Tunnel effect of fractal fault and transient S-wave velocity rupture (TSVR) of in-plane shear fault

Transient S wave velocity rupture (TSVR) means the velocity of fault rupture propagation is between S wave velocity α and P wave velocity β . Its existing in the rupture of in plane ( i.e . strike slip) fault has been proved, but in 2 dimensional classical model, there are two difficulties in transient S wave velocity rupture, i.e ., initialization difficulty and divergence difficulty in interpreting the realization of TSVR. The initialization difficulty means, when v ↑ v R (Rayleigh wave velocity), the dynamic stress strength factor K 2(t) →+0, and changes from positive into negative in the interval ( v R, β ). How v transit the forbidden of ( v R, β )? The divergence difficulty means K 2(t) →+∞ when v ↓ β . Here we introduce the concept of fractal and tunnel effect that exist everywhere in fault. The structure of all the faults is fractal with multiple cracks. The velocity of fault rupture is differentiate of the length of the fault respect to time, so the rupture velocity is also fractal. The tunnel effect means the dynamic rupture crosses over the interval of the cracks, and the coalescence of the intervals is slower than the propagation of disturbance. Suppose the area of earthquake nucleation is critical or sub critical propagation everywhere, the arriving of disturbance triggers or accelerates the propagation of cracks tip at once, and the observation system cannot distinguish the front of disturbance and the tip of fracture. Then the speed of disturbance may be identified as fracture velocity, and the phenomenon of TSVR appears, which is an apparent velocity. The real reason of apparent velocity is that the mathematics model of shear rupture is simplified of complex process originally. The dual character of rupture velocity means that the apparent velocity of fault and the real velocity of micro crack extending, which are different in physics, but are unified in rupture criterion. Introducing the above mentioned concept to the calculation of K 2 (t) , the difficulty of initialization can be overcome, and the integral equation of triggering the initialization of TSVR is given quantitatively. By solving this integral equation, the lower limit of TSVR is 1.105 3 β , not β , and the divergence difficulty is overcome. TSVR is unstable solution, and may degenerate to sub Rayleigh wave velocity rupture immediately where the non critical condition can be measured. The results of this paper show that the initialization and continuum depends on the condition of earthquake nucleation in seismogenic area.

Guaranteeing the Fault Transient Performance of Aerospace Multiphase Permanent Magnet Motor System: an Adaptive Robust Speed Control Approach

To enhance the fault transient performance of aerospace multiphase permanent magnet synchronous motor(PMSM)system,an adaptive robust speed control is proposed regardless of the phase open-circuit(OC)and short-circuit(SC)fault in this paper,which can be applied for both the redundant motor system and fault tolerant motor system.For aerospace multiphase PMSM system,besides external load disturbance and system parameter perturbation,there inevitably exists the electromagnetic torque ripple in fault transient process,which can degrade the system performance and even cause the system instability.To cope with this issue,the electromagnet torque ripple of the multiphase PMSM system in fault transient process is first analyzed.Then,by considering the electromagnet torque fluctuation caused by fault transient as a system uncertainty,a novel adaptive robust speed control scheme is proposed,while the adaptive law is constructed to emulate the total system uncertainty bound,which include the load disturbance,the parameter variation,and the electromagnetic torque fluctuation due to fault transient.The resulting control can ensure the speed control performance even in fault transient process regardless of the uncertainty,in which no prior estimation of the uncertainty bound is required.In addition,the proposed adaptive robust speed control is demonstrated by a six-phase PMSM experimental platform.The novelty of this research is to explore a novel adaptive robust speed control to strengthen the fault tolerance performance of multiphase PMSM system even in fault transient process,which requires no prior estimation of the uncertainty bound.

Transient Fault Locating Method Based on Line Voltage and Zero-mode Current in Non-solidly Earthed Network

为解决配电网小电流接地故障时故障点定位困难的问题，提出一种基于线电压和零模电流暂态分量的故障定位新方法。该方法借助馈线自动化（feeder automation，FA）系统实现，不需要额外增加设备。馈线终端检测线电压和零模电流信号，利用暂态线电压的希尔伯特变换与暂态零模电流的乘积计算故障方向参数，FA主站根据故障点前后方向参数极性相反的特征确定故障点所在的线路区段。介绍基于线电压的小电流接地故障检测和接地故障相确定的算法。数字仿真与试验结果表明该方法是正确可行的。

Field experiment using transient energy method to locate a single-phase to ground fault

Distribution networks in China and several other countries are predominantly neutral inefficiently grounding systems(NIGSs),and more than 80%of the faults in distribution networks are single-phase-to-ground(SPG)faults.Because of the weak fault current and imperfect monitoring equipment configurations,methods used to determine the faulty line secti ons with SPG faults in NIGSs are in effective.The developme nt and application of distributi on-level phasor measurement units(PMUs)provide further comprehensive fault information for fault diagnosis in a distribution network.When an SPG fault occurs,the transient energy of the faulted line section tends to be higher than the sum of the transient energies of other line sections.In this regard,transient energy-based fault location algorithms appear to be a promising resolution.In this study,a field test plan was designed and implemented for a 10 kV distribution network.The test results dem on strate the effective ness of the transient en ergy-based SPG locati on method in practical distributi on networks.

A New Transient Impedance-Based Algorithm for Earth Fault Detection in Medium Voltage Networks

This paper presents a new earth-fault detection algorithm for unearthed （isolated） and compensated neutral medium voltage （MV） networks. The proposed algorithm is based on capacitance calculation from transient impedance and dominant transient frequency. The Discrete Fourier Transform （DFT） method is used to determine the dominant transient frequency. The values of voltage and current earth modes are calculated in the period of the dominant transient frequency, then the transient impedance can be determined, from which we can calculate the earth capacitance. The calculated capacitance gives an indication about if the feeder is faulted or not. The algorithm is less dependent on the fault resistance and the faulted feeder parameters; it mainly depends on the background network. The network is simulated by ATP/EMTP program. Several different fault conditions are covered in the simulation process, different fault inception angles, fault locations and fault resistances.

Enhancement of Transient Stability of the Nigeria 330 kV Transmission Network Using Fault Current Limiter

The dynamic responses of generators when subjected to disturbances in an interconnected power system have become a major challenge to power utility companies due to increasing stress on the power network. Since the occurrence of a disturbance or fault cannot be completely avoided, hence, when it occurs, control measures need to be put in place to limit the fault current, which invariably limit the level of the disturbances. This paper explores the use of Superconductor Fault Current Limiter (SFCL) to improve the transient stability of the Nigeria 330 kV Transmission Network. During a large disturbance, the rotor angle of the generator is enhanced by connecting a Fault Current Limiter (FCL) which reduces the fault current and hence, increases transient stability of the power network. In this study, the most affected generator was taken into consideration in locating the SFCL. The result obtained reveals that the Swing Curve of the generator without FCL increases monotonically which indicates instability, while the Swing Curve of the System with FCL reaches steady state.

Transient and Permanent Fault Injection in VHDL Description of Digital Circuits

The ability to evaluate the testability of digital circuits before they are actually implemented is critical for designing highly reliable systems. This feature enables designers to verify the fault detection capability of online as well as offline testable digital circuits for both permanent and transient faults, during the design stage of the circuits. This paper presents a technique for transient and permanent fault injection at the VHDL level description of both combinational and sequential digital circuits. Access to all VHDL blocks a system is straight forward using a specially designed single fault injection block. This capability of inserting transient and permanent faults should help in evaluating the testability of a digital system before it is actually implemented.

A Transient Enhancement Method for Two-Stage Helicopter Gearbox Fault Diagnosis Based on ALE

Periodical impulse component is one of typical fault characteristics in vibration signals from rotating machinery. However, this component is very small in the early stage of the fault and masked by various noises such as gear meshing components modulated by shaft frequency, which make it difficult to extract accurately for fault detection. The adaptive line enhancer (ALE) is an effective technique for separating sinusoidals from broad-band components of an input signal for detecting the presence of sinusoids in white noise. In this paper, ALE is explored to suppress the periodical gear meshing frequencies and enhance the fault feature impulses for more accurate fault diagnosis. The results obtained from simulated and experimental vibration signals of a two stage helical gearbox prove that the ALE method is very effective in reducing the periodical gear meshing noise and making the impulses in vibration very clear in the time-frequency analysis. The results show a clear difference between the baseline and 30% tooth damage of a helical gear which has not been detected successfully in author’s previous studies.

The simulation research for transient current variation in short circuit fault of urban rail transportation

Urban rail transit is one of the most important way for urban residents. However, frequent power failure, especially the short fault hinders the safe and stable operation of rail transit. The research of the transient variation of line electrical parameters in short circuit fault is the basis of researches for technology of line protection and short circuit fault location. Based on Matlab/Simulink, a 24-pulse rectifier circuit model is established, the resistance and inductance value of the catenary and rail network are calculated. The short Circuit fault simulation model of DC traction power supply system is established. The short-circuit fault of the traction network at close and distant points are simulated, the transient variation values of fault current with the different fault distance are analyzed. The simulation results show that the transient current peak of the nearby short circuit is oscillatory and convergent due to the nonlinear devices, which proves the accuracy of the model and provides a reference for the precise configuration of the line protection equipment.

Pressure Transient Analysis of an Intersecting Rollover Faulted Crest Boundary in Niger Delta Oil Field

Pressure transient analysis has been extensively applied to detect anomalies in a reservoir system.These anomalies may be presented in the form of an intersection of the crestal and the antithetic fault associated with a growth fault.Interpretation of this fault can only be achieved through the use of pressure transient analysis.The objective of the research work is to analyze and test the faulted crest,depth of the anticline structure and examine the near well bore conditions in order to evaluate whether the well productivity is governed by wellbore effects(skin effects+well bore effect)or the reservoir at large.A case study of a well in the Niger delta is considered with a series of build up test carried out in two intervals of both upper and lower gauge readings.In this study,a computer aided design which uses a pressure derivative approach is used in this work to match the pressure derivative of an intersecting fault(angle)model to the field data,and the model assumes the characteristics of the reservoir.Based on the result of the interpreted data,simulation is done by using a non linear regression method(least square).The simulated data interpreted are achieved through the regression coefficient which provides a quantitative measure of the agreement between field data and the model.In conclusion,the best cases are taken from all the results and a nodal analysis is performed to diagnose the inflow performance of the well through the transient analysis in order to optimize the recovery of the oilfield.

A Novel Transient Current-Based Differential Algorithm for Earth Fault Detection in Medium Voltage Distribution Networks

This paper presents a novel transient current differential algorithm for earth fault detection in unearthed （isolated） and compensated neutral medium voltage （MV） networks. The proposed algorithm uses the transient residual currents, which are very sensitive for earth faults detection. The transient values of residual currents are calculated for each feeder in the network and used as an earth fault indicator. The flow of residual currents is investigated. It is found that the residual current for the faulted feeder is equal to the summation of all residual currents for all other healthy feedersl Based on this investigation, a differential technique is proposed. A percentage restrain performance is proposed to ensure the selectivity and security of the algorithm. The transient algorithm is very sensitive for earth fault incidence. To apply the proposed algorithm, the residual currents can be measured easily by one sensor for each feeder with no need to voltage measurement. The proposed algorithm is less dependent on the fault resistance and the faulted feeder parameters. The network is simulated by ATP/EMTP program. Different fault conditions are covered in the simulation process： different fault inception angles, fault locations and fault resistances.

中性点柔性接地配电网故障相恢复电压暂态时域特征分析

配电网接地故障过零熄弧后的电压暂态恢复特性决定了系统过电压水平及电弧重燃特性,目前,中性点柔性接地配电网故障熄弧后暂态恢复电压变化机理尚不明确,为此建立柔性接地配电网接地故障暂态等值电路,理论解析故障过零熄弧后故障恢复电压的时域表达式。在此基础上,对比分析配电网谐振接地与柔性接地方式下,系统参数变化对故障相恢复电压暂态峰值与恢复速度的影响,揭示暂态时间尺度下故障相恢复电压特征随注入零序电流值与电流注入时机的变化规律,阐明通过中性点注入可控零序电流抑制故障暂态过电压的机理。在PSCAD/EMTDC仿真环境与10 kV真型配电网实验场中模拟各种运行和故障工况,仿真与真型实验结果均验证柔性接地配电网故障相恢复电压时域解析特征与变化规律的正确性。

虚拟同步机电流受限暂态电压支撑机理与改进故障穿越控制研究

针对虚拟同步机在电网低、过电压故障下所面临的无功电压支撑不足、特性差等问题,建立考虑电流限幅特性的虚拟同步机等效电路模型,并基于拓扑同伦原理,给出不同无功电压控制在等效电路相量图上的几何表征方法。利用该方法,揭示几种常见无功电压控制下的虚拟同步机电流受限暂态电压支撑机理,并由此提出一种改进的故障穿越控制策略,有效改善电网低电压、过电压故障下的暂态电压控制能力和支撑特性,进而缓解故障期间的暂态功角稳定问题。基于PSCAD/EMTDC仿真对所提机理和故障穿越控制方法进行详细验证,最后,在3机9节点系统中对其在近、远区电网故障下的支撑特性进行仿真验证。

高比例新能源送端系统暂态电压运行风险分析

针对交、直流故障下的高比例新能源送端系统暂态电压演化传播机理及运行风险尚不明晰的问题,首先,基于交直流系统间的无功电压交互作用机理分析,明确了交、直流系统故障下的暂态电压特性及主导影响因素,阐明了高比例新能源送端系统电力电子设备主导的暂态电压演化传播路径。其次,从“交直流故障强耦合作用持续加强,暂态无功功率成分复杂”、“新能源比例不断提升,暂态电压问题凸显”及“故障承载与调节能力下降,连锁脱网风险增大”三方面系统地阐述了暂态电压运行风险。然后,基于DIgSILENT/PowerFactory建立了实际高比例新能源多直流外送系统仿真模型,不同新能源占比、不同故障工况下的仿真结果验证了暂态电压运行风险分析的正确性。最后,从增强耦合运行特性机理认识、提升新能源涉网性能、增加多尺度协同控制策略、加强交流网架结构等方面提出了应对暂态电压运行风险的技术展望。

基于限流电抗器两侧特定频段暂态能量比的MTDC电网单端量保护方案

柔性直流输电技术有利于未来大量分布式能源接入电网,而配置快速、可靠的保护方案是柔性直流技术发展的关键。基于直流电网等效模型,提出一种基于限流电抗器两侧电压特定频段暂态能量比差异性的单端量故障区域识别方法。该方法依据贝瑞隆等效模型计算出限流电抗器两侧电压比,通过广义S变换提取限流电抗器两侧特定频段电压,根据故障时正负极限流电抗器的电压幅值差的差异性实现故障选极。最后在PSCAD/EMTDC平台搭建仿真模型,分析出发生区内外故障时差异性明显,具备较强的耐过渡电阻与抗噪声干扰能力。

动力学耦合分析下反应堆被动容错可靠性控制

反应堆长时间、高负荷的运转,使内部各设备出现不同程度磨损,易发生故障。由于反应堆变量复杂,导致其控制难度较大。为此,提出动力学耦合分析下反应堆被动容错可靠性控制方法。根据差分格式、因子分解理论求解反应堆相关变量,即密度、能量、位置及其运动方向等,按照燃料与冷却剂的温度、密度求解每个区域的截面,确定反应堆运行状态;运用事件触发机制设计反应堆被动容错控制程序,使用故障分布矩阵分析每个设备故障程度,检测出故障位置,通过控制率重组理念修改正常状态反馈回路增益,使修改后系统与正常系统性能一致。实验结果表明,所提方法故障检测结果与实际情况一致,且控制误差小,有效提升了反应堆被动容错控制的可靠性。

VSC输出电流反馈型虚拟同步控制技术

基于输出功率反馈的虚拟同步机(VSG)技术在网侧故障时,难以保持电压源暂态特性并实现精准暂态冲击电流限制,同时极易出现暂态同步失稳问题。为解决上述问题,提出一种基于电压源型变流器(VSC)输出电流反馈型VSG技术。外环控制直接采用VSC输出电流作为反馈控制量,不仅能实现构网和电压/频率主动支撑功能,还能保证在故障状态下外环控制具备稳定平衡点,降低暂态同步失稳风险,同时还能实现稳态下的电流限幅控制。电压内环采用基于相量分析的虚拟阻抗自适应选取方法,依赖就地量测信息进行虚拟阻抗快速自适应调整,以抑制故障瞬间暂态冲击电流。在PSCAD/EMTDC中搭建详细电磁暂态仿真模型,并构建相应的物理验证平台,仿真和实验结果表明,所提方法可以较好地抑制故障瞬间暂态冲击电流。

基于VMD模糊熵与GG聚类的直流配电网故障检测方法

针对直流配电网存在的故障信号难以提取、不易对各类故障进行诊断等问题,提出一种基于变分模态分解(VMD)模糊熵与Gath-Geva(GG)聚类的故障检测方法。首先,提取出暂态电流,采用VMD算法将故障暂态电流分解成若干个固有模态分量(IMF)。然后,分别计算分解得到的若干个IMF的模糊熵,将其作为特征向量。最后,采用GG聚类算法对故障特征的特征向量进行聚类识别。GG聚类的主要算法为将聚类样本划分为c类,设出隶属度矩阵,通过设定迭代来计算聚类中心与最大似然估计距离,更新隶属度矩阵,当隶属度矩阵满足条件矩阵时终止迭代,从而实现对单极故障、极间故障以及区外交流侧接地故障的聚类识别。仿真结果表明,所提保护方案可靠性强、准确率高,在不同故障类型、故障位置和过渡电阻等工况下均能可靠检测直流线路故障并准确识别故障类型,且具备一定的抗干扰能力。

一种可选择中断的混合式直流断路器拓扑

传统的混合式直流断路器应对瞬时性故障时必须先切断故障电流,再进行重合闸,会造成短暂性的电能供应中断。对此,提出一种适用于中压直流的可选择中断混合式直流断路器拓扑。该断路器可根据不同的故障类型选择运行方式,在与主导通支路串联的桥式结构中增加电容和限流电感抑制故障的电流上升,并储存能量,通过释能电阻对能量进行释放。对所提出的拓扑进行工作过程和理论分析。在单端直流等效系统中进行仿真验证,该结构在应对永久性短路故障时,可在9 ms内切除故障;应对瞬时性故障时,可使系统在不中断电流的情况下恢复正常运行,并释放故障时产生的能量。仿真结果验证了该拓扑的优越性。

含跟网和构网型新能源发电单元的混联电力系统暂态同步稳定分析

在新能源发电单元与同步发电机共同接入的混联电力系统中,不同同步方式新能源间,新能源与同步发电机间耦合复杂,深刻影响系统的暂态同步稳定性。为揭示电网对称短路故障下不同发电单元间的动态耦合机理及其对系统暂态同步稳定性的作用机制,该文首先建立故障条件下混联系统的暂态稳定分析数学模型。随后,利用空间矢量图示法与相平面法分析跟网型新能源发电单元注入电流、锁相环参数以及构网型新能源发电单元有功控制环参数等因素对混联系统内各发电单元暂态同步稳定性的影响规律,并据此给出系统控制器参数的设计原则。最后,通过不同工况下的仿真验证理论分析的正确性。