Line Current Measurements Research Articles

Design and Implementation of Advanced Output Feedback Control for VSC-HVDC Transmission System

This paper introduces a backstepping control scheme incorporating a nonlinear observer for Voltage Source Converter-based High Voltage Direct Current (VSC-HVDC) systems. The proposed strategy relies on observer design to estimate previously inaccessible states within the system, including remote states along the HVDC cable and parameters of the power grids. The strategy requires only the measurement of line currents for implementation. Simulation results demonstrate the efficacy of the developed approach. Furthermore, a semi-experimental implementation, utilizing a Process-in-Loop (PiL) test, is conducted to validate the feasibility of the proposed methodology in practical scenarios. The outcomes of this study contribute to the advancement of control strategies for VSC-HVDC systems, offering valuable insights for improving system stability and performance.

Predictive Control of Four-Legged Inverter Using Sliding-Window Discrete Fourier Transform Computation for Harmonic Recession

—Shunt active power filters are the most promising solution for power quality challenges. It injects compensating current at the point of common coupling to recede harmonic content and to attain unity power factor. The proposed control strategy comprises of (a) Model predictive control (MPC) for switching state selection and (b) Sliding-window Discrete fourier transform (SDFT) technique for computing reference compensating current in a four-legged shunt active power filter. This paper incorporates MPC and SDFT control as a single-step algorithm for a four-leg inverter. The absence of modulator, look-up tables and complex mathematical operations support the easy implementation of the proposed controller digitally. The proposed scheme involves unique features like improved cost function in MPC, flexible sampling window size in SDFT, reduced computational complexity and execution time. Also, the compensation principle of the controller requires only line current measurement in contrast to the classical compensation techniques which require the distortion level and reactive power demand of the load. The efficacy of the proposed control method is tested for steady-state, dynamic conditions and parameter uncertainties. The system is validated by simulation using level-2 S-function block in MATLAB/Simulink for various case studies.

Decentralized Estimation of Two-Port Equivalents for Power Transmission Lines

Two-port equivalent model of the system around a transmission line is commonly used for various line protection related analyses. The main aim of the paper is to present methods that can be adopted in a decentralized manner at the substation level for estimating such an equivalent model. Firstly, the paper contributes to methods for estimation of simple two-source equivalents based on events such as fault on the line or shunt element switching at its terminals. The paper extends a discussion towards limitations of such models in the presence of a transfer path across the line terminals and proposes an extension of the estimation techniques to overcome the issue. Lastly, the paper proposes methods for updating the two-port equivalent model when network topology in the vicinity of the line of concern changes. This contribution differs in the aspect that it only seeks to update the two-port equivalent model, unlike the previous contributions wherein the aim is to estimate the equivalent model without assuming the availability of an initial solution. The methods for updating utilize the equivalent model parameters in a base network scenario and the measurements excited from a topology event. The proposed methods use only limited measurements of bus voltages and line currents, and model parameters of the line of concern and other neighboring apparatus (such as other incident lines or shunt reactors/capacitors). This is an advantage as the availability of the complete network model at any substation is always a challenge. Therefore, the methods can be deployed directly at substations in a decentralized manner. The proposed solutions are computationally easy and amenable for implementation in the framework of digital substations with advanced communication infrastructure. Testing and analysis are done using a simple two source transmission system and the IEEE 39 bus test system.

Parametric Reconstruction of Multiple Line Currents Based on Magnetic Sensor Array

Current measurement is of great importance for the state monitoring and parameter identification in a power grid. This article proposed a contactless magnetic-based sensor array method for the acquisition of line current parameters, aiming at the measurement for arbitrary line currents. The inverse problem between the line current with arbitrary parameters and the magnetic field was introduced. Due to the nonlinearity of the inverse problem, a comprehensive algorithm consisting of metaheuristic algorithms and interior point method was employed. The influences of structural parameters on the calculation accuracy have been explicitly studied, indicating the optimal sensor array design parameters concerning the number of sensors, the distance between adjacent sensors, and the shape of sensor array. The sensor array was implemented by utilizing the dual-axial tunneling magnetoresistive (TMR) magnetic-field measurement device. In terms of the 2-D magnetic-field measurement results for two currents with all parameters unknown, the current magnitude error was 0.6%, proving the effectiveness of the comprehensive algorithm together with the annular sensor array. The proposed method for current measurement gives a promising solution for various line current measurement requirements in the power grid.

Fault diagnosis in grid‐connected PV NPC inverters by a model‐based and data processing combined approach

This study presents a fault detection and isolation (FDI) method for open‐circuit faults (OCFs) in the switching devices of a grid‐connected neutral‐point‐clamped (NPC) inverter for photovoltaic (PV) applications. The proposed methodology addresses the fault diagnosis problem by a combined model‐based and data processing perspective to study single and simultaneous faults in the NPC inverter. For the model‐based scheme, a bank of sliding‐mode proportional–integral observers is suggested to estimate the fault profiles under an additive model. Thus, from the estimated fault profiles, and by performing a directional residual evaluation in a fixed reference frame, single and simultaneous fault scenarios can be isolated in the NPC inverter. However, for some fault classes, there is some ambiguity by just the model‐based approach that is overcome by employing the average line currents to construct extra fault signatures. The proposed FDI scheme only requires the measurements of line currents and grid voltages in the diagnosis media and can isolate single OCFs and simultaneous OCFs in the order or lower than a fundamental period of the grid frequency. Our new FDI methodology is validated through experimental data from a practical PV system in a closed‐loop grid‐connected NPC inverter under single and simultaneous OCF conditions.

Quantitative Infrared Thermography Resolved Leakage Current Problem in Cathodic Protection System

Leakage current problem can happen in Cathodic Protection (CP) system installation. It could affect the performance of underground facilities such as piping, building structure, and earthing system. Worse can happen is rapid corrosion where disturbance to plant operation plus expensive maintenance cost. Occasionally, if it seems, tracing its root cause could be tedious. The traditional method called line current measurement is still valid effective. It involves isolating one by one of the affected underground structures. The recent methods are Close Interval Potential Survey and Pipeline Current Mapper were better and faster. On top of the mentioned method, there is a need to enhance further by synthesizing with the latest visual methods. Therefore, this paper describes research works on Infrared Thermography Quantitative (IRTQ) method as resolution of leakage current problem in CP system. The scope of study merely focuses on tracing the root cause of leakage current occurring at the CP system lube base oil plant. The results of experiment adherence to the hypothesis drawn. Consequently, reso

Novel Fault Location in MTDC Grids With Non-Homogeneous Transmission Lines Utilizing Distributed Current Sensing Technology

This paper presents a new method for locating faults in multi-terminal direct current (MTDC) networks incorporating hybrid transmission media, including segments of underground cables and overhead lines. The proposed traveling wave type method uses continuous wavelet transform applied to a series of line current measurements obtained from a network of distributed optical sensors. The technical feasibility of optically-based dc current measurement is evaluated through laboratory experiments using Fiber–Bragg Grating sensors and other commercially available equipment. Simulation-based analysis has been used to assess the proposed technique under a variety of fault types and locations within an MTDC network. The proposed fault location scheme has been found to successfully identify the faulted segment of the transmission media as well as accurately estimating the fault position within the faulted segment. Systematic evaluation of the method is presented considering a wide range of fault resistances, mother wavelets, scaling factors, and noisy inputs. Additionally, the principle of the proposed fault location scheme has been practically validated by applying a series of laboratory test sets.

Distribution network fault section identification and fault location using wavelet entropy and neural networks

Fault location in power system distribution networks is especially difficult because of the existence of several laterals/tap-offs in distribution networks. This implies that the calculated fault point can be wrongly estimated to be in any of the laterals. This paper proposes a new hybrid method combining Discrete Wavelet Transform (DWT) and artificial neural network (ANN) for fault section identification (FSI) and fault location (FL) in power system distribution networks. DWT was used in the analysis and extraction of the characteristic features from fault transient signals of the three phase line current measurements obtained at a single substation relaying point, rather than the double-ended approach used in the existing literature. Entropy Per Unit (EPU) indices are afterwards computed from the DWT decomposition, and are used as input to multi-layer ANN models serving as FSI classifiers and FL predictors respectively. The proposed hybrid method is tested using a benchmark IEEE 34-node test feeder. Comparisons, verification, and analysis made using the experimental results obtained from the application of the method showed very good performance for different fault types, fault locations, fault inception angles, and fault resistances. The proposed hybrid method is unique because of the pre-processing stage done with the DWT-EPU indices, the use of only line current measurements from a single relaying point, and the division of the FSI and FL tasks into sub-problems with respective ANN models.

A new control strategy for SSSC to improve low-frequency oscillations damping

When power systems are expanded and connected together with weak tie lines, the low-frequency oscillations are increased and the stability margin of the power system decreases. Therefore, when designing the transmission system to be used, it is necessary to maintain the dynamic stability of the power system, and to make sure to have the most possible stability margin. SSSC is a FACTS device connected in series with power transmission lines. SSSC can control power flow very effectively and can inject series inductive or capacitive voltages into the line. In this paper, a new control strategy based on voltage measurement for the SSSC is proposed. The commonly used strategy for SSSC is based on line current measurement; consequently, the injected voltage is in quadrature with the line current. But in the proposed strategy, the injected voltage is in quadrature with the ac voltage at the point of common coupling (PCC) of SSSC. With modifications done in the proposed strategy, compared with the conventional control method, it can be adjusted easily to control the power flow of the transmission line. The simulation is performed in single-machine and multi-machine power systems. The analysis of the results under different disturbances show that the proposed strategy has an appropriate response with respect to the changes in the system states and it is relatively faster in damping power system oscillations, compared with the conventional strategy.

Instantaneous positive‐sequence current applied for detecting voltage sag sources

This study proposes a method for detecting voltage-sag sources, using only the measurements of line currents. Instantaneous symmetrical components are introduced for accommodating the transient nature of voltage sag events, where a magnitude and phase change in the instantaneous positive-sequence current is used as a criterion. The proposed method is compared with conventional phasor-based methods known from the literature. All the discussed methods for voltage sag source detection, both the already known and the proposed ones, were evaluated by applying extensive simulations, laboratory tests and field testing. When compared with the phasor-based methods, the proposed method showed faster response, a higher degree of confidence and superior effectiveness, especially for transient voltage sag events in networks with distributed generation and active loads.

Detection of voltage sag sources based on the angle and norm changes in the instantaneous current vector written in Clarke’s components

Abstract The presented research reflects those methods for detecting voltage sag sources that only use measurements of line currents. It is shown that the phasor-based method known from the literature is unsatisfactory, especially in the cases of transient voltage sag events. Therefore, a generalised method is proposed that is based on the instantaneous current vector written in Clarke’s components. The phasor-based method and the proposed method for voltage sag source detection were evaluated by applying extensive simulations, laboratory tests, and field testing. The obtained results show considerably higher effectiveness for the proposed method. The correctness of the instantaneous vector-based approach is verified in this way. Moreover, the proposed method that uses only measurements of line currents is just as effective as some other instantaneous vector-based methods that use measurements of line currents and line voltages.

Virtual Impedance-Based Selective Harmonic Compensation (VI-SHC) PWM for Current Source Rectifiers

To mitigate the line current harmonics of a high-power current source rectifier (CSR) system, the selective harmonic elimination (SHE) scheme is frequently used due to its low switching frequency and superior harmonic performance. However, the SHE scheme only focuses on the harmonics generated by the converter itself. It cannot cope with the line current harmonics caused by the background grid voltage harmonics. In this paper, a selective harmonic compensation scheme using the virtual impedance concept (VI-SHC) is presented. This method compensates for the preexisting grid background harmonics using only the line current measurement, and provides superior line current harmonic performance. The proposed method does not require measuring the grid voltage harmonics (which are typically low), does not rely on an accurate CSR system model, and therefore is very robust for practical implementation. Thi s PWM control scheme has been verified by real-time experiments on a CSR prototype.

Speed Estimation by Using EKF Techniques for Sensor-Less DTC of PMSM with Load Torque Observer

This paper proposes a Direct Torque Control (DTC) of a Permanent Magnet Synchronous Motor (PMSM) without mechanical speed and position sensors. These later are estimated by using the Extended Kalman Filter (EKF) only by measurement of the stator line voltages and currents. Moreover, DTC uses no current controller and no motor parameters other than the stator resistance, which yields a faster torque response and lower parameter dependence than with others motor control techniques. The Kalman filter is an observer for linear and non-linear systems. Also, due to an angle modification scheme with error tracking, the Sensor-less drive system is robust to parameter variations. A load torque can also be estimated by using Luenberger Observer. A simulation model is developed in MATLAB/SIMULINK and is used to verify the basic operation (performance) of the Sensor-less DTC of PMSM

Zero sequence power line current measurement by using magnetic field sensor array

Summary Knowledge of the zero sequence current (ZSC) in an overhead power line is very important for troubleshooting grounding-related power quality problems. Unfortunately, no simple and easy-to-use method for measuring the ZSC is available. This article presents a simple, portable, and non-contact ZSC measurement method based on the concept of the magnetic field sensor array. This innovative method uses magnetic field sensors located on the ground, vertically below an overhead power line. The ZSC is calculated by using the measured magnetic fields associated with the power line currents. The proposed method is a non-contact and power disturbance-free device. Its theory and basic operation principle are presented. The results of the simulation studies carried out for evaluation are reported. A laboratory set-up was developed accordingly, and extensive experimental results confirmed the feasibility and validity of the proposed method. Copyright © 2014 John Wiley & Sons, Ltd.

Generic scalable fault diagnosis system for multimachine power grids

A new approach for fault diagnosis in power grids is presented in this paper. The approach is capable of detecting, classifying and locating, with high speed and accuracy, any type of faults anywhere in the grid using bus voltage or line current measurements only. Fault detection and classification is accomplished by applying logic on measured data while fault location is determined by fault location identification functions generated off-line by using a least-square support vector machine. The high speed and accuracy aspects of the proposed approach are verified through case studies in three test power systems.

Advanced DC zonal marine power system protection

A new active impedance estimation based protection strategy which is suitable for utilisation in a DC zonal marine power distribution system is presented. This method uses two triangular current ‘spikes’ injections for system impedance estimation and protection when faults are detected. By comparing the estimated impedance with the pre-calibrated value, the fault location can be predicted and fault can be isolated without requiring communication between two injection units. Using co-ordinated double injections and line current measurement (directional fault detection), faults in the system with same impedance and different fault positions can be distinguished, located and isolated. The proposed method is validated using experimental test results derived from a 30 kW, 400 V, twin bus DC marine power system demonstrator. The experimental tests were applied to both faults during normal operation and faults that occur during system restoration.

Automatic Power Factor Correction Based on Alienation Technique

In modern digital protection and control systems, an alienation technique has recently become the workhorse of quantitative research and analysis. In this paper, an alienation technique is developed for calculations of original power factor on-line, active and compensation reactive powers and determination of the required number of capacitor banks to get the desired power factor. Alienation coefficients are calculated between phase voltage and current signals of power supply. These calculations are performed within one-cycle. Thus, the algorithm is well suited for implementation in a digital reactive power control scheme. This scheme is able accurately to identify the required capacitor rating to get the desired power factor under different loading levels. It does not need any extra equipment as it depends only on the voltage and line-current measurements which are mostly available at the relay location. Alternative transient program (ATP) and MATLAB programs are used to implement the proposed technique.

Magnetoelectric sensor with miniature universal tunable bias magnetic circuit

This paper presents a miniature alternating magnetic field sensor made from magnetoelectric (ME) laminated materials with a universal tunable bias magnetic circuit. By adjusting the width of the bypass passage in the bias magnetic circuit, the magnetic flux in the ME materials could be tuned and make the ME sensor work under the optimal bias magnetic field. In our design, the sensor's dimension is as small as 8 mm along the detecting direction. Due to the excellent linearity when measuring low frequency alternating magnetic fields of 50 Hz, this miniature sensor is ideally suited for power line current measurement.

Led Tabanlı Yüksek Gerilim Hatları İkaz Sistemi

LED-based system, running with the current of high-voltage lines and converting the current flowing through the line into the light by using a toroid transformer, has been developed. The transformer’s primary winding is constituted by the high voltage power line. Toroidal core consists of two equal parts and the secondary windings are evenly placed on these two parts. The system is mounted on the high-voltage lines as a clamp. The secondary winding ends are connected in series by the connector on the clamp. LEDs are supplied by the voltage at the ends of secondary. Current flowing through highvoltage transmission lines is converted to voltage by the toroidal transformer and the light emitting LEDs are supplied with this voltage. The theory of the conversion of the current flowing through the line into the light is given. The system, running with the current of the line and converting the current into the light, has been developed. System has many application areas such as warning high voltage lines (warning winches to not hinder the high-voltage lines when working under the lines, warning planes to not touch the high-voltage lines), remote measurement of high-voltage line currents, and local illumination of the line area

Experimental study of induction motor misalignment and its online detection through data fusion

Most of the induction motor (IM) fault detection schemes are based on one sensor with one detection logic which are generally incapable of bringing out any consistent feature related to rotor misalignment. Moreover, these logics do not consider simultaneously the asymmetric load condition with variable speed operation. In this study, a data fusion-based misalignment related fault identification algorithm is presented, which isolates fault features from similar features generated because of other operating conditions. In the proposed scheme, the feature vector is constructed by using signatures created from frequency-domain characteristics obtained from stator vibration and line current measurements. Thereafter, the feature fusion technology, by means of the weighted linear combination concept, is adopted to take advantage of the best features from both sensors and to discern the pattern of misalignment with other signatures. The technique is validated experimentally on a 5.5 hp IM and the results are presented.