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The main objective of the research described in the article was to determine the following: Is it possible to estimate the magnetic flux linkage in the core of a voltage transformer using analogue or digital methods? Will it be possible to estimate it approximately both in the normal state and in the state of deep core saturation (ferroresonant state)? The research aimed to identify the advantages and disadvantages of both proposed estimation methods. As part of the research described in this paper, a simulation model was developed and executed in the MATLAB/Simulink environment to generate a series of secondary voltage and flux waveforms in voltage transformers. The secondary voltage and flux waveforms were modelled under ground fault conditions, initiating ferroresonance oscillations in the medium-voltage network. To determine the associated flux from the simulated secondary voltages of the voltage transformers, an analogue integration circuit, a voltage analogue input circuit and a numerical integration algorithm with offset elimination were developed and implemented in an STM32 microcontroller. The obtained reference flux waveforms were used to verify the accuracy of the estimation of flux waveforms obtained using the analogue and digital methods. As a result, it was determined that both methods allow for a relatively accurate estimation of the periodic component of the magnetic flux. It also presented how both methods respond to the presence of slowly changing (aperiodic) components. Possible applications were proposed in order to create an innovative criterion for detecting ferroresonance oscillations. [ABSTRACT FROM AUTHOR]

The practice of using relay protection and automation devices shows that, despite the measures taken to prevent ferroresonance overvoltages, this phenomenon continues to be observed in 6 – 35 kV distribution networks. It is concluded that the recognition of ferroresonance is an important issue and that the regulatory requirements for relay protection and automation should be modified. The relevant literature is reviewed, and ferroresonance modes are classified. Practical issues of detecting ferroresonances are considered. [ABSTRACT FROM AUTHOR]

The nonlinear resonance between the saturated inductance of a transformer and capacitance of the switching device in a substation induces overvoltages and overcurrents. The voltage transformer experience 2–4 pu overvoltages due to the different modes of nonlinear resonance. Though many overvoltage suppression circuits are being proposed, the transformer does not have a single suppression circuit against all modes. A memristor-based suppression circuit has been proposed already for the fundamental (periodic) mode of ferroresonance. In this paper, an aperiodic mode of ferroresonance has been addressed with same memristive circuit along with meminductive circuit. A subharmonic mode of ferroresonance overvoltage of 3.13 pu has been induced in a (400 kV/ √ 3 )/(110 V/ √ 3 ) CVT model according to IEC 61869 -5 standards. The primary current got increased from 23.3 mA to 1.56 A and has subharmonic frequency components. A meminductor circuit is proposed as a suppression circuit against ferroresonance for a Substation CVT. A gas discharge lamp T8 Philips 18 W with low-frequency magnetic ballast emulated peculiar pinched hysteretic characteristics of a memristor. The relation between charge and flux termed as memristance of the memristor circuit is used to mitigate the nonlinear resonance oscillations. A mutator circuit for mitigation requirement has been connected to the lamp model to emulate meminductor characteristics. The mitigation performance shows that the meminductor circuit dominantly recovers the secondary voltage of CVT in 0.188 s with a reduction of 1/3rd, 1/5th, and 1/7th harmonic components by 35.4%, 78.15%, and 90.41%, respectively. [ABSTRACT FROM AUTHOR]

Atmospheric pressure cold plasmas have recently been the subject of intense research and applications for solving problems in the fields of energy, environmental engineering, and biomedicine. Non-thermal atmospheric pressure plasma sources, with dielectric barrier discharges, plasma jets, and arc discharges, are non-linear power loads. They require special power systems, which are usually designed separately for each type of plasma reactor, depending on the requirements of the plasma-chemical process, the power of the receiver, the type of process gas, the current, voltage and frequency requirements, and the efficiency of the power source. This paper presents non-linear phenomena accompanying plasma generation in the power supply plasma reactor system, such as harmonic generation, resonance, and ferroresonance of currents and voltages, and the switching of overvoltages and pulse generation. When properly applied, this can support the operation of the above-mentioned reactors by providing improved discharge ignition depending on the working gas, thus increasing the efficiency of the plasma process and improving the cooperation of the plasma-generation system with the power supply. [ABSTRACT FROM AUTHOR]

It is a known fact that the world's dependence on electrical energy is increasing day by day. The fact that electrical energy has some advantages over other types of energy, the increasing world population and changing living conditions can be considered among the reasons for this increase. This increase in dependence on electrical energy can be met by expanding existing facilities and establishing new facilities. In these studies, the transmission of electrical energy from the place where it is produced to the place where it is consumed poses important problems as the system expands. Some work is required to eliminate these technical and economic problems and to ensure stable operation of the system. These are problems that were not considered beforehand as the system grew. One of these problems is the ferroresonance phenomenon that occurs at the fundamental frequency due to the nonlinear magnetization characteristics of transformers. Ferroresonance is a resonance phenomenon that occurs in an electrical circuit containing an iron-core self-coil as a nonlinear element. This resonance manifests itself with sudden oscillations in the output size of the system caused by a small change in the amplitude or frequency of a magnitude applied to the input of the system. High voltage transmission lines are double-circuit lines that share the same pole. In special cases such as maintenance or malfunction of such a transmission system, one of the lines can be disconnected from the system and continue energy transmission with the other line. In the high voltage transmission line, the system may oscillate due to the stored energy in the magnetic field of the transformer inductance on the disabled line and the electric field of the line capacity. This oscillation disappears after a certain period of time due to iron losses and other circuit losses. When these losses are covered by the other transmission line, permanent oscillations and over voltages may occur at the transformer terminals. All these events are the negative effects of ferroresonance on transmission systems. In the energy transmission system, ferroresonance phenomenon occurs. Over voltages may occur in case of idle power transformers in star point/isolated networks. In medium voltage networks, ferroresonance occurs due to the melting of a fuse, the opening and closing of voltage transformers with one pole, and the dissymmetry that occurs as a result of a connection process. These negative effects caused by ferroresonance in the energy transmission power system are discussed in detail within the subject of this study. [ABSTRACT FROM AUTHOR]

Ferroresonance in power networks is a dangerous phenomenon, which may result in overcurrents and overvoltages, causing damage to power equipment and the faulty operation of protection systems. For this reason, the possibility of the occurrence of ferroresonance has to be identified, and adequate methods need to be incorporated to eliminate or reduce its effects. The aim of this paper is to evaluate the effectiveness of ferroresonance damping in auxiliary power systems of high-voltage substations by selected damping devices. Laboratory experiments, the results of which created bases for the development of models of selected damping devices, are presented. These models were used to simulate the effectiveness of ferroresonance damping in an auxiliary power system of a 220/110 kV substation in the EMTP-ATP program. The analyses showed that control systems with different algorithms of operation are used in damping devices. This knowledge is important when selecting parameters and settings of the applied damping devices for a given network and the disturbances in it. The presented research results have proved the effectiveness of commercially available damping devices, provided their parameters are correctly coordinated with the settings of the power system protection. [ABSTRACT FROM AUTHOR]

The main objective of the research described in the article was to determine the following: Is it possible to estimate the magnetic flux linkage in the core of a voltage transformer using analogue or digital methods? Will it be possible to estimate it approximately both in the normal state and in the state of deep core saturation (ferroresonant state)? The research aimed to identify the advantages and disadvantages of both proposed estimation methods. As part of the research described in this paper, a simulation model was developed and executed in the MATLAB/Simulink environment to generate a series of secondary voltage and flux waveforms in voltage transformers. The secondary voltage and flux waveforms were modelled under ground fault conditions, initiating ferroresonance oscillations in the medium-voltage network. To determine the associated flux from the simulated secondary voltages of the voltage transformers, an analogue integration circuit, a voltage analogue input circuit and a numerical integration algorithm with offset elimination were developed and implemented in an STM32 microcontroller. The obtained reference flux waveforms were used to verify the accuracy of the estimation of flux waveforms obtained using the analogue and digital methods. As a result, it was determined that both methods allow for a relatively accurate estimation of the periodic component of the magnetic flux. It also presented how both methods respond to the presence of slowly changing (aperiodic) components. Possible applications were proposed in order to create an innovative criterion for detecting ferroresonance oscillations.

Ferroresonance is an oscillation in a nonlinear circuit containing transformers at light load or no load coupled with a capacitor. The non-linear behavior of the core material of the transformer at no load is represented by a nonlinear equation. The capacitive effects of the power network are treated as a capacitor in series with the transformer equivalent circuit. As the system contains a nonlinear equation, it was difficult to analyze the model using the linear method. The finite Element Method is used here for the simulations of ferroresonance. The Finite Element Method allows a field solution to be obtained, even with time-varying fields with non-homogeneous or non-linear fields. This method helps to find out the changes that occur in the magnetic structure of the core under ferroresonance. Supply voltage is taken as the variable parameter. Capacitor and transformer voltages along with the phase plane are analyzed before and after the occurrence of ferroresonance over-voltage. Distribution and change in the magnetic flux during the triggering of ferroresonance are also examined. [ABSTRACT FROM AUTHOR]

Ferroresonance, as an undesirable disturbance, leads to significant overvoltage and distorted waveforms. This phenomenon can be highly damaging to voltage transformers and other parallel-connected equipment and can entail catastrophic consequences. This paper aims to design and study a solid-state ferroresonance-suppressing circuit (SSFSC) to protect voltage transformers (VTs) together with other parallel-connected equipment in wind generation systems from the adverse effects of the ferroresonance phenomenon. The proposed structure consists of low-voltage circuits, including power IGBTs. The excellent performance of the proposed SSFSC in suppressing ferroresonance overvoltage in wind generation VTs has been authenticated by analyses conducted utilizing a wind generation system model. In order to validate the performance of the proposed SSFSC, detailed analytical studies and time-domain simulations have been carried out employing a MATLAB/Simulink environment. The results verify that the proposed SSFSC can effectively suppress ferroresonance phenomena in VTs and mitigate their accompanying overvoltages with a high operational speed. [ABSTRACT FROM AUTHOR]

Ferroresonance in power networks is a dangerous phenomenon, which may result in overcurrents and overvoltages, causing damage to power equipment and the faulty operation of protection systems. For this reason, the possibility of the occurrence of ferroresonance has to be identified, and adequate methods need to be incorporated to eliminate or reduce its effects. The aim of this paper is to evaluate the effectiveness of ferroresonance damping in auxiliary power systems of high-voltage substations by selected damping devices. Laboratory experiments, the results of which created bases for the development of models of selected damping devices, are presented. These models were used to simulate the effectiveness of ferroresonance damping in an auxiliary power system of a 220/110 kV substation in the EMTP-ATP program. The analyses showed that control systems with different algorithms of operation are used in damping devices. This knowledge is important when selecting parameters and settings of the applied damping devices for a given network and the disturbances in it. The presented research results have proved the effectiveness of commercially available damping devices, provided their parameters are correctly coordinated with the settings of the power system protection.

Considering that distribution networks of 6-35 kV are the longest among electrical networks, one of the specialaspects of improving the reliability of power supply is the study of the effect of ferroresonance on the performance of voltage transformers (VT). Since the ferroresonant mode is quasi-stationary and occurs both at the fundamental frequency and at the subharmonic, the key role in the study is given to the creation of a dynamic model of the nonlinear inductance of the VT. The mathematical models and characteristics of the non-linear inductance of the VT and the resulting mathematical expressions proposed in well-known scientific papers are approximate and do not have sufficient accuracy for the analysis and qualitative assessment of ferroresonance in electrical networks of 6-35 kV. Since ferroresonance is characterized by non-linear abrupt modes of saturation of the VT magnetic circuit, the paper proposes a generalized dynamic model of the nonlinear VT inductance and more accurate analytical equations for the effective analysis of ferroresonance in 6-35 kV electrical networks.

Oscillatory processes in nonlinear multiphase electro ferromagnetic circuits (EFMC) have an exceptional variety and complexity, and therefore their research is also associated with solving complex physical problems. Theoretical analysis, in order to identify the main patterns of excitation of subharmonic oscillations of various orders, and the development of engineering calculation methods are of particular importance in designing and creating various switching-type converter devices. On the other hand, two-phase self-oscillating circuits are physical models of power transmission lines (power lines). Consequently, the study of the excitation of the existence of subharmonic oscillations in two-phase systems allows us to establish some patterns of overvoltage with power lines with capacitive compensation caused by harmonic oscillations, and, if possible, take measures to prevent these abnormal modes or mitigate their negative consequences. This article discusses the process of excitation of subharmonic oscillations ω/2 in two-phase EFMC. Using the method of energy relations, the areas of existence and critical values of the circuit parameters are determined.

Ferroresonance is a complex nonlinear electrical phenomenon that can cause significant dielectric and thermal stresses in power equipment, leading to potential faults, equipment damage, power supply interruptions, etc. Three-phase networks with isolated neutral point and single-phase isolated inductive voltage transformers are susceptible to ferroresonance, caused by the interaction of the transformer's nonlinear inductances and zero sequence capacitance of power network. The paper analyzes the possibility of ferroresonance occurrence in a real 6 kV power network, with an isolated neutral point, using the electromagnetic transients program ATP/EMTP. A detailed network model is developed, taking into account the nonlinearity of voltage and power transformers, which is utilized to analyze various configurations, switching operations, and faults in the network that could trigger ferroresonance. It is shown that, under certain circumstances, ferroresonance can occur, with faults clearing being the most common initiators of ferroresonance. The efficiency of different measures to suppress ferroresonance is also analyzed. The impact of the resistance values of voltage transformer's open delta winding dumping resistor on the suppression of ferroresonance occurrence, is considered.

This study presents a comprehensive investigation of ferroresonance, a dangerous electrical phenomenon that poses significant financial risks. Using real electrical transmission line parameters, we simulated synthetic ferroresonance scenarios on a model and analyzed the resulting data using high-order spectral analysis methods, including the Wigner-Ville method, Welch method, frequency-power analysis, and spectral methods. Our analysis revealed changes in frequency and power before and after ferroresonance, with third and fourth-order cumulants being calculated. We confirmed the accuracy of the power transmission line’s base frequency and power before the ferroresonance event and determined the frequency and power values before and after ferroresonance with frequency-power analysis. Our cumulative analysis results showed symmetrical results that are consistent with the properties of ferroresonance. Additionally, we found that the Wigner Ville method’s high-resolution results were significantly more effective than conventional methods. Our study’s findings provide valuable insights into ferroresonance’s behavior and may inform the development of more effective prevention and mitigation strategies.

Nowadays, many modern electrical power systems are designed for transmission and distribution using underground systems. Such systems minimize visual impact, reduce congestion, and increase security and reliability. However, the technology utilized has increased the capacitance effect, which can lead to the system being more susceptible to the occurrence of the ferroresonance phenomenon. Ferroresonance can cause dielectric or thermal damage and consequently makes the system susceptible to faults in the electrical power equipment and installations. This paper analyzes the ferroresonance phenomenon after switching maneuvers in a real underground distribution feeder to detect possible conditions of ferroresonance. The analysis is carried out in a typical underground distribution system with distribution transformers connected in wye-grounded/wye-grounded (Ynyn), and modeled using the ATP/EMTP software.

Copyright of International Journal of Engineering Research & Development (IJERAD) is the property of International Journal of Engineering Research & Development and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The use of advanced low-power sensing technologies instead of traditional solutions used in the distribution, measurement and control of the power grid has introduced core instrument transformers due to their physical limitations and other reasons. This situation has also brought about the design of low-power voltage transformers. As can be understood from here, analogue measurement and control systems used in power centres are approaching the end of their useful life. This substations need digital automation solutions and new technologies for more efficient performance. Since no iron core is used in the low-power electronic voltage transformer structure, it is robust against network disturbances such as ferroresonance and ferroresonance formation is not encountered. In this study, a low-power electronic voltage transformer is designed and performed experiments are presented. The most essential feature expected in a voltage sensor is that the conversion rate is precise and unchanging. For this reason, the temperature coefficient and leakage capacitance values of the voltage sensor have been designed to have the lowest margin of error. Performance tests were applied to the voltage sensor using mains frequency endurance, partial discharge, accuracy class, linearity and temperature distribution tests. The results of the performance tests show that it has been successfully applied for the design of a precision voltage sensor with an accuracy class conforming to the IEC 61689-11 standard. [ABSTRACT FROM AUTHOR]

Ferroresonance, as an undesirable disturbance, leads to significant overvoltage and distorted waveforms. This phenomenon can be highly damaging to voltage transformers and other parallel-connected equipment and can entail catastrophic consequences. This paper aims to design and study a solid-state ferroresonance-suppressing circuit (SSFSC) to protect voltage transformers (VTs) together with other parallel-connected equipment in wind generation systems from the adverse effects of the ferroresonance phenomenon. The proposed structure consists of low-voltage circuits, including power IGBTs. The excellent performance of the proposed SSFSC in suppressing ferroresonance overvoltage in wind generation VTs has been authenticated by analyses conducted utilizing a wind generation system model. In order to validate the performance of the proposed SSFSC, detailed analytical studies and time-domain simulations have been carried out employing a MATLAB/Simulink environment. The results verify that the proposed SSFSC can effectively suppress ferroresonance phenomena in VTs and mitigate their accompanying overvoltages with a high operational speed.

Inductive voltage transformers are the basic components of the switchgear equipment or electrical substations. This article presents problems related to their operation. Inductive voltage transformers were exposed to specific working conditions in the form of ferroresonance oscillations with the participation of measurement and protective transformers. The disadvantage and negative significance of the phenomenon contributed to the development of the most convenient elimination methods, which is the main goal and achievement of the publication. The analysis of the proposed solutions were carried out on a theoretical model of a 30 kV power network model created and run in the Electromagnetic Transients Program/Alternative Transients Program (EMTP/ATP). The article presents several results of computer simulations carried out together with their complete characteristics (phase voltage waveforms on the primary side of voltage transformers), which allowed us to indicate the disadvantages and advantages of the solutions developed, and choose the most favorable methods to eliminate nonlinear oscillations. In the article, we present an analysis of all aspects contributing to the solution to the problem. This has permitted an appropriate conclusion to be made indicating the advantage of the method based on the use of a damping resistor in the open delta circuit compared to other solutions. Current solutions are largely based on a product using active variation of the resistance of an open delta attached resistor. The concept in this paper is based on a fixed resistance value, which is a different approach to the problem. By using a switch, the resistor is only connected when a fault occurs. Thanks to this solution, the secondary winding of the open delta is not additionally loaded (despite the very high resistance) at all times during the operation of the power network, as is the case with the available solution. [ABSTRACT FROM AUTHOR]

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Aberrant system oscillations cause electrical network components to malfunction in a catastrophic way. Additionally, this results in saturation of the ferromagnetic core components. These variables cause a significant increase in voltage and/or current, as well as aberrations in the waveforms of voltage and current. The contribution of Distributed Generation (DG), to the decrease in ferroresonance investigation in the distribution zone, is discussed in this paper. A new method to reduce ferroresonance using the High Ohmic Reactor (HOR) as a Shunt Limiter (SL) is presented. It is based on the measurements of the negative-sequence components. The proposed HOR-SL reduced the ferroresonance occurrence in the Distribution System (DS) by a time value of no more than 23 milliseconds. The proposed HOR-SL method is compared with the Series Resistance (SR) and Series Tuned LC Limiter (STLCL) methods. The results obtained using the proposed HOR-SL are better than the ones obtained using SE and STLCL. In terms of the voltage and the time taken to mitigate the ferroresonance. The ferroresonance phenomenon is modelled with the help of the PSCAD/EMTDC software. The results obtained demonstrated the effectiveness of implementing the suggested HOR-SL for suppressing ferroresonant oscillations to restore the original state of stability of the distribution network. Case studies strongly proved the effectiveness and robustness of the proposed method in reducing ferroresonance oscillations and maintaining the security of the electrical components in the distribution network.

Geomagnetic disturbance (GMD) arises during space weather and solar activity can result in geomagnetically induced current (GIC) flow in the grounded power transformers in the power network. This GIC may cause half-cycle saturation of transformers and lead to severe damage or blackout. To block the GIC flow into the power transformers, the neutral blocking devices (NBDs) based on capacitor banks are often installed in the neutral ground paths of transformers to mitigate the GIC. However, the high voltage (HV) can build up across these capacitors during ground faults and may cause a ferroresonance phenomenon in the power network. This phenomenon generates high voltages/currents in the transformer windings and results in transformer failure. This work investigates the effect of connected NBDs to the power transformers on the potential power network ferroresonance in Peninsular Malaysia. The complete analysis was carried out using the Power System Computer-Aided Design for Electromagnetic Transients including Direct Current (PSCAD/EMTDC) software. These transformers were selected in the power network due to the sensitivity of their locations to GMD events. The NBD systems were tested under different working conditions. The simulation results found that the metal oxide varistors (MOVs) arresters in NBDs fault protection mode effectively clamped ferroresonance overvoltages below the protection level under faulty conditions. Also, the results showed that GIC protection modes with 1 $\Omega $ and 3180 $\mu \text{F}$ in the mitigation systems had the lowest ferroresonance overvoltages in the neutrals of the transformers under faulty conditions. Based on the results, the recommendations were provided to the local power utility which will help to improve the reliability of the power supply to the consumers.

The paper analyses the ferroresonance phenomenon using measurements, modeling and simulations. The measurements are performed on a ferroresonant system in a laboratory set-up as an equivalent to an existing powernetwork subsystem in which a three-phase three-legged power transformer is brought to a ferroresonance state by applying irregular switching of a circuit breaker. An equivalent model of a three-phase three-legged power transformer is used taking into account both the magnetic coupling of the three legs over a zero-sequence inductance and the magnetic asymmetry of the transformer legs. The experimentally obtained nonlinear magnetization curve is well approximated using the proposed double exponential function. The numerical results with the presented mathematical model are verified by comparing them with the results of the corresponding measurements. [ABSTRACT FROM AUTHOR]

While much attention was given in the literature to improve the fault ride through (FRT) capability of a doubly-fed induction generator (DFIG)-based wind energy conversion system (WECS) during various faults at the grid side, not much attention was given to investigate and improve the performance of the DFIG-WECS under ferroresonance conditions. This paper investigates the impact of ferroresonance on the overall performance of a DFIG-WECS. The paper also presents a new technique to improve the high voltage ride through capability of the investigated system under such condition. The proposed technique relies on incorporating a superconducting coil within the dc-link of the DFIG grid-side and rotor-side converters. Energy exchange between the coil and the system is controlled through regulating the duty cycle of the dc-chopper interfacing the coil with the dc-link. In this regard, a simple but yet effective proportional-integral (PI) controller is employed to regulate the dc-chopper duty cycle. Parameters of the PI controller are optimized using elephant herding optimization algorithm. Simulation results verify the effectiveness of the proposed controller in improving the overall performance of a DFIG-WECS during ferroresonance events. [ABSTRACT FROM AUTHOR]

This article addresses the study regarding possible occurrences of ferroresonance and self-excitation phenomena in Subsea Power Systems (SPS). SPS are essentially composed of synchronous generators installed on a platform (Topside), a three-phase umbilical cable and loads on the seabeds. The latter is mainly constituted by induction machines located on the seabed and connected to the umbilical through a power transformer and power electronic converters. Such phenomena are conceptually stated and characterized in the scope of SPS and the simulations carried out in the PSCAD/EMTDC software, in its parallel processing environment. The study will investigate possible occurrences of such problems in a typical scenario of subsea distribution system. [ABSTRACT FROM AUTHOR]

The concept of symmetric ferroresonance is introduced as one of the possible modes of the rLC-oscillator circuit with nonlinear inductance the pattern of which is identical to that observed at ferroresonance in electrical networks. The mode is periodic, and the sequential half-periods differ only in the signs of currents and voltages. Part of each half-period corresponds to the saturated state of the magnetic circuit, while the rest of the time it is unsaturated. The analysis of symmetric ferroresonance using the known piecewise linear approximation of the inductance magnetization curve allows one not only to explain the physical processes occurring in the circuit, but also to obtain a simple physically obvious and fairly accurate estimates of the current, voltages, and ranges of existence of the process. The adequacy of the "physical" approach to ferroresonance is verified by calculations. [ABSTRACT FROM AUTHOR]

Ferroresonance occurrence represents a very dangerous phenomenon to electric power systems. Concerning the recent trend of the applications of gridconnected wind farms, this phenomenon can lead to undesired overvoltages stressing the wind farm components. In this paper, the ferroresonance overvoltages are studied and mitigated for the grid-connected wind farm. Single-pole switching of the breaker is considered, where it is the most famous reason behind the ferroresonance transient events in the electric power systems. During the ferroresonance period, the transient voltage of the network is increased to more than three times the voltage level and associated with harmonics. Surge arrester is suggested to mitigate the ferroresonance transient overvoltages, in which the arrester coordination setting of its residual voltage is selected to be 1.2 of the nominal voltage value. Evaluation of the dynamic interaction of the installed surge arrester with the ferroresonance overvoltages is investigated, and the mitigation is attained, successfully. Furthermore, the magnitudes of the harmonics created due to ferroresonance are reduced by installing the surge arresters, but they are not diminished completely. However, the arresters are found under stress if their dissipating energies exceed the withstand capability. The simulations are carried out using the alternative transient program/electromagnetic transient program (ATP/EMTP), and the waveforms are digitally processed using MATLAB software. [ABSTRACT FROM AUTHOR]

Ferroresonance is a complex phenomenon and can compromise power system sustainability in transformer cores during the electromagnetic saturation process. Over‐voltage can be induced in the inductive core of transformers in an oscillation imbalance circuit; thus causing short circuits or permanent damage to a transformer. Hence, this paper developed a teaching application that combined a graphical user interface (GUI) in MATLAB with a SIMULINK function to model a ferroresonance circuit, to undergraduate engineering students at a Chinese University, as a part of a high‐ voltage engineering course. Students can adjust the parameters in the model to test different types of resonance voltage waveforms to obtain the corresponding power frequencies directly in the GUI. Through the interactive GUI environment, the difficulties that undergraduate students experience in distance education can be eliminated. A questionnaire of the 63 students who took the course was administered to measure student perceptions of this project‐based learning experience, and the responses are included in this paper. [ABSTRACT FROM AUTHOR]

Inductive voltage transformers are the basic components of the switchgear equipment or electrical substations. This article presents problems related to their operation. Inductive voltage transformers were exposed to specific working conditions in the form of ferroresonance oscillations with the participation of measurement and protective transformers. The disadvantage and negative significance of the phenomenon contributed to the development of the most convenient elimination methods, which is the main goal and achievement of the publication. The analysis of the proposed solutions were carried out on a theoretical model of a 30 kV power network model created and run in the Electromagnetic Transients Program/Alternative Transients Program (EMTP/ATP). The article presents several results of computer simulations carried out together with their complete characteristics (phase voltage waveforms on the primary side of voltage transformers), which allowed us to indicate the disadvantages and advantages of the solutions developed, and choose the most favorable methods to eliminate nonlinear oscillations. In the article, we present an analysis of all aspects contributing to the solution to the problem. This has permitted an appropriate conclusion to be made indicating the advantage of the method based on the use of a damping resistor in the open delta circuit compared to other solutions. Current solutions are largely based on a product using active variation of the resistance of an open delta attached resistor. The concept in this paper is based on a fixed resistance value, which is a different approach to the problem. By using a switch, the resistor is only connected when a fault occurs. Thanks to this solution, the secondary winding of the open delta is not additionally loaded (despite the very high resistance) at all times during the operation of the power network, as is the case with the available solution.

Ferroresonance is a phenomenon that occurs in the transformer core, and is characterized by the presence of abnormal voltages. An electrical circuit that can cause ferroresonance has elements of resistance (R), capacitance (C), and non-linear inductance (L). In this research, the phenomenon of a surge in the value of the transformer current and voltage, which has changed drastically (jump phenomenon) after being triggered by an increase in the source voltage of about 1%, has been found out. The emergence of this jump phenomenon can trigger the emergence of ferroresonance. This will cause the transformer not to work normally in its linear region but in non-linear (saturation) regions. The test has been carried out on a 220 V 3-phase low-voltage transformer with H-core type and M-core type. Then the initiation factors such as source voltage variation and capacitance variation have been given to the system. Trends in the waveforms of voltage, current, voltage at source, transformer capacitor have been analyzed. The test results have showed that the given initiation factor can explain the correlation between the jump phenomenon characteristics and the presence of ferroresonance in the H-core and M-core transformers. When ferroresonance has appeared, the voltage value has been relatively high in the H-core type transformer. The largest value of voltage and current of the transformer occurs at 30 uF in S-phase with a transformer voltage value of 265.8 V and a current value of 5.7 A. Whereas, the ferroresonance mode in H-core and M-core is the fundamental ferroresonance mode. [ABSTRACT FROM AUTHOR]

This research paper presents a comprehensive procedure on how to perform a ferroresonance study in a system dealing with the addition of subsea cable interconnector-2 between two 230 kV substations which is previously linked by subsea cable interconnector-1. Addition of a subsea cable interconnector-2 needs to be investigated for ferroresonance in planning and designing stages itself since the interaction between cable capacitive reactance and power transformers-magnetizing core which is a non-linear inductance may cause ferroresonance. The investigation is conducted in three stages namely energisation, de-energisation and stuck pole conditions of circuit breaker. Each stage concentrates on the overvoltage patterns as ferroresonance is characterized by overvoltage. The analysis is conducted in PSCAD/EMTDC software and the modelling of entire study network is done according to the CIGRE WG C4.307. The maximum overvoltage for each stage is found by performing 200 cases of statistical simulation and it is compared with the rated withstand voltage of the equipment. Through a rigorous analysis of overvoltage characteristics under different scenarios, suggestion has been given whether the subsea cable interconnector-2 can be safely operated during the studied cases without the risk of ferroresonance. [ABSTRACT FROM AUTHOR]

This paper presents a study on ferroresonance occurring in a high voltage 400 kV transmission grid due to energization of power transformer under no-load conditions. The system scenarios analyzed in the present paper are considered as critical for development and modernization plans as currently announced by the national grid operator in Poland. The PSCADsimulation modelwas developed and applied for several study cases of a system with double-circuit arrangement of a transmission line. It is shown that the ferroresonant oscillations can be initiated by two-phase switching operation of a line circuit breaker. The impact of the double-circuit length on the ferroresonance mode and severity is demonstrated with the use of the Poincaré map analysis and Short Time Fourier Transform. It is demon- strated that the length of the transmission line that is mutually coupled in the double-circuit arrangement has a significant impact on the ferroresonance occurrence and on its mode. As the ferroresonance can pose severe threat to the power system components due to the severe overvoltage and overcurrent oscillations, the analysis presented in this paper demonstrates the necessity of the ferroresonance analyses for any re-designed transmission system.

Ferroresonance often occurs in power systems during system switching, which creates overvoltage situations and poses great risks to the equipment safety. In this article, a single-phase ferroresonance incident during a system energization process is presented, which occurred at a single-phase station service transformer in an ungrounded system, causing a surge arrester's failure. This incident is investigated through the PSCAD simulation and the analytical analysis. To validate the PSCAD simulation model, the relay field record is compared with the PSCAD simulation results. Several case studies are conducted using PSCAD simulation to evaluate contributing factors to this ferroresonance incident. The root cause is found to be lack of ground in the system during energization. Field practices are recommended to avoid such incidents, which were proved to be effective by successfully energizing the system in the field. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This paper presents a case study of three-phase ferroresonance in a low-voltage power factor correction system and investigates the influence of harmonic distortion on the occurrence of ferroresonance. Ferroresonance is an extremely dangerous and rare phenomenon that causes overvoltages and overcurrents in the system and degrades the power quality. The study is carried out on real field measurements in an industrial plant where ferroresonance occurs in the power factor correction (PFC) system at the detuned reactor. The three-phase ferroresonance analysed in this paper is an extremely rare phenomenon that has never been reported in this type of configuration. The measurement results have shown that in this type of configuration the high harmonic distortion is a necessary condition for ferroresonance to occur. In such conditions, switching on the capacitor stage triggers the ferroresonance with quasi-periodic oscillations supported by the medium voltage grid. The main contribution is the analysis of the three-phase ferroresonance in the detuned PFC system and the influence of the harmonics on the occurrence of the ferroresonance in such a case. The possible solutions to this problem and recommendations to avoid this phenomenon are discussed. [ABSTRACT FROM AUTHOR]

Frequency response analysis (FRA) is regarded as the most effective technique to detect mechanical faults of transformers. Over the years, FRA measurement data have been collected by utilities into transformer asset databases. The characteristic of FRA data is fundamentally determined by the transformer's equivalent electrical circuit, which consists of inductance and capacitance parameters that are windings' design and structure dependent. Different winding types tend to have different FRA characteristics, and a transformer's design information such as winding type, dimension etc. is often not known to the utility but critically important for asset management. This study reviews the state-of-the-art transformer FRA databases and application of machine learning techniques in this field, and proposes to apply a support vector machine (SVM) model onto the FRA data to identify the winding type. The SVM model is first trained by FRA traces of transformers with known winding types, and after testing, the SVM model is then applied to FRA traces with unknown winding information. A set of data from the UK's National Grid FRA database, was used to demonstrate and verify the SVM model. All transformers used in this study are 400/275/13 kV transmission transformers, which were designed using four different winding types, namely multiple layer, plain disc, interleaved disc and single helical windings. The proposed method can successfully identify the correct winding type.

Three asymmetrical faults of singe-phase grounding, singe-phase line breakage and ferroresonance in coal mine power network are easily misjudged, and existing methods hardly identify the three faults correctly. In order to solve above problems, fault sequence characteristics of singe-phase grounding, singe-phase line breakage and power-frequency ferroresonance were analyzed, and distribution laws of sequence current in coal mine power network were obtained, which showed that negative-sequence current only flowed through fault line and preceding power network, while negative-sequence current in non-fault lines was zero , and there was no negative-sequence current and only weak zero-sequence current in power network under the condition of ferroresonance fault. On this basis, an identification and location method of asymmetrical faults in coal mine power network was proposed. The method uses negative-sequence current to judge ferroresonance fault, zero-sequence current to identify singe-phase grounding or singe-phase line breakage fault, and distribution coefficient of negative-sequence current to locate fault line. The simulation results show that the method can identify and locate the three asymmetrical faults in coal mine power network correctly and reliably.

Purpose: An annual substation equipment failure report says 3/7 capacitive voltage transformer (CVT) got damaged because of ferroresonance overvoltage. The conventional mitigation circuit fails to protect the transformer as the overvoltage may fall in the range between 2 and 4 per unit. It is necessary to develop a device to suppress the overvoltage as well as overcurrent of the CVT. This study aims to propose the suitability of memristor emulator as a mitigation circuit for ferroresonance. Design/methodology/approach: The literature implies that a nonlinear circuit can protect the transformer against ferroresonance. An attempt is made with a memristor emulator using Operational Amplifier (OPAMP) for the mitigation of ferroresonance in a prototype transformer. The circuit is simulated using PSpice and validated for its ideal characteristics using hardware implementation. The nonlinear memductance is designed which is required to mitigate the ferroresonance. The mitigation performance has been compared with conventional method along with fast Fourier transform (FFT) analysis. Findings: While the linear resistor recovers the secondary voltage by 74.1%, the memristor emulator does it by 82.05% during ferroresonance. Also, the total harmonic distortion (THD) of ferroresonance signal found to be 22.06% got improved as 2.56% using memristor emulator. Research limitations/implications: The suitability of memristor emulator as a mitigation circuit for ferroresonance is proposed in this paper. As ferroresonance occurs in instrument transformers which have extra high voltage (EHV) rated primary windings and (110 V/[110 V/1.732]) rated secondary windings, the mitigation device is proposed to be connected as a nonlinear load across the secondary windings of the transformer. This paper discusses the preliminary work of ferroresonance mitigation in a prototype transformer. The mitigation circuit may have memristor or meminductor for ferroresonance mitigation when they are commercially available in future. Practical implications: The electronic component-based memristor emulator may not work at 110 V practically as they may be rated at low power. Hence, chemical component-based memristor emulator was developed to do the same. The authors like to clarify that the memristor will be a solution for ferroresonance in future not the memristor emulator circuit. Social implications: With the real form of memristor, the transistor world will be replaced by it and may have a revolution in the field of electronics, VLSI, etc. This contribution attempts to project the use of memristor in a smaller scale in high-voltage engineering. Originality/value: The electronic component-based memristor emulator is proposed as a mitigation circuit for ferroresonance. The hypothesis has been verified successfully in a prototype transformer. Testing circuit of memristor emulator involves transformer, practically. The mitigation performance has been compared with conventional method technically and justified with FFT analysis. [ABSTRACT FROM AUTHOR]

This paper reports a practical challenge in Distributed Energy Resources (DER) operation: open phase detection. The paper presents a wide variety of naturally occurred open phase events recorded by power quality meters in DER commercial operations. The events demonstrate the complexity of open phase detection due to electrical and magnetic interphase couplings through transformer winding and core configurations. The coupling effect could recreate the missing phase in various patterns so that the DER control and protection systems or control room operators may not detect the anomaly for prolonged period of time. This paper shares experiences of timely DER open phase detection by using power quality data and suggests practical detection guidelines based on waveform signature analytics. The original field records provide credible benchmarking references for algorithm development to meet the new DER open phase detection requirement in the IEEE Stdandard 1547–2018 revision. [ABSTRACT FROM AUTHOR]