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The protection of traditional high‐voltage capacitor banks relies on an unbalance relay which operates when an internal fuse is blown. However, the unbalance relay cannot indicate the cause of the fault. Thus, an operator wastes time and human resources investigating the fault issues. In this paper, a fault which occurred in a 230‐kV power system of Electricity Generating Authority of Thailand was observed by performing simulations using the Power Systems Computer Aided Design (PSCAD) program. The study system based on the double bus station and 72 MVAR capacitor banks was installed in the form of a back‐to‐back topology. Three scenarios were considered: normal condition, fault occurrence in one capacitor bank and fault occurrence in both capacitor banks. Current characteristics such as the current phase and difference in unbalance current were considered. In addition, discrete wavelet transform was applied to solve the ambiguity of current generated from the PSCAD. The authors' results suggest that identifying fault events using a coefficient of wavelet is more efficient than relying on the current amplitude. The findings mentioned in this paper can be applied in a traditional power system protection scheme to enhance a system's reliability. [ABSTRACT FROM AUTHOR]

Abstract Modular multi‐level converters (MMCs) are a mainstay in many HVDC transmission projects worldwide. Half‐bridge MMC (HB‐MMC) is mostly used in the current project. The large capacitor of sub modules (SMs) is often required in MMC to ensure the low voltage ripple. Here, the three‐stage switching MMC (TSS‐MMC) topology is proposed, which can greatly reduce the capacitor voltage ripple of SMs by dynamically adjusting the position of inductance on the upper and down bridge arms. The principle of reducing capacitor voltage ripple based on equal capacitance theory is introduced. The selection of the inductance value of each part in TSS‐MMC is introduced. The start‐up process strategy, capacitor voltage ripple reduction strategy in steady‐state operation, and DC fault ride‐through strategy of TSS‐MMC are proposed. The effectiveness and engineering practicability of the proposed TSS‐MMC is verified by transient simulation program built on PSCAD/EMTDC. The simulation results show that compared with MMC with circulating current suppressing controller (CCSC), it can effectively reduce the capacitor voltage ripple by over 50%. Furthermore, the total used inductance of TSS‐MMC can also be reduced. A comprehensive assessment of TSS‐MMC is also carried out.

Abstract Even though shunt compensation of transmission lines (TLs) is a common practice to limit the overvoltages stemming from the Ferranti effect, it may cause transient and steady‐state resonant overvoltages when one phase is left open due to the single‐pole‐open condition following the temporary phase‐to‐ground (Ph‐g) fault. Furthermore, the existing shunt reactors potentially increase the duration of the secondary arc current at the fault point and hence prevent offering fast single‐pole reclosing. To exploit the mentioned issues, in recent studies, a neutral reactor is introduced, which is installed in the neutral point of the shunt reactors; nonetheless, obtaining the appropriate amount of it is remarkably challenging. In this paper, an optimal neutral reactor (ONR) is determined based on an optimization problem, which minimizes the neutral reactor cost subject to limiting both resonant overvoltages and the duration of the secondary arc current. In modelling, the Laplace domain is employed rather than the phasor domain to consider both transient and steady‐state conditions since this technique allows having better control over transient overvoltages as well as transient secondary arc.

Modular multi‐level converters (MMCs) are a mainstay in many HVDC transmission projects worldwide. Half‐bridge MMC (HB‐MMC) is mostly used in the current project. The large capacitor of sub modules (SMs) is often required in MMC to ensure the low voltage ripple. Here, the three‐stage switching MMC (TSS‐MMC) topology is proposed, which can greatly reduce the capacitor voltage ripple of SMs by dynamically adjusting the position of inductance on the upper and down bridge arms. The principle of reducing capacitor voltage ripple based on equal capacitance theory is introduced. The selection of the inductance value of each part in TSS‐MMC is introduced. The start‐up process strategy, capacitor voltage ripple reduction strategy in steady‐state operation, and DC fault ride‐through strategy of TSS‐MMC are proposed. The effectiveness and engineering practicability of the proposed TSS‐MMC is verified by transient simulation program built on PSCAD/EMTDC. The simulation results show that compared with MMC with circulating current suppressing controller (CCSC), it can effectively reduce the capacitor voltage ripple by over 50%. Furthermore, the total used inductance of TSS‐MMC can also be reduced. A comprehensive assessment of TSS‐MMC is also carried out. [ABSTRACT FROM AUTHOR]

Even though shunt compensation of transmission lines (TLs) is a common practice to limit the overvoltages stemming from the Ferranti effect, it may cause transient and steady‐state resonant overvoltages when one phase is left open due to the single‐pole‐open condition following the temporary phase‐to‐ground (Ph‐g) fault. Furthermore, the existing shunt reactors potentially increase the duration of the secondary arc current at the fault point and hence prevent offering fast single‐pole reclosing. To exploit the mentioned issues, in recent studies, a neutral reactor is introduced, which is installed in the neutral point of the shunt reactors; nonetheless, obtaining the appropriate amount of it is remarkably challenging. In this paper, an optimal neutral reactor (ONR) is determined based on an optimization problem, which minimizes the neutral reactor cost subject to limiting both resonant overvoltages and the duration of the secondary arc current. In modelling, the Laplace domain is employed rather than the phasor domain to consider both transient and steady‐state conditions since this technique allows having better control over transient overvoltages as well as transient secondary arc. [ABSTRACT FROM AUTHOR]

This paper is devoted to the development of a model of an autonomous electric power system to study random processes of voltage, current and power changes in emergency and dynamic operation modes. A diagram for calculating short-circuit currents has been presented, which was focused on a typical wide range of autonomous power plants with three diesel generator units. Amodel of an autonomous power plant has been developed, allowing to solve the assignments of determining short-circuit currents and starting currents of electric power machines. The equivalent network of the studied power system for transient calculations has been presented. Thus, the voltage waveforms have been obtained. A comparative assessment of theoretical calculation methods and simulation analysis demonstrated a high degree of accuracy of the simulation results. The use of approach suggested in the article and the developed model allows to increase the accuracy of conclusions when testing the abruptly variable processes and to make the most reasonable choice of measures to improve the quality of electricity and the reliability of electrical equipment. In particular, simulation analysis and obtaining transient curves for starting powerful consumers allow more accurately choose the type of circuit breakers used and the related configuration parameters. [ABSTRACT FROM AUTHOR]

The fast development of renewable energies leads to an increase in the power electronics penetration in transmission systems. This is particularly true if one considers a 100% renewable energies power system, where wind and solar photovoltaic energies, which make most of the renewable energies connections today, are connected to the grid through power electronics converters. Because power electronics-based generators and synchronous machines-based generators have very different dynamic behaviours, some approximations usually used to run transient simulations of transmission systems might not be optimal for future grids. The systematic use of the phasor approximation applied to the power lines, implemented in most of the Transient Simulation Programs, is indeed not relevant any more. To avoid the use of Electromagnetic Transient simulations, that are resource-demanding and time-consuming, this paper presents a novel Model Order Reduction technique for large grids with a high penetration of power electronic devices. Compared to the classical phasor approximation, this event-based state residualization approximation allows accurate transient simulations and at the same time an optimal reduction of the number of the system’s state variables depending on the observed variables, the considered events and the tolerated approximation error. [ABSTRACT FROM AUTHOR]

Assessing the transient behavior of electric power transmission/distribution systems, when they are subjected to major disturbances such as lightning discharges, is an essential procedure to ensure the operational security of these systems, in order to supply good quality power to all consumers. Electromagnetic transient studies are routinely performed in the planning and operation phases of these systems, by using world widely known computer programs, among which stands out the Alternative Transient Program (ATP), via its graphical interface ATPDraw. However, preparing files for running case studies by using ATPDraw can become a time-consuming and human error-prone task. To overcome this drawback, this paper presents a toolbox for automatic generation and execution of Alternative Transient Program input files based on information directly obtained from technical databases of distribution utilities. This toolbox aims to reduce modeling time and susceptibility to human errors in the process of describing the grid in the software input file, which constitute the biggest obstacles to the extensive use of this program in real electric transmission/distribution networks. For the toolbox validation, a comparison was made between the input file generated by the ATPDraw auxiliary graphic interface and the file generated by the proposed toolbox by using the IEEE 13-bus and IEEE 34-bus test feeders. Besides that, the simulation results of both feeders for both softwares were compared, so that the correct operation of the Alternative Transient Program automatic case creator and executor proposed in this article were proved. In addition, the automatic generation of ATP cases for larger grids is exemplified with the IEEE 123-bus test feeder.

This study presents a novel multi-rate algorithm for the co-simulation of power system transients using base-frequency dynamic phasor solver for frequency adaptive simulation of transient (BFAST) and electromagnetic transient (EMT) solvers. The BFAST solver alters its solution technique from dynamic phasors to EMT based upon the frequency contents of the waveforms being simulated. A changeover algorithm between the two solvers is also presented. The BFAST solver is then integrated with an industrial-grade EMT solver to develop a BFAST–EMT multi-rate co-simulator. The interface between the two solvers is established using transmission lines at the partitioning locations. The co-simulator combines the benefits of dynamic phasors, frequency adaptive simulation of transients, parallel processing, and multi-rate simulation. The study describes the several solution modes of the proposed co-simulator. Illustrative examples are included to demonstrate the accuracy and computational benefits of the proposed co-simulator.

This study presents a novel multi-rate algorithm for the co-simulation of power system transients using base-frequency dynamic phasor solver for frequency adaptive simulation of transient (BFAST) and electromagnetic transient (EMT) solvers. The BFAST solver alters its solution technique from dynamic phasors to EMT based upon the frequency contents of the waveforms being simulated. A changeover algorithm between the two solvers is also presented. The BFAST solver is then integrated with an industrial-grade EMT solver to develop a BFAST–EMT multi-rate co-simulator. The interface between the two solvers is established using transmission lines at the partitioning locations. The co-simulator combines the benefits of dynamic phasors, frequency adaptive simulation of transients, parallel processing, and multi-rate simulation. The study describes the several solution modes of the proposed co-simulator. Illustrative examples are included to demonstrate the accuracy and computational benefits of the proposed co-simulator. [ABSTRACT FROM AUTHOR]

Currently, an issue of relay protection (RP) settings determination that ensures its correct operation in electric power systems (EPSs) has not been resolved completely. The main reason for this is the lack of methods and tools for adequate consideration of transients during a fault existence for RP settings calculation. In this study, a novel approach for RP settings determination is presented. Its main feature is the application of detailed mathematical models reproducing simultaneously processes in the entire set of elements in the RP scheme, including instrumental transformers, and in large‐scale EPS mathematical model as a whole. This key feature can be achieved via the hybrid power system simulator – hybrid real‐time power system simulator – implementing a methodically accurate analogue–digital solution of the EPS mathematical model. The numerical transformer differential protection (NTDP) based on this approach was set up via the standard dual‐slope tripping characteristic. Also, a novel approach to the formation of the tripping characteristic is proposed. The key feature of this approach is applying a flexible curve that enveloping all fault characteristics Idiff = f (Irest) of those modes in which the NTDP should not trip. [ABSTRACT FROM AUTHOR]

The traditional electromagnetic transient (EMT) model of transmission line is very slow for the large-scale power systems simulation due to the small step. To accelerate the electro-magnetic transient program (EMTP) calculation, a modified line model used for realising multi-step simulation is proposed. This model is based on the timescale transformation of single-phase coordinate which can transform the primary high-frequency signal into a lower one. By this means, the part which needs to be simulated in detail, such as power electronic devices, can be calculated with a small time step, and a large time step can be used for the other part. In this article, the basic theory of timescale transformation is introduced firstly, and then the new line model is deduced in detail. Finally, a simple system is simulated by the new and traditional model, respectively, and the validity of this approach is verified by comparing with the traditional EMTP simulation. Furthermore, due to the large-step simulation, the calculation speed is improved.

As a most widely applied real-time digital simulation system, real time digital simulation (RTDS) is however quite limited on scale of simulation by the number of hardware purchased. Through frequency-dependent network equivalent (FDNE), scale of simulation of RTDS could be largely increased by frequency equivalent on limited hardware. Based on basic principles of FDNE, function limitations and problem are analysed, taking the Shanghai Sijing district power grid as an example; detailed simulation model and FDNE equivalent module are built, transient characteristics under faults before and after FDNE equivalent are analysed. Furthermore, the fault characteristics of high-voltage direct current (HVDC)-Sijing power grid is also studied, which provides a realistic means for real-time digital simulation of AC–HVDC hybrid power grid with limited hardware of RTDS.

In order to correctly simulate the simultaneous switching of power electronics circuits and to solve the problems of virtual power loss existing in the traditional interpolation algorithm, this article proposes interpolation algorithm considering simultaneous solution and instantaneous solution. After each integration, it searches for the switching events and determines the simultaneous switching. The simultaneous switching events are solved simultaneously. Instantaneous solution is carried out at forced commutation switching instant. The historical terms calculation method in instantaneous solution under different conditions is given, and the exact power loss of forced commutation switch is obtained. After processing all switching events during one time-step, the half-step interpolation is performed to eliminate numerical oscillations. The proposed algorithm is applied to the electromagnetic transient programme of advanced digital power system simulator (ADPSS), and the correctness and effectiveness of the algorithm are verified by simulation tests for typical power electronics circuits. The simulation results show that the proposed algorithm has high simulation accuracy and can satisfy requirements of power electronics simulation.

This study presents a multi‐scale transient model of cascaded H‐bridge (CHB) converter for distribution network‐interactive studies, which is capable of simulating slow‐changing dynamics up to high‐frequency switching transients. The switching pulse behaviours of H‐bridges are described using the waveform propagation theory. By taking individual H‐bridge sub‐modules into account, a semi‐analytic function (SAF) model of the CHB multilevel converter is developed. It allows for accelerated simulation of switch‐type electromagnetic transients (EMTs). During slow‐changing dynamics, the developed SAF is converted to a shifted‐frequency phasor (SFP) model using the Fourier series expansion. Due to the consistent modulation and complex analytical signal processes, smooth transitions between the SAF and SFP are achieved for different running stages. Moreover, the proposed model is readily integrated with external multi‐scale models of the distribution network. The validity of the proposed multi‐scale model is performed through case studies that include the CHB internal fault, distribution network faults, and also interactive dynamics between them. The accuracy and efficiency of the multi‐scale model is verified through comparisons of the results with those obtained from the full EMT‐type programmes. [ABSTRACT FROM AUTHOR]

The results of an electromechanical transient simulation can be viewed as a time series data set. Storing these data requires a sizeable space, and the considerable data size renders comparative analysis difficult. For mitigating these problems, a method for analysing and describing a discrete‐event chain in the dynamic process of a power system is proposed. Based on the symbolic description, the continuous dynamic process is represented as a discrete‐event chain, resulting from the change in state variables beyond the given threshold. Therefore, the event‐driven electromechanical transient simulation is developed, and the continuous dynamics and discrete‐event chain simulation results are obtained. Subsequently, the event relation matrix is obtained, normalised, and then converted into a bitmap. Finally, the k‐means method is used for the cluster analysis on the bitmap of the simulation result. Two test cases involving an IEEE 39‐bus system and a practical system are considered. Case studies demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The increasing utilization of HVAC underground power cables gives rise to technical challenges related to the occurrence of electromagnetic transients. This paper discusses measurements with sensors based on open air capacitances sensing the electric fields from the line having a wide frequency bandwidth and excellent electromagnetic compatibility performance. However, since the sensors are open air capacitors, they also intercept field lines from other phases and measurement decoupling is necessary. Results from measurements, using the differentiating/Integrating technique, at a 380 kV mixed overhead line underground power cable connection obtained at a transition point and at a substation are presented and compared with PSCAD/EMTDC simulations. The measurement system gives accurate results for low and high frequency transients, while the effect of uncertainties in the decoupling is minor. For switching transients, the simulation model was validated in terms of measured and simulated voltage waveforms resulting in similar maximum overvoltage and frequency content. [ABSTRACT FROM AUTHOR]

As a most widely applied real-time digital simulation system, real time digital simulation (RTDS) is however quite limited on scale of simulation by the number of hardware purchased. Through frequency-dependent network equivalent (FDNE), scale of simulation of RTDS could be largely increased by frequency equivalent on limited hardware. Based on basic principles of FDNE, function limitations and problem are analysed, taking the Shanghai Sijing district power grid as an example; detailed simulation model and FDNE equivalent module are built, transient characteristics under faults before and after FDNE equivalent are analysed. Furthermore, the fault characteristics of high-voltage direct current (HVDC)-Sijing power grid is also studied, which provides a realistic means for real-time digital simulation of AC–HVDC hybrid power grid with limited hardware of RTDS. [ABSTRACT FROM AUTHOR]

In order to correctly simulate the simultaneous switching of power electronics circuits and to solve the problems of virtual power loss existing in the traditional interpolation algorithm, this article proposes interpolation algorithm considering simultaneous solution and instantaneous solution. After each integration, it searches for the switching events and determines the simultaneous switching. The simultaneous switching events are solved simultaneously. Instantaneous solution is carried out at forced commutation switching instant. The historical terms calculation method in instantaneous solution under different conditions is given, and the exact power loss of forced commutation switch is obtained. After processing all switching events during one time-step, the half-step interpolation is performed to eliminate numerical oscillations. The proposed algorithm is applied to the electromagnetic transient programme of advanced digital power system simulator (ADPSS), and the correctness and effectiveness of the algorithm are verified by simulation tests for typical power electronics circuits. The simulation results show that the proposed algorithm has high simulation accuracy and can satisfy requirements of power electronics simulation. [ABSTRACT FROM AUTHOR]

The traditional electromagnetic transient (EMT) model of transmission line is very slow for the large-scale power systems simulation due to the small step. To accelerate the electro-magnetic transient program (EMTP) calculation, a modified line model used for realising multi-step simulation is proposed. This model is based on the timescale transformation of single-phase coordinate which can transform the primary high-frequency signal into a lower one. By this means, the part which needs to be simulated in detail, such as power electronic devices, can be calculated with a small time step, and a large time step can be used for the other part. In this article, the basic theory of timescale transformation is introduced firstly, and then the new line model is deduced in detail. Finally, a simple system is simulated by the new and traditional model, respectively, and the validity of this approach is verified by comparing with the traditional EMTP simulation. Furthermore, due to the large-step simulation, the calculation speed is improved. [ABSTRACT FROM AUTHOR]

The increasing interdependence between electric power and natural‐gas systems requires integrated simulation tools applicable to the coupled system. Therefore, this study proposes steady‐state and transient simulation tools for electricity‐gas integrated energy systems (IESs) by using convex optimisation. Steady‐state IES simulation is designed for long‐term planning studies while transient IES simulation, which includes line‐pack storage, is designed for real‐time operational research. The proposed convex steady‐state gas flow model introduces binary variables to represent gas flow directions, and employs the second‐order cone (SOC) to relax non‐convex pipeline gas flow equations. As a result, steady‐state gas flow analysis is formulated as a mixed integer SOC programming problem. The proposed transient gas flow model employs the implicit finite difference method to transform partial differential equations into algebraic difference equations. Moreover, the short‐term gas flow directions are specified and SOC relaxations are used. Simulation results on an integrated IEEE 24‐node system and Belgian 20‐node gas system verify the effectiveness of the proposed SOC models. The impacts of wind power forecast errors on multi‐period gas network operations are also investigated. [ABSTRACT FROM AUTHOR]

EMI modeling of power converters is crucial to develop EMI attenuation solutions. Recently, more and more modeling and mathematical analysis of electromagnetic interference (EMI) sources and propagation path had allowed a better understanding of EMI generation mechanism. Calculation times and accuracy determine the efficiency of EMI models in the studied circuit frequency range. In this paper, a priori model (circuit-based model) for predicting the spectra of conducted interferences in a DC/DC converter was developed in the scope of reducing calculation times of temporal simulations. The proposed new approach for high-frequency disturbance estimation is based on the knowledge of circuit parasitic elements and semiconductor devices parameters. A good tradeoff between simulation time and accuracy was registered; this is considered as an interesting step for power converters design. [ABSTRACT FROM AUTHOR]

Traditionally, extra high voltage (EHV) transmission systems consist exclusively of overhead lines (OHL) but in the recent years the utilization of high voltage AC (HVAC) power cables is increasing due to environmental, political and operational aspects. To study the impact of HVAC power cables on temporary overvoltages and slow front transients, a simulation model of the large-scale network is required. Guidelines concerning the modeling detail for the surrounding network need to be established to ensure sufficient accurate results. Existing guidelines for purely OHL transmission networks may not be adequate since the integration of HVAC power cables shift the harmonic impedance of the network to lower frequencies and that can affect the extent of the needed simulation model. Much effort can be saved from obtaining detailed data for an extensive but proper model, but a less detailed model might not describe the network behavior with sufficient accuracy. In this study, simplification options are considered, for which the time to construct and analyze a simulation model can be reduced. The simplification options are compared with the reference model (full detail), and judged based on three indicators for the level of accuracy: frequency and amplitude of the main resonance, and maximum over-voltage. As a result, guidelines on the extent of the simulated network and in which detail the model has to be built are proposed. The inverse approach, i.e. increasing level of detail until simulation results hardly change leads to similar results, but requires equivalent short-circuit networks for the rest of the grid. The method is tested for the Dutch 380 kV grid where an underground cable connection of 10.8 km length is introduced in 2013 and a second connection is planned for 2017. [ABSTRACT FROM AUTHOR]

This paper proposes a new approach for power system transient stability simulation, which is based on a semi-analytical solution (SAS) of power system differential-algebraic equations. In this paper, an SAS is derived using the Adomian decomposition method as a closed-form explicit function of symbolic variables such as time, the initial state, and other variables on system conditions and; hence, it can directly give a power system's dynamic trajectory being accurate for a certain time window. Unlike a traditional numerical integration based simulation approach, the proposed new approach offline derives an SAS and online evaluates the SAS by plugging in values of symbolic variables for a series of time windows making up the desired simulation period. This paper further studies the maximum length of the time window for an SAS being accurate and proposes a divergence indicator for simulation using adaptive time windows. Implementation of this new approach on parallel computers is also studied. The new approach is validated through contingency simulation of the IEEE 10-generator 39-bus system with detailed generator models. [ABSTRACT FROM AUTHOR]

In a multiterminal HVDC network, dc circuit breakers (CBs) are required at each end of a line to selectively isolate a fault. Several CB concepts have been implemented in PSCAD, which differ significantly in their structure and performance. This paper describes the interaction of the different HVDC CB topologies with a meshed four-terminal network and assesses their performance in terms of maximum currents and voltages. The tradeoff between network parameters and CB requirements is analyzed. [ABSTRACT FROM PUBLISHER]

HVDC short-circuit calculation standards will be required to simplify the dimensioning and selection of circuit breakers (CBs) in future HVDC networks. This paper proposes new analytical formulas for the calculation of the ac-side contribution through the blocked half-bridge-based converters during pole-to-ground faults in multiterminal HVDC cable networks. Analytic approximations are derived for the steady-state short-circuit currents and the peak of the transient response for point-to-point HVDC links and extended to multiterminal HVDC cable networks with arbitrary grid topology. The results of the proposed expressions are compared with simulations in PSCAD and provide accurate calculations for the transient peak and steady-state values of the ac-side fault current contribution to the prospective CB current. [ABSTRACT FROM PUBLISHER]

With the increasing penetration of distributed generation, distribution networks are evolving from passive to active. New transient simulation methods are required to study the detailed dynamic characteristics of large‐scale active distribution networks. A model order reduction method based on Krylov subspace theory is introduced in this study to reduce the overall model scale of active distribution networks for transient simulations. A modified state‐space model of linear distribution networks is developed to replace the conventional models for improvement in model reduction efficiency, while guaranteeing the passivity and stability of the reduced models. The proposed model order reduction method is validated with the IEEE 123‐node test network. The results prove that the proposed method is effective for different applications to improve the simulation efficiency of large‐scale active distribution networks. [ABSTRACT FROM AUTHOR]

This paper studies the average value modelling (AVM) of medium frequency (200 Hz–2000 Hz) dc–dc converters, which are becoming increasingly important in high-power dc grids and distributing microgrids. The most convenient modelling is based on transfer function and power components which are available in common simulation platforms, such as PSCAD/EMTDC. However, these models are found to require very small simulation steps and the achieved time-domain accuracy is not satisfactory for medium frequency converters. The core issue of accuracy loss is identified and corresponding improvement is proposed. User written state-space models in the abc frame and the dq frame are analyzed in depth. Different solvers, including the Dommel's method, the Heun's method, and the Runge-Kutta method were adopted and compared in solving the state-space models. A high-power 2-kHz LCL dc-dc converter is taken as the test system. It is found that the AVM in the dq rotating frame based on the Runge-Kutta solver is able to generate very accurate time-domain responses compared to the detailed switching model with almost 100 times improvement in simulation speed. It is demonstrated that a dc-dc converter with 2-kHz inner ac circuit frequency can be accurately simulated at a 50-\mus time step. [ABSTRACT FROM PUBLISHER]

Abstract: The present work shows how a new genre of problem solution techniques called compressive sensing (CI) can be utilized for solving power quality problems. Specifically speaking, this work undertakes the power system transient recognition problem and solves it using sparse representation based classification (SRC) technique, a popular, recently emerging technique in CI. The method employs SRC based classification in combination with a feature extraction procedure, carried out using dual tree complex wavelet transform (DTCWT). The proposed method uses statistical characteristics to extract features from the DTCWT coefficients obtained from each signal and then these extracted features are used as input arrays for the SRC based classifier. The PQ disturbance events considered in this work include four different transient conditions, namely, transients due to capacitor switching, transformer inrush currents, transients due to motor switching and transients due to short circuit faults. The proposed algorithm could achieve perfect classification accuracy of the order of 100% and could comfortably outperform several similar contemporary methods known for identical power system transient classification problems. [Copyright &y& Elsevier]

Electromagnetic Transients Program (EMTP) is widely used in power system dynamics studies. However, in most cases EMTP is found inadequate for dealing with the realistic size power systems due to the small time step resulting in relatively slow simulation speeds. To accelerate the EMTP simulations of power system dynamics, a novel frequency-adaptive methodology is proposed. In this method, a new transformation is presented. The properties of the transformation and the numerical solutions based on the transformation are discussed. The component models obtained by discretizing the differential equations at the branch level are also given which are convenient for EMTP implementation. The proposed method allows using large time steps without sacrificing accuracy, which greatly improves the simulation speed. To validate the proposed methodology, a general program has been developed. Furthermore, various case studies substantiate the claims and demonstrate the application of the method. [ABSTRACT FROM PUBLISHER]

This paper is the first of a series of publications detailing the development of an AI-based adaptive autoreclosing (AA) algorithm. In part 1, a detailed model of the Scottish 132 kV network has been constructed on a real-time digital simulator. The system model is discussed, including the network topology, line and source modeling, and the doubly fed induction generator-based wind farm model. An initial investigation on the penetration of harmonics from local wind farms is conducted using short circuit faults on two transmission lines in the network. This is necessary to ascertain to what extent wind farms may interfere with the AA scheme. Along with validating the model, the results suggest that penetration of harmonics is only significant on lines adjacent to the wind farms. [ABSTRACT FROM AUTHOR]

This paper studies real-time estimation of stability margin of a power system under disturbances by continuous measurement data. The paper presents a ball-on-concave-surface (BOCS) mechanics system as a power system's adaptive equivalent representing its real-time status and the stability region about a monitored variable. The parameters of the equivalent are adaptive to the operating condition and can online be identified from the phase-plane trajectories of the monitored variable. Accordingly, the stability margin and risk of instability can be estimated. Case studies on a two-generator system and a 179-bus system show that the BOCS system can be applied either locally or for wide-area stability monitoring in real-time calculation of stability margin. This paper proposes a new idea for using real-time measurements to develop and identify a power system's adaptive equivalent as a basis for online prediction of instability. [ABSTRACT FROM PUBLISHER]

In this paper, the authors present a method to synthesize a power autotransformer model that takes into account high-frequency effects. The proposed procedure implements data usually available for this kind of transformer: the results of lightning electromagnetic pulse tests generally carried out on these machines in accordance with standard prescriptions. Furthermore, it makes use of a well-established model synthesis technique, namely, the fast relaxed vector fitting. A simple application example, involving lightning overvoltage effects, is also described in order to compare model behavior with simplified approaches. [ABSTRACT FROM AUTHOR]

Modeling and analysis of power and power-electronic systems' transients using digital programs enables testing new design concepts in modern electric grid and many industrial and commercial products and applications. This paper gives an overview of dynamic average-value modeling techniques for representing static switching converters for the system-level studies. Concepts and desirable properties of averaged models for conducting large-signal time-domain transient studies and small-signal frequency-domain analysis for control design tasks are discussed. Basic approaches for developing average models for dc/dc and dc/ac converters are briefly reviewed and summarized. Finally, the desirable properties of the average-value models are demonstrated through an example system. [ABSTRACT FROM PUBLISHER]

Abstract: An installed 900kW fixed speed stall controlled soft-started wind turbine connected to a weak distribution grid was modeled under start-up conditions. Generator and soft-start control and design parameters were not available, so a modeling process independent of this information was developed. Field measured transients were closely reproduced in simulation using a full-order generator model with generic parameters and a thyristor-based graduated interconnection to the grid. A Static VAR Compensator model was then added to the wind turbine model to explore a method of reducing start-up transients. It was found that for the specific transients modeled, a 300kVAR SVC supplied sufficient reactive power to limit line voltage variations to within 3% of steady state values. Model details and simulation output are presented in this paper. [Copyright &y& Elsevier]

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]

Abstract: Simulators of the Electromagnetic Transients Program (EMTP) type are widely used for the study of high-frequency transients in power electric systems. For the study of electromechanical transients, where the main interest is to focus only on deviations from the ac waveform, the EMTP approach is not efficient. In this paper, a branch companion model that is suitable for both electromagnetic and electromechanical transients simulation is proposed. It processes analytic signals whose Fourier spectrum can be shifted in accordance with the objective of the study. The proposed method opens the way for a unified description of electromagnetic and electromechanical transients simulation. [Copyright &y& Elsevier]

This article presents a theoretical simulation and analysis of all possible factors due to transient overvoltages (TOVs) that could contribute to electrical failures of electric submersible pump (ESP) motors used in oil fields. A transient calculations software package PSCAD is used to simulate a single cable-fed, 3.3-kV induction motor including the mains of the 33-kV distribution system. The factors studied are cable length, earthing resistance and parameters (insulation permittivity and permeability), opening time of CB and its location, switching via pre-insertion resistance, characteristics of the TVSS and its internal structure, and transformer connections and ratings [ABSTRACT FROM PUBLISHER]

The U.S. Navy is looking for methods to maximize the survivability of combat ships during battle conditions. A shipboard power distribution system is a stiff isolated power system that is vulnerable to voltage sags, which arise due to faults or pulsed loads, which can cause interruptions of critical loads. A series voltage injection type flywheel energy storage system (FESS) is used to mitigate voltage sags and maximize the survivability of the ship. The basic circuit consists of an energy storage system, power electronic interface, and a series injection transformer. In this case, the energy storage system consists of a flywheel coupled to an induction machine. The stored energy is used for sag correction for the critical load. Indirect field-oriented control (IDFOC) with space-vector pulsewidth modulation (SVPWM) is used to control the induction machine. Sinusoidal PWM is used for controlling the power system side converter. This paper presents the modeling, simulation, and analysis of a FESS with a power converter interface using PSCADIEMTDC. [ABSTRACT FROM AUTHOR]

In this paper, two methods for analyzing nonuniform multiconductor transmission lines in the frequency domain are considered. The first one is based on the cascaded connection of chain matrices of uniform line segments. In the second method, a space-variant linear system is solved. Besides, a technique to introduce the effect of incident electromagnetic fields into the nonuniform line model is presented. To obtain the solution in the time domain, the numerical laplace transform (NLT) is applied. Several application examples are analyzed, and comparisons with the ATPIEMTP and with experimental measurements published elsewhere are provided. [ABSTRACT FROM AUTHOR]

Power system simulation involves a wide range of timeframes, starting at microseconds when simulating fast electromagnetic transients and extending to several years in system planning studies. The same system may have to be modeled and solved in many different ways, depending upon the studied event of interest. It has been desirable to have a single software platform from which several power system analysis functions can be easily activated for the same power system. The network under study may go through changes due to switching events, outages of equipment, generators, or loads. Such changes should be recorded only once and recognized by all applications running under this platform. Each application should have easy access to the results produced by any other application. This allows modular development, updating, or replacement of various applications independent of each other. Power Education Toolbox (PET) is such a software package and has been under development at Texas A&M University for several years. The GUI of PET allows users to create one-line diagrams of systems, specify components and simulation parameters, and view output [ABSTRACT FROM PUBLISHER]