Alternative Approaches for Distinguishing between Faults and Inrush Current in Power Transformers

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.

The Discrimination of Inrush Current from Internal Fault of Power Transformer based on EMD

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.

Investigation and Mitigation of Transformer Inrush Current during Black Start of an Independent Power Producer Plant

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.

A double-stage start-up structure to limit the inrush current used in current mode charge pump

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.

基于正弦同源-概率空间协同互补的涌流闭锁方案

为了取消正弦相似性原理中的最小二乘法等中间环节,获得直接固定标准正弦波形所需要的能量信息。借鉴时域概率分布的方法论,从优势互补的角度出发,设计了一种基于Wasserstein距离算法的变压器励磁涌流闭锁方案。该方案采用特征离散化的方式,提取目标对象和模板信号并转化为状态向量作为样本标签,以此来判别两者之间的能量分布差异,从而达到正弦场景同源识别的效果。理论分析与仿真结果表明,该方法实现简便,不需要频域计算。相比于现有正弦相似性原理,降低了保护流程的复杂程度,具有更强的实际应用价值和速动性能。通过PSCAD/MATLAB平台对现场合闸的录波数据进行测试分析,验证了所提方案对促进变压器保护性能的积极意义。

考虑铁心结构的三相变压器励磁涌流和角型绕组环流分析

基于三相组式、五柱式和三柱式铁心结构变压器的磁路特征和运行方程,首先,提出运用星形侧零序电流和电压来拟合角型绕组环流的数值方法,并进一步研究不同铁心结构变压器的角型绕组环流和励磁涌流的特点;然后,进行软件仿真和现场录波以验证该数值方法的有效性,可判断三相组式和五柱式变压器的各相绕组差流即为对应相的励磁涌流,而三柱式变压器某相的绕组差流并不是对应相的励磁电流;最后,进一步的理论分析与仿真验证表明,在3类铁心结构的变压器从星形侧空载合闸时,星形侧任意两相的线电流之差可以认为是这两相等效磁路的励磁涌流之差。研究结论可以为不同铁心结构三相变压器的励磁涌流识别提供依据。

励磁涌流引起换流变瓦斯继电器误动的振动及油流特性研究

在实际直流输电工程中,换流变压器在空载合闸时产生的励磁涌流导致其瓦斯继电器误动的事故频发,由于对励磁涌流下换流变压器振动及其油流特性的研究不足、故障机理不明确,瓦斯继电器误动等事故时有发生。为此,本文以某实际换流站中换流变压器网侧绕组空载合闸为例,搭建换流变压器励磁涌流电磁暂态模型,分析不同剩磁及合闸角下的换流变压器励磁涌流波形;搭建换流变压器电磁-力-流耦合的有限元模型,研究涌流作用下换流变压器的振动特性,箱体及油管内油流压强及流速特性。研究成果可为换流变压器瓦斯继电器在励磁涌流下的误动故障机理的分析提供有效参考。

柔性低频输电系统的主变稳态负序差动保护

为了解决常规纵差保护难以适用于低频系统的问题,通过分析低频系统的序分量抑制策略,并根据低频系统故障进入稳态后单侧有负序注入的特征,提出一种基于稳态负序分量的主变差动保护方法。为防止该差动保护在区外故障时因电流互感器饱和出现误动,通过对比分析三类制动电流计算方式的制动性能,得到了差动保护的制动方程和制动系数。为解决励磁涌流、电流互感器断线可能导致误动的问题,提出了相电压突变量的差动保护开放条件。仿真分析表明,该方法能够灵敏反映区内金属性故障及轻微故障,在区外故障伴随电流互感器饱和时有可靠的制动裕度。

基于LC谐振单元的多回路开关电容型均衡电路

传统的串并联开关电容型均衡电路在工作过程中会产生影响电路可靠性的冲击电流,为了改善该问题对电路性能的影响,同时提升电路的均衡速度,提出一种基于LC谐振单元的多回路开关电容型均衡电路。电路的LC谐振单元由均衡电容串联电感元件组成,所有开关器件均工作在零电流开关模式下,这将有效降低开关损耗,并有效抑制电路中的冲击电流,从而延长开关器件的使用寿命,提高电路的可靠性。所提出的均衡电路采用两个LC谐振单元作为储能元件组的组间均衡支路,可以同时实现储能元件单体与单体之间以及储能元件组与组之间的均衡,在保证均衡精度的同时,有效地提升电路均衡的速度。详细地分析了电路的特点与工作原理,通过搭建仿真平台,将所提出电路与现有的同类型均衡电路对比,验证了所提出均衡电路对均衡速度的提升作用。搭建了五个串联超级电容的实验平台,实验结果表明,所提出的电路可以提升55.85%的均衡速度,并且对冲击电流有显著的抑制作用。

Research on uninterruptable power supply technology for auxiliary winding of electric locomotive while passing the neutral section

Purpose–Auxiliary power system is an indispensable part of the train;the auxiliary systems of both electric locomotives and EMUs mainly are powered by one of the two ways,which are either from auxiliary windings of traction transformers or from DC-link voltage of traction converters.Powered by DC-link voltage of traction converters,the auxiliary systems were maintained of uninterruptable power supply with energy from electric braking.Meanwhile,powered by traction transformers,the auxiliary systems were always out of power while passing the neutral section of power supply grid and control system is powered by battery at this time.Design/methodology/approach–Uninterrupted power supply of auxiliary power system powered by auxiliary winding of traction transformer was studied.Failure reasons why previous solutions cannot be realized are analyzed.An uninterruptable power supply scheme for the auxiliary systems powered by auxiliary windings of traction transformers is proposed in this paper.The validity of the proposed scheme is verified by simulation and experimental results and on-site operation of an upgraded HXD3C type locomotive.This scheme is attractive for upgrading practical locomotives with the auxiliary systems powered by auxiliary windings of traction transformers.Findings–This scheme regenerates braking power supplied to auxiliary windings of traction transformers while a locomotive runs in the neutral section of the power supply grid.Control objectives of uninterrupted power supply technology are proposed,which are no overvoltage,no overcurrent and uninterrupted power supply.Originality/value–The control strategies of the scheme ensure both overvoltage free and inrush current free when a locomotive enters or leaves the neutral section.Furthermore,this scheme is cost low by employing updated control strategy of software and add both the two current sensors and two connection wires of hardware.

基于长短时记忆神经网络的励磁涌流与故障电流识别方法

变压器空载合闸时产生励磁涌流导致差动保护误动作的问题至今仍未能被完全解决.针对该问题,提出一种利用长短时记忆(LSTM)神经网络识别励磁涌流与故障电流的方法.首先,在PSCAD软件平台上搭建变压器空载合闸及内部故障仿真模型,通过仿真产生大量三相电流瞬时采样数据作为训练神经网络的样本集;然后,利用Keras平台搭建LSTM神经网络模型并完成训练;最后,利用新的仿真数据和现场故障录波数据对训练好的LSTM神经网络进行测试.结果表明LSTM神经网络可以快速准确地区分各种情况下的励磁涌流和故障电流,从而证实该方法的有效性.

基于环流相似度的变压器零模涌流识别与零序保护方法

随着我国电力系统规模的扩大和输电容量的增加,Yd连接的高阻抗变压器得到了广泛应用。传统的变压器零序差动保护采用二次谐波比进行涌流制动,但该方法在空投于内部故障时会出现拒动情况。提出了一种基于环流相似度的变压器零模涌流识别与零序保护方法,该方法计算原方零模涌流和副方环流的波形相似度,再根据变压器三相的饱和系数识别内部故障,综合实现变压器准确的涌流闭锁。仿真和实验结果表明,所提保护方法在变压器和应涌流及空投于内部故障情况下均能正确动作。

换流站交流滤波器过负荷保护误动作机理及防误动策略

换流站是耦合交直流系统的关联区域,站内设备众多、运行环境复杂。交流滤波器配置的保护虽然较为齐全,但在各类异常扰动情况下,电气量特殊的暂态特征仍会引发过负荷等保护的误动作。通过分析典型过负荷和励磁涌流工况下交流滤波器电阻支路电流波形的特点,揭示涌流引起交流滤波器过负荷保护误动作的机理。从波形相似度角度考虑,结合斯皮尔曼等级相关系数,提出了基于斯皮尔曼等级相关系数的交流滤波器过负荷保护辅助判据,并利用仿真试验验证该判据识别励磁涌流工况扰动的有效性,以防止保护误动的发生,提高保护的可靠性。

涌流抑制器在海洋平台电力系统的应用

海洋平台空间小,发电机装机容量有限,负荷量大,变压器的负载率高。变压器空载合闸时的励磁涌流对变压器和发电机都造成巨大冲击,也会造成合闸失败。多数产品采用分相操作来控制合闸角实现对变压器合闸涌流的抑制。而由于发电机、变压器的断路器为三相联动,使得实际应用中的效果不理想。Vizimax MVX涌流抑制器通过对剩磁的测量和控制,大大降低了涌流幅值,并减少了谐波分量,确保了每次合闸的成功,改善了电能质量,延长了变压器、发电机等核心电气设备的寿命,可为今后类似工程项目提供经验借鉴。

基于冲击发电机系统的中压断路器背对背电容器组开合试验技术

背对背电容器组开合试验用于考核断路器开合电容器组的重击穿概率,是重要的型式试验项目。针对关合涌流峰值I_(bi)和涌流频率f_(bi)在试验过程中难以准确调控,文中在分析国家标准对试验回路要求的基础上,提出以冲击发电机为试验电源的背对背电容器组三相开合试验回路,应用等效电路推导了涌流峰值I_(bi)和涌流频率f_(bi)的一般计算公式,并得出在试验电压12 kV,关合涌流峰值20 kA,开断电流分别为400 A和800 A时,线路长度l和电容值CS、涌流频率f_(bi)之间的量化关系,结果表明线路长度l与电容值C_(S)呈正相关,与涌流频率f_(bi)呈负相关。最后,应用3200 MVA冲击发电机试验系统,配置电源回路和负载回路的三相电容器组,进行了额定电压12 kV断路器背对背电容器组开合试验,关合涌流峰值I_(bi)和涌流频率f_(bi)均满足标准要求,验证了文中计算方法和试验回路的正确性和有效性。

基于简化模型的变压器励磁涌流计算方法

提出一种基于简化模型的变压器励磁涌流及电压计算方法。将变压器励磁电路的电流-磁通特性由非线性模型简化为线性模型,基于线性模型进行公式推导,得到励磁涌流及电压计算公式,并进行验证试验。试验结果表明,利用简化计算公式得到的励磁涌流和电压与瞬时分析法相比误差不超过0.012%。本文方法能够有效防止励磁涌流误动,提高电网系统的继电保护水平。

基于波形复杂特性的励磁涌流快速识别算法研究

针对电力变压器空载合闸于CT饱和、轻微匝间故障等扰动因素下励磁涌流快速识别困难的应用需求,提出一种基于电流波形复杂特性的励磁涌流快速识别算法;通过研究空载合闸、CT饱和、匝间故障等扰动因素下的励磁涌流波形复杂特性,提出采用改进变分模态分解算法,以实现固有模态分量的快速准确分解,同时,研究励磁涌流波形复杂特性的数值表征,提出波形复杂特性的数值表征策略,并选定样本熵和值作为励磁涌流快速识别的判据;模拟建立多场景扰动下的励磁涌流特性仿真模型,验证了所提出算法在空载合闸、合闸于CT饱和、合闸于匝间故障、变压器运行时发生内部及区内故障等工程场景下应用的快速性和可靠性。其中,该算法能够实现首个周波电流采集下的快速模态分解,并具有抗40 dB噪声干扰的抗噪性能,易于复杂扰动下励磁涌流信号快速、可靠辨识的工程应用。

低压成套无功功率补偿装置国内外标准差异研究

无功功率补偿装置是电力系统网络中不可或缺的设备,对于提高电能质量、减少谐波污染具有重要作用。为了从标准层面提升无功功率补偿装置的质量,本文立足无功功率补偿装置的产品特点,对其涌流、动态响应、谐波抑制三个关键项目进行了国内外标准分析。通过标准分析,得出了现行检测标准中存在的问题及不足,为开展低压成套无功功率补偿装置产品的认证试验提供重要技术参考。