The Experts below are selected from a list of 309 Experts worldwide ranked by ideXlab platform
Jakub Furgał - One of the best experts on this subject based on the ideXlab platform.
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Overvoltage Impact on Internal Insulation Systems of Transformers in Electrical Networks with Vacuum Circuit Breakers
Energies, 2020Co-Authors: Marek Florkowski, Jakub Furgał, Maciej Kuniewski, Piotr PająkAbstract:Vacuum circuit breakers are increasingly used as switching apparatus in electric power systems. The vacuum circuit breakers (VCBs) have very good operating properties. VCBs are characterized by specific physical phenomena that affect overvoltage exposure of the insulation systems of other devices. The most important phenomena are the ability to chop the current before the natural zero crossing, the ability to switch off high-frequency currents, and the rapid increase in dielectric strength recovery. One of the devices connected directly to vacuum circuit breakers is the distribution transformer. Overvoltages generated in electrical systems during switching off the transformers are a source of internal Overvoltages in the windings. The analysis of the exposure of transformers operating in electrical networks equipped with vacuum circuit breakers is of great importance because of the impact on the insulation systems of switching Overvoltages (SO). These types of Overvoltages can be characterized by high maximum values and atypical waveforms, depending on the phenomena in the circuit breaker chambers, system configuration, parameters of electrical devices, and overvoltage protection. Overvoltages that stress the internal insulation systems are the result of the windings response to Overvoltages at transformer terminals. This article presents an analysis of Overvoltages that stress the transformer insulation systems, which occur while switching off transformers in systems with vacuum circuit breakers. The analysis was based on the results of laboratory measurements of switching Overvoltages at transformer terminals and inside the winding, in a model medium-voltage electrical network with a vacuum circuit breaker.
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Analysis of Internal Overvoltages in Transformer Windings during Transients in Electrical Networks
Energies, 2020Co-Authors: Jakub Furgał, Maciej Kuniewski, Piotr PająkAbstract:Due to the increasing requirements for the reliability of electrical power supply and associated apparatus, it is necessary to provide a detailed analysis of the overvoltage risk of power transformer insulation systems and equipment connected to their terminals. Exposure of transformer windings to Overvoltages is the result of the propagation condition of electromagnetic waves in electrical networks and transformer windings. An analysis of transformer winding responses to transients in power systems is of particular importance, especially when protection against surges by typical overvoltage protection systems is applied. The analysis of internal Overvoltages in transformers during a typical transient related to switching operations and selected failures is of great importance, particularly to assess the overvoltage exposure of insulation systems in operating conditions. The random nature of overvoltage phenomena in electrical networks implies the usage of computer simulations for the analysis of overvoltage exposures of electrical devices in operation. This article presents the analysis of the impact of transient phenomena in a model of a medium-voltage electrical network during switching operations and ground faults on Overvoltages in the internal insulation systems of transformer windings. The basis of the analysis is simulations of Overvoltages in the windings, made in the Electromagnetic Transients Program/Alternative Transients Program (EMTP/ATP) using a model with lumped parameters of transformer windings. The analysis covers the impact of the cable line length and the ground fault resistance value on internal overvoltage distributions.
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Influence of Lightning Current Model on Simulations of Overvoltages in High Voltage Overhead Transmission Systems
Energies, 2020Co-Authors: Jakub FurgałAbstract:The analysis of lightning Overvoltages generated in electrical power systems has a great meaning for the designers and exploitation engineers because it creates bases for the optimization of construction overhead transmission lines and high voltage substations, reducing costs and increasing reliability of the transmission and distribution of electrical energy. Lightning Overvoltages generated in electrical power systems with overhead transmission lines are a result of complex, nonlinear, and surge phenomena occurring in the structure of line towers and electrical substation when the lightning current is flowing through them. Methods of overvoltage stress analysis are intensely developed, and one of the directions is working out models of high voltage electrical devices and phenomena in electrical networks, which influence the shape and values of overvoltage risks. The model of lightning current has a significant influence on the courses of Overvoltages in high voltage transmission systems. The paper is focused on the analysis of the influence of the model of lightning current making use of simulations of the shape, and maximal values of Overvoltages generated in high voltage transmission systems during a direct lightning strike to the overhead lines. Two models of lightning current used in simulations with the Electromagnetic Transients Program/Alternative Transient Program (EMTP/ATP) were analyzed, i.e., the Heidler model and CIGRE (Conseil International des Grands Réseaux Électriques) model. The EMTP/ATP computer program is very often used in simulations of Overvoltages in electrical networks. Unfortunately, the users get no information on the criterion to be used when selecting the model of lightning current used in the simulations. The analysis presented in the paper gives practical knowledge about the effect of the use of a particular kind of lightning current model on the results of simulations of lightning overvoltage propagation in electrical networks, overvoltage protection, as well as on theoretical and practical aspects of the insulation coordination in high voltage transmission systems.
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Investigation of Overvoltages in distribution transformers
2017 18th International Scientific Conference on Electric Power Engineering (EPE), 2017Co-Authors: Marek Florkowski, Jakub Furgał, Maciej Kuniewski, Piotr PajakAbstract:Nowadays voltage transients in electrical power systems can take different shapes related to properties of distortion source and physical phenomenon appearing in systems. Usually Overvoltages contain oscillation components of different frequencies, which are propagating along lines reaching transformer terminals. Overvoltages impact power transformer insulation systems in spite of used overvoltage protection. Analysis of Overvoltages in winding insulation systems have strong importance in proper and reliable work of transformers. Due to complex configuration of transformer winding different Overvoltages levels can occur inside winding than at winding terminals. This article presents investigation of internal Overvoltages in distribution transformer windings. Analysis was based on measurements results of transient voltages and frequency characteristics. Investigation of resonance frequencies based on winding admittance measurements was made also.
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Propagation of high frequency Overvoltages in transformers
2014 ICHVE International Conference on High Voltage Engineering and Application, 2014Co-Authors: Marek Florkowski, Pawel Klys, Jakub Furgał, Maciej KuniewskiAbstract:In modern grids and networks more and more switching and reconfiguration operations are present. In addition external stresses like lightning may cause Overvoltages. Thus, such transients may subject the electric insulation system of power equipment. The crest value of Overvoltages appearing at the transformer terminals are limited by protective devices such as surge arresters to the level determined by the insulation coordination. Those values are usually much higher than maximum nominal voltage. In some cases Overvoltages may influence transformers despite of overvoltage protection systems. Usually Overvoltages contain oscillating dumped components in broad frequency range. Thus, often the internal Overvoltages formed inside the insulation system of high voltage equipment are caused by internal resonance in windings. Particularly some switching transients of oscillating character may cause high amplitude internal Overvoltages. Overvoltages manifesting such character and having lower amplitude than the protection level of the surge arresters are not attenuated at the transformer terminal. They arrive to the transformer input practically without any changes both in amplitude and waveform. The paper will present comparison of overvoltage propagation in different types of transformer design, taking into account also impact of steel and amorphous core. Both resonance and transfer Overvoltages will be analyzed.
Piotr Pająk - One of the best experts on this subject based on the ideXlab platform.
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Overvoltage Impact on Internal Insulation Systems of Transformers in Electrical Networks with Vacuum Circuit Breakers
Energies, 2020Co-Authors: Marek Florkowski, Jakub Furgał, Maciej Kuniewski, Piotr PająkAbstract:Vacuum circuit breakers are increasingly used as switching apparatus in electric power systems. The vacuum circuit breakers (VCBs) have very good operating properties. VCBs are characterized by specific physical phenomena that affect overvoltage exposure of the insulation systems of other devices. The most important phenomena are the ability to chop the current before the natural zero crossing, the ability to switch off high-frequency currents, and the rapid increase in dielectric strength recovery. One of the devices connected directly to vacuum circuit breakers is the distribution transformer. Overvoltages generated in electrical systems during switching off the transformers are a source of internal Overvoltages in the windings. The analysis of the exposure of transformers operating in electrical networks equipped with vacuum circuit breakers is of great importance because of the impact on the insulation systems of switching Overvoltages (SO). These types of Overvoltages can be characterized by high maximum values and atypical waveforms, depending on the phenomena in the circuit breaker chambers, system configuration, parameters of electrical devices, and overvoltage protection. Overvoltages that stress the internal insulation systems are the result of the windings response to Overvoltages at transformer terminals. This article presents an analysis of Overvoltages that stress the transformer insulation systems, which occur while switching off transformers in systems with vacuum circuit breakers. The analysis was based on the results of laboratory measurements of switching Overvoltages at transformer terminals and inside the winding, in a model medium-voltage electrical network with a vacuum circuit breaker.
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Analysis of Internal Overvoltages in Transformer Windings during Transients in Electrical Networks
Energies, 2020Co-Authors: Jakub Furgał, Maciej Kuniewski, Piotr PająkAbstract:Due to the increasing requirements for the reliability of electrical power supply and associated apparatus, it is necessary to provide a detailed analysis of the overvoltage risk of power transformer insulation systems and equipment connected to their terminals. Exposure of transformer windings to Overvoltages is the result of the propagation condition of electromagnetic waves in electrical networks and transformer windings. An analysis of transformer winding responses to transients in power systems is of particular importance, especially when protection against surges by typical overvoltage protection systems is applied. The analysis of internal Overvoltages in transformers during a typical transient related to switching operations and selected failures is of great importance, particularly to assess the overvoltage exposure of insulation systems in operating conditions. The random nature of overvoltage phenomena in electrical networks implies the usage of computer simulations for the analysis of overvoltage exposures of electrical devices in operation. This article presents the analysis of the impact of transient phenomena in a model of a medium-voltage electrical network during switching operations and ground faults on Overvoltages in the internal insulation systems of transformer windings. The basis of the analysis is simulations of Overvoltages in the windings, made in the Electromagnetic Transients Program/Alternative Transients Program (EMTP/ATP) using a model with lumped parameters of transformer windings. The analysis covers the impact of the cable line length and the ground fault resistance value on internal overvoltage distributions.
Maciej Kuniewski - One of the best experts on this subject based on the ideXlab platform.
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Overvoltage Impact on Internal Insulation Systems of Transformers in Electrical Networks with Vacuum Circuit Breakers
Energies, 2020Co-Authors: Marek Florkowski, Jakub Furgał, Maciej Kuniewski, Piotr PająkAbstract:Vacuum circuit breakers are increasingly used as switching apparatus in electric power systems. The vacuum circuit breakers (VCBs) have very good operating properties. VCBs are characterized by specific physical phenomena that affect overvoltage exposure of the insulation systems of other devices. The most important phenomena are the ability to chop the current before the natural zero crossing, the ability to switch off high-frequency currents, and the rapid increase in dielectric strength recovery. One of the devices connected directly to vacuum circuit breakers is the distribution transformer. Overvoltages generated in electrical systems during switching off the transformers are a source of internal Overvoltages in the windings. The analysis of the exposure of transformers operating in electrical networks equipped with vacuum circuit breakers is of great importance because of the impact on the insulation systems of switching Overvoltages (SO). These types of Overvoltages can be characterized by high maximum values and atypical waveforms, depending on the phenomena in the circuit breaker chambers, system configuration, parameters of electrical devices, and overvoltage protection. Overvoltages that stress the internal insulation systems are the result of the windings response to Overvoltages at transformer terminals. This article presents an analysis of Overvoltages that stress the transformer insulation systems, which occur while switching off transformers in systems with vacuum circuit breakers. The analysis was based on the results of laboratory measurements of switching Overvoltages at transformer terminals and inside the winding, in a model medium-voltage electrical network with a vacuum circuit breaker.
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Analysis of Internal Overvoltages in Transformer Windings during Transients in Electrical Networks
Energies, 2020Co-Authors: Jakub Furgał, Maciej Kuniewski, Piotr PająkAbstract:Due to the increasing requirements for the reliability of electrical power supply and associated apparatus, it is necessary to provide a detailed analysis of the overvoltage risk of power transformer insulation systems and equipment connected to their terminals. Exposure of transformer windings to Overvoltages is the result of the propagation condition of electromagnetic waves in electrical networks and transformer windings. An analysis of transformer winding responses to transients in power systems is of particular importance, especially when protection against surges by typical overvoltage protection systems is applied. The analysis of internal Overvoltages in transformers during a typical transient related to switching operations and selected failures is of great importance, particularly to assess the overvoltage exposure of insulation systems in operating conditions. The random nature of overvoltage phenomena in electrical networks implies the usage of computer simulations for the analysis of overvoltage exposures of electrical devices in operation. This article presents the analysis of the impact of transient phenomena in a model of a medium-voltage electrical network during switching operations and ground faults on Overvoltages in the internal insulation systems of transformer windings. The basis of the analysis is simulations of Overvoltages in the windings, made in the Electromagnetic Transients Program/Alternative Transients Program (EMTP/ATP) using a model with lumped parameters of transformer windings. The analysis covers the impact of the cable line length and the ground fault resistance value on internal overvoltage distributions.
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comparison of transformer winding responses to standard lightning impulses and operational Overvoltages
IEEE Transactions on Dielectrics and Electrical Insulation, 2018Co-Authors: Marek Florkowski, Maciej Kuniewski, Jakub Furgal, Piotr PajakAbstract:During operation transformers are typically subjected to Overvoltages with different wave shapes. Even though overvoltage protection systems, such as metal oxide surge arresters, are often employed, the Overvoltages generated in power systems can still have a significant impact on the insulation systems of the windings of a power transformer. There are numerous examples of transformer failures as a result of Overvoltages occurring during operation, even in cases that standard impulse voltage tests show no indication of potential problems and the transformers are protected by surge arresters. Comparisons of the internal Overvoltages generated in transformers during voltage tests as well as those generated during standard operation of electrical networks provides fundamental insights into these Overvoltages; insights which in turn can be used to improve the construction of insulation systems and overvoltage protection approaches and ultimately increase the reliability of transformers. In this paper, internal Overvoltages occurring in the windings of selected transformer during standard voltage tests are compared with those which occur during typical operation of a transformer in an electrical power system. Overvoltages measured in the windings of the transformer form the basis of this comparison. Measurements were conducted with the transformer being subjected to voltage impulse tests, as well as transient voltages with waveforms simulating Overvoltages generated in electrical power systems. In order to investigate the response of the windings to voltage strokes, full and chopped lightning voltage impulses were applied to the transformer. The waveforms of Overvoltages generated in the electrical power systems were modelled as a rectangular voltage stroke, sinusoidal voltage, voltage with shape of “sweep sinus” also often referred to as a chirp signal and voltage with shape of “sweep ramp”.
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Investigation of Overvoltages in distribution transformers
2017 18th International Scientific Conference on Electric Power Engineering (EPE), 2017Co-Authors: Marek Florkowski, Jakub Furgał, Maciej Kuniewski, Piotr PajakAbstract:Nowadays voltage transients in electrical power systems can take different shapes related to properties of distortion source and physical phenomenon appearing in systems. Usually Overvoltages contain oscillation components of different frequencies, which are propagating along lines reaching transformer terminals. Overvoltages impact power transformer insulation systems in spite of used overvoltage protection. Analysis of Overvoltages in winding insulation systems have strong importance in proper and reliable work of transformers. Due to complex configuration of transformer winding different Overvoltages levels can occur inside winding than at winding terminals. This article presents investigation of internal Overvoltages in distribution transformer windings. Analysis was based on measurements results of transient voltages and frequency characteristics. Investigation of resonance frequencies based on winding admittance measurements was made also.
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Propagation of high frequency Overvoltages in transformers
2014 ICHVE International Conference on High Voltage Engineering and Application, 2014Co-Authors: Marek Florkowski, Pawel Klys, Jakub Furgał, Maciej KuniewskiAbstract:In modern grids and networks more and more switching and reconfiguration operations are present. In addition external stresses like lightning may cause Overvoltages. Thus, such transients may subject the electric insulation system of power equipment. The crest value of Overvoltages appearing at the transformer terminals are limited by protective devices such as surge arresters to the level determined by the insulation coordination. Those values are usually much higher than maximum nominal voltage. In some cases Overvoltages may influence transformers despite of overvoltage protection systems. Usually Overvoltages contain oscillating dumped components in broad frequency range. Thus, often the internal Overvoltages formed inside the insulation system of high voltage equipment are caused by internal resonance in windings. Particularly some switching transients of oscillating character may cause high amplitude internal Overvoltages. Overvoltages manifesting such character and having lower amplitude than the protection level of the surge arresters are not attenuated at the transformer terminal. They arrive to the transformer input practically without any changes both in amplitude and waveform. The paper will present comparison of overvoltage propagation in different types of transformer design, taking into account also impact of steel and amorphous core. Both resonance and transfer Overvoltages will be analyzed.
Marjan Popov - One of the best experts on this subject based on the ideXlab platform.
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probabilistic analysis of switching transients due to vacuum circuit breaker operation on wind turbine step up transformers
Electric Power Systems Research, 2020Co-Authors: Sajjad Ghasemi, Mehdi Allahbakhshi, Behzad Behdani, Mohsen Tajdinian, Marjan PopovAbstract:Vacuum circuit breaker operation causes transient Overvoltages that may lead to severe damages to transformer insulation. Since the parameters affecting these Overvoltages have stochastic nature, a statistical analysis may provide detailed insight into the Overvoltages from the point of view of insulation coordination applications. In this paper, a statistical analysis of the overvoltage variations of the step-up transformer during vacuum circuit breaker operation is conducted. Some variables, including switching angle, current chopping, high-frequency current quenching capability, and wind turbine power, are assumed as random variables. Besides, some indicators representing the switching overvoltage characteristics such as the amplitude, the number of restrikes, and the rate of rise are extracted. By performing a probabilistic analysis, the destructiveness due to switching Overvoltages on typical transformer insulation can be investigated. The sensitivity of different surge protective devices and their effectivities are also analyzed and statistically evaluated. The applied methodology is very useful because of the stochastic nature of the switching Overvoltages. In this work, the impact of protective equipment on each of the overvoltage indicators is analyzed. It is also found that considering only the amplitudes of transient Overvoltages is not enough to draw conclusions about the safety of the transformer when exposed to frequent switching surges.
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statistical analysis of energization Overvoltages in ehv hybrid ohl cable systems
IEEE Transactions on Power Delivery, 2018Co-Authors: Hossein Khalilnezhad, Lou Van Der Sluis, Marjan Popov, Jorrit A Bos, Akihiro AmetaniAbstract:Energization Overvoltages are among the severest Overvoltages stressing insulations of EHV power system components. Since these Overvoltages have a statistical nature, the insulation level should be determined with the use of a statistical approach by which the distribution of Overvoltages is calculated. Literature has properly studied the distribution of energization Overvoltages in purely overhead line (OHL) or cable systems, but such a study is not available for hybrid systems consisting of both OHLs and cables. It is expected that the overvoltage distributions change substantially when both OHLs and cables are used in a transmission line. This paper tackles this issue by analyzing the overvoltage distributions due to the energization of a 380 kV hybrid OHL-cable circuit, in which the cable length is variable. The study includes various sensitivity analyses to find out the impact of system parameters and topology on Overvoltages. By the statistical analysis, it has been discovered that energization Overvoltages of a hybrid OHL–cable circuit are higher than those of a fully-cable circuit and very likely lower than those of a fully-OHL circuit with the same transmission lengths.
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Analysis of switching transient Overvoltages in the power system of floating production storage and offloading vessel
Electric Power Systems Research, 2014Co-Authors: Haoyan Xue, Marjan PopovAbstract:Abstract Large transient Overvoltages can be caused by the switching operation of vacuum circuit breakers (VCBs) during disconnection of induction motors. In this paper VCBs, cables, generators, busbars, induction motors and surge arresters are modeled by making use of ATP-EMTP. Switching transient Overvoltages of four typical induction motors under the starting, the full load and the light load working conditions in the power system of the selected floating production storage and offloading (FPSO) vessel are analyzed. A suitable protection against the switching transient overvoltage is proposed and the results are presented accordingly.
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Analysis of Switching Transient Overvoltages in the Power System of Floating Production Storage and Offloading Vessel
2013Co-Authors: Haoyan Xue, Marjan PopovAbstract:Large transient Overvoltages are normally caused by vacuum circuit breaker (VCB) switching operation during disconnection of induction motors. In this paper VCBs, cables, generators, busbars, induction motors and surge arresters are modeled by making use of ATP-EMTP. Switching transient Overvoltages of four typical induction motors are analyzed under starting, full load and light load working conditions in a power system of a Floating Production Storage and Offloading (FPSO) vessel. A suitable protection against the switching transient overvoltage is proposed and the results are presented.
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Comparison of two vacuum circuit breaker arc models for small inductive current switching
Proceedings ISDEIV. 19th International Symposium on Discharges and Electrical Insulation in Vacuum (Cat. No.00CH37041), 2000Co-Authors: Marjan Popov, Lou Van Der SluisAbstract:The goal of this paper is to present two different methods of modelling the reignitions caused by switching of small inductive currents with a vacuum circuit breaker (VCB). Both models are presented for different VCBs which are described by their measured characteristics. For a detailed modelled system, the Overvoltages caused by unloaded transformer switching are calculated and the statistical overvoltage distribution is estimated.
Marek Florkowski - One of the best experts on this subject based on the ideXlab platform.
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Overvoltage Impact on Internal Insulation Systems of Transformers in Electrical Networks with Vacuum Circuit Breakers
Energies, 2020Co-Authors: Marek Florkowski, Jakub Furgał, Maciej Kuniewski, Piotr PająkAbstract:Vacuum circuit breakers are increasingly used as switching apparatus in electric power systems. The vacuum circuit breakers (VCBs) have very good operating properties. VCBs are characterized by specific physical phenomena that affect overvoltage exposure of the insulation systems of other devices. The most important phenomena are the ability to chop the current before the natural zero crossing, the ability to switch off high-frequency currents, and the rapid increase in dielectric strength recovery. One of the devices connected directly to vacuum circuit breakers is the distribution transformer. Overvoltages generated in electrical systems during switching off the transformers are a source of internal Overvoltages in the windings. The analysis of the exposure of transformers operating in electrical networks equipped with vacuum circuit breakers is of great importance because of the impact on the insulation systems of switching Overvoltages (SO). These types of Overvoltages can be characterized by high maximum values and atypical waveforms, depending on the phenomena in the circuit breaker chambers, system configuration, parameters of electrical devices, and overvoltage protection. Overvoltages that stress the internal insulation systems are the result of the windings response to Overvoltages at transformer terminals. This article presents an analysis of Overvoltages that stress the transformer insulation systems, which occur while switching off transformers in systems with vacuum circuit breakers. The analysis was based on the results of laboratory measurements of switching Overvoltages at transformer terminals and inside the winding, in a model medium-voltage electrical network with a vacuum circuit breaker.
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comparison of transformer winding responses to standard lightning impulses and operational Overvoltages
IEEE Transactions on Dielectrics and Electrical Insulation, 2018Co-Authors: Marek Florkowski, Maciej Kuniewski, Jakub Furgal, Piotr PajakAbstract:During operation transformers are typically subjected to Overvoltages with different wave shapes. Even though overvoltage protection systems, such as metal oxide surge arresters, are often employed, the Overvoltages generated in power systems can still have a significant impact on the insulation systems of the windings of a power transformer. There are numerous examples of transformer failures as a result of Overvoltages occurring during operation, even in cases that standard impulse voltage tests show no indication of potential problems and the transformers are protected by surge arresters. Comparisons of the internal Overvoltages generated in transformers during voltage tests as well as those generated during standard operation of electrical networks provides fundamental insights into these Overvoltages; insights which in turn can be used to improve the construction of insulation systems and overvoltage protection approaches and ultimately increase the reliability of transformers. In this paper, internal Overvoltages occurring in the windings of selected transformer during standard voltage tests are compared with those which occur during typical operation of a transformer in an electrical power system. Overvoltages measured in the windings of the transformer form the basis of this comparison. Measurements were conducted with the transformer being subjected to voltage impulse tests, as well as transient voltages with waveforms simulating Overvoltages generated in electrical power systems. In order to investigate the response of the windings to voltage strokes, full and chopped lightning voltage impulses were applied to the transformer. The waveforms of Overvoltages generated in the electrical power systems were modelled as a rectangular voltage stroke, sinusoidal voltage, voltage with shape of “sweep sinus” also often referred to as a chirp signal and voltage with shape of “sweep ramp”.
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Investigation of Overvoltages in distribution transformers
2017 18th International Scientific Conference on Electric Power Engineering (EPE), 2017Co-Authors: Marek Florkowski, Jakub Furgał, Maciej Kuniewski, Piotr PajakAbstract:Nowadays voltage transients in electrical power systems can take different shapes related to properties of distortion source and physical phenomenon appearing in systems. Usually Overvoltages contain oscillation components of different frequencies, which are propagating along lines reaching transformer terminals. Overvoltages impact power transformer insulation systems in spite of used overvoltage protection. Analysis of Overvoltages in winding insulation systems have strong importance in proper and reliable work of transformers. Due to complex configuration of transformer winding different Overvoltages levels can occur inside winding than at winding terminals. This article presents investigation of internal Overvoltages in distribution transformer windings. Analysis was based on measurements results of transient voltages and frequency characteristics. Investigation of resonance frequencies based on winding admittance measurements was made also.
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Propagation of high frequency Overvoltages in transformers
2014 ICHVE International Conference on High Voltage Engineering and Application, 2014Co-Authors: Marek Florkowski, Pawel Klys, Jakub Furgał, Maciej KuniewskiAbstract:In modern grids and networks more and more switching and reconfiguration operations are present. In addition external stresses like lightning may cause Overvoltages. Thus, such transients may subject the electric insulation system of power equipment. The crest value of Overvoltages appearing at the transformer terminals are limited by protective devices such as surge arresters to the level determined by the insulation coordination. Those values are usually much higher than maximum nominal voltage. In some cases Overvoltages may influence transformers despite of overvoltage protection systems. Usually Overvoltages contain oscillating dumped components in broad frequency range. Thus, often the internal Overvoltages formed inside the insulation system of high voltage equipment are caused by internal resonance in windings. Particularly some switching transients of oscillating character may cause high amplitude internal Overvoltages. Overvoltages manifesting such character and having lower amplitude than the protection level of the surge arresters are not attenuated at the transformer terminal. They arrive to the transformer input practically without any changes both in amplitude and waveform. The paper will present comparison of overvoltage propagation in different types of transformer design, taking into account also impact of steel and amorphous core. Both resonance and transfer Overvoltages will be analyzed.
