In this paper,a new simulating method is presented,using only the normal magnetizing curve (B-H) of the transformer core material,its geometric dimensions,the no-load power loss data and the concept of instantaneous p...In this paper,a new simulating method is presented,using only the normal magnetizing curve (B-H) of the transformer core material,its geometric dimensions,the no-load power loss data and the concept of instantaneous power. At the end of this paper the simulating calculation using EMTP has been also performed for the same transformer. The comparison shows that the two sets of results are very close to each other,and proves the correctness of the new method. The new method presented in this paper is helpful to verify the correctness of the power transformer design,analyze the behavior of the transformer protection under switching and study the new transformer protection principles.展开更多
This article gives an overview of the main passive solutions and active techniques, based on AC switches to limit inrush currents in medium power AC-DC converters （up to 3.7 kW） for electric vehicle charging systems...This article gives an overview of the main passive solutions and active techniques, based on AC switches to limit inrush currents in medium power AC-DC converters （up to 3.7 kW） for electric vehicle charging systems. In particular, a strategy, based on SCR （silicon controlled rectifier） phase, shift control in a mixed rectifier bridge with diodes and thyristors, is proposed. The challenge is to help designers optimize the triggering delay of SCRs to both limit the peak value of inrush current spikes and optimize the charge duration of the DC-link capacitor. A mathematical model （Mathcad engineering tool） has been defined to point out, the interest of a variable triggering delay to control SCRs to meet the expectations described previously. Experimental measurements using an industrial evaluation board of the AC-DC converter demonstrate the robustness of the method.展开更多
The primary winding of the transformer will generate large inrush current due to the saturation of iron core when an unloaded transformer is switched-on. The inrush current not only causes mechanical interaction force...The primary winding of the transformer will generate large inrush current due to the saturation of iron core when an unloaded transformer is switched-on. The inrush current not only causes mechanical interaction force due to which the windings are damaged, but also induces the differential protection relays to operate incorrectly. In this paper, the mathematical model of unloaded single phase transformer in switch-on is analyzed; the computation formulas of the inrush current and its interruption angle are presented. The experiment investigation of single phase transformers with different capacities shows that the inrush current measurement result is consistent with theoretical analysis. The inrush current waveform is typically a steeple top waveform with high order harmonics and damping in one direction. In the same condition, large inrush current amplitude will be induced with smaller switching angle, larger residual flux and smaller saturation flux.展开更多
The method is based on that the waveform of the inrush distorts seriously, while the fault current nearly keeps sinusoid. The complicated signal can be decomposed into a finite intrinsic mode functions (IMF) by the EM...The method is based on that the waveform of the inrush distorts seriously, while the fault current nearly keeps sinusoid. The complicated signal can be decomposed into a finite intrinsic mode functions (IMF) by the EMD, then define and compute the projection area on X-axis of each IMF—, the specific gravity of SIMF—, and the maximum of —. We can get a new scheme of transformer-protection based on comparing the difference between inrush and fault current. Theoretical analysis show that the method can precisely discriminate inrush and fault current, fault clearance time is about 20ms. Moreover, it is convenient to achieve and hardly be affect by not-periodic component.展开更多
In this study, we will cover the basic methods used to distinguish between inrush current and fault current in power transformers. First, the nature of inrush current is presented compared to the fault current. Then t...In this study, we will cover the basic methods used to distinguish between inrush current and fault current in power transformers. First, the nature of inrush current is presented compared to the fault current. Then the nature of the magnetizing current due to energizing a power transformer at no-load is explained. The first generation of methods used to disable the protective relay system during inrush current, namely the Desensitizing and Tripping Suppressor, is introduced. The second generation, the harmonic restraint method and the waveform-based restraint method with their different versions, is explained. Then we will explore thoroughly the fictitious equivalent resistance method as an example of the third generation of model type restraining or blocking methods. Finally, a comparison between these methods and conclusion is carried out.展开更多
The energizing of large power transformers has long been considered a critical event in the operation of an electric power system. When a transformer is energized by the utility, a typical inrush current could be as h...The energizing of large power transformers has long been considered a critical event in the operation of an electric power system. When a transformer is energized by the utility, a typical inrush current could be as high as ten times its rated current. This could cause many problems from mechanical stress on transformer windings to harmonics injection, and system protection malfunction. There have been numerous researches focusing on calculation and mitigation of the transformer inrush current. With the development of smart grid, distributed generation from independent power producers (IPPs) is growing rapidly. This paper investigates the inrush current due to black start of an IPP system with several parallel transformers, through a simulation model in DIgSILENT Power Factory software. The study demonstrates that a single genset is capable of energizing a group of transformers since the overall inrush current is slightly above the inrush of the transformer directly connected to the generator. In addition, a simple method is proposed to mitigate the inrush current of the transformers using an auxiliary transformer.展开更多
A double-stage start-up structure to limit the inrush current used in current-mode charge pump with wide input range,fixed output and multimode operation is presented in this paper.As a widely utilized power source im...A double-stage start-up structure to limit the inrush current used in current-mode charge pump with wide input range,fixed output and multimode operation is presented in this paper.As a widely utilized power source implement,a Li-battery is always used as the power supply for chips.Due to the internal resistance,a potential drop will be generated at the input terminal of the chip with an input current.A false shut down with a low supply voltage will happen if the input current is too large,leading to the degradation of the Li-battery＇s service life.To solve this problem,the inrush current is limited by introducing a new start-up state.All of the circuits have been implemented with the NUVOTON 0.6 μm CMOS process.The measurement results show that the inrush current can be limited below 1 A within all input supply ranges,and the power efficiency is higher than the conventional structure.展开更多
Through an example of a main transformer switch-in with load during the reverse transmission of a 750 kV power plan,the paper introduces the basic principle of transformer switch-in with load.EMTPE program that is use...Through an example of a main transformer switch-in with load during the reverse transmission of a 750 kV power plan,the paper introduces the basic principle of transformer switch-in with load.EMTPE program that is used to establish a calculation model,at the same time mainly considers the excitation characteristics of the transformer,the transient model of the circuit breaker,and the model of high voltage transformer,and calculated the inrush current with transformer switch-in with load in this plan.During system debugging in the plan,the two sets of main transformers passed the closing and opening test,and the data of inrush current in the test are recorded and analyzed.The simulation calculation and measured data show that the results are consistent.The simulation calculation also shows that it is not recommended to perform on-load closing of the transformer except for special circumstances,because of the influence of hysteresis characteristic when the transformer was switched in with load or the terminal voltage of the transformer resumed normal level from a low one after an external near-end fault was cleared,which various transformer differential protection using the characteristics of inrush to implement block scheme may mal-operate.展开更多
双馈风电场在低电压穿越策略下所输出的短路电流存在偏频特性,导致送出变压器传统差动保护动作延时过长。针对上述问题,首先,研究了低电压穿越策略下的双馈风机短路电流特性及其偏频特性对风电场送出变压器傅里叶工频算法提取二次谐波...双馈风电场在低电压穿越策略下所输出的短路电流存在偏频特性,导致送出变压器传统差动保护动作延时过长。针对上述问题,首先,研究了低电压穿越策略下的双馈风机短路电流特性及其偏频特性对风电场送出变压器傅里叶工频算法提取二次谐波分量的影响;其次,分析了传统差动保护在双馈风电场送出变压器中的适应性;然后,提出了基于全相位快速傅里叶变换(all-phase fast Fourier transform,apFFT)的双馈风电场送出变压器差动保护新方法;最后,通过PSCAD/EMTDC仿真对所提方法进行了验证,结果表明,新方法不仅能够正确识别励磁涌流,而且提高了内部故障时差动保护的速动性。展开更多
文摘In this paper,a new simulating method is presented,using only the normal magnetizing curve (B-H) of the transformer core material,its geometric dimensions,the no-load power loss data and the concept of instantaneous power. At the end of this paper the simulating calculation using EMTP has been also performed for the same transformer. The comparison shows that the two sets of results are very close to each other,and proves the correctness of the new method. The new method presented in this paper is helpful to verify the correctness of the power transformer design,analyze the behavior of the transformer protection under switching and study the new transformer protection principles.
文摘This article gives an overview of the main passive solutions and active techniques, based on AC switches to limit inrush currents in medium power AC-DC converters （up to 3.7 kW） for electric vehicle charging systems. In particular, a strategy, based on SCR （silicon controlled rectifier） phase, shift control in a mixed rectifier bridge with diodes and thyristors, is proposed. The challenge is to help designers optimize the triggering delay of SCRs to both limit the peak value of inrush current spikes and optimize the charge duration of the DC-link capacitor. A mathematical model （Mathcad engineering tool） has been defined to point out, the interest of a variable triggering delay to control SCRs to meet the expectations described previously. Experimental measurements using an industrial evaluation board of the AC-DC converter demonstrate the robustness of the method.
文摘The primary winding of the transformer will generate large inrush current due to the saturation of iron core when an unloaded transformer is switched-on. The inrush current not only causes mechanical interaction force due to which the windings are damaged, but also induces the differential protection relays to operate incorrectly. In this paper, the mathematical model of unloaded single phase transformer in switch-on is analyzed; the computation formulas of the inrush current and its interruption angle are presented. The experiment investigation of single phase transformers with different capacities shows that the inrush current measurement result is consistent with theoretical analysis. The inrush current waveform is typically a steeple top waveform with high order harmonics and damping in one direction. In the same condition, large inrush current amplitude will be induced with smaller switching angle, larger residual flux and smaller saturation flux.
文摘The method is based on that the waveform of the inrush distorts seriously, while the fault current nearly keeps sinusoid. The complicated signal can be decomposed into a finite intrinsic mode functions (IMF) by the EMD, then define and compute the projection area on X-axis of each IMF—, the specific gravity of SIMF—, and the maximum of —. We can get a new scheme of transformer-protection based on comparing the difference between inrush and fault current. Theoretical analysis show that the method can precisely discriminate inrush and fault current, fault clearance time is about 20ms. Moreover, it is convenient to achieve and hardly be affect by not-periodic component.
文摘In this study, we will cover the basic methods used to distinguish between inrush current and fault current in power transformers. First, the nature of inrush current is presented compared to the fault current. Then the nature of the magnetizing current due to energizing a power transformer at no-load is explained. The first generation of methods used to disable the protective relay system during inrush current, namely the Desensitizing and Tripping Suppressor, is introduced. The second generation, the harmonic restraint method and the waveform-based restraint method with their different versions, is explained. Then we will explore thoroughly the fictitious equivalent resistance method as an example of the third generation of model type restraining or blocking methods. Finally, a comparison between these methods and conclusion is carried out.
文摘The energizing of large power transformers has long been considered a critical event in the operation of an electric power system. When a transformer is energized by the utility, a typical inrush current could be as high as ten times its rated current. This could cause many problems from mechanical stress on transformer windings to harmonics injection, and system protection malfunction. There have been numerous researches focusing on calculation and mitigation of the transformer inrush current. With the development of smart grid, distributed generation from independent power producers (IPPs) is growing rapidly. This paper investigates the inrush current due to black start of an IPP system with several parallel transformers, through a simulation model in DIgSILENT Power Factory software. The study demonstrates that a single genset is capable of energizing a group of transformers since the overall inrush current is slightly above the inrush of the transformer directly connected to the generator. In addition, a simple method is proposed to mitigate the inrush current of the transformers using an auxiliary transformer.
基金supported by the National Natural Science Foundation of China(No.61106026)
文摘A double-stage start-up structure to limit the inrush current used in current-mode charge pump with wide input range,fixed output and multimode operation is presented in this paper.As a widely utilized power source implement,a Li-battery is always used as the power supply for chips.Due to the internal resistance,a potential drop will be generated at the input terminal of the chip with an input current.A false shut down with a low supply voltage will happen if the input current is too large,leading to the degradation of the Li-battery＇s service life.To solve this problem,the inrush current is limited by introducing a new start-up state.All of the circuits have been implemented with the NUVOTON 0.6 μm CMOS process.The measurement results show that the inrush current can be limited below 1 A within all input supply ranges,and the power efficiency is higher than the conventional structure.
文摘Through an example of a main transformer switch-in with load during the reverse transmission of a 750 kV power plan,the paper introduces the basic principle of transformer switch-in with load.EMTPE program that is used to establish a calculation model,at the same time mainly considers the excitation characteristics of the transformer,the transient model of the circuit breaker,and the model of high voltage transformer,and calculated the inrush current with transformer switch-in with load in this plan.During system debugging in the plan,the two sets of main transformers passed the closing and opening test,and the data of inrush current in the test are recorded and analyzed.The simulation calculation and measured data show that the results are consistent.The simulation calculation also shows that it is not recommended to perform on-load closing of the transformer except for special circumstances,because of the influence of hysteresis characteristic when the transformer was switched in with load or the terminal voltage of the transformer resumed normal level from a low one after an external near-end fault was cleared,which various transformer differential protection using the characteristics of inrush to implement block scheme may mal-operate.
文摘双馈风电场在低电压穿越策略下所输出的短路电流存在偏频特性,导致送出变压器传统差动保护动作延时过长。针对上述问题,首先,研究了低电压穿越策略下的双馈风机短路电流特性及其偏频特性对风电场送出变压器傅里叶工频算法提取二次谐波分量的影响;其次,分析了传统差动保护在双馈风电场送出变压器中的适应性;然后,提出了基于全相位快速傅里叶变换(all-phase fast Fourier transform,apFFT)的双馈风电场送出变压器差动保护新方法;最后,通过PSCAD/EMTDC仿真对所提方法进行了验证,结果表明,新方法不仅能够正确识别励磁涌流,而且提高了内部故障时差动保护的速动性。
