Influence of generator load conditions on third-harmonic voltages in generator stator winding

The influence of changes in load conditions of the generator-transformer unit on the operating conditions of the 100% ground-fault protection of the generator stator winding based on the third-harmonic voltages was analyzed. The analyzed stator ground-fault protection system is by ratio of the voltages third harmonic in generator neutral and at the generator terminals. The third-harmonic voltages were determined on the base of the experimental tests (measurements) run in real conditions at changes in active and reactive load conditions of the generator. It was found that mainly the generator active load influences the voltage feeding the measuring element of ground-fault protection. Therefore, determining operating conditions of ground-fault protection the influence of the generator active and reactive load should be deeply considered. This can ensure the proper operation of the ground-fault protection based on the voltage third harmonics in the whole range of the changes in generator load. Considering the influence of changes in generator load on the third-harmonic voltages (feeding measuring element of the protection system) will allow eliminating irregular generator tripping as a result of unselective operation of these protections.     

Ground-fault currents in unit-connected generators with differentelements grounding neutral

The results of the analysis of zero-sequence currents flowing in generator neutral and at ground-fault location during the generator normal operation and during ground-faults in the stator windings are presented. The influence of different methods of grounding the generator neutral on these currents in the primary circuits for different parameters of generators, transformers and additional capacitance to ground of the generator breakers was determined. This influence was analyzed for generators with ungrounded neutral, for generators with the resistance in neutral and for generators with ground-fault neutralizer (GFN) grounding the generator neutral. The analysis has been done for real resistance of the breakdown channel during ground-faults along the whole length of generator stator winding. It has been found that the applied method of grounding the generator neutral, the parameters of generator and transformer, the additional capacitance to ground of the generator breakers, level of fault resistance and ground-fault location have a substantial influence on currents flowing in the generator neutral and at ground-fault location in the breakdown channel in the main insulation of a generator stator winding     

注入式定子接地保护接地变压器参数设计方法及应用

为选择适合的接地变压器变比及二次侧负载电阻以提高20Hz注入式定子接地保护的测量精度,本文推导出注入信号与中性点接地变压器参数之间的数值关系,并确定二次侧负载电阻以及变比的选型原则,最后以该原则为依据编译了MATLAB/GUIDE可视化程序。以某电厂发电机组为例,通过对原始参数以及优化参数数值化结果进行对比,验证了设计原则的可行性及优越性,通过该方法得到的参数可更好地提升20Hz注入式定子接地保护的性能。     

谐振补偿在大型发电机中性点接地中的应用

详细分析了发电机中性点经消弧线圈谐振补偿接地方式的应用原理,提出一种发电机中性点接地方式,并且与中性点经接地变压器高电阻接地方式进行比较。这种中性点接地方式可以更好地限制定子单相接地时的故障电流,从而保护了定子铁心和绕组。采用多回路分析方法对三峡左岸一种700 MW的大型发电机进行仿真计算,仿真结果表明此方法是可行的。     

基于DSP的发电机转子接地保护装置设计

针对发电机实际运行中常出现励磁回路接地故障,提出了一种基于微机(DSP)的发电机转子接地保护装置的设计方案.在研究发电机转子接地保护原理的基础上,给出并分析了硬件系统方案设计及转子接地检测系统软件设计,试验测试结果表明,该装置灵敏性、可靠性较高,现场运行效果良好.     

A brushless, exciterless, single-phase, sinusoidal wave synchronousmachine having an auxiliary stator winding

Analytical and experimental studies of a brushless, exciterless, single-phase, sinusoidal-wave synchronous machine operating as a generator or a motor, derived from a three-phase machine, are reported. One phase armature winding of the three-phase machine is used as an auxiliary stator winding of the single-phase machine and is used to supply the exciting power for the other two-phase armature windings acting as the load winding of the single-phase machine. A 1.5 kW, 200 V, 60 Hz, four-pole synchronous machine was used the experiments. It is shown that the waveforms of the armature terminal voltage and the load current are nearly sinusoidal. The advantages of the single-phase machine as a portable generator or small-load motor are discussed     

Improved transient simulation of salient-pole synchronous generators with internal and ground faults in the stator winding

An improved model for simulating the transient behavior of salient-pole synchronous generators with internal and ground faults in the stator winding is established using the multi-loop circuit method. The model caters for faults under different ground conditions for the neutral, and accounts for the distributed capacitances of the windings to ground. Predictions from the model are validated by experiments, and it is shown that the model accurately predicts the voltage and current waveforms under fault conditions. Hence, it can be used to analyze important features of faults and to design appropriate protection schemes.     

Ground control for alternate power

In this article, the author argues that a number of factors should be considered when coordinating transfer switching and grounding of engine generator sets. He argues that the proper grounding and selection of transfer switches assures safety of personnel, protection of equipment, reliable ground-fault sensing, and continuity of power to electrical loads.     

A novel technique for measuring grounding capacitance and groundingfault resistance in ineffectively grounded systems

A principle for resonance measurement based on injecting a resonant frequency signal is presented in this letter. Using this principle, the grounding capacitance of lines and equipment and the grounding fault resistance can be measured on-line in ineffectively grounded systems. Based on this, Petersen-coil automatic tuning is implemented and 100% stator grounding fault protection for generator stator windings is also proposed. The prototype for Petersen coil tuning has been tested on networks for many years. The new method for generator stator grounding fault protection is verified by simulation     

发电电动机定子端部绕组电磁-结构耦合场计算

针对发电电动机定子端部绕组在电磁力作用下易发生故障的问题,以广州抽水蓄能电站B厂的发电电动机为例,建立了发电电动机定子端部绕组的三维模型,通过有限元法对模型电磁与结构顺序耦合进行仿真计算,得到了额定运行时电机端部绕组的应力和应变分布。结果表明,该方法能够有效地分析发电电动机定子端部绕组在电磁力作用下的应力应变分布,计算精确度比较高。     

基于光学电流互感器的发电厂保护优化研究

本文总结了采用柔性光学电流互感器的发电厂继电保护针对不同场景的优化研究和探索,介绍了发电机主保护方案优化、转子绕组匝间保护、选择性定子接地保护、核电辅助变断相监测保护、抽水蓄能等变频启动机组保护优化等保护优化方案和效果,利用柔性光学TA良好的传变特性和灵活的安装方式,较好地解决了现有发电厂保护存在的问题,可为现场类似场景的问题解决提供参考思路。     

双层叠绕组发电机单元件横差保护特性分析

通过1号机横差保护动作的现象,对故障进行分析,得出测量双星形中性点电流作为双层叠绕组发电机单元件横差保护的,横差动作的原因可能是定子绕组匝间发生短路,也可能是转子匝间短路或者转子偏心引起磁场不均匀也会引起的结论,该结论对现场维护人员有一定得指导意义。     

A novel technique for measuring grounding capacitance and groundingfault resistance in ineffectively grounded systems

A principle for resonance measurement based on injecting resonant frequency signal is presented in this paper. The grounding capacitance of lines and equipment and the grounding fault resistance can be measured online in ineffectively grounded systems. Petersen-coil automatic tuning is implemented, and 100% stator grounding fault protection for generator stator windings is also proposed. The prototype for Petersen-coil tuning has been tested on networks for many years. In addition, the new method for generator stator grounding fault protection is verified by simulation     

一起机端断路器非全相合闸案例的分析与思考

本文介绍了一起带机端断路器(GCB)机组非全相合闸并网的实例,分析了并网前后的零序电压接地保护动作情况,对故障时GCB两侧电压特征量进行了理论分析,并结合实际录波数据进行了验证.通过分析与研究,提出了增设机端断路器非全相保护的必要性与可行性,给同类型接线方式的发变组运行维护提供参考,提升发电机安全运行水平.     

浅析汤峪水电站发电机纵差保护误动作存在问题与处理

纵差保护作为防御发电机定子绕组及其引出线相间短路的主保护,对发电机安全高效运行起着重要作用。本文仅对该水电站机电设备运行过程中出现的纵差保护误动作四种可能性加以分析和处理,保证了发电机的安全运行。     

Diagnosis of stator winding insulation of large generator based on partial discharge measurement

The Stator winding insulation is aged by exposure to a combination of thermal, electrical, mechanical, and environmental stresses. Diagnosis of stator winding insulation is an important measure of ensuring the safe operation and extending the remaining life of large generator. In the paper, two new parameters are proposed for the diagnosis of stator winding insulation based on the test results of multistress accelerating aging test of stator bars. The test results show that the skewness of partial discharge phase resolved distribution and the high-frequency crest of partial discharge (PD) impulse change much more remarkably with the aging time than do the conventional parameters. Therefore, the two parameters could be considered as characteristic parameters for the diagnosis of stator winding insulation of the large generator. With these characteristic parameters, authors successfully assessed the insulation condition of actual stator bars removed from several large generators.     

一起大型发电机定子接地事故分析及处理

针对某大型发电机定子接地故障,建立发电机单相接地故障模型,根据故障时的现场故障录波波形和数据,利用Matlab软件分析计算出故障时的零序电压和过渡电阻,并获得零序电压随接地电阻变化的轨迹,准确定位出故障点位置,分析结果与现场故障数据相吻合,进而给出故障处理方法,对设备制造、安装等提出了参考建议,可为今后类似故障分析、处理提供参考依据。     

A brushless self-exciting three-phase synchronous generatorutilizing the 5th-space harmonic component of magneto motive forcethrough armature currents

A novel brushless self-exciting three-phase synchronous generator is proposed. It consists of three-phase armature windings on the stator, one field winding and one exciting winding with five times as many poles as that of the armature winding on the rotor, and a three-phase reactor connected to the terminal of the armature windings. By utilizing the 5th-space harmonic component of armature electromotive force, small voltage regulation for various loads and no oscillatory tension occurring at the rotor shaft were realized. The basic constitution, principle of operations, and exciting characteristics are described. The experimental results obtained from using a trial generator demonstrated its practical usefulness     

Propagation of partial discharge signals in stator windings of turbine generators

We studied the propagation of partial discharge pulses in a stator winding by means of measurements on a dismantled 35-MW generator and found that a stator winding acts as a transmission line. Therefore, a partial-discharge (PD) signal manifests itself at the generator terminals after a transit time that depends on the location of the discharge. Due to capacitive and inductive couplings in the end-winding region, a second propagation mode is present for higher frequencies. This "fast mode" manifests itself at the terminals without appreciable time delay. The capacitive and inductive couplings also cause crosstalk between the phases. As a consequence, a signal measured in one phase does not necessarily originate from a discharge in that phase. The amplitudes of the fast mode and, to a lesser extent, the slow mode (or transmission-line mode) are heavily damped when the discharge occurs further away from the measuring terminal. The consequence is that only discharges close to the measuring terminal can be observed. The propagation of a PD signal is not only influenced by the construction of the generator but also by its external connections.     

Performance evaluations of 50 MVA airgap winding stator forsuperconducting generator

Structural features of a trial-manufactured air-gap winding stator for a 50 MVA superconducting generator and results of various characteristic tests are described. The stator has an improved winding section, strengthened against electromagnetic force and smaller due to use of a four-layer water-cooled helical air-gap armature winding. The axial flux through the stator core, assumed to be generated by the circumferential current of the helical winding, is too low to pose any practical problems, as shown by a three-dimensional magnetic-field analysis taking into account the magnetic anisotropy due to the laminated iron core. The air-gap armature winding electromagnetic force in the radial and axial directions (which does not contribute to the generator output) increases when the running power factor decreases. The helical winding is shown to be applicable to the armature winding of large superconducting generators