Electromagnetic transient study on flexible control processes of ferroresonance

The increasing complexity of power systems and the need for analyses that ensure the safe and reliable operation of the system have led to the development and use of software tools that simulate system behaviour. In this context, Electromagnetic transient (EMT) studies are essential for understanding high-frequency phenomena in power systems, most often occurring during switching operations and atmospheric discharge.This paper discusses the application of SCAD/EMTDC, one of the leading software tools for EMT studies. It provides an example of modelling and energization of an overhead transmission line, with a focus on overvoltages and inrush currents that occur in the process. A detailed explanation of line modelling using the frequency-dependent model in PSCAD/EMTDC will be provided, as this level of detail is necessary for studies involving frequencies higher than the system’s fundamental frequency. Since switching overvoltages depend on the instantaneous voltage values in each phase, energization will be performed at different time instants within a single cycle to capture the worst-case overvoltage scenario. The simulation results will be analysed and compared with official technical recommendations for grid connection. Additionally, the study will provide insights into potential issues arising from switching operations and propose mitigation measures to reduce overvoltage stresses.

Amorphous alloy is increasingly widely used in the iron core of power transformer due to its excellent low loss performance. However, its potential harm to the power system is not fully studied during the electromagnetic transients of the transformer. This study develops a simulation model to analyze the effect of transformer iron core materials on ferroresonance. The model is based on the transformer π equivalent circuit. The flux linkage–current (ψ–i) Jiles–Atherton reactor is developed in an Electromagnetic Transients Program-Alternative Transients Program and is used to represent the magnetizing branches of the transformer model. Two ferroresonance cases are studied to compare the performance of grain-oriented Si-steel and amorphous alloy cores. The ferroresonance overvoltage and overcurrent are discussed under different system parameters. Results show that amorphous alloy transformer generates higher voltage and current than those of grain-oriented Si-steel transformer and significantly harms the power system safety.

Guest Editorial: Situational awareness of integrated energy systems

36 - Electromagnetic Transients

The authors analyze interarea mode phenomena in stressed power systems, following large disturbances. It is shown that the interarea mode phenomenon could occur as a result of a nonlinear interaction of the natural modes of oscillation in the system. A technique for determining the interaction is developed and the machines participating in the interaction are identified. A procedure for predicting the onset of the interarea mode is presented. The technique was tested on two realistic sample test systems: a 50 generator system and a 126 generator system. The results of this analysis indicate that the procedure can detect the onset of the interarea mode phenomenon and also detect the machines which participate in the interacting natural modes of oscillation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Phasor measurement based on IEC 61850-9-2 and Kalman–Filtering

Chaotic oscillation is an undesirable phenomenon in power system and it can destroy the stability of power system. The objective of this paper is to propose variable speed synergetic control to eliminate chattering phenomenon in sliding-mode control and avoid undesirable phenomena when suppressing chaotic oscillation in power system. The prominent advantage of proposed control scheme is that it can adjust convergence speed according to the system response thus avoiding undesirable phenomena in the control process. Simulation results show that our control scheme avoids undesirable phenomena in the control process and speeds up convergence rate.

A method based on a Lure Lyapunov function is developed to analyse subsynchronous resonance (SSR) phenomena in power systems. An improved Lure Lyapunov function used to analyse the stability of a power system including the turbine-generator (T-G) shaft is presented first. Then, a standard Lure control model for a power system with a T-G shaft is obtained. The stability of such nonlinear systems at the equilibrium points is discussed in detail. The stable operation region of the system is discussed with the proposed method. The effectiveness of the proposed method is verified by a case study. This study has shown potential benefits and the validity of the Lyapunov direct method in the subsynchronous resonance analysis. Compared with the conventional analysis method, such as eigenvalue and frequency scanning techniques, the proposed method is based on the original nonlinear system. Error, that may be introduced by linearisation, is avoided completely. Moreover, the stable operation region of power systems can be obtained by the proposed method.

Power systems dominated by inverter-based resources (IBR) have experienced oscillations that span various frequencies. The lack of complete data of IBRs and the heavy computational requirement of detailed electromagnetic transient (EMT) studies limit the analysis of such dynamic oscillations by system operators. This research presents a universal methodology to gain insight into the nature of oscillations between individual subcomponents of power systems comprising various IBR technologies, parameters, and controls. Black-box impedance models and linear circuit principles are leveraged to decompose IBR-injected currents into various dynamic interaction components (in the frequency domain) with other IBRs, loads, and the grid. The amalgamation of these components represents the potential oscillatory modes of the system. The real-time system operation requires online detection and automated fixation of interaction issues, This work puts forth a framework for the same wherein the impact of various system and control parameters on these oscillations are studied and verified through EMT simulations of various benchmark test systems in MATLAB/Simulink.

Yenilenebilir enerji kaynaklarının hızlı gelişimi, dağıtık üretim tesislerinin entegrasyonu ve dijitalleşmedeki ilerlemeler dünya genelindeki güç sistemlerinde karmaşık bir değişime neden olmaktadır. Güç sistemlerinin karmaşıklığı hem lisans hem de lisansüstü öğrencilerinin güç sistemleri ile ilgili çalışmalarını sıkıcı, zor ve zaman alıcı hale getirmektedir. Bununla birlikte, simülasyon araçlarının kullanılması, güç sistemleri çalışmalarıyla ilgili hesaplama işlemlerini büyük ölçüde basitleştirmiştir. Yalnızca güç sisteminin mevcut çalışma koşulları altında çalışmasını değil, aynı zamanda gelecekteki genişlemelerin planını ve tasarımını da değerlendirmek için güç akışı çalışmaları giderek daha gerekli hale gelmektedir. Bu makale, öğrencilerin güç sistemlerindeki karmaşık olayları daha iyi anlamalarına yardımcı olmak için gelişmiş görselleştirme teknikleri kullanan PowerWorld Simülatör ile güç akışı analizinin bir incelemesini sunmaktadır. Bu amaçla, Stevenson’ın 5 baralı güç sisteminin güç akışı analizi Newton-Raphson, Gauss-Seidel ve Hızlı Ayrık metotları ile incelenmiştir. Simülasyon sonuçları hem görsel olarak hem de tablo olarak verilmiştir. Sonuç olarak, PowerWorld Simülatör ile öğrencilerin geleneksel çözümlere ek olarak güç sistemi analiz problemlerini daha iyi anlayacağı görülmüştür.

High Voltage Direct Current (HVDC) systems are increasingly popular in electric power grids. Control system of such devices can cause instabilities when interacting with other equipment in a power system. Depending on the control system dynamics, instability and resonance can occur in a wide range of frequencies (up to few kHz). Low and high frequency resonances have been registered in several power electronics based project. In this article, several realistic test cases where oscillations can occur between HVDC links and power system components are illustrated using electromagnetic transient (EMT) simulations. In order to analysis and identify the cause of such instabilities, this paper illustrates how to conduct a frequency domain analysis by means of EMT time domain simulation. As EMT-type models provided by the manufacturers are often inaccessible (or black-boxed), the method presented considers black-boxed HVDC link model.

Guest Editorial

A multiscale power system modeling methodology for the integrative simulation of electromagnetic and electromechanical transients is introduced, implemented and validated. It makes use of frequency-adaptive simulation of transients (FAST) in which the shift frequency appears as a new parameter in addition to the time step size. For fast electromagnetic transients, tracking of instantaneous waveforms as in the Electromagnetic Transients Program (EMTP) is performed. When slower electromechanical transients involving power oscillations prevail, the Fourier spectra of the waveforms are shifted by typically either 50 or 60 Hz to eliminate the ac carrier and enable envelope following as in phasor-based simulation. An algorithm for the automatic setting of both shift frequency and time step size is proposed. Multiscale models of transformers, synchronous machinery, and transmission lines based on FAST are developed. The line model is distinguished in that it bridges both lumped and distributed parameters to efficiently emulate scale-bridging phenomena from steady state to traveling waves. The overall methodology is thoroughly validated: first against a staged field test involving transients of line energization and recovery on the network of the Bonneville power administration (BPA); then through comparison with an EMTP-type simulator in modeling diverse transients on a four-machine two-area power system.

The wavelet transform is introduced as a method for analyzing electromagnetic transients associated with power system faults and switching. This method, like the Fourier transform, provides information related to the frequency composition of a waveform, but it is more appropriate than the familiar Fourier methods for the nonperiodic, wide-band signals associated with electromagnetic transients. It appears that the frequency domain data produced by the wavelet transform may be useful for analyzing the sources of transients through manual or automated feature detection schemes. The basic principles of wavelet analysis are set forth, and examples showing the application of the wavelet transform to actual power system transients are presented.

The electromagnetic transient can be used to analyze the stability of power systems. In the paper, the electromagnetic transient of an AC-DC interconnected system under different faults is investigated, and interaction between the AC system and DC system is analyzed. Firstly electromagnetic transient models for the components in a high voltage direct current (HVDC) transmission system are presented, including model for converter transformer, harmonic filters, transmission line and control system. Then simulation based on electromagnetic transient model for a ± 800 kV bipolar HVDC-AC interconnected system is carried out, and both the steady state and step response performance are checked to verify the accuracy of the model. Finally electromagnetic transient of the system under different faults is investigated, including different grounding faults on AC side, fault on DC side and fault of filters. Transient responses are analyzed, including the recovering time from oscillation caused by faults and possibility of commutation failure (CF).