Impedance-based Methods Research Articles

A Comparison of Impedance-Based Fault Location Methods for Power Underground Distribution Systems

In the last few decades, the Smart Grid paradigm presence has increased within power systems. These new kinds of networks demand new Operations and Planning approaches, following improvements in the quality of service. In this sense, the role of the Distribution Management System, through its Outage Management System, is essential to guarantee the network reliability. This system is responsible for minimizing the consequences arising from a fault event (or network failure). Obviously, knowing where the fault appears is critical for a good reaction of this system. Therefore, several fault location techniques have been proposed. However, most of them provide individual results, associated with specific testbeds, which make the comparison between them difficult. Due to this, a review of fault location methods has been done in this paper, analyzing them for their use on underground distribution lines. Specifically, this study is focused on an impedance-based method because their requirements are in line with the typical instrumentation deployed in distribution networks. This work is completed with an exhaustive analysis of these methods over a PSCADTM X4 implementation of the standard IEEE Node Test Feeder, which truly allows us to consistently compare the results of these location methods and to determine the advantages and drawbacks of each of them.

A comparison and accuracy analysis of impedance-based temperature estimation methods for Li-ion batteries

In order to guarantee safe and proper use of Lithium-ion batteries during operation, an accurate estimate of the battery temperature is of paramount importance. Electrochemical Impedance Spectroscopy (EIS) can be used to estimate the battery temperature and several EIS-based temperature estimation methods have been proposed in the literature. In this paper, we argue that all existing EIS-based methods implicitly distinguish two steps: experiment design and parameter estimation. The former step consists of choosing the excitation frequency and the latter step consists of estimating the battery temperature based on the measured impedance resulting from the chosen excitation. By distinguishing these steps and by performing Monte-Carlo simulations, all existing methods are compared in terms of accuracy (i.e., mean-square error) of the temperature estimate. The results of the comparison show that, due to different choices in the two steps, significant differences in accuracy of the estimate exist. More importantly, by jointly selecting the parameters of the experiment-design and parameter-estimation step, a more-accurate temperature estimate can be obtained. In case of an unknown State-of-Charge, this novel method estimates the temperature with an average absolute bias of 0.4°C and an average standard deviation of 0.7°C using a single impedance measurement for the battery under consideration.

Time-based fault location method for LV distribution systems

Due to the utilization of fundamental frequency, current impedance-based fault location methods are able to locate only permanent and linear faults. The duration of the arc in low and medium voltage systems can be as short as a quarter of a cycle. This period, which is normal for intermittent faults, is insufficient for fundamental frequency-based fault location algorithms. Therefore, available methods are not applicable for intermittent arcing fault location. In this paper, the time-based method previously proposed by the authors has been developed to locate short duration faults in LV distribution systems. The advantage of the proposed method over available methods is its capability for locating faults using fewer samples, which enable the user to locate both arcing faults as well as normal faults in the network. The main characteristics of an arcing fault, i.e., non-linearity and short duration, have been addressed in the proposed algorithms methodology. Various characteristics of a LV distribution system (i.e., heterogeneity, unbalanced load and line, etc.) have been taken into account in the current enhanced algorithm. The validity of the devised algorithm is studied within PSCAD-EMTDC environment and the obtained results show a good accuracy.

Assessment of piezoelectric sensor adhesive bonding

Piezoelectric transducers are widely utilized in Structural Health Monitoring (SHM). They are used both in guided wave-based and electromechanical impedance-based methods. Transducer debonding or unevenly distributed glue underneath the transducer reduce the performance and reliability of the SHM system. Therefore, quality assessment methods for glue layer need to be developed. In this paper, the authors present results obtained from two methods that allow the quality assessment of adhesive bonds of piezoelectric transducers.The electromechanical impedance method is utilized to analyze transducer adhesive bonding. An improperly prepared bonding layer is a source for changes in the electromechanical impedance characteristics in comparison to a perfectly bonded transducer. In the resistance characteristics of the properly bonded transducer the resonance peaks of the structure were clearly visible. In the case when adhesive layer is not equally distributed under sensor, the amplitudes of structural resonance peaks are reduced. In the case of completely detached transducer, the structural resonance peaks disappear and only resonance peaks of the transducer itself are visible. These peaks (peaks of free transducer hanging on wires) are significantly larger than the resonance peaks of the investigated structure in the considered frequency interval.The bonding layer shape is also analyzed using time-domain terahertz spectroscopy in reflection mode. This method allows to visualize the adhesive layer distribution based on C-scan analysis. C-scans of signals or envelope-detected signals can be used to estimate the area of proper adhesion between bonding agent and transducer and hence provides a more quantitative approach towards transducer inspection.

Optimized Assistive Human-Robot Interaction Using Reinforcement Learning.

An intelligent human-robot interaction (HRI) system with adjustable robot behavior is presented. The proposed HRI system assists the human operator to perform a given task with minimum workload demands and optimizes the overall human-robot system performance. Motivated by human factor studies, the presented control structure consists of two control loops. First, a robot-specific neuro-adaptive controller is designed in the inner loop to make the unknown nonlinear robot behave like a prescribed robot impedance model as perceived by a human operator. In contrast to existing neural network and adaptive impedance-based control methods, no information of the task performance or the prescribed robot impedance model parameters is required in the inner loop. Then, a task-specific outer-loop controller is designed to find the optimal parameters of the prescribed robot impedance model to adjust the robot's dynamics to the operator skills and minimize the tracking error. The outer loop includes the human operator, the robot, and the task performance details. The problem of finding the optimal parameters of the prescribed robot impedance model is transformed into a linear quadratic regulator (LQR) problem which minimizes the human effort and optimizes the closed-loop behavior of the HRI system for a given task. To obviate the requirement of the knowledge of the human model, integral reinforcement learning is used to solve the given LQR problem. Simulation results on an x - y table and a robot arm, and experimental implementation results on a PR2 robot confirm the suitability of the proposed method.

Impedance-Based Local Stability Criterion for DC Distributed Power Systems

This paper addresses the stability issue of dc distributed power systems (DPS). Impedance-based methods are effective for stability assessment of voltage-source systems and current-source systems. However, these methods may not be suitable for applications involving variation of practical parameters, loading conditions, system's structures, and operating modes. Thus, for systems that do not resemble simple voltage-source systems or current-source systems, stability assessment is much less readily performed. This paper proposes an impedance-based criterion for stability assessment of dc DPS. We first classify any converter in a dc DPS as either a bus voltage controlled converter (BVCC) or a bus current controlled converter (BCCC). As a result, a dc DPS can be represented in a general form regardless of its structure and operating mode. Then, the minor loop gain of the standard dc DPS is derived precisely using a two-port small signal model. Application of the Nyquist criterion on the derived minor loop gain gives the stability requirement for the dc DPS. This proposed criterion is applicable to dc DPSs, regardless of the control method and the connection configuration. Finally, a 480 W photovoltaic (PV) system with battery energy storage and a 200 W dc DPS, in which the source converter employs a droop control, are fabricated to validate the effectiveness of the proposed criterion.

Diagnosis of a Pipeline System for Transient Flow in Low Reynolds Number with Impedance Method

This study explores the comprehensive calibration potential of impedance-based methods implementing several unsteady friction models for a pipeline system with or without leakage. The corresponding response functions in the frequency domain approach have been derived by the impulse response method and incorporated into the genetic algorithm-based calibration method. Unsteady models addressed either frequency-dependent friction or acceleration-based frictions. Parameter calibration exercises with experimental data have shown that the impedance-based approach provides a versatile and feasible optimization framework via the fitting of an objective function based on the predicted and measured pressure head variation. To check the impact of pressure pulsation and noise, extended calibration tests were performed using oscillated and disturbed pressure data bounded by the frequency and amplitude of a pump system and the measurement error of a conventional pressure transducer. The performance of the integrated optimization examples demonstrates the robustness of the impedance-based approach, both in the representation of a real-life system and the configuration of various system characteristics.

Fault location on transmission lines little longer than half-wavelength

AC transmission lines little longer than half-wavelength have been widely investigated as an alternative for bulk power transmission in power networks where the generation plants are very distant from the load centers. However, studies regarding the performance of fault location methods applied to this type of line have not been done. In this paper, two contributions are presented. First, it is shown that conventional impedance-based fault location methods may fail to correctly identify the fault point even when the line shunt capacitance effect is taken into account. Then, to overcome this drawback, an innovative two-terminal impedance-based fault location algorithm is proposed. The algorithm considers the distributed parameter line model with line shunt capacitances thereby is able to reliably identify and correct erroneous fault point estimations that arise due to atypical operational features of this particular type of transmission line. The performance evaluation of the proposed algorithm is carried out by means of Electromagnetic Transients Program (EMTP) simulations, from which a wide variety of faults in a 1000kV AC transmission line 2613km long is analyzed. The obtained results indicate high reliability of the proposed algorithm, which is almost insensitive to the fault characteristics, power system load flow, power factor and line transposition schemes.

New impedance-based fault location method for unbalanced power distribution systems

Summary This paper presents a novel formulation of impedance-based fault location method for overhead unbalanced distribution systems. The proposed method uses a general fault location equation that is applicable to all possible single and compound shunt fault types. This is in contrast with existing impedance-based methods which use an equation for each fault type and do not cover all types. The proposed method also overcomes the limitation of the conventional method, which requires the identification of fault type. Only the fundamental values of voltages and current measured at the substation terminal are required for the proposed method. The single-phase and three-phase laterals and the capacitive effect of distribution line are considered in this paper. The proposed method was evaluated and tested on a modified IEEE 34-bus distribution system using PSCAD/EMTDC software. Test results verify the accuracy and robustness of the proposed method. Copyright © 2014 John Wiley & Sons, Ltd.

Applying Dynamic Load Estimation and Distributed-parameter Line Model to Enhance the Accuracy of Impedance-based Fault-location Methods for Power Distribution Networks

Precise load modeling and load value estimation at each node of power distribution systems are very important for determining the exact location of fault in impedance-based fault-location algorithms. In this article, a modified impedance-based fault-location algorithm is proposed by applying dynamic load estimation and distributed-parameter line model. The load value at each node is estimated by its load factor and power factor. In the proposed fault-location algorithm, the power distribution system and power factor of each node are estimated first, just before the fault, using the recorded data of voltage and current at the beginning of the main feeder. Then, using this information, the initial location of the fault is obtained by analyzing each section. In this process, multiple positions for the fault can result. Thus, the faulted section is determined by analyzing the operation of protective equipment, i.e., fuses, fault indicators, and reclosers, performed by investigating the current patterns at the beginning of feeder. The performance of the proposed method is evaluated based on a real feeder in an Iranian distribution network under different fault conditions. The obtained results show the efficiency and accuracy of the proposed method.

Fault location scheme for a multi-terminal transmission line based on current traveling waves

As very little research on the fault location for multi-terminal transmission lines based on current traveling waves only has been done, a new fault location scheme on this is proposed. The proposed scheme is different from the traditional ones based on fundamental impedance. Fast Intrinsic Mode Decomposition (FIMD) and Teager Energy Operator (TEO) are combined (FIMD&TEO) to detect the arrival time of the traveling wave at each terminal. Fault Distance Ratio Matrix (FDRM) and rules for identifying faulted sections of a multi-terminal transmission line are proposed and the method for building FDRM is presented in this paper. After several couples of local and remote terminals connecting through the faulted section are got, their fault distances are calculated by means of a two-ended traveling wave method, and then the fault point can be located by averaging the fault distances. Many simulations under various fault conditions have been done, and the results show that the proposed scheme can locate faults more accurately than existing impedance-based methods.

Integrated Fault Location System for Power Distribution Feeders

A fast accurate fault location solution for power distribution feeders enables utility companies to clear a fault quicker and reduce the outage duration. Traditional impedance-based fault location methods assume that all feeder sections have the same impedance characteristics. This assumption introduces errors on feeders that have branches and line sections with different conductor types and tower configurations. Automated meter reading and trouble call systems provide fault location estimation only for faults that are isolated by field devices. This paper presents a new impedance-based method that estimates all possible fault locations by using a detailed feeder model and fault event reports, complemented with information from other intelligent field devices. Field test results show significant benefits from using the new method over the traditional method. This paper also describes a real-world fault location system that implements the reported method and provides automated fault location estimation within 1 min after the fault occurs.

Accurate Unbalanced Fault Location Method for Multi-Ended Multi-Tapped Structures

The accurate fault location is an important criterion for protection system. Accurate and fast fault location decreases the outage time, consumers dissatisfaction and operation cost. Different methods have been proposed to determine the fault location. The impedance-based methods are usually used to protect power systems. The accuracy of these methods depends on system parameters and the structure of power systems. Also, these methods require an iterative process, the phase alignment and a high volume of data. Another algorithm has been newly presented based on negative sequence parameters, which is not iterative and the amount of data communicated between relays is small. Besides, this algorithm is not affected by pre-fault load flow, zero-sequence mutual coupling and fault resistance. This algorithm has been applied for one-tapped systems. But, that method is not applicable for multi-ended structures with more than one tap. In this paper, a new algorithm is introduced to extend the negative sequence method for multi-ended structures with more than one tap. This new algorithm covers a larger area of the power system. Hence, it improves the reliability of power systems. It decreases the amount of relays necessary for the fault location. So, it can noticeably reduce the costs. Also, in this paper, a new idea is presented to reduce the time of the fault location process. The proposed methods are implemented in PSCAD/EMTDC and MATLAB software. The results of simulations will show the effectiveness and accuracy of proposed methods.

Damage detection in beam-type structures via PZT's dual piezoelectric responses

In this paper, practical methods to utilize PZT\'s dual piezoelectric effects (i.e., dynamic strain and electro-mechanical (E/M) impedance responses) for damage detection in beam-type structures are presented. In order to achieve the objective, the following approaches are implemented. Firstly, PZT material\'s dual piezoelectric characteristics on dynamic strain and E/M impedance are investigated. Secondly, global vibration-based and local impedance-based methods to detect the occurrence and the location of damage are presented. Finally, the vibration-based and impedance-based damage detection methods using the dual piezoelectric responses are evaluated from experiments on a lab-scaled beam for several damage scenarios. Damage detection results from using PZT sensor are compared with those obtained from using accelerometer and electric strain gauge.

Bioelectrical impedance validation studies: alternative approaches to their interpretation

Cross-validation of methods of body composition assessment necessitates statistical evaluation of the degree to which the two methods are in agreement. Typically, impedance-based methods for predicting body composition are assessed against other methods using limits of agreement and correlation analysis. Alternative approaches are presented with reference to example body composition data obtained using bioimpedance spectroscopy (BIS) and dual-energy X-ray absorptiometry (DXA). A randomly selected data set, drawn from a body composition database, was analysed by limits of agreement analysis and error grid analysis. The precision of BIS-derived predictions of percentage body fat relative to that of DXA can be determined from limits of agreement analysis. The importance of knowing the precision of the reference method in such analyses was highlighted. Error grid analysis has the potential to aid interpretation of method comparison data in an intuitively understandable way. Alternative ways of comparing analytical methods that are in use in other branches of biomedical research may prove useful when evaluating the utility of impedance-based methods and other methods for the assessment of body composition in cross-validation studies.

Distribution Fault-Locating Algorithms Using Current Only

Traditional impedance-based fault-locating methods implemented in modern overcurrent protection relays require voltage and current measurements to provide reasonable fault-location estimates. Although they capture voltage and current, depending on field condition or due to equipment failure, relays may record current measurements only. Voltage measurements are thus missing or unavailable. The objective of this paper is to develop practical impedance-based fault-locating algorithms with current data (magnitude or phasors) as the only input and demonstrate the efficacy of the algorithms with simulated and actual field data. These algorithms use the circuit model of the distribution feeder and Kirchhoff's circuit laws in estimating the fault voltage at the relay location and then use impedance-based methods for fault location. Based on the analysis conducted on actual fault data, error in estimation is generally less than 0.5 mi from the actual location of the fault.

Solar-powered multi-scale sensor node on Imote2 platform for hybrid SHM in cable-stayed bridge

In this paper, solar-powered, multi-scale, vibration-impedance sensor node on Imote2 platform is presented for hybrid structural health monitoring (SHM) in cable-stayed bridge. In order to achieve the objective, the following approaches are proposed. Firstly, vibration- and impedance-based hybrid SHM methods are briefly described. Secondly, the multi-scale vibration and impedance sensor node on Imote2-platform is presented on the design of hardware components and embedded software for vibration- and impedance-based SHM. In this approach, a solar-powered energy harvesting is implemented for autonomous operation of the smart sensor nodes. Finally, the feasibility and practicality of the smart sensor-based SHM system is evaluated on a full-scale cable-stayed bridge, Hwamyung Bridge in Korea. Successful level of wireless communication and solar-power supply for smart sensor nodes are verified. Also, vibration and impedance responses measured from the target bridge which experiences various weather conditions are examined for the robust long-term monitoring capability of the smart sensor system.

Intermittent Fault Location in Distribution Feeders

Due to the utilization of fundamental frequency, current impedance-based fault-location methods are able to locate only permanent and linear faults. The duration of the arc in low- and medium-voltage systems can be as short as a quarter of a cycle. This period, which is normal for intermittent faults, is insufficient for fundamental frequency-based fault-location algorithms. Therefore, available methods are not applicable for an intermittent arcing fault location. In this paper, a novel method is proposed for arcing fault location in radial feeders, utilizing time-based formulation considering the short duration of the faults. The advantage of the proposed method over available methods is its capability for locating faults using fewer samples, which is suitable for arcing faults as well as normal faults in the network. Also, different types of faults are taken into account in the proposed algorithm. The validity of the devised algorithm is studied within the PSCAD-EMTDC environment and the results obtained show good accuracy for arcing faults. The application of the proposed algorithm in real systems is based on the availability of measured voltage and current waveforms at one end of the network and knowledge of cable/line parameters (self and mutual impedances).

Investigating the Superhydrophobic Behavior for Underwater Surfaces Using Impedance-Based Methods

We have investigated the impedance behavior of immersed superhydrophobic (SH) polymethylene surfaces by tailoring the surface tension of the contacting liquid phase to gradually transition the surface from the Cassie to the Wenzel state. Control over the surface tension is accomplished by varying the ethanol content of the aqueous phase. To establish the mechanism of the transition, we imaged the interface of the film and identified three distinct events of this process: a nucleation event at low concentrations of ethanol in which small areas beneath the liquid phase transition into the Wenzel state, a propagation event characterized by the enlargement of the Wenzel domains and the lateral displacement of air, and a final event at higher concentrations of ethanol in which the thin air layer at the interface morphs into isolated pockets of air. Using this visualization of the transition, we characterized the Cassie and the Wenzel states by measuring the impedance at a frequency of 1 kHz for an initially SH film that changes its wetting behavior upon addition of ethanol. Establishment of the Cassie and Wenzel state conditions was based on concepts of electrochemical impedance spectroscopy (EIS) and quantitatively validated using both the Helmholtz theory and the analytical description of the electrochemical system in terms of the circuit model of a metal surface covered by a polymer film. Finally, we apply this strategy to determine the possibility for SH polymethylene (PM) films to reversibly transition between the Cassie and the Wenzel states. Results show that after rinsing and drying at ambient conditions for 24 h, the film recovers the SH state, suggesting the applicability of these SH films in outdoor environments with occasional periodic submersion in water.

Hybrid acceleration-impedance sensor nodes on Imote2-platform for damage monitoring in steel girder connections

Hybrid acceleration-impedance sensor nodes on Imote2-platform are designed for damage monitoring in steel girder connections. Thus, the feasibility of the sensor nodes is examined about its performance for vibration-based global monitoring and impedance-based local monitoring in the structural systems. To achieve the objective, the following approaches are implemented. First, a damage monitoring scheme is described in parallel with global vibration-based methods and local impedance-based methods. Second, multi-scale sensor nodes that enable combined acceleration-impedance monitoring are described on the design of hardware components and embedded software to operate. Third, the performances of the multi-scale sensor nodes are experimentally evaluated from damage monitoring in a lab-scaled steel girder with bolted connection joints.