Electromagnetic Transient Simulation Program Research Articles

Electromagnetic Transients Simulation Program: A unified simulation environment for power system engineers

Electromagnetic Transients Simulation Program: A unified simulation environment for power system engineers

An improved high-accuracy interpolation method for switching devices in EMT simulation programs

This paper presents an interpolation with Backward Euler (BE) method that enhances the switching simulations accuracy in an electromagnetic transient (EMT) simulation with a fixed time-step. Because of the switching operations on discrete instants, the simulations can show artificial voltage spikes and numerical oscillations (chatter), compromising the accuracy and producing misleading results. We thus present a method that eliminates the spurious switching losses and improves the accuracy by combining interpolation and extrapolation with a half-time-step BE solution over existing interpolation-based approaches to resolve the issues above. In addition, this improved method requires the same calculation steps as the industry-accepted instantaneous interpolation. Analytical discussion reinforced by the simulation studies for a simple and complex power electronic circuits demonstrates the accuracy and efficacy of the proposed interpolation with BE method.

Measurement of switching transient overvoltages with a capacitive electric field sensor

This paper presents a case study of measurements of switching transient overvoltages using a capacitive electric field sensor. The system was developed and installed in a substation after the failure of a surge arrester during the energization of a 420 kV transmission line. First, the closing operation was simulated in an electromagnetic transient simulation program to estimate the switching transient overvoltages for this event. Then, the concept and design of the measurement system are explained. The system calibration performed in the high-voltage laboratory is presented. Afterward, the installation of the measurement system in the substation is discussed, with a special focus on the calibration of the voltage ratio considering the physical configuration where it is installed. Finally, the measurement results are presented and compared with simulations. The results show that the transient overvoltages caused by the energization of the transmission line should not cause the failure of the surge arrester. The measurement system has been demonstrated to be capable of measuring switching transient voltages of a 420 kV transmission line and can be considered a flexible solution for the long-term monitoring of transient overvoltages in substations.

Research on over-voltage characteristics of ultra high-voltage direct current transmission system

Load dumping overvoltage has a significant effect on insulation coordination of direct current (DC) transmission system. Based on the PSCAD/EMTDC electromagnetic transient simulation programs, this paper has built the electromagnetic transient calculation model of ultra high-voltage direct current (UHVDC) transmission system. Respectively, we have done comparative research on the overvoltage during load dumping under three rated-load operations, which are the bipolar operation with ground return, unipolar operation with metal return, unipolar operation with ground return, concluding that alternating current (AC) load dumping on the inverter side under these three operations can result in overvoltage no less than 50% on the DC polar line, DC valve top, as well as both ends of the converter transformer valve and the upper six pulses bridge also produce a large overvoltage. Besides, we observed a similar overvoltage level between unipolar ground return operation and unipolar metal return operation. These conclusions can provide suggestions for insulation coordination in various operations.

Neutral Reactor Structures for Improved Single Phase Auto Reclosing in Multi-Circuit Multi-Voltage Transmission Lines

In this paper, novel neutral reactor structures are proposed to mitigate the secondary arc current (SAC) in non-conventional Multi-circuit Multi-voltage Transmission lines (MCMVTLs). The parameters of the reactors in the structure are optimized using the Non-dominated Sorting Genetic Algorithm II (NSGA-II). The optimization algorithm, coded in Python, regulates the multiple runs of an Electromagnetic Transients (EMT) simulation program to minimize the secondary arc current. The optimization trials are run in parallel on a 64 core computer to minimize the solution time. A detailed arc model was tested on the EMT program (PSCAD). Using this model and optimized parameters in the proposed neutral reactor schemes, the SAC is indeed extinguished in acceptable times. The SAC and TRV for neutral reactors with optimized parameters are up-to 68 and 77%, respectively, lower than the ones with parameters calculated by the conventional approach which ignores inter-circuit coupling. Meanwhile, the extinction times are up-to 46% faster. As a result, single-phase auto-reclosing in MCMVTLs is viable.

Analysis of Induced Voltage on Pipeline Located Close to Parallel Distribution System

Gas and oil pipelines are widely used to supply customers. They are often laid in parallel with high voltage power lines, sharing right of way. When the pipeline is located near overhead high-voltage power, corrosion caused by induced voltages from AC power lines can occur in utility pipelines. Therefore, the calculation of induced voltage is always required for both interference and maintenance workers as well as pipeline facility safety. For parallel distribution lines, the calculation method for the induced voltage is not suitable due to the excessive error caused by using the screening factors of the neutral current. For a more practical analysis of the induced voltage, a new analysis is needed using the actual neutral current and which also considers the overhead ground conductor and the neutral conductor. This paper analyzed the induced voltage from a parallel distribution system using Carson’s formula and vector analysis. Simulation analysis results are verified by separate Electromagnetic Transient Program (EMTP) simulation.

Average-Value Modeling of Line-Commutated AC–DC Converters With Unbalanced AC Network

AC–DC line-commutated converters (LCCs) are widely utilized in existing and emerging ac–dc power systems. Analysis of such systems under balanced and unbalanced conditions is often carried out using electromagnetic transient (EMT) simulation programs. Therein, the detailed switching models of LCCs are often the computational bottlenecks for system-level studies. Recently, the parametric average-value models (PAVMs) have been developed to achieve fast and efficient simulations of switching converters. In this paper, the PAVM methodology is extended to consider operation of LCCs under unbalanced conditions in the ac network. This is done in the extended PAVM by formulating the ac-side harmonics in positive and negative sequences as well as the dc-side harmonics (i.e., ripples) with respect to the ac network imbalance. The new PAVM is validated experimentally and by simulations, and is demonstrated to be accurate in reconstructing the ac and dc waveforms under unbalanced conditions in the ac network. Meanwhile, the proposed PAVM is computationally much faster than its detailed switching model counterpart.

Simulation study on power system short circuit fault based on EMTP

Electromagnetic transient simulation program EMTP is a common simulation commercial software in power system. It can effectively analyze and study power system. In this paper, EMTP is used to build the power system simulation model, and a variety of short-circuit faults in the power system are simulated and analyzed. The results show that the results accord with the actual theory, and the waveform can accurately and intuitively investigate the dynamic characteristics of power system faults. In addition, through the simulation comparison and analysis between different faults, it can be seen that the three-phase short-circuit fault is the most serious fault in the power system, which should be avoided in the actual production and life. This shows that EMTP is a powerful tool for power system simulation research, and provides a reference for the actual equipment selection requirements of the project.

Transient Performance Analysis of Reactive Power Compensators at LCC-HVDC Station Feeding Weak AC System

This paper focuses on analyzing the dynamic performance of various reactive power compensators at weak LCC-HVDC terminals. Four scenarios based on combination of active and passive reactive power compensation schemes are presented. The comparative performance analysis of various compensators in different types of AC and DC system faults are evaluated using electromagnetic transient simulation program PSCAD/EMTDC. The analysis shows that fixed capacitor has poor performance and results in reducing effective short circuit ratio of system, while STATCOM on the other hand, increases AC system strength and has significant performance in areas like immunity to commutation failure, suppression of temporary overvoltage, AC bus voltage regulation and fault recovery time.

Performance analysis of a transient-based earth fault protection system for unearthed and compensated radial distribution networks

This paper deals with the protection against earth faults in distribution networks with unearthed or compensated neutral. A transient-based protection system is proposed and assessed through electromagnetic transient program (EMTP) simulations. The fault detection algorithm is based on the estimation of the angle between the zero-sequence voltage and current phasors. The estimation is carried out at the dominant transient frequency of the network response within the first milliseconds after the fault. The implementation of an improved filter and a zero-padding process allows for the identification of high resistance faults with a relatively low sampling frequency. An operation zone is proposed and assessed, also for unbalanced or mixed bare and cable line networks. The performances of the protection system are evaluated for a distribution network in both the cases of unearthed and compensated neutral through a Monte Carlo method that considers the fault resistance, incidence angle and fault location variations as random variables in the EMTP simulations.

Analytical Approach for Fast Frequency Response Control of VSC HVDC

The importance of the auxiliary control of power electronic devices such as HVDC and FACTs is growing owing to the increase in the generation capacity of renewable energy sources. This paper presents a temporary frequency support strategy using the electrostatic energy in voltage-sourced converter-type high-voltage direct current systems. An analytical derivation for selecting the optimal droop constant to improve the frequency nadir was established. The optimal droop constant was derived via system frequency response analysis by using the support termination time. Furthermore, the optimality of the support was computed using numerical equations. Modified outer control loops were implemented in the master controller to utilize the proposed method in voltage-sourced converter control. The effect of the fast frequency support control strategy was verified via a time-domain electromagnetic transient program simulation based on case studies. To examine the practical applicability of the proposed strategy, the parameter robustness was investigated by performing deviated system parameter simulations. The results validated the proposed strategy.

Enhanced Efficient EMT-Type Model of the MMCs Based on Arm Equivalence

The large number of switching elements in modular multilevel converters (MMCs) contribute a tremendous computational burden for electromagnetic transient (EMT) simulation programs. Detailed equivalent models (DEMs) and average value model (AVMs) are currently two major types of accurate and efficient model. However, the DEMs are still computationally inefficient for the simulation scenarios in large-scale MMC based high-voltage direct current (MMC-HVDC) grids, as the models represent all submodule (SMs) switching events, and memorize all individual capacitor voltages. Though the AVMs provide a faster simulation speed by using a single equivalent capacitor on the DC side, they have a relatively low simulation accuracy compared to DEMs, especially under blocked mode. This paper proposes an enhanced computationally efficient model based on arm equivalence (AEM), which can accurately represent the dynamic behaviors in both de-blocked and blocked modes. Compared to the DEMs, the proposed AEM is more efficient, with no loss of accuracy, and the simulation speed is irrespective of the SM number. The accuracy and computational efficiency of the proposed model were validated against the DEM and AVM through several simulation scenarios in a two-terminal MMC-HVDC system on the power systems computer aided design/ electromagnetic transient in DC system (PSCAD/EMTDC) program.

EMT Simulation of Very-Fast Transients in Gas-Insulated Substations Using Modified Carson's Formula

This article proposes modified formulas of Carson's and approximate earth-return impedances for overhead lines which can deal with high-frequency displacement currents. The calculated results by the proposed methodology are compared with those calculated by accurate formulas, and a satisfactory accuracy of the proposed methodology is confirmed. The proposed formulas are applied to very-fast transients (VFTs) in a gas-insulated substation, and it is made clear that the proposed formulas with the earth-return admittance cause no numerical instability of electro-magnetic transient (EMT) program simulation, while the original Carson's formula and its approximate one implemented in existing EMT-type programs result in the numerical instability. EMT simulation of VFTs can be easily performed using the proposed simple formulas with the earth-return admittance.

Application of Principal Component Analysis for Fault Classification in Transmission Line with Ratio-Based Method and Probabilistic Neural Network: A Comparative Analysis

The proposed work illustrates a simple research approach to identify the type of fault in a three-phase overhead single-end-fed long transmission line. Multivariate statistical methods like principal component analysis (PCA) alone, and in combination with probabilistic neural network (PNN), have been applied here to classify fault. An attempt has been made to use the PCA features obtained from the analysis of electrical parameters for each of the faults, in two ways. The first approach of fault classification is based on analyzing the PCA features by a modified ratio-based analysis. In the second method, an attempt has been made to use the PCA features directly to a structured PNN model. Electromagnetic Transient Program simulation software has been used to simulate a transmission line model. Sending-end three-phase line currents corresponding to various faults carried out at different geometric distances along the transmission line have been analyzed in MATLAB environment. The proposed algorithms are tested with unknown and intermediate distant faults with variable fault resistance to validate the same. Finally, a comparative analysis of the proposed two methods is illustrated, which shows 100% classifier accuracy of both the models.

Cause identification of electromagnetic transient events using spatiotemporal feature learning

This paper presents a spatiotemporal feature learning method for cause identification of electromagnetic transient events in power grids. The proposed method is formulated based on the availability of time-synchronized high-frequency measurements and using the convolutional neural network as the spatiotemporal feature representation along with softmax function for the classification. Despite the existing threshold-based, or energy-based events analysis methods, such as support vector machine autoencoder, and tapered multi-layer perceptron neural network, the proposed feature learning is carried out with respect to both time and space. The effectiveness of the proposed feature learning and the subsequent cause identification is validated through the Electromagnetic Transients Program (EMTP) simulation of different events such as line energization, capacitor bank energization, lightning, fault, and high-impedance fault in the IEEE 30-bus, and the real-time digital simulation of the WesternSystemCoordinating Council (WSCC) 9-bus system.

Development of a Voltage-Dependent Line Model to Represent the Corona Effect in Electromagnetic Transient Program

This paper describes a new method to represent single-phase overhead transmission lines (TL) under corona effect in electromagnetic transient simulation program. Based on Bergeron model and the scheme proposed by Dommel to represent transmission lines in Electromagnetic Transients Programs (EMT), a voltage-dependent line model (VDLM) was developed. This model can be represented through of an equivalent impedance network and easily combined with other components of the electric power system. To solve the nodal equations of the network a simple technique is proposed, which is suitable to calculate lightning overvoltages transients and avoids the necessity of iterative methods, increasing the efficiency of the algorithm. The proposed method was implemented in Matlab software, and the simulation's results were compared with field measurements to verify the accuracy of the model. Comparisons were also made with the traditional linear Corona Model. A good agreement could be observed between them.

Hybrid Parametric Average-Value/Detailed Modeling of Line-Commutated Rectifiers

Simulations and analysis of power-electronic-based systems are conventionally done using detailed switching models of power-electronic converters that are available in many electromagnetic transient (EMT) simulation programs. Although being accurate, such detailed models typically require small time-steps for accurate detection and handling of switching events, which makes them computationally expensive. Recently, a parametric average-value modeling (PAVM) approach has been developed for system-level modeling and fast simulations of line-commutated rectifiers (LCRs) including several selected ac harmonics. In this paper, a new hybrid parametric methodology is presented, which has the capability of operating at large time-steps while including the details of the ac- and dc-side variables similar to the detailed switching models (but without the need for locating switching events, i.e., zero crossings), or operating as an average-value model. Extensive simulation studies demonstrate advantageous numerical efficiency and accuracy of the proposed hybrid parametric AVM/detailed model compared to the previous PAVMs as well as the detailed switching models of LCRs when using large time-steps for system-level studies.

Dynamic Modeling of Sequential Service Restoration in Islanded Single Master Microgrids

This paper presents a methodology for generating restoration sequences in distribution systems and microgrids with emphasis on deriving optimal switching times for remote control switches. Microgrid architecture considered are assumed to be operating in islanded single master mode. Control methods for handling the unbalance inherent in distribution systems using single-phase controlled PQ inverters were developed and incorporated in the proposed method. The problem of considering simultaneously both energy optimization and dynamic stability of the system, which is lacking in existing methods, was addressed by studying the transient behavior of microgrids based on extended electromagnetic transients program (EMTP) simulations and then approximate and incorporate these behaviors into the optimization formulation for restoration. The approach is based on multi-objective optimization of final restored load and total restoration time. The methodology was studied on a modified IEEE 123 node test feeder. An EMTP simulation in PSCAD of the formed microgrids was used to validate the accuracy of the dynamic and steady-state characteristics of the resulting systems. By considering the transient behavior of distributed generators (DGs) during restoration, a better restoration sequence that does not trigger protection relays could be realized.

Electromagnetic Transient Analysis of 500 kV XLPE Submarine Cable Interconnection Project from Zhenhai to Zhoushan

In Zhenhai-Zhoushan transmission project, 500kV XLPE submarine cable lines are used for the first time in the world. Using electromagnetic transient simulation program(EMTP), electromagnetic transient problems in this project are investigated including electrical parameter of submarine cable lines, power frequency overvoltages, secondary-arc currents and recovery voltages during the single-phase reclosing, power frequency resonance overvoltages, induced voltages and induced currents, switching surges and so on. On the basis, the recommended configuration scheme of HV shunt reactors and neutral reactors is proposed. In addition, it is suggested to install closing resistors of 400ohm on both sides of line breakers in order to restrict switching overvoltages and ensure safe operation of submarine cable lines.

Time-Domain Implementation of Damping Factor White-Box Transformer Model for Inclusion in EMT Simulation Programs

White-box detailed transformer models are used by manufacturers for predicting internal overvoltages in transformer windings during the lightning impulse test. One such model is the d -factor model, which is based on a lumped-parameter description based on winding discretization with the inclusion of losses via an empirical, frequency-dependent damping factor. This paper shows a procedure for direct inclusion of the d -factor model in electromagnetic transients simulation programs for use in general studies of network overvoltages. Proper utilization of the model's diagonal structure is utilized in combination with real-valued arithmetic for maximum speed in transient simulations, with optional initialization from sinusoidal steady-state conditions. The model can be used both as a terminal equivalent and for calculation of internal voltages with use of an augmented input data set. The method is demonstrated for a single-phase three-winding transformer that is applied in a simulation study of transient resonant voltage buildup in the tertiary winding.