Power System Transients Research Articles

Over current protection of distribution system with impact of solar and wind generation using DIgSIlent power factory

The utilization of renewable resources has been growing very fast worldwide recently to manage the increasing energy gap, but it also raises some challenges like protection issues, transient stability issues and security issues in the power system operation. Mainly, wind and solar photovoltaic renewable power generation sources are account for bulky renewable energy share. The transients in power systems including renewables are reduced and have recently attracted wide attention. The impact of renewables generation on power system transients should be effectively analyzed and evaluated to improve power system reliability, stability, operation and security. DIgSILENT Power Factory software is more powerful and useful for providing phasor of fundamental power frequency components better than other existing software’s; therefore, DIgSILENT Power Factory is proposed for modeling and analysis of the system.

Computation of Lightning-Induced Voltages Considering Ground Impedance of Multi-Conductor Line for Lossy Dispersive Soil

Soil conductivity and permittivity have a substantial influence on lightning-electromagnetic transients in power system. In this paper, lightning-induced voltages are computed on a multi-conductor overhead line due to nearby first and subsequent return strokes. Besides, this study considers the longitudinal complex inductance of the line due to the penetration depth of electromagnetic fields through finitely conducting ground as well as the frequency dependent soil parameters using the finite-difference time-domain method. Various case studies in light of variations of return stroke velocity, line height, and soil conductivity are explored for thoughtful investigations. The obtained results reveal that the influence of this complex inductance on peak values of lightning induced voltages changes with varying the return stroke velocity. Also, the frequency dependence of soil parameters markedly impacts the computed lightning-induced voltages particularly for poor soil conductivity.

Evaluation of time-domain and phasor-domain methods for power system transients

The computational process of both time-domain and phasor-domain algorithms is evaluated in this work. The following methods are used: circuit-based time-domain (TD), dynamic phasors (DP), three-phase phasor-domain (3pPD), and classic positive sequence phasor-domain (PD). The IEEE-118 benchmark is used to test all solution approaches implemented on the same computational platform. Furthermore, the advantages and differences in modeling methodologies are examined for the IEEE-118 benchmark. The experiments demonstrate important new facts on phasor-domain methods and, more specifically, on dynamic-phasors compared to TD algorithms.

Tower Models for Power Systems Transients: A Review

Fast-front transients play an important role in the insulation design of any power system. When a stroke hits the shield wire or the tower of high-voltage overhead power lines, flashover may occur either along the span or across tower insulators, depending on the relevant voltages and insulation strength. As a result, backflashover may take place from the tower structure to the phase conductor whenever a huge impulse current flows along the tower towards considerably high footing impedances. For these reasons, tower modeling for transients studies is an important step in the insulation design, and also for lower voltage applications, where indirect lightning effects may play a predominant role. However, after decades of research on tower modeling, starting from the 1930s with the first model proposed by Jordan, no consensus has been reached neither on a widely accepted tower model nor on the quantitative effect of the tower models on insulation design. Moreover, the fundamental mechanisms at the base of the transient response of towers and the definition of some fundamental parameters have not been totally clarified yet. The aim of this review is to present the available tower models developed through the years in the power community, focussing mainly on lumped/distributed circuit models, and to help the reader to obtain a deeper understanding of them.

On the Choice of Methods for Numerically Integrating the Equations of Transients in Electric Power Systems

Algorithms for solving the system of differential-algebraic equations describing electromechanical transients in electric power systems are considered along with matters concerned with ensuring the reliability and required accuracy of the solution results. Classical explicit methods, methods for implicit numerical integration and simultaneous solution of differential-algebraic systems of equations are used to model dynamic processes in power systems. On the basis of the methods used, difference models of electric power system components are obtained. The equations of transients in electric power systems are written in a homogeneous coordinate basis with the use of nodal voltage equations. A comparative analysis of algorithms based on the explicit Runge-Kutta method and implicit methods of Euler, trapezoids, Euler with fitting coefficients is carried out. The analysis results have shown that in terms of stability and accuracy, the trapezoid method has the greatest advantages, which is not inferior to the 4th order Runge-Kutta method and allows calculations with a large integration step to be carried out. The effectiveness of the combined method is shown, in which the Euler method with fitting is used to solve the differential equations describing electromagnetic processes, and the trapezoid method is used to solve the equations of electromechanical motion.

Inclusion of Neutral Points in Measurement-Based Frequency-Dependent Transformer Model

Measurement-based wide-band black-box transformer models are well suited for simulation studies of high-frequency transients in power systems. The inclusion of neutral points in such models can be difficult when the model is required to simulate voltage transfer to windings with high-impedance loads. The difficulty arises because it is then necessary to include the small winding capacitive currents in the measurement and model extraction procedure, while at the same time the capacitances can be asymmetrical with respect to the winding ends. This paper introduces a new measurement procedure which can accurately capture the effect of such capacitive asymmetries. The procedure is demonstrated for a wye-wye connected transformer. The measurement and subsequent passive rational modeling results in two alternative models. The first is a four-terminal model with bonded high-voltage and low-voltage terminals, suitable for simulation of lightning overvoltages in distribution systems. The second is a full eight-terminal model, suitable for general purpose transient studies.

Mitigation of Power System Transients in a Multi- Machine System Using STATCOM

Abstract: The tremendous expansion of linked power systems as a result of rising electrical energy consumption has created a slew of problems. FACTS (Flexible Alternating Current Transmission System) controllers become crucial in these situations. This paper investigates the transient stability enhancement of IEEE 9 bus system using STATCOM. The damping power oscillations and power swings and setting time is observed with and without STATCOM. Keywords: PI controller Power, D-Q theory. Reactive and Active Power STACOM

Dynamic Equivalents in Power System Studies: A Review

In this paper, the available methods and procedures for creating equivalents for the analysis of electromagnetic transients in power systems are presented and discussed. General requirements of power system representation during simulation of electromagnetic transients are shown. The main available procedures are shown, along with an assessment of their advantages and disadvantages. Methods to search for the optimal replacement of structures in time and frequency domains are discussed. Optimization and direct methods in the frequency domain are presented. Each of these methods is discussed with respect to their possible use in determining the structure of the equivalent circuit for the study of electromagnetic phenomena. Methods to reduce a complex power system, as one of the approaches to determining the structure and parameters of the equivalent circuit, are also presented. Contraindications to the search for equivalents in the frequency domain to study electromagnetic transients are discussed. An analysis of methods for the identification of parameters of the equivalents is presented. The latest advances in the search for the structure and parameters of equivalents are presented, particularly the use of artificial neural networks in the process of replacing parts of systems. Finally, the analyses conducted in this study, together with recommendations regarding the choice of the procedure during the search for equivalents for the analysis of electromagnetic transient phenomena, are summarized.

An Enhanced Shunt Active Filter Based on Synchronverter Concept

This article proposes a shunt active filter (SAF) operating as a Synchronverter to enhance its performance, including the virtual inertia functionality. The SAF behaves as a voltage source with a low-impedance path for harmonic contents. Synchronverter behavior is used together with selective filtering through proportional-resonant controllers to provide selective harmonic filtering of the load current, selective harmonic blocking of the source current, and low-impedance path for nonselected harmonic contents from the load and the source currents. The virtual inertia functionality aims to contribute to frequency stability during power system transients. Besides filtering unbalanced and harmonic contents and compensating for reactive power, the SAF contributes to inertia response during frequency transients. A tuning design method is proposed to ensure stability and proper conditioning of the power-quality issues. The reduced quantity of parameters to be tuned is another advantage of the proposed controller. Simulation and experimental results validate the compensation performance of the SAF.

Электротепловые переходные процессы в сети с высокотемпературным сверхпроводящим трансформатором с функцией токоограничения

The results of a study of thermal and electromagnetic transients in an electric power system containing a high-temperature superconducting (HTS) transformer with a current limiting function are presented. For carrying out the research work, an experimental HTS transformer sample with windings made of Y1Bа2Cu3O7 superconductor and with liquid nitrogen at an operating temperature of 77 K serving as dielectric medium was developed. It has been demonstrated, taking the experimental sample as an example, that transformers with HTS windings can be used to limit short-circuit currents in electrical systems. By using the developed mathematical model of a three-phase single-machine network containing an HTS transformer, it became possible to perform an in-depth analysis of electromagnetic transients in the current limiting mode and to study the thermal and electrodynamic effects produced by the short-circuit current in varying the short-circuit fault kind (single-phase, two-phase and three-phase short-circuit faults) and the type of connected load (active, active-inductive, and active-capacitive) on the current limiting degree. It has been determined that significant heat flows arise at the current limitation moment, which also should be limited. A positive effect of HTS transformers on the electric power system operating modes is shown. The obtained results of theoretical and experimental studies of HTS transformers prove a high efficiency of their current limiting function.

Toward Model Reduction for Power System Transients With Physics-Informed PDE

This manuscript reports the first step towards building a robust and efficient model reduction methodology to capture transient dynamics in a transmission level electric power system. Such dynamics is normally modeled on seconds-to-tens-of-seconds time scales by the so-called swing equations, which are ordinary differential equations defined on a spatially discrete model of the power grid. Following Seymlyen (1974) and Thorpe, Seyler, and Phadke (1999), we suggest to map the swing equations onto a linear, inhomogeneous Partial Differential Equation (PDE) of parabolic type in two space and one time dimensions with time-independent coefficients and properly defined boundary conditions. We illustrate our method on the synchronous transmission grid of continental Europe. We show that, when properly coarse-grained, i.e., with the PDE coefficients and source terms extracted from a spatial convolution procedure of the respective discrete coefficients in the swing equations, the resulting PDE reproduces faithfully and efficiently the original swing dynamics. We finally discuss future extensions of this work, where the presented PDE-based modeling will initialize a physics-informed machine learning approach for real-time modeling, $n-1$ feasibility assessment and transient stability analysis of power systems.

Diagnosis of small-sample measured electromagnetic transients in power system using DRN-LSTM and data augmentation

Artificial intelligence has performed exceptionally on power systems, motivating its application in electromagnetic transient (EMT) diagnosis on smart grids. However, owing to the insufficient number of measured EMTs, existing models for EMT diagnosis tend to be built using simulated EMT data which are not distributed like measured EMT data, leading to degrading generalization performance of the models in industrial applications. This paper proposes a novel DRN-LSTM model applicable to a small-sample measured EMT dataset and data-augmentation methods that boost the generalization of the model. The DRN-LSTM model includes a deep residual network, long short-term memory, and a fully connected layer, and it can make an effective diagnosis on measured EMT data. Data-augmentation methods, namely random cropping and data consolidation, effectively enlarge the data volume of the small-sample dataset. Experimental comparisons show that the proposed DRN-LSTM model has better generalization than classical and state-of-the-art artificial-intelligence-based models on measured EMT data, after random cropping and data consolidation of the small-sample set. The proposed DRN-LSTM model and data-augmentation methods provide a competitive solution for the diagnosis of EMTs and other transients for which it is difficult to collect sufficient data.

An Effective Islanding Detection Method With Wavelet-Based Nuisance Tripping Suppressing

The reactive power control (RPC) technique is a hopeful solution for the islanding issue in distributed generation (DG). Existing RPC approaches have downsides of inhibiting the required load reactive power or injecting/drawing undesirable excessive reactive power into the utility during normal operation. To overcome these limitations, the positive sequence voltage of point common coupling (PCC) is included in the reference of reactive power, which helps the frequency to deviate rapidly outside its thresholds. Further, power system transients which considered normal events can drift the frequency and result in a false islanding detection. In this article, different operating conditions such as load switching, voltage variations, and faults are considered. To address this issue, the suggested strategy includes a second decision-making criterion based on the discrete wavelet transform of the subtraction of sensed and nominal positive sequences of the PCC voltage. Simulation and experimental findings show that the suggested islanding detection method detects islanding rapidly and with zero nondetection zone. Furthermore, the DG and load reactive powers are closely matched under normal operation, and nonislanding situations are successfully prevented.

Physical and mathematical modeling of transients in a synchronous generator utilizing synchronized phasor measurements

There have been quite a few attempts to compute synchronous generator parameters based on voltage and current synchrophasors taken under power system transients. However, we have not seen any publications with thorough analysis as to how soon the phasor measurement unit reacts to disturbance conditions, which components of the transient are filtered out and which are passed through, as well as what the total vector error is. The goal of this research is to determine all of these characteristics of a phasor measurement unit when playing back transient oscillograms for a stator short circuit obtained through mathematical modeling. The transient oscillograms have been derived via both a full Park-Gorev system of flux linkage equations as well as the MATLAB/Simulink Synchronous Machine block. Physical modeling was then conducted via a real-time digital simulator (RTDS) along with a dedicated phasor measurement unit ENIP-2 (PMU), and the stator current phasors were recorded. Our analysis has shown that both RTDS and ENIP-2 (PMU) almost entirely filter out the exponentially decaying DC component of the fault current while closely following the periodical signal envelope. The total vector error has been estimated to become below 1–2 % after around 0,02–0,03 s into the fault when selecting the “P” class filters according to IEEE C37.118. We have come to a conclusion that synchrophasor measurements under power system disturbances could be utilized for estimating the synchronous, transient, and subtransient generator parameters. The selected synchronous machine model in the form of flux linkage equations is correct, as the obtained transient oscillograms are exactly the same as those produced by Simulink. “P” class phasor measurements can be recommended for representing transients in the stator circuit of a synchronous generator. The results of this investigation are meant to be employed for synchronous machine parameter estimation based on phasors sourced from RTDS and, hopefully, from phasor measurement units installed at power plants.

Islanding detection method for distributed generation with wavelet based nuisance tripping suppression

This paper deals with modified reactive power control (RPC) for islanding detection. The RPC approach is an effective technique for detecting islanding in distributed generation (DG). However, existing RPC methods have limitations of injecting/drawing unnecessary reactive power into/from the grid. Furthermore, RPC methods may be affected by disturbances such as power system transients resulting in false islanding detection. This paper proposes a new controller’s reference reactive power based on the positive sequence voltage of the point of common coupling (PCC) and a reactive mismatch coefficient to overcome the aforementioned drawbacks. Furthermore, the Discrete Wavelet Transform (DWT) of the difference between the amplitude of actual and nominal PCC voltages is incorporated in the decision criteria. An entropy function based on DWT is defined to improve the reliability of the RPC method under disturbances. The proposed islanding detection method (IDM) is evaluated under various load and disturbance conditions to show its performance. Simulation and experimental finding indicate that the proposed IDM can detect islanding quickly and with a negligible Non-Detection Zone. Moreover, the DG and load reactive powers are nearby matched during the normal operation, and non-islanding events are effectively prevented.

Induction Machine Modeling Considering Magnetizing Flux Saturation With Air-Gap Harmonics

Accurate and computationally-efficient models of induction machines (IMs) are essential for many simulation programs and analysis of power systems transients. Conventionally, when modeling magnetic saturation in the classical qd models, only the fundamental component of magnetizing flux is considered. To represent the saturation air-gap flux harmonics, fairly complicated phase-domain and/or implicit models have been proposed in the prior literature. In this paper, a new explicit two-axis IM model is developed to include the air-gap harmonics caused by magnetic saturation. The new model is validated by experimental measurements and simulations in various steady state and transient scenarios, and is shown to provide accurate results while being simple to implement.

Parallel computation of power system EMTs through Polyphase-QMF filter banks

The analysis of electromagnetic transients in power systems often requires intensive computations. Various methods have been proposed to reduce execution times and computational costs. A new technique is proposed here in which the system model is synthesized in the Laplace domain and is simulated in the time domain through long convolutions. The nodal matrix of the system under analysis is reduced by Kron's method to leave only the nodes related to observations and to changes in explicit form. State vectors derived from the reduced matrix are convolved with auxiliary signals to simulate transient events and the convolutions are performed in parallel by an algorithm based on polyphase QMF filter-banks. The proposed technique is applied in the simulation of a transient on a 17-bus network. The obtained results are compared with those from PSCAD / EMTDC and from the conventional Laplace Transform. Finally, the suitability of this technique for parallel processing is demonstrated by a basic implementation on an FPGA.

Analysis of gray Box Modelling of Transformers,

Calculation of power system transients involving transformers require models that incorporate capacitive behavior. The paper outlines how classical low-frequency transformer models can be extended with capacitances and how to fit the parameters based on typical values, test report and frequency response measurements. Justified tuning factors are proposed. The responses of the models are compared to measurements in frequency domain, and with detailed black-box models in studies of transient recovery voltage and lightning. The models show reasonable agreement including the first resonance point, but with too low damping without proper adjustments.

Improving Numerical Accuracy in Time-Domain Simulation for Power Electronics Circuits

In time-domain simulations of power system transients, trapezoidal integration with fixed step-size is the most common method due to its accuracy and ease of implementation. Discontinuities occurring within fixed time-step when simulating power electronics circuits, may cause numerical oscillations and errors. Several methods are available in the literature for interpolation and handling of discontinuities. This paper intends to analyze how accuracy is affected by existing techniques for handling discontinuities in time-domain simulations based on the trapezoidal integration method. New algorithms are proposed to improve accuracy.

Characterization of Switching Transients in Low Voltage Power Systems of Tea Factories in Sri Lanka

Voltage transients caused by various motors and electrical equipment of tea factories in Sri Lanka have been observed and analyzed. While reporting the major components of transients, this work extends it aspires to investigate the risk of having faults in a three-phase induction motor by monitoring and analyzing the transient voltage waveforms during the starting period. Therefore, common mode transient investigations have been followed. Transient voltage signals have been obtained from high end test setup and altogether 588 waveforms have been analyzed in both the time and frequency domains. In DOL and Star-Delta starting, highest transient amplitude of 688.2 V and 572.1 V have been observed respectively. Highest transient amplitude of 976.4 V and 980.5 V were observed in DOL and Star-Delta switching respectively. Withering and rolling sections dominates over other stages, generating high amplitude transients in average, reflecting same endangerment in energy calculations as presented in voltage integral. DOL starting transients carries fast rise times as 14 ns and in Star-Delta it is 28 ns. In order to assist with the exegesis of these data, transient parameters like rise time, duration, highest peak, etc.… have also been presented in statistical basis.