Comparison of DC Pollution Flashover Performance of Various Types of Long String Insulators

With the development of EHV/UHV DC transmission projects, it is inevitable to study DC pollution flashover performance of long insulator strings. The DC artificial pollution tests of five types of porcelain and glass insulators have been carried out in the artificial climate chamber. The paper analyzes the relationship between 50% flashover voltage U50 and string length, the relationship between U50 and salt deposit density, flashover voltage gradients and valid creepage distances of DC polluted insulators. Based on the test results of insulator strings of 5 - 23 units, there are linear relationship between the 50% DC flashover voltages and string length. The experimental results show that the pollution flashover performances of various types of insulators are different, and that the pollution degree exponents of polluted insulators are affected ainsulator materials and shapes, whose values are 0.3 to 0.36. Under the same pollution degree, the pollution performances of glass insulators have advantage of those of porcelain insulators with the same configuration and the flashover voltage gradient along creepage distance and valid creepage distances of glass insulators are higher than those of porcelain insulators.     

Power Frequency Electric Field Caused by EHV Lines and Its Effect

Mathematical model of power frequency electric field is established based on Charge Simulation Method(CSM) to analyze power frequency electric field caused by EHV lines with overhead ground wires and its effect, which are entering the megalopolis. Calculative method on the electric field under the transmission lines is analyzed and validated. According to the criterion of environmental evaluation, the distributing characteristic of electric field is summarized, in case of various arrangement manners of lines. At last, some advice and methods of eliminating electric field under the transmission lines entering the megalopolis is proposed with regard to protecting environment.     

Channel Characteristics of Low Voltage Power Line

In order to make good use of power line carrier to communicate, it is necessary to analyze the time-variable, impedance,attenuation and noise characteristics of low voltage power line. The waves of every characteristic have been experimented. At the same time, aiming at these characteristics, some available measures are given in order to conquer the disadvantage factors. The experimental results show that some suitable carrier communication modes must be adopted to realize ideally the carrier communication on low voltage power line.     

A Numerical Method for Transmission Line Equations

Transient analysis of transmission line has recently been received more attention because operating speeds in high-speed digital electronics are increasing. Transmission line equations are hyperbolic partial differential equations, firstly this paper deduces how to change transmission line equations into quasilinear differential equations , thus the transmission line equation numerical result is gotten by computing the differential formation of quasilinear differential equations. The constraint of voltage and current is be considered and lumped equivalent circuit mode at boundary network collaborated at the same time in finding boundary conditions. Finally the paper computes transient response of transmission line with two typical boundary conditions. Numerical result shows that this approach is an effective way. It is explicit algorithm with less CPU consumption which can get time field response directly. The agree-upon effective way does be frequency field method, however it could not get time response unless the numerical inverse laplace transformation (NILT) be introduced. Thus this approach is more effective than FFT algorithm.     

A New Fault Location Method Based on Two Terminal Information of Self synchronous Rectification

In accordance with the high and extra high voltage long distance transmission line,this paper presents a fault location method based on two terminal information of self synchronous rectification.We adopt the long transmission line model,consider the effect of distribution capacity and can correct the sample phase angle difference in the real time btween two terminals.So that this method can avoid the fault location error owing to asynchronous message on the two terminals.Tested by a lot of simulations,the results are very satisfied.     

Method of Computing Sinusoidal Steady-state Solutions of Lossy Uniform Transmission Lines

There is no universal method of finding the analytic solutions to transmission lines discribed by partial differential equations,so many researchers are studying and developing transmission line theories.Computing steady-state solutions of uniform transmission lines is one part of the study.The paper introduces another method of computing sinsoidal steady-state solutions of lossy uniform transmission lines.First,the complex expressions of voltage and current with zero initial state are obtained from the complex frequency-domain model of lossy uniform tansmission lines.The network functions,which are the ratios of voltage and current's image functions to the excitation's image function,can be found from the complex expressions.Sinusoidal steady-state solutions can be obtained by using the relation between network function and system's frequency characteristic.Finally,the method is demonstrated to be effective by an example.     

Numerical Simulation of Dynamic Response of Suspension Insulator String

Finite element method is applied to analyze the windage of suspension insulator strings under dynamic wind loads. The dynamic response of a suspension insulator string of 500 kV high voltage transmission line is numerically simulated with ABAQUS software, and results demonstrate that the windage angle of suspension insulator string is larger than that calculated by the conventional design code, which might be one of the main reasons of the frequently happened windage flashover accidents.     

Disscussion in the Rural Power Network Construction in the New Rural Construction

To adapt to the continuous improvement of rural power consumption level in the new rural construction,in particular,with the continuous development of the rural economy,the actual operation of the rural power network has emerged as the high loss of electrical power which leads to a greater cost of the electricity,lower power supply reliability,the supply voltage and frequency do not satisfiy with requirements,etc.Through analysis of a typical rural power network,from the overall planning of the transmission to distribution equipments(such as lines,transformers and reactive-load compensation devices),the author proposes some specific measures such as reducing power loss and improving the voltage quality and reliability methods.Through calculation for lines power loss rate and percent of voltage pass,the results show that the methods proposed by the author are effective.The directions to the development trend of the rural power network is given.     

Formula for jump height of overheadtransmission lines after ice shedding

This paper numerically investigates the jump heights of overhead transmission lines after ice shedding by the finite element method, and simulates the dynamic responses of the transmission lines, with different structure parameters, in different ice shedding conditions. Based on the results, it obtains the quantitative relations between the jump height of conductor and the amplitude difference of the two static states of the conductors before and after ice shedding, and proposes a simplified formula for the jump height of conductors in continuous span after ice shedding for the determination of the clearance distance between the conductors at different phases in the design of high voltage transmission lines located in heavy ice zones.     

FDTD Method''s Application in the Research of Television Interference From High Voltage Transmission Line

The mechanism of television interference is discussed from High voltage transmission line. Then the computational model is established, and scattering fields are calculated with the finite-difference time-domain(FDTD) method, and the results are visualized. The scattering effects of High voltage transmission lines on horizontal polarization waves (corresponding to TM mode) are greater than on vertical polarization waves (corresponding to TE mode).     

应用STATCOM的DFIG风力发电机低电压穿越能力分析

针对DFIG（double fed induction generator）风电机组低电压穿越能力（LVRT,low voltage ride through）问题,笔者基于STATCOM研究了一种电压外环与电流内环相结合的双闭环反馈控制策略,并仿真验证了所提出方法的有效性。将STATCOM分别安装风电机组机端、并网点高压侧和低压侧,且设置不同电压跌落深度,比较其补偿效果。实验结果表明,安装在风电机组机端时补偿效果最好。在电网电压跌落时,STATCOM能快速为电网输入无功,抬高风力机的机端电压,从而提高风电场的LVRT能力,从STATCOM输出无功大小和风电场机端电压被抬升的比例两方面分析,对于不同深度的电压跌落,STATCOM补偿效果都较为显著。     

Self Excitation Simulation for Hydro-Synchronous Generators

The capacity,voltage,and length of modern electric power system are increasing ceaselessly.Synchronous generators will cause self excitation with the help of armature reaction,its stator current and voltage will increase.The self excitation conditions and the transient process are two aspects for studying self excitation.Now,self excitation conditions are mathematical formulas under certain postulate.The model of transient process of self excitation is linear.The conditions of self excitation are presented based on simulation,and the results of self excitation effected by the electromagnetic parameters of hydro generators operating extra high voltage long transmission line are simulated,based on a saturation model of hydro generators.The conclusions are very helpful for operation and design of hydro generators.     

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.     

Low Voltage Power Line Communication Based on MSK

For that the characteristics of low voltage power line channel are complicated and variable, how to use low voltage power line to realize reliable and high speed communication has always been the hottest question in power line communication field. This article introduces how to apply MSK to the low voltage power line communication. It analyses the application elements of MSK and structures the model of low voltage power line communication based on MSK. simulation result indicates that MSK modulation technology can satisfy the characteristics that the bandwidth of power line communication channel is narrow and the attenuation to the amplitude of signal is time variable and frequency selected. Also, it makes better use of the spectrum.     

Dynamic responses of ultra high voltage transmission line ice shedding

Numerical models of typical 500 kV ultra high voltage (UHV) transmission lines are set up in ABAQUS/CAE software. The dynamic response of the transmission lines with different structure parameters under various ice shedding load cases are analyzed, and th     

Control Method of Voltage-reactive Power of Substation Based on the Real Time Adjusting Voltage Calculation

The main means of the voltage-reactive power control of substation are adjusting the taps of load-tap-changing transformer or the reasonable capacity of parallel compensating capacitors according to the operation condition of substation.The "nine-area control strategy" is widely used to adjust voltage in the stated range and reduce the transmission capability of reactive power for power system at present.By analyzing the existent shortages of nine-area control mode for voltage-reactive power,an adjusting voltage calculation method is put forward,input data of which are the real time data of current,voltage and power of the substation.Then operation decision of voltage-reactive power control method of substation is made.By the simulating analysis,predigesting method of upper system is built,based on which an applied real time calculating model and calculating steps is given.     

Harmonic Analysis and Suppression of High-frequency Welding Devices

This paper analyzes the structure and line current waveform of 3-phase AC voltage regulation circuit. As an application of 3-phase AC voltage regulation circuit, a high-frequency welding device's simulation model and harmonic analysis of line current are presented. Results of simulation are compared to field measurements. The two are in a good agreement, so this simulation model is correct. Two single-tuning filters and one second-order HPF are designed according to the device's harmonic condition. Simulation results of the circuit with filters indicate decrease of the harmonics in current of power supply, and the waveform is close to sinusoidal wave, which prove correctness of the solution to harmonics pollution.     

Parameters design of powertrain system of electric vehicle with two-speed gearbox

The Brilliouin optical time domain analysis (BOTDA) is a newly developed technique adopted to measure and monitor the strain and temperature generated along optical fibers. The BOTDA has the characteristics of distributed measurement, long distance, high precision and durability, so it is suitable to structural health monitoring. Then a new optical fiber sensor embedded method based on air-blowing and vacuum grouting is introduced. It can lay the long distance distributed optical fiber into the concrete easily in short time. An experiment has been set up to study the validity of the new method, which shows that the embedded optical fiber can measure the concrete strain accurately, and it can realize the comprehensive, long-term, stable and real-time health monitoring to the civil structure.     

A NEW ON LINE AND REAL TIME METHOD FOR DETERMINING HARMONIC AND REACTIVE CURRENTS

According to the basic idea of phasar analysis and by applying a special multiplier, a new on line and real time method is derived for determining harmonic current and reactive current of an electric network. This method has a good dynamic response characteristic and solves for the first time the determining problem for the compensation system in single phase system,which is also appliable to the three-phase system.