Prediction of Core Losses of Three-Phase Distribution Transformer

Transformers are normally designed and built for use at rated frequency and sinusoidal load current. A non-linear load on a transformer leads to harmonic power losses which cause increased operational costs and additional heating in transformer parts. It leads to higher losses, early fatigue of insulation, premature failure and reduction of the useful life of the transformer. To prevent these problems, the rated capacity of transformer which supplies harmonic loads must be reduced. In this work, a typical 50 kVA three-phase distribution transformer with real practical parameters is taken under non-linear loads generated due to domestic loads. The core losses is evaluated using the three dimensional model of the transformer developed in FEM （finite element method） program based on valid model of transformer under high harmonic conditions. And finally a relation associated with core losses and amplitude of high harmonic order are reviewed ＆ analyzed and then a comparison is being carried out on the results obtained by different excitation current in transformer windings.

结合变种残差模型和Transformer的城市公路短时交通流预测

城市公路交通流的预测受到历史交通流量和相邻车道交通流量的影响,蕴含了复杂的时空特征。针对传统交通流预测模型卷积长短时记忆(ConvLSTM)网络进行交通流预测时,未将时空特征分开提取而造成的特征提取不充分、特征信息混淆和特征信息缺失等问题,对ConvLSTM模型作出改进。首先,提取每个采样时刻的交通流数据的短期时间特征和空间特征,并在特定的维度下将交通流的短期时空特征融合;其次,进行残差映射;最后,将映射后的短期时空特征交由Transformer模型捕捉交通流数据长期的时空特征,并根据所捕捉的长期特征对未来时刻每个采样点交通流进行预测。使用加州城市快速路数据对模型进行验证,以平均绝对误差(MAE)作为模型评价指标时,所提模型相较于Conv-Transformer模型,预测精度提高了18%,验证了所提模型的有效性。

THE COMBINED HOUGH TRANSFORM

On the basis of researching the generalized Hough transform and its im-provements,this paper presents a combined Hough transform(CHT)for recognizing arbi-trary shapes.The combined Hough transform introduces the idea of the adaptive Houghtransform(AHT)into the double Hough transform(DHT).It not only maintains the de-sirable features of the DHT,but also improves the speed of execution and resistanceagainst disturbance,and reduces the memory requirements greatly.The CHT canaccurately recognize objects,partially occluded in complex background.Therefore,it ispossible to implement the CHT in real-time application.

Research on system combination of machine translation based on Transformer

Influenced by its training corpus,the performance of different machine translation systems varies greatly.Aiming at achieving higher quality translations,system combination methods combine the translation results of multiple systems through statistical combination or neural network combination.This paper proposes a new multi-system translation combination method based on the Transformer architecture,which uses a multi-encoder to encode source sentences and the translation results of each system in order to realize encoder combination and decoder combination.The experimental verification on the Chinese-English translation task shows that this method has 1.2-2.35 more bilingual evaluation understudy(BLEU)points compared with the best single system results,0.71-3.12 more BLEU points compared with the statistical combination method,and 0.14-0.62 more BLEU points compared with the state-of-the-art neural network combination method.The experimental results demonstrate the effectiveness of the proposed system combination method based on Transformer.

Transformation Matrix for Combined Loads Applied to Thin-Walled Structures

This paper transforms combined loads, applied at an arbitrary point of a thin-walled open section beam, to the shear centre of the cross-section of the beam. Therein, a generalized transformation matrix for loads with respect to the shear centre is derived, this accounting for the bimoments that develop due to the way the combined loads are applied. This and the authors’ earlier paper (World Journal of Mechanics 2021, 11, 205-236) provide a full solution to the theory of thin-walled, open-section structures bearing combined loading. The earlier work identified arbitrary loading with the section’s area properties that are necessary to axial and shear stress calculations within the structure’s thin walls. In the previous paper attention is paid to the relevant axes of loading and to the transformations of loading required between axes for stress calculations arising from tension/compression, bending, torsion and shear. The derivation of the general transformation matrix applies to all types of loadings including, axial tensile and compression forces, transverse shear, longitudinal bending. One application, representing all these load cases, is given of a simple channel cantilever with an eccentrically located end load.

Expression of transforming growth factor-β in local bony callus in traumatic brain injury combined with extremity fracture in rats

Objective To investigate gene expression of transforming growth factor-β(TGF-β)in local bony callus in tracumatic brain in jury combined with extremity long bone fracture in rats.Methods Eighty male SD rats were randomized into 2 even

Function Combined Method for Design Innovation of Children's Bike

As children mature, bike products for children in the market develop at the same time, and the conditions are frequently updated. Certain problems occur when using a bike, such as cycle overlapping, repeating function, and short life cycle, which go against the principles of energy conservation and the environmental protection intensive design concept. In this paper, a rational multi-function method of design through functional superposition, transformation, and technical implementation is proposed. An organic combination of frog-style scooter and children’s tricycle is developed using the multi-function method. From the ergonomic perspective, the paper elaborates on the body size of children aged 5 to 12 and effectively extracts data for a multi-function children’s bike, which can be used for gliding and riding. By inverting the body, parts can be interchanged between the handles and the pedals of the bike. Finally, the paper provides a detailed analysis of the components and structural design, body material, and processing technology of the bike. The study of Industrial Product Innovation Design provides an effective design method to solve the bicycle problems, extends the function problems, improves the product market situation, and enhances the energy saving feature while implementing intensive product development effectively at the same time.

Exact Solutions to a Combined sinh-cosh-Gordon Equation

Based on a transformed Painlev~ property and the variable separated ODE method, a function transfor- mation method is proposed to search for exact solutions of some partial differential equations （PDEs） with hyperbolic or exponential functions. This approach provides a more systematical and convenient handling of the solution process of this kind of nonlinear equations. Its key point is to eradicate the hyperbolic or exponential terms by a transformed Painleve property and reduce the given PDEs to a variable-coefficient the resulting equations by some methods. As an application, are formally derived. ordinary differential equations, then we seek for solutions to exact solutions for the combined sinh-cosh-Gordon equation

Hierarchy of Combined TL-RTL Equations and an Associated （2＋l）-Dimensional Lattice Equation

A new （29-1）-dimensional lattice equation is presented based upon the first two members in the hierarchy of the combined Toda lattice and relativistic Toda lattice （TL-RTL） equations in （19991） dimensions. A Darboux transformation for the hierarchy of the combined TL-RTL equations is constructed. Solutions of the first two members in the hierarchy of the combined TL-RTL equations, as well as the new （29-1）-dimensional lattice equation are explicitly obtained by the Darboux transformation.

基于LightGBM-Transformer算法的短期电力负荷预测

高精度的短期电力负荷预测是优化电网运行策略和提高电网运行效率的可靠保障。为进一步提高短期电力负荷预测精度,提出轻量梯度提升机(light gradient boosting machine,LightGBM)-Transformer组合模型。该模型考虑时间特征和天气因素对短期电力负荷预测的影响,首先利用LightGBM算法获取特征重要性,排除无关噪声的影响,再将选择后的特征向量作为Transformer模型的输入,最后完成短期电力负荷预测。实验以澳大利亚能源市场运营商(Australian energy market operators,AEMO)检索的开放数据集为基础,并与多种类似模型进行对比。结果表明,LightGBM-Transformer组合模型的平均绝对百分比误差(mean absolute percent error,MAPE)为1.87%,误差指标显著低于其他对比模型,具有较高的预测精度,验证了该模型应用于短期电力负荷预测的可行性和有效性。

Effect of Surface Charge on Flashover for Oil-Pressboard Insulation under AC-DC Combined Electric Field

For converter transformer, AC-DC combined electric field can trigger space charge accumulation on oil-impregnated pressboard interface. The accumulation of space charge on oil-pressboard interface can result in electric field distortion, trend to trigger surface discharge of barriers. This paper studied the influence of surface charge on flashover voltage of oil-impregnated pressboard under AC-DC combined electric field. The study finds that the flashover voltage of oil-pressboard interface under negative polarity DC superimposed AC electric field is higher than that.of positive DC superimposed AC voltage to form composite electric field. It was found that homopolar surface charge has been accumulated on the interface of oil-pressboard with positive or negative DC voltage through measuring surface potential by the electrostatic capacitive probe. The surface charge produced electric field in the opposite direction, which weakening the synthetic electric field strength. What＇s more, under the same conditions, the negative surface charge density oil-pressboard is much larger than the positive.

Surface Partial Discharge Characteristics of Oil-paper Insulation Under Combined AC-DC Voltage

The valve side windings of converter transformers bear AC, DC, impulse, and reversal-polarity voltages during operation, which could result in serious insulation problems of the equipment. By performing experiments with surface discharge model of oil-paper insula- tion at 80 ℃ under combined AC-DC voltage for 200 h, we studied the spectrums and statistical parameters of partial discharges at different discharge stages. Furthermore, some fingerprint parameters were calculated in order to estimate the development situation of par- tial discharge, while the characteristic gases dissolved in the transformer oil were measured by gas chromatography. The surface discharges in the experiments were observed using a high speed camera, and a full discharge process could be marked off into four stages as follows. ①The elementary stage. When a partial discharge occurs near electrodes, electrical charges are injected into the region near electrodes and causing bubble generation. ②Due to their high resistivity and low dielectric constant, the bubbles would bare the major part of the voltage applied to samples. Therefore, discharge happens inside the small bubbles, and it emits a lot of light. ③Micromolecules of gas are produced in discharge, and further ionization in the transformer oil takes place simultaneously when high-energy electrons collide with oil molecules. ④The carrier charge moves forward to electrodes driven by the applied electric field, till they neutralize with the charge from electrodes, and hence discharge channels are formed subsequently.

Analysis of the flow pattern and periodicity of gas–liquid–liquid three-phase flow in a countercurrent mixer-settler

In contrast to the concurrent mixer-settler,the interaction between the mixing and settling chambers have to be taken into account in the simulation of the countercurrent mixer-settler,and no work has been reported for this equipment.In this work,a three-phase flow model based on the Eulerian multiphase model,coupled with a sliding mesh model is proposed for a countercurrent mixer-settler.Based on this,the dispersed phase distribution,flow pattern,and pressure distribution are investigated,which can help to fill the gap in the operation mechanism.In addition,the velocity vector distribution at the phase port shows an intriguing phenomenon that two types of vectors with opposite directions are distributed on the left and right sides of the same plane,which indicates that the material exchange in the mixing and settling chambers is simultaneous.Analysis of this variation at this location by a fast Fourier transform(FFT)method reveals that it is mainly influenced by the mixing chamber and is consistent with the main period of the outlet flow fluctuations.Therefore,by monitoring the fluctuation of the outlet flow and then analyzing it by the FFT method,the state of the whole tank can be determined,which makes it promising for the design of control systems for countercurrent mixer-settlers.

Voltage Profile Enhancement and Power Loss Reduction with Economic Feasibility Using Small Capacity Distribution Transformers

Usually,rural areas can be electrified via three-phase distribution transformers with relatively large capacities.In such areas,low voltage lines are used for long distances,which cause power losses and voltage drop for different types of consumers.Reducing losses and improving voltage profiles in rural distribution networks are significant challenges for electricity distribution companies.However different solutions were proposed in the literature to overcome these challenges,most of them face difficulties when applied in the conventional distribution network.To address the above issues,an applicable solution is proposed in this paper by installing a number of small-capacity distribution transformers instead of every single large-capacity transformer in rural areas.The proposed approach is implemented in the branch network of Al-Hoqool village,which belongs to the Nineveh distribution network.The network has been inspected on-site,drawn,and analyzed using the electrical systems analysis program(ETAP).The analysis showed that using the single-phase pole-mounted transformers can improve the voltage in the network’s end by 29%and enhance the voltage profile for all consumers.The analysis has also demonstrated that the modification can reduce the total power losses by 78%compared to the existing network.Concerning the economic aspect,the payback period for the proposed network is assigned to be 20 months.

Combining Cubic Spline Interpolation and Fast Fourier Transform to Extend Measuring Range of Reflectometry

The reflectometry is a common method used to measure the thickness of thin films. Using a conventional method,its measurable range is limited due to the low resolution of the current spectrometer embedded in the reflectometer.We present a simple method, using cubic spline interpolation to resample the spectrum with a high resolution,to extend the measurable transparent film thickness. A large measuring range up to 385 m in optical thickness is achieved with the commonly used system. The numerical calculation and experimental results demonstrate that using the FFT method combined with cubic spline interpolation resampling in reflectrometry, a simple,easy-to-operate, economic measuring system can be achieved with high measuring accuracy and replicability.

串联电抗器式高阻抗变压器运行状态评估模型

基于准确评估串联电抗器式高阻抗变压器运行状态的目的,诊断其故障级别,构建串联电抗器式高阻抗变压器运行状态评估模型。此模型从影响变压器运行状态的电气类、油气类、油化类、物理类因素着手,构建评估指标体系后,利用基于客观修正主观的评估指标组合赋权方法,以客观修正主观的方式,为指标组合赋权;通过基于模糊综合评估的运行状态评估模型,计算全部赋权后评估指标因素隶属度,分析指标因素标准值后,计算全部指标因素评分值后,结合运行状态级别标准,判断变压器运行状态级别。结果可得,此模型对变压器运行状态级别信息评估结果准确,可得到100%一致的结果。

基于鲸鱼算法的10 kV组合互感器失真电流校正

对于10 kV组合互感器而言,电流失真会使输出电流的数值水平异常增大,并且长时间不恢复至常规电流状态,从而影响互感器的正常运行。为解决上述问题,设计基于鲸鱼算法的10 kV组合互感器失真电流校正方法。构建10 kV组合互感器结构模型,完善鲸鱼算法流程,基于鲸鱼算法获取失真的电流计量数值,实现组合互感器的失真特性判定,完成基于鲸鱼算法的10 kV组合互感器失真电流校正算法的设计。实验结果表明,经过设计方法对互感器失真电流进行校正处理后,可在2 min之内将失真电流恢复至与常规电流完全相同的数值状态,校正效果较好。

基于特征波段选择的芦苇LAI高光谱遥感估测

选取典型芦苇湿地基于芦苇叶片实测高光谱数据和叶面积指数(Leaf Area Index,LAI),在原始光谱的基础上进行了平滑(R)、一阶微分(FD)、倒数(RT)、对数(LT)、倒数一阶微分(RTFD)、对数一阶微分(LTFD)等六种光谱变换,利用竞争性自适应重加权算法(CARS)对不同变换下芦苇LAI特征光谱波段予以筛选,进而用筛选的特征波段采用逐波段组合法(BCI)构建芦苇LAI敏感光谱指数,利用随机森林(RF)、极端梯度提升(XGBoost)以及支持向量机(SVM)回归算法,构建芦苇LAI的高光谱估算模型。结果表明,采用CARS算法筛选不同变换光谱的特征波段构建模型,发现经过FD变换(R^(2)=0.417,RMSE=0.905)的模型效果最优。在CARS基础上使用筛选过后的特征波段构建植被指数进行建模比较,模型效果最好的是XGBoost(R^(2)=0.620,RMSE=0.826)。