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.     

Reliability Evaluation Model of Composite Generation and Transmission System Incorporating FACTS Devices

The utilization of Flexible AC Transimssion System(FACTS)technology has significant impact on power system reliability performance.Series FACTS devices such as Thyristor Controlled Phase Shifting Transformers(TCPSTs) and Thyristor Controlled Series Compensators(TCSCs) can change the natural allocation of the power flow and effectively alleviate transmission congestion.Parallel FACTS devices such as Static Var Compensators(SVCs)can provide reactive power support and maintain voltage stability.So it is important to quantitatively evaluate their benefits to the power system reliability.The traditional models of the composite generation and transmission system reliability evaluation are mainly focused on conventional generation and transmission facilities.This paper researches the power flow model of TCPST and TCSC,and then presents the optimal load shedding model incorporating TCPSTs,TCSCs and SVCs and effectively incorporates them into the reliability evaluation model.The proposed method is tested on the RBTS and the obtained results show that the system reliability can be improved effectually by FACTS devices.     

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.     

Vibration characteristics of face-gear transmission system with parametric excitation

In order to study the influences of different factors on nonlinear dynamics of face-gear transmission system, a nonlinear dynamic model is presented. This model includes backlash, general transmission error, time-varying meshing stiffness, meshing damping, bearings and external load, etc. Based on numerical analysis theory of nonlinear dynamics, the equations are solved and the bifurcation characteristics with different parameters are obtained. And the calculation results show that increasing the backlash and time-varying meshing stiffness will augment the dynamic load of system, but increasing the mesh damping will reduce the dynamic load effectively.     

AN A. C. LOAD FLOW ANALYSIS OF THE RELIABILITY EVALVATION OF COMPOSITE GENERATION AND TRANSMISSION SYSTEMS

An A. C. load flow analysis of the reliability evaluation of composite generation and transmission systems is presented on the basis of a fast outage simulation algorithm and an optimal model of active and reactive power adjustment after outage contingencies. The information of the first -level outage events is utilized for simulating higher -level outage events in the fast outage simulation algorithm ; the optimal model is satisfactory in speed and accuracy with the application of concentric relaxation and linear increment constraint on the comprehensive adjustment of active and reactive power. As an example. the IEEE Reliability Test System is tested and the results show that the method is accurate and well-matched in speed with the method studied by R. Bllinton, et al.     

Research on Calculation of the Automobile Air Conditioner's Cooling Load

In this paper a nonsteady heat flux equation for car body is established and the formulationof transmission function coeficient of the cooling load is derived. The composition of the automobile airconditioner's cooling load has been analysed and a computer program for calculating the cooling loadhas been compiled, It has proved to be exact from the example, So these results are of practical value.     

A COMPUTER METHOD FOR COMPARISON BETWEEN EHVAC AND EHVDC TRANSMISSIONS

A computer method for comprehensive comparison between EHVAC and EHVDC is presented in this paper after analyzing the fundamental characteristics and studying the design methods of these two types of transmi-sson schemes. Some formulas are developed and an appropriate mathematical model is established. A generally applicable computer program is exploited which is acceptable to IBM-pc and its compatible micro-computers. The results of numerical practical project of the program are given to prove the correctness of the model and the program described in this paper,and it also shows that the method proposed is an efficient one with the practical values in power system planning.     

AUTOMATIC CONTINGENCY SELECTION AND RANKING USING AN UNIFIED MODEL AND ALGORITHM FOR P - AND Q - SUBPROBLEM

A new approach of the automatic contingency selection and ranking with the network flow programming (NFP) is presented in this paper. NFP is adaptable to change the network topology as the transmission or generation branches arc in single or multiple outage. Thus the fast calculation of the contingency states by NFP cm provide the urgent information in real time N- 1 security analysis. In the paper, automatic contingency selection and ranking forP- and Q-type subproblem arc solved by an unified network flow model and algorithm. It is based on the existence of weak coupling between real and reactive quantities in power systems. The performance indices to assess the severity of contingencies are defined as the total real and reactive load required to be curtailed. The proposed ACS technique including the model and its algorithm are examined with IEEE 5-, 14-, 30-, 57- and 118- bus test systems on M-340. And the encouraging results are given in the paper.     

General Phasor Diagram and Power-angle Characteristic Equations of Extra High Voltage Long Distance Transmission Line

Installing compensation equipments is a good manner to improve line transmission capacity and maintain power system stability in the extra high voltage(EHV) long distance transmission line.It is of benefit to analysis and control by describing the effect of compensation equipment correctly.At present,for predigesting analysis or increasing real-time calculating speed,concentrated parameter circuit model is widely used to analyze 500 kV EHV long distance transmission line which may cause bigger error.So it is necessary to get a more reasonable model.On the basic of voltage and current distributed equations of even distributed long distance line,this paper deduces phasor diagram and power-angle character equations of uncompensated long line.Then the authors analyze the effect of compensators and define two characteristic parameters,namely,equivalent impedance x_(eq) and voltage coefficient K_V.Any compensating states of EHV long distance transmission line,example installing the compensators in the line or not or which type of compensators,is described by the general phasor diagram and power-angle characteristic equations.Furthermore,increment calculation(equations) of two characteristic parameters is presented by the compensator parameters which may make the concepts clear and predigests analysis easily.     

Bending Stress Analysis on Backlash Adjustable Worm Transmission

The full name of variable tooth thickness plane worm gear transmission is. Backlash adjustable plane worm gear with variable tooth thickness enveloping worm transmission, which is a new kind of accurate power transmission that is intervenient between traditional motion transmission and power transmission. Tooth surface equations of the variable tooth thickness plane worm gear transmission are deduced based on the theory of engagement. Basing on the result, the authors create a finite analysis model of backlash adjustable variable tooth thickness plane enveloping worm with perfect tooth shape by using I-DEAS software, and then has done finite element analysis of backlash adjustable variable tooth thickness plane enveloping worm transmission. Finally, the author drew a conclusion about distribution of principal stress and load distribution between teeth, which offer some references for strength and performance analysis of worm transmission.     

风电齿轮箱传动误差分析及振动噪声预估

针对一级行星两级平行轴风电齿轮传动系统,综合考虑齿轮时变啮合刚度、啮合阻尼、传递误差等因素,建立31个自由度的弯扭轴耦合集中参数动力学模型,采用变步长Runge-Kutta法对系统动力学微分方程进行求解,得出齿轮传动系统各级传动误差;借助软件建立风电齿轮箱刚柔耦合动力学模型,并导入传动误差,采用模态叠加法求得齿轮箱轴承支反力,并将其作为声振耦合模型的边界条件,采用声学有限元法对风电齿轮箱进行振动噪声预估,并与试验结果对比分析,两者吻合良好。     

AUTOMATIC CONTINGENCY SELECTION AND RANKING BY NETWORK PROGRAMMING APPROACH

This paper presents a new approach ,to the automatic contingency selection and ranking by the network flow programming (NFP). A complex cost optimisation model based on economy and security, and several simplified models are proposed in the paper. The performance index is the total load curtailment or its weighted value. All the solution algorithms are OKA. The model and its algorithm is tested on IEEE 30-Bus System and the encouraging results are obtained.     

A RELIABILTY CAPACITY OPTIMIZATION ALGORITHM FOR STOCHASTIC FLOW NETWORKS

A model and a heuristic algorithm for reliabilty op timi zation in generalized stochastic flow networks are proposed in this paper. The stochastic characteristic of the demands at terminal nodes is considered in the model. The algorithm proposed is powerful and can be applied to optimal planning of transmission capacity for large scale stochastic flow networks, because it can facilitate a fast location of optimal capacity expansion from the information obtained by the last iteration by making full use of the relationships of the k-weak link set and failure events set to the paramsters in generalized stochastic flow networks     

A Fault Location Algorithm for Transmission Lines in Circle Network

A fault location algorithm for transmission lines in circle network is presented.The algorithm uses local data. Its location accuracy is independent of power # flow, transient resistance and variation of remote system impedance. Simulation results are satisfactory.     

Tooth contact analysis of helical beveloid gear with parallel axis

The study object of this paper is helical beveloid gears with parallel axis. Based on the gear Mshing Principles and the tooth-surface equations of pinion and gear,the mathematical model of tooth contact is developed under standard installation and installations with center distance error,axis error and multiple error respectively. The MATLAB solver is used to obtain the contact trace and the transmission error under different installing conditions and the comparative analysis is made. The results indicate that this gear drive is sensitive to axis installation errors,it forms the edge contact and cause the periodic transmission error. It can provide the foundation for designs and analysis of this gear transmission.     

Dynamic optimization design of gear transmission system for wind turbine

The differential equation which governs the behavior of the gear transmission system of 1.5 MW wind turbine is established. The external excitation caused by wind speed fluctuation is discussed and the internal excitation due to time varying mesh stiffness and comprehensive error is also analyzed. The calculating formulations of the harmonic balance method of nonlinear dynamic equations are presented. Then, the multi objective dynamic optimization model is developed to minimize the value of vibration acceleration and the overall volume. The optimization of a practical example using mixed discrete combined programming is performed. The result shows that the proposed method of modeling and optimization design can effectively reduce the wind turbines gearbox vibration levels and weight.     

Optimal Load Curtailment in Bulk Power System Reliability Evaluation

This paper studies the question for considering optimal load curtailment in bulk power system adequacy evaluation. A minimization model of load curtailment is utilized for the contingency states which may have load curtailment. In order to calculate realistic bus indexes, two practical load curtailment philosophies are incorporated in the minimization model of load curtailment, which is achieved in computer program developed for bulk power system reliability evaluation. The minimization model of load curtailment, correlated algorithms, and flow chart of program are given in this paper. The effectiveness and availability of the model are verified from two case studies.     

Power Model of Bond Graph and Dynamic Simulation of Hoist System for Multi-Flow Transmission

The double drive hoist reducer developed in the planetary gear is a new generation of energy saving and environment protecting hoist product. The multi flow transmission system theory of hoist is analyzed. With the theory and method of bond graph,a bond graph model with coupled vibration is established for hoist multi flow transmission system for the first time. The state equation of the system is developed and dynamic simulation analysis is also carried out. The internal changing law and relationship of the system for the state variable are got. Therefore, the dynamic properties and gearing features of this system are revealed comprehensively. The research results can provide the dynamic analysis method and design basis for multi flow transmission system of hoist.     

Transmission Congestion Management Based on Power Influence Coefficient

Basing eliminating on the idea that the generator who has the most influence on the power flow of line is mostly in favor of transmission congestion, the model of congestion management with the object of minimizing adjustments of bufions varied with generation outputs is proposed. It can eliminate the congestion effectively by judging the generators who should be adjusted and the amounts of adjustment. The test on IEEE-RTS24 buses system and other practical systems show that the proposed method is effective.     

Gear-bearing coupling dynamics characteristics of wind turbine planetary gear transmission system under variable load

Considering that the transmission system of wind turbine works in complex and changing load environment caused by stochastic wind speed,this paper uses sparse least squares support vector machine(SL-SVM) to simulate wind speed of true wind field,and obtains time-varying wind load caused by stochastic wind speed. The lumped-parameter method is used to develop a dynamic model of planetary gear transmission system of wind turbine coupled with bearing. The model includes the varying wind load,time-vary mesh stiffness of gear pair and time-vary stiffness of rolling element bearing. The numerical method is used to simulate the dynamic performance of planetary gear system of Multibrid Technology Wind Turbine with 1.5 MW rated power. The vibration displacement responses of the transmission system are obtained as well as dynamic meshing force each pair of gear and nonlinear bearing forces. The research can provide a foundation for optimizing dynamic performance and reliable design of gear transmission system of wind generator.