Vibration and noise mechanism of a 110 kV transformer under DC bias based on finite element method

Global energy and environmental issues are becoming increasingly problematic,and the vibration and noise problem of 110 kV transformers,which are the most widely distributed,have attracted widespread attention from both inside and outside the industry.DC bias is one of the main contributing factors to vibration noise during the normal operation of transformers.To clarify the vibration and noise mechanism of a 110 kV transformer under a DC bias,a multi-field coupling model of a 110 kV transformer was established using the finite element method.The electromagnetic,vibration,and noise characteristics during the DC bias process were compared and quantified through field circuit coupling in parallel with the power frequency of AC,harmonic,and DC power sources.It was found that a DC bias can cause significant distortions in the magnetic flux density,force,and displacement distributions of the core and winding.The contributions of the DC bias effect to the core and winding are different at Kdc=0.85.At this point,the core approached saturation,and the increase in the core force and displacement slowed.However,the saturation of the core increased the leakage flux,and the stress and displacement of the winding increased faster.The sound field distribution characteristics of the 110 kV transformer under a DC bias are related to the force characteristics.When the DC bias coefficient was 1.25,the noise sound pressure level reached 73.6 dB.

Effect of applied dc bias voltage on composition, chemical bonding and mechanical properties of carbon nitride films prepared by PECVD

Carbon nitride films were deposited on Si (100) substrates using plasma-enhanced chemical vapor deposition (PECVD) technique from CH4 and N2 at different applied dc bias voltage. The microstructure, composition and chemical bonding of the resulting films were characterized by Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The mechanical properties such as hardness and elastic modulus of the films were evaluated using nano-indentation. As the results, the Raman spectra, showing the G and D bands, indicate the amorphous structure of the films. XPS and FTIR measurements demonstrate the existence of various carbon-nitride bonds in the films and the hydrogenation of carbon nitride phase. The composition ratio of N to C, the nano-hardness and the elastic modulus of the carbon nitride films increase with increasing dc bias voltage and reach the maximums at a dc bias voltage of 300 V, then they decrease with further increase of the dc bias voltage. Moreover, the XRD analyses indicate that the carbon nitride film contains some polycrystalline C3N4 phase embedded in the amorphous matrix at optimized deposition condition of dc bias voltage of 300 V.

First IEC standard of DC bias suppression devices to be issued

IEC TS 60076-23,the first IEC standard on DC bias suppression devices approved by IEC/TC 14 in November 2017,is expected to be published and put into force in 2018,overcoming the lack of such IEC standards in the field.The Shanghai branch of SGCC has carried out studies and researches on DC bias effect for more than 10 years,and it has led the standard development based on its R&D and the application of DC bias suppression devices in China.

Finite Element Simulation and Experimental Study on Vibration Characteristics of Converter Transformer Under DC Bias

To clarify the electromagnetic,vibration,and loss characteristics of the internal components of a converter transformer under DC bias conditions and their influencing mechanisms,a series of studies are conducted using the finite element method and model experiments.This paper quantifies the influence of different DC contents on the magnetic flux density,force,and displacement distribution characteristics of the iron core and winding and analyzes the internal relationship between various indicators.The inflection point of the DC bias coefficient on the vibration is obtained and the contribution mechanism of the different responses of the iron core and winding to this inflection point is explained.The value of the DC bias coefficient for changing the main vibration frequency is determined.When the DC bias coefficient is 1.0 and 1.5,the main frequency of vibration moves to the right to 250 Hz and 350 Hz.Based on the principle of similarity,a DC bias vibration experimental platform for converter transformers is developed,and DC bias magnetic experiments are conducted to verify the reliability of the simulation results.

DC BIAS ELECTRIC FIELD DEPENDENT PIEZOELECTRICITY FOR[001]POLED Pb(In_(1/2)Nb_(1/2))O_(3)-Pb(Mg_(1/3)Nb_(2/3))O_(3)-PbTiO_(3) CRYSTALS

The longitudinal piezoelectric response of[001]poled rhombohedral and orthorhombic Pb(In_(1/2)Nb_(1/2))O_(3)-Pb(Mg_(1/3)Nb_(2/3))O_(3)-PbTiO_(3)crystals were investigated with respect to DC bias electric field,being in the range of-2-15 kV/cm.For rhombohedral crystals with compo-sitions far away from morphotropic phase boundary(MPB),the piezoelectric response generally decreased with increasing positive DC bias field,while for crystals with MPB compositions,the piezoelectric response firstly decreased and then increased as function of DC bias.The piezo-electric response was found to decrease drastically when DC bias larger than phase transition feld.On the other hand,the piezoelectric response was slightly enhanced for all the crystals as function of negative DC bias prior to the depolarization.To explain the obtained results,the field dependent piezoelectric cofficients in domain engineered crystals were analyzed based on ther-modynamic approach.

EFFECT OF NEGATIVE BIAS ON DIAMOND NUCLEATION IN MICROWAVE PLASMA ASSISTED CHEMICAL VAPOR DEPOSITION SYSTEM

Effect of direct current negative bias on diamond nucleation in microwave plasma assisted chemical vapor deposition system was discussed. The influence of the magnitude of negative bias value,bias duration and methane concentration in the gas mixture on nucleation density of diamond films was studied respectively. It is demonstrated that direct current negative bias can drastically enhance the diamond nucleation at a suitable value.Long bias duration and high methane concentration are helpful for diamond nucleation.

HVDC中直流偏磁电力变压器叠片铁心损耗及磁通分布

为了研究高压直流输电系统中直流偏磁电力变压器叠片铁心中的损耗及磁通分布,提出并研制了完全按照电力变压器铁心的标准设计和叠装工艺制作的叠片铁心模型。通过模型实验获得了叠片材料在不同偏置磁场作用时的损耗曲线,解决了直流偏磁条件下叠片铁心三维电磁场数值计算中所需要的材料性能数据问题。考察了不同偏置磁场作用下变压器铁心取向硅钢片中的损耗和磁通分布,研究不同偏置磁场强度对取向硅钢片特性的影响,提出解决计算三维非线性和各向异性涡流问题的实用措施。研究表明,不同偏磁工况下模型铁损和磁通的计算结果和测量结果具有较好一致性,所得结果和结论有助于通过优化设计来提高电力变压器的性能指标。

HVDC直流偏磁电力变压器铜屏蔽中涡流损耗分析与仿真

为了研究高压直流输电系统中直流偏磁电力变压器铜屏蔽中涡流损耗分布,基于Problem 21基准族中的P21c-EM1简化模型进行了详细实验研究和仿真分析。重点考察不同激励方式下变压器结构件(如:变压器油箱等)铜屏蔽中涡流损耗的分布,研究交流激励源和直流激励源之间的交叉作用对铜屏蔽损耗特性的影响。通过模型实验分别获得了电力变压器铜屏蔽在不同直流偏置磁场强度作用时和标准的正弦激励作用时的损耗分布情况并进行了对比分析。提出采用三维瞬态场计算电力变压器直流偏置涡流场的实用措施,不同偏磁工况下,模型涡流损耗的计算结果和测量结果具有较好一致性,所得结果和结论有助于通过优化设计来提高电力变压器的性能指标。

Excitation-wavelength-dependent THz wave modulation via external bias electric field

A theoretical model was proposed to describe the effects of external bias electric field on terahertz(THz)generated in air plasma.The model predicted that for a plasma in a bias electric field,the amplification effect of the THz wave intensity increases with the increase of the excitation laser wavelength.We experimentally observed the relationship between the THz enhancement effect and the electric field strength at different wavelengths.Experimental results showed a good agreement with the model predictions.These results enhance our understanding of the physical mechanism by which femtosecond lasers excite air to generate THz and extend the practical applications of THz generation and modulation.

基于DCO-OFDM的帧内信号时域调整技术研究(英文)

在传统OFDM系统中,OFDM码元在信道特性不佳时可能会超出保护间隔并严重影响相邻码元,从而造成码间干扰和载波间干扰.针对此类干扰,在高速非相干光OFDM通信系统中,提出了一种基于直流偏置光OFDM的帧内信号时域调整方案.该方案运用傅里叶变换的基本性质,通过简单的频域子信道预处理,便可以将直流偏置光OFDM时域信号进行帧内交叉性时序搬移,使信号能量从码元边缘部分集中到中间部分.数值模拟表明,该方案能显著降低因码元超出保护间隔而引起的码间干扰和载波间干扰,从而有效改善系统的误码率性能.对于某些通过减小保护间隔来提高信息传输有效性的光OFDM系统,该方案也具有很大意义.

用于DC-DC变换器中稳定性保护模块的设计

针对现代电子系统中预偏置电压保护与电压边际界限的情况,提出了一种应用于DC/DC数字控制芯片的预偏置电压保护与电压边际界限功能模块的设计。利用CPLD验证该模块的正确性,实现了预偏置电压保护与电压边际界限功能。

Study on Earth Surface Potential and DC Current Distribution around DC Grounding Electrode

DC magnetic biasing problem,caused by the DC grounding electrode, threatened the safe operation of AC power grid. In this paper, the characteristics of the soil stratification near DC grounding electrode was researched. The AC-DC interconnected large-scale system model under the monopole operation mode was established. The earth surface potential and DC current distribution in various stations under the different surface thickness was calculated. Some useful conclusions are drawn from the analyzed results.

Research on the Optimized Network Configuration of DC Blocking Device

HVDC transmission system has considerable impact on the surrounding power transformers when the system is running in the unipolar ground mode, which will cause the DC magnetic biasing phenomenon on transformers. This problem would be more serious, after commission and operation of UHVDC transmission system in China. According to the Guangdong power grid under the influence of DC magnetic bias seriously, but little research about the using of blocking device, this paper proposed an optimization scheme about the usage of blocking device combination. Firstly, the subject studied the method of suppressing transformer neutral point DC depending on analysis the mechanism of magnetic biasing, and then found out the changes of power grid after using the capacitance blocking device which is popular used by Guangdong power grid. The particle swarm optimization (PSO) has been used to find a better way to suppress the DC in power grid, and combined with NSGA to solve the mixed integer programming problem. The final data validation of this method is valuable in engineering application.

New Topologies of High Torque Density Machine Based on Magnetic Field Modulation Principle

With the increasing demand for high torque density in motors,more and more new topologies emerge.Furthermore,the magnetic field modulation principle is widely concerned and has evolved into an effective analysis method for studying the new motor topology.This paper introduces the principle of magnetic field modulation.And the research on high torque density in recent years is reviewed from the perspective of magnetic field modulation,including permanent magnet vernier machine(PMVM),flux reverse machine(FRM),flux switching machine(FSM),dual permanent magnet(DPM)machine,and DC biased machine.The principle of magnetic field modulation makes it possible to propose higher torque density topologies in the future.

考虑短路电流非周期分量影响的磁偏置型超导故障限流器设计方法及其限流特性分析

随着电力负荷快速增长,电力系统的故障电流水平持续上升,甚至超出了现有断路器的开断能力;为有效限制故障电流,超导故障限流器(superconducting fault current limiter,SFCL)逐渐投入应用。SFCL在正常运行时呈现零阻抗,故障发生后迅速转为高阻抗,可作为配合断路器开断的理想选择,提高电力系统的运行安全性。介绍了一种磁偏置型超导故障限流器(magneto-biased superconducting fault current limiter,MBSFCL),提出了考虑短路电流非周期分量影响的MBSFCL设计方法,对于MBSFCL的制造具有一定的指导意义。通过搭建仿真模型,验证了所提出方法的可行性,并对MBSFCL的限流特性进行了深入分析,讨论了不同非周期分量对断路器的开断影响,以及MBSFCL中电感、电阻参数变化对短路电流及其分量的限流效果影响。分析结果表明,在所提出MBSFCL设计方法中必须考虑非周期分量,且MBSFCL的电阻参数变化对短路电流的抑制效果更为显著。

采用不对称功率器件布局的双三相直流偏置型同步电机功率变换器设计

直流偏置型同步电机采用带直流偏置的正弦电流驱动电机运行,它特殊的相电流对功率变换器提出了特殊的需求。为降低功率变换电路的整体成本和系统体积,提高系统可靠性,开发直流偏置型同步电机使用的低成本高功率密度功率变换器非常迫切。提出了采用不对称功率器件布局的直流偏置型同步电机功率变换器,针对传统对称式布局功率变换器成本高、功率密度受限等问题提供了简单有效的解决方案。为了使各器件的功耗和温升更加平衡,提出了一种上桥臂采用高功率等级和下桥臂采用低功率等级功率器件的不对称双三相逆变器。通过理论分析确定了两组功率器件对应的功率等级,作为不对称功率器件的选型依据。结合仿真实验,对双三相直流偏置型同步电机功率变换器的功率器件电流等级以及散热布局的不对称特性进行了验证。证明了提出的不对称功率器件布局方式对降低电力电子器件的成本,增加系统功率密度,提升逆变器整体寿命具有重要意义。

变压器直流偏磁在线监测系统在辽宁电网的应用

分析辽宁电网变压器直流偏磁问题产生的原因及危害,并针对现场直流偏磁检测方法中存在的不足,结合智能运检建设需求,研发了一种变压器直流偏磁在线监测系统;目前该系统已经在辽宁徐家500 kV变电站得到应用,有效提升了该变电站2组主变压器的运行可靠性。

直流偏磁条件下变压器励磁电流的实验与分析

直流偏磁工作条件下,变压器励磁电流的实验与分析是研究变压器直流偏磁电磁特性的关键问题。本文基于产品级的叠片铁心模型,模拟直流偏磁变压器铁心的实际工作状态;研究了因高压直流输电引起电力变压器直流偏磁工作条件下,变压器励磁电流的实验测量方法及其仿真计算与分析。提出并利用Matlab计算软件实现了直流偏磁励磁电流的工程解法,数值计算的结果证明了本文方法的有效性和正确性。

基于瞬态场路耦合模型的变压器直流偏磁计算

利用变压器瞬态场路耦合模型,计算单相变压器的直流偏磁问题。对比在一次侧和二次侧注入直流时变压器的直流偏磁情况,结果说明两种注入方式下交流电流的波形基本相同。分析变压器直流偏磁时交流磁场和电路等效参数的变化,变压器直流偏磁时励磁电流波形畸变,其峰值与各次谐波含量均随直流电流增大而增加;动态电感取决于励磁的饱和程度,其波形在交流励磁的正负半周并不对称,两种运行方式下场路耦合参数受直流影响的变化规律相同。负载运行直流偏磁时动态漏电感波形畸变,外侧一次绕组的漏磁通增大。当直流电流超过一定值时,变压器发生偏磁时的励磁电流峰值与直流电流近似呈线性关系。最后,通过实验验证了瞬态场路耦合方法的准确性和可行性,为变压器直流偏磁计算提供新方法。

直流偏磁对变压器的影响

对江苏电网500 kV变压器受到直流偏磁的影响所产生和问题进行分析,直流偏磁导致变压器噪声增加、变压器铁心过热、变压器温升增大,对电网安全运行极为不利。通过理论分析和实测数据计算,分析直流偏磁对电网设备的影响。