Suppression of ferroresonance using passive memristor emulator

Power system inherently consists of capacitance and inductance in its components. Equipment with saturable inductance and circuit capacitance provides circumstances of generating ferroresonance, resulting in overvoltage and overcurrent in the connected system. The effects of ferroresonance result in insulation failure and hence damage to the equipment is unavoidable. Though many devices are proposed for mitigating such circumstances, a promising technology of using memristors may provide better performance than others in the future. A memristor emulator using the N-channel JFET J310 is used in this work. Unlike other electronic components that replicate memristor properties, the chosen memristor emulator is a passive device since it does not need any external power supply. Simulation and experimental results verify the design of a memristor emulator and the characteristics of an ideal memristor. Experimental results prove that the memristor emulator can suppress the fundamental ferroresonance induced in a prototype single phase transformer. The results of the harmonic analysis also validate the memristor performance against the conventional technique.

Effect of New Suggested Ferroresonance Limiter on the Stability Domain of Chaotic Ferroresonance in the Power Transformer with Linear Core Model

This Paper studies the effect of new suggested ferroresonance limiter on controlling ferroresonance oscillations in the power transformer. It is expected that this limiter generally can control the ferroresonance. For studying these phenomena, at first ferroresonance is introduced and a general modeling approach is given. A simple case of ferroresonance in a three phase transformer is used to illustrate these phenomena. Then, effect of new suggested ferroresonance limiter on the onset of chaotic ferroresonance and control of these oscillations in a power transformer including linear core losses is studied. Simulation is done on a three phase power transformer while one of its phases is opened, and effect of varying input voltage on occurring ferroresonance overvoltage is studied. Results show that connecting the ferroresonance limiter to the transformer exhibits a great controlling effect on the ferroresonance overvoltage. Phase plane diagram, FFT analysis along with bifurcation diagrams are also presented. Significant effect on occurring chaotic ferroresonance, the range of parameter values that may lead to overvoltage and magnitude of ferroresonance overvoltage is obtained, showed and tabulated.

Studying Effect of Magnetizing Curve Nonlinearity Index on the Occurring Chaotic Ferroresonance Oscillation in Autotransformers

This paper investigates the effect of iron core saturation characteristic degree on the onset of chaotic ferrore-sonance and duration of transient chaos in an autotransformer. The transformer chosen for study has a rating of 50 MVA, 635.1 kV, the magnetization characteristic of the autotransformer is modeled by a single-value two-term polynomial with q = 5, 7, 11. The core loss is modeled by a linear resistance and is considered a fix value for it. Simulation results are derived by using MATLAB software and nonlinear dynamics tool such as bifurcation and phase plan diagrams. It is shown settling down to the chaotic region is increased when degree of core nonlinearity is gone from 5 to 11.

Analysis of Chaotic Ferroresonance Phenomena in Unloaded Transformers Including MOV

We study the effect of a parallel metal oxide surge arrester on the ferroresonance oscillations of transformers. It is expected that the arresters generally cause ferroresonance drop out. Simulation has been done on a three phase power transformer with one open phase. Effect of varying input voltage is studied. The simulation results reveal that connecting the arrester to transformers poles, exhibits a great mitigating effect on ferroresonant over voltages. Phase plane along with bifurcation diagrams are also presented. Significant effect on the onset of chaos, the range of parameter values that may lead to chaos and magnitude of ferroresonant voltages is obtained, shown and tabulated.

Impacts of Water-Tree Fault on Ferroresonance in Underground Cables

Nowadays, more and more electrical power is being distributed to customers by underground cables rather than overhead transmission lines due to their advantage of providing better protection in inclement weather. They also have significantly reduced electromagnetic field emission because of their copper shielding. But underground cables have larger capacitance than transmission lines per unit. Thus, ferroresonance is more likely to occur in distribution systems using underground cables. Moreover, soil humidity at a depth of one meter remains 100 percent for most of the year, a factor that risks the occurrence of water tree (WT) in cables. Consequently, both ferroresonance and WT are prone to occur in underground cable systems. The objective of this paper is to determine the relationship between ferroresonance and water tree. A test system was designed to simulate and analyze ferroresonance in a cable system caused by single-phase switch and water tree. Eight scenarios of water tree were compared in the simulation. There sponses of ferroresonance are presented in this paper and two common patterns are observed from the simulation results.

AN APPLICATION OF BIFURCATION OF PERIODIC SOLUTIONS TO FERRORESONANCE OVER-VOLTAGE IN POWER SYSTEMS

Ferroresonance over-voltage is a destructive factor in power systems and keeps on causing accidents. So far no correct approaches have been found in the theoretical analysis of this complex physical process. In order to avoid difficulties, people usually explain the mechanism of ferroresonance over-voltage with the help of the knowledge about resonance in nonlinear oscillating systems with single degree of freedom. From this point of view, some measures of removing ferroresonance over-voltage have been proposed. However, power systems are not definitely the systems with single degree of freedom, the aforementioned explana-

Simulation and experimental research on methods to suppress ferroresonance in potential transformers

Ferroresonance in distribution networks is usually hard to be identified and predicted because it is nonlinear and dependent on multiple factors and conditions.This study discusses different common antiferroresonance methods by numerical simulations and experimental tests.In order to study the reliability of the anti-ferroresonance measures,a 10 kV ferroresonance testing system was setup.Then a number of simulations and experiments were carried out to show the ferroresonance phenomena initiated by single-phase grounding faults and/or single-phase disconnection faults.In addition,potential transformer models with the characteristic of non-linear magnetic excitation were developed and used in PSCAD-based simulation studies.These studies investigated the performance of primary resonance eliminators and arc suppression coils on restraining the ferroresonance under multiple power system parameters and initialisations.In addition,a joint anti-ferroresonance method is proposed and verified.The simulation and experimental studies can provide guidelines for evaluating the anti-ferroresonance methods in distribution networks.

Ferroresonance Overvoltage Mitigation Using STATCOM for Grid-connected Wind Energy Conversion Systems

We present the ferroresonance overvoltage mitigation concerning the power systems of the grid-connectcd wind energy conversion systems(WECSs).WECS is considered based on a doubly-fed induction generator(DFIG).Ferroresonance overvoltage associated with a single-pole outage of the line breaker is mitigated by fast regulating the reactive power using the static compensator(STATCOM).STATCOM controller is introduced,in which t>\o incorporated proportional-integral(PI)controllers are optimally tuned using a modified flow-er pollination algorithm(MFPA)as an optimization technique.To show the capability of the proposed STATCOM controller in mitigating the ferroresonance overvoltage,two test cases are introduced,which are based on the interconnection status of the power transformer used with the grid-connected DFIGs.The results show that the ferroresonance disturbance can occur for the power transformers installed in the wind farms although the transformer terminals are interconnected,and neither side of the transformer is isolated.Furthermore,as a mitigation method of ferroresonance overvoltage,the proposed STATCOM controller succeeds in improving the system voltage profile and speed profile of the wind turbine as well as protecting the system components against the ferroresonance overvoltage.

Effect of Metal Oxide Arrester on Chaotic Behavior of Power Transformers

This paper investigates the Effect of Metal Oxide Arrester (MOV) on the Chaotic Behaviour of power transformers considering nonlinear model for core loss of transformer. The paper contains two parts. In part (1): effect of nonlinear core on the onset of chaotic ferroresonance in a power transformer is evaluated. The core loss is modeled by a third order power series in voltage. in part (2): Effect of Metal Oxide Arrester(MOV) on results in part (1) will be studied. The results reveal that the presence of the arrester has a mitigating effect on ferroresonant chaotic overvoltages. resulted bifurcation diagrams and phase plane diagrams have also been delivered.

Analytical Approach for the Systematic Research of the Periodic Ferroresonant Solutions in the Power Networks

Ferroresonance is a complex and little known electrotechnical phenomenon. This lack of knowledge means that it is voluntarily considered responsible for a number of unexplained destructions or malfunctioning of equipment. The mathematical framework most suited to the general study of this phenomenon is the bifurcation theory, the main tool of which is the continuation method. Nevertheless, the use of a continuation process is not devoid of difficulties. In fact, to continue the solutions isolats which are closed curves, it is necessary to know a solution belonging to this isolated curve (isolat) to initialise the continuation method. The principal contribution of this article is to develop an analytical method allowing systematic calculation of this initial solution for various periodic ferroresonant modes (fundamental, harmonic and subharmonic) appearing on nonlinear electric system. The approach proposed uses a problem formulation in the frequency domain. This method enables to directly determine the solution in steady state without computing of the transient state. When we apply this method to the single-phase ferroresonant circuits (series and parallels configurations), we could easily calculate an initial solution for each ferroresonant mode that can be established. Knowing this first solution, we show how to use this analytical approach in a continuation technique to find the other solutions. The totality of the obtained solutions is represented in a plane where the abscissa is the amplitude of the supply voltage and the ordinate the amplitude of the system’s state variable (flux or voltage). The curve thus obtained is called “bifurcation diagram”. We will be able to then obtain a synthetic knowledge of the possible behaviors of the two circuits and particularly the limits of the dangerous zones of the various periodic ferroresonant modes that may appear. General results related to the series ferroresonance and parallel ferroresonance, obtained numerically starting from the theoretical and real cases, are illustrated and discussed.

Effect of metal oxide arrester on the chaotic oscillations in the voltage transformer with nonlinear core loss model using chaos theory Effect of metal oxide arrester on the chaotic oscillations in the voltage transformer with nonlinear core loss model using chaos theory

In this paper, controlling chaos when chaotic ferroresonant oscillations occur in a voltage transformer with nonlin- ear core loss model is performed. The effect of a parallel metal oxide surge arrester on the ferroresonance oscillations of voltage transformers is studied. The metal oxide arrester （MOA） is found to be effective in reducing ferroresonance chaotic oscillations. Also the multiple scales method is used to analyze the chaotic behavior and different types of fixed points in ferroresonance of voltage transformers considering core loss. This phenomenon has nonlinear chaotic dynamics and includes sub-harmonic, quasi-periodic, and also chaotic oscillations. In this paper, the chaotic behavior and various ferroresonant oscillation modes of the voltage transformer is studied. This phenomenon consists of different types of bifur- cations such as period doubling bifurcation （PDB）, saddle node bifurcation （SNB）, Hopf bifurcation （HB）, and chaos. The dynamic analysis of ferroresonant circuit is based on bifurcation theory. The bifurcation and phase plane diagrams are il- lustrated using a continuous method and linear and nonlinear models of core loss. To analyze ferroresonance phenomenon, the Lyapunov exponents are calculated via the multiple scales method to obtain Feigenbaum numbers. The bifurcation diagrams illustrate the variation of the control parameter. Therefore, the chaos is created and increased in the system.

Mitigation of Transients in Capacitor Coupled Substations Using Traditional RLC Filter Techniques

This article presents an extensive examination and modeling of Capacitor Coupled Substations (CCS), noting some of their inherent constraints. The underlying implementation of a CCS is to supply electricity directly from high-voltage (HV) transmission lines to low-voltage (LV) consumers through coupling capacitors and is said to be cost-effective as compared to conventional distribution networks. However, the functionality of such substations is susceptible to various transient phenomena, including ferroresonance and overvoltage occurrences. To address these challenges, the study uses simulations to evaluate the effectiveness of conventional resistor-inductor-capacitor (RLC) filter in mitigating hazardous overvoltage resulting from transients. The proposed methodology entails using standard RLC filter to suppress transients and its associated overvoltage risks. Through a series of MATLAB/Simulink simulations, the research emphasizes the practical effectiveness of this technique. The study examines the impact of transients under varied operational scenarios, including no-load switching conditions, temporary short-circuits, and load on/off events. The primary aim of the article is to assess the viability of using an established technology to manage system instabilities upon the energization of a CCS under no-load circumstances or in case of a short-circuit fault occurring on the primary side of the CCS distribution transformer. The findings underscore the effectiveness of conventional RLC filters in suppressing transients induced by the CCS no-load switching.

A positive-sequence current based directional relaying approach for CCVT subsidence transient condition

In this work,a directional relaying algorithm is proposed for transmission line to prevent relay maloperation during coupling capacitor voltage transformer(CCVT)subsidence transient.The effect of CCVT subsidence transient during single-pole-tripping condition is highlighted in this paper.The proposed method which is based on phase angle difference of post fault and prefault positive sequence current can help the directional relay to take accurate decision during erroneous CCVT secondary response.The available CCVT model in PSCAD is not able to generate significant subsidence transient in the secondary side.So,a new CCVT model is developed in EMTDC/PSCAD domain for transient response analysis and to check the relay operation.Next,the performance of different voltage and current information based directional relaying techniques have been analyzed and compared with the proposed method.The results are evaluated for different system and fault conditions.Results demonstrate the accuracy of the proposed method.