Search

This article presents the measurement verification of a novel strategy for inrush current reduction in an unloaded three-phase Dy transformer. The strategy combines appropriate pre-magnetization of transformer cores with an original control switching system using initial phase values of the supply voltage as control variables. Measurements were recorded for primary voltages and currents as well as secondary voltages during transient states at start-up under no-load conditions. Various inrush scenarios were examined across the full angular spectrum of initial phase angles, both polarities, and in regard to different pre-magnetization current values. A detailed analysis of the inrush currents was performed using proprietary automated software based on the recorded data. A comparative study with a nonlinear mathematical model of the transformer was also conducted. Additionally, key technical aspects of the designed system for implementing the proposed pre-magnetization strategy with controlled voltage energization are discussed. [ABSTRACT FROM AUTHOR]

In this paper, a numerical model for the analysis of electromagnetic transients in a power system, based on the finite element technique, was developed. The simplicity of the finite element technique is manifested in the fact that the problem of solving any mathematically described phenomena in an area is reduced to solving those same phenomena in a small part of that area, i.e., finite elements. Based on appropriate mathematical models, numerical models of the synchronous generator and other parts of the power system have been developed. System of differential equations of each power system element have been included in the numerical model in such a way that we employ numerical integration of the differential equations using the generalized trapezoidal rule (ϑ -method) and reduce it to a system of algebraic equations in each time step. In a practical sense, this method enables a very simple solution to the problem of a real power system, i.e., a system with many generators, transformers, transmission lines and other elements. The accuracy of the developed numerical model for the analysis of electromagnetic transients in a power system has been confirmed by comparing the calculated results with the results obtained using the EMTP software (version 3.3) package. [ABSTRACT FROM AUTHOR]

This article presents the results of an experimental verification of three-phase Dy transformer dynamics under no-load conditions. This study is motivated by previous ferroresonance analyses where the occurrence of inrush currents has been observed. The measurements covered all available electrical quantities in a transient state (12 measured and 3 additionally computed waveforms) during the device's start-up under no-load conditions, as well as in a long-term steady state. A detailed analytical analysis is carried out for the obtained comprehensive set of measurement results. As a result of the conducted research, the mathematical model of the pre-magnetized three-phase Dy transformer is modified. Particular attention is paid to the issue of residual magnetism of the transformer core and its consideration in further research. The original strategy for energizing a three-column three-phase Dy transformer with a suitable pre-magnetization of its columns and original control switching system with a given/set value of the initial phase in the supply voltage is put to the test. The evolution of the induced inrush phenomenon up to the quasi-steady state under given (forced) conditions is documented (currents, voltages and the dynamics of changes taking place in the core (hysteresis loops)). This article represents a continuation of ongoing work on the study of transient states (dynamics of transformer inrush currents). At present, the Dy three-phase transformer is analyzed because of the requirements of industrial operators. [ABSTRACT FROM AUTHOR]

The significant increase of converter interfaced generation, consumption, storage, and transmission in power systems, results in the need to consider converter-driven stability in detail, as well as to study modelling and analysis methods with which such stability effects can be represented and investigated. Due to the multiple causes of converter-driven stability effects, a classification into further categories of fast and slow converter-driven stability is necessary, which is systematically presented in this paper. We further provide a detailed overview on appropriate modelling methods including static, quasi-dynamic and dynamic modelling and their respective applications. Typical analysis methods such as eigenvalue and impedance based analysis are explained and related to the previous modelling approaches. Based on that, a guide to which modelling and analysis method is appropriate for which type of converter-driven stability, is provided. In addition, open and recent research questions with regard to studies on nonlinear analyses of large systems with acceptable computational costs are pointed out.

This article presents the measurement verification of a novel strategy for inrush current reduction in an unloaded three-phase Dy transformer. The strategy combines appropriate pre-magnetization of transformer cores with an original control switching system using initial phase values of the supply voltage as control variables. Measurements were recorded for primary voltages and currents as well as secondary voltages during transient states at start-up under no-load conditions. Various inrush scenarios were examined across the full angular spectrum of initial phase angles, both polarities, and in regard to different pre-magnetization current values. A detailed analysis of the inrush currents was performed using proprietary automated software based on the recorded data. A comparative study with a nonlinear mathematical model of the transformer was also conducted. Additionally, key technical aspects of the designed system for implementing the proposed pre-magnetization strategy with controlled voltage energization are discussed.

This paper presents a novel three-phase transmission line model for electromagnetic transient simulations that are executed directly within the time domain. This model relies on distributed and frequency-dependent parameters, as well as employs modal transformation for its implementation. The single-phase model of the exact equivalent π -circuit is utilized for each propagation mode. This model combines discrete components, such as resistors, inductors, and capacitors, to accurately emulate the transmission line behavior via linear circuit elements. This model can be seamlessly integrated into various electrical circuit simulation software, thus allowing easy utilization and incorporating time-varying elements to analyze transmission lines. The JMarti model, which comes by default in the Alternative Transient Program, and the numerical Laplace transform method implemented in MATLAB were utilized to validate the proposed solution across various scenarios. An advantage of this model is its independence from the prior calculation of travel time and its exemption from convolutions, inverse Laplace transforms, and Fourier transforms, thus streamlining the simulation process. [ABSTRACT FROM AUTHOR]

In this work, a procedure to obtain two-port admittance models of buried cables illuminated by incident electromagnetic fields for the analysis of transients in the frequency domain is presented. The procedure is based on cascading two-port admittance models of various cable segments, avoiding the numerical problems that chain matrix representations may have. To obtain results in the time domain, the Numerical Laplace Transform method is used. [ABSTRACT FROM AUTHOR]

The paper considers transients in an autonomous power system consisting of a generator, a transformer, and a general load. The numerical method for simulating transients includes the possibility of the asymmetry of stator windings and magnetic core saturation of a generator and a transformer. The asymmetry is usually observed under synchronous machine faults such as turn-to-turn short circuits in the stator winding. The method is based on the solution of differential equations for the equilibrium of electromotive force and voltage drops in windings in phase coordinates in combination with the rotor rotation equation. In this case, a circuit of each phase stator winding is described by an equation that considers the difference in phase parameters. The mathematical model is developed in MATLAB. The model includes an unequal number of turns in phase windings that allows simulating the turn-to-turn short circuits without considering the occurrence of additional short-circuited circuits. The analysis of simulation results was performed under no-load operating conditions and in the presence of load. The obtained results demonstrated the influence of the saturation of magnetic systems on the parameters of normal and abnormal operating conditions in the power system.

In this paper, a numerical model for the analysis of electromagnetic transients in a power system, based on the finite element technique, was developed. The simplicity of the finite element technique is manifested in the fact that the problem of solving any mathematically described phenomena in an area is reduced to solving those same phenomena in a small part of that area, i.e., finite elements. Based on appropriate mathematical models, numerical models of the synchronous generator and other parts of the power system have been developed. System of differential equations of each power system element have been included in the numerical model in such a way that we employ numerical integration of the differential equations using the generalized trapezoidal rule (ϑ-method) and reduce it to a system of algebraic equations in each time step. In a practical sense, this method enables a very simple solution to the problem of a real power system, i.e., a system with many generators, transformers, transmission lines and other elements. The accuracy of the developed numerical model for the analysis of electromagnetic transients in a power system has been confirmed by comparing the calculated results with the results obtained using the EMTP software (version 3.3) package.

This article presents the results of an experimental verification of three-phase Dy transformer dynamics under no-load conditions. This study is motivated by previous ferroresonance analyses where the occurrence of inrush currents has been observed. The measurements covered all available electrical quantities in a transient state (12 measured and 3 additionally computed waveforms) during the device’s start-up under no-load conditions, as well as in a long-term steady state. A detailed analytical analysis is carried out for the obtained comprehensive set of measurement results. As a result of the conducted research, the mathematical model of the pre-magnetized three-phase Dy transformer is modified. Particular attention is paid to the issue of residual magnetism of the transformer core and its consideration in further research. The original strategy for energizing a three-column three-phase Dy transformer with a suitable pre-magnetization of its columns and original control switching system with a given/set value of the initial phase in the supply voltage is put to the test. The evolution of the induced inrush phenomenon up to the quasi-steady state under given (forced) conditions is documented (currents, voltages and the dynamics of changes taking place in the core (hysteresis loops)). This article represents a continuation of ongoing work on the study of transient states (dynamics of transformer inrush currents). At present, the Dy three-phase transformer is analyzed because of the requirements of industrial operators.

The deployment of Li-ion batteries has been increasing extensively due to recent technological/economic breakthroughs and their high suitability to a range of applications. In this context, this paper (i) develops a simulation algorithm programmed in MATLAB® with a graphical user interface designed in Excel® to assess the transient responses in multiple Li-ion battery technologies and (ii) performs a comparative assessment of the transient responses to verify if there are significant differences. The simulation interface is required since the battery parameters are dependent on the state of charge; hence, conventional electromagnetic transients programs (e.g., ATPDraw®) cannot be directly applied to perform the simulations. Results demonstrate that the differences in the transient responses (terminal voltage) are considerable, particularly when applying robust input currents to the batteries (e.g., decreasing square wave and dynamic stress test). Among analyzed technologies, the Panasonic NCR18650B Li-ion battery showcased the most volatile transients. Hence, the results contradict the common sense that transients in Li-ion batteries are equivalent. The simulation interface is made available to foster further research on the topic. [ABSTRACT FROM AUTHOR]

The Kopernikus ENSURE Co-Demonstration Platform enables the investigation of components and processes for the changing power system with grid models adapted to the respective problem. The platform is developed from the power system's perspective. A central aspect of the platform is to analyze several technical solutions of different stakeholders in shared power system models. Furthermore the platform enables the investigation of interactions between different technologies, the system stability or protection scenarios that cannot be simulated in the real power system or only to a very limited extent. The comparison of solution approaches on a common model basis enables reliable overall systemic statements. To realize this, a multi-domain and multi-vendor approach is pursued, covering electromagnetic transients, electromechanical transients, continuous power flow simulations, and real-time simulators from different manufacturers. The core components of the platform are distributed real-time simulations, including the coupling of different laboratories in Germany and the developed power system models. Investigations with the real-time capable platform can be carried out purely simulatively or, depending on the connected laboratory, as Control/Power-Hardware-in-the-Loop simulations.

Enhanced environmental standards are leading to an increasing proportion of microgrids (MGs) being integrated with renewable energy resources in modern power systems, which brings new challenges to simulate such a complex system. In this work, comprehensive modeling of a grid of microgrids for faster-than-real-time (FTRT) emulation is proposed, which can be utilized in the energy control center for contingencies analysis and dynamic security assessment. Electromagnetic transient (EMT) modeling is applied to the microgrid in order to reflect the detailed device processes of the converter and renewable energy sources, while the AC grid utilizes the transient stability modeling to reduce the computational burden and obtain a high acceleration value over real-time execution. Consequently, a dynamic power injection interface is proposed for the coexistence of the two simulation types. The reconfigurability and parallelism of the field-programmable gate arrays (FPGAs) enable the whole system to be executed in FTRT mode with 51 times acceleration over real-time. Meanwhile, three case studies are emulated and the results are validated by the off-line simulation tool Matlab/Simulink®.

Abstract The theory of multiconductor transmission lines is based on the principle of superposition. According to this principle, any electric or magnetic field can be represented as the sum of individual electric or magnetic fields. This theory is used to analyze and design electrical systems involving multiple conductors. In this work, the procedures for analyzing electromagnetic transients in 3-conductor transmission lines are presented, which is the last step for generalization in the case of lines to “n” conductors. The paper presents elementary cases and a more general one to illustrate such an approach.

With the rapid development of new energy technology, the number of grid-connected systems and switching control frequency are also increasing. It makes the operation state of the power grid more complicated. Therefore, a small step real-time model is urgently needed to monitor the operation of power grid. Based on the existing computing hardware, FPGA has the characteristics of high concurrency and multi-pipeline computing, which ensures the real-time performance of the simulator. Because non-isolated bidirectional half-bridge DC–DC converter is widely used in power grid system, the real-time simulation design based on FPGA is carried out in this paper. This paper proposes an improved Associated Discrete Circuit (ADC) method and derives the formula of the optimal conductivity parameters. By using the transient initialization method, the accuracy of the ADC modeling method is promoted. The simulation model of the non-isolated bidirectional half-bridge converter is built on FPGA with a time-step of 1μs. Under the premise of real-time performance, the relative error of the proposed simulation module is controlled at about 3%.

Grounding electrodes play a fundamental role in the operation of power systems. In this context, precise computation of grounding impedance must consider the frequency-dependence of the soil parameters and the ground organized in stratified layers of soil. This paper proposes an ABCD matrix approach to compute the harmonic grounding impedance of rods buried in frequency-dependent stratified soils directly in the frequency domain. This technique is based on the traditional ABCD matrix used for overhead multi-phase transmission lines extended to grounding systems. In this approach, each rod segment is modeled as a short transmission line where the equivalent harmonic grounding impedance is calculated. Then, the Ground Potential Rise (GPR) waveforms are computed by lightning currents injected into the rods buried in different scenarios. Results indicated that the ABCD matrix approach has shown a good agreement with those obtained using a full-wave electromagnetic software FEKO. The frequency-dependence of the soil electrical parameters causes a significant modification in the harmonic impedance of grounding rods which reduces the GPR peaks considerably, being this reduction more pronounced in homogeneous and 2-layer soils. The proposed technique is an attractive tool since that considers the frequency dependence on each layer of soil, with a low computational cost and good accuracy from 100 Hz up to 1 MHz.

Specific features of electromagnetic transient processes in electric machines place raised demands on the algorithm of digital processing of short-circuit current in a small time window. The fast bus transfer system needs a procedure for rapid determination of the orthogonal components of a short-circuit current. This problem is solved here by directed suppression of all significant components of the current, except for one of the two elementary components of the imaginary fundamental frequency, the second component being suppressed as well. It is shown that decaying components with unknown attenuation coefficient are better suppressed using two-stage stop filters. Such a filter of orthogonal components has multiple sections, shifts the frequency along the imaginary axis, suppresses non-zero frequency components, and smoothes the output signal. The suppression sections are modified depending on the complexity of the transient process. The smoothing window, which also additionally suppresses the harmonics that are not suppressed individually, is selected in a similar way. The multi-section filter was tested against three-phase and phase-to-phase short-circuit currents in a synchronous electric machine. [ABSTRACT FROM AUTHOR]

This work proposes a fully circuit-based method for modelling electrical transformers. This method not only offers the advantages of circuit-based methods and can be implemented in electromagnetic transient (EMT) type software, but it can also provide a detailed representation of transformers, comparable to the finite element method (FEM). The proposed method enables a detailed geometrical modelling, as well as representation of magnetic flux paths and consideration of iron core saturation. It can be implemented in EMT-type software to see the effect of power networks on transformers. In addition, the proposed method can represent internal faults in transformers. The problem is constrained to a 2-D domain, which is often used in FEMs to represent the magnetic behavior of power equipment. Finite element analysis based on ANSYS Maxwell is used to verify the proposed method. [ABSTRACT FROM AUTHOR]

The theory of multiconductor transmission lines is based on the principle of superposition. According to this principle, any electric or magnetic field can be represented as the sum of individual electric or magnetic fields. This theory is used to analyze and design electrical systems involving multiple conductors. In this work, the procedures for analyzing electromagnetic transients in 3-conductor transmission lines are presented, which is the last step for generalization in the case of lines to "n" conductors. The paper presents elementary cases and a more general one to illustrate such an approach. [ABSTRACT FROM AUTHOR]

This paper aims at assessing the relevance of the coupling effects among the main components of overhead power lines in their lightning response, namely, tower, grounding electrodes, and shield wire(s). Mutual coupling effects are investigated by simulation, using an electromagnetic model. The analyses are performed in the frequency and time domain, by considering, respectively, the input impedance at the node of current injection and the overvoltages rising at the same node. The study is conducted considering different configurations for current excitation and three arrangements of grounding electrodes, with the corresponding soil properties. From the analysis of the results, it appears that the effects of electromagnetic coupling among the considered system components affects only marginally the lightning response of the line, being much less relevant than the effects of the uncertainties on the values of electrical parameters of the local soil. This confirms the validity of the macromodeling approach and denotes that the accuracy of the results is overall dependent on the suitability of models adopted for each component; in particular, the proper representation of the grounding system is proven as essential to the successful prediction of overvoltages at the tower top. • Electromagnetic (EM) coupling among main components of overhead lines is studied. • A typical transmission line tower hit by a lightning current is considered. • EM interactions among tower, shield wire, and grounding system (GS) are limited. • Tower-to-shield wire EM coupling mainly influences the computed input impedances. • Macromodeling can be adopted, yet towers and GSs should be conveniently modeled. [ABSTRACT FROM AUTHOR]

• High-voltage circuit-breaker EMTP model uses multi-unit parametrization. • Voltage transients are simulated in between circuit-breaker making and breaking units (MBUs). • Non-simultaneity simulated for opening operation can result in multiple re-ignitions. • Case studies depict multiple prestrikes phenomenon inside multi-unit circuit-breakers. • Simulations underline some challenges for high-voltage vacuum circuit-breaker design. High-voltage (HV) circuit-breakers (CBs) often consist of several making and breaking units (MBUs) in series. A multi-unit circuit-breaker EMTP® model is proposed to analyse the effects of non-simultaneity between MBUs of the same pole. The model allows for simulations of high-frequency voltage and current transients during opening or closing operations. The simulations include the non-simultaneity of MBUs of the same pole or differences in dielectric withstand characteristics for vacuum circuit-breakers (VCBs) and SF 6 CBs. According to simulation results, the maximum non-simultaneity of MBUs of the same pole, as permitted per international standards, can lead to multiple re-ignitions during opening or excessive overvoltages during closing operations. These phenomena are rarely simulated with conventional CB models. The simulations also highlight the important challenges facing high-voltage VCB design due to the inherent characteristics of vacuum bottle technology. The proposed models serve as useful tools for understanding and studying the effect of multi-unit CBs in various system studies and advanced diagnostics. [ABSTRACT FROM AUTHOR]

This work examines two strategies for enhancing the rational approximation of Frequency-Dependent Network Equivalents (FDNE) using an 8-port FDNE featuring a frequency response marked by numerous peaks and valleys. Firstly, we employ Complex Vector Fitting (CVF), an alternative to the Vector Fitting (VF). CVF eliminates the constraint of complex conjugate pairs and was originally conceived for modeling baseband equivalents through scattering parameters. The implications of CVF for admittance (or impedance) matrix synthesis have not yet been previously reported in specialized literature. To enhance code performance and remove dependence on commercial software such as MATLAB®, VF and CVF were implemented in the C-language, utilizing a low-level linear algebra package and exploiting parallelism. We evaluated performance by varying the model order, number of ports, and frequency samples. The results confirm the feasibility of our approach, prompting a more in-depth exploration of the potential benefits regarding FDNE realization. • The constraint relaxation of the Complex Vector Fitting enhanced model's accuracy. • The Complex Vector Fitting achieved a model order reduction of 48%. • The parallel implementation improved computational efficiency using free libraries. [ABSTRACT FROM AUTHOR]

• Inaccuracy of fdLine model in simulating transients in TLs with underbuilt wires assessed. • Higher errors in 100 kHz-1 MHz range, linked to lightning overvoltage wavefronts. • Errors increase with soil resistivity; up to 25 % difference in peak transient voltages. • Prefer ULM over fdLine for transient analysis in TLs with underbuilt wires using EMT programs. This paper investigates the potential inaccuracies associated with using a modal-domain model featuring a real and frequency-independent transformation matrix in simulating electromagnetic transients on power overhead lines equipped with underbuilt wires. Three transmission line configurations are examined: one without underbuilt wires, one with a single underbuilt wire, and another with two underbuilt wires. Comparisons between the simulated voltages computed using the modal-domain approach and a more accurate phase-domain model as a reference reveal that the modal-domain approach leads to inaccuracies in the simulated voltages. These inaccuracies intensify with an increase in the number of underbuilt wires and the soil resistivity. Differences of up to approximately 24 % in the peak values of the simulated voltages were observed, considering the transmission line geometry analyzed in this study. Based on these findings, it is recommended that for simulating transients in overhead lines with installed underbuilt wires, phase-domain models, such as the Universal Line Model, should be employed. [ABSTRACT FROM AUTHOR]

This paper presents a novel three-phase transmission line model for electromagnetic transient simulations that are executed directly within the time domain. This model relies on distributed and frequency-dependent parameters, as well as employs modal transformation for its implementation. The single-phase model of the exact equivalent π-circuit is utilized for each propagation mode. This model combines discrete components, such as resistors, inductors, and capacitors, to accurately emulate the transmission line behavior via linear circuit elements. This model can be seamlessly integrated into various electrical circuit simulation software, thus allowing easy utilization and incorporating time-varying elements to analyze transmission lines. The JMarti model, which comes by default in the Alternative Transient Program, and the numerical Laplace transform method implemented in MATLAB were utilized to validate the proposed solution across various scenarios. An advantage of this model is its independence from the prior calculation of travel time and its exemption from convolutions, inverse Laplace transforms, and Fourier transforms, thus streamlining the simulation process.

This paper presents a novel model for transformer windings to accurately represent the duality between electrical and magnetic circuits. The model can be used for the calculation of high-frequency transients in power systems and the design of high-frequency transformers, for example, those to be used in solid-state (utility-grade) transformers and power electronic converters. Existing circuit models do not consider the flux linkage in the winding thickness in a physical (dual) way. Duality is achieved by discretizing the winding thickness into thin sub-sections and distributing the proposed model building block across the winding. Analytical calculations are carried out to compare the accuracy of the proposed circuit for the computation of the terminal impedance, flux duality, and current distribution in the physical geometry of the winding. Further discretization is performed to extend the circuit to represent high-frequency phenomena: eddy currents and capacitive effects. The model can be easily implemented in any circuit simulation program using available circuit elements. The circuit parameters are computed with very simple expressions. The model is validated with finite element simulations. Differences of around 1% are obtained for relatively low model orders for high frequencies.

Real-time device-level multi-domain emulation can provide an accurate insight into behavioral transients of the hydrogen fuel-cell hybrid electric bus (HEB). However, the conventional electromagnetic transient (EMT) simulation suffers from the computation burden caused by the complex multi-domain subsystems. This paper develops a hybrid recurrent neural network (RNN) and EMT method for device-level multi-domain emulation for fuel-cell and battery HEB. Two recurrent neural networks (RNN) are designed and trained to create device-level models of permanent magnet synchronous motor (PMSM) and the modular multilevel converter (MMC), respectively. The IGBTs’ behavioral transients and thermal performance are integrated into the RNN-based MMC model. Moreover, the EMT models represent the energy behaviour of onboard fuel-cell stacks and battery stacks. The proposed multi-domain hybrid models are implemented on the Xilinx Versal™ adaptive compute acceleration platform (ACAP), where multiple AI engines and the programmable logic deal with the RNN and EMT models, respectively. The real-time hardware emulation is carried out at the time-step of 0.1 $\mu \text{s}$ for device-level transients. The results show that the hybrid model has 96.3% accuracy; furthermore, it significantly reduces the HEB emulation time compared to conventional EMT methods.

After the high proportion of new energy is connected, the decrease of the proportion of synchronous machine in power system will cause a series of stability hazards, such as the lack of inertia. The distributed asynchronous condenser provides a solution for the above problems because of its high controllability, high inertia and high phase advance ability. In this paper, the performance parameters of the distributed asynchronous condenser are analyzed to further optimize its structure. At the same time, the advantages and disadvantages of different excitation schemes are compared and analyzed, and the best scheme is selected; Secondly, a multi physical domain model is established to analyze the magnetic field distribution in steady-state operation and verify the error between the design value and the simulation value; Finally, the transient characteristics of distributed asynchronous condenser under different fault types and different fault parameters are analyzed. Through the above research, this paper verifies that the distributed asynchronous condenser plays the role of reactive power support and voltage regulation on the stability of new energy system.

Electromagnetic Transients Program make extensive use of transmission line models for the simulation of electromagnetic transients. This paper proposes a circuit representation of the modal transformation, more specifically Clarke’s matrix. The arrangement of ideal transformers we propose allows modal transformation to be directly implemented in software such as Alternative Transient Program - Electromagnetic Transients Program. We combined the proposed circuit with single-phase transmission line models that consider frequency independent and frequency dependent parameters to represent transposed three-phase transmission lines. The main advantage of the proposed approach is that it allows the implementation of new transmission line models without depending on models provided in applications. To show this capability, we included the frequency dependence of soil parameters in the simulations. Results show that the proposed model is accurate both in the frequency domain and in the time domain.

For being the world’s largest low voltage direct current (LVDC) microgrid (MG) in space, the power generation and distribution systems aboard the International Space Station (ISS) employ a hierarchical assortment of electric power sources, energy storage, control devices, power electronics, and loads operating cooperatively at multifarious system dispositions and multi-stage configurations. At the early phase of design, for such time-critical systems, the trade-off between reliability and convergence rate of device modeling, varying accuracy requirements of control flows, and especially the implementation for real-time performance have brought new challenges and problems for testing and validation of the MG. One of the solutions presented by this paper is to use the hardware-in-the-loop (HIL) emulation, where the MG is emulated using the field-programmable gate array (FPGA) hardware platform. In parallel with the emulation effort, comprehensive modeling solutions for both large-scale photovoltaic (PV) solar array wings (SAWs) and nonlinear behavior model (NBM) of insulated-gate bipolar transistors (IGBTs) have been utilized based on machine learning (ML) concepts of artificial neural network (ANN) and recurrent neural network (RNN). Both system-level (validated by Matlab/Simulink) and device-level (validated by SaberRD) transient simulations are carried out, and the results exhibit high accuracy and fidelity of the models and significant improvements in execution speed and hardware resource consumption.

This article presents an outline of Electric Transient Disturbances (ETDs), represented by the ElectroStatic Discharge (ESD) in accordance with the Human-Body Model (HBM), on the AC-DC transfer measurement standard, represented by the Single-Junction Thermal Converter (SJTC) Thermal Element (TE). Mitigation technique against the power dissipation build-up, higher than the operational margins recommended by a manufacturer, on the TE were proposed and modelled using Laplace Transform (LT) analysis. A mathematical model and an optimization algorithm were developed to determine the equivalent circuit model parameters of a Transient Overload Protection Module (TOPM) that would offer adequate protection against destructive power dissipation levels build-up on the TE. The mathematical model was developed using an 8 kV ESD, which was expected to deliver short-circuit current with a peak value of approximately 5.33 A through a load impedance of approximately 1 m\varOmega. The ESD stress signal was injected into the TOPM connected in parallel with the TE. The active power dissipated by the SJTC TE per period of transient response was calculated from the current and voltage obtained from the mathematical analysis, and the results indicate a power dissipation of 10 mW by the TE. From the algorithm, the model parameter that noticeably influences the power dissipation capabilities of the TOPM is the inductance and it must be smaller than 1.2 nH. A CAD based simulation model was developed and analysed. The simulation results agreed with the mathematical model.

This work presents a transmission line model for simulating electromagnetic transients directly in the time domain. For this purpose, the exact equivalent $\pi $ -circuit is used, which represents the line taking into account its distributed and frequency-dependent parameters. The admittances that constitute the exact equivalent $\pi $ -circuit are approximated by rational functions using the vector fitting technique. Then, for each admittance, an electrical circuit is synthesized, consisting of an association of discrete elements (resistors, inductors, and capacitors) aiming at modeling the transmission line, thus allowing its use in any circuit simulation software and the eventual connection of nonlinear elements. From the simulation results, it is reasonable to state that the proposed model is a feasible representation, which aggregates the same features of the exact equivalent $\pi $ -circuit directly in the time domain, not only in steady state, but mainly during transients and also without the need for using convolutions, as well as inverse Laplace or Fourier transforms.

The increasing complexity of modern AC/DC power systems poses a significant challenge to a fast solution of large-scale transient stability simulation problems. This paper proposes the hybrid parallel-in-time-and-space (PiT+PiS) transient simulation on the CPU-GPU platform to thoroughly exploit the parallelism from time and spatial perspectives, thereby fully utilizing parallel processing hardware. The respective electromechanical and electromagnetic aspects of the AC and DC grids demand a combination of transient stability (TS) simulation and electromagnetic transient (EMT) simulation to reflect both system-level and equipment-level transients. The TS simulation is performed on GPUs in the co-simulation, while the Parareal parallel-in-time (PiT) scheduling and EMT simulation are conducted on CPUs. Therefore, the heterogeneous CPU-GPU scheme can utilize asynchronous computing features to offset the data transfer latency between different processors. Higher scalability and extensibility than GPU-only dynamic parallelism design is achieved by utilizing concurrent GPU streams for coarse-grid and fine-grid computation. A synthetic AC/DC grid based on IEEE-118 Bus and CIGRÉ DCS2 systems showed a good accuracy compared to commercial TSAT software, and a speedup of 165 is achieved with 48 IEEE-118 Bus systems and 192 201-Level detail-modeled MMCs. Furthermore, the proposed method is also applicable to multi-GPU implementation where it demonstrates decent efficacy. [ABSTRACT FROM AUTHOR]

In this paper, the validity of two extended transmission line approaches proposed for calculating the ground-return impedance and admittance of an underground insulated cable is evaluated taking as reference a full-wave approach based on the 3-D finite-difference time-domain (FDTD) method. The transient responses of an underground cable with realistic radius are calculated for a wide range of soil resistivities and cable lengths. It is shown that the extended transmission line approaches lead to transient waveforms in good agreement with the FDTD method even for relatively short cables and high soil resistivity. The limitations of a traditional formulation that neglects the influence of the ground-return admittance on the calculation of the cable parameters are also demonstrated. Overall, the results confirm the accuracy of the newly-proposed expressions for the calculation of underground cable parameters. [ABSTRACT FROM AUTHOR]

In this work, saturation and hysteresis loops are included in a four-port transformer model for electromagnetic transients computation in the frequency domain. Approximations with linear segments of the hysteresis characteristic and saturation curve are used. To obtain time domain results, the numerical Laplace transform is employed and the results are compared with those obtained from ATP. [ABSTRACT FROM AUTHOR]

This paper presents a robust fault location method that can be used for radial or meshed power systems. It addresses several challenges encountered in previous work such as signal attenuation by power transformers, measurement errors, the impact of Inverter Based Power Sources (IBPSs), differentiating faults from other events. This is accomplished via a KMeans clustering of DFRs and using a weighted directed tree model enabling accurate fault location. The proposed algorithm is tested on both transmission and distribution systems under different fault scenarios. [ABSTRACT FROM AUTHOR]

A review of the literature on the use of pulsed electric current to create the electro-plastic effect in metal parts is per-formed. Inductor with a U-shaped magnetic core and pulsed current is investigated for processing thin-walled metal plates with rectilinear welds. With a saturated magnetic core relative magnetic permeability can be low, so using a magnetic core can be impractical. The aim of the work is to establish the influence of a magnetic core of an induction system on voltage, current and magnetic forces when reaching the eddy current density of 109 A/m2 in the weld of a non-magnetic thin-walled metal plate. A two-dimensional model of the induction system with and without the magnetic core is investigated here. Simulation of the distribution of electromagnetic fields with the reduction of the parameters of the two-dimensional model to three-dimensional is performed. A capacitor charged to a certain voltage is a source of pulsed currents in inductor winding. The equation of the electric circuit for determining the current in the inductor’s winding is solved. The influence of the dimensions of the magnetic core on voltage and currents in the inductor’s wind-ing is determined. The influence of the magnetic core on the transients of voltages of capacitor and inductor, the cur-rents in the winding and the weld of the metal non-magnetic plate, the magnetic forces in the weld is studied. The influ-ence of the magnetic core on the distribution of magnetic field strength, currents, and magnetic forces on the surface of the plate in the area of the weld is studied. Ref. 13, fig. 4, table.

This work proposes an improved broadband equivalent circuit model of the winding system of an ultrahigh-voltage direct current (UHVDC) converter transformer and the validation experiment of the model conducted on a tapped transformer. The matrices of the inductance, capacitance, and resistance parameters in the improved model were all obtained by the finite element method according to the winding system structure of a UHVDC transformer. Then, the potential distributions along the windings under impulse voltages with different waveforms were studied in detail. Finally, the relationship between the potential gradient and waveforms was obtained. This work provides a convenient method to acquire the broadband electromagnetic transient characteristics of the winding systems within UHVDC converter transformers. [ABSTRACT FROM AUTHOR]

Modular multilevel converters have become the technology of choice in high voltage direct current systems. They are composed of a large number of submodules, which poses significant computational challenges to electromagnetic transient simulations. To address this issue, scholars proposed several approaches that are a trade-off between simulation accuracy and computational burden, which mainly achieve numerical efficiency by adopting reduced and simplified models of the converter arm submodules. This paper proposes a different simulation paradigm based on sub-circuit isomorphism. It is suited for the analysis of intrinsically modular electronic circuits, as it exploits the common behavior of structurally identical submodules by clustering them together. This method does not require any simplification of the submodule electrical model and minimizes the number of equations to be solved at each time step of the time domain analysis, thereby significantly reducing the computational effort. Thus, this method is suitable for thorough simulations of ac/dc networks, which may require the implementation of detailed transistor-level representations of the converter submodules. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of the ground admittance correction and the frequency dependence of ground conductivity and permittivity on the simulation of electromagnetic transients in overhead lines. Line parameters are calculated using an accurate formulation that considers ground displacement currents, ground admittance correction, and a rigorous voltage definition. The frequency dependence of ground parameters is calculated considering a causal model based on measurements over a wide frequency range. The calculations are performed in the frequency domain and time domain results are obtained from Laplace numerical transform. Two test cases are considered, namely a vertical 138-kV line and a horizontal 230-kV line. The results show that the frequency dependence of the electrical parameters of ground may be relevant in the simulation of lightning transients in overhead lines considering the injection of currents representative of first and subsequent lightning strokes, especially if the transmission line is located above a poor conducting ground. The effect of frequency dependence of ground parameters is more significant in the case of subsequent stroke currents since they present higher frequency content compared to first strokes. Also, it is shown that the use of Carson's approximation leads to significant deviations in lightning transient's simulation in overhead lines, taking as reference the results obtained from the use of a more accurate formulation for line ground-return parameters calculation, mainly in the case of high-resistivity soils. On the other hand, in the case of line switching transients, the influence of frequency dependence of ground parameters and ground admittance correction is negligible, and Carson's approximation leads to accurate results. [ABSTRACT FROM AUTHOR]

• Analysis of lightning-induced voltages on a realistic LV line configuration. • Systematic evaluation of the effects of various parameters on the induced voltages. • Analysis of the behaviors of phase-to-ground and phase-to-neutral induced voltages. • Comparisons of the effects of typical first and subsequent strokes. Special attention has been drawn to transients in low-voltage systems in recent years. As the surge withstand capabilities of low-voltage networks are much lower than those of medium-voltage lines, they are more susceptible to lightning-caused disturbances. One of the primary sources of overvoltages is related to indirect lightning strokes. Such overvoltages are highly dependent on the soil characteristics and generally tend to increase with the soil resistivity. Considering realistic conditions, this paper discusses the effects of different parameters on the phase-to-ground and phase-to-neutral lightning-induced voltages on the low-voltage side of a typical distribution transformer. In the case of high-resistivity soils or high ground resistance values, phase-to-ground voltages induced by indirect strokes can reach several tens of kilovolts. Phase-to-neutral voltages higher than 5 kV may be common if surge protective devices are not applied. [ABSTRACT FROM AUTHOR]

This paper proposes a methodology for modeling and simulating electromagnetic transients in power transmission cables with arbitrary cross-sections, usually applied in offshore power transmission and variable speed machine drive. This way, a sector-shaped cable is modeled taken into account its frequency-dependent parameters. Both impedance and admittance parameters are calculated by using the Finite Element Method, without analytic formulations based on the approach by an equivalent cylindrical cross-section, which leads to several inaccuracies. In sequence, the cable is decoupled into its four propagation modes by using an approximate modal transformation matrix with real and constant terms. Finally, each mode is modeled directly in the time domain by equivalent electric circuits, in which the lumped circuit elements are obtained from the rational function approach and fitting techniques. • Electrical parameters of submarine cables based on geometric characteristics and finite elements method. • Frequency-dependent equivalent circuit in the time domain by using the Vector Fitting algorithm. • Determining the modal transformation matrix with more than three propagation modes. • Modeling and simulation methodology applied to cables with arbitrary cross section and multiple modes. [ABSTRACT FROM AUTHOR]

This work presents a comparison of the three phasor extraction algorithms proposed in the literature for the co-simulation of transient stability and electromagnetic transients programs. Initially, a brief mathematical review of two algorithms widely used in the literature is made: the discrete Fourier transform and the adjustment of the least-squares curve. In addition, a technique proposed by the authors based on the use of the generalized second-order integrator is presented. Then, these three techniques will be implemented and evaluated numerically through a comparative performance study extracting the fundamental phasor component of a test signal. [ABSTRACT FROM AUTHOR]

In this paper, we propose a transmission line model to represent three-phase untransposed transmission lines with vertical symmetry. Here, we decouple a transmission line into its propagation modes using Concordia's matrix, which is the proper orthogonal form of Clarke's matrix that has its columns normalised. Due to the usage of Concordia's matrix, the transmission line is decoupled into two coupled modes and one uncoupled mode. We represent the uncoupled mode by a single-phase transmission line, and the coupled modes by a two-phase transmission line without vertical symmetry. We compute voltages and currents for the single-phase transmission line using the classic Lumped Parameter Model. Voltages and currents in the two-phase transmission line are calculated using a cascade of coupled L circuits pairs. Modal voltages and currents are then transformed back to the phase domain. We compare the results obtained with the proposed model to those obtained with two well-known time domain models, the classic modal lumped parameter model and the lumped parameter model available in the Alternate Transients Program ATP. Results show that the proposed model agrees with time-domain models and has the advantage that is developed in the time domain without needing any inverse transformations. [ABSTRACT FROM AUTHOR]

This article presents an outline of Electric Transient Disturbances (ETDs), represented by the ElectroStatic Discharge (ESD) in accordance with the Human-Body Model (HBM), on the AC-DC transfer measurement standard, represented by the Single- Junction Thermal Converter (SJTC) Thermal Element (TE). Mitigation technique against the power dissipation build-up, higher than the operational margins recommended by a manufacturer, on the TE were proposed and modelled using Laplace Transform (LT) analysis. A mathematical model and an optimization algorithm were developed to determine the equivalent circuit model parameters of a Transient Overload Protection Module (TOPM) that would offer adequate protection against destructive power dissipation levels build-up on the TE. The mathematical model was developed using an 8 kV ESD, which was expected to deliver short-circuit current with a peak value of approximately 5.33 A through a load impedance of approximately 1 mΩ. The ESD stress signal was injected into the TOPM connected in parallel with the TE. The active power dissipated by the SJTC TE per period of transient response was calculated from the current and voltage obtained from the mathematical analysis, and the results indicate a power dissipation of 10 mW by the TE. From the algorithm, the model parameter that noticeably influences the power dissipation capabilities of the TOPM is the inductance and it must be smaller than 1.2 nH. A CAD based simulation model was developed and analysed. The simulation results agreed with the mathematical model. [ABSTRACT FROM AUTHOR]

The finite-element analysis is a powerful method to obtain detailed insight into the operation of any electromagnetic equipment. However, the required computational power to solve a finite-element modeled power equipment is so heavy that most Newton-Raphson-method-based algorithms can barely achieve real-time simulation. The low latency and hardware parallelism of the field-programmable gate array (FPGA) provides a path forward. In this paper, a parallel and deeply pipelined adaptive transmission-line modeling method with preconditioned conjugate gradient solver is designed in hardware and implemented on two Xilinx® XCVU37P FPGAs for the finite-element modeling of a three-phase transformer. The accuracy of the transformer solver under both current-excited and voltage-excited conditions of the transformer was validated against the commercial FE simulation tool.

Converter-based generators are increasingly replacing classical synchronous generation, resulting in significant challenges to the operation and planning of modern power systems. Power electronics (PE)-based equipment, along with non-linear PE-driven loads, introduce time-varying characteristics and fast switching behavior that increases the complexity of the power system model. Faster control actions are needed to overcome the fast switching dynamics to ensure the reliability and stability of future power systems. Thus, this requires advanced and detailed simulation methods and tools with highly accurate equivalent models to embody the relatively slower electromechanical to faster electromagnetic transient (EMT) phenomena. Conventional transient stability analysis using positive-sequence simulators has become inadequate for representing converter-dominated power systems, while EMT simulators suffer from the high computational burden. This review paper presents accelerated EMT simulation methods and tools that are categorized and discussed in three topics: system equivalents, simulation methods, and accelerating tools. Dynamic system equivalent techniques are discussed to model small to large interconnected external systems of the grid network. Moreover, a systematic review is made for existing EMT simulation methods, along with advanced co-simulation methods, for addressing simulation speed and accuracy issues in large power system networks. Emerging hardware-based simulation tools are reviewed that reduce the computational burden and increase the simulation efficiency of the power system model. Challenges and trends in EMT simulation are also presented and concluded by providing perspectives on this research topic.

Due to the complex sending terminal structure of offshore wind transmission systems, conventional on-line monitoring-based protection cannot work well. The electromagnetic transient faults are also difficult to locate due to a short time span with fast characteristics that are affected by various power electronic devices and control algorithms. To solve the aforementioned problems, a new offshore wind transmission line protection scheme based on active detection of submarine cable sheath current is proposed. This method uses a normalized coding cooperation to realize the risk levels and failure locations of the transient defects, and then the sheath currents become a characteristic input data source, which can build a clear system protection boundary. Case studies using MATLAB and ATP simulations are carried out, where three types of transient faults represented by sheath currents are studied, i.e., loss of electrical continuity of grounding device, short circuit of segmented metal sheath of cable joint, and water immersion of junction box. Testing results illustrated that the proposed method could achieve fast fault detection and precise fault location of the electromagnetic transients. Moreover, compared with conventional wind farm protection techniques, it only needs to add few signal injection modules with high sampling frequency into the submarine optical fibers.

Onshore wind farms are usually connected to the power grid by 35 kV transmission lines. Due to the high altitude of the wind turbines and their associated long transmission corridors, lightning activities are more frequent for onshore wind farms compared to the power plant in plain areas. In addition, the insulation levels of 10–35 kV distribution lines are generally low. All these facts make proper lightning strike protection a technical challenge for onshore wind farms. Taking a typical onshore wind farm as the testing object, the structure of the 35 kV distribution line connected to this wind farm is modeled by EMTP software in this paper. The leakage current and absorbed energy of the arrester at the head tower when lightning currents of different amplitudes inject into the overhead line are studied. By calculating the energy accumulated in the arrester within 100 µs, the causes of the lightning trip and damage to the arrester of the distribution line, i.e., the energy accumulation mechanism, are clarified. Eventually, the lightning protection updating scheme for this distribution line is proposed: a combination of refitting the porcelain cross arm at the head and end of the tower and filling the grounding body of the tower with a drag-reduction agent, which shows that the lightning resistance level of the distribution can be improved by 50 times in maximum.