基于有限元分析的大型汽轮发电机中性点CT温度高问题研究

汽轮发电机保护用电流互感器（CT）是保护装置中的一种重要设备。大型发电机用电流互感器一般都运行在较强的电磁环境中,为保证电流互感器精度,大电流互感器一般都采用屏蔽绕组屏蔽外界磁场的干扰。外界强大的交变磁场必然使电流互感器的屏蔽绕组感应出很大电流,如果该电流超过屏蔽绕组的承受力,就会造成屏蔽绕组严重发热甚至电流互感器损坏。本文基于COMSOL多物理场有限元软件分析大型汽轮发电机中性点电流互感器温升异常问题,研究了屏蔽绕组设计方式、屏蔽绕组线径、屏蔽绕组匝数等因素对屏蔽绕组损耗的影响,为电流互感器的改进方案提供了依据。     

罗戈夫斯基线圈电流传感头测量影响因素的试验研究

介绍了罗戈夫斯基线圈(罗氏线圈)电流传感头的测量原理及特点,对影响传感头性能的外界干扰磁场、被测导线位置等因素进行了详细分析,并给出了改善措施。设计了一种基于印制电路板(PCB)骨架的罗氏线圈,在信号处理电路的基础上对其进行了试验研究。结果显示,PCB型罗氏线圈测量电流精度高,有较好的抗外界干扰能力,符合设计要求。     

基于PCB的平面型空心线圈电流互感器性能分析及设计

通过电磁理论分析,提出了一种基于印刷电路板(PCB)的平面型空心线圈电流互感器.该新结构的空心线圈由多个平面螺旋线圈串接构成,一次导体紧绕半数不相邻的螺旋线圈绕制,二次输出一个正比于被测电流变化率的电压信号,再经过积分器还原成电流信号.推导出了线圈互感系数的计算公式,并分析了其抗外磁场干扰的机理,设计了实验模型.测试结果显示:测量精度达到了0.2级,具有较强的抗电磁干扰能力.这对于开发新型的电子式电流互感器具有积极的意义.     

插接式智能组合电器中电子式电流传感器的结构特性分析

电力系统中电子式电流传感器替代传统电磁式电流互感器是发展方向。首先简要介绍一种应用在插接式智能组合电器中的电子式电流传感器的基本测量原理 ,然后对传感器的结构特性进行分析 ,主要包括温度、线圈的多层绕制与不均匀绕制、电流源的放置方式以及磁场的不均匀分布等因素对测量结果的影响 ,最后对多种因素共同作用下的影响进行综合分析 ,分析结果对改善电流传感器的性能有指导作用。     

超磁致伸缩驱动器驱动磁场仿真分析

为了充分发挥超磁致伸缩驱动器的特性,提高超磁致伸缩驱动器驱动磁场的性能,通过采用电流励磁法,建立基于磁感应强度为控制变量的单层空心线圈、多层空心线圈和带超磁致伸缩棒的多层线圈的轴线磁感应强度数学模型,分析超磁致伸缩棒、线圈长度和线圈半径对驱动磁场的均匀性和驱动磁场大小的影响.仿真结果表明,减小超磁致伸缩棒与驱动线圈之间的气隙,能提高驱动磁场的线性度;在满足设计要求的范围内,增加线圈长度,减小线圈半径,能够提高驱动磁场均匀性;仿真结果对超磁致伸缩驱动器驱动磁场的设计提供了一定的理论依据.     

电流互感器误差影响因素与应用分析

电流互感器是电能计量装置重要组成部分,其误差是电能计量装置误差主要来源之一。本文分析了电流互感器误差的影响因素。分析表明:电流互感器的误差主要受两方面影响:一是电流互感器的结构,如铁芯尺寸、形状、材料以及线圈匝数;二是电流互感器的工作条件,即一次电流大小和二次绕组的负载阻抗,并就减小误差方法进行分析。最后,介绍了实际使用中如何根据参数选择合适的电流互感器。     

电流互感器误差影响因素与应用分析

电流互感器是电能计量装置重要组成部分,其误差是电能计量装置误差主要来源之一。本文分析了电流互感器误差的影响因素。分析表明：电流互感器的误差主要受两方面影响：一是电流互感器的结构,如铁芯尺寸、形状、材料以及线圈匝数;二是电流互感器的工作条件,即一次电流大小和二次绕组的负载阻抗,并就减小误差方法进行分析。最后,介绍了实际使用中如何根据参数选择合适的电流互感器。     

基于性能最优的磁流变阻尼器励磁线圈缠绕方法研究

双线圈活塞式磁流变阻尼器是一种通过励磁线圈产生磁场,以控制输出阻尼力的器件,其励磁线圈的缠绕方法直接影响磁流变阻尼器磁场分布和动态响应时间。在磁流变阻尼器性能模型的研究基础上,以阻尼动力和动态性能为最优目标,分析了两励磁线圈多种缠绕方法对阻尼间隙的磁场分布和控制电路的响应时间的影响,综合考虑了外界控制电路的电流负担和电能损耗,获得了励磁线圈采用反向串联的最优缠绕方法。研究结果为磁流变阻尼器的结构设计和参数优化提供了参考依据。     

PCB空心线圈的电流测量动态特性研究

PCB空心线圈具有测量准确度高、稳定性和参数一致性好、设计和加工方便等优点,适合用作电子式电流互感器.但由于结构和制作工艺不同于常规空心线圈,因此其电磁参数也不同于常规空心线圈.按通常的单纯优化负载电阻阻值的方法可能无法同时满足高准确度和高动态特性的要求.通过对线圈等效电路模型及电磁参数的分析,提出了在PCB空心线圈的输出端串联一个校正网络并优化配置零极点的方法.仿真及实验结果表明,该方法能有效抑制线圈输出的高频振荡,在保证稳态0.2 S准确度等级的情况下实现了其动态性能的优化.     

两种保护用电流采样电路的比较及应用

介绍了两种电流互感器的特性,设计了适用于不同互感器的交流采样和处理电路,并作了相应的分析。通过对比可知,采用空心线圈电流互感器的交流采样方式完全能满足电力系统保护和测量的需要,而且还能实现更宽电流范围的保护。     

光纤电流互感器中Rogowski线圈的设计与分析

Rogowski线圈作为传感头是光纤电流互感器的关键部分,文章分析了Rogowski线圈的测量原理和等效电路,得出了测量关系,并根据分析设计了一个Rogowski线圈。实验表明该Rogowski线圈具有良好的线性度;频率特性分析显示该Rogowski线圈有非常充裕的带宽,进而为设计高精度的光纤电流互感器奠定了基础。     

An ultralow noise current amplifier based on superconducting quantum interference device for high sensitivity applications

An integrated ultrahigh sensitive current amplifier based on a niobium dc superconducting quantum interference device (SQUID) has been developed. The sensor design is based on a multiturn signal coil coupled to a suitable SQUID magnetometer. The signal coil consists of 60 square niobium turns tightly coupled to a superconducting flux transformer of a SQUID magnetometer. The primary coil (pick-up coil) of the flux transformer has been suitably designed in order to accommodate the multiturn input coil. It has a side length of 10 mm and a width of 2.4 mm. In such a way we have obtained a signal current to magnetic flux transfer coefficient (current sensitivity) as low as 62 nA∕Φ(0). The sensor has been characterized in liquid helium by using a direct coupling low noise readout electronic and a standard modulated electronic in flux locked loop configuration for the noise measurements. Beside the circuit complexity, the sensor has exhibited a smooth and free resonance voltage-flux characteristic guaranteeing a reliable and a stable working operation. Considering a SQUID magnetic flux noise of S(Φ)(1∕2) = 1.8 μΦ(0)∕Hz(1∕2) at T = 4.2 K, a current noise as low as 110 fA∕Hz(1∕2) is obtained. Such a value is about a factor two less than the noise of other SQUIDs of the same category. As an application, Nyquist noise measurements of integrated test resistors using the current sensing noise thermometer technique are reported. Due to its high performance such a sensor can be employed in all applications requiring an extremely current sensitivity like the readout of the gravitational wave detectors and the current sensing noise thermometry.     

Aircore mechanism during draining based on influence of pressure difference and drain port diameter

An understanding of the mechanism of aircore phenomenon during draining is very important. In this study, numerical simulations were conducted for different pressurized and suction pressure water tanks, as well as for different drain port diameters, to explain and validate the proposed aircore mechanism. It was found that increasing the pressure at the top surface of the tank results in suppression of the aircore, whereas an increase in the suction pressure at the drain port outlet enhances the development of the aircore. For different drain port diameters, it was observed that the duration of the aircore during draining decreases with a decrease in the drain port diameter, and that the aircore is suppressed for a very small drain port diameter.     

组合式电子互感器的研究与设计

在分析电子式电流、电压互感器当前技术和发展的基础上,系统总结并提出了组合式电子互感器的原理和设计要求。给出了以Rogowski线圈测量电流和以电容分压器测量电压的电子式电流/电压互感器的原理和设计方法,论述了组合式电子互感器的优点和性能。     

Liftoff insensitive thickness measurement of aluminum plates using harmonic eddy current excitation and a GMR sensor

This paper describes the implementation of a device that measures the thickness of metallic plates. A pancake coil for magnetic field sinusoidal excitation is used and detection is performed with a bridge giant magneto-resistor sensor. The paper uses the theory of the linear transformer to explain the liftoff effect with a special attention to the point of interception phenomenon. The transformer model shows that to attain the interception points with instantaneous measured voltages independent of the liftoff gap the excitation coil must be driven with imposed current. This effect was explored to show that a simultaneous process of thickness and conductivity measurement is feasible.     

新型一体化开放式高频功率变压器设计

研制了一种带中心抽头的一体化开放式结构的新型高频功率变压器。变压器结构将散热器、变压器与整流桥设计为一体,使得变压器副边及输出整流电路的结构非常简洁紧凑,变压器制作容易,散热与密封性能好,可用于电镀与电解加工设备的电源中。本文对变压器的结构设计、磁芯材料的选择、磁芯与线圈的参数和结构及绕制工艺等要素进行详细介绍。实践表明,该新型一体化开放式高频功率变压器可以成功地应用在1000A大功率软开关逆变式电镀与电解电源中。     

Study of aircore phenomenon and influence of water height during liquid draining

Draining of liquids through cylindrical tanks is a very common phenomenon and has many applications. Understanding the aircore formation and its growth during draining has attracted appreciable interest in the literature. In this study, water draining through cylindrical tanks was studied using experimental and numerical techniques. Eight different initial heights of water in the tank between 310 and 450 mm with a 20-mm increment were tested in each experiment. The numerical study shows good agreement with the experimental data and promotes understanding of the generation and disappearance of an aircore during draining. For the different initial water heights, the experiments were performed with and without initial rotation of the tank. It is found that in the experiments without initial tank rotation, the drain time of water increases with increasing initial height. On the other hand, the drain time remains almost the same for all initial heights tested with initial tank rotation. The small variation in the drain time even when the initial water level is reduced is explained by the aircore duration during draining. Also, the mechanism of generation and disappearance of aircore is proposed with the help of numerical results.

     

Rogowski coil current transducer compensation method for harmonic active power error

In the harmonic active power measurement, the highest uncertainties are generally introduced by the current and voltage transducers. In a previous paper, the authors showed that the current transformer (CT) can introduce significant errors in such measurement, especially if the phase shift between voltage and current is close to ±90°. In such condition the errors on harmonic power measurement are mainly due to the CT phase displacement. This paper shows that better results can be achieved with more linear transducers, such as the Rogowski coil current transducers (RCCTs), whose metrological performance in distorted condition can be improved, by means of a proper compensation method. The proposed method for RCCTs compensation is based on the frequency response and it allows to reduce the errors on harmonic power measurement, also for phase shift close to ±90°. The study is supported by several experimental tests.     

An accurate continuous calibration system for high voltage current transformer

A continuous calibration system for high voltage current transformers is presented in this paper. The sensor of this system is based on a kind of electronic instrument current transformer, which is a clamp-shape air core coil. This system uses an optical fiber transmission system for its signal transmission and power supply. Finally the digital integrator and fourth-order convolution window algorithm as error calculation methods are realized by the virtual instrument with a personal computer. It is found that this system can calibrate a high voltage current transformer while energized, which means avoiding a long calibrating period in the power system and the loss of power metering expense. At the same time, it has a wide dynamic range and frequency band, and it can achieve a high accuracy measurement in a complex electromagnetic field environment. The experimental results and the on-site operation results presented in the last part of the paper, prove that it can reach the 0.05 accuracy class and is easy to operate on site.