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The simulation of electric field transients in HVDC cables can be a fundamental tool to support insulation system design when operation dynamics, which includes voltage polarity inversions and load variation, becomes significant during the expected cable life. The field behavior during voltage and temperature transients is associated with intrinsic and extrinsic ageing processes that can affect the cable design life. Traditional models employed for electric field simulations consider only the non–linear, steady–state dependence of conductivity on temperature and field magnitude, but they neglect the transient behavior of permittivity and conductivity, that is, polarization and charge trapping phenomena. These processes impact on the duration of the field transient and thus ageing. This paper discusses the numerical implementation of an electro–quasistatic model that can be used to perform transient simulations of electric fields in HVDC cables insulation. With respect to the model traditionally employed, the presented one is extended with Debye's equations for dielectric polarization processes. The model is implemented numerically using finite differences, or the Occhini equivalent circuit: this paper demonstrates that the two approaches are equivalent. Numerical simulations show that, during transients, polarization processes slow down the electric field dynamics and reduce its maximum intensity. [ABSTRACT FROM AUTHOR]

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, an improved dynamic state estimation (DSE) based protection (DSEBP) scheme is proposed for transmission lines in MMC-HVDC grids. Firstly, a dynamic model of the protection zone (DC line of interest) is constructed using differential and algebraic equations. The impact of frequency dependent line parameters is mitigated through the utilization of the “line mode” transmission line model. Then, a novel Runge-Kutta (RK) discretization scheme is proposed to consider the dynamics of the control variables during electromagnetic transients, yielding reduced discretization error as compared to the conventional RK scheme. Finally, the batch mode regression framework based DSE is developed to formulate the protection logic considering errors of both measurements and historical estimates. Numerical experiments have shown that the proposed DSEBP scheme can dependably detect and trip internal faults, and securely ignore the external faults. The proposed scheme achieves improved reliability and operational speed as compared with the existing DSEBP schemes. The proposed scheme only requires a typical sampling rate of 10k samples per second, has the robustness to measurement noises, and the calculation burden is low enough for practical implementations. [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]

Expansion of power grids has resulted in the construction of multiple transmission lines within constrained spaces inevitably making them nonuniform in nature. Existing transmission line models available in electromagnetic transient (EMT) simulators are based on classical multiconductor transmission line (MTL) theory with the assumption that the transmission lines are infinitely long and have uniform cross-sectional dimensions. This paper develops a time-domain model, namely dispersive scattered field transmission line (DSFTL) model, for multiconductor dispersive nonuniform overhead transmission lines above lossy, frequency-dependent ground. The proposed model which consists of closed-form equations in the time-domain has been implemented using a modified finite-difference time-domain (MFDTD) algorithm and integrated into an EMT simulator (PSCAD/EMTDC). Results have been compared with and verified by those obtained using a full-wave approach and measured data available in the literature. Simulations of nonuniform structures that include nonlinear components (such as breakers) have also been carried out under fault conditions. [ABSTRACT FROM AUTHOR]

With widespread application of voltage source converter (VSC) as a key energy-conversion power electronic device by using the phase-locked loop (PLL) technique for synchronization, the system dynamics has become much complicated. In this paper, the nonlinear dynamics and transient stability of the PLL-based VSC system are investigated, within a unified framework of the (normalized) generalized swing equation. It is found that there are three different types of bifurcation, including the generalized saddle-node, Hopf, and homoclinic bifurcations. Within the coexistence parameter region, the basin boundary of the stable equilibrium point shows either a closed-loop or a fish-like pattern. With the help of the equal area criterion (EAC), the transient stabilities under different transient disturbances including short circuit, voltage dip, and power rise are analyzed. Because the equivalent damping of the VSC is state-dependent, the theoretical results based on the EAC are examined. Furthermore, based on the analytical results from the generalized swing equation, the principle for all major transient stability enhancement methods is uncovered. All these findings are well verified by extensive electromagnetic transient simulations. Therefore, the generalized swing equation provides a deeper physical insight and plays a crucial role in transient stability problems in power-electronic-dominated power systems, similar to the swing equation in traditional power systems. [ABSTRACT FROM AUTHOR]

Power system electro-magnetic transient programs (EMTP) have been popular among researchers and practitioners due to their detailed component modeling and high simulation accuracy for complex system operations. Despite broad applications in simulations with wide range of timescales, the small discretization step of these programs makes their use very time-consuming for system studies with long time span. Facing the increasingly complex power system transient characteristics and simulation demands, a multiscale algorithm that integrates the simulations of the electromagnetic and slower electromechanical transients is desirable. The multiscale simulation algorithm preserves the high fidelity of the EMTP and attains higher efficiency for the overall transient simulation. In this paper, we achieve this goal by exploiting the unique properties of the matrix exponential function. The proposed algorithm is capable of utilizing large step sizes to speed up the simulation of slow dynamics, whereas the fast transients are accurately reconstructed through efficient dense output mechanism, which is built upon the matrix exponential function computation. Numerical studies including a large-scale wind farm simulation are conducted to demonstrate the effectiveness of the proposed multiscale algorithm. [ABSTRACT FROM AUTHOR]

This paper presents a novel approach to modeling magnetic cores for high-frequency transient analyses in power system applications. A method is presented to obtain a frequency-dependent, nonlinear equivalent circuit model of magnetic cores, suitable for simulations of transients in high-frequency and high-current conditions. The model can be used in any Electromagnetic Transients Program (EMTP)-like simulation software for power system transient analyses and hardware design of transient mitigation solutions. The model has been developed based on the frequency characteristics of the complex impedance of a magnetic core, measured for different operating points on the magnetization curve. Based on the measured characteristics and on some basic material properties, a nonlinear equivalent model composed of a set of lumped elements was established. The presented method is generic; however, the results are presented for a magnetic core of nanocrystalline type and the model implementation is shown in EMTP simulation software. The exemplary model is dedicated for the frequency range $f=$ 1 kHz $\div $100 MHz, and for the current range $I=0\div 10$ kA. The model accuracy was validated with selected measurement results, and the accuracy of the method is thoroughly discussed. [ABSTRACT FROM PUBLISHER]

Improving the fault ride-through (FRT) capability of doubly fed induction generators (DFIGs) in wind power applications is a very important challenge for the wind power industry. The mathematical models of such generators enable us to analyze their response under generic conditions. However, their mathematical complexity does not contribute to simplifying the analysis of the system under transient conditions and hence does not help in finding straightforward solutions for enhancing their FRT. This paper presents a simplified model of the DFIG, which has been extracted from the classical fifth-order model, which can accurately estimate the behavior of the system while significantly reducing its complexity. In this paper, the mathematical deduction of this model will be presented, and simulations and experimental results will be shown to demonstrate the accuracy and reliability of the proposed algorithm. [ABSTRACT FROM AUTHOR]

This paper presents a decision tree based method for out-of-step prediction of synchronous generators. For distinguishing between stable and out-of-step conditions, a series of measurements are taken under various fault scenarios including operational and topological disturbances. The data of input features and output target classes are used as the input-output pairs for decision tree induction and deduction. The merit of decision tree based detection of transient instability lies in robust classification of new unseen samples. The performance of the proposed method is verified on two test cases including a 9-bus dynamic network and the practical 1696-bus Iran national grid. The simulation results are presented for various input features and learning parameters. [ABSTRACT FROM PUBLISHER]

Power system damping in the transient condition generally depends on system parameters and modeling hypotheses. The dependence can be very nonlinear. In this paper, a polynomial approximation method is proposed to obtain a representation of the damping torque and damping torque coefficient of the original detailed stability model. [ABSTRACT FROM PUBLISHER]

This paper presents three algorithms for identification of dominant inter-area oscillation paths: a series of interconnected corridors in which the highest content of the inter-area modes propagates through. The algorithms are developed to treat different sets of data: 1) known system model; 2) transient; and 3) ambient measurements from phasor measurement units (PMUs). These algorithms take feasibility into consideration by associating the network variables made available by PMUs, i.e., voltage and current phasors. All algorithms are demonstrated and implemented on a conceptualized Nordic Grid model. The results and comparison among three algorithms are provided. The applications of the algorithms not only facilitate in revealing critical corridors which are mostly stressed but also help in indicating relevant feedback input signals and inputs to mode meters which can be determined from the properties of dominant paths. [ABSTRACT FROM PUBLISHER]

In this paper, a generalized approach is presented for time-domain adjoint sensitivity analysis of lossy multiconductor transmission lines (MTLs) with respect to electrical and/or physical parameters. While the new approach provides all the advantages of an adjoint sensitivity analysis, it is independent of the specifics of the MTL macromodel used. Several numerical examples are presented to demonstrate the validity and accuracy of the proposed approach. [ABSTRACT FROM PUBLISHER]

The purpose of this paper is to analyze the behavior of residual current devices at frequencies higher than the rated one. Many experiments are carried out by measuring tripping current and time of devices of different typology, produced by different manufacturers. The attention is mainly devoted to verify the satisfaction of the current–time safety curve at high frequency and experiment tripping and immunity to unwanted tripping in the presence of harmonics. Conduced tests show that the behavior of residual current devices at high frequency is strongly influenced by their typology rather than the values assumed by their physical parameters. In addition, a mathematical model is developed, and simulations are compared with measurements showing satisfactory agreement in the entire frequency range under study. [ABSTRACT FROM AUTHOR]

This paper presents a dynamical model for simulating combined cycle power plants to be used for assessing the plant behavior during large transients and for restoration procedures. The 80th dynamic order model considers the complex structure of the heat recovery steam generator and calculates the main variables that are critical during these transients. The model has the double purpose of studying both the plant behavior under the usual control systems as well as innovative logics and control strategies for increasing its performances in terms of regulation and emergency services. The possible use of combined cycle power plants for supplying a restoration area is finally investigated adopting different control strategies that also involve the regulating capacity of the steam turbine. [ABSTRACT FROM PUBLISHER]

This is the first part of a two-paper series and presents the modeling methodology for all of the main components of a typical wind power plant for power system transient studies. The models developed are intended for investigation of the temporary overvoltages, switching overvoltages, and lightning overvoltages. The component models developed include the high-frequency models of the vacuum and SF6 circuit breakers, three core cables for the collector grid, and quad core cables for the wind turbine tower, turbine transformer, doubly fed asynchronous generator, and surge arrester. The models developed are wideband in nature and can be used for all studies, except the transformer model which requires two variations for the low–mid frequency range and mid–high frequency range. Detailed user-defined models developed for both vacuum and SF6 circuit breakers take account of the restrikes, reignitions, prestrikes, low-frequency high-current interruption, and high-frequency low-current interruption. The generator and transformer transient models include a representation of the various high-frequency capacitive couplings. The success criteria for each individual component model are discussed, and the model performance is validated against these criteria. [ABSTRACT FROM AUTHOR]

Electric power distribution systems of many commercial and industrial sites often employ variable frequency drives and other loads that internally utilize dc. Such loads are often based on front-end line-commutated rectifiers. The detailed switch-level models of such rectifier systems can be readily implemented using a number of widely available digital programs and transient simulation tools, including the Electromagnetic Transient (EMT)-based programs and Matlab/Simulink. To improve the simulation efficiency for the system-level transient studies with a large number of such subsystems, the so-called dynamic average models have been utilized. This paper presents the average-value modeling methodologies for the conventional three-phase (six-pulse) front-end rectifier loads. We demonstrate the system operation and the dynamic performance of the developed average models in discontinuous and continuous modes, as well as under balanced and unbalanced operation. [ABSTRACT FROM PUBLISHER]

This paper introduces an approach which enables very large power systems to be modeled on real-time electro-magnetic transients (EMT) digital simulators. This is achieved using an improved wide-band multi-port equivalent, which reduces a large power network into a small manageable equivalent model that preserves wide-band behaviors. The low-frequency or electromechanical transients are captured with a transient stability analysis (TSA) type electromechanical equivalent derived using coherency-based reduction techniques. The high-frequency behavior is accurately captured by placing in parallel with the TSA equivalent, a passive frequency dependant network equivalent (FDNE). The validity of the proposed technique is demonstrated by comparing the approach with detailed electromagnetic simulations of a modified version of the New England 39-bus test system that includes an HVDC infeed. The power of the method is demonstrated by the real-time electromagnetic transient simulation of a large 2300-bus 139-generator system. [ABSTRACT FROM PUBLISHER]

The calculation of voltages induced by external electromagnetic fields on multiconductor transmission lines (MTLs) has been the subject of several studies. In this paper, discrete equations for MTLs exposed to incident fields are derived based on the time-domain finite-element method and the backward differentiation formula. Based on these equations, a value-delivery table characterizing the MTLs is presented. Combining this table with modified node analysis formulation, it is convenient for analyzing the responses of transmission lines composed of complex termination networks or complex transmission-lines networks. The validity and efficiency of the proposed algorithm is demonstrated using several examples. Finally, a 1-km 35 kV overhead line above an imperfectly conducting ground is studied, and the influences of ground wire and a metal-oxide arrester to the lightning-induced voltage are both discussed. [ABSTRACT FROM PUBLISHER]

This paper presents a hybrid time–frequency domain methodology to calculate midfrequency transients of an electrical network that includes transmission lines (TLs) and considering that the simulation is carried out on a partitioned-time basis. Basically, the line is modeled as a two-port element and the network simulation is performed in the frequency domain for each time subinterval. The transition between subintervals is made by calculating an equivalent current source for each end of the line. These sources represent the initial conditions for a subsequent subinterval, and their calculation is based on a rational approximation of the two-port line parameters. The conversion of frequency-domain variables to the time domain is efficiently performed through numerical Laplace transform operations. A sequential closure of a three-phase TL is presented for illustration of the proposed methodology. [ABSTRACT FROM AUTHOR]

In this paper, we carry out a 2-D transient analysis of field-plate GaAs metal–semiconductor field-effect transistors (FETs) by taking surface states into account. Quasi-pulsed current–voltage curves are derived from the transient characteristics. We show that drain lag and current slump (power slump) due to surface states are reduced by introducing a field plate because the fixed potential at the field plate mitigates the trapping effects of the surface states. The dependence of lag and current slump on the field-plate length and the \SiO2 passivation layer thickness is also studied. We show that it is possible to reduce the current slump and maintain the high-frequency performance of GaAs FETs at optimum values of the field-plate length and the \SiO2 layer thickness. [ABSTRACT FROM PUBLISHER]

Induction motor drive systems fed with cables are widely used in many industrial applications. Accurate prediction of motor terminal overvoltage, caused by impedance mismatch between the long cable and the motor, plays an important role for motor dielectric insulation and optimal design of dv/dt filters. In this paper, a novel modeling methodology for the investigation of long-cable-fed induction motor drive overvoltage is proposed. An improved high-frequency motor equivalent circuit model is developed to represent the motor high-frequency behavior for the time- and frequency-domain analyses. The motor equivalent circuit parameters for the differential mode (DM) and common mode (CM) are extracted based on the measurements. A high-frequency cable model based on improved high-order multiple-\pi sections is proposed. The cable model parameters are identified from the DM impedances in open circuit (OC) and short circuit (SC). To obtain a computationally efficient solution that could potentially be integrated with the motor drive controller, the system equations are discretized and solved using transmission-line modeling (TLM) approach. The proposed methodology is verified on an experimental 2.2-kW ABB motor drive benchmark system. The motor overvoltage transients predicted by the proposed model is in excellent agreement with the experimental results and represents a significant improvement compared with the conventional models. [ABSTRACT FROM PUBLISHER]

An improved mathematical model for transient simulations of commutator machines is presented in this paper. This model can simulate and predict the line current harmonics during healthy and faulty operation conditions. A lumped parameter model that considers every single coil in the stator and rotor as a separate electrical and magnetic circuit is proposed. Self and mutual inductances of the coils are estimated by means of the winding function approach (WFA), accounting for the most relevant space harmonics in the machine air gap. The commutation is modeled by using the real brush width and assuming that the brush-commutator contact resistance is a function uniquely of their contact area, which depends on the armature position. Short circuits between adjacent commutator bars are investigated. It is shown that the model achieves good accuracy, reproducing fairly well the armature current ripple for healthy and faulty operation of the machine. [ABSTRACT FROM AUTHOR]