Ferroresonance suppression in power transformers using chaos theory

Based on the harmonic analysis of power system voltage, a linearized model of a metal oxide varistor (MOV) is developed for series compensation system short-circuit and stability calculations requiring linear impedances. Using this model in short-circuit program, one can obtain not only the fault current but also the waveform of voltage across the MOV and the energy absorbed by the MOV in each circle. The accuracy of the model was verified through comparisons against the results obtained using time-domain simulations (EMTP).

Due to the increasing penetration of gas-fired units and power to gas facilities, the electrical power system and natural gas system are more and more bi-directionally coupled. To tackle the challenges on the optimal scheduling operation of an integrated gas and power systems (IGPS), this article focuses on developing a novel approach to build a continuous spatial-temporal optimal operation schedule model. In the light of different time constants of the electrical power and natural gas systems, the continuous spatial-temporal optimal operation schedule model of IGPS is formulated in function space. Additionally, Bernstein polynomials are used to reformulate the continuous spatial-temporal optimization problem of IGPS to mixed-integer linear programming. In the study cases, the simulation results of a simple integrated system and a combined IEEE 39-bus power system and Belgian natural gas network demonstrate the accuracy and effectiveness of the proposed model.

Indices that report how much a contingency is stable or unstable in an electrical power system have been the object of several studies in the last decades. In some approaches, indices are obtained from time-domain simulation; others explore the calculation of the stability margin from the so-called direct methods, or even by neural networks.The goal is always to obtain a fast and reliable way of analysing large disturbance that might occur on the power systems. A fast classification in stable and unstable, as a function of transient stability is crucial for a dynamic security analysis. All good propositions as how to analyse contingencies must present some important features: classification of contingencies; precision and reliability; and efficiency computation. Indices obtained from time-domain simulations have been used to classify the contingencies as stable or unstable. These indices are based on the concepts of coherence, transient energy conversion between kinetic energy and potential energy, and three dot products of state variable. The classification of the contingencies using the indices individually is not reliable, since the performance of these indices varies with each simulated condition. However, collapsing these indices into a single one can improve the analysis significantly. In this paper, it is presented the results of an approach to filter the contingencies, by a simple classification of them into stable, unstable or marginal. This classification is performed from the composite indices obtained from step by step simulation with a time period of the clearing time plus 0.5 second. The contingencies originally classified as stable or unstable do not require this extra simulation. The methodology requires an initial effort to obtain the values of the intervals for classification, and the weights. This is performed once for each power system and can be used in different operating conditions and for different contingencies. No misplaced classification occurred in any of the tests, i.e., we detected no stable case classified as unstable or otherwise. The methodology is thus well fitted for it allows for a rapid conclusion about the stability of th system, for the majority of the contingencies (Stable or Unstable Cases). The tests, results and discussions are presented using two power systems: (1) the IEEE17 system, composed of 17 generators, 162 buses and 284 transmission lines; and (2) a South Brazilian system configuration, with 10 generators, 45 buses and 71 lines.

Reliability and survivability of electric power systems (EPS) depend on transient stability assessment (TSA). One of the most effective way to TSA is time-domain simulation. However, large-scale EPS mathematical model contains a stiff nonlinear system of high-order differential equations. Such system cannot be solved analytically. At the same time, numerical methods are imperfectly applied for such system due to limitation conditions. To make it appropriate, the EPS mathematical model is simplified and additional limitations are used. These simplifications and limitations reduce reliability of simulation results. Consequently, their validation is needed. The most reliable approach to provide it is to compare the simulation results with the field data. However, in practice, there are not enough data for such validation. This paper proposes an alternative approach for validation - the application of a reference model instead of field data. A hardware-software system HRTSim was used as a reference model. This power system simulator has all the necessary properties and capabilities to obtain reliable information required for comprehensive validation of transient stability calculations in EPSs. Main disturbances leading to instability in EPSs are investigated to conduct the validation (processes in cases of faults, single-phase auto-reclosing operation and power system interconnection). Fragments of corresponding experimental studies illustrate the efficiency of the proposed approach. Obtained results confirmed the possibility of the developed approach to identify the causes of numerical calculation errors and to determine disturbances calculated with the significant error. In addition, experimental studies have revealed that numerical calculations error depends on disturbances intensity.

Guest Editorial: Situational awareness of integrated energy systems

<div class="section abstract"><div class="htmlview paragraph">Many More-Electric Aircraft (MEA) Electric Power System (EPS) architecture paradigms are being studied in order to provide the on-board electrical loads with high-quality supply and to ensure safe operation. EPS with dc distribution appears to be more promising due to higher efficiency, higher reliability, easier integration and lower overall weight. Another advantage of dc systems is the ease of sources paralleling, together with the optimization of load power sharing, this can lead to further EPS weight reduction. The DC bus can be fed by multiple sources such as generators, batteries and other energy storage devices.</div><div class="htmlview paragraph">Many loads in MEA EPS are tightly controlled by power electronic converters and often behave as constant power loads (CPL). These are known as main contributors to the degradation of EPS stability margins. Therefore, stability study is one of the key topics in the assessment of potential EPS architecture candidates.</div><div class="htmlview paragraph">This study deals with stability study of an example EPS consisting of two permanent-magnet starter-generators feeding a mixed load. The generators are controlled in flux-weakening mode and they feed the main dc bus with currents according to the droop characteristics. The mathematical model of such EPS is developed and used for detailed stability study. The system eigenvalues contours are investigated with the variation of the key system parameters including bandwidth of main control loops, length of the cables, load power level and others. The achieved analytical results are verified by the time-domain simulations.</div></div>

Ferroresonance is a complex electrical phenomenon, which can cause overvoltages in the electrical power system and endangers the system reliability and continuous safe operating. This paper studies the effect of linear and nonlinear core losses on the chaotic ferroresonance in a voltage transformer. For confirmation this aspect simulation has been done on a one phase voltage transformer rated 100VA, 275kV. The magnetization characteristic of the transformer is modeled by a single-value two-term polynomial with q=7. The simulation results reveal that considering the nonlinear core losses on the voltage transformer, exhibits a great effect on ferroresonance overvoltages. Significant effect on the onset of chaos, the range of parameter values that may lead to chaos along with ferroresonance voltages has been obtained and presented.

In recent years, machine learning (ML) tools have gained tremendous momentum and received wide-spread attention in different segments of modern-day life. As part of digital transformation, the power system industry is one of the pioneers in adopting such attractive and efficient tools for various applications. Apparently, a nonthreatening, but slow-burning issue of the electric power systems is the low-frequency oscillations (LFO), which, if not dealt with appropriately and on time, could result in complete network failure. This paper addresses the role of a prominent ML family member, particle swarm optimization (PSO) tuned adaptive neuro-fuzzy inference system (ANFIS) for real-time enhancement of LFO damping in electric power system networks. It adopts and models two power system networks where in the first network, the synchronous machine is equipped with only a power system stabilizer (PSS), and in the other, the PSS of the synchronous machine is coordinated with the unified power flow controller (UPFC), a second-generation flexible alternating current transmission system (FACTS) device. Then, it develops the proposed ML approach to enhance LFO damping for both adopted networks based on the customary practices of statistical judgment. The performance measuring metrics of power system stability, including the minimum damping ratio (MDR), eigenvalue, and time-domain simulation, were used to analyze the developed approach. Moreover, the paper presents a comparative analysis and discussion with the referenced works’ achieved results to conclude the proposed PSO-ANFIS technique’s ability to enhance power system stability in real-time by damping out the unwanted LFO.

A power transformer needs continuous monitoring and fast protection as it is a very expensive piece of equipment and an essential element in an electrical power system. The most common protection technique used is the percentage differential logic, which provides discrimination between an internal fault and different operating conditions. Unfortunately, there are some operating conditions of power transformers that can mislead the conventional protection affecting the power system stability negatively. This study proposes the development of a new algorithm to improve the protection performance by using fuzzy logic, artificial neural networks and genetic algorithms. An electrical power system was modelled using Alternative Transients Program software to obtain the operational conditions and fault situations needed to test the algorithm developed, as well as a commercial differential relay. Results show improved reliability, as well as a fast response of the proposed technique when compared with conventional ones.

In this study, a chaos-theoretic method is proposed to model the case of ferroresonance that can occur under nominal conditions in power systems, and the factors that determine the types of ferroresonance to occur are examined. In the ferroresonance chaotic system modeled in Matlab environment, the length of the transmission line and the breaker capacities in the circuit are fixed and its relationship with the transformer efficiency is investigated. In the proposed chaotic modeling, considering the situations that may occur in practical applications, the ferroresonance situations that occur when the single-phase remains open in the three-phase system are examined. In the study, ferroresonance, which occurs when one phase is open in a three-phase system, is analyzed by considering the situations that may happen during practical implementations. The similarity between the mathematical expressions obtained from the systems that create ferroresonance and Duffing oscillator is evaluated. In the chaotic system, fundamental ferroresonance, subharmonic ferroresonance, and chaotic ferroresonance situations are created depending on the transformer loss. Additionally, ferroresonance that occurs when the chaotic system is of fractional-order is analyzed, and it is observed that results of ferroresonance with different fractional-order values are not different. The results show that transformer loss is a significant element to determine the type of ferroresonance in power transformers. Also, when the chaotic system is operated in the fractional-order setting, the ferroresonance cases that occur are re-examined, and it is observed that the system can exit from the chaotic situation and prevent the formation of ferroresonance when fractional-order control is applied. According to the results, the fractional-order method can be used to control ferroresonance.

Electromechanical oscillations mean relative motions of generator shafts and resultant fluctuations of electrical variables. In modern large‐scale electrical power systems, long transmission distances over weak grids, highly variable generation patterns, heavy loading, and so on, tend to increase the probability of appearance of sustained wide area electromechanical oscillations. Consequently, most researches on damping oscillations focus on developing different controllers, like power system stabilizers (PSSs), and thyristor controlled series compensators (TCSCs), in order to improve system damping. The models of damping controllers considered in the chapter are described to facilitate readers' understanding of the developed model predictive control (MPC) controllers. The control rules are determined in off‐line studies using time domain simulations such as Prony or Eigen analysis, and remain fixed in practice. The chapter shows that the hierarchical MPC is more robust than the distributed one because of its better performances in different test cases.

—To reduce the negative effects of wind farms connection on power system stability, many countries have elaborated grid code requirements. Low-voltage ride through (LVRT) capability is the core of these requirements. This paper presents a framework to design and apply the series resonance fault current limiter (SRFCL) with a metal oxide varistor (MOV) for LVRT performance enhancement of doubly fed induction Machine (DFIG)-based wind farms. The main advantages of the SRFCL are simplicity, high reliability and automatically operation during fault condition for enhancing the LVRT performance. To demonstrate the capability of the SRFCL, a comparative study of the SRFCL and the bridge-type fault current limiter (BFCL) is performed. The study wind farm has been modeled with equivalent aggregated DFIG. Simulations were carried out in PSCAD/EMTDC environment. Simulation results demonstrate that the SRFCL provides a simple and effective solution to enhance the LVRT and reduce the fault current contribution of wind farms.

International Journal of Computational Engineering ScienceVol. 05, No. 01, pp. 81-89 (2004) No AccessEVOLUTIONARY PROGRAMMING BASED ECONOMIC DISPATCH WITH LINE FLOW CONSTRAINTSP. SOMASUNDARAM, K. KUPPUSAMY, and R. P. KUMUDINI DEVIP. SOMASUNDARAMSchool of Electrical and Electronics Engineering, Anna University, Chennai, Tamil Nadu 600 025, India Search for more papers by this author , K. KUPPUSAMYSchool of Electrical and Electronics Engineering, Anna University, Chennai, Tamil Nadu 600 025, India Search for more papers by this author , and R. P. KUMUDINI DEVISchool of Electrical and Electronics Engineering, Anna University, Chennai, Tamil Nadu 600 025, India Search for more papers by this author https://doi.org/10.1142/S1465876304002277Cited by:1 PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail AbstractThis paper presents an efficient, simple and new method for solving Economic Dispatch (ED) problem with line flow constraints through the application of Evolutionary Programming (EP). The controllable system quantities in the base-case state are optimized to minimize some defined objective function subject to the base-case operating constraints. A 10-bus system is taken for investigation. The ED results obtained using EP are compared with those obtained using quadratic programming. The investigations reveal that the proposed algorithm is relatively simple, reliable, efficient and suitable for on-line applications.Keywords:Power System OptimizationEconomic DispatchEvolutionary ProgrammingLine Flow Constraints References B. H. Chowdhury and S. Rahman, IEEE Transaction on power systems 5(4), 1248 (1990). Crossref, Google Scholar Nanda, L. Hari and M. L. Kothari, IEE Proceedings-C 141(1), 1 (1994). Google ScholarJ. Nandaet al., IEE Proceedings-C 139(1), 39 (1992). Google ScholarJ. Y. Fan and L. Zhang, IEEE Transactions on Power Systems 13(2), 320 (1998). Crossref, Google ScholarP. K. Hota, R. Chakrabarti and P. K. Chattopadhyay, Institute of Engineers (India) Journal-EL 81, 21 (2000). Google ScholarJ. Nanda and R. Badri Narayanan, Electrical Power and Energy Systems 24, 723 (2002). Crossref, Google Scholar D. B. Fogel , Evoluationary Computation: Toward a New Philosophy of Machine Intelligence ( IEEE Press , USA , 1995 ) . Google ScholarL. L. Lai and J. T. Ma, IEEE Transactions on Power Systems 12(1), 198 (1997). Crossref, Google ScholarH. T. Yang, P. C. Yang and C. L. Huang, IEEE Transactions on Power Systems 11(1), 112 (1996). Crossref, Google ScholarK. P. Wong and J. Yuryevich, IEEE Transactions on Power Systems 13(2), 301 (1998). Google ScholarT. Jayabarathi, G. Sadasivam and V. Ramachandran, Electric Power Systems Research 52, 261 (1999). Crossref, Google ScholarT. Jayabarathi and G. Sadasivam, European Transaction on Electrical Power 10(3), 167 (2000). Crossref, Google ScholarP. Attaviriyanupapet al., IEEE Transactions on Power Systems 17(2), 411 (2002). Crossref, Google Scholar FiguresReferencesRelatedDetailsCited By 1FDR PSO-based Transient Stability Constrained Optimal Power Flow Solution for Deregulated Power IndustryM. Anitha, S. Subramanian and R. Gnanadass28 Aug 2007 | Electric Power Components and Systems, Vol. 35, No. 11 Recommended Vol. 05, No. 01 Metrics History KeywordsPower System OptimizationEconomic DispatchEvolutionary ProgrammingLine Flow ConstraintsPDF download

Series capacitors can increase the power carrying capacity of subtransmission and distribution lines by reducing voltage regulation. When considering series capacitor compensation of distribution lines and subtransmission lines careful consideration needs to be given to capacitor location, ferroresonance, ohmic reactive value, transient behaviour, short circuit withstand and capacitor protection. Conventional design approaches include shunt connected resistors, spark gaps, metal oxide varistors, thyristor controlled reactors and bypass switches. The use of a saturating choke and damping resistor to control ferroresonance, transients, and through-fault currents is described. A small-scale laboratory nonlinear single-phase ferroresonant circuit was constructed with realistic per unit component values. Both 3rd and 2nd subharmonic ferroresonance modes were predicted by modelling and generated in practice. Choke and damping resistor parameters were selected by modelling to eliminate all the unwanted ferroresonant states. Experimental work confirmed that all the unwanted ferroresonant states were eliminated from the laboratory circuit. The transient and short circuit performance of the system is considered. The proposed arrangement offers an effective countermeasure to ferroresonance for series compensated distribution lines. The system also allows some control of system fault levels and transient circuit behaviour. The technique is simple, effective and requires no sophisticated control, protection or bypass switch systems.

This paper presents a color sequential light‐emitting diode (LED) backlight power system for large‐scale LCD panels. The proposed power system uses ripple‐free circuit to improve image quality. In the proposed circuit structure, a set of power converter is operated in interleaving fashion and with switching regulation for generating two sets of output voltages to respectively supply red, green and blue LEDs by switch control. with this approach, an inductor for achieving ripple—free feature is adopted in each phase of the proposed interleaving converter. Compared to the conventional color—sequential LED backlight power system, the proposed power converter can be reduced its power converter counts, size, volume and cost, and increased its conversion efficiency significantly. Simulated results obtained from the proposed power system have been verified its feasibility.