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Wind turbine generators in a windfarm are connected by underground cables. Lightning sometimes strikes a nacelle or a blade. Lightning overvoltages due to a direct lightning strike to the system cause damages in the underground cable. Many parameters should be investigated to establish a rational lightning protection design for wind power generation system. Numerical simulation is a useful method to discuss the influence of the parameters on the lightning overvoltages. This paper uses an Electro-Magnetic Transients Program for the lightning surge analysis. This paper discusses the influence of grounding method of metallic sheath of the cable and grounding resistance on the lightning overvoltages for the direct lightning strike to the generation system. [ABSTRACT FROM AUTHOR]

This paper contributes to the accurate and efficient computation of control system equations in electromagnetic-transient simulation tools. The proposed approach is based on the formulation of a reduced rank Jacobian matrix in a fully iterative Newton method. In addition, this paper compares the accuracy and efficiency for the proposed method's variants, including a hybrid approach with a fixed-point solution. [ABSTRACT FROM PUBLISHER]

The risk of unstable subsynchronous oscillations (SSO) in DFIG-based wind parks radially connected to transmission lines with series capacitive compensation is typically assessed with numerous electromagnetic transient (EMT) simulations, which is a time-consuming process. However, not all operating scenarios present risk of SSO and require such a detailed investigation. This paper proposes two charts based on impedance equivalents of wind generators obtained through frequency scans to quickly map which combinations of parameters can create unstable SSOs and which combinations are risk-free. With the information, engineers can immediately filter out scenarios with no risk of instability and conduct detailed studies on fewer scenarios that are truly critical. These charts can be obtained with simple equations that use only information readily available in practice to engineers, without the need to run any computer simulation. The charts also reveal the key operating conditions that can increase the risk of an unstable SSO and provide real-time quantitative insights into how close a wind park is to an instability. Application examples are provided to illustrate how this approach can help engineers speed up studies to identify the risk of SSO. [ABSTRACT FROM AUTHOR]

In this paper, a self-adaptive protection system is proposed for adjusting the time dial (TD) of reclosers found in electrical power distribution systems (EPDSs). The self-adjustment is carried out in both phase and ground protection. The methodology considers the fuses along the feeder to obtain the fuse-saving philosophy. This feature allows less interference on the protection system already implemented by the electrical power distribution utilities. This methodology also allows using other frameworks, such as the estimation of the fault distance. The software used for computer modeling and simulation was PSCAD™/EMTDC™. The flexibility provided by the method, which allows the incorporation of new logic and changes in decision-making, resulted in an adaptive method with a good performance against different locations, types, and fault impedance. It also resulted in better coordination between the protection devices (PDs). The results compared with well-coordinated conventional protection have shown significant performance gain with the adaptive system. [ABSTRACT FROM AUTHOR]

The tip size of metal protrusions is an important factor affecting corona discharge, since it influences the electric filed, the ionization range and strength around the protrusion defect. Most existing studies on the influence of protrusion tip size on corona discharge are implemented by experimental methods. However, these studies are difficult to obtain the microphysical process of charged particles, which is related to the generation of current pulses and electromagnetic (EM) waves. In this paper, a hydrodynamic simulation model is proposed to study the effect of protrusion tip size on the microphysical process and current pulses of negative corona discharge. A mapping relationship between microscopic behaviors of charged particles and current pulses is established by this simulation method. Based on the comparison of microphysical quantities, the effect of defect tip size on the detailed parameters of current pulses is clearly explained. It shows that with the increase of tip size under a constant voltage, all the five parameters of current pluses increase. The rising time is related to the effective ionization coefficient, while the falling time is dependent on the velocities of positive and negative ions. The experiment and simulation results coincide in current waveforms and all five parameters. [ABSTRACT FROM AUTHOR]

The paper presents the results of experimental registrations and numerical simulations of the transient overvoltages caused by single phase intermittent arc earth fault in 35 kV network with isolated neutral. Experimental laboratory investigation is performed in order to implement appropriate arc fault model for arcs with low and discontinuous current. Single phase to earth arc fault is created in field in 35 kV network. Numerical model of the system is created in EMTP-ATP software. Overvoltage waveshapes and overvoltage factors are calculated and compared to measured values. Good agreement between the measured and calculated results is achieved. [ABSTRACT FROM AUTHOR]

The method to identify the sources of the neutral-to- earth voltage (NEV) rise as presented in a companion paper is verified in this paper through extensive simulation studies and field measurements. Sensitivity studies are conducted to determine factors that affect the performance of the proposed method. The results show that the NEV contribution factor index is effective in identifying load unbalance caused NEV and its contributors. The current return ratio index is effective in diagnosing poor grounding caused NEV and its contributors. An NEV trouble shooting strategy and a system-wide NEV condition monitoring strategy are proposed based on the findings. [ABSTRACT FROM AUTHOR]

Modular multilevel converters (MMC) are presently the converter topology of choice for voltage-source converter high-voltage direct-current (VSC-HVDC) transmission schemes due to their very high efficiency. These converters are complex, yet fast and detailed electromagnetic transients simulation models are necessary for the research and development of these transmission schemes. Excellent work has been done in this area, though little objective comparison of the models proposed has yet been undertaken. This paper compares for the first time, the three leading techniques for producing detailed MMC VSC-HVDC models in terms of their accuracy and simulation speed for several typical simulation cases. In addition, an improved model is proposed which further improves the computational efficiency of one method. This paper concludes by presenting evidence-based recommendations for which detailed models are most suitable for which particular studies. [ABSTRACT FROM AUTHOR]

An effective computational tool for the simulation and design of voltage dividers has been realized. It takes advantage of a finite-element procedure for the accurate computation of the divider stray capacitances. These latter are then the input of a circuit solver procedure based on the modified node potential technique, which provides the divider frequency response. Furthermore, a test divider has been set up for the purpose of the tool validation. A very good agreement has been found between measured and computed results. This paper highlights that a correct representation of the resistors is necessary in the finite-element method (FEM) model, during the computation of the stray parameters. This issue has been clarified for the first time in this paper. In addition, a comparison between the FEM and boundary-element method has been carried out before the implementation of the numerical code, stating the superior effectiveness of FEM. The computational tool has been finally tested on a real voltage divider. Good results have been found in terms of computational accuracy. Limited discrepancies between measured and computed results have been found up to 10 kHz, with 5.7% for the scale factor and less than 24 mrad for the phase error. [ABSTRACT FROM PUBLISHER]

One of the impacts of harmonic resonances in wind parks is to overload wind park components. The process of identifying a problematic component may be time-consuming due to the number of scenarios and different components (capacitors, transformers, cables and generators) that must be analyzed. In this context, this paper develops a first-screening approach to narrow down the number of scenarios that must be studied in detail. It first identifies that the capacitor bank is the most critical component. Then, it uses the operating limits of the capacitor bank and the harmonic distortions measured at the wind park entrance to obtain a chart that maps the problematic operating conditions of the park. Detailed investigations are needed only if the wind park condition is in specific regions of the chart. The proposed chart is attractive for practical applications as it is obtained with a simple equation, without the need to run any computer simulation, and can be consulted with few information from the wind park that is readily available to engineers. [ABSTRACT FROM AUTHOR]

This paper proposes a fast dc short-circuit fault detection method for HVdc grids, which relies on the voltage across the dc fault-current-limiting reactor. In the proposed approach, primary detection uses only the single-terminal dc reactor voltage information and is shown to be able to identify the faulted line as well as the faulted pole within 1 ms. The backup detection is primarily required for high resistance faults and uses communication between the two sides of the line. Its speed is dependent on the travel time of signals between the two ends, but will operate, as shown in the paper, typically in 2 ms or less. The approach is justified using analytical calculations and exhaustively validated via electromagnetic transient simulation for pole-to-pole and pole-to-ground faults, different fault resistance, fault locations, and dc reactor values. The validation shows that the method is able to identify all genuine dc line faults, but is not prone to misoperation with ac line faults, different loading levels, and so on. [ABSTRACT FROM AUTHOR]

This paper presents an algorithm for fast, directional detection of phase-to-ground faults in isolated neutral distribution grids. The method reacts directionally and very fast to fault conditions (1–2 samples after fault inception, even without large di0/dt). Moreover, the method is able to detect low- and high-impedance faults (HIF), permanent or transient faults. The algorithm is independent of the sampling frequency, very robust to noise, and does not need calibration of the sensors. The direction detection method relies on the fault model identification, based on the zero-sequence grid capacitance estimate for isolated neutral grids. The estimate is obtained from the fault circuit differential equation, solved with the least-squares method, where appropriate numerical modifications have been introduced. The sign of the estimate provides the directional information, whereas the magnitude of the modified estimate indicates the fault. The directional principle is validated in simulation and the fault detection method is validated with real fault records from the RedNA project. The paper reworks the equations that define the nondetection zone, so that the method is comparable to the classical residual overcurrent and overvoltage functions, typically used to detect HIF. [ABSTRACT FROM AUTHOR]

This paper describes the establishment of a large-area outdoor experimental facility at the Dinorwig pumped-storage power station in North Wales for investigating the performance of practical grounding systems. The facility itself and arrangements of test electrodes and measurement equipment are described, providing a background for subsequent test methodologies. In addition, tests to determine the variation in the water and reservoir bed resistivities have been undertaken, resulting in a survey data set that better informs experimental work and simulations of vertical ground rod and grid electrodes. It is proposed that this facility may also be used to calibrate grounding meters and for validating computational modelling techniques. In a complementary paper, results of low-voltage dc, ac, and impulse tests of varying magnitudes are described, and experimental results are compared with computed values obtained from numerical models. [ABSTRACT FROM AUTHOR]

This paper presents the results of a comparative analysis among three methods for attributing responsibilities of voltage unbalance in the electrical network, namely, the IEC, three-phase power flow, and conforming and nonconforming currents methods. To do this, computational and experimental simulations are carried out based on employing a system comprised of a perfectly transposed transmission line and two loads that are not always balanced. The cases selected for this study also permit the identification of the main advantages and disadvantages of each method under evaluation. This work is characterized as a topic of great interest to the regulatory agencies responsible for establishing regulations, and for utilities and consumers. It is relevant because by using the methods investigated in this paper, the identification of the sources, which generates unbalance, the division of responsibilities, and the application of penalties due to limit transgression will be possible. [ABSTRACT FROM AUTHOR]

In this paper, a linearized small-signal model for a six-pulse HVDC system is presented. In this paper, the effects of on and off states resistances, forward voltage drop, and snubber circuits of the thyristors and filter circuits are taken into account. RL series circuits are used for modeling of the converter transformer and ac system. To validate the model developed in this paper, a comparison is made with the PSCADIEMTDC time-domain simulation program. [ABSTRACT FROM AUTHOR]

The capacitor energizing transient as a kind of typical disturbance is used in the studies of power quality, condition monitoring, and other fields, and all studies heavily rely on transient characteristics. However, most characteristics are established based on the three-phase capacitor synchronous energizing (SE), and the effect of asynchronous energizing (AE) is neglected, which may affect the relevant studies. In this paper, the main characterizations of the capacitor AE transient, such as the oscillation frequency, time constant, and transient magnitude are analyzed considering the operation modes of the system and capacitor neutral points. The effect of the three-phase circuit asymmetry on the characterizations is investigated. The downstream voltage magnification phenomena in not only positive-sequence circuit but also zero-sequence circuit caused by the capacitor AE are also revealed. The theoretical analysis, computer simulation and lab experiment results have verified the effectiveness of the characteristics. [ABSTRACT FROM AUTHOR]

Power transmission through power cables installed in ventilated tunnels is increasingly used worldwide and offers a complex thermal environment. Established correlations currently in use have been deduced from a nonfully developed turbulent flow and the effect of the proximity to a tunnel wall is not accounted for. This paper details the experimental and numerical investigations conducted on a mock-up of the heat transfer from a single cable in a fully developed turbulent airflow, with emphasis on the effect of the cable spacing from the tunnel wall. Nusselt numbers have been compared for different spacing and Reynolds numbers. The overall heat transfer is found to be meaningfully lower than in previous studies as only a third of the heat transfer is found, possible explanation of these differences are given in this paper. A threshold value is observed for the heat transfer while the cable rating depreciation is more gradual. The radiative heat exchange is found to be up to 30% of the total heat loss. An improved cooling law for the case of a single cable in tunnel taking into account the proximity of the wall has been developed from this study and confronted to the experimental and simulated data. [ABSTRACT FROM AUTHOR]

In this paper, a simplified method for channel capacity estimation has been derived based on the transmission-line theory under the condition of high-bandwidth utilization. This method decouples the channel capacity into several independent components which may help to investigate the effects of backbone and branch, respectively. Analysis of backbone effects with respect to the available bandwidth reveals the applicable condition for the simplified method. Single branch effects are investigated considering branch length together with the loads. Besides, coupling effects caused by branch interactions are studied in a statistical way. The simulation results show great consistencies by using the proposed method and the conventional one and reveal the way that branches affect the channel capacity in different power networks. [ABSTRACT FROM AUTHOR]

Power system loads are one of the crucial elements of modern power systems and, as such, must be properly modelled in stability studies. However, the static and dynamic characteristics of a load are commonly unknown, extremely nonlinear, and are usually time varying. Consequently, a measurement-based approach for determining the load characteristics would offer a significant advantage since it could update the parameters of load models directly from the available system measurements. For this purpose and in order to accurately determine load model parameters, a suitable parameter estimation method must be applied. The conventional approach to this problem favors the use of standard nonlinear estimators or artificial intelligence (AI)-based methods. In this paper, a new solution for determining the unknown load model parameters is proposed—an improved particle swarm optimization (IPSO) method. The proposed method is an AI-type technique similar to the commonly used genetic algorithms (GAs) and is shown to provide a promising alternative. This paper presents a performance comparison of IPSO and GA using computer simulations and measured data obtained from realistic laboratory experiments. [ABSTRACT FROM AUTHOR]

The aim of this paper is to present the first full-scale experimental validation of the very fast transient (VFT) wave damping capability of high-frequency resonators in gas-insulated switchgear (GIS). In this regard, the numerical eigenvalue analysis method implemented in COMSOL is used to design and tune the HF resonators. The accuracy of the numerically computed resonance frequencies using this method is validated against the alternative finite-difference time domain method implemented in CST Microwave Studio and against the experimental data from low-voltage measurements. The designed resonator was then implemented in the test setup of a realistic 550-kV GIS where it was subject to VFT waves resembling the disconnector switching operations. The damping mechanism is achieved by using a lossy cylinder in the resonator gap. It is shown that the presence of the lossy resonator results in damping of the VFT wave total energy by 27% even though its first peak is slightly enhanced. The damping efficiency in terms of the voltage amplitude at the resonance frequency is about 60%. [ABSTRACT FROM AUTHOR]

Black-box models are a valuable tool to simulate dynamic arc-network interactions, such as those that occur during fault current interruption in ac or HVDC circuit breakers. However, accurate determination of characteristic arc parameters from voltage and current measurements is very challenging. This paper aims to improve the accuracy in arc characterization. A new arbitrary current source is used to simplify arc parameter determination through a more complex current waveform, for example, a series of staircase-like increasing steps. With this, the stationary and transient arc characteristics can be measured independently from each other. Therefore, current steps are well suited to: 1) validate the choice of a specific black-box model and 2) determine the arc parameters of the chosen model with higher accuracy. In principle, the source is also well suited to fill a table of the arc voltage response U,\, \mathdot U at various current levels and slopes I,\, \mathdot I. Thus, it would be possible to characterize arcs independent of any black-box model, but it would not be well suited to compare different arcs. Therefore, this paper focuses on an improved black-box parameter determination and the experimental validation of the Schwarz model, with P and \tau being free functions of g. [ABSTRACT FROM PUBLISHER]

This paper presents a new adaptive approach to improve the performance of the power transformer differential relay. The proposed approach distinguishes internal faults and disturbances based on the differential current trajectory and adopted weighting factors depending on the differential current locus in the relay characteristic. The traditional dual-slope differential characteristic is divided into three operating regions with the corresponding weighting factors. Two other control regions, that is, inrush and current-transformer (CT) saturation detection regions are utilized to avoid maloperation of the proposed relay in the case of inrush and CT saturation conditions. Meanwhile, a combination of phase differential units is introduced as a new technique to decrease relay operation time. The proposed relay rapidly detects all studied internal faults, while it is stable during transformer energization and CT saturation due to external faults. A real 230/63-kV power transformer is simulated using PSCAD/EMTDC for evaluating the performance of the proposed relay. Extensive simulation studies show that the proposed approach results in a faster and smarter differential protection scheme. [ABSTRACT FROM AUTHOR]

Based on a proposed analytical approach and time- domain simulation, this paper investigates the operating condition of single-phase transformers under steady-state and quasi-dc transient of the geomagnetically induced current (GIC). The analytical approach employs a two-slope piecewise linear magnetization characteristic and facilitates the development of generic characteristics for system studies to reduce the risk of power system instability and blackout during geomagnetic disturbances (GMDs). In addition, such characteristics can be used to estimate the transformer GIC, reactive power, and harmonic currents in the absence of direct measurements. The results obtained from the proposed approach are compared with the laboratory GIC test results of 500-kV and 230-kV transformers. In addition, the estimated dynamic behavior of a 500-kV autotransformer during a GMD event is compared with the measurements obtained from Hydro One SCADA and GIC monitoring systems. The study results reveal that under steady-state conditions, the transformer reactive power increases with GIC with an initial slope equal to the transformer ac peak voltage which is equivalent to 2.0 on a per-unit basis. Depending on the transformer air-core inductance, the slope decreases at higher GIC levels. Unlike the steady-state conditions, the GIC behavior of the transformer during a GMD event is influenced by the core kneepoint and the transformer delta winding. [ABSTRACT FROM PUBLISHER]

In this paper, the results of an experimental study and finite-element method (FEM) of the impulse characteristics of simply built practical earthing systems consisting of 2, 3, and 4 rods are reported. These electrodes are installed at three outdoor test sites having nonuniform soil and different soil profiles to provide variation in the result analysis. The tests on these electrodes were intended to determine the nonlinear characteristics of earthing systems which can be seen from their voltage and current traces and reduction of their impulse resistance values. Two-rod electrodes in the highest soil resistivity profile showed the largest reductions in impulse resistance due to soil ionization compared with other earth electrodes. Computer simulations of all the nine earthing systems using the FEM are also conducted, which showed good agreement with the measured results. It was also found from FEM that threshold electric field Ec is dependent on the earthing systems configurations, soil profile, and impulse resistances. [ABSTRACT FROM AUTHOR]

This paper shows that there is great potential for saving money when reconfiguring distribution systems at an optimal frequency. Studies are conducted on hourly, daily, weekly, monthly, and seasonal reconfiguration plans, based on the 8760 hourly loads of a year. Switches that actively participate in the reconfiguration process are first identified. These sectionalizers are substituted by smart (remotely controlled) switches. According to the results, two economic indices: total savings and return on investment are used to determine the optimal switching frequency. Numerical simulations are conducted on three distribution systems including one with 119 buses that is commonly used as a benchmark for reconfiguration of large-scale distribution systems. The results reveal that there exist large potential gains on frequent switching reconfiguration. Therefore, detailed studies must be carried out to determine the benefits of the dynamic reconfiguration for particular distribution systems. [ABSTRACT FROM AUTHOR]

This paper proposes an effective scheme for real-time operation and protection of microgrids based on the distributed dynamic state estimation (DDSE) that is applied to a single renewable distributed energy resource (DER) or other components. First, the DDSE can be used for setting-less component protection that applies dynamic state estimation on a component under protection with real-time measurements and dynamic models of the component. Based on the results, the well-known chi-square test yields the confidence level that quantifies the goodness of fit of models to measurements, indicating the health status of the component. With this approach, renewable DERs in microgrids can be protected on an autonomous and adaptive basis. Meanwhile, the estimated state variables of each component are converted to phasor data with time tags, and then collected to the distributed energy resources management (DERMS) of microgrids. These aggregated phasor data that are once filtered by the DDSE are input to the static state estimation in the DERMS along with unfiltered data sent from conventional meters, relays, and digital fault recorders, ultimately generating real-time operating conditions of microgrids. This paper also provides numerical simulations for comparing the DDSE-based approach with the conventional centralized state estimation in terms of data accuracy and computational speeds. [ABSTRACT FROM AUTHOR]

Modular multilevel converters (MMCs) have become the converter topology of choice for voltage-source converter–high-voltage direct-current systems. Excellent work has previously been conducted to develop much needed average value models (AVM) for these complex converters; however, there a number of limitations as highlighted in this paper. This paper builds on the existing models, proposing numerous modifications and resulting in an enhanced MMC-AVM, which is significantly more accurate and which can be used for a wider range of studies, including DC faults. [ABSTRACT FROM PUBLISHER]

The reduced-scale model of HVDC transmission lines in the laboratory is widely used to investigate the ionized fields. This paper is aimed at analyzing impact factors of the ion-current density measurement system based on Wilson plates in the laboratory. Both experimental and numerical simulation methods are used to obtain the characteristics of the measurement system. The results show that measurement data can be calibrated with different Wilson plates, and suitable parameters are proposed in this paper to meet the requirement of measurements. The measurement system described in this paper can be used in other similar applications. [ABSTRACT FROM PUBLISHER]

In this paper, design formulas for the calculation of the leakage inductance of toroidal transformers are presented. The formulas are obtained from the analytical integration of the stored energy. The formulas are sufficiently simple and accurate to be introduced in the loop of a design program avoiding expensive finite element simulations. It is found that toroidal transformers naturally produce the minimum leakage inductance possible for medium-voltage power transformers. To limit the short-circuit currents in power and distribution systems, a larger than the minimum leakage inductance is often required. This paper presents two methodologies to increase the leakage inductance of toroidal distribution transformers: selectively enlarging the inter-winding spacing and inserting a piece of ferromagnetic material in the leakage flux region between the windings. Extensive validation with 2D and 3D finite element simulations is performed. Additionally, experimental verification of both formulas and numerical simulations was carried out comparing the calculations against measurements on prototypes. [ABSTRACT FROM AUTHOR]

This paper presents a new method for islanding detection of inverter-based distributed generation (DG). The main idea of this paper is to change the dc-link voltage considering the PCC voltage changes during islanding condition. A simple islanding detection scheme has been designed based on this idea. The proposed method has been studied under multiple-DG operation modes and the UL 1741 islanding tests. The simulations results, carried out by MATLAB/Simulink, show that the proposed method has a small nondetection zone. Also, this method is capable of detecting islanding accurately within the minimum standard time. [ABSTRACT FROM AUTHOR]

International Electrotechnical Commission (IEC) standard 61850 proposes the Ethernet-based communication networks for protection and automation within the power substation. Major manufacturers are currently developing products for the process bus in compliance with IEC 61850 part 9-2. For the successful implementation of the IEC 61850-9-2 process bus, it is important to analyze the performance of time-critical messages for the substation protection and control functions. This paper presents the performance evaluation of the IEC 61850-9-2 process bus for a typical 345 kV/230 kV substation by studying the time-critical sampled value messages delay and loss by using the OPNET simulation tool in the first part of this paper. In the second part, this paper presents a corrective measure to address the issues with the several sampled value messages lost and/or delayed by proposing the sampled value estimation algorithm for any digital substation relaying. Finally, the proposed sampled value estimation algorithm has been examined for various power system scenarios with the help of PSCAD/EMTDC and MATLAB simulation tools. [ABSTRACT FROM AUTHOR]

In this paper, an extension to the multiwinding BCTRAN model is proposed for the study of low-frequency saturating transients in single-phase transformers. The conventional experimentally obtained BCTRAN (winding leakage) susceptance matrix is retrofitted with a previously missing experimentally obtained nonlinear (core magnetizing) model. The assembled model gives accurate results for transients in all terminals. The model parameters can be acquired from information available in the nameplate plus terminal tests without the need of detailed transformer design or construction information. Only needed are standard no-load and impedance tests plus a newly introduced saturation test. Very simple formulas are proposed to compute the parameters. Illustrative examples on how the parameters are computed are given for three transformers rated 1.8, 5, and 75 kVA. For model validation, laboratory inrush currents tests are carried out and compared with simulations using the EMTP-RV. The results show that the simulations and experimental results match very closely giving great confidence in the model correctness and parameter estimation method. [ABSTRACT FROM AUTHOR]

Reliable models to predict the fast transient response of transformer windings are categorized into three groups: 1) white box; 2) black box; and 3) gray box models. Each group is applicable to solve a certain problem and includes its own advantages, hardly replacable by another group. The gray box methodology is a compromise between black and white box approaches which is investigated profoundly in this paper. A new method based on design geometry estimation is applied to accomplish transient simulation. The introduced procedure is probed on a noninterleaved double disk winding. Simulation and experimental results confirm that the gray box approach is applicable to both terminal and internal response estimation of a transformer when there is no knowledge of the transformer's internal specifications. The parameter identification of the model is performed by the particle swarm optimization algorithm. [ABSTRACT FROM AUTHOR]

This paper presents an analysis of multi infeed highvoltage dc (HVDC) interactions using small-signal analysis techniques. The modeling details that are necessary to adequately represent the dynamics of the HVDC converters and the ac network are investigated, and the models are validated against an Electromagnetic Transient Simulation program. The paper shows that ac network dynamics must be modeled in order to obtain meaningful results from the small-signal stability study. A small test system with two HVDC infeecls is then used to demonstrate the presence of interactions in that system. The case studies presented in this paper indicate that it is possible to have interactions between the HVDC terminals in an ac system. This paper recommends that a small-signal interaction study, which is similar to what is presented in this paper, should be performed to identify these interactions. [ABSTRACT FROM AUTHOR]

This paper presents an integrated model for recognizing power-quality disturbances (PQD) using a novel wavelet multiclass support vector machine (WMSVM). The so-called support vector machine (SVM) is an effective classification tool. It is deemed to process binary classification problems. This paper combined linear SVM and the disturbances-versus-normal approach to form the multiclass SVM which is capable of processing multiple classification problems. Various disturbance events were tested for WMSVM and the wavelet-based multilayer-perceptron neural network was used for comparison. A simplified network architecture and shortened processing time can be seen for WMSVM. [ABSTRACT FROM AUTHOR]

Temperature rise simulation deals with different physical domains describing heat generation and heat dissipation effects. Cigré working group A3.36 has conducted a study on temperature rise simulation of switchgear for distribution and transmission level. The working group built up new, manufacturer independent devices. Members of the working group simulated the temperature rise in advance to the tests, which were performed at laboratories of universities, as independent parties. In order to assess the simulation accuracy, the simulation results are compared to each other and to the measured results. This paper summarizes the main findings from the medium voltage device. The study has shown that when simulating the temperature rise on a completely new design, with reliable input values of contact resistances and emissivity coefficients, an accuracy of about 25% could be expected. Primary reason seems to be based on the complexity of simulating the heat dissipation mechanisms. To get a more accurate result, verification and validation is needed in order to adjust the parameters determining the heat dissipation. This study has also illustrated that it requires good knowledge (especially of the radiation) in order to adjust these parameters properly. [ABSTRACT FROM AUTHOR]

In this paper, we present a new computer model to simulate the impulse-type noise that appears in bursts on a high- voltage (HV) power line during transient and emergency situations. The computer model is designed for investigations of the effects of impulse noise on communication channels implemented over an HV power line. The simulation process relies on an authentic record of measured noise whose modified replicas we use to compose a train of short-time impulses evenly distributed in time. The recorded noise sequence is referred to as a kernel data sequence over which we apply digital-signal-processing (DSP) techniques to randomize its length and its amplitudes. Noise impulses produced by the simulator achieve and retain the sharp front ends and spectral properties of the original noise. A variable digital filter is implemented to examine the influences of impulse noise on communication channels. Performances of simulated noise have been compared with those of measured noise published in CIGRÉ, IEEE, and IEC documents. Comparisons demonstrate a good agreement between the characteristics of measured and simulated noise. [ABSTRACT FROM PUBLISHER]

The strength is an important concept in planning studies for voltage stability analysis of hybrid multi-infeed HVDC (HMIDC) systems, which include both VSC- and LCC- HVDC links. However, the accuracy of earlier strength indices is very limited because they are developed by the empirical reasoning rather than rigorous theoretical derivation. In this paper, a virtual single-infeed model of HMIDC systems is firstly established utilizing the reduced-order equivalent nodal assessment of the inverter bus current-voltage equations. While incorporating the inter-inverter interactions, the virtual model is a strict dual-bus equivalent of the original complicated multi-infeed model. This enables easier and simpler analysis to be implemented. Secondly, the virtual model is employed to propose the hybrid multi-infeed interactive effective short-circuit ratio (HMIESCR) strength index for HMIDC systems by the rigorous theoretical derivation. Compared to earlier indices, the HMIESCR can depict the voltage stability much more accurately. This is because the critical HMIESCR (CHMIESCR) indicative of the stability limit is explicitly and solely evaluated to 1.5 according to the PV sensitivity based stability criterion, while the critical values of earlier indices are ambiguous. Finally, case studies by extensive numerical simulations on the classical hybrid four-infeed HVDC system validate the HMIESCR along with good robustness. [ABSTRACT FROM AUTHOR]

Recently, one main trend in the development of high-power gas circuit breakers (GCBs) has been to review and reapply the current interruption principle of self-blast GCBs because GCBs need to be compact in size and interrupt high current with low driving energy. A simulation algorithm was designed to analyze arc gas flow during the current interruption in an self-blast GCB. One model of self-blast GCBs was chosen as the test subject in order to validate the results of the algorithm. This paper shows that the simulation algorithm calculated and visualized the entire arc quenching process, and nozzle ablation has been taken into account. Pressure rise in the cylinder presented a great difference between considering the arc radiation effect and not. Both arc temperatures have a range of 13 000–28 000 K, except near the current zero point. Based on the development of the algorithm, the other two results were proposed to clearly validate precision in calculation. One had the results calculated by varying the radius of the nozzle throat in the self-blast GCB and another calculated arc gas flow of a hybrid puffer GCB with piston compression. [ABSTRACT FROM AUTHOR]

In order to improve the performance of the conventional distance protection scheme under high-resistance fault, an adaptive distance protection scheme is proposed in this paper. First, according to the geometric distribution characteristics of voltage and current in the system, the equation of voltage drop from the relaying point to the fault point is established. Second, the fault point is determined by the measured current and the measured negative-sequence current. And then, the new adaptive distance protection criterion is formed according to the relationship between the fault point and the protection zone. Simulation tests on the Real Time Digital Simulator verify that the proposed scheme is able to modify the protection setting value adaptively online, and is immune to the impact of transition resistance and load current. Besides, it has the potential to be applied in a real power system because of small computation amount and high accuracy. [ABSTRACT FROM AUTHOR]

The surface potential gradient is a critical design parameter for planning overhead lines since it determines the level of corona loss, radio interference, and audible noise. The majority of existing surface gradient calculations are based on analytical methods which restrict their application in simulating complex surface geometry. This paper proposes a novel method which utilizes both analytical and numerical procedures to predict the surface gradient. With this method, stranding shape, protrusions, the proximity of tower, the type of tower, bundle spacing, and bundle arrangement can be taken into consideration when calculating surface potential gradients. A sensitivity study on the factors affecting surface gradient distribution is performed. [ABSTRACT FROM PUBLISHER]

This paper proposes a graph-based matrix level partitioning methodology for parallel electromagnetic transient (EMT) simulation. By partitioning the graph associated with the admittance matrix, an efficient bordered block diagonal matrix form is obtained, which is particularly suitable for parallel implementation. Even without the presence of distributed transmission lines, fully automatic system partitioning and parallelization of the simulation are achieved. The parallelized algorithm is implemented on a shared memory computer and assessed using two scalable test cases. The first involves an underground cable with many distributed parameter cascaded sections. The second is an interconnection of multiple instances of the IEEE 14-bus system, where only lumped transmission-line models are used. The tests show that EMT simulation can be significantly accelerated. The scalability is tested with up to 64 cores. [ABSTRACT FROM PUBLISHER]

This paper investigates the temperature rise of vertical/horizontal high-voltage direct current (HVdc) grounding electrodes by simulations and field tests. Based on a field-circuit coupling current distribution model and a three dimensional (3-D) finite element model, a comprehensive methodology is proposed to analyze the transient temperature rise. Since soil resistivity varies with temperature around the electrodes, the temperature-dependent soil resistivity is tested, and then approximated by an empirical formula. Moreover, two practical tests are implemented to validate the simulation model. By ignoring the underground water fluctuations, the calculation results match test results nicely, which demonstrates that the terminal effect of the vertical electrode significantly affects the temperature distribution. But for a horizontal grounding electrode, the current distribution is more uniform than the vertical one. This study provides valuable references for design of HVdc grounding electrodes. [ABSTRACT FROM PUBLISHER]

High values and uneven distribution of the transient ground potential rise (TGPR) at grounding grid conductors in cases of lightning can disrupt the system safety and reliability. To assess the transient performance of grounding grids under lightning currents, a parametric analysis was performed with a computer simulation of 13,978 cases of time-domain responses with a broad range of parameters. From this study, graphs of impulse impedance and a new formula for the effective area have been developed. The graphs are general, describe grids of any shape and size and depend on three parameters: grid conductor spacing, the resistivity of earth, and the zero-to-peak time of the lightning current pulse. Although the parametric analysis was based on a uniform soil model, the graphs can also be used for the two-layer soil model. In this paper, graphs and formula are used in a simple procedure to estimate the effectiveness of a mitigation measure to reduce the TGPR by increasing the grounding grid mesh density in a limited area around the current injection points. The results from the procedure are compared with experimental results, and the application and limitations of the procedure are illustrated by considering large grounding grids as examples. [ABSTRACT FROM AUTHOR]

This paper revisits the generalized alpha plane (GAP) formulation applied to differential protection of multi-terminal apparatus. The GAP formulation is improved by aiming for three main goals: 1) control over the internal fault settlement region (FSR); 2) enabling a simple operation characteristic instead of a restraint characteristic; and, 3) The adjustments are not dependent to the device type. For this purpose, the GAP formulation is redefined in terms of two settings, which transform the FSR into a circumference with a controllable center and radius. Thereby, a circular operation characteristic with an adjustable radius is enabled around the FSR, for to improve security. To validate and test the performance of the improved GAP, numerous computer simulations have been carried out using Alternative Transients Program on different multi-terminal equipment (i.e., busbars, transmission lines, and power transformers). Furthermore, massive data analysis is held as a means to highlight the GAP's sensibility. The obtained results demonstrate a well-stable pre-fault point, a consistent circular FSR, and the effectiveness of the improved GAP even under severe conditions. [ABSTRACT FROM AUTHOR]

This paper proposes a cooperative multihop amplify-and-forward (AF) relay protocol for a medium-voltage (MV) power-line access network. The relay transmission scheme is a promising protocol since it provides enhanced network channel capacity which exploits cooperative diversity by combining the relayed signal and the direct signal. We propose a new signaling model for the cooperative multihop AF relay protocol and derive a closed-form expression of the channel capacity. The channel capacity of the proposed protocol is analyzed over the MV power-line channel and noise models. Numerical simulations show that the proposed protocol introduces a notable capacity increase compared to conventional multihop schemes. [ABSTRACT FROM PUBLISHER]

This paper presents modeling guidelines and a benchmark system for power system simulation studies of grid-connected, three-phase, single-stage Photovoltaic (PV) systems that employ a voltage-sourced converter (VSC) as the power processor. The objective of this work is to introduce the main components, operation/protection modes, and control layers/schemes of medium- and high-power PV systems, to assist power engineers in developing circuit-based simulation models for impact assessment studies, analysis, and identification of potential issues with respect to the grid integration of PV systems. Parameter selection, control tuning, and design guidelines are also briefly discussed. The usefulness of the benchmark system is demonstrated through a fairly comprehensive set of test cases, conducted in the PSCAD/EMTDC software environment. However, the models and techniques presented in this paper are independent of any specific circuit simulation software package. Also, they may not fully conform to the methods exercised by all manufacturers, due to the proprietary nature of the industry. [ABSTRACT FROM AUTHOR]

This paper presents a generalized, parallel implementation methodology for real-time simulation of ac machine transients in an FPGA-based real-time simulator. The proposed method adopts nanosecond range simulation time-step and exploits the large response time of a rotating machine to: 1) eliminate the need for predictive-corrective action for the machine electrical and mechanical variables, 2) decouple the solution of the dq0 stator currents, and 3) enable the use of one-time-step delayed interface between the machine and the rest of the system which decouples the machine solution from that of the rest of the system. The proposed method simplifies the solution of the machine model without compromising accuracy or numerical stability of the simulation. This paper also presents a massively parallel, customized hardware architecture tailored to the solution of the mathematical model of ac machines. The proposed method and the developed hardware architecture are tested and verified based on the implementation of a permanent-magnet synchronous machine model and an induction machine-based ac-drive system in a field-programmable gate-array-based simulator. Real-time simulation is achieved with a computation time of 44 ns within the simulation timestep. [ABSTRACT FROM AUTHOR]

This paper analytically determines the nondetection zone (NDZ) of an active islanding detection method, and proposes a solution to obviate the NDZ. The method actively injects a negative-sequence current through the interface voltage-sourced converter (VSC) of a distributed generation (DG) unit, as a disturbance signal for islanding detection. The estimated magnitude of the corresponding negative-sequence voltage at the PCC is used as the islanding detection signal. In this paper, based on a laboratory test system, the performance of the islanding detection method under UL1741 anti-islanding test conditions is evaluated. Then, determining the NDZ of the method and proposing the countermeasure, the existence of the NDZ and the performance of the modified method to eliminate the NDZ is verified based on simulation results in PSCAD/EMTDC software environment and experimental tests. [ABSTRACT FROM AUTHOR]

The electromagnetic transient programs (EMTP-like tools) are based on the nodal (or modified nodal) equations that enable an efficient numerical solution and, subsequently, fast time-domain simulations. The state-variable-based simulation programs, such as Simulink, are also used for studying the dynamics of electrical systems. Both the offline and real-time versions of these two types of simulation tools are widely used by the researchers and engineers in industry and academia to study the transient phenomena and dynamics in power systems with rotating electrical machines. This paper provides a summary of the interfacing techniques that are utilized to integrate the general-purpose models of electrical machines with the rest of the power system network for these studies. The interfacing methods are broadly classified as indirect and direct approaches. The paper also describes the numerical properties as well as limitations imposed by the interfacing of the commonly used machine models that should be considered when selecting the simulation parameters and assessing the final results. [ABSTRACT FROM AUTHOR]