变压器空载电流谐波低频测量方法

变压器空载电流谐波的幅值及成分可以检查铁心的饱和程度,并判断是否有匝间故障。变压器出厂试验时通常采用容量较大的工频电源进行空载电流谐波测量。为了减小试验电源容量,提出一种采用低频电源代替工频电源进行变压器空载电流谐波测量的低频测量法。该方法通过施加两个低频率的电压测量低频下的涡流电流和空载电流谐波幅值,再根据对涡流电流的补偿计算折算至工频下的空载电流各次谐波含量和总谐波含量。并对单相变压器进行仿真和试验验证,采用15Hz的折算结果与工频50H实测的空载电流各次谐波含量K(k)及总谐波含量THDi误差均小于1%。结果表明,所提方法折算准确度高,而且能成倍减小试验电源容量。

变压器空载电流谐波低频测量方法研究

变压器空载电流谐波幅值及构成可以检查铁心的饱和程度和判断是否有匝间故障。变压器出厂试验时通常采用容量较大的工频电源进行空载电流谐波测量。为了减小试验电源容量,提出了一种采用低频电源代替工频电源进行变压器空载电流谐波测量的低频测量法。该方法通过施加两个低频率的电压测量低频下的涡流电流和空载电流谐波幅值,再根据对涡流电流的补偿计算折算至工频下的空载电流各次谐波含量和总谐波含量。并对单相变压器进行仿真和试验验证,采用15Hz的折算的结果与工频50Hz实测结果的空载电流各次谐波含量K(k)和总谐波含量THDi误差均小于1%。结果表明,本方法折算准确度高,而且能减小试验电源容量。

低噪声屏蔽电机定子屏蔽套激振力和受迫振动分析

三相屏蔽电机是屏蔽电泵专属特种电机,该电机的性能优劣对系统振动噪声有很大影响。屏蔽电机气隙内的旋转磁场在定子屏蔽套中感应出涡流,除产生屏蔽套涡流损耗外,该涡流还将与气隙合成磁场相互作用形成径向和切向高频电磁激振力。考虑到定子屏蔽套是薄壁件,与定子齿冠间存在一定的安装间隙,所以在电磁激振力下定子屏蔽套将产生电磁振动和噪声。首先从解析的角度推导得到了径向和切向电磁激振力的数学表达式,进而采用有限元法计算定子屏蔽套典型位置点磁通密度时间谐波和圆周方向上磁通密度空间谐波分布规律及谐波含量,得到了不同屏蔽套材质时的涡流电流密度分布。计算了定子屏蔽套采用哈氏合金时的电磁激振力变化曲线,并与解析计算结果进行了横向对比,验证了解析计算的正确性。最后,计算分析定子屏蔽套的工作模态和在电磁激振力作用下的机械形变,为后续屏蔽电机的减振降噪提供理论依据。

储能飞轮径向磁轴承设计

提出了一种新型的径向涡流斥力场磁轴承方案。通过对气隙磁场的分析,提出了双层永磁体的斥力场结构,从而降低磁场的法向分量,并增加产生回复力的磁场切向分量。设计了转子无偏移时内部零磁通的8字形闭合线圈结构,并对稳态及转子径向偏移时闭合线圈的受力情况进行了分析。分析结果表明转子存在很小偏移时,径向产生极大的恢复力。

电磁阀驱动装置

电磁阀驱动装置由常开电磁铁、常闭电磁铁以及换向控制阀和两个弹簧组成。由这些元器件共同组成的弹簧一质量系统,主要用来控制阀的换气。

Design and Experiment of Streamlined Piezoelectric Pump with Low Vortex and Large Flow Rate

Valveless piezoelectric pump is widely used in the medical,however,there is a general and difficult problem to be solved:Low vortex and large flow rate are not compatible,resulting in the blood prone to thrombosis during blood delivery.In this paper,a new valveless piezoelectric(PZT)pump with streamlined flow tubes(streamlined pump)is proposed.The design method and the working principle of the pump are analyzed.The velocity streamlines are simulated,and the results demonstrate that there are no obvious vortexes in the flow tube of the streamlined pump.Five prototype pumps(two cone pumps and three streamlined pumps)are designed and fabricated to perform flow rate and flow resistance experiments.The experimental results illustrate that the maximum flow rate of the streamlined pump is 142 mL/min,which is 179%higher than that of the cone piezoelectric pump,demonstrating that the streamlined pump has a large flow rate performance.This research provides an inspiration for future research on simple structure,low vortex and large flow rate volume-type pumps,and also provides a useful solution for thrombosis preventing.

Path transition of the western boundary current with a gap due to mesoscale eddies: a 1.5-layer, wind-driven experiment

Using a 1.5 layer nonlinear shallow-water reduced-gravity model, we executed numerical simulations to investigate the possibility of a western boundary current (WBC) path transition due to mesoscale eddies based on the background of the Kuroshio intrusion into the South China Sea (SCS) from the Luzon Strait. Because the WBC existed different current states with respect to different wind stress control parameters, we chose three steady WBC states (loop current, eddy shedding and leaping) as the background flow field and simulated the path transition of the WBC due to mesoscale eddies. Our simulations indicated that either an anticyclonic or cyclonic eddy can lead to path transition of the WBC with different modes. The simulation results also show that the mesoscale eddies can lead to path transition of the WBC from loop and eddy shedding state to leaping state because of the hysteresis effect. The leaping state is relatively stable compared with the mesoscale eddies. Moreover, an anticyclonic eddy is more effective in producing the WBC path transition for the path transition than a cyclonic eddy. Our results may help to explain some phenomena observed regarding the path transition of the Kuroshio due to the mesoscale eddies at the Luzon Strait.

Eddy formation and surface flow field in the Luzon Strait area during the summer of 2009

The formation of mesoscale eddies and the structure of the surface flow field in the Luzon Strait area were examined using in-situ CTD data, Argo float data, and multi-satellite remote sensing data collected from May to August 2009. The results show that vigorous water exchange between Kuroshio water and South China Sea （SCS） water began to emerge over the 200 m water column throughout the strait. Based on an objective definition of surface currents, float A69 tracked an anti-cyclonic eddy southwest of Taiwan Island under a Lagrangian current measurement. The salinity inside the anti-cyclonic eddy was higher than in typical SCS water but lower than in Kuroshio mainstream water, indicating that this eddy was induced by Kuroshio frontal intrusion through the Luzun Strait and into the SCS. From hydrographic data, we propose that continuous horizontal diffusion with high-salinity characteristics in the subsurface layer could extend to 119°E or even further west. The high-temperature filament, large positive sea level anomaly and clockwise geostrophic current all confirmed the existence of this warm eddy in May and June. A strongly negative wind stress curl maintained the eddy until it died. The surface flow field during July and August was rather complicated. Float A83 described an east-west orientated shuttle run in the 20°N section that was not reported by previous studies. At the same time, float A80 indicated a Kuroshio bend into the north-central region of Luzon Strait but it did not cross 120.5°E. The water mass rejoining the Kuroshio mainstream from the southern tip of Taiwan Island was less saline, indicating an entrainment of water from SCS by the Kuroshio bend.

Comparison of three formulations for eddy-current problems in a spiral coil electromagnetic acoustic transducer

Three differential equations based on different definitions of current density are compared. Formulation I is based on an incomplete equation for total current density （TCD）. Formulations II and {I1 are based on incomplete and complete equations for source current density （SCD）, respectively. Using the weak form of finite element method （FEM）, three formulations were applied in a spiral coil electromagnetic acoustic transducer （EMAT） example to solve magnetic vector potential （MVP）. The input impedances calculated by Formulation III are in excellent agreement with the experimental measurements. Results show that the errors for Formulations I ＆ II vary with coil diameter, coil spacing, lift-off distance and external excitation frequency, for the existence of eddy-current and skin ＆ proximity effects. And the current distribution across the coil conductor also follows the same trend. It is better to choose Formulation I instead of Formulation Ili to solve MVP when the coil diameter is less than twice the skin depth for Formulation I is a low cost and high efficiency calculation method.

Giant magneto-impedance and low-frequency magneto-resistance effect in NiFeB coated composite wires

Composite wires of 100 μm insulated CuBewire plated with a layer of NiFeB were produced by elec-troless-deposition, and their magnetic properties were stud-led. The results showed that a good magneto-impedance (MI)effect can be obtained at relatively low frequency. The largestMI ratio (△Z/Z)max obtained is 250% at 500 kHz. Mag-neto-resistance effect was also observed at low frequency,with the (△R/R)max observed to be -8.5% at 540 Hz and 38.7% at 10 kHz. Results are discussed, and the equivalent resistance and inductance as the result of the NiFeB layer are taken into account.

An approach to explore the eddy currents of the new type divertor for EAST device using ANSYS code

An effective method for eddy current calculation has been developed for EAST’s new divertor by using ANSYS.A 3D model of a double null divertor for the EAST device was built to evaluate eddy currents and electromagnetic(EM)forces on these components.The main input to the model is the plasma current and poloidal field coil currents,which are loaded into the model using experimental data measured from the EAST discharges.These currents generate magnetic fields that match those producing an EAST discharge,and the time variation of these fields produces the eddy currents in the divertors,along with from the resulting EM forces.In addition,the first 10 time steps were discussed for the eddy current generation and changing trend.It indicates that a static analysis before a transient mode start can solve the eddy current origination in the initial time steps.With this method,the EM transient response of EAST’s new divertor can be predicted based on ANSYS simulations.Furthermore,the method is also an effective approach to estimate the EM results for the in-vessel components of a fusion reactor during a disruption.