An improved dynamic model of transformer hotspot temperature based on top oil temperature

The winding hot spot temperature of the oil immersed power transformer is an important parameter. It has a great influence on the transformer insulation aging and a close relationship with the transformer top oil temperature. The changes of non linear thermal resistance, open circuit impedance, and oil viscosity and winding losses with temperature are also taken into account. An improved model added on the transformer top oil temperature to calculate transformer winding hot spot temperature by using the viscosity and loss correction factors is proposed. Model parameters are estimated by Levenberg Marquardt method. In the end, by comparing with the measured data tested under different conditions, the model shows good consistency under underload (90%), rated load (100%) and overload (110%) conditions respectively, and describes the temperature variation more accurately in the dynamic loading profiles.     

Simulation Propagation of Partial Discharge UHF Signals in Transformer

Many factors affect the propagation of ultra high frequency(UHF) signals caused by partial discharge(PD) on the waveforms and energy of signals in transformer.To investigate the relationshi Pof factors and UHF signals,simulation model of transformer for PD study are established.UHF signals in simulation model of transformer caused by PD are calculated using finite difference time domain method.By means of amplitude and cumulative energy plot of simulation signals,and combing the measured result,the following factors:distance between PD source and detection position,different metallic conductor position around detection position and iron core and winding are researched,which contribute to comprehend the propagation characteristic of UHF signals and detect UHF signals accurately.     

AN ON-LINE ALGORITHM FOR PREDICTING THE TEMPERATURE OF POWER TRANSFORMER WINDINGS

The paper presents an on-line algorithm for predicting the average temperature of power transformer winding according to its load current. The algorithm has accounted for the whole history of load current and variations of ambient temperature. The overload capabilities of transformer can be increased by monitoring and controlling the winding temperature and the necessary durability of the transformer can be ensured. The algorithm can also forecast the future winding temperature and the time of reaching the max, permitted the assumed future load current and oil temperature.     

The Influence of Air Inlet on Ventilation Effect in Indoor SubstationTransformer Rooms

Ventilation design is the difficulty of transformer room design. Temperature field and velocity field in a transformer room was simulated by CFD method . By comparing simulation value with the experimental value in related document , the effectiveness of the mathematical model was verified. Based on it, an indoor substation transformer built was taken as the simulation object, then designed and simulated six kinds of ventilation condition by changing the location and area of air inlet, focused on the influence of air inlet on the ventilation effect by comparing the temperature field ,velocity field and temperature characteristic value in different condition. The simulation results show that when air inlet area is fixed, the air inlet should be arranged in the radiator side and its center height should be controlled in the radiator center height or slightly offset position, it should not be higher than the radiator. When the air inlet location is fixed, air inlet area should be increased along the high direction to improve ventilation effect. The conclusions can provide technical support for the ventilation design of transformer room.     

Hybrid Lumped Parameter Transformer Winding Model for Very Fast Tansient

The very fast Transient over-voltage generated due to the switchgear in GIS switching off or on is very harmful to transformer insulation. The model presented is a winding hybrid lumped parameter model which combines the branch model based on parallel cables in one turn with grouped-turns model of two discs to efficiently simulate the very fast transient in the coil. Under quasi-stationary electromagnetic field, network topology and element size are derived from the geometry and properties of the transformer, whose inductance and capacitance are assumed to be passive and to have linear characteristics, however which have an inherent feature of a medium, which propagates waves. The formula of parameters are obtained. Based on the built winding model, the voltage gradients between discs and turns are found out, according to the simulation results, the reasonable winding insulation design can be made.     

Three Phase Harmonic Power Flow Using PhaseComponent for Asymmetric Network

With the increasement of the harmonic quantity in power system ,single phase harmonic power flow calculation can't meet the needs. This paper discusses the components model in detail under harmonic condition in three phase distribution power system, include generator,transformer,line and load. Particularly, the transformer model considers the winding connection, the phase shifting among primary and secondary windings, and the off-normal tapping.The three-phase model of transformer, used in traditional harmonic power flow, may the preuent the model from converging, so the paper proposes a three phase back forward sweep harmonic load flow algorithm based on phase-components. At last, a test example was used to prove the algorithm. The results indicate that the proposed method is efficient.     

Study on the Recognition of Transformer Winding Deformation Using Wavelet Transform

This paper illustrates the methods of extracting characteristic parameters and deformation recognition using wavelet transfor,which applied in low voltage impulse(LVI) method on the transformer winding deformation detection.The results show that it is effective to eliminate the noise using wavelet transform,meanwhile,it can also make measurement has repetitivity and has a property on model recognition on defomation.     

Operational Parameters of Hybrid Radiant Cooling Floor and Displacement Ventilation Air Conditioning System

The simulation model of hybrid radiant cooling floor and displacement ventilation air conditioning system was built and analyzed by software EnergyPlus. By comparing the simulation results and experimental data, it is shown that the simulated indoor air temperature and cooling capacity provided by radiant floor was ±7% deviated from the experimental data. Based on the model, with the change of supply air parameters or supply water parameters, the cooling capacity provided by radiant floor and displacement ventilation, surface temperature of radiant floor, indoor air average temperature, AUST temperature were obtained. Combined with the indoor thermal comfort model, when indoor thermal comfort index PMV varied between -0.5 and 0.5, the recommended supply air and supply water parameters were obtained to provide reference for engineering design and application.     

Cold Simulated Experiment of Mixed Condition in Boiler Using Gas Reburning for NOx Reduction

The principle of NO x reduction using gas reburning in boiler is analyzed. The experimental device is set up according to the principle of cold simulation. Replacing natural gas with hot air, the cold simulated experiment of mixed condition in boiler has been done. The method reflecting the mixed condition in boiler by means of surveying the uniformity of temperature is put forward on the basis of the similarity of momentum, heat and mass transfer processes. In the meantime, the temperature of different sections in furnace is measured and mean square difference of temperature field is calculated. The effect of flow rate and position of nozzle on the mixed condition in boiler is investigated.     

基于PID算法对热风炉热风温度控制及仿真分析

在农作物金银花干燥期间,为了满足干燥热风的温度和风速的稳定性要求,针对热风炉出风口热风温度与设定的温度值滞后和稳定性差等问题,设计了一套以单片机STM32作为核心处理器和模糊自适PID算法作为参数控制器的控制系统,实现模糊自适PID算法对参数进行调整。利用Matlab语言建立模型,对整套控制系统进行仿真分析。结果表明:出风口热风温度的稳定性能达到95%以上,该研究方法提高控制系统的性能,有利于农作物干燥的质量和效率。     

THE ERRECT OF HIGH HARMONICS ON THE SELECTION OF THE SIZE OF TRANSFORMER CONDUCTOR

This paper analyses the additional stray losses of transformer winding caused by harmonics,and suggests that the influence of harmonics should be taken into consideration in the selection of the conductor' s size in rectifier transformer and converter transformer design.     

Electromagnetic field models and their influences onthe temperature field of large hydro generator

To accurately analyze the loss and heat of large hydro generator,the finite element models of 2D steady state electromagnetic field,moving electromagnetic field and field circuit coupling are established respectively.As an example,the losses of the rotor iron and damper winding of a 36 MW tubular hydro generator are calculated.Furthermore,the influences of 3 different electromagnetic field models on the thermal sources and temperatures are analyzed by 3D finite element calculation of the temperature field.The results are compared with the test data and indicate that the precision of the field circuit coupling model is better.The losses of each damp bar are different and the heat of the damp bar at the lee side is larger than that at the windward with the full load.The maximal temperature of the rotor is located at the damper winding,instead of the field winding.The research is valuable for improving the calculation precision of the rotor losses and temperature field and enhancing the reliability of the hydro generator design and operation.     

Flow Stress Behavior of 3104 Aluminum Alloy

According to different deformation conditions required in working process for manufacturing of 3104 aluminum alloy, the authors design the simulation experiments of hot rolling process at different deformation temperature and strain rates, analyze the relationships of deformation resistance, flow stress and strain rate, deformation temperature when alloy deformation. Based on experimental data analysis, it was concluded that the dominant factors affecting flow stress were the strain rate and deformation temperature, and the two parameters were also important for deforming process control.     

The Experimental Study of Drying Process of Wet Silkworm Chrysalises

The drying process of wet silkworm chrysalises, which are the subproducts of the silk production industry, is experimentally studied. The mode of forced convection drying with hot air permeating vertically is adopted. The influence of temperature and velocity of the hot air as well as the thickness of the chrysalises layer in the drying process is analyzed on the basis of the experimental results. An experimental relation of exponental model for wet silkworm chrysalises drying process is obtained.     

基于WRF的城市热岛效应高分辨率评估方法

为解决城市总规尺度气候评估工具缺乏的问题,分析了不同气候评估方法的特点和应用范围,研究了气象学工具WRF在城市热岛效应评估中的应用方法及有效性。建立了针对城市总规尺度的高精度城市规划信息数据库、气象数据库生成WRF模拟边界的方法;明确了高精度城市热岛效应模拟所需的WRF物理方案。以沿海城市大连夏季典型晴朗高温天气为例,利用WRF模型进行了300 m的高分辨率模拟。结果表明,WRF可以较好地模拟出城市热岛效应的强度和时空变化;将模拟结果与气象站和现场观测值进行了对比,两者变化趋势一致,偏差在可接受的范围之内。     

基于U-Net的玉米叶部病斑分割算法

本文旨在提出一种基于U-Net算法模型的玉米病程分级方法,实现对玉米常见4类叶部病害程度的快速、准确、客观分级.该方法以两组U-Net模型并行运算实现对玉米叶部病斑图像的语义分割任务.经测试图像分割试验中病斑分割MIoU值达到93.63％,叶片分割MIoU值达到96.33％,且运算速度均在1秒内完成.试验结果表明,该研...     

Application of Mathematical Experimentation with Computer in Hydraulic Control

Computer mathematical experimentation technology is applied in pressure hydraulic .The non-linear mathematical model of stage mechanical control system is established by the application of computer mathematical software Maple. The computational results agree with experimental data, and precision is satisfied. The mathematical model is the first apply in the control system of stage mechanical elevator. The method has a wide application in computer auxiliary and simulation of mechanical control system.     

Influential factors analysis on photoacoustic signal of photoacoustic spectroscopy monitoring trace gases

Photoacoustic spectroscopy (PAS) is a highly sensitive gas analyzing method without the shortcoming of gas consumption, which can be used in transformer oil trace gases dissolved in on line monitoring. The photoacoustic signal is detected with a microphone, which is the only feature in gas concentration analysis. A portable and tunable experimental setup has been developed based on the photoacoustic spectroscopy fundamental. Through the photoacoustic signal stimulate mechanism analysis, this paper thoroughly discusses the influences of gas pressure, temperature, laser power, gas concentration, background gas, chopped frequency and the resonant frequency drift on the gas photoacoustic signal. The theoretical and experimental results supply reference and technical support for further improvements in oil gas photoacoustic spectroscopy of on-line monitoring system.     

A Three-Dimensional Numerical Model and Experimental Research for U-Tube Ground Heat Exchanger in Heating Operation

In terms of the theory of a transient energy balance on the finite controlled volume, in this paper, a transient three-dimensional heat transfer model for the simulation of a single vertical U-tube ground heat exchanger based on finite-difference methods is systematically proposed. The model is also compared with experimental results during the heating operation in winter. What's more,based on test data and domestic and foreign literature, the equations to determine the undisturbed ground temperature for wet and heavy soil in Chongqing are presented. These formulae are essential conditions to calculate the heat transfer model.     

Error Analysis for In-situ Measurement of Heat-transfer Coefficient of Building Envelope

The in-situ measurement of heat-transfer coefficient of external wall is the major content of building energy efficient measurement. A new test method and error assessment function were put forward. Computer simulation was conducted to analysis the influence of hot-box size, air temperature in hot box, structure and thickness of external wall on the result error to provide the theoretical guidance for test apparatus development. The results show that, size of hot-box and thickness of external wall is the major factors which decide the error in test. In-situ measurements were conducted according to the computer simulation results and show fine accuracy.