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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 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]

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.

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]

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.

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]

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]

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.

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.

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]

Ferroresonance has been a widely studied area in the last few decades due to the nonlinear behavior and power quality problems it presents. Some power quality problems related to the ferroresonance phenomenon are sustained overvoltage and overcurrent and maintained levels of waveform distortions. The phenomenon can lead to the dielectric breakdown of electrical equipment, thermal problems, and misoperation of protective relays. It can present itself in a circuit that involves a nonlinear inductance associated with capacitance and low losses. This paper analyzes the ferroresonance test in a capacitor voltage transformer through Simulink® simulation. It divided a cycle of a sine wave into 72 different points to apply controlled short-circuits in the secondary terminal of the transformer. The aim is to study the relationship between the time when a short-circuit is applied, and the peak voltage of the first positive half-cycle after the short-circuit is removed. Therefore, the worst-case scenario of the short-circuit application was verified. Results demonstrate that there is a most critical situation during short-circuits at the CVT's secondary terminals. [ABSTRACT FROM AUTHOR]

The performance of measurement transformers especially in transient phenomena affects the monitoring, control and protective devices. Coupling capacitor voltage transformer (CCVT) is a measurement transformer that may experience ferroresonance phenomenon due to the presence of capacitors and non‐linear reactors. This study provides a probabilistic framework for investigation of ferroresonance phenomenon in CCVT. The aim of this investigation is to find out the area of the power system in which a CCVT is highly prone to experience ferroresonance phenomenon. Also through this framework the behaviour of the different types of ferroresonance suppression circuits and possible solutions to avoid or reduce the chance of ferroresonance will be discussed. The effects of several factors such as switching moment, different fault type and the fault inception angle are investigated. The investigation will be conducted considering the effects of single‐pole auto‐reclosing, three‐pole auto‐reclosing and capacitor failure in the CCVT. As shown in the simulation results, the presented framework can provide some useful information regarding the exposure level and severity of CCVT ferroresonance in the system. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study of the magnetic effects of steel tanks on different three-phase transformers. Removable steel tanks are designed and built for transformers with distinct sizes and core topologies. Corresponding tanks of nonmagnetic materials are also built to study the effects of tank material. Zero-sequence tests, open-circuit (no-load) tests, ferroresonance, geomagnetically induced current (GIC), and energization (inrush current) tests are performed on the transformers with and without tanks. The results indicate that steel tanks have a significant effect on the zero-sequence impedance, ferroresonance performance, GIC, and no-load losses in steady state, while the tank has no appreciable effect on inrush currents. [ABSTRACT FROM AUTHOR]

Arresters are widely used in power systems to protect other equipment against overvoltages. However, in some conditions, they can’t operate successfully. One of the disturbances leading to the failure of the riser pole arresters is the ferroresonance overvoltages. In this paper, at first the influence of different transformer simulation models of ATP software on the occurrence of ferroresonance is studied and then the effect of ferroresonance on the riser pole arrester has been scrutinized through the thermal and electrical performance of the arrester in an underground distribution system. The results show that the arrester temperature rises due to energy dissipation in a ferroresonance circumstance, which indeed may result into the explosion of the arrester. Also, applying different models of the transformer in the ATP software and comparing the results, it is shown that the available models do not show the same effect on the arrester.

For different types of fault in transmission line, the generation mechanism of tripping and closing over-voltage is analysed. To built the double power supply system of high-voltage transmission line simulation model by PSCAD/EMTDC, finally, for the operation of over-voltage, when the line occurs of different types faults, simulation to study tripping and closing over-voltage's size and the extent of influence, derived its tripping and closing over-voltage suppression measures and control strategies. The results showed that: for the circuit breaker tripping and closing over-voltage, the circuit breaker shunt reactor has better effect on the over-voltage suppression and improves the reliability of operation and the safety of protection of the system.

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.

This provides an overview of ferroresonance phenomena, modeling aspects and practical experience in recognizing and mitigating the effect of ferroresonance in the power network. In particular, we will present symptoms of ferroresonance. In this study, ferroresonance phenomenon are investigated under the modelling of the underground cable of 15 MVA, 33/11/0.415 kV with four feeders supply over 31 distribution transformers of Garki 1 service unit, Abuja, conducted using MATLAB/SIMSCAPE software package. The network is subjected to switching resulting in the formation of a series LC combination prone to ferroresonance. The waveforms and total harmonic distortion charts obtained are observed, analyzed and then used to design Harmonic filters which have been implemented to mitigate ferroresonance in the network. The simulated ferroresonance phenomenon was suppressed using Shunt Active Harmonic Filter connected in parallel to the network. A reduced harmonic content and dampened event when compared to a non-filtered event was observed. Application of Shunt Active Harmonic filter reduces ferroresonance effect by 67.743%. [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. [ABSTRACT FROM AUTHOR]

Subsynchronous resonance (SSR) is a phenomenon in which electrical energy is exchanged between the generator and the transmission system below power frequency. SSR occurs due to the interaction of a series-compensated transmission line with a generator. It results in shaft oscillation and out-of-step (OOS) condition. During SSR, the magnitude of voltage and current is increased. It also increases probable occurrence of ferroresonance. It is obviously clear that protective relays are affected in such conditions. In this article, Manitoba Hydro electrical network is examined with series capacitors by PSCAD/EMTDC to investigate the impact of SSR on the operation of different types of protective relays. SSR is mostly concerned with transmission lines. In addition, swing characteristic of impedance during SSR causes activation of the OOS blocking (OSB) element of distance relay and OOS protection of generator. Hence, an adaptive algorithm based on subharmonic measurement and ferroresonance analysis in the time domain is proposed for OOS characteristic of generator protective relay to recognize SSR condition and make a decision on behavior of the function. Finally, the algorithm is examined in SSR condition to certify the correct operation. [ABSTRACT FROM AUTHOR]

Ferroresonance causes overvoltage and excessive current flow on potential transformers (PT), which can cause substantial damage to PTs and interrupt the power system normal operation. In this article, a sustained overvoltage event on a de-energized 138 kV bus after the circuit breakers were opened to clear a phase A to ground fault at a Canadian transmission utility power grid is investigated. The power systems computer aided design (PSCAD) simulation model is created and validated using the field measurement data. The PSCAD simulation results indicate that the ferroresonance due to a limb-type open-core magnetic PT interacting with the grading capacitors of circuit breakers is the root cause of the problem. Due to the linearized magnetizing characteristic, the limb-type open-core PT is generally believed to be immune from ferroresonance; however, the event and simulation in this article demonstrate that the ferroresonance can still occur using this type of PT. The mitigation methods for the ferroresonance in this system are proposed; case and sensitivity studies using these methods are conducted to validate their effectiveness. In this article, the criterion on how to properly size a damping resistor or a damping reactor at the PT secondary is proposed, and the performance comparison using a damping resistor or a damping reactor for this system is demonstrated through case and sensitivity studies. [ABSTRACT FROM AUTHOR]

Deformation of the windings is one of the main causes of the power transformers failure. Here, for the first time, the electromagnetic forces exerted on the windings are computed in ferroresonance condition and compared with that of the inrush current for a typical power transformer. In both cases, the magnetic core of the transformer saturates and the leakage flux around the windings increases, which leads to large forces on the windings carrying high currents. Therefore, precise modelling of the transformer core is required to calculate the forces inside the transformer. For this purpose, the Jiles–Atherton vector hysteresis model is employed in conjunction with finite element method (FEM) to simulate the laminated grain‐oriented steel core, and then the radial and axial forces inflicted on the windings are estimated. [ABSTRACT FROM AUTHOR]

This paper presents possibilities offered by a diagnostic system called FeD. The system is completely original; it has been developed by the authors on the basis of Arduino platform. The system has been designed to perform and record measurements and to carry out different numerical operations. The real-time function for several operations is incorporated in this system. The necessary input data for the system consist of the electrical voltage waveforms only. Rescaled voltage quantities can be displayed, measured, recorded or computed in any chosen way. The system has been developed particularly for measurements and computations in the ferroresonant circuits. The strongest part of the system is its versatility. It works with a standard PC and supports a universal connection (USB standard). This is undeniably a cost-wise solution. Driving and control of the system functions are carried out using the authors' original software implemented in SciLab environment. This is free software, similar to and compatible with other existing CAD programs such as Octave and MATLAB. The obtained data, scripts and results can be freely transferred between them. The program is equipped with a transparent GUI. The need of constructing a special system to diagnose the ferroresonant circuit has emerged during earlier ferroresonance analyses and computations. Every ferroresonant circuit requires specific kind of diagnostics to estimate and display its base features in order to determine the best scientific approach to the problem. The ferroresonance phenomenon belongs to the domain of nonlinear problems. Its analysis requires excellent skills in mathematics and physics as well as computer science. Moreover, this subject also requires specialized engineering knowledge, particularly in the field of power engineering and power system equipment. Modern mathematical models and analyses used in ferroresonant computations are quite accurate; however, in case of a common user, they are often difficult to understand or implement. This paper provides full description of construction, features and test results of the developed hardware/software system designed for diagnostics of ferroresonant circuits. The test circuit case study has been performed in the entire power supply range. Results of measurements and computations as well as screenshots captured from authors' original software are shown in different figures. The developed software and recorded data have been finally used in modeling and further simulations. During this, the application of the fractional derivative iron core coil model to ferroresonance analysis has been shown. The waveforms obtained from computer simulations have been compared with those obtained from measurements performed in the test circuit. [ABSTRACT FROM AUTHOR]

It is vital in the prevention of the ferroresonance to consider this phenomenon from new side. The design of the equipment needs deep studies to avoid such disturbance. This paper presents a new way in ferroresonance studies, by the use of the Root Cause Analysis (RCA) in a systematic step by step process to discover the true cause of this problem. A fault tree is built to identify all possible causes leading to the unwanted top event, that is the False Trip Analysis (FTA). Among large statistics of disturbances, the probability of occurrence of ferroresonance is stated, and using the most studied causes of this event, the tree of analysis is built till reaching the main disturbance. In each step, well-known possible causes are shown. Then, a barrier or possible solution corresponding to the cause is presented. The new probability of occurrence is then calculated. The obtained result is compared to the initial probability and a set of protection system is proposed. The advantage of this study is the possibility to reduce the occurrence of the ferroresonance by gathering the maximum detailed amount of possible causes and by choosing the best barrier corresponding to the cause. [ABSTRACT FROM AUTHOR]

For different types of fault in transmission line, the generation mechanism of tripping and closing over-voltage is analysed. To built the double power supply system of high-voltage transmission line simulation model by PSCAD/EMTDC, finally, for the operation of over-voltage, when the line occurs of different types faults, simulation to study tripping and closing over-voltage's size and the extent of influence, derived its tripping and closing over-voltage suppression measures and control strategies. The results showed that: for the circuit breaker tripping and closing over-voltage, the circuit breaker shunt reactor has better effect on the over-voltage suppression and improves the reliability of operation and the safety of protection of the system. [ABSTRACT FROM AUTHOR]

The Ferranti effect could cause a rise in voltage along the cables on a wind farm if the circuit breakers at the receiving ends are switched off. Ferroresonance could also occur due to stuck pole(s) of the circuit breaker during de-energization. This paper reports on the temporary overvoltage (TOV) arising from the de-energization of the circuit breaker connecting the wind turbine to the feeder, the feeder breaker connecting an array of wind turbines to the point of common coupling (PCC), and the opening of the circuit breaker connecting the onshore to the offshore substation. Ferroresonance was characterized using a phase plane diagram and Poincaré map and was identified to be chaotic. The effect of the nonlinear characteristic of the wind transformer core on the ferroresonant overvoltage was examined and increased with the steepness of slope of the transformer curve. A damping resistor, shunt reactor and surge arrester were used to mitigate the overvoltage experienced during the ferroresonant event. The damping resistor was able to reduce the overvoltage to 1.24 P.U. and damped the ferroresonance from chaotic to fundamental mode.

Ferroresonance occurrence is a source of damage, causing overvoltage on voltage transformer (VT) and isolators of the grid equipment. Some solutions are available to protect VTs from the ferroresonance overvoltage. However, they just act after the ferroresonance occurrence. In this letter, to prevent the occurrence of ferroresonance, a dc reactor-based protection device is introduced. Analytical studies and simulations by MATLAB/Simulink and Maxwell ANSYS demonstrate the capability of the proposed protection device as a VT ferroresonance inhibitor. Experimental results from a scaled-down laboratory prototype are also provided to verify the proposed solution. [ABSTRACT FROM AUTHOR]

The paper discusses the problem of the ferroresonance phenomenon occurring in a medium voltage grid with an ungrounded neutral point of the supply transformer. Results of a study of ferroresonance in the auxiliary grid at Żarnowiec Pumped Storage Power Plant are presented. Analysis of the study results has led to the development and implementation of an effective method of preventing the adverse ferroresonance phenomenon.

Power quality events associated with the occurrence of ferroresonances in medium voltage (MV) isolated‐neutral distribution power systems are well known but they still happen in nowadays grids. This work deals with the study of ferroresonance events in a distribution grid region characterised by having distributed generators and being lightly loaded. The study shows that well‐known solutions, i.e. voltage transformer damping, are difficult to apply due to the legal considerations and, alternatively, the distribution system operator can take actions to minimise their effect on the distribution system. The data provided and the obtained results correspond to a three‐year measurement campaign at a real MV isolated‐neutral distribution power system. The measurements and analysis given allow reaching general conclusions about the distribution system operation oriented to minimise the effect of ferroresonances. [ABSTRACT FROM AUTHOR]