The Experts below are selected from a list of 327120 Experts worldwide ranked by ideXlab platform
Jasmin Smajic - One of the best experts on this subject based on the ideXlab platform.
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Behaviour of Cellulosic Oil Impregnated Insulation Material at High Frequency Stress Used for High Voltage Solid State Transformer Applications
Proceedings of the 21st International Symposium on High Voltage Engineering, 2020Co-Authors: Michael Schueller, U. Kaminskis, Richard Christen, P. Schmitt, Jasmin SmajicAbstract:Solid state Transformers (SSTs) are a new type of Transformers where power electronics and conventional transforming elements are combined into one. The basic principle is that the voltage gets converted into the kHz range before it is transformed to another voltage level. The main advantage of this technology is the size of the Transformer - due to the used higher frequency the Transformer core and thus the whole apparatus can be built smaller than traditional 50/60 Hz power Transformers. Currently there are no oil impregnated cellulosic insulation systems available for high-voltage high-frequency applications. This is partly because the exact breakdown mechanism at high frequency (HF) stress is still unclear and partly because long-term behavior of cellulosic insulation systems under HF-stress is unknown. The main goal of this publication is to provide new experiments and data to contribute on the research of the HF breakdown mechanism in oil impregnated cellulosic insulation systems. For this purpose breakdown experiments on oil impregnated paper samples were conducted at frequencies of 50 Hz, 20 kHz and 40 kHz with unipolar voltage pulses. Tests were performed at 20 ℃ and 90 ℃ in synthetic ester fluid Midel 7131. As voltage source a special self-developed pulsed HF generator was used that provides high-voltage high-frequency voltage up to 6.5 kV between 50 Hz and 40 kHz. As expected, decrease in breakdown voltage with increasing frequency could be shown. But more important, the findings presented in this paper surprisingly also suggest that contrary to most literature not heating due to increased polarization losses is the main responsible breakdown mechanism at high frequency stress.
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development of a pulsed high frequency source for testing cellulosic insulation material for high voltage solid state Transformer applications
IEEE International Conference on High Voltage Engineering and Application, 2018Co-Authors: Michael Schueller, Giuliano Gatti, Schmitt Ph, S Jaufer, Krause Ch, Richard Christen, Jasmin SmajicAbstract:Solid state Transformers (SSTs) are believed to play a major role in the near future due to their additional features compared to conventional Transformers. SSTs are a combination of power electronics and a conventional Transformer. The function of this device is to commute the signal into the kHz range before it is transformed to another voltage with the conventional Transformer within the SST. Many different topologies for the power electronic part in SST applications have been implemented and presented in literature. Many newer publications use SiC MOSFETs due to their high achievable blocking voltage and fast switching speed. The transforming element in SST applications, where a higher amount of power is needed, will still be a conventional Transformer with conventional insulation. Thus the oil paper insulation system has to be investigated experimentally in respect of the higher frequency stress. For these investigations a source is needed that can deliver voltage stress which is present in SST applications. Thus a pulsed high frequency (HF) source had to be developed to be able to test and study the insulation in detail. In this publication we show the development and function of such a pulsed HF source for voltages up to 5 kV. Also first measurement results of tests at 20 kHz and 40 kHz are presented and compared with 50 Hz measurements.
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development of a pulsed high frequency source for testing cellulosic insulation material for high voltage solid state Transformer applications
IEEE International Conference on High Voltage Engineering and Application, 2018Co-Authors: Michael Schueller, Giuliano Gatti, Schmitt Ph, S Jaufer, Krause Ch, Richard Christen, Jasmin SmajicAbstract:Solid state Transformers (SSTs) are believed to play a major role in the near future due to their additional features compared to conventional Transformers. SSTs are a combination of power electronics and a conventional Transformer. The function of this device is to commute the signal into the kHz range before it is transformed to another voltage with the conventional Transformer within the SST. Many different topologies for the power electronic part in SST applications have been implemented and presented in literature. Many newer publications use SiC MOSFETs due to their high achievable blocking voltage and fast switching speed. The transforming element in SST applications, where a higher amount of power is needed, will still be a conventional Transformer with conventional insulation. Thus the oil paper insulation system has to be investigated experimentally in respect of the higher frequency stress. For these investigations a source is needed that can deliver voltage stress which is present in SST applications. Thus a pulsed high frequency (HF) source had to be developed to be able to test and study the insulation in detail. In this publication we show the development and function of such a pulsed HF source for voltages up to 5 kV. Also first measurement results of tests at 20 kHz and 40 kHz are presented and compared with 50 Hz measurements.
Charles J. Mozina - One of the best experts on this subject based on the ideXlab platform.
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Improvements in protection and commissioning of digital Transformer relays at medium voltage industrial facilities
IEEE Conference Record of Annual Pulp and Paper Industry Technical Conference, 2011Co-Authors: Charles J. MozinaAbstract:The application of multifunction digital relays to protect medium voltage power Transformers has become a common industrial practice. Industrial Transformers, unlike utility Transformers, frequently use neutral grounding resistors to limit ground current during faults to 200–400A range on medium voltage systems. This paper will discuss why these types of Transformers require sensitive ground differential protection. The paper will also discuss the basics of Transformer protection including: phasing standards, through-fault withstand capability, differential/fusing/overcurrent protection, slope, CT requirements, harmonic restraint, and communicating these requirements properly when programming and commissioning new digital relays. The rationale for providing Transformer overexcitation protection on all major Transformers within industrial facilities is also addressed. Advancements in digital technology have allowed relay manufacturers to include more and more relay functions within a single hardware platform as well as address more and more Transformer winding configurations. This has resulted in digital Transformer relays requiring an experienced protection engineer to set and an experienced relay testing technician to commission. Since there are fewer experienced professionals among us now, the next generation of Transformer relays needs to concentrate on this complexity issue in addition to technical improvements. This paper addresses these issues that the author believes are the major shortcomings of existing digital Transformer protective relays.
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improvements in protection and commissioning of digital Transformer relays at medium voltage industrial facilities
Petroleum and Chemical Industry Technical Conference, 2010Co-Authors: Charles J. MozinaAbstract:The application of multifunction digital relays to protect medium voltage power Transformers has become a common industrial practice. Industrial Transformers, unlike utility Transformers, frequently use neutral grounding resistors to limit ground current during faults to 200–400A range on medium voltage systems. This paper will discuss why these types of Transformers require sensitive ground differential protection. The paper will also discuss the basics of Transformer protection including: phasing standards, through-fault withstand capability, differential/fusing/overcurrent protection, slope, CT requirements, harmonic restraint, and communicating these requirements properly when programming and commissioning new digital relays. The rationale for providing Transformer overexcitation protection on all major Transformers within industrial facilities is also addressed. Advancements in digital technology have allowed relay manufacturers to include more and more relay functions within a single hardware platform as well as address more and more Transformer winding configurations. This has resulted in digital Transformer relays requiring an Einstein to set and an Edison to commission. Since there are few Einstein's and Edison's among us, the next generation of Transformer relays needs to concentrate on this complexity issue in addition to technical improvements. This paper addresses these issues that the author believes are the major shortcomings of existing digital Transformer protective relays.
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protection and commissioning of multifunction digital Transformer relays at medium voltage industrial facilities
Pulp and Paper Industry Conference, 2005Co-Authors: Charles J. MozinaAbstract:The application of multifunction digital relays to protect medium voltage power Transformers has become a common industrial practice. Industrial Transformers, unlike utility Transformers, frequently use neutral grounding resistors to limit ground current during faults to the 200-400-A level on medium voltage systems. This paper will discuss why these types of Transformers require sensitive ground differential protection. The paper will also discuss the basics of Transformer protection including phasing standards, through-fault withstand capability, differential/fusing/overcurrent protection, slope, current Transformer (CT) requirements, and harmonic restraint, and communicating these properly to new digital relays. The rationale for providing Transformer overexcitation protection on all major Transformers within mill facilities is also addressed. Advancements in digital technology have allowed relay manufacturers to include more and more relay functions within a single hardware platform as well as address increasingly more Transformer winding configurations. This has resulted in digital Transformer relays requiring an Einstein to set and an Edison to commission. Since there are few Einsteins or Edisons among us, the next generation of Transformer relays needs to concentrate on this complexity issue in addition to technical improvements. This paper addresses these issues that the author believes are the major shortcomings of existing digital Transformer protective relays.
Michael Schueller - One of the best experts on this subject based on the ideXlab platform.
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Behaviour of Cellulosic Oil Impregnated Insulation Material at High Frequency Stress Used for High Voltage Solid State Transformer Applications
Proceedings of the 21st International Symposium on High Voltage Engineering, 2020Co-Authors: Michael Schueller, U. Kaminskis, Richard Christen, P. Schmitt, Jasmin SmajicAbstract:Solid state Transformers (SSTs) are a new type of Transformers where power electronics and conventional transforming elements are combined into one. The basic principle is that the voltage gets converted into the kHz range before it is transformed to another voltage level. The main advantage of this technology is the size of the Transformer - due to the used higher frequency the Transformer core and thus the whole apparatus can be built smaller than traditional 50/60 Hz power Transformers. Currently there are no oil impregnated cellulosic insulation systems available for high-voltage high-frequency applications. This is partly because the exact breakdown mechanism at high frequency (HF) stress is still unclear and partly because long-term behavior of cellulosic insulation systems under HF-stress is unknown. The main goal of this publication is to provide new experiments and data to contribute on the research of the HF breakdown mechanism in oil impregnated cellulosic insulation systems. For this purpose breakdown experiments on oil impregnated paper samples were conducted at frequencies of 50 Hz, 20 kHz and 40 kHz with unipolar voltage pulses. Tests were performed at 20 ℃ and 90 ℃ in synthetic ester fluid Midel 7131. As voltage source a special self-developed pulsed HF generator was used that provides high-voltage high-frequency voltage up to 6.5 kV between 50 Hz and 40 kHz. As expected, decrease in breakdown voltage with increasing frequency could be shown. But more important, the findings presented in this paper surprisingly also suggest that contrary to most literature not heating due to increased polarization losses is the main responsible breakdown mechanism at high frequency stress.
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development of a pulsed high frequency source for testing cellulosic insulation material for high voltage solid state Transformer applications
IEEE International Conference on High Voltage Engineering and Application, 2018Co-Authors: Michael Schueller, Giuliano Gatti, Schmitt Ph, S Jaufer, Krause Ch, Richard Christen, Jasmin SmajicAbstract:Solid state Transformers (SSTs) are believed to play a major role in the near future due to their additional features compared to conventional Transformers. SSTs are a combination of power electronics and a conventional Transformer. The function of this device is to commute the signal into the kHz range before it is transformed to another voltage with the conventional Transformer within the SST. Many different topologies for the power electronic part in SST applications have been implemented and presented in literature. Many newer publications use SiC MOSFETs due to their high achievable blocking voltage and fast switching speed. The transforming element in SST applications, where a higher amount of power is needed, will still be a conventional Transformer with conventional insulation. Thus the oil paper insulation system has to be investigated experimentally in respect of the higher frequency stress. For these investigations a source is needed that can deliver voltage stress which is present in SST applications. Thus a pulsed high frequency (HF) source had to be developed to be able to test and study the insulation in detail. In this publication we show the development and function of such a pulsed HF source for voltages up to 5 kV. Also first measurement results of tests at 20 kHz and 40 kHz are presented and compared with 50 Hz measurements.
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development of a pulsed high frequency source for testing cellulosic insulation material for high voltage solid state Transformer applications
IEEE International Conference on High Voltage Engineering and Application, 2018Co-Authors: Michael Schueller, Giuliano Gatti, Schmitt Ph, S Jaufer, Krause Ch, Richard Christen, Jasmin SmajicAbstract:Solid state Transformers (SSTs) are believed to play a major role in the near future due to their additional features compared to conventional Transformers. SSTs are a combination of power electronics and a conventional Transformer. The function of this device is to commute the signal into the kHz range before it is transformed to another voltage with the conventional Transformer within the SST. Many different topologies for the power electronic part in SST applications have been implemented and presented in literature. Many newer publications use SiC MOSFETs due to their high achievable blocking voltage and fast switching speed. The transforming element in SST applications, where a higher amount of power is needed, will still be a conventional Transformer with conventional insulation. Thus the oil paper insulation system has to be investigated experimentally in respect of the higher frequency stress. For these investigations a source is needed that can deliver voltage stress which is present in SST applications. Thus a pulsed high frequency (HF) source had to be developed to be able to test and study the insulation in detail. In this publication we show the development and function of such a pulsed HF source for voltages up to 5 kV. Also first measurement results of tests at 20 kHz and 40 kHz are presented and compared with 50 Hz measurements.
Richard Christen - One of the best experts on this subject based on the ideXlab platform.
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Behaviour of Cellulosic Oil Impregnated Insulation Material at High Frequency Stress Used for High Voltage Solid State Transformer Applications
Proceedings of the 21st International Symposium on High Voltage Engineering, 2020Co-Authors: Michael Schueller, U. Kaminskis, Richard Christen, P. Schmitt, Jasmin SmajicAbstract:Solid state Transformers (SSTs) are a new type of Transformers where power electronics and conventional transforming elements are combined into one. The basic principle is that the voltage gets converted into the kHz range before it is transformed to another voltage level. The main advantage of this technology is the size of the Transformer - due to the used higher frequency the Transformer core and thus the whole apparatus can be built smaller than traditional 50/60 Hz power Transformers. Currently there are no oil impregnated cellulosic insulation systems available for high-voltage high-frequency applications. This is partly because the exact breakdown mechanism at high frequency (HF) stress is still unclear and partly because long-term behavior of cellulosic insulation systems under HF-stress is unknown. The main goal of this publication is to provide new experiments and data to contribute on the research of the HF breakdown mechanism in oil impregnated cellulosic insulation systems. For this purpose breakdown experiments on oil impregnated paper samples were conducted at frequencies of 50 Hz, 20 kHz and 40 kHz with unipolar voltage pulses. Tests were performed at 20 ℃ and 90 ℃ in synthetic ester fluid Midel 7131. As voltage source a special self-developed pulsed HF generator was used that provides high-voltage high-frequency voltage up to 6.5 kV between 50 Hz and 40 kHz. As expected, decrease in breakdown voltage with increasing frequency could be shown. But more important, the findings presented in this paper surprisingly also suggest that contrary to most literature not heating due to increased polarization losses is the main responsible breakdown mechanism at high frequency stress.
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development of a pulsed high frequency source for testing cellulosic insulation material for high voltage solid state Transformer applications
IEEE International Conference on High Voltage Engineering and Application, 2018Co-Authors: Michael Schueller, Giuliano Gatti, Schmitt Ph, S Jaufer, Krause Ch, Richard Christen, Jasmin SmajicAbstract:Solid state Transformers (SSTs) are believed to play a major role in the near future due to their additional features compared to conventional Transformers. SSTs are a combination of power electronics and a conventional Transformer. The function of this device is to commute the signal into the kHz range before it is transformed to another voltage with the conventional Transformer within the SST. Many different topologies for the power electronic part in SST applications have been implemented and presented in literature. Many newer publications use SiC MOSFETs due to their high achievable blocking voltage and fast switching speed. The transforming element in SST applications, where a higher amount of power is needed, will still be a conventional Transformer with conventional insulation. Thus the oil paper insulation system has to be investigated experimentally in respect of the higher frequency stress. For these investigations a source is needed that can deliver voltage stress which is present in SST applications. Thus a pulsed high frequency (HF) source had to be developed to be able to test and study the insulation in detail. In this publication we show the development and function of such a pulsed HF source for voltages up to 5 kV. Also first measurement results of tests at 20 kHz and 40 kHz are presented and compared with 50 Hz measurements.
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development of a pulsed high frequency source for testing cellulosic insulation material for high voltage solid state Transformer applications
IEEE International Conference on High Voltage Engineering and Application, 2018Co-Authors: Michael Schueller, Giuliano Gatti, Schmitt Ph, S Jaufer, Krause Ch, Richard Christen, Jasmin SmajicAbstract:Solid state Transformers (SSTs) are believed to play a major role in the near future due to their additional features compared to conventional Transformers. SSTs are a combination of power electronics and a conventional Transformer. The function of this device is to commute the signal into the kHz range before it is transformed to another voltage with the conventional Transformer within the SST. Many different topologies for the power electronic part in SST applications have been implemented and presented in literature. Many newer publications use SiC MOSFETs due to their high achievable blocking voltage and fast switching speed. The transforming element in SST applications, where a higher amount of power is needed, will still be a conventional Transformer with conventional insulation. Thus the oil paper insulation system has to be investigated experimentally in respect of the higher frequency stress. For these investigations a source is needed that can deliver voltage stress which is present in SST applications. Thus a pulsed high frequency (HF) source had to be developed to be able to test and study the insulation in detail. In this publication we show the development and function of such a pulsed HF source for voltages up to 5 kV. Also first measurement results of tests at 20 kHz and 40 kHz are presented and compared with 50 Hz measurements.
Zoran Gajic - One of the best experts on this subject based on the ideXlab platform.
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Differential Protection for Arbitrary Three-Phase Power Transformers
2008Co-Authors: Zoran GajicAbstract:This thesis describes how to provide standardized, current based, differential protection for any three-phase power Transformer, including phase-shifting Transformers with variable phase angle shift and Transformers of all construction types and internal on-load tap-changer configurations. The use of standard Transformer differential protection for such applications is considered impossible in the protective relaying standards and practices currently applied. The first part of the thesis provides the background for different types of power Transformers and the differential protection schemes currently applied. After that a complete mathematical proof for the new, universal Transformer differential protection principle, based on theory of symmetrical components, is derived. It is demonstrated that it is possible to make numerical differential protection relays which can properly calculate differential currents for any power Transformer, regardless of whether it is of fixed or variable phase angle shift construction and whether current magnitude variations are caused by on-load tapchanger(s). It is shown how to correctly calculate differential currents by simultaneously providing on-line compensation for current magnitude variations, on-line compensation for arbitrary phase angle shift variations and settable zero-sequence current reduction on any power Transformer side. By using this method differential protection for arbitrary power Transformers will be ideally balanced for all symmetrical and nonsymmetrical through-load conditions and external faults. The method is independent of individual Transformer winding connection details (i.e. star, delta or zigzag), but dependent on having the correct information about actual on-load tap-changer(s) position if they are built-in within the protected power Transformer. The implementation and practical use of this new universal principle is quite simple, as all necessary Transformer data is commonly available on the protected power Transformer rating plate. Practical application of the universal method for the differential protection of standard Transformers, special Transformers and phase shifting Transformer is presented. Detailed testing of this new universal differential protection method is given and it is based on actual field recordings captured by numerical relays in existing phase-shifting Transformer installations and on simulations from the Real Time Digital Simulator for a practical dual-core, symmetrical phaseshifting Transformer. The implementation of the universal Transformer differential method for analogue and numerical Transformer differential relays is also described. Problems for the differential protection caused by Transformer inrush currents are discussed. The mathematical relationship between differential protection and directional protection is derived. Then it is shown that through the addition of supplementary directional criteria security and speed of the operation of the Transformer differential protection can be improved. Finally, the use of additional directional criteria to significantly improve the sensitivity of the differential protection for Transformer winding turn-to-turn faults is suggested. Captured disturbance files from numerical differential relays in actual power Transformer installations, during internal and external faults, have been used to demonstrate the performance of additional directional criteria. (Less)
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Differential Protection for Special Industrial Transformers
IEEE Transactions on Power Delivery, 2007Co-Authors: Zoran GajicAbstract:Power Transformer differential protection has been used for decades on standard three-phase power Transformers. However, special industrial Transformers, such as 24-pulse converter Transformers, could not typically be protected easily with the standard power Transformer differential relays. The main reason is the nonstandard phase angle shift of 24-pulse converter Transformers. Such 24-pulse converter Transformers are often used in industrial and railway applications. This paper will show that it is possible to provide differential protection for such special Transformers by using standard numerical Transformer differential protection relays and external interposing current Transformers (CTs). However, the external interposing CTs can be designed in a standardized way. This approach will significantly simplify the application of differential protection for special industrial Transformers.
