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Knowledge about moisture content in oil impregnated paper insulation is essential when estimating remaining lifetime of power transformers. Direct evaluation of moisture content is rarely possible due to inaccessibility of the internal insulation system in transformers. Therefore, various indirect estimation techniques are utilized. Frequency domain spectroscopy (FDS) measurements of transformer insulation belong to this group. To perform high quality interpretation of results of FDS measurements a good knowledge on dielectric responses in oil impregnated pressboard and paper is required, especially as it refers to their variation with water content and temperature. The aim of this paper is to provide an open access to the frequency domain spectra of oil impregnated paper and pressboard samples, which can then be used in modeling of the results of diagnostic measurements in power transformers. [ABSTRACT FROM AUTHOR]

An extensive revision of the IEEE C37.011 ‘Application Guide for TRV for AC High-Voltage circuit Breakers’ has been in process for the last four years. The main aim was to introduce the two- and the four- parameter description of the transient recovery voltage (TRV) as used in IEC Switchgear standards that have been introduced in the revisions of Standards C37.04 and C37.06. These two standards are being concurrently revised, but IEEE C37.011 provides the necessary explanations on TRV characteristic in advance. Non-specialist engineer users of the guide will better understand these standards. [ABSTRACT FROM AUTHOR]

The article presents the cross-sectional results of analyzes of authentic conducted disturbances introduced into public power networks by various types of loads installed at end users. The foundation for the research was a set of 260 identified cases of Power Line Communication (PLC) transmission disturbances based on the Open Smart Grid Protocol (OSGP) technology, which were recorded in the urban network of the distribution system operator covering over 400,000 smart meters. The paper presents a quantitative assessment of the share of loads that most often cause problems with transmission efficiency. Moreover, a qualitative assessment of the detected disturbance cases was carried out in terms of conditions relating to the structure of the power grid and real transmission levels and disturbance levels. The authors made a pioneering analysis in the so-called “communication path” where the PLC communication disturbance was identified, i.e., from the installation point of the PLC concentrator to the metering point where the energy meter, with which the connection was lost, was installed. [ABSTRACT FROM AUTHOR]

This two-part paper is intended to inform power system engineers, electrical engineering academicians, and suppliers of electrical apparatus of the threat of wildfires initiated from mal-operation of electrical grids and the unexploited opportunity to develop proper solutions and preventive means to such lethal events. This part (Part I) reviews and categorizes research in different fields of science and industrial projects that attempt to address wildfire issues. The topics include prediction and prevention means, detection methods, monitoring and surveillance techniques, suppression methods, allocation and mapping algorithms, and a summary of research and educational efforts. Subsequently, this paper highlights the damages and negative effects that a wildfire can cause to the electric grid and the interruptions to its continuous operation. Finally, this paper analyzes and categorizes the various scenarios of faulty electrical networks that may lead to wildfires. Part I of this paper provides the ground work and information for the solutions and discussions presented in Part II. [ABSTRACT FROM AUTHOR]

A distributed zero-sequence-current (ZSC) carrier signal injection via current transformer (CT) is proposed for underground cable single-phase-to-ground fault location in neutral isolated medium voltage (MV) distribution networks. High-frequency ZSC carrier signal is directly injected to a high-voltage underground cable of an energized distribution network via CT. The injected carrier signal travels along the cable to the receiving center in the substation, and is processed for quick fault line selection and fault location. No external power supplies or signal generators are needed due to the self-contained nature of the injector. The device can be constructed as a sleeve to be mounted around the underground power cable. This permits economical retrofitting to existing installations of power line communication (PLC) devices. In this paper, the operational principle and the application considerations for such an injection device and fault location tricks are explained, followed by the theory behind the proposed technique. Finally, MATLAB based numerical simulations are performed and a low-voltage prototype is tested to verify the validity of the proposed approach. [ABSTRACT FROM AUTHOR]

In the event of a single line to ground (SLG) fault in a non-effectively grounded distribution network, the faulted current is weak (only a few amperes or less) and the existing devices cannot accurately judge the faulted feeder. In this paper, we proposed algorithms that combine complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) and Hilbert transform to construct a multi-criteria comprehensive voting method. First, CEEMDAN algorithm is used to decompose the zero-sequence current to obtain the IMF1(the first intrinsic mode function) component and the Hilbert transform is used to calculate the instantaneous amplitude and instantaneous phase. Then, according to the three largest instantaneous amplitudes information, we constructed the characteristic instantaneous phase, characteristic instantaneous energy relative entropy and characteristic instantaneous zero sequence current polarity criteria from the phase, energy and polarity, respectively. Finally, we proposed a comprehensive voting method, which is specifically shown as follows: when two or more criteria show that one feeder or the bus has an SLG fault, it is voted that the feeder or the bus has an SLG fault. In contrast, if the judgment results of the three criteria are inconsistent, then we would return to recalculation and then vote. Compared with existing method, simulation tests and field experiments show that the method proposed in this paper has higher accuracy and a faster calculation speed. [ABSTRACT FROM AUTHOR]

Foil-winding transformers with high currents in low voltage winding normally have copper/aluminum bars as leads of the coils. A practical solution for locating bar leads without increasing the size of the active part is to flatten the coil in the leads zone causing a deformation. Abnormalities in the leakage reactance have been identified in this type of transformers. In order to take this effect into account, this paper proposes a correction to the mathematical formulation for calculating the leakage reactance in transformers with deformations in the low voltage winding. Three methods for calculating the leakage reactance have been compared for four real case studies: the proposed formulation, the commonly used formulation, and detailed simulations with the finite element method in three-dimension (FEM3D). The leakage reactance calculated with the proposed method has been found to have an improved accuracy compared with the one calculated using the formulation without correction in all case studies. The main contribution of this paper is that the proposed correction in the formulation makes it possible to increase the accuracy in the calculation of leakage reactance, avoiding the need to resort to detailed simulations with FEM3D. [ABSTRACT FROM AUTHOR]

A novel traveling-wave-based fault-location algorithm for multiterminal transmission lines is introduced in this paper. Existing traveling-wave fault-location methods that based on the data measured at line terminals lack reliability and accuracy because time synchronization is needed, which brings error. To solve this problem, the complex structure of multiterminal power system is divided into several fault identification branches, current at the midpoint of each branched is measured, a novel fault-location algorithm is proposed, and the time synchronization error is eliminated. A line-based device is designed to measure the current at the midpoint of each branch. An accurate value of the traveling wave speed can be obtained by merely applying the data record in one measuring device. Thus, the fault-location accuracy is improved. The system model applied in this paper comprises one transmission line and two tapped lines, and the proposed method applies to networks with more terminals. Performance of this method is tested by different cases by PSCAD. The hardware platform has been tested in Sichuan Province, China. [ABSTRACT FROM AUTHOR]

This paper proposes a novel method for voltage dip classification using deep convolutional neural networks. The main contributions of this paper include: 1) to propose a new effective deep convolutional neural network architecture for automatically learning voltage dip features, rather than extracting hand-crafted features; 2) to employ the deep learning in an effective two-dimensional (2-D) transform domain, under space-phasor model (SPM), for efficient learning of dip features; 3) to characterize voltage dips by 2-D SPM-based deep learning, which leads to voltage dip features independent of the duration and sampling frequency of dip recordings; and 4) to develop robust automatically-extracted features that are insensitive to training and test datasets measured from different countries/regions. Experiments were conducted on datasets containing about 6000 measured voltage dips spread over seven classes measured from several different countries. Results have shown good performance of the proposed method: average classification rate is about 97% and false alarm rate is about 0.50%. The test results from the proposed method are compared with the results from two existing dip classification methods. The proposed method is shown to outperform these existing methods. [ABSTRACT FROM AUTHOR]

Circuit models of horizontal and vertical grounding electrodes are traditionally used in high-frequency (HF) analysis, although underlying approximations limit their accuracy in some low-frequency ranges. Recently, a number of new circuit models have been introduced, but the improvement of the accuracy at HF has not been systematically evaluated. In this paper, we show that new circuit models can be directly derived from method of moments solutions of the integral forms of Maxwell equations by introducing different assumptions. This approach helps to categorize different models into only a few categories based on underlying approximations. To determine the applicable range, we analyze the error for impedance to ground computed by different circuit models in comparison to that calculated by a rigorous full-wave model over wide ranges of parameters, such as electrode length, soil resistivity, and frequency. This paper: 1) provides a parametric analysis that enables the estimation of the applicability of the particular circuit model for application to a practical case based on its accuracy; 2) presents a unified systematic approach to derive circuit models with different capabilities; and 3) reveals that the modeling of the mutual coupling between different parts of the grounding electrode is the key factor for radically improving the accuracy of circuit models at HF. [ABSTRACT FROM AUTHOR]

In this paper, an experimental validation of three-dimension multiconductor cell analysis (MCA) is presented: a measurement campaign has been performed on Capri–Torre Annunziata three-core 29.5 km long submarine cable link. All the theoretical conclusions derived by the authors in a previous paper are now experimentally confirmed and the model is, therefore, validated. Based on the example in this paper, the maximum difference between MCA results and measurements is 7% on the positive sequence resistance at power frequency. A 10% difference occurs in the evaluation of positive sequence reactance. The agreement between MCA and real measurements in zero sequence impedance is very good with differences lower than 5% in real and imaginary parts. [ABSTRACT FROM AUTHOR]

A comprehensive time series power flow (TSPF) framework is proposed for the analysis of fault-induced delayed voltage recovery (FIDVR). TSPF bridges the gap between static power flow simulations and time-domain simulations for FIDVR analysis. FIDVR events can be simulated faster with TSPF, while transient simulations normally require much longer time. In the TSPF framework, a random model for the disconnection of the induction motors is proposed to determine the load for different “snapshots” during FIDVR events. Regression analysis is used to predict the parameters needed in the simulations. There is no need to simplify the network topology or aggregate loads into clusters as in measurement-based load modeling approaches. The techniques presented in this paper successfully reproduced two FIDVR events recorded in heavily meshed distribution networks in New York City in 2010 and 2015. The paper uncovers that the proper modeling of motor protections (thermal and under-voltage) is key to properly predict FIDVR events. [ABSTRACT FROM AUTHOR]

This paper proposes a new modulated model predictive control method for the control of modular multilevel converters (MMCs) in voltage source converter-high voltage dc systems. The proposed method retains the advantages of the conventional finite control set-model predictive control methods by programing the nonlinear properties of the MMC into the design calculations while minimizing the ac line and circulating current ripples and steady-state error by generating modulated switching signals with a fixed switching frequency. In this paper, first, the predictive modeling of the MMC is provided. Next, the proposed control method is described. Then, the application of the proposed method to an MMC system is detailed. Finally, experimental results from an MMC system connected to a three-phase grid are provided to validate the theoretical outcomes. [ABSTRACT FROM AUTHOR]

An online approach based on application of search coil for transformer winding fault detection is presented in this paper. Earlier attempts report use of search coil for the detection of transformer interturn fault. This paper extends application of search coil for detection of winding displacement in addition to interturn fault identification. Experimental results based on specially designed 10-kVA transformer are presented to analyze search coil voltages during healthy and faulty conditions. The algorithm detects phase ($U$ , $V$, $W$), side (LV, HV), and precise location of the fault. Discrimination between interturn fault and winding radial displacement is also achieved by search coil voltage analysis. The results are experimentally verified based on impedance analyzer plots. Experimental analysis indicates that the proposed method is independent of load on the transformer, vector group, nature of winding, balanced or unbalanced source voltage, source voltage harmonics, inrush, and overexcitation conditions. [ABSTRACT FROM AUTHOR]

This paper presents the challenges that the power converters with $dq$ -frame-based control confront when subjected to ferroresonance. This is mainly due to two main properties of the widely used $dq$-frame control systems. It is demonstrated in this paper that regardless of the phase-to-ground or phase-to-phase voltage measurement, the $dq$-frame control only responds to phase-to-phase voltage variations. Furthermore, the PI controllers, which are employed in conjunction with the $dq$ reference frame, can inherently only track dc references and reject dc disturbances. Consequently, a $dq$ -based PI controller can only respond to the positive-sequence phase-to-phase voltage variations, effectively. This, in turn, limits the disturbance mitigation capability of the power converter. This study investigates the impacts of the ferroresonance phenomenon on the control system response and the operating conditions of the power converters. Based on a droop-based $dq$ frame controller, the behavior of an electronically interfaced distribution generation system is studied, under various transient conditions. In spite of a promising performance under the load change and islanding scenarios, the $dq$-frame-based controller of the power converter fails to detect and respond to the voltage fluctuation and excessive overvoltages as a result of ferroresonance. [ABSTRACT FROM AUTHOR]

In this paper, typical strengths, fault levels, and source impedances are thoroughly analyzed and calculated for the study of quality of supply in 230/400 V 50 Hz distribution systems. Considering all the disparity in distribution network design, this study is based on a comprehensive database containing typical arrangements and equipment in U.K./European systems, as well as on fully documented generic network models supplying four residential load subsectors in the U.K., i.e., from metropolitan to rural areas. Thus, this paper proposes an alternative method for determining reference values of network supply impedances and short-circuit fault levels at different points and locations of the medium-to-low voltage distribution system. The aim of this study is to provide a wider range of benchmark values than those stipulated in the IEC 60725 Standard, which only defines a single-reference threshold of public supply impedances for all types of distribution systems and residential customers. In order to assist network operators in the planning and design of their distribution systems, these values are further disaggregated and classified in this paper according to network/demand type. [ABSTRACT FROM PUBLISHER]

In this paper, a new dc switchyard structure for a multiterminal dc (MTDC) grid is proposed. Fast fault current breaking capability, which is essential for a dc grid, can be achieved with available HVDC breaker solutions (e.g., ABB's hybrid HVDC breaker). However, the hybrid HVDC breaker concept also opens up possibilities for unconventional (relative to ac) switchyard solutions which may be more cost effective. The main aim of this paper is to expound how the proposed dc switchyard can be built with hybrid HVDC breakers in a configuration where the number of components is much less compared to a conventional switchyard structure. After that, the switchyard operation, fault current handling flexibility, and actions against component failure are described conceptually. Finally, the performance of the proposed switchyard is validated and compared with that of a conventional double breaker double busbar switchyard structure for selected cases through time-domain simulations [ABSTRACT FROM PUBLISHER]

In Australia and many other countries, distribution network service providers (DNSPs) have an obligation to their customers to provide electrical power that is reliable and of high quality. Failure to do so may have significant implications ranging from financial penalties theoretically through to the loss of a license to distribute electricity. In order to ensure the reliability and quality of supply are met, DNSPs engage in monitoring and reporting practice. This paper provides an overview of a large long-running power-quality monitoring project that has involved most of Australia's DNSPs at one time or another. This paper describes the challenges associated with conducting the project as well as some of the important outcomes and lessons learned. A number of novel reporting techniques that have been developed as part of the monitoring project are also presented. A discussion about large-volume data management, and issues related to reporting requirements in future distribution networks is included. [ABSTRACT FROM PUBLISHER]

This paper presents a new simulation approach based on the functional mock-up interface standard for parallel and multistep simulation of electromagnetic transients in power grids with computationally expensive control systems. The control systems are represented by slave subsystems, which are decoupled in memory from the power network and encapsulated in functional mock-up units. The simulation modes are either asynchronous or synchronous. In the asynchronous mode, the subsystems are simulated in parallel, whereas in the synchronous mode, the simulation of each subsystem is executed in a sequential multistep environment. Considerable computation time gains in both modes have been observed in power system protection studies on large-scale networks with accuracy properly maintained. [ABSTRACT FROM AUTHOR]

This paper proposes a voltage sag estimation approach based on a deep convolutional neural network. The proposed approach estimates the sag magnitude at unmonitored buses regardless of the system operating conditions and fault location and characteristics. The concept of system area mapping is also introduced via the use of bus matrix, which maps different patches in input matrix to various areas in the power system network. In this way, relevant features are extracted at various local areas in the power system and used in the analysis for higher level feature extraction, before feeding into a fully-connected multiple layer neural network for sag classification. The approach has been tested on the IEEE 68-bus test network and it has been demonstrated that the various sag categories can be identified accurately regardless of the operating condition under which the sags occur. [ABSTRACT FROM AUTHOR]

The smartening of distribution systems with distributed generation, storage devices, and intelligent loads have created challenges for the operation of distribution feeders, which can be addressed with power-electronics based controllers. However, the capital-intensive nature of these controllers is an obstacle for their wide use. The Hybrid Power Flow Controller (HPFC) is shown here to provide an adequate solution to the application of flexible ac transmission systems controllers to distribution systems, and hence the merits and the added value of this controller are discussed here through detailed modeling and simulations, examining its impact on a distribution system under different conditions. Thus, in this paper, a detailed dynamic model of the HPFC is developed and implemented in PSCAD, describing and proposing control strategies to properly operate this controller in distribution-system applications, such as an effective and simple procedure for starting up the device. The developed model is used to demonstrate the effectiveness of the controller for solving problems in distribution systems, such as voltage sags associated with feeder faults and power flow fluctuations due to intermittent renewable generation using a benchmark network as an illustrative example. [ABSTRACT FROM AUTHOR]

This paper presents a decision tree based high-speed intelligent scheme for series-compensated transmission line protection using differential phase angle of superimposed current (DPASC). The conventional distance relaying scheme undergoes many shortcomings in transmission line protection in the presence of series compensation devices. The proposed scheme calculates the differential phase angle of current signals using full cycle discrete Fourier transform. The DPASC for each phase is used as an input to the data mining model known as decision tree (DT). The DT is used to generate thresholds to detect and classify the faults since determination of robust thresholds is an important challenge in protective relay engineering. The proposed method has been tested for different operating modes of transmission line in SIMIULINK/MATLAB software. Simulation results indicate that the proposed method is able to detect and classify the faults with acceptable accuracy, in less than half cycle. [ABSTRACT FROM AUTHOR]

To meet the growing power demand of the future, utilities and researchers have considered the addition of dc circuits in existing transmission corridors. The previous research has focused on analyzing the field environment, steady state induction and the negative effects of induction in the hybrid transmission lines. The overhead ground wires (OHGWs) have been used only for improving the lightning performance of overhead lines (OHL). In this paper, the spatial position of OHGWs has been studied with the objective of minimizing the steady state induction between power conductors as well as poorly grounded metallic objects like railroads and fences present near the ac-dc OHL. Candidate space for placement of OHGWs having shielding failure rate of less than four is identified using the conventional electro-geometric model. The steady state induction in the power conductors and nearby metallic objects is studied as a function of position of OHGWs using electro-magnetic transient simulation. The results indicate a strong correlation between the height of OHGWs and magnitude of induced voltage in power conductors, and metallic objects underneath the transmission line. The conscious effort in placement of OHGWs can reduce the magnitude of induced voltages while ensuring adequate lightning performance. [ABSTRACT FROM AUTHOR]

The presence of power system uncertainties results in variations of the harmonic resonance behaviors. There is, therefore, a need to perform the probabilistic assessment in harmonic resonance study. In this paper, a systematic methodology for probabilistic harmonic resonance assessment considering power system uncertainties is presented. First, potential system uncertainties are analyzed and modeled. The stochastic behavior of harmonic resonance due to system uncertainties is then studied using both Monte Carlo approach and harmonic resonance mode analysis technique. A modified power iteration method is further used to efficiently reduce the calculation time. Three indices, including probabilistic expressions of 1) resonance frequency band, 2) modal impedances in the resonance band, and 3) sensitivity information at the bus-level and the element-level are used to represent the stochastic behaviors of harmonic resonance. In addition, the resonance mitigation scheme based on probabilistic resonance frequency band shift technique is described. The effectiveness of the proposed method is demonstrated through case studies in an uncertain power system. Its potential applications are also discussed. [ABSTRACT FROM AUTHOR]

Single-phase autoreclosing (SPAR) is among the alternatives for mitigating the many harmful effects that a line-to-ground fault in a transmission line (TL) may cause. This procedure basically consists of opening the compromised phase, waiting a preset time span (dead time), and recomposing the previously isolated phase. In the vast majority of SPAR implementations, the open phase switching proceeds with no guarantee of whether the TL is still faulted. Switching the open phase into a fault might represent a more severe threat to the system than simply disconnecting the TL in the first place. Hence, in an effort to ensure higher levels of operational reliability to SPAR, the present paper offers a new methodology to check the soundness of the open phase during the dead time before its reclosing. First, the method's fundamental concepts are exposed. Second, a huge number of steady-state tests are presented, for which both the system topology and its operative condition were varied. To conclude, the SPAR is simulated in the time-domain with the most critical condition found in the steady-state analysis. The proposed strategy was capable of correctly identifying whether the system was faulted in every performed simulation. [ABSTRACT FROM AUTHOR]

This paper presents a methodology to perform application tests in protective relays. It is based on using the Gabriel graph to select, from a large number of events generated by a Monte Carlo-based procedure, a smaller subset that is able to predict the relay performance without compromising the quality of the estimator. The proposed methodology is successfully applied to test the behavior of differential protective relays in two situations: turn-to-ground faults and transformer energizations. In both cases, the proposed methodology significantly reduces the number of tests required to predict the success rate of the tested relays for a desired confidence level and variance. It is observed that the efficiency of the method increases as the estimated success rate of the relay increases. This means that if the estimated success rate is high, the proposed methodology leads to larger reduction in the number of events that are actually necessary to test the relay. The validity of the proposed methodology is demonstrated by means of tests performed with an actual protective relay. [ABSTRACT FROM AUTHOR]

The traditional active power direction (APD) method has been proven to be unreliable to determine the dominant harmonic source at a point of common coupling (PCC), when both sides have the harmonic sources. In view of this shortcoming, this paper proposes an improved APD by imposing certain constraints to the traditional one. The constraints are developed based on the voltage and current measurements at the PCC and the impedance properties of the two sides. Through rigorous mathematical analysis, it has been proven that when those constraints are satisfied, the improved APD method is guaranteed to provide accurate results. Performance and effectiveness of the proposed method are demonstrated through simulation and field case verifications. [ABSTRACT FROM AUTHOR]

The axial magnetic field (AMF)-type contact is utilized in vacuum interrupters (VIs) due to its effectiveness in current interruption. This paper deals with the study of the eddy current phenomenon occurring in the AMF VIs. The residual AMF beyond current zero is directly the result of eddy currents in the contact plate and, thus, is dependent on the contact plate geometry. Considering that the contact plate is analogous to a disk winding, an analytical formulation is developed to compute the eddy current decay constant as a function of contact plate parameters. The analytical predictions are verified using finite-element method (FEM) simulations of the step response of a circular plate placed in a uniform magnetic field. A linear relationship is established between the contact plate parameters and the eddy current decay constant. The analytical formulation is then used to predict the residual flux decay constant in the context of AMF contact model simulations. A coil-type AMF contact is analyzed using FEM simulations, and parametric studies are carried out to study the effect of the contact opening velocity and radial slots on distribution of the contact gap AMF. The results reported in this work will enable VI engineers to improve the contact design by better control of contact plate parameters. [ABSTRACT FROM AUTHOR]

This paper presents a time-domain protection solution based on integrated quantities. In order to provide a deterministic differential protection method, two algorithms that use voltage and current samples to estimate energy flow and reactive power entering a protection zone are used. The algorithms work by integrating time-domain measurements and generated signals in order to achieve stable quantities that are afterwards used for protection. After the description of the differential fault identification method, a phase selection scheme is presented in order to provide a complete protection solution. The proposed system was extensively tested on simulations based on data from five actual transmission lines, the power systems were simulated using ATP/EMTP and the protection was implemented using GNU Octave software. Thousands of cases were generated using automation scripts in order to validate the protection algorithms. The work also describes the conducted sensitivity test, which includes current transformer saturation, and unsynchronized measurements. The proposed solution proved itself secure and dependable under the tested conditions. [ABSTRACT FROM AUTHOR]

Lightning electromagnetic fields can couple to overhead power transmission and distribution lines, causing serious effects to the power system. Lightning electromagnetic fields that couple to overhead lines have a nonuniform distribution along the line conductors. Therefore, to ensure the accuracy of the numerical calculation results, a large number of discretization points are needed along the line, which might dramatically increase the computation time since the evaluation of lightning electromagnetic fields in the presence of a lossy soil involves, in general,Sommerfeldintegrals, or, even in the case of a perfectly conducting ground, numerical integration along the channel. This paper proposes a new approach to address this problem. The proposed approach is based on the Agrawalet al. coupling model, in which the horizontal lightning electric field along the line is represented by the complex exponential functions in the frequency domain using the matrix pencil method. The method is highly efficient in terms of computation time since the lightning-induced response of the line can be solved semi-analytically. The proposed approach is validated by two different validation examples. [ABSTRACT FROM AUTHOR]

Unstable subsynchronous control interaction (SSCI) between wind farms (WFs) and series-compensated grid has posed a big threat to the safety of equipment and the stability of system. Many studies have been conducted on its analysis and control. However, very little research has been done on the protection. To fill the gap, this paper proposes a system-wide protection against unstable SSCI in wind power systems with fixed series compensations. The protection is composed of a centralized protection coordinator (CPC) and several distributed protection relays (DPRs). Local DPRs measure the subsynchronous impedances of WFs in real time. These impedances are next collected by the CPC to calculate the sensitivities of tripping for each WF. The sensitivities are then used to determine the candidate WFs and the number of WTGs to trip at those WFs, so as to stabilize the SSCI. The effectiveness of the proposed protection is verified with detailed electromagnetic simulations on a wind power system that had experienced actual SSCI incidents. [ABSTRACT FROM AUTHOR]

This paper aims to extract simple formulae for estimating the ground resistance values of wind turbines (WT) installed at terrains that can be modeled by a two-layer soil structure. Several grounding system configurations, applied in construction practice, were used as case studies. Various combinations of soil resistivity values for the upper and the lower layer of a two-layer soil model, as well as for the depth of the upper layer, are carefully selected in order to cover a wide range of nonuniformities in the ground. Thereafter, the ground resistance value is estimated from software simulations, for each combination among the examined two-layer models and the predefined ground electrodes geometry. Furthermore, regression analysis techniques are applied to create a model describing the behavior of the ground resistance and to fit the equations using data from the aforementioned simulations. The whole procedure has been algorithmized, so that the process is easily replicable. Finally, the model is verified and its accuracy is tested through applicable validation datasets. [ABSTRACT FROM AUTHOR]

Controlled switching technology operates circuit breakers at the minimum arcing time for short-circuit current interruption. However, there is no report to reveal a relationship between the short-circuit current interrupting capability with the minimum arcing time and the opening velocities of vacuum interrupters. The objective of this paper is to reveal a relationship between the short-circuit current interrupting capability with the minimum arcing time and the opening velocities of vacuum interrupters. A 40.5-kV fast vacuum circuit breaker prototype was built up which was equipped with a commercial 40.5 kV–31.5 kA vacuum interrupter and it was driven by an electromagnetic repulsion mechanism. It provided an average velocities ranging from 2.5 to 5.5 m/s. A total of 50 times of 40-kA short-circuit current interrupting tests were carried out in a synthetic circuit. Test results showed that the minimum arcing time of successful interruption decreased with the increasing of the average opening velocity. The minimum arcing gap was determined as 1.8 mm and it kept as a constant as the average opening velocity increased. The experimental results also showed a relationship between the arc energy density and the arc extinguishing gap, which acted a linear boundary between the successful and failure short-current interruptions. [ABSTRACT FROM AUTHOR]

This paper presents an effective finite-difference time-domain (FDTD) thin-wire model for lossy wire structures with noncircular cross section in transient analysis. Unique correction factors of field quantities and surface electric field of wire structures are introduced in the model. These parameters are both frequency-dependent and position-variant. They are evaluated in an initialization process and are applied in the updating process using an iterative convolution technique. The proposed method is validated with the transmission line theory analytically and the traditional FDTD method numerically. Three types of wire structures are tested, including rectangular, H-shape, and cross-shape structures. Good agreements are observed. It is found that the computation time is reduced to 1% of that with the conventional FDTD method, and the computer memory to 30% in the tested case. General guidelines on wire zone meshing are provided as well. Finally, this method is applied to analyze lightning surges in a light rail system under a direct lightning stroke. [ABSTRACT FROM AUTHOR]

On transmission lines where switching surges are not mitigated with closing resistors and/or surge arresters, high-speed reclosing on a line with trapped charge will produce high overvoltages that have been measured above 3 p.u. Careful simulations of these switching events using available electromagnetic transient (EMT) programs consistently produce significantly higher voltages than the measurements. This indicates a phenomenon present on the line that acts to reduce the switching surge magnitudes but is not typically modeled. This paper aims to identify the required simulation practices in reproducing the field measured overvoltages in EMT simulations and investigates the sensitivity of results to modeling approaches and electrical parameters. Field measurements from a switching surge test of a 230-kV line without surge mitigation have been used for model comparisons. Variations in frequency-dependent line modeling, ground resistivity, skin effect, shunt conductance, parallel lines, and source-side detail have been tested in an unsuccessful attempt to decrease the difference between the field measurements and the higher simulation overvoltages. It is demonstrated that even though the pattern of the transient voltage waveforms can be reproduced very well using frequency-dependent line models, the magnitude of the maximum overvoltage is significantly overestimated unless the effect of corona is considered. Two types of corona models are tested, and both demonstrate that corona is the primary factor that allows the simulations to correctly reproduce high peak overvoltage measurements. [ABSTRACT FROM AUTHOR]

A current sampled signal in a faulted transmission line can contain multiple dc components, namely a primary decaying dc component (DDC), a secondary DDC, an auxiliary DDC, and a bias DDC, and these may be due to a faulted line, current transformer, internal transformer, and analog-to-digital converter in the numerical relay, respectively. The intensity of the primary DDC is much higher than those of other DDCs. The elimination of the phasor-estimation error due to the primary DDC is the main issue in numerical relays, where the presence of other DDCs can deteriorate the phasor-estimation accuracy. This paper proposes a discrete Fourier transform (DFT)-based method using a second-order finite-impulse response (FIR) notch filter to combine multiple DDCs as a certain DDC through DFT. The FIR notch filter is designed to minimize the calculation complexity of the identification. Phasor-estimation errors that are due to the multiple DDCs are corrected by identifying the combined DDC. The proposed method can be applied for both full-cycle DFT (FCDFT) and half-cycle DFT. The feasibility of the proposed FCDFT-based method is compared with those of conventional FCDFT-based methods using simulations on DDCs, harmonics, noise, and a faulted transmission line. [ABSTRACT FROM AUTHOR]

Energization overvoltages are among the severest overvoltages stressing insulations of EHV power system components. Since these overvoltages have a statistical nature, the insulation level should be determined with the use of a statistical approach by which the distribution of overvoltages is calculated. Literature has properly studied the distribution of energization overvoltages in purely overhead line (OHL) or cable systems, but such a study is not available for hybrid systems consisting of both OHLs and cables. It is expected that the overvoltage distributions change substantially when both OHLs and cables are used in a transmission line. This paper tackles this issue by analyzing the overvoltage distributions due to the energization of a 380 kV hybrid OHL-cable circuit, in which the cable length is variable. The study includes various sensitivity analyses to find out the impact of system parameters and topology on overvoltages. By the statistical analysis, it has been discovered that energization overvoltages of a hybrid OHL–cable circuit are higher than those of a fully-cable circuit and very likely lower than those of a fully-OHL circuit with the same transmission lengths. [ABSTRACT FROM AUTHOR]

Harmonic loads and unbalanced loading in a distribution transformer lead to higher losses, an increase in temperature that leads to premature failure, and a shorter lifetime. To prevent these difficulties, the rated power of a transformer supplying nonlinear loads or unbalanced load is reduced; commonly known as derating. In this paper, an alternative to traditional loss based derating is proposed. It is shown that derating might actually not be required when contrasted with the traditional approach. A perspective is presented on how to make the kVA rating “adaptive” and utilize the same kVA rating with or without harmonics. Actual field data are presented to support this viewpoint. [ABSTRACT FROM AUTHOR]

It is commonly assumed that power swings are symmetrical phenomena that impose almost identical effects on the three-phase voltages and currents of the power system. However, there is another type of power swings which is asymmetrical and occurs mainly during single-pole tripping. In the nowadays heavily loaded power systems, the likelihood of occurrence of this phenomenon is increased considerably. Although the effects of symmetrical power swings on distance protection are widely analyzed in the literature, asymmetrical power swings have been less studied so far. This paper focuses on this type of power swings and their effects on distance protection. Besides, two new techniques are proposed to detect faults during asymmetrical power swings and enhance performance of power swing blocking schemes. The first technique is based on the rate of change of zero sequence current, while the second one is based on the magnitudes of voltage and current in each phase, as well as their relative phase angle. The presented analyses and proposed methods are validated using two benchmark test systems and promising results are obtained. [ABSTRACT FROM AUTHOR]

This paper presents a new passivity enforcement technique for frequency-dependent network equivalents expressed as rational models. The main feature of the proposed technique is that only a few residues of the rational model are perturbed, so that the passivity enforcement procedure becomes computationally more efficient compared to existing methods. The proposed technique is verified on practical network cases. It is demonstrated that the accuracy of the perturbed model is maintained in frequency-domain fitting and time-domain simulations of transients. [ABSTRACT FROM AUTHOR]

In this paper, a multihypothesis-based centralized Failure Diagnosis in Protection System (FDProSys) tool using phasor measurement units (PMU) data has been proposed to systematically and automatically detect malfunctions or failures in protective devices. The proposed diagnostic algorithm and FDProSys tool employs synchrophasor measurements to select a section of the network called ProNet, with possible device malfunction. Multiple hypotheses have been generated automatically based on node incidence matrices and multihypothesis theory. The malfunction of the protective devices in the presence of fault and relay operation is identified by comparing the five-digit message of the real event with multiple hypotheses. Trustworthiness of PMU data caused by common failures, such as communication outage and GPS problems, has also been considered by the proposed algorithm using the PMU status flag. The developed tool FDProSys can also work with supervisory control and data acquisition data assisted by manual analysis with less accuracy and is robust enough to several PMU/relay failures. Simulation results using the IEEE 14-bus, IEEE 57-bus, and IEEE 300-bus systems demonstrate the accuracy of the developed algorithm. [ABSTRACT FROM AUTHOR]

The paper presents a novel adaptive stator ground fault protection scheme with fault location capability for high-impedance grounded synchronous generators. The protection scheme uses already available neutral grounding signals in the existing subharmonic injection protection to obtain a Kalman adaptive filter (KAF) for real-time stator insulation parameter estimation. The KAF estimator yields a method of continuous tracking of stator insulation condition during healthy operations. This information is then used for real-time stator ground fault detection as well as fault location. The effectiveness of the proposed method is verified using extensive experiments performed on a lab-scale unit-connected generating station. [ABSTRACT FROM AUTHOR]

Installing lightning arresters is an effective way to protect distribution lines from lightning-induced voltages. Spacing effectiveness of lightning arresters is one of the main concerns in the industry. Different separation distances of arresters have been proposed in the literature. In these studies, the simulations are made with simplified circuit models, which are not sufficient to support their conclusions. This paper presents a hybrid finite-difference time-domain (FDTD) SPICE method for analyzing lightning-induced overvoltages on a distribution line with arresters being installed. The FDTD method gives a full-wave solution of the induced voltages. To handle nonlinear lightning arresters, this FDTD method is integrated with a circuit solver SPICE. A diode-based model for the arrester is proposed using a SPICE subcircuit and is coupled to the FDTD domain as a connecting port. For the verification purpose, the method is compared with the results obtained in the rocket-triggered lightning experiment, in which no arresters were installed. Lightning-induced overvoltages on the distribution line with different arrester spacing arrangements are analyzed finally. Efficient arrester spacing under both first and subsequent strokes is investigated. [ABSTRACT FROM AUTHOR]

Lightning-related outages are of great concern for power utility companies especially in the tropical regions. Tenaga Nasional Berhad as the system operator in Malaysia realized the importance of this issue. In this paper, statistical information on transmission line outages, together with lightning stroke data, are presented. Lightning data were obtained from TNB Lightning Detection Network which generates lightning density map and other information, such as peak current, polarity, and location of the detected strokes with 500-m location accuracy. A case study on the 500 kV A-to-B line represents statistical information of collected strokes where 18 kA and 14 kA were reported as median values of current peak for negative and positive strokes, respectively. Mean values are 22 kA for negative strokes and 17 kA for positive strokes. About 93% of 658 619 collected strokes from 2004 to 2015 are negative whereas the remaining are positive. A total of 582 (90%) negative strokes and 65 (10%) positive strokes were recorded along a selected case line where 83% of outages were reported to occur on the top phase. Lightning stroke density, terrain characteristics, tower footing resistance, and monsoon activities were highlighted as contributing factors on line performance due to lightning in this study. [ABSTRACT FROM AUTHOR]

The conventional transverse differential protection has some drawbacks, such as low sensitivity, long successive operation zone, and being significantly influenced by operation mode when applied in high-voltage and asymmetric power systems. To overcome these drawbacks, an innovative integrated transverse differential protection scheme is proposed in this paper. This scheme includes three parts: faulty phase selection, faulty line selection, and tripping and reclosing strategy. The phase-selection criterion regards the two circuits as a whole and selects only the faulty phase. The criterion of line-selection distinguishes the faulty line with the faulty phase based on the transverse impedance ratio. Tripping and reclosing strategy decreases the number of operations of breakers and achieves quasi-three-phase operation as far as possible. Results of studies with PSCAD/EMTDC and on a dynamic physical model show that the proposed protection scheme can improve the accuracy of fault discrimination, decrease the successive operation zone, and maintain more transmission power after the fault. [ABSTRACT FROM AUTHOR]

Inductive coordination between power lines and pipelines has focused on the 60/50 Hz component in the past. Through field measurements and circuit-model based analysis, this research shows that harmonic currents in power lines can cause more significant voltage induction on pipelines. It is due to the relatively higher frequency and zero-sequence nature of some of the harmonic currents. In view of the findings, this paper presents two methods for assessing the severity of harmonic voltage induction. One is a circuit-model-based method and the other is a field measurement-based method. [ABSTRACT FROM AUTHOR]

This paper compares the application of the Weibull distribution and the Crow-AMSAA (C-A) model to the analysis of cable joint failures. The procedures on how to use the two models to analyze failure data and to predict the future number of failures have been described before the models are applied to a set of early failure data. The data, which include 16 failures and 1126 suspensions, were collected from a regional power-supply company in China. This paper proves that the Weibull distribution provides more reliable results in the analysis of early-failure data since it considers the time to failure of each event. Whilst the method is more straightforward and requires less information, applying the C-A model can yield confusing results if not handled carefully. When analyzing the events, using time as x-axis and using the cable joint population as an axis can complement each other. Separating those data into subsections and analyzing them independently can yield useful information. Recent failure data can better reflect the current state of cable joints. The results of this paper should help utility asset managers better analyze their past failure events. [ABSTRACT FROM PUBLISHER]

Some new methods, based on characterization of the dielectric response of transformer insulation in time and frequency domains, have been pointed out by CIGRE as suitable to assess moisture content in pressboard and paper. Measuring devices available today on the market are quite robust in field conditions; however there is a risk that undesired internal and external factors might influence the measurements. These influences can lead to mistaken interpretation of insulation wetness. Operators should therefore be aware of the risks appearing at different measuring conditions and of the precautions that can be taken to minimize their effects. This work presents a systematic investigation on the influence of some factors on the results of dielectric response measurements in field conditions. The errors that can be committed during the measurements if certain precautions are not taken, with different equipment connected in parallel, are evaluated. The influence of rain and electromagnetic disturbances are also analyzed proposing solutions to attenuate their effects. Finally, a discussion on the influence of temperature distribution follows. The work is concentrated on frequency response measurements, although some results from the use of polarization and depolarization current technique are also discussed. [ABSTRACT FROM AUTHOR]

A new wind turbine transformers protection method against high du/dt switching transients taking place during a wind turbine operation is described. High-frequency transients, characterized by a high rate of voltage rise (du/dt) and overvoltage at the wind turbine transformer high-voltage terminals may be a result of operations of the turbine switchgear typically comprising a vacuum circuit breaker. The protection concept described in this paper is a follow up of research activities on a transients suppressing method dedicated for distribution transformers. The principle of operation of the protective device proposed and parameters optimization procedures for windmill transformers are provided in this paper. The performance of the device was verified by means of Alternative Transients Program–Electromagnetic Transients Program simulations. The physical device was built and experimentally verified by full-scale functional tests reflecting a real wind turbine power network. [ABSTRACT FROM AUTHOR]

AC overvoltage emerges on dc buses of a magnetically controlled shunt reactor when a turn-to-turn fault occurs within the control winding (CtrW). Overvoltage protections are thus employed. However, this paper addresses a problem in the application of overvoltage protection against CtrW turn-to-turn faults where such a protective scheme may operate in an unacceptable time delay or even malfunction in some fault cases. It is shown that the ac overvoltage on dc buses during a turn-to-turn fault tends to be intermittent voltage spikes rather than standard sinusoidal waveform, and the fault feature may even not exist in some cases. The cause of the problem is investigated in this paper by dividing the operating state for the excitation system into three stages. It is proved that the appearance of overvoltage on dc buses is dependent on zero-crossing of the total control current. Simulation results and physical model tests have demonstrated the theoretical analysis in this paper. Moreover, a new protective scheme that is capable of detecting a 2% CtrW turn-to-turn fault by using the fundamental component in the total control current is proposed. [ABSTRACT FROM AUTHOR]