Relay Location Research Articles

High‐speed algorithm for fault detection and location in DC microgrids based on a novel time–frequency analysis

AbstractProtecting DC microgrids (DCMGs) from faults is critical due to the rapid current changes that occur in milliseconds. However, ensuring fast and accurate protection in DCMGs is more challenging than in AC systems. This study proposes a novel protection algorithm using traveling waves (TWs) for fault detection and localization. The high‐order synchrosqueezing transform (FSSTH) is applied to precisely identify TWs at the relay location. FSSTH offers a sharp time–frequency representation, enhancing the accuracy and speed of fault detection. This method can accurately detect transient phenomena like TWs in DCMGs, even with noise and variable fault resistance. By using the spectral envelope with FSSTH, ridges in time–frequency representations are extracted, improving fault diagnosis. The approach differentiates external from internal faults and recognizes fault direction by assessing TW polarity. Testing on two different DCMGs showed this algorithm's high efficiency and accuracy, with fault location errors ranging from 1 to 50 meters in low‐voltage and 13 to 64 meters in medium‐voltage DCMGs, even under challenging conditions like high resistance (up to 500 Ω) and low signal‐to‐noise ratio (5 dB). These results demonstrate the method's superior accuracy and robustness compared to existing techniques.

Performance analysis of fixed gain relay-assisted vertical UWOC systems with generalized misalignment fading model

Underwater wireless optical communication (UWOC) as a potential underwater transmission technology has attracted increasing attention due to its high speed, low delay, and wide range of applications. In addition to absorption and scattering, ocean turbulence fading and misalignment fading seriously affect system performance. Thus, the relay assistance methods have been presented as an effective technique for fading mitigation in optical channels. In this paper, we propose a fixed gain amplify-and-forward (AF) relay-assisted vertical UWOC system with a generalized misalignment fading model over multi-layer cascaded gamma-gamma turbulence channels. For the relay-assisted system, the cumulative distribution function (CDF) and the probability density function (PDF) of the end-to-end instantaneous signal-to-noise ratio (SNR) are derived with the help of the Meijer-G function and the bivariate Fox-H function. Subsequently, based on these statistical analyses of SNR, we derive the closed-form expressions of the outage probability and ergodic capacity. Furthermore, we provide a very tight asymptotic expression for the outage probability in terms of simple functions under high SNR, and the diversity order is analyzed. Finally, results from Monte Carlo simulations are used to validate our derived results. Numerical results for different relay position deployments and alignment error levels reveal that the relay-assisted vertical UWOC system performs better when the relay node is located near the source, while the increase of alignment error level can damage the system performance.

Achievable secrecy rate analysis of OFDM‐based multi‐user untrusted relay networks with imperfect CSI

AbstractThis study investigates the impact of imperfect channel state information (CSI), caused by channel estimation errors and feedback delays, on the physical‐layer security performance of multi‐user relay networks. More specifically, a multi‐user untrusted half/full‐duplex (HD/FD) uni/bi‐directional wireless amplify‐and‐forward (AF) relay network is studied, adopting orthogonal frequency division multiplexing (OFDM). In order to minimize the information leakage, it is considered that a limited number of friendly jammers affect the untrusted relay. In this context, the achievable secrecy rate of the relay network is theoretically analyzed and optimization problems are formulated and solved for the untrusted relay's location and power allocation. Monte Carlo simulations are conducted to validate the theoretical findings, revealing that channel estimation errors cause coding gain losses for low signal‐to noise ratio (SNR) while their impact becomes negligible for high SNR. Also, a large number of user‐pairs achieves higher secrecy rate while FD relaying further improves the secrecy performance. Finally, bi‐directional relaying provides higher achievable secrecy rate over uni‐directional relaying.

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.

Optimal Estimation of Under-Frequency Load Shedding Scheme Parameters by Considering Virtual Inertia Injection

Under-frequency load shedding (UFLS) schemes are the latest safety measures applied for safeguarding the integrity of the grid against abrupt frequency imbalances. The overall inertia of electrical power systems is expected to decrease with an increased penetration of renewable energy as well as elements connected through power electronic interfaces. However, voltage source converter-based high voltage direct current (VSC-HVDC) links can provide virtual inertia through a control loop that allows for a reaction to occur at certain frequency fluctuations. This paper evaluates a UFLS scheme that considers the injection of virtual inertia through a VSC-HVDC link. A genetic algorithm (GA) is used to determine the location of the UFLS relays, the activation threshold of each stage, the delay time and the percentage of load shedding at each stage. It was found that the virtual inertia causes the nadir to delay and sometimes reach a greater depth. Furthermore, the implemented GA approximates the frequency response to the limits set with the constraints, reducing the load shedding but achieving a steeper nadir and a lower steady-state frequency level than traditional UFLS. The simulations were performed using the IEEE 39-bus test system.

Research on UWB-Based Cooperative Relay Positioning Mechanism for Firefighters

Research on UWB-Based Cooperative Relay Positioning Mechanism for Firefighters

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.

FER-Restricted AUV-Relaying Data Collection in Underwater Acoustic Sensor Networks

Relaying is an effective method to achieve reliable and timely data collection, which is one of the most important parts of underwater acoustic sensor networks (UASNs). Considering that the relay position determines the reliability of relay communication, we study the problem of relay placement and place an autonomous underwater vehicle (AUV) to mobile relay data transmission and realize the reliable, low-latency, and low-energy data collection in UASNs. First, we formulate the relay positions that can meet a certain frame error rate (FER) requirement as the FER-restricted area (FRA), and approximate FRA with a three-dimensional geometry formula. The problem of reliable and timely data collection becomes planning a short AUV relaying trajectory under the FRA constraint. To this end, we propose a nearest-community (N-C) trajectory planning algorithm to design the AUV relay trajectory. A member grouping method and the necessity of position (NoP) concept are proposed to further reduce the relay positions and trajectory length of the AUV. Simulation results verify that the approximate FRA is more than 90% consistent with the real FRA and show that the N-C using NoP-based member grouping can successfully receive more packets per minute and consume fewer sensors’ energy than other algorithms.

Impact of power flow on the apparent impedance calculated by the distance protection in transmission lines

AbstractThe reach of primary protection zones of transmission lines distance relays is affected when large power flows circulate through the transmission line prior to a short circuit occurrence. This can cause improper operation of the protection system in certain scenarios. In practice, protection zone adjustments are made by considering the apparent impedances obtained from short‐circuit simulations in the line of interest using standard methods such as IEC 60909‐0 or ANSI/IEEE C37.010. However, these short‐circuit calculation methods omit the existing operating conditions prior to the fault. Therefore, this work proposes a set of equations developed for calculating the apparent impedance seen by the distance relay in view of different types of short circuits, including the effects of power flow prior to the fault. These equations are then used to establish the distance primary protection zone settings. The analysis uses the mathematical expressions proposed of voltages and currents at the relay location, and the impedance diagrams obtained from simulated short circuits. Subsequently, the settings obtained with these equations are compared to those achieved using the IEC 60909‐0 standard, allowing for the differences in settings and their effectiveness. Finally, this procedure is applied to a part of the Ecuadorian Transmission System.

A Method for Researching the Influence of Relay Coil Location on the Transmission Efficiency of Wireless Power Transfer System

The transfer distance of the wireless power transfer (WPT) system with relay coil is longer, so this technology have a better practical perspective. But the location of the relay coil has a great impact on the transmission efficiency of the WPT system, and it is not easy to analyze. In order to research the influence law of the relay coil location on the transmission efficiency and obtain the optimal location, the paper firstly proposes the concept of relay coil location factor. And based on the location factor, a novel method for studying the influence of the relay coil location on the transmission efficiency is proposed. First, the mathematical model between the transmission efficiency and the location factor is built. Next, considering the transfer distance, coil radius, coil turns and load resistance, a lot of simulations are carried out to analyze the influence of the location factor on the transmission efficiency, respectively. The influence law and the optimal location factor were obtained with different parameters. Finally, a WPT system with relay coil was built for experiments. And the experiment results verify that the theoretical analysis is correct and the proposed method can simplify the analysis progress of the influence of relay coil location on the transmission efficiency. Moreover, the proposed method and the research conclusions can provide guidance for designing the multiple coils structure WPT system.

A Novel Approach for Elimination of Defects of Blocking and Unblocking in Distance Relays during Power Swing

In power systems, distance relays are commonly employed as the primary protection for transmission lines, and their operation is of utmost importance. Power swings are a type of phenomenon that can lead to improper functioning of conventional distance relays, posing a threat to the uninterrupted flow of electrical power. The occurrence of a power swing disrupts the impedance measured by the relay, causing it to deviate from the normal load condition and enter the relay tripping zones. This research paper introduces a novel method based on the Prony method for extracting current waveform components, enabling fault detection during power swings. Subsequently, the proposed method’s accuracy is assessed through simulations implemented on a nine-bus power system, involving three-phase current signal processing and the application of the proposed algorithm. Various fault scenarios encompassing varying fault distances from the relay position, fault resistances, and power angles within the 9-bus system are simulated to encompass a wide range of fault environments. The simulation results demonstrate the effectiveness of the proposed algorithm in detecting all types of faults, including symmetrical and asymmetrical faults, during power swings.

A Real-Time Setting-Free Synchronous Generator Out-of-Step Protection Scheme Based on Voltage Trajectory

This article proposes a real-time, setting-free out-of-step (OOS) protection strategy for a single synchronous generator (SG) connected to a multimachine power system. To do so, the fundamental frequency phasor of the voltage at the generator terminal is measured. It will be shown that at the point of OOS, the imaginary part of the voltage crosses the zero point and becomes negative, whereas the real part of the voltage holds a negative value. On the other hand, it will be shown that during stable power swings, the imaginary part of the voltage behaves as per an OOS event, whereas the real part of the voltage becomes positive. Therefore, this principle can be used as the criterion to detect an SG OOS. Moreover, it will be shown that the proposed principle can count the number of SG pole slip occurrences so that it can trip the generator after a certain number of pole slips. The proposed scheme is a response-based algorithm and uses only locally measured voltage at the relay location. Furthermore, the network configuration and parameters do not affect the proposed scheme. Unlike the legacy impedance-based OOS detection method, which demands rigorous offline simulation studies to determine settings, the proposed scheme does not need any setting to operate. Rigorous mathematical analyses and illustrated simulation study results are presented to substantiate the efficiency of the proposed method. The performance of the proposed scheme and the polygonal relay and concentric blinder scheme are compared through comprehensive simulation studies. The results prove that the proposed scheme can be served as an efficient method for SGs OOS protection.

Optimization of Mobile Robotic Relay Operation for Minimal Average Wait Time

This paper considers trajectory planning for a mobile robot which persistently relays data between pairs of far-away communication nodes. Data accumulates stochastically at each source, and the robot must move to appropriate positions to enable data offload to the corresponding destination. The robot needs to minimize the average time that data waits at a source before being serviced. We are interested in finding optimal robotic routing policies consisting of 1) locations where the robot stops to relay (relay positions) and 2) conditional transition probabilities that determine the sequence in which the pairs are serviced. We first pose this problem as a non-convex problem that optimizes over both relay positions and transition probabilities. To find approximate solutions, we propose a novel algorithm which alternately optimizes relay positions and transition probabilities. For the former, we find efficient convex partitions of the non-convex relay regions, then formulate a mixed-integer second-order cone problem. For the latter, we find optimal transition probabilities via sequential least squares programming. We extensively analyze the proposed approach and mathematically characterize important system properties related to the robot’s long-term energy consumption and service rate. Finally, through extensive simulation with real channel parameters, we verify the efficacy of our approach.

LOS Coverage Area in Vehicular Networks with Cox-Distributed Roadside Units and Relays

We develop an analytical framework to examine the line-of-sight (LOS) coverage area in vehicular networks with roadside units (RSU) and vehicle relays. In practical deployment scenarios, RSUs and vehicle relays are spatially correlated and we characterize this by employing Cox point processes to model the locations of RSUs and vehicle relays simultaneously. Leveraging the random blockage model, we model the LOS coverage area as Boolean models on these Cox point processes. The LOS coverage area is then evaluated by its area fraction. We show that relays can increase the area fraction of LOS coverage by nearly 50% even when RSUs and relays are spatially correlated. By presenting a stochastic geometry model for a vehicular network with RSUs and relays and then by providing a tool to capture its LOS coverage, our work assesses the viability of vehicle relays for modern vehicular networks exploiting LOS coverage.

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.

Position optimization for mobile relay communications with constrained energy over a whole horizontal plane

This paper concerns the position optimization problem of a mobile relay over a whole horizontal plane. This problem is important because the position of a mobile relay directly affects the end-to-end performance, e.g., reliability, connectivity, and data rate. In this paper, we propose a new position optimization scheme of a mobile relay over a whole horizontal plane based on the one-bit feedback information from the destination node, which improves the performance over the prior scheme whose position of the mobile relay is optimized over a fixed orbit. In the proposed scheme, the mobile relay is equipped with merely one single onboard antenna. Moreover, no prior information about the positions of both the source node and the destination node is required. Thus, the proposed scheme can work at low network resources scenario, which is particularly suitable for mobile relay communication with constrained energy, e.g., the communications in a disaster area where the infrastructure is heavily damaged, volcano monitoring, and wireless powered communication networking. According to the characteristics of the proposed scheme, we further design two heuristic implementations to calculate the optimal position of a mobile relay over a whole horizontal plane. The first implementation has better steady performance whereas the second implementation has better convergence speed. We implement the proposed scheme and conduct an extensive performance comparison between the proposed scheme and prior schemes to verify the advantages of the proposed scheme.

Achieving Energy Efficiency and Impact of SAR in a WBAN Through Optimal Placement of the Relay Node.

Wireless Body Area Network (WBAN) is an emerging and promising specialized area in Wireless networks that deals with crucial health-related datasets. Unlike other wireless networks, as this type of network deals with medical facts, losing it is fatal. WBAN is a highly constrained network. Reducing energy consumption and enhancing lifetime are the two most important challenges of WBANs. One way to achieve these is by deploying relay nodes optimally in WBANs. Generally, a relay node is placed at the midpoint of the line joining the source and the destination (D) nodes. We show that such simplistic deployment of the relay nodes is not the optimal deployment, which can hamper the overall lifetime of WBANs. In this paper, we have investigated the best location to deploy a relay node on a human body. We assume that an adaptive decode and forward relay node (R) can move linearly between the source (S) and the destination (D) nodes. Moreover, the assumption is that a relay node can be deployed linearly and that the body part of a human is a flat surface and hard. We have investigated the most energy-efficient data payload size based on the optimally placed relay location. The impact of such a deployment on different system parameters, such as distance (d), payload (L), modulation scheme, specific absorption rate, and an end to end outage () are examined as well. It is observed that in every aspect optimal deployment of the relay node performs an important role to enhance the lifetime of wireless body area networks. Sometimes linear relay deployment is very difficult to implement, especially on the different body parts of the human body. To address these issues, we have examined the optimal region for the relay node based on a 3D non-linear system model. The paper provides guidance for both linear and non-linear relay deployment along with the optimal data payload size under various circumstances and also considered the impact of specific absorption rates on the human body.

The Test Bench for Simulation Phase Fault and Ground Fault Analysis Protection Concept Using Symmetrical Components

Various laboratory experiment platforms have been developed to provide students with theoretical knowledge and practical experience. Understanding concepts related to the process for determining the design of protection settings requires practical experience, which can be achieved by repeated trials. In this paper, the mechanism of a ground fault in a medium voltage feeder is done using a simulator substation as a case study. This process must be carried out twice, once for the ground-fault relays protection based on residual currents and then repeated based on residual voltage. For further understanding of the electrical distribution network, the system will be operated at 20 kV on the primary and 380 V on the secondary. The model uses smaller nominal voltages consisting of 380 V on the primary and the secondary. The result of one phase fault protection mechanism works well at each point of interference, and voltage transformers are protected from overheating and damage. The lowest value of the single-phase to ground short circuit that occurs at the fault location at the farthest point of interference from the protection relay location is used for the threshold setting on the voltage relay. The one phase fault protection mechanism works well at each point of interference, and the voltage transformer is protected from overheating and damage. For residual current ground fault protection effective, the threshold setting of phase fault inverse time delay with threshold setting I> is 1.5 ampere, and instantaneous I>> is 7.5 ampere. The effective threshold setting for residual ground fault protection wasUo> = 22% dan UO>> = 33,2%.

Performance of TAS/MRC in NOMA energy harvesting relay networks

This paper investigates the outage probability (OP) performance for multiple-input multiple-output non-orthogonal multiple access (MIMO-NOMA) based energy harvesting (EH) relaying network. The base station communicates multiple users with the assistance of EH-relay. The optimal transmit antenna selection/maximal ratio combining (TAS/MRC) and sub-optimal majority-based TAS (TAS-maj)/MRC are employed in the first and second hops, respectively. We first derive the signal-to-interference-and-noise ratio (SINR) expressions. Then, the derived SINR expressions are used to obtain expressions of OP for each user in closed form in Nakagami-m fading channels. We finally verify the exactness of the theoretical analysis with the numerical results through Monte Carlo simulations. The results show that the outage performance improves considerably with the increased number of transmit and/or receive antennas and the enhanced channel conditions. Furthermore, regardless of the antenna’s configurations, the optimal position of the EH-based relay has to be close to the base station, while the optimal power division ratios for users vary. Moreover, the proposed TAS/MRC scheme is superior to the previous schemes, such as max–max–max and max–min–max-based MRC.

Intelligent Fault Diagnosis Using Deep Learning for a Microgrid with High Penetration of Renewable Energy Sources

—Fault diagnosis is essential to attain the microgrid’s stable, reliable, and economical operation. However, a microgrid’s fault current varies drastically based on the connected operating mode and connected renewable energy sources. This paper develops an intelligent fault detection and identification scheme for microgrids with high renewable energy penetration by combining Fourier-based Continuous Wavelet Transform (FTCWT) and Deep Learning (DL) methods. Several time-domain case studies representing different microgrid operating conditions were obtained and pre-processed in MATLAB/SIMULINK. The time-series data at the relay location are processed using an FTCWT to get time-frequency representation, and the sequence components waveforms were computed. The time-frequency representation and sequence components waveform contain helpful information, including fault conditions and healthy operating conditions for grid-connected and islanded microgrids that act as input datasets to the DL models. The proposed DL models perform fault location identification, fault type identification, and fault phase-detection for different operating modes. The development of the DL model for the fault detection/classification unit and fault location identification unit is carried out in the PyTorch framework. The experimental results show that the proposed model is more accurate when compared to the state-of-the-art methods.