基于变压器绕组中谐振过电压识别的传输函数(英文)

Power transformer insulation systems are subjected to many stresses during normal operation due to lightning and switching.If the spectrum of incoming surge voltage matches the winding one,the corresponding resonance will be excited.Therefore external transients occurring in power systems might trigger internal overvoltages with large maximum value in transformer windings.Overvoltages having such characteristic have been the root cause of many power transformer failures.The paper presents an approach to the identification of sensitive zones in the transformer windings based on the measurements of overvoltages inside windings and frequency dependences of admittance of the power transformer.The frequency characteristic of the transformer winding may determine those regions in the frequency spectrum.The presented approach might be used both for design optimization and diagnostics of distribution and power transformers.     

Feasibility and Application Study of Optical Voltage/Current Sensors Using FBG

This paper concludes the case study work on the optical sensor, which is a new method for voltage and current measurement. Fiber Bragg gratings (FBG) have been developed and used for decades in the telecommunication industry. In recent years, FBG sensors have found wide applications in monitoring strain, temperature, voltage and current across all industries. As the process of constructing a robust smart grid, thousands of miles of optical-fibers have been deployed along the power transmission lines for the purpose of power production communication. This paper focuses on using the power optical fiber as voltage/current sensors instead of those copper wired traditional current transformers. By using piezoelectric layers, the optical sensor is able to transform voltage/current magnitude into optical signal, as well as transmit the signal through the optical fiber. The application of using optical fiber will significantly reduce the cost of deploying traditional current transformers all around the power grid. Moreover, the optical sensor is more stable, more accurate and faster, with such characteristics, the smart grid monitoring system could be much better. The application of combining the optical composite low-voltage cable (OPLC) and the optical current sensor in the distribution network for smart distribution monitoring has been analyzed.     

电压响应方法在电力变压器状态评估中的应用(英文)

Power transformer is one of the most important equipment in the power system.Its operating condition affects the reliability of power supply directly.Therefore,in order to guarantee transformer operation safely and reliably,it is necessary to assess condition of power transformer accurately.Return voltage method based on voltage response measurements is still a new non-intrusive diagnosis method for internal insulation aging of transformer.In this paper the technique and application of return voltage measurement and some results of voltage response measurements of several transformers was introduced.Voltage response measurements were performed on various transformers with different voltage grades,various operating periods,different moisture contents and aging degrees on site.Derived moisture contents from return voltage measurement were compared with the corresponding moisture contents obtained from the analysis of oil samples.Based on on-site experiments and theoretical analysis,the criteria for insulation state of transformer are proposed.Moisture condition of transformer insulation can be determined by using return dominant time constant,and a good correlation between aging degree and the return voltage initial slopes of the aged transformers.Field test performed on several transformers,its interpretation of results are also presented,which proves that return voltage measurements can be used as a reliable tool for evaluating moisture content in transformer insulation.     

基于统计分布和相关分析的变压器油中溶解气体注意值计算方法(英文)

Before diagnosed by DGA (dissolved gas analysis) methods, gas caution values, which index the level of gas formation, must be used to evaluate the possibility of incipient faults to reduce the misdiagnosis in the normal state. However, the calculation of these values is now only based on cumulative percentile method without taking into account operating conditions. To overcome this disadvantage, a new approach to calculate the transformer caution values is presented. This approach is based on statistical distribution and correlation analysis, and it takes the individual variation and fluctuation caused by internal and external factors into consideration. Then 6550 transformer DGA data collected from North China Power Grid are analyzed in this paper. The results show that the volume fraction of TH (total hydrocarbon) approximately obeys normal distribution when the 3-sigma rule is used to calculate its caution value. The volume fraction of CO has a strong positive correlation with oil temperature. For H2, the negative correlation with oil temperature is significant when the volume fraction is not very low. The caution value curves for CO and H2 are obtained by regression analyses. Thus, the gas caution values/curves obtained using the new method are not always constant, but vary with oil temperature, which is an advantage of the proposed method compared with cumulative percentile method. The variation of gas caution values/curves also reflects the influence of the external factors, for instance, va- rying with monitoring time ensures that the gas caution values are always consistent with operating status.     

Winding Capacitance Dividing Method for Powerformer

It presents a method which can equivalently arrange the capacitance distribution along with the winding of the generator on the terminal and neutral respectively in a reasonable partition,particularly for a type of high-voltage graded insulated cable wound generator,Powerformer.The winding of the Powerformer adopts graded insulation,which leads to the various cable thicknesses in different portion of the winding,and thus,the uneven capacitance distribution.The large capacitive currents and large transient outrush currents resulting from the cable consisting of the stator winding of Powerformer may cause problems to the generator differential protection.Most of literatures available in the field of compensated differential protection focus on the charging current compensation for long transmission line,instead of for generator.The authors give a method which can be used to compensate the capacitive current wholly to improve the reliability of the differential protection of Powerformer.It is proved that the distributed capacitance can be equivalent as the lump circuit with a capacitance partition coefficient ρ,and ρ is proved as a constant no matter whether the generator experiences the normal operation,external phase(s) fault or internal phase(s) fault.The formula of the partition coefficient is provided and the corresponding equivalent circuit of the Powerformer cable to calculate capacitance currents is given.An analysis programming resolving the minimum value of the coefficient ρ is written in MATLAB 7.0/m according to this formula,using the function fmincon() which can work in any type of constraint condition.The program always gets the same global minimum points under the different initial values condition which proves our point by mathematical test.With this new approach to winding capacitance dividing method,the protection scheme used for Powerformer can be validated and improved accordingly.     

The Direct Measurement Method of Magnetics Winding Losses Based on AC Power

正The winding losses as the important part of magnetics losses are difficult to separate from the total losses.At present,there is no effective method to measure winding losses under the given excitation condition,and to measure directly the winding losses of     

Steady-state Performance Analysis of 15-phase Induction Machines Under Open-circuited Fault Conditions

正With the higher number of phases,multiphase induction machines can be designed with a full-pitch concentrated winding configuration to improve its winding factor.Thus nonsinusoidal voltage supply can be employed to enhance iron material utilization and torque density.However,the fault probability of     

基于部件划分和熵权的变压器绝缘状态评估策略(英文)

Failure mechanisms of power transformers are complex and uncertain; it is difficult to determine index weights of insulation state. Therefore, it is a challenge to acquire an accurate assessment of insulation state of power transformers. In this paper, an assessing strategy for transformer insulation is proposed base on part-division of transformer and a comprehensive weight determination method. An index system of transformer is established on the basis of part-division of transformer. Each index’s weight is consisted of two parts, the constant weight and the variable weight, which are determined by improved analytic hierarchy process (AHP) and entropy method respectively. Af- ter categorizing insulation state into four levels and standardizing assessing indexes, a Cauchy membership function is forged, and a fuzzy algorithm is employed to simulate the uncertainty of the insulation state. Finally, a confidence criterion is employed to perform part-division based condition assessment of transformer. Case studies reveal that the proposed assessing strategy method is effective, convenient, and practical; with the new strategy, potential failures of transformers can be forecasted and insulation state of transformer parts can also be as- sessed. Furthermore, the assessing results can be used to guide condition-based maintenance.     

A Temperature Prediction Model for Oil-immersed Transformer Based on Thermal-circuit Theory

This paper proposed an improved temperature prediction model for oil-immersed transformer.The influences of the environmental temperature and heat-sinking capability changing with temperature were considered.When calculating the heat dissipation from the transformer tank to surroundings,the average oil temperature was selected as the node value in the thermal circuit.The new thermal models will be validated with the delivery experimental data of three transformers: a 220 kV-300 MV.A unit,a 110 kV40 MV.A unit and a 220 kV-75 MV.A unit.Meanwhile,the results from the proposed model were also compared with two methods recommended in the IEC loading guide.     

IDENTIFICATION OF TRANSFORMER INRUSH CURRENT USING MORPHOLOGICAL SIGNAL DECOMPOSITION

Based on Mathematical Morphology (MM), this paper presents a new method for discrimination between internal fault and magnetising inrush conditions for power transformer protection. The proposed algorithm is to decompose the signal with a class of morphologically simple function, known as Blum functions, to allow the unique feature associated with the inrush current waveform to be preserved, while suppressing other irrelevant features. The proposed scheme has been applied to simulated signals generated by PSCAD/EMTDC. The results confirm that features extracted by the MM filtering have a distinctive property, on which simple identification criteria can be applied for detecting an inrush current from internal fault conditions.     

变压器绕组测温光纤光栅传感器设计及性能测试

为实现油浸式变压器绕组温度的直接测量,设计并制作了预埋光纤光栅传感器的绕组电磁线,对电磁线结构及绕组制作工艺进行了适当的改进,对绕组电磁线预埋光纤光栅传感器制作过程中的应力状态进行了监测,并对其测温性能进行了测试。结果表明:绕组电磁线预埋光纤光栅传感器制作过程及线圈绕制过程中光纤光栅传感器受到的应力较小,光纤光栅传感器保持了良好的机械强度和测温性能,其测温线性度>0.99,灵敏度约为10pm/°C,与理论值接近,测量准确度可达到±0.5°C,可满足变压器绕组温度精确测量的要求。     

基于荧光衰减原理的光纤绕组测温技术研究

随着变压器向超大容量、特高压、智能化发展,为保证变压器安全运行,利用光纤测温系统直接测量变压器绕组的热点温度逐渐成为测温方式重要发展方向。本文从测温原理、可靠性、适用范围和型式试验等多方面研究了基于荧光衰减原理(FOT)的光纤测温技术,为今后主变压器绕组直接测温技术的发展和应用提供参考。     

光纤传感器在预装式变电站绕组热点温度监测中的应用

针对目前预装式变电站变压器室内部绕组热点温度在线监测困难的问题,提出了一种光纤传感应用方案,通过在变压器内布置光纤温度传感器,可以对变压器的热点温度进行监测,同时结合变压器负载情况对变压器的寿命损失进行评估。额定负载和过负载试验数据表明,该光纤在线监测系统能够准确、及时捕捉到变压器的热点温度,并给出过负载工况下的合理建议。     

基于半导体吸收的电力变压器绕组温度在线监测技术研究

变压器绕组温度的监测问题已日益受到重视,由于测温场合条件特殊,直接或间接检测绕组温度一直是一个难题。在寻求温度传感器的其他替代手段的所有研究中,光纤测温以其抗电磁干扰能力强、体积小、耐高压、耐腐蚀等优点逐步受到重视。根据变压器绕组测温的实际情况提出一种简单可行的测温新方法,即基于半导体吸收式的光纤测温技术。试验结果表明了该方法应用于变压器绕组温度在线监测的可行性。     

大电机定子线棒光纤光栅准分布式测温技术

为了使大型发电机具备内部温度场实时监测能力,将联有多个光纤布拉格光栅(fiber Bragg gratings,FBG)的光纤植入定子线棒中,将光纤光栅置于被关心的温度点,实现了定子线棒温度的准分布式多点测量。植入实验表明,裸FBG很容易在植入过程中损坏,且温度特性易受绝缘材料影响;不锈钢毛细管封装FBG可以抵抗定子线棒加工过程中的高温高压及外力的损害,是一种可行的植入方案。在选择植入位置时,实心铜股线和换位绝缘是能够植入FBG的位置。植入FBG后线棒的温度实验表明,嵌入线棒内部的FBG波长随温度变化的线性度为0.999 66,FBG波长时间响应曲线与对应点热电偶温度时间响应曲线有很好的一致性,具有几乎相同的响应时间。基于光纤光栅的准分布式测温技术实现定子线棒温度的实时测量是可行的。     

基于侧边抛磨光纤布拉格光栅的变压器油中溶解氢气传感器

针对变压器油中溶解气体在线监测装置,常规取油样-油气分离-气体检测的模式存在操作繁琐、检测环节多、检测误差大、试验周期长等缺点。为此提出基于光纤布喇格光栅的油中溶解氢气传感器和检测方案。为了提高光纤光栅氢气传感的灵敏度,通过侧边抛磨增敏设计,采用轮式抛磨法对布喇格栅区的光纤进行抛磨,使用磁控溅射的方法在光纤表面溅射氢敏钯膜材料,制备侧边抛磨深度为20?m的光纤光栅氢气传感器。在实验室搭建油中氢气传感测试平台,开展多次溶解氢气传感灵敏度和重复性试验,测试灵敏度达到0.477?L/L,具有较高的重复性,可以满足实际变压器油中溶解氢气的传感需求。基于侧边抛磨的光纤布喇格光栅油中氢气传感器实现了变压器油中溶解气体的直接测量,为油中溶解氢气在线监测提供了一种传感思路和技术手段。     

BOTDA技术在变压器绕组温度监测中的应用

分析了变压器内部温度升高的机理,给出了光纤布里渊传感技术的温度测量原理.针对现有绕组温度监测方法存在局限性的问题,在比较现有几种监测方法的基础上,设计了基于布里渊光时域分析技术的变压器绕组温度在线监测系统,并对传感光纤的布放和系统的组网方式进行了探讨.     

混合绝缘液浸电力变压器的热-流耦合场分析及绝缘和散热器结构的改进

由于传统的变压器温升计算公式不再适用于混合绝缘结构的液浸式新型电力变压器设计,为此笔者采用传热学和流体动力学原理建立了变压器热流耦合场的有限元模型,模型中考虑了变压器油热力学参数的非线性和绕组结构中垫快、纸筒对散热的影响,并根据不同的绕组形式进行单元离散。通过对混合绝缘结构的液浸式变压器热-流耦合问题的求解,得到了变压器内部各点的温度和流场分布状况,高低压绕组平均温升与试验结果吻合。结合计算和试验结果对变压器的绝缘材料进行了改进,充分发挥了材料的耐温特性和经济性。最后,提出了通过升高散热器进出口的高度差来达到降低变压器热点温升的有效方法。     

油浸式变压器绕组测温两表偏差异常分析及减小措施

针对油浸式变压器绕组测温装置运行时两表偏差较大以及远方监视中断等问题,通过对测温原理及综合因素的分析,阐述了一种通过采用独立式温度转换模块并更改测温接线方式以消除缺陷的改进措施,进一步提高了远方测温的精确度。     

“内模式”传感器在变压器温升监测中的应用

牵引变压器的温升是变压器运行中的一个重要参数,该参数直接关系到主变压器运行的健康与安全。为了有效监测主变压器的温升,实现变压器冷却系统的优化控制,提出了一种基于支持向量机"内模式"传感器在线监测主变压器温升的方法。在一定程度上解决了牵引主变压器依靠传统方法测量温度,准确度差且不能在线实时检测温升的不足。通过现场主变实际运行的电气参数,由支持向量机算法建立的传感器,经训练后输出主变的温升数值。实验结果表明,该方法能够较准确在线检测主变压器的温升,对优化控制冷却系统,估计线圈绕组绝缘剩余寿命,保证主变安全运行,有较好的工程应用前景。