Practical on-line partial discharge tests for turbine generatorsand motors

Several utilities have found partial discharge testing to be very useful for identifying motors or generators with deteriorated stator winding insulation. Such partial discharge tests are sensitive to problems associated with overheated insulation, loose stator bars, and pollution, all of which can cause in-service failures with long associated outages and high repair/rewind costs. Unfortunately, the partial discharge test is not widely applied since present test methods require considerable skill to perform, and/or require machine outages. These problems are due to the stator winding partial discharges being masked by high levels of internal and external electrical noise. The authors describe how partial discharge tests have now been developed which eliminate the effect of noise, thus allowing plant personnel to perform the test without any machine outage     

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.     

Power correlation for vertical axis wind turbines with varying geometries

In this paper, a new predictive model that can forecast the performance of a vertical axis wind turbine (VAWT) is presented. The new model includes four primary variables (rotor velocity, wind velocity, air density, and turbine power output) as well as five geometrical variables (rotor radius, turbine height, turbine width, stator spacing, and stator angle). These variables are reduced to include the power coefficient (C_p) and tip speed ratio (TSR). A power coefficient correlation for a novel VAWT (called a Zephyr Vertical axis Wind Turbine (ZVWT)) is developed. The turbine is an adaptation of the Savonius design. The new correlation can predict the turbine's performance for altered stator geometry and varying operating conditions. Numerical simulations with a rotating reference frame are used to predict the operating performance for various turbine geometries. The case study includes 16 different geometries for three different wind directions. The resulting 48 data points provide detailed insight into the turbine performance to develop a general correlation. The model was able to predict the power coefficient with changes in TSR, rotor length, stator spacing, and stator angle, to within 4.4% of the numerical prediction. Furthermore, the power coefficient was predicted with changes in rotor length, stator spacing, and stator angle, to within 3.0% of the numerical simulations. This correlation provides a useful new design tool for improving the ZVWT in the specific conditions and operating requirements specific to this type of wind turbine. Also, the new model can be extended to other conditions that include different VAWT designs. Copyright © 2010 John Wiley & Sons, Ltd.     

A new sensor for detecting partial discharges in operating turbinegenerators

A partial discharge (PD) sensor has been developed which is able to unequivocally differentiate between PD in the winding and all types of electrical interference. Thus, the sensor will permit an online test for turbine generators, similar to the test now used for hyrogenerators. The sensor requires no high-voltage connection to the winding, and is easily installed in the stator slot, underneath the wedges. Noise is differentiated from PD by the shapes of the electrical pulses from the sensor. The sensor, called the Stator Slot Coupler (SSC), is essentially a directional electromagnetic coupler. Calculations as well as laboratory tests indicate that the couplers can easily survive the electrical, thermal, magnetic, and mechanical stresses in the generator     

Relationship between partial discharge pulse height analysis andsubsequent voltage endurance of stator bars and coils

A method has been developed for screening stator bars and coils using a particular type of partial discharge (PD) detector. The objective in making PD screening tests was to identify those bars or coils which are more likely to fail on voltage endurance in a relatively short time. The majority of the examples given pertain to a project involving ten hydroelectric generators which had a total of 10800 stator bars. Evidence is presented which suggests that the test method is more sensitive to internal discharges than to those associated with the end grading surfaces     

一级半轴流式透平级内部若干非定常流动现象的试验研究

设计研制了具有亚音速透平高压级气动特性的一级半轴流式试验透平,采用试验方法对时序效应、叶栅壁面非定常静压幅频特性以及动叶出口非定常速度场进行了研究。结果表明:时序效应具有改善轴流式透平气动性能的潜力;动、静叶排压力有势场干涉引发的基频信号和上游静叶尾迹片段引发的两阶倍频信号,构成了第二列静叶壁面静压非定常分量的基本频率特征,其间还伴随高达六阶的倍频信号,主要由动叶尾缘高频脱落的涡街扰动产生;尚未完成掺混的第一列静叶尾迹片段出现在动叶出口,由其引发的负射流显著改变了动叶出口局部位置处的气流偏转角。     

灯泡贯流式水轮发电机定子铁心松动的原因及改造分析

针对某水电厂两台灯泡贯流式水轮发电机相继出现的定子铁心松动的问题,从电磁设计和结构设计方面对导致定子铁心变形、松动的原因进行了详细分析,并在此基础上进行了发电机改造分析。     

Novel Sensor for Locating Partial Discharges in High-Voltage Rotating Machines

The online partial discharge (PD) diagnosis has been recently accepted as an effective technique for the evaluation of the insulation condition of stator windings in high-voltage rotating machines. There are several types of sensors used for detecting PD in rotating machines. The so-called capacitive coupler, which is connected to the conductor, has been used most widely. Another sensor, the so-called stator slot coupler (SSC), is used by inserting it between the wedge and the top stator coil. However, these are not economically efficient for small-size rotating machines due to their high installation costs. Also, it takes a long time for insertion to take place and it a difficult process, if the SSC is inserted into small-size rotating machines. In this paper, a novel sensor called the partial discharge locating coupler (PDLC) was developed, which is easily mounted into the small-size rotating machines for the PD measurement, and tested to characterize its detectable frequency band and sensitivity. As a result, it was found that the PDLC has a detection frequency band up to several tens of megahertz, and it detects the induced signals with reasonable sensitivity. The PDLC combined with the digital filtering technique enables us to locate the PD activities. Also, it was found that the radiation or end-winding coupling of the PD signals is initiated >13 MHz.     

海上石油平台风燃互补发电孤立小电网稳定性研究及应用

"渤海海上风力发电示范工程"于2007年初批准正式立项,建设国内第一台海上风力发电机组,容量为1.5MW。由于风能具有间歇性和随机性的特点,为了实现绥中36-1CEP平台孤立电网与风电机组互补发电,并且保证该电网的平稳运行,进行了海上平台孤立小电网的稳定性研究。海上石油平台电网允许的正常频率波动范围为±0.25Hz,频率偏差报警为±0.5Hz,电网频率将随着透平发电机组输出有功功率的变化而波动。当风力发电机组在额定输出有功功率跳闸退出电网时,对电网频率的影响最大;当风力发电机组在额定风速启动并网时,对电网频率的影响较大。在特定的风燃互补孤立小电网中,采用电网负荷频率调节方程,可以计算风力发电机组容量与电网总负荷之比和频率波动的关系。海上平台风燃互补发电孤立小电网稳定运行的条件为风力发电机组的容量与平台电网总容量的比值小于10%。在满足风力发电机组引起平台电网最大频率波动范围为±0.25Hz的条件下,额定有功功率为1.5MW的风力发电机组,可并入最低总有功功率为15MW的电网。将稳定性研究结论应用于渤海风力发电示范项目,保证了示范工程的顺利进行,实现了国内第一台海上风力发电机组与生产平台并网发电的稳定运行。     

The ability of diagnostic tests to estimate the remaining life ofstator insulation

Stator windings from three generators and one motor were subjected to a wide variety of diagnostic tests. Diagnostic tests included insulation resistance, polarization index, capacitance, dissipation factor tip-up, partial discharge magnitude, and discharge inception voltage. The destructive tests included breaking down individual coils with either AC, DC, or impulse voltages. Since the results of the diagnostic tests did not correlate with the breakdown voltages, it is concluded that remaining life cannot be predicted on the basis of diagnostic tests alone. Equations and other relationships recently developed in Japan to predict the remaining life of the stator groundwall insulation systems could not be confirmed. Diagnostic tests are thought to be most useful for indicating the trend in insulation aging in a particular machine     

Partial discharge screening test for internal voids anddelaminations in stator coils and bars

Beginning in 1989 a partial discharge screening test was applied to stator coils and bars for which the measuring frequency bandwidth was approximately 8 MHz to 100 MHz. In this frequency range, the measurement is more sensitive to partial discharges in internal voids and delaminations than is the case for discharges associated with surface coatings. Recently changes have been made to the test circuit which have improved the repeatability of the measurement. Selection of the operating voltage for particular stator coils and bars based on their partial discharge screening test results may reduce the risk of future problems with the winding     

应用撬棒电路的双馈型风力发电机低电压穿越分析

风电场规模已经变得越来越大,风电机组的解列会严重影响系统的稳定性,这就要求风电机组具有低电压穿越能力以应对电网电压跌落。由于DFIG的定子侧直接与电网相联,在电网电压突然跌落时,定转子中会出现很大的电压和电流,需采用Crowbar电路（撬棒电路）来旁路转子侧变流器。文中分析了Crowbar电路的控制原理,然后在理论分析的基础上进行了仿真,仿真结果验证了Crowbar电路能够帮助DFIG在故障期间实现低电压穿越,最后进一步分析了Crowbar电路投切时间的选取。     

Experimental study of inter-laminar core fault detection techniques based on low flux core excitation

A comparison between two inter-laminar stator core insulation failure detection techniques for generators based on low flux core excitation is presented in this paper. The two techniques under consideration are: 1) the iron core probe based method developed recently and 2) the existing air core probe based method. A qualitative comparison of the two techniques is presented along with an experimental comparison on a 120-MW generator stator core. The test results are compared in terms of fault detection sensitivity, signal to noise ratio, and ease of interpretation, which are the main requirements for stator core inspection. In addition to the comparison, the performance of the iron core probe technique for machines with short wedge depression depth is presented along with the recent improvements in the algorithm. It is shown that the main requirements for stator core inspection are significantly enhanced with the new iron core probe-based core fault detector.     

Advances in online monitoring and localization of partial discharges in large rotating machines

Some of the problems facing partial discharge (PD) measurements in rotating machines, especially during online measurements are: i) calibration of the measurements; ii) high noise levels interfering with both the measurement system and the winding under the test; as well as iii) attenuation and distortion of PD signals during transmission from the source point to the winding terminals. This paper presents a new technique and a measuring system for online PD monitoring of large rotating machines, developed by the authors. With this technique, the above mentioned problems are improved considerably. PD detection is implemented for every stator coil and the coil that PD comes from can also be identified. Inductive coils are used for decoupling of PD pulses and processing of the detected signals is in accordance with the developed technique, denoted "Intech". Remote monitoring and navigation via a telephone link is one of the system features. The system was tested on both hydro and turbo generators with good results. The detection sensitivity of the system for the conventional machines is about 1 nC under operating condition.     

变几何涡轮的损失研究

变几何涡轮与定几何涡轮相比,在静叶顶部多了一个端部间隙,端部间隙大小的选取十分重要,既要保证间隙损失不至于过大,又要保证其能够自由转动,不至于受热而被卡死。所以,在保证静叶能够转动的前提下,静叶的端部间隙应尽可能的小。以某一四级动力涡轮为例,分析了第一级静叶的端部间隙大小以及第一级静叶转角给涡轮损失带来的影响,建议变几何动力涡轮的静叶端部间隙选取为静叶叶高的1.8%。     

Influence of Tower Shadow and Wind Turbulence on the Performance of Power System Stabilizers for DFIG-Based Wind Farms

The aim of the paper is to demonstrate the way in which mechanical power variations, due to tower shadow and wind turbulence, influence control performance of power system stabilizer (PSS) loops for doubly-fed induction generators (DFIGs). The PSS auxiliary loops are applied on a specific DFIG control scheme, the flux magnitude and angle controller (FMAC). However, since the PSS signal is applied at the output of the basic controller, the PSS performance characteristics displayed are deemed typical for DFIG control schemes in general. The relative capabilities of PSS controllers based on stator power, rotor speed, and network frequency, when the DFIG turbine is subjected to aerodynamic torque variations, are investigated via simulation studies. A two-generator aggregate model of a wind farm is introduced, which enables the influence of tower shadow and wind turbulence on both an individual turbine and on the overall wind farm itself to be assessed.     

Numerical Modelling of the Aeroelastic Behaviour and Variable Loads for the Turbine Stage in 3D Transonic Flow

Introduction Aeroelastic phenomena in the turbine stage are characterized by instability, continuous interaction and energy exchange between the fluid and the structure; so they cannot be studied properly in the frame of each of uncoupled domains separately (aerodynamics or structural dynamics). The traditional approach in flutter calculations of bladed disks is based on frequency domain analysis[1,2], in which the blade motion is assumed to be a harmonic function of time with a constant phas…     

A hybrid power system using alternative energy facilities in isolated island

A hybrid power system uses many wind turbine generators in isolated small islands. The output power of wind turbine generators is mostly fluctuating and has an effect on system frequency. In order to solve this problem, we propose a new power system using renewable energy in small, isolated islands. The system can supply high-quality power using an aqua electrolyzer, fuel cell, renewable energy, and diesel generator. The generated hydrogen by an aqua electrolyzer is used as fuel for a fuel cell. The simulation results are given to demonstrate the availability of the proposed system in this paper.     

基于89C51单片机的定桨距失速型风电机组软并网装置研究

基于89C51单片机的软并网装置成功地应用在定桨距失速型600kW风力发电机组的软并网系统中，该软并网装置通过控制斜坡电压的步长和电压平台的延迟时间，最大限度的改善了传统的斜坡电压软启动方式造成的电机转动力矩随定子电压的升高，转矩一时间曲线呈抛物线形发散增大的弊端。为了适应风电机组对并网过程的具体要求，该装置从软件和硬件两方面提高了抗干扰性和控制精度。     

XLPE电缆附件局部放电UHF和VHF联合检测

介绍了电磁耦合法测量XLPE电缆局部放电故障原理以及应用方法,重点比较了基于VHF(甚高频)传感器和UHF(特高频)传感器的检测方法在XLPE电缆局部放电在线监测技术中的应用。结合2种检测方法各自的优点与存在的弊病(VHF:衰减慢,可标定放电量,抗干扰能力差;UHF:抗干扰能力强,衰减快,不可标定放电量),推荐了XLPE电缆附件局部放电的UHF和VHF联合检测方法。