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.     

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.     

Simulation analysis of the thermal-electric analogy calculation model of transformer winding hot-spot temperature

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.     

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.     

A novel control method for controllable reactor of transformer type

Conventional control methods for controllable reactor of transformer type generally depend on the parameters of transformer and cannot control capacitor voltage effectively. A novel control method for controllable reactor of transformer type is proposed. Based on a novel algorithm for fundamental extraction, the proposed approach can control the reactance accurately in real time mode by monitoring the condition of primary voltage and current. It also can control the capacitor voltage effectively and keep the capacitor voltage stable by introducing the feedback of capacitor voltage to control the phase of secondary current. Simulation has been carried out to proof the effectiveness of the method.     

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.     

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.     

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.     

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.     

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.     

Research of the winding ratio to prevent yarn overlapping

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.     

Partial Discharge in Oil-paper Insulation of Transformer

Based on the analysis of defect in oil-paper insulation of transformer, 5 corresponding PD models were made to simulate the actual defects existed in transformers. Aging experiment was carried out at different temperature and test voltage. The developing process of different types of PD was studied and the influence of temperature and voltage on PD in oil-paper insulation, were analyzed. Gray images show differences for different typrs of PD or one type of PD at different precedures. Gray images can be used to recognize PD patterns and discharge stage. The research resalts coutribute for further research on PD pattern recognition and insulation aging of transformer.     

变流量冷冻水系统温差控制法的适用性

研究了末端设置通断控制阀的一次泵变流量系统在温差控制下的水力特性,并结合风机盘管与房间的非线性换热耦合特性,进一步探讨了温差控制的适用条件以及变温差控制温差值的设定方法。结果表明：末端设置通断控制阀的系统,当管网整体负荷分布均匀且各开启用户的负荷变化规律相近时,温差控制同样是较为适用的,此时系统的水力失调对室内温湿度的影响较小;采用变温差控制时,仅以不同的总负荷率分段设置温差值,并不能获得良好的室内温湿度控制效果,建议以优先保证风盘除湿能力和室内干球温度为原则设定温差值,相比于目前的方法,在同等的室内相对湿度波动下,室内温度的稳定性可以得到保证。     

Content-aware Load Balancing Strategy in Web Cluster System

The capacity problem of web server can be solved by web cluster technology. The key point is load balancing strategy and algorithm. Traditional slrategies are effective to some kinds of web sites, but not suitable for all. The paper analyses the load characters of different kind of web sites. A content-aware web cluster load balancing strategy and algorithm is proposed. The efficiency will be evaluated through emulation experiments.     

An Attentive Problem of 35 kV Power Lines in Mountain Area on Protecting Against

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.     

The Application of Fuzzy Theory to Power Load Forecasting

A new method was presented for power load forecasting.Based on the fuzzyclustering technique,the historical samples of power load and its relative environmental factors wereclassified into several typical categories,the fuzzy numbers and sets were then used to describe thepatterns of load variation and the features of the environmental factors for every class. Finally,byunderstanding the state of future environmental factors, the future power load can be predictedthrough determining the category of load variation pottern. The validity of the proposed method wasverified with a practical medium-term load forecasting.     

Optimum Design of Individual Foundation and Its Application

On the basis of analysing the defaults occuring in normal design,a new method of optimum design for individual foundation is put forward in this paper.This method can solve some problems successfully such as the strengh and deformation can be considered at the same time,which cannot be done in the current specification.The optimal mathematical models of individual foundation design and the bottom surface dimension design under eccentric load are derived.The optimal solution is decided by method of optimization and the method selected is penalty function and complex method, and the programs of optimum algorithm have been compiled and design and drawing of individual foundation have been completed. The final result suggests that a fair-sized economic efficiency can be obtained by using optimum method for foundation design.     

Recognizing the reliability non-coherence components ofdistribution substation typical configuration

Reliability non-coherence components (RNC) may exist in a power system due to the effects of distribution substation connection modes, components reliability performance, load level, and other factors. Recognizing RNCs and removing them from a power system can improve system reliability. The reliability non-coherence phenomenon is analyzed and the reliability non-coherence probability, frequency and energy indices, which can describe the degree of the system reliability non-coherence feature, are proposed. Based on the reliability evaluation theory of substation configuration, recognizing technique of RNCs of distribution substation is proposed. The theoretical analysis and example show that the breaker connects high voltage buses may be the RNC when the rated capacity of one transformer can meet the load requirement, and the reliability parameters of breakers have some effects on the reliability non-coherence features of the typical substation configuration.     

Parameter Modifiability Based Transformer Substation State Estimation

The accuracy of transformer substation state estimation is widely low,and one reason of that is inaccurate(parameter) of model.Recently,most of papers about state estimation(SE) focus on improving algorithm.Based on classic SE and parameter estimation(PE),this paper takes advantage of the methods that putting parameters into state vector and putting parameters both into state vector and measurement vector in discussing the influence of parameter on transformer substation SE via simulation.The result of simulation shows: First,the error of parameters will be too high if only putting them into state vector,although the result of SE will be much better.Second,putting parameters both into state vector and measurement vector and giving them appropriate coefficient will lead a better result that can be used by engineering.     

A Fuzzy Regression Method for Long-Term and Medium-Term Load Forecasting

In view of the observation data fuzziness and load pattern fuzziness,a new fuzzy regression prediction method was presented for long-term and medium-term load forecasting. With the established fuzzy regression model, the future load value can be forecasted based on the fuzzy historical observation data. The validity of the proposed method was verified with the numerical example of a practical system.