共查询到20条相似文献，搜索用时 15 毫秒
1.
The winding hot-spot temperature is one of the most critical parameters that determines the power transformer overloading capability and the aging rate of the oil-paper insulation. Based on the traditional thermal theory, the paper proposes a simulation model to predict transformer winding hot spot temperature taking into account oil viscosity changes with temperature, and combined with the thermal-electric analogy method and hot spot temperature rise model recommended by IEEE. The Runge-Kutta method is used to calculate top-oil temperature and winding hot-spot temperature of the transformer, and then compare them with the measured data obtained from the 100 kVA/5 kV (ONAN) experimental transformer. The simulation results are in good agreement with experimental data. 相似文献
2.
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. 相似文献
3.
Unapt winding parameters may cause yarn overlapping with the problems of low yarn density, winding vibration, breaking and disorder when unwinding yarn and others. The yarn arrangement rules and its relationship with the winding ratio are analyzed using geometrical and mathematical methods. It is revealed that winding ratio is an important parameter to prevent yarn overlapping. When the winding ratio is proper, the yarn can be staggered regularly and yarn overlapping can be prevented effectively. A new method for the determination of the proper winding ratio is introduced. The alteration of yarn angle and interval and their effect for the determination of the winding ratio are discussed. The particular process of the method is given and an example is presented. 相似文献
4.
Zhu Jizhong Xu Guoyu 《保鲜与加工》1989,(6):40-47
This paper reports on application of network flow programming to the real power economic redispatch with security constraints. For the contingency state which violates the line security constraints , the re-dispatching is performed by eliminating the curtailment of real loads. The network flow model is incremental, and is solved by OKA. Therefore, it is very simple, fast and accurate. The model and its solution algorithm are tested on JEEE 30 bus system and the encouraging results are obtained. 相似文献
5.
To counteract capacitive current and resume power system, the neutral point of 35 kV power system at the mountainous area is grounding through the arc winding widely. In fact, there is great difficult in selecting the arc winding to satisfy the requirement of system. In a 35 kV power system which neutral point is grounding through the arc winding, the capacitance current are measured in site when a single-phase is grounding. From the measure data, the imbalance of three-phase voltage whether the arc winding exist or not and the operating situation of arc winding are discussed, and bring forward an attentive problem about operation of arc winding and decrease of lightning outage rates. 相似文献
6.
在油气钻井工程中,由岩石蠕变引起的井眼缩径或井壁坍塌时有发生,本文基于能量守恒定律分析岩石蠕变的3个阶段,阐述传统的蠕变模型难以研究岩石加速蠕变阶段的原因。为此,在西原模型的基础上串联了一个绕组元件,建立改进西原模型及相应的本构方程。根据油气开发过程中所钻遇地层部分岩心的蠕变实验数据,对建立的改进西原模型进行验证,表明该模型能够很好地反映出岩石的蠕变特性,尤其是在岩石所受荷载大于长期强度的情况下,对凸显岩石加速蠕变阶段效果明显。该改进西原模型的提出可为进一步揭示岩石蠕变的客观规律提供理论依据。 相似文献
7.
Based on the real size and constrain of the wet clutch, the friction pair of temperature, stress fields coupling model, and the heat convection coefficient model are established. The transient thermal-structural coupling and the thermoelastic instability of the phenomenon of friction discs generated in overload tests are numerically simulated and analyzed with ANSYS/LS-DYNA. Additionally, the distribution of the hot spots in the circle direction and surface of the friction discs are revealed, the distribution of the stress and strain caused by the thermoelastic instability is analyzed and tested. The results show that hot spots and contact pressure are mutual promotion. The thermal expansion and stress concentration caused by temperature gradient lead to steel disc warp. The heat fading caused by the thermoelastic instability leads to steel disc failure. 相似文献
8.
The forecasting of water quality variation is very important in the process of sewage treatment, which helps the control system work reliably and steadily. In this paper, the compensative fuzzy neural network (CFNN) based on compensative fuzzy logic and neural network and its study arithmetic are introduced. Considering its features as fast speed, steady studying course, global dynamic optimization, CFNN is applied to establish water quality forecasting model. The practical example indicates that the model is not sensitive to initial parameters and has better forecasting precision and faster convergence. 相似文献
9.
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. 相似文献
10.
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. 相似文献
11.
According to different construction ways and materials, three kinds of roof, that is ,passive evaporated roof with freedom water surface , water stored roof by means of pore material and hygroscopic roof,are introduced in this paper . Meanwhile the theory of heat insulation and energy efficiency on passive evaporation roofs and suitable weather and places to be used are also discussed .The results show that all kinds of passive evaporated roofs have high efficiency in heat insulation because of water's high specific heat and large quantity of absorbed latent heat,and that they can be adopted according to the practical local weather ,natural resource and economical development. 相似文献
12.
The surface of EPS is of hydrophobic nature, which can not wet binding material. As in the freshly mixed mortar, EPS particle is not affined with cement paste and has a low bulk density, which will be apt to make EPS particle buoy, and lead to the segregation of mortar, the decrease of water retentivity and affect its workability. When pretreated, the surface of EPS can be changed into that of hydrophilic nature, and be wetted by freshly mixed silicate paste. The technology channel of EPS surface modification is that select proper high-molecular binder and coupling agent, prepare polymer silicate binding material of low water-cement ratio, and utilize the double effect of binder and coupling agent to form silicate grout of hydrophilic nature on the surface of EPS, by composite binding material wrapping the surface of EPS. A new thermal insulating mortar with good properties of thermal engineering, weather-resisting and crack-resisting can be made by modified EPS as light aggregate and cement as binder, modification with fiber and polymer. This new type of insulating mortar can be used as outer thermal insulation of outside wall, which breaks the limitation of traditional insulating mortar only as interior insulation. It has been widely used in the building energy-saving model project. 相似文献
13.
随着智能化GIS设备的发展,GIS设备上集成了大量电子设备。GIS设备开关操作产生的特快速瞬态电磁过程主要经由“传感器—二次电缆—智能组件”这段电路对电子设备产生电磁影响。笔者首先基于传输线网络理论建立了开关操作产生的地电位升对“传感器—二次电缆—智能组件”回路的耦合计算模型,然后通过验证实验证明了计算模型的有效性和准确性,最后对不同屏蔽层接地方式下的各传感器端口和智能组件各端口及端口间的骚扰电压进行了仿真研究。计算结果显示,各骚扰电压受接地方式的影响较大;通过选择合适的接地方式,可以有效地抑制开关操作电磁骚扰。 相似文献
14.
For azimuthal anisotropy seismic exploration, it is very important to separate the fast and slow shear waves splitting in this type of anisotropic media. Many researchers have worked on this problem, but their methods are not realistic in exploration. In this paper, a new method of separating the shear waves splitting in EDA media is presented, that can be directly applied to actual use. Through numerical examples, it can be found that the method is highly efficient and accurate. 相似文献
15.
Many residential buildings use externally insulated wall structures in Chongqing, P.R. China. The process of determining the economic insulation thickness was based on degree days and present worth factor when wall structure adopted different insulation materials. The optimal economic insulation thickness was related to the region of the building, air conditioning operating time, and price of insulation material. Insulation materials with better thermal performance have a shorter payback time and wider prospects for application. 相似文献
16.
持续低温及低温连阴天气下几种典型日光温室保温性能评价 总被引：8，自引：2，他引：6
为准确评价天津地区新建的几种典型日光温室在冬季持续低温及低温连阴天2种灾害性天气条件下的保温性能,笔者在冬季对土墙、二代砖墙、高标准砖墙3种结构类型日光温室内夜间的平均温度、最高温度、最低温度、温度低于10℃的持续时间、夜间最低温度偏离度等指标进行观测与统计分析。结果表明,土墙日光温室在2种灾害性天气条件下保温性能均最佳,高标准砖墙温室在连阴天条件下,保温性能差于土墙,但与二代砖墙温室保温性相差不大,而在低温条件下,高标准砖墙温室保温性明显好于二代砖墙温室,二代砖墙温室保温性能最差,并获得了定量化的指标。该结果对防御日光温室冬季低温灾害影响有较好的指导意义。 相似文献
17.
Fiber measurement technology has many advantages, such as no electromagnetic interference, good insulation and small volume. A kind of fiber current sensor is giver, which bases material mechanics and electromagnetic induction, and also makes a cantilever beam and F-P together for measurement. Phase demodulation way is adopted in this paper. The sensor principle and measurement principle of F-P are analyzed. This paper builds up the mathematical model of the F-P gap and gave a current measurement equation. At last some experiments are done to validate it. Advantages of this sensor are small volume, high sensitivity and comoact structure. 相似文献
18.
Analytical and Experimental Study on Performances of MR Fluid Dampers Employing Plates Channel Model
The numerical model,which combines the two-dimensional river model and ship maneuvering mathematical model,is built.The influence of Nanjing Fourth Bridge to be built across the Changjiang River on river's condition is studied.The change of river conditions around the Bridge pier is analyzed and the tracks of ship transit along the reach of the Changjiang River are simulated for the cases of before and after building the Nanjing Fourth Bridge.The parameters of navigation in sail course have been obtained.The result shows that the influence on rivers condition of the Nanjing Fourth Bridge on Changjiang River is very small,and its influence on navigation is not significant. 相似文献
19.
20.
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. 相似文献