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Single‐phase loads and photovoltaic generation cause three‐phase imbalance in distribution systems, and prospective growth of normal chargers of electric vehicles may even increase the imbalance. The analysis of such unbalanced systems requires the three‐phase power‐flow calculation. Since existing methods require the admittance matrices of three‐phase transformers, they must be derived for all possible winding connection patterns in advance to its computer‐code implementation. This paper proposes a three‐phase power‐flow calculation method which formulates circuit equations using the modified nodal analysis, making it possible to automatically handle any winding connection. The power‐flow constraints are then embedded into the circuit equations using a fixed‐point iteration. Newton‐Raphson, backward/forward sweep and fixed‐point iteration methods are the existing three categories of solution methods. Newton‐Raphson methods may show convergence problems due to the high R/X ratios of distribution lines. Backward/forward sweep methods cannot be used, because loops are temporarily formed in a distribution system during circuit switching. These justify the use of a fixed‐point iteration. In this paper, the proposed method is validated by practical examples. [ABSTRACT FROM AUTHOR]

Accurately calculating the transmission‐line constants of underground cables is important for various types of power system simulations such as electromagnetic transient, power flow, and transient stability simulations. The transmission line constants of cables installed in a tunnel must be calculated taking the skin and proximity effects into account, since the cables are spaced closely to each other and also to a wall face of the tunnel. However, the conventional method, which is capable of considering the skin and proximity effects, has been restricted to circular cross‐section conductors such as cables and a circular tunnel. Therefore, the method cannot handle a tunnel with a rectangular cross section. In this paper, a method for calculating the transmission‐line constants of a conductor system in which both circular and rectangular cross‐section conductors present in the same space is proposed. Then, the walls of a rectangular tunnel are represented by eight rectangular conductors, and cables represented by circular conductors are placed inside the eight rectangular conductors. In this paper, the proposed method is verified by experiments using a conductor system in which three circular conductors are arranged in a rectangular conductor. Calculated results obtained by the proposed method agree well with the measured results. [ABSTRACT FROM AUTHOR]

This article compares five modeling methods of grid-tied inverters for the electromagnetic transient simulation of power system, clarifies their differences, and discusses the suitable model for each simulation purpose. The comparison was made under the same conditions between the conventional switching model, and four simplified models—voltage interpolation, average-value, controlled current-injection, and simplified current-injection model. The comparison of the simulated waveforms clarifies the behaviors that can be simulated and cannot be simulated by each simplified model. The comparison of the computing time reveals the significant decrease of the computing time by selecting the proper simplified modeling method. Based on these comparisons, this article discusses the selection of the modeling methods for each simulation purpose to perform simulations accurately and efficiently. [ABSTRACT FROM AUTHOR]

The electromagnetic transient (EMT) simulation of a power system involving power-electronics converters requires a fairly small time-step size to consider switching of the converters, thus leading to a heavy computational burden. To accelerate such simulations, this article generalizes the time average method (TAM), originally developed for real-time simulations, so that it becomes suitable to offline EMT simulations. For obtaining accurate current waveforms with a large time step, the TAM and the proposed method represent each leg of an inverter by voltage sources, and its output voltage is modified by interpolation at an instance of switching. The original TAM was intended for the primitive backward Euler method. This article contributes to generalize it for the trapezoidal integration method, which is widely used in offline simulation programs. In addition, the proposed method uses a simple formula to identify the switching instance for the implementation on off-the-shelf PCs, rather than a hardware counter in an field programmable gate array as used in the TAM. This article shows that the proposed method enables to extend the time step by a factor of five without deteriorating the accuracy. A case study demonstrates reduction of computational time by a factor of three for the offline simulation of a single-phase grid-connected inverter with reasonable reproduction of harmonics. [ABSTRACT FROM AUTHOR]

At the time of the commissioning of an underground cable transmission line, it is a common practice to perform measurement of its electrical constants. In such measurement performed by a cable manufacturer, the following straightforward method is used for each circuit of the cable line. A three‐phase voltage source is used to apply a balanced three‐phase voltage at the power frequency to one end of the cable circuit with the other end short circuited, and the positive‐sequence impedance is obtained by the measured voltage and current. To obtain the zero‐sequence impedance, a single‐phase voltage at the power frequency is applied to the bonded three phases of one end of the cable circuit, to the ground, with all phases at the other end grounded. If there is no parallel cable circuit in service, this method gives an accurate result. However, if there are one or more parallel cable circuits in service, the cable circuit under measurement gets electromagnetic induction from the magnetic flux generated by the currents on the parallel circuits. This induction generates superimposed currents and, thus, makes the measured result inaccurate. Considering this point, a method to measure a voltage and a current at a frequency different from the power frequency so as to separate the power‐frequency current component generated by the electromagnetic induction and obtain the impedance value at that frequency is proposed in this article. Using impedance values measured at two frequencies different from the power frequency, the power‐frequency impedance value is then obtained by linear approximation. The proposed method is applied to obtain the impedances of a 132‐kV underground cable line, and a reasonable result is obtained. [ABSTRACT FROM AUTHOR]

Transient analysis is an indispensable tool for analyzing the voltage fluctuation of distribution systems according to the penetration of distributed generations with grid‐connected inverters. Electromagnetic transient (EMT) analysis is suitable for the purpose because it enables detailed modeling of the inverters and accurate simulation of their dynamic behavior. However, the EMT analysis requires a smaller calculation time step by a factor of 500 if the simulated power system includes the inverters. Simulation of the inverters is a bottleneck in speeding up the EMT analysis. This paper proposes a novel average‐value modeling method for the grid‐connected inverters. The proposed inverter model operates in a larger calculation time step, and speeds up the EMT analysis of distribution systems containing the inverters. The maximum error in the output power was 8% compared to the result by the conventional model. Dynamic voltage simulations are demonstrated with a test case, which includes tap changing transformers with a voltage controller and a photovoltaic generation facility. The proposed model reduces the required calculation time by a factor of 754 compared to the conventional model whereas there is no significant difference in the simulated result. [ABSTRACT FROM AUTHOR]

This paper proposes using Bergeron's equivalent circuit with traveling time equal to the simulation time step as an element for frequency-dependent modeling of transmission lines for electromagnetic transient (EMT) simulations of power systems. According to the simulation time step used, a transmission line is divided into aforementioned Bergeron's equivalents, each of which is called a 'Bergeron cell' in this paper. In this way, the traveling-wave nature of a line is represented by the cascaded Bergeron cells. Then, the frequency-dependent loss nature of the line is represented by a matrix partial fraction expansion, and this is inserted at each connection point of the Bergeron cells in the form of a multiphase Norton equivalent. Since the frequency-dependent loss is modeled in the dimension of impedance, the change of the line length is easily taken into account by a simple multiplication. This methodology thus allows variable-length modeling and completely avoids modal decomposition in both model identification and EMT simulation stages. The proposed methodology is applied to the frequency-dependent modeling of overhead and submarine-cable transmission lines, and its accuracy is assessed. [ABSTRACT FROM AUTHOR]

• 33-kV dedicated cable supply system for feeding EV fast chargers is introduced. • Due to the large capacitance of the cable system, harmonics may be concerned. • The condition of harmonic resonance is analytically given. • The harmonic resonance phenomenon is verified by EMT simulations. • When the cable length is about 1 km, the chances of resonance are high. To achieve carbon neutrality by 2050, electric vehicles (EVs) are promoted and EV fast chargers are expected to become part of the public infrastructure. To feed power to EV fast chargers installed in highway rest areas, the authors have proposed a 33-kV dedicated cable supply system installed along the highway. Due to the large capacitance of a cable system, harmonics may be of concerns for the operation of the proposed system. Therefore, this paper presents a study of harmonics occurring in the 33-kV dedicated cable supply system to feed EV fast chargers. First, the cause of the harmonics is identified by deriving resonance frequencies of the equivalent circuit of the cable supply system. Then, the harmonic resonance phenomenon is verified by electromagnetic transient (EMT) simulations. The results indicate conditions with which harmonic resonance may occur in the cable supply system. To perform the simulations, the EMT simulation models of distribution substations and EV fast chargers are picked up from the generic EMT simulation models prepared in XTAP (eXpandable Transient Analysis Program) for distribution and microgrid simulations. It should be noted that the harmonics simulations mentioned above can readily be performed by picking up necessary models from the model library. [ABSTRACT FROM AUTHOR]

Electromagnetic transient (EMT) simulations are often performed to analyze disturbances which occur during a steady-state operation of the power grid. In modern transmission and distribution power grids, a number of voltage-source converters (VSCs) are used for renewable energy interconnections and system control. To perform EMT simulations with such VSCs, a time step of the order of microseconds is used to represent the switching operations of the VSCs. In order to avoid a prohibitively-long computation time, a steady-state initialization method is required to directly start from a steady state. This paper proposes a systematic and heuristic procedure for the steady-state initialization of generic VSCs. Using an AC steady-state solution, detailed portions in the circuit part and the control-system part of a VSC are systematically initialized. For validation, EMT simulations of a 6.6-kV distribution grid with two VSCs are performed with and without the proposed initialization procedure in this paper. Practically no transient is observed in the result with the proposed procedure, and therefore it is confirmed that directly starting from a steady state is made possible. On the other hand, the result without the proposed procedure does not reach the steady state even after continuing the EMT simulation for 300 ms. • A systematic steady-state initialization procedure for generic VSCs is proposed. • Detailed portions in the circuit and control-system parts of a VSC are initialized. • Directly starting from a steady state for a simulation with VSCs is made possible. • A prohibitively-long computation time is thus avoided by the proposed procedure. • Using a 6.6-kV grid with two VSCs, the proposed procedure has been validated. [ABSTRACT FROM AUTHOR]

SUMMARY Electromagnetic transient (EMT) simulations of relatively large power systems have become quite common, for instance, in the case where simulations of HVDC converters are carried out with large ac power systems connected to the converters. Thus, the increase in computation time is a serious concern. To reduce computation time, this paper proposes a method to reduce computational demand of a remote power system which is located far from the source of a transient event to be simulated. In the proposed method, the remote power system, which is supposed to be represented by a three-phase EMT-based model, is reduced to a single-phase phasor-based model, and the size of the circuit to be simulated is thus reduced and the dynamics calculations of inductors and capacitors included in the remote power system are neglected. The calculation algorithm of generator models included in the remote power system is also simplified. The proposed method has been applied to EMT simulations of the WEST 10 benchmark power system prepared by the IEEJ, and it has been shown that the computation time is remarkably reduced without significant loss of accuracy if the portion assumed to be the remote power system is sufficiently far from the source of a transient event. [ABSTRACT FROM AUTHOR]

Electromagnetic-transient (EMT) simulations of relatively-large power systems with generator mechanical dynamics have become quite common especially for studies of power systems including power-electronics converters. The Power and Energy Society of the Institute of Electrical Engineers of Japan (IEEJ) prepared benchmark power system models for transient stability (TS) simulations. Among those, the West-10 benchmark power system model approximately represents the long radial power system in the western part (60-Hz part) of Japan with ten generators. In this paper, the West-10 benchmark power system model is expanded and converted to an EMT model, and it is shown that the results obtained by the EMT model agree well with those obtained by the TS model in most cases. It is also found that when the dc components of fault currents are large the results obtained by those two simulation methods are different due to current zero missing of circuit breakers. [ABSTRACT FROM AUTHOR]

This paper shows that a previously proposed linear-system identification method based on frequency partitioning and adaptive weighting can be successfully applied to the phase-domain frequency-dependent modeling of overhead transmission lines for electromagnetic transient simulations. As the framework of the phase-domain modeling, the universal line model is used, and the frequency responses of the characteristic admittance and propagation function matrices are realized by linear equivalents obtained by the identification method mentioned before, instead of the well-known Vector Fitting method. In this paper, numerical techniques to enhance the identification method for this phase-domain line modeling application are also presented. For validation, the proposed approach is applied to modeling an existing 500-kV double-circuit transmission line. The effectiveness of the numerical techniques for enhancements are shown through the modeling process, and transient waveforms obtained by the proposed approach are compared with those by the rigorous Laplace transform method and with a field-test result. [ABSTRACT FROM PUBLISHER]

To suppress the lightning-induced voltages on a distribution line, lightning arresters and/or overhead shielding wire can be installed, and the effectiveness of these countermeasures are usually studied by simulations. Traditionally, field-to-transmission line coupling techniques based on the distributed-parameter circuit theory are used for the calculation of the lightning-induced voltages. Recently, the finite-difference time-domain (FDTD) method that directly and numerically solves Maxwell's equations was applied to the calculation of the lightning-induced voltages. Compared with the conventional methods, the FDTD-based calculation is advantageous in terms of the modeling of inhomogeneous ground parameters, 3-D structures, and grounding systems. But, in the previous works, the distribution line was simulated simply by a single-phase line. Moreover, the representation of lightning arresters in the FDTD method was not yet established. This paper proposes a technique to incorporate the lightning arresters in the FDTD-based lightning overvoltage calculations. In this technique, the voltage–current relationships of the lightning arresters are represented by piecewise linear curves, which can be obtained directly from the data sheets or measured results. For validation purpose, the lightning-induced voltages on a three-phase distribution line equipped with the lightning arresters and a multipoint-grounded overhead shielding wire are calculated by the proposed method, and the results are compared with those obtained by the conventional method and a very good agreement is found. [ABSTRACT FROM PUBLISHER]

When we consider global warming, the reduction of CO2 emissions is one of the most important issues which require urgent solutions. One option is to integrate low-CO2-emission generators to the grid as much as possible. Another option is to replace inefficient vehicles based on internal-combustion engines with electric ones (EVs). Due to the latter, we can easily predict that most consumers will charge EVs' batteries during nighttime. Thus, excessive voltage drops due to nighttime simultaneous charging are expected to be a possible future problem. This paper proposes a method for compensating the voltage drops by injecting reactive power from EV battery chargers. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 184(1): 19-29, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22390 [ABSTRACT FROM AUTHOR]

This paper describes the challenges and lessons learned when developing industrial-grade data translators aimed for the interfacing of power-flow programs with Electromagnetic Transients Program-type programs. It has been found that the greatest challenges to overcome include: 1) the lack, in the databases used in power-flow programs, of vital pieces of information necessary to perform transient studies; 2) inconsistency in the format of data files; 3) the presence of data entry mistakes in very large databases; 4) the validation of the translated data; and 5) the analysis of the large amount of data that transient simulations provide. Several examples are presented to show the implemented solutions. Finally, recommendations based on experience are made to help future developers of interfacing tools. [ABSTRACT FROM PUBLISHER]

This paper presents a brief review of techniques available for reducing large systems to smaller equivalents. This paper is divided into high frequency equivalents, low frequency equivalents, and wideband equivalents. Numerical examples are presented to demonstrate selected methods of high frequency equivalencing. [ABSTRACT FROM PUBLISHER]

This paper presents a robust and efficient iterative scheme for solving nonlinear circuits as a solution method for electromagnetic transient (EMT) simulations. In most EMT simulations, the characteristics of nonlinear components can be represented by piece-wise linear curves. With this assumption, the Newton–Raphson (NR) method shows high efficiency, but it is prone to get into an infinite loop, resulting in nonconvergence. First, the NR method is extended to utilize the information of both axes of the nonlinear characteristics, and this modified method is called a biaxial NR method. The biaxial NR method shows a significantly improved convergence performance with additional computation. Next, an iterative scheme, which combines the standard NR, the biaxial NR, and the Katzenelson method is proposed. It first tries the standard NR that is the most efficient but the least convergent. If it fails to converge, the biaxial NR, which is more convergent but less efficient, is employed. Just in case when the biaxial NR does not converge, finally, the Katzenelson method, whose convergence is mathematically guaranteed but least efficient, is used. In this way, the proposed scheme always converges with a relatively small number of iterations. Illustrative and practical examples are shown to validate the proposed scheme. [ABSTRACT FROM AUTHOR]

Recently, the focus of lightning protection measures for distribution lines has moved from a nearby lightning stroke to a direct lightning stroke. Studies of direct lightning stroke countermeasures are generally carried out by digital simulations using the EMTP (Electro-Magnetic Transients Program). Thus, components of a distribution line must be modeled appropriately in the EMTP for accurate simulations. The authors have previously clarified the surge response of a distribution line by pulse tests using a reduced-scale distribution line model. In this paper, first, the results of the pulse tests are simulated in the EMTP using a conventional model which represents a distribution pole by a single lossless distributed-parameter line model, and comparisons with the test results show that transient overvoltages generated at the insulators cannot accurately be reproduced by the conventional model. This indicates that a special treatment is required to represent the transient response of a distribution pole and wires. Then, this paper proposes new EMTP models of the pole and wires which can reproduce the transient overvoltages at the insulators. The parameter values of the proposed models can be determined based on a pulse test result. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 173(1): 11–23, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.21001 [ABSTRACT FROM AUTHOR]

For distribution lines in Japan, protection measures against lightning-induced overvoltages have been taken and can be considered almost complete. The focus of lightning protection measures has moved to overvoltages due to direct lightning strokes. Studies of such overvoltages require simulations using the EMTP (Electro-Magnetic Transients Program), and components of a distribution line must be modeled appropriately in the EMTP simulation environment. The authors have proposed an EMTP model of a distribution line in a separate paper. This paper consists of two parts. The first part presents surge characteristics of a distribution line obtained by measurement using an actual-scale test distribution line. In particular, the result reveals noteworthy characteristics of the surge impedance of a reinforced concrete pole and the wavefront-time dependence of insulator voltages. The second part presents a validation of the distribution line model previously proposed by the authors. The validation shows that the distribution line model accurately reproduces the measured voltage and current waveforms for various wavefront times of the injected currents. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 173(1): 1–10, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.21002 [ABSTRACT FROM AUTHOR]

Steady-state simulation plays a vital role in power system analysis and design. Over the past 25 plus years, various steady-state methods have been proposed. Most of these methods only deal with how to obtain steady-state waveforms of a system in an efficient manner. Only a few of them also take power-flow constraints into account. The majority of these "power-flow" methods are implemented in the frequency domain, which inevitably suffers from harmonic truncation errors. Moreover, the problem of model incompatibility will rise when they are used for the steady-state initialization of a time-domain electromagnetic transient (EMT) program. This paper presents a harmonic power-flow method, which is implemented entirely in the time domain. The proposed method essentially extends a time-domain steady-state method, called "shooting method" to include the power-flow constraints and to account for aggregate loads in the power-flow calculations. [ABSTRACT FROM AUTHOR]

Abstract-This paper proposes applying the two-stage diagonally implicit Runge-Kutta (2S-DIRK) method of numerical integration to the calculation of electromagnetic transients (EMT5) in a power system. The accuracy and the numerical stability of 2S-DIRK are almost the same as those of the trapezoidal method, while 2S-DIRK does not produce sustained numerical oscillation due to a sudden change of an inductor current or a capacitor voltage unlike the trapezoidal method. First, this paper reviews the 2S-DIRK integration scheme and derives the 2S-DIRK formulas of inductors and capacitors for both linear and nonlinear cases. Then, analytical comparisons of 2S-DIRK with the trapezoidal, backward Euler, and Gear-Shichman methods are carried out, and numerical examples which verify the analytical comparisons are shown. Finally, 2S-DIRK is compared with critical damping adjustment (CDA) implemented in Electromagnetic Transients Program (EMTP) for some simulation cases. [ABSTRACT FROM AUTHOR]

This paper describes a method for deriving a transmission tower model for EMTP lightning overvoltage studies from a numerical electromagnetic field simulation result obtained by the FDTD (Finite Difference Time Domain) method. The FDTD simulations carried out in this paper take into account the following items which have been ignored or oversimplified in previously presented simulations: (i) resistivity of the ground soil; (ii) arms, major slant elements, and foundations of the tower; (iii) development speed of the lightning return stroke. For validation purpose a pulse test of a 500-kV transmission tower is simulated, and a comparison with the measured result shows that the present FDTD simulation gives a sufficiently accurate result. Using this validated FDTD-based simulation method the insulator-string voltages of a tower for lightning strokes are calculated, and based on the simulation result the parameter values of the proposed tower model for EMTP studies are determined in a systematic way. Since previously presented models include trial-and-error process in the parameter determination, it can be said that the proposed model is more general in this regard. As an illustrative example, the 500-kV transmission tower mentioned above is modeled, and it is shown that the derived model closely reproduces the FDTD simulation result. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(1): 8–20, 2008; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/eej.20675 [ABSTRACT FROM AUTHOR]

Abstract: This paper presents new features recently added to a general-purpose surge simulation code based on the Finite Difference Time Domain (FDTD) method. The added features include various-shape conductor models, lumped-parameter circuit-element models, a lightning-channel model, and an integrated analysis environment (IAE). For precisely modelling the shapes of various conductors, the following conductor models have been added: inclined thin wire; disc; square plate; cylinder; cone; and quadrangular pyramid. The lumped-parameter circuit-element models allow the user to represent the lumped impedance of an apparatus placed inside the analysis space. The lightning-channel model realizes a return-stroke development at a speed slower than the light speed. The IAE includes a Graphical User Interface (GUI), which allows the user to enter geometrical data in a visual way. It also provides a waveform plotting program for viewing voltage, current, electric-field, and magnetic-field waveforms and a movie program for displaying the animation of a transient electric/magnetic field intensity distribution. For an illustrative example, the lightning overvoltage calculation of a transmission tower is presented. [Copyright &y& Elsevier]

This is an introductory paper on z-transform-based methods for electromagnetic transient simulations of power systems. Since the theory of the z-transform was originally developed for the analysis of time series data defined at equidistant time steps, simulation models developed using z-transforms can readily be used in electromagnetic transient simulations based on the same time step. First, this paper briefly introduces the basics of the z-transform, and then applications to electromagnetic transient simulations of power systems are reviewed. [ABSTRACT FROM AUTHOR]

Wind turbine generation systems are built at locations where few tall structures are found nearby so as to obtain good wind conditions, and thus, they are often struck by lightning. To promote wind power generation, lightning-protection methodologies for such wind turbine generation systems have to be established. This paper presents the result of an experimental study of lightning overvoltages in wind turbine generation systems using a reduced-size wind turbine model. Overvoltages observed at wavefronts of lightning surges are focused on in this study. In the experiments, lightning strokes to one of the blades and to the nacelle were considered, and voltages and currents at various positions of the wind turbine model were measured. The following points have been deduced from the results: (i) The voltage rise due to the tower footing resistance can cause a significant voltage difference between the tower foot and an incoming conductor led from a distant point. Also, a voltage difference between the bottom of down conductors installed inside the tower and an incoming conductor can be of significance. (ii) The lightning current flowing through the tower body induces voltages in main and control circuits which form loops, and the induced voltages can cause overvoltages and malfunctions. (iii) Traveling-wave phenomena in a wind turbine generation system for a lightning strike to the tip of a blade and to the nacelle have been clarified from the measured waveforms. This information can be used for developing an EMTP simulation model of wind turbine generation systems. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 158(4): 22– 30, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20466 [ABSTRACT FROM AUTHOR]

This paper proposes a simple closed-form formula of the ground-return impedance of horizontal parallel wires above a lossy ground plane. It is derived by a double logarithmic approximation of the integral term with a semi-infinite interval in Carson's ground-return impedance formula. The proposed double logarithmic approximation gives better accuracy compared to a similar approximation proposed by Pizarro and Eriksson, and this is achieved by an advanced optimization technique used for determining the coefficients in the double logarithmic approximation and also by incorporating an additional variable which minimizes errors. In this paper, it is shown, using practical examples, that the derived formula gives more accurate results compared with other existing approximate formulas. It is also shown that a graphical interpretation of the double logarithmic approximation is to replace a homogeneous lossy ground with a pair of perfectly conducting return planes located at different complex depths. [ABSTRACT FROM AUTHOR]

This paper presents an algorithm for identifying a multiphase network equivalent for electromagnetic (EM) transient calculations. Conventional rational fitting methods intrinsically get into ill condition because the sn terms in the rational function take a wide range of values which cannot be accurately treated within machine arithmetic accuracy. The proposed algorithm averts the ill conditioning by partitioning the given frequency response into sections along the frequency axis. Rational fitting is applied to each section of the frequency response to identify the poles, and then the corresponding residue matrices are obtained by a standard least-squares procedure using the entire frequency response. Adaptive weighting, column scaling, and iteration step adjustment are utilized to facilitate the rational fitting. The proposed identification algorithm is applied to obtain a reduced-order equivalent of a 500-kV power network, and the equivalent is used in a switching transient simulation to demonstrate its performance. [ABSTRACT FROM PUBLISHER]

This paper presents the result of a study on the error in propagation velocity introduced by the staircase approximation of a thin wire in the finite difference time domain (FOTU) surge simulation. The FDTD method directly solves Maxwell's equations by discretizing the space of interest into cubic cells. Thus, it is suitable for solving very-fast surge phenomena which cannot be dealt with by conventional techniques based on the lumped- and distributed-parameter circuit theories. However, FDTD has a limitation that the shape of a conductive object must be modeled by a combination of sides of cells with forced zero electric fields. This indicates that a thin wire, one of the most important components in the surge simulation, results in a staircase approximation, if the wire is not parallel to any of the coordinate axes used for the discretization. A staircase approximation gives a slower propagation velocity due to the zigzag path which is longer than the actual length of the wire. For precise simulations, the error in propagation velocity has to be clarified quantitatively. In this paper, extensive simulations are carried out to obtain the velocity versus inclination characteristic, and it is deduced that the maximum error in propagation velocity is less than 14%. [ABSTRACT FROM AUTHOR]

This paper proposes an algorithm for obtaining the periodic steady-state solution of a multiphase network including nonlinear, switching, and frequency dependent elements. Unlike existing methods which deal with nonlinear and switching elements in the time domain, the approach presented is entirely in the harmonic domain. The method will be used for the harmonic analysis of power systems and for steady-state initialization in electromagnetic transient analysis. The algorithm takes rigorously into account the inter-harmonic couplings in the Jacobian matrix of the proposed Newton-Raphson iteration process so that a quadratic convergence rate is achieved. Linear, nonlinear, switching, and frequency dependent elements are modeled in a modular approach, and any network topology can be handled by extending the Modified Nodal Equations approach to the harmonic domain case. First the algorithm is described and then applied to a test case to demonstrate its computational performance. [ABSTRACT FROM AUTHOR]

This paper presents a new concept called harmonic domain dynamic transfer function (HDDTF), which characterizes the dynamics of a nonlinear, time-periodic network as seen from a port (or multiple ports), in terms of the frequency response of harmonic perturbations superimposed on its underlying periodic steady state. It pertains to the transient behavior superimposed on the steady state. The HDDTF is a transfer-function matrix H(s) relating the vectors of harmonic domain input and output endowed with s-domain properties. Because the network can contain saturable (nonlinear) elements and periodically-switching (time-periodic) power electronics components, the HDDTF may be used for the analysis of power quality problems. It may also serve for the identification of a reduced-order dynamic equivalent of a nonlinear, time-periodic network to be used in time-domain transient simulations. The HDDTF is obtained by linearization, about the periodic steady state, of the nonlinear state equations describing a given network. Following the derivation of the HDDTF, a modal analysis to characterize the HDDTF by its diagonalization is presented. Two test systems are used to produce numerical examples. [ABSTRACT FROM AUTHOR]

This paper presents a methodology for the identification of a reduced-order dynamic equivalent of a nonlinear power network for the simulation of electromagnetic transients. The equivalent is deduced from the observer companion form of the state equations with periodic coefficients and includes the effects of the nonlinearity of the power network at its operating point. A previously proposed concept, the harmonic domain dynamic transfer function (HDDTF), is used to characterize the network's transient behavior, superimposed on the steady state. The HDDTF is obtained by linearization of the nonlinear state equations of the network corresponding to harmonic perturbations applied to the steady-state operating point. Then, reduced-order companion-form state equations with periodic coefficients are fitted to the HDDTF in the frequency domain using a least-squares procedure based on the SVD and QR algorithms. The fitting procedure includes sequential weighting, column scaling, and vertical partitioning to improve computational accuracy and efficiency. The SVD algorithm serves to determine an appropriate model order. A test network with nonlinear inductances is used to demonstrate the performance of the identification method as well as the time-domain simulation results. [ABSTRACT FROM AUTHOR]

This paper investigates the charge versus voltage (q-v) curves of surge corona on transmission lines. Two measurement methods of the q-v curves are proposed, and field test results are shown to validate the methods. Since the new methods do not require a charge-measuring conductor, such as a corona cage, the q-v curves are measured in the real electric-field distribution. One of the methods obtains the amount of charges q by numerically integrating the digitally stored waveform of injected current, assuming that the line is short in length and open ended. Thus, it is suitable for measurement using an experimental setup. The other calculates q from voltage and current waveforms based on the traveling-wave theory, assuming that the line is long enough to expect no reflected waves, and it is applicable to existing "real" transmission lines. Measured q-v curves are compared with simulated ones, and their physical properties are discussed in the paper. [ABSTRACT FROM AUTHOR]

This paper proposes a model of core-type distribution transformers for electromagnetic (EM) transient studies. The model accurately reproduces not only the impedance characteristics seen from each terminal of a core-type distribution transformer but also the surge-transfer characteristics between the primary and secondary sides in a wide range of frequencies. Due to the above capability, the proposed model enables the accurate evaluation of overvoltages on distribution lines including consumer-side overvoltages. In this paper, a 10-kVA transformer is modeled, and transient-simulation results agree well with laboratory-test ones. [ABSTRACT FROM AUTHOR]

Examines the simulation of surge phenomena in a three-dimensional structure of thin wires using finite difference time domain (FDTD). Simulation of electromagnetic wave propagation on wires and steel flames; Development of general surge analysis program based on FDTD method; Assessment of interference of lightning surges; method.

This paper proposes a language—Circuit Description Language (CDL)—to describe the information of a circuit for computer-aided analysis and design. The syntax of CDL provides strong modularity, making it possible to build a circuit using other previously defined circuits (building-block construction of a circuit). This feature allows building a library of standard power-system models. In this paper, example circuits are described using CDL in order to show the power of modularity. © 2000 Scripta Technica, Electr Eng Jpn, 133(4): 1–7, 2000 [ABSTRACT FROM AUTHOR]

For transmission-line surge studies, the inclusion of corona discharge due to high voltage surges is important as well as the inclusion of frequency-dependent effects. Because the charge-voltage (q-v) curve of a lightning surge is different from that of a switching surge, a corona model should reproduce different q-v curves for different wave-front times. The present paper proposes a wave-front time dependent corona model which can express the dependence by a simple calculation procedure as accurately as a rigorous finite-difference method which requires an enormous calculation time. The simplicity enhances the incorporation of the corona model into a line model, because a large number of models are to be inserted into the line model by discretization. The q-v curves calculated by the proposed method agrees well with field tests. This paper also proposes an efficient method to deal with nonlinear corona branches in distributed-parameter line model using the trapezoidal rule of integration and the predictor-corrector method. © 1999 Scripta Technica, Electr Eng Jpn, 129(1): 29–38, 1999 [ABSTRACT FROM AUTHOR]

For fault-surge studies, the most important and also most difficult part of the simulation is inclusion of the frequency dependence of the transmission line, because the simulation requires high accuracy in a wide frequency range, from the power frequency to a few megahertz. The authors have developed a highly efficient method of modeling a transmission line considering its complete frequency dependence, which cannot be dealt with in the present line models in the Electro-Magnetic Transients Program (EMTP). According to the method, a transmission line is modeled directly in the phase domain in order to avoid model transformation and thus to eliminate the problems of representing its frequency dependence. The method also includes sophisticated acceleration of transient calculations by means of an autoregressive moving average (ARMA) model. This paper presents a method of steady-state initialization of the phase-domain ARMA line model for applying it to fault-surge calculations. The calculated results agree well with rigorous frequency-domain simulations and show improved accuracy compared with an existing frequency-dependent line model (J. Marti model) widely used as a standard model in the EMTP. © 1998 Scripta Technica, Inc. Electr Eng Jpn, 121(3): 27–35, 1997 [ABSTRACT FROM AUTHOR]

This article presents a comparison between simulation and laboratory-test results of lightning surge propagation from a distribution line to a consumer entrance via a pole-mounted transformer. The simulation result, obtained using a transformer model previously proposed by the authors, closely reproduces the laboratory-test result. [ABSTRACT FROM AUTHOR]

This letter shows that the frequency-partitioning-fitting (FpF) method can be successfully applied to the phase-domain frequency-dependent modeling of underground cables for electromagnetic-transient simulations. This letter is a continuation of a separate paper that has presented the applicability of the FpF method to overhead transmission-line modeling. In addition, this letter introduces a technique to efficiently identify a modal traveling time and a technique to reduce the number of poles for the model realization. [ABSTRACT FROM PUBLISHER]

Because of the presence of large capacitance, measuring the series resistance of a cable as a voltage drop is not an easy task especially at high frequencies. Considering this fact, this letter proposes a method to extract series resistance values of a single-core cable at high frequencies from the measured frequency response of its open-ended input impedance. The proposed method has been applied to the measurement of the series resistance of an existing 66-kV underground cable, and the result is presented. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

This letter presents a numerical simulation of transient electromagnetic fields using the finite-difference time-domain (FDTD) method for obtaining the step response of a 500-ky transmission tower. The purpose of this simulation is to reproduce the result of a field test which has been carried out for obtaining the step response of the tower as fundamental data for lightning over- voltage studies. From the comparison between the calculated and measured results, the accuracy of the FDTD method, when applied to lightning overvoltage studies, is examined. The simulation carried out in this letter takes into account the following items that have been ignored or oversimplified in the existing simulations. One is the resistivity of the ground soil, and the other is the detailed structures of the arms, the lattice elements, and the foundations. The calculated result obtained closely reproduces the field-test result. [ABSTRACT FROM AUTHOR]

Previously, a method for identifying a multiphase network equivalent for electromagnetic transient calculations using partitioned frequency response has been proposed. The method accurately and robustly identities an equivalent of the target network by dividing its frequency response into sections, but no specific algorithm for the frequency-region partitioning has been proposed. To make the entire identification process automatic, this letter proposes a binary partitioning algorithm. [ABSTRACT FROM AUTHOR]