through Curve on the Protection System of a Wind Power Plant

. This paper presents the implementation of the low voltage ride-through (LVRT) curve in two commercial numerical relays, assessing the features and limitations of each protection device. The LVRT curve is defined in grid codes of several countries, especially those who already have or are planning a high share of wind power in their electric power systems. The functionality of the wind turbine grid protection system is tested in a power system using the PSCAD/EMTDC simulation tool. The fault ride through capability curve applied in the test system is as defined in the Brazilian grid code and the protection system responses evaluated at the point of common coupling of the wind power plant when the power network is under symmetrical and unsymmetrical faults. The biggest challenge to adhere the system operator requirements is to ensure the highest conformity to the defined LVRT curve, because most relays only gives you the option of tuning in discrete time intervals.

Modern numerical relays in protection of power transformer

This paper presents various protection schemes and their respective modern numerical protection relays to protect the power transformer. Proper protection is needed for the economical and safe operation of electrical power systems. The power transformer protective relay should block the tripping during an external fault or magnetizing inrush and speedily operate the tripping during internal faults. The objective of this paper is to implement protection during in-zone and outzone faults and to operate the relay with proper selective discrimination. The basic approach is to disconnect the power transformer feeder against in-zone faults and prevent disconnection of the power transformer feeder due to other operating conditions. The protection relay was able to discriminate between 2nd harmonic inrush, in-zone fault, and out-zone fault conditions. The protection scheme consists of high-speed protection relays and circuit breakers, which are required for the protection of substation equipment against abnormal conditions. A protective relay senses the fault and determines the location of the fault. Then, the protective relay sends the tripping command to the circuit breaker. Therefore, proper care should be taken in designing and selecting an appropriate relay that is reliable, efficient, and fast in operation. The PT and CT continuously measure the voltage and current of the substation and are connected to the relays to enable them to detect abnormal conditions. This paper describes numerical protection for power transformers, especially when the rating of the system is 50 MVA, 110/33 Kv, and Dyn11 at the substation. The protection relay employed in the transformer feeder is 7SR24 type (Siemens make).

Power System Fault Detection and Analysis Using Numerical Relay in Power grid Corporation Limited, Shoolagiri

The faults in a power system may be of various nature and they may affect the stability of the power system by causing outage of the line, there by overloading other connected lines and also causing cascading effect in the system. In order to access the nature of fault and analyze the impact of the same in a power system, fault analysis is required to be carried out as the same will be useful for the system operation and to take quick decisions in securing the system. In this paper we discuss the various types of faults in EHV system that may occur in line or substation. These faults are identified by Numerical relays which use IEDs [Intelligent Electronic Device]. The faults identified includes symmetrical and unsymmetrical faults in power system. Further in this project, we have taken into consideration the theoretical and practical study of the fault analysis through Numerical relays. In case of occurrence of Transient faults, Auto re-closure works with dead time of 1 sec. Current, voltage, Breaker status (open, close) are graphically represented by Disturbance Recorder. Events are recorded by Event logger. The above mentioned project for faults and analysis of faults in line or substation were carried out at Power grid Corporation Limited, 400 / 230kv Sub-Station Shoolagiri.

Optimal data-driven adaptive overcurrent relay coordination for active distribution networks

Massive integration of distributed generation originates the active distribution networks, introducing new control, protection and operation challenges. This paper proposes a strategy for adaptively protecting active distribution networks that undergo frequent changes in operating conditions. Numerical overcurrent relays capable of storing multiple setting groups, each with different settings designed to address various operating conditions, are used to overcome this issue. The proposed strategy uses locally acquired voltage and current measurements to accurately identify the operating conditions during fault occurrence. The identified condition is then used to select the appropriate overcurrent relay settings using a strategy which includes signal characterisation, data recognition, and optimisation to minimise the operating time for both primary and backup relays. Validation of the protection strategy is conducted on the IEEE 34-Bus test system, and the results indicate its ability to accurately detect different operating conditions in both connected and islanded operating modes, even in the presence of high-impedance faults and load variation. The performance rate exceeds 97.27% for all analysed cases, and the proposal identifies the operating condition in less than 20 ms after fault inception, demonstrating its low computational burden and suitability for implementation in field applications.

Multiagent System-Based Adaptive Numerical Relay Design and Development: Part I - Firmware

Protection relays that incorporate advanced microprocessors are vital to electrical grids, providing fast and reliable responses to faulty conditions using efficient communication protocols. Instant detection and response to various faults are essential to minimise the risk of damage. Numerical relays can identify faulty conditions and trigger circuit breakers to open, thus preventing further damage to the system. Due to the lack of autonomous decision-making capabilities, existing numerical relays require manual reconfiguration in situations such as a change in network configuration and protection settings. These relays also do not have the ability to coordinate fault clearance when multiple sources supply power to the grid. A comprehensive overview of the research aimed at developing a multiagent system (MAS)-based adaptive protection relay will be provided by dividing it into separate articles such as firmware and hardware. This first part delves into the firmware aspects of this innovative relay, highlighting its adaptive capabilities and key considerations in its development. The second part will provide detailed design descriptions for the hardware features of the relay. An STM32MPU multicore advanced microprocessor is utilised to design and develop the adaptive numerical relay firmware. It incorporates several protection relay ANSI codes, communication protocols, and MAS-based adaptive protection schemes as part of the firmware.

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.

Practical Implementation of Multithreaded Communication Protocols in Modern Protection Relays

Microprocessor-based protection relays that provide reliable and fast responses to abnormal conditions are of paramount importance to electrical grids. Modern numerical relays constitute communication protocols to facilitate data exchange among protection devices. Though it has become an integral part of electrical substation devices, there has not been any significant article that puts forth a detailed description of the preemptive multithreading implementation of multiple communication protocols for protection relays. Hence, this article is aimed at designing a preemptive multithreading system comprising IEC 61850 Manufacturing Message Specification (MMS), Generic Object-Oriented Substation Event (GOOSE), and Sampled Values (SV) along with Modbus TCP/IP and IEC 60870-5-104 communication protocols for protection relays. Latest products from prominent manufacturers of protection relays adopt preemptive multithreading on a real-time Linux operating system. In this work, the designed multi-protocol communication system is implemented on a real-time embedded Linux-based cortex-A7 core of the STM32MP157D-DK1 device. The designed system is verified by conducting an interoperability test with ABB REF615 and Thytronic NA11 protection relays.

A new protection scheme for feeders of microgrids with inverter-based resources

Due to the unavailability of a suitable relay for microgrid protection, various utilities are fitting available IEDs for the protection of microgrids. At present, microgrid protection is achieved using a combination of conventional numerical relays. These numerical relays are not suitable for all kinds of microgrid architectures and do not provide complete protection with inverter-based generators. Since these relays were designed considering the fault characteristics of synchronous generators, they fail to respond to the fault characterized by inverter-based generators. This paper proposes a new protection technique that is independent of the type of generating sources, control philosophy of inverters as well as microgrid architecture. Simulations are performed using PSCAD/EMTDC and performance of the protection scheme is also evaluated in real-time using RTDS. Pertinent results are presented which demonstrate the effectiveness of the proposed scheme.

Amplitude Based Pilot Protection for Transmission Line

Abstract: Distance protection and differential protection schemes are the two primary types of protection schemes employed in gearbox line protection today. However, industrial practice has shown that commonly used gap prevention techniques are limited in tripping speed and selectivity. The timing of the samples in each of the two relays located at the gearbox line terminals also affects the differential protection mechanism. On the other hand, pilot safety schemes using only the communication link to exchange local decision-making about fault conditions are not affected. These method include protection of Extra High Voltage (EHV) and Ultra High Voltage (UHV) transmission lines. Synchronization of time. The problem of creating a fast and accurate fault detection system for the safety of EHV/UHV transmission lines, which is crucial in present power systems, is the subject of this master's thesis. The protection method described in this thesis is the foundation for the detection and analysis of waves travelling wave along transmission at fault initiation. This method compares the arrival of the first traveling waves at both ends of the protected line with respect to direction. This will establish whether the fault is located in the safe zone or not. Based on high voltage transmission network safety requirements a suitable phase sequence algorithm is developed to control single phase tripping. Finally, through simulations conducted in the MATLAB environment, practical design concerns for incorporating the newly proposed protection algorithm into a numerical relay unit are investigated.

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.

$\Delta V-\Delta I$ Plane-Based Line Faults Detection and Classification in DC Microgrid

The high fault current rise due to instantaneous capacitor discharge necessitates quick line fault detection in DC microgrids. Hence, this paper proposes a communication-less <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Delta V-\Delta I$</tex-math></inline-formula> plane-based line faults detection and classification scheme in a Low-Voltage (LV) DC microgrid using local parameters. Simultaneous threshold violations of difference of successive line current and bus voltage samples, with sum of squared currents and disagreement of instantaneous line current to its average echo, aid the scheme to identify forward and backward faults and categorize Pole-to-Ground (PG) and Pole-to-Pole (PP) faults. The proposed scheme is time-efficient as it quickly detects and classifies the worst possible close-in and line-end PG and PP High Resistance Faults (HRFs) within 0.72 ms. The proposed method's feasibility is validated in Real-Time Digital Simulator (RTDS), Numerical Relay Development Environment (NRDE), and microcontroller-based hardware in loop setup. Comparison with previous techniques and tests on two LV DC microgrids indicate that the thresholds in the proposed scheme can aid in quick fault (even line-end HRFs) detection. Also, the proposed scheme is robust to grid-connected and islanded modes of operation, ring and radial configurations, noise, and non-fault events, like load switching, varying power output of sources, and AC side and internal converter faults.

Modeling of power numerical relay digitizer harmonic testing in Wavelet transform

In today’s modern power devices and rapid growth power demands, the need for precise and accurate protection relays is a must for the power distribution system. That is, to segregate faulty sectors within fewer cycles, power relays should perform at the highest level of accuracy to detect abnormal conditions in power distribution. Therefore, this work will investigate the enhancement of the numerical relay testing in terms of harmonic distortions effect on the digitized output waveform as direct causes of relay failures. However, as it is an expensive process of testing the digitizing element of the numerical relay, this paper proposes a new algorithm of Wavelet transforms in power quality signal processing testing using MATLAB simulation. As this newly proposed method of advanced waveform analysis algorithm will enhance the testing process of digitizing elements, and reduce data compiling complexity, a comparison between conventional Fourier Transforms testing and Wavelet algorithm under abnormal conditions will be simulated based on inserting multi harmonics effect. As a result, based on the Wavelet bank of filters, de-noising, and decomposition structure filters, Wavelet has provided promising results in defining the effect of waveform distortion tripping time, fault location, total harmonic distortion, signal-to-noise ratio, and spurious-free dynamic range.

Radio resource management in energy harvesting cooperative cognitive UAV assisted IoT networks: A multi-objective approach

Cooperative communication through energy harvested relays in Cognitive Internet of Things (CIoT) has been envisioned as a promising solution to support massive connectivity of Cognitive Radio (CR) based IoT devices and to achieve maximal energy and spectral efficiency in upcoming wireless systems. In this work, a cooperative CIoT system is contemplated, in which a source acts as a satellite, communicating with multiple CIoT devices over numerous relays. Unmanned Aerial Vehicles (UAVs) are used as relays, which are equipped with onboard Energy Harvesting (EH) facility. We adopted a Power Splitting (PS) method for EH at relays, which are harvested from the Radio frequency (RF) signals. In conjunction with this, the Decode and Forward (DF) relaying strategy is used at UAV relays to transmit the messages from the satellite source to the CIoT devices. We developed a Multi-Objective Optimization (MOO) framework for joint optimization of source power allocation, CIoT device selection, UAV relay assignment, and PS ratio determination. We formulated three objectives: maximizing the sum rate and the number of admitted CIoT in the network and minimizing the carbon dioxide emission. The MOO formulation is a Mixed-Integer Non-Linear Programming (MINLP) problem, which is challenging to solve. To address the joint optimization problem for an epsilon optimal solution, an Outer Approximation Algorithm (OAA) is proposed with reduced complexity. The simulation results show that the proposed OAA is superior in terms of CIoT device selection and network utility maximization when compared to those obtained using the Nonlinear Optimization with Mesh Adaptive Direct-search (NOMAD) algorithm.

Secrecy analysis of cooperative NOMA-FDR systems with imperfect CSI and colluding eavesdroppers

This paper analyzes the secrecy attributes of a full-duplex relay (FDR) non-orthogonal multiple access (NOMA) system, where the best relay is chosen from a set of numerous relays by using the partial relay selection (PRS) protocol. This best relay assists the communion from source to two NOMA users under the attendance of many colluding eavesdroppers. We obtain the expressions in closed-form of the exact secure outage probability (SOP) of each user, the approximate SOP, and the exact ergodic secrecy capacity (ESC) of the proposed system, taking into consideration the impacts of outdated channel state information (CSI) at source and imperfect CSI at colluding eavesdroppers. We also give the SOP and ESC of the NOMA-FDR system with PRS protocol for comparison with other benchmark systems such as half-duplex (HD)-NOMA, FD-orthogonal multiple access (OMA) systems with PRS protocol, and NOMA-FDR system with multiple-relay (MR) protocol. The simulation results verify the accuracy of our analysis results. Numerical results demonstrate that the SOP and ESC of the NOMA-FDR system greatly vary according to the number of relays and eavesdroppers, SI cancellation capability, channel estimation error, and the correlation coefficient of outdated channels. Most importantly, the NOMA-FDR system has better secrecy performance than all benchmark relay systems.

Detection and isolation of faulty line in an active distribution network using intelligent numerical relay

• The Intelligent Numerical Relay (INR) placed at substation majorly performs three functions, i.e., Over Current Relay (OCR), Distribution System State Estimator (DSSER) and Faulty Line Locator (FLL) to identify exact faulty line. • In OCR operation, it collects all possible supply current data from substation CT as well as PMUs at DG buses. it compares the total supply current with pickup value and identify the fault as well as faulty phase. • In DSSER operation, it collects data from optimal PMUs and estimates the states of entire system using linear Weighted Least Square (WLS) algorithm. • In FLL operation, it observes the voltage magnitudes at each bus based on estimated voltages. FLL identifies the exact faulty line which is in between maximum change in voltage bus and second maximum change in voltage bus. • After identification of faulty line, the INR remotely operates the intelligent switchgear of faulty line to isolate it. This method could detect the exact faulty line almost instantaneously, i.e., before the fuse melts. • The proposed technique is tested and validated for IEEE 33 bus active distribution network under different types of faults at various locations. In recent days Passive distribution networks are being transformed to Active Distribution Networks. The operation of Active Distribution Networks is becoming more complex with increasing energy demand and integration of distributed generations. Currently, identifying a faulty line in the distribution system is a tedious task which causes long interruptions to the consumers. Therefore, a real-time system is mandatory to monitor and control distribution network. This paper presents a novel method to detect the exact faulty line in Active Distribution Networks using an Intelligent Numerical Relay. The Intelligent Numerical Relay placed at substation collects the data from optimally placed Phasor Measurement Units and performs several functions. It operates as Over Current Relay to identify the fault, acts as Distribution System State Estimator to estimate the state of the system, and also acts as Faulty Line Locator to identify the faulty line. This Intelligent Numerical Relay placed at substation acquires all-possible supply currents data from substation current transformers as well as Phasor Measurement Units at Distributed Generator buses. In its Over Current Relay operation, it detects the fault by comparing total supply current with pick up value. The faulty line detection is performed by Faulty Line Locator using estimated voltages from Distribution System State Estimator based on optimal Phasor Measurement Units data. Faulty Line Locator observes the estimated voltages at each bus, it identifies the exact faulty line which is in between the buses with maximum change in voltage and second maximum change in voltage. After the identification of faulty line, the Intelligent Numerical Relay remotely operates the intelligent switchgear present at the faulty line to isolate it. The main advantage of this method is that, it could detect the exact faulty line almost instantaneously, i.e., before the fuse blows. IEEE 33 bus active distribution system is considered for testing and validation of the proposed method.

Design and Performance Evaluation of Numerical Relay for Three-Phase Induction Motor Protection

Design and Performance Evaluation of Numerical Relay for Three-Phase Induction Motor Protection

New Procedure for Estimation of Power Fundamental Phasor Parameters in Presence of Decaying DC Components

The paper proposes a new algorithm for the estimation of the fundamental phasor in a power system, based on the removal of exponentially decaying DC components (DDCs). These components, as well as high-order harmonics and noise components, have a considerable effect on accuracy and speed of convergence in numerical and digital relays – speed of the protection relay operation. A Discrete Fourier Transform (DFT) based approach with a modified Prony method was used to calculate and remove the unwanted effect of DDCs in a time interval slightly longer than the period of the fundamental harmonics. The proposed procedure offers the possibility to estimate the parameters of unwanted DDCs in a simpler and analytically more precise way, thus facilitating its program implementation. The algorithm offers the ability to easily adjust the response speed - detection time. This flexibility of the algorithm provides a compromise in terms of response speed as well as expected reliability and security of fault detection. The developed procedure enables the monitoring of the very demanding dynamics of the current signal in short-circuit conditions, and thus the estimation of the phasor parameters of the energy signal so that the relay protection can respond to this emergency in the most adequate (adaptive) way - it becomes more precise and faster in its response. The algorithm has low numerical and computational complexity while maintaining its high performance even in conditions of a very strong noise signal. The simulation results for different test signals demonstrate high precision in the estimation of the fundamental phasor of the proposed algorithm.

Fault Current Phasor Estimation Below One Cycle Using Fourier Analysis of Decaying DC Component

The full-cycle discrete Fourier transform (FCDFT) is commonly used to estimate phasors in numerical relays because of its immunity to harmonics and accurate identification of a decaying dc component (DDC) in a fault current. For fast protection of power systems, it is necessary to speed up the phasor estimation by using a data window below one cycle. The conventional least squares (LS) methods below one cycle approximate the DDC as the first several terms of the Taylor series expansion, which degrades the phasor-estimation accuracy. This paper proposes an LS method that uses Fourier analysis for approximation of the DDC to speed up phasor estimation without accuracy degradation. The phasor-estimation accuracy of the proposed method is investigated for the data-window length in simulations using synthetic data of fault currents containing DDC, harmonics, and measurement noise. The phasor-estimation speed is also investigated with respect to the delay of the antialiasing filter in the numerical relay. The proposed method is compared with the conventional LS and FCDFT methods in simulations using synthetic fault-current data. The feasibility of the proposed method is demonstrated through the phasor estimation of simulated transmission-line faults.