Weak Current And Strong Magnetic Model Establishing And Distance Protection Setting Optimization Of EHV Transmission Lines

With the national economy development,electrical energy demand shows a quickl -y increasing trend,which swift improves the constructing of power grid.We should speed up the constructing of power grid and utilize the land validly,reduce the invest -ment of power constructing at the same time,the compact extent of line corridor is also deepening,the double lines which are erected in the same towers and the same corridors are getting more and more.The double lines and the multi-lines will be the important component of power grip.So the value of zero-sequence mutual induction will inevitably be more greater in the double lines and the multi-lines,the influence of zero-sequence mutual induction to relaying protection will be increasingly austere,ma -lfunction and miss operation will happen under many circumstances,which is gone by the name of"weak current and strong magnetic phenomenon" in the EHV power grid parallel double lines."Weak current and strong magnetic phenomenon"in the EHV power grid parallel double lines will easily induce that zero sequence protection malfunction.So the main part in the relaying protection and fault analysis will be the influence of weak current and strong magnetic phenomenon to pilot zero sequence protection and other protectio -ns.So in the one hand we should put more energy to study the influence of weak curre -nt and strong magnetic phenomenon to relaying protection,in the other hand,we shoul -d take much comprehensive consideration for the influence of weak current and stron -g magnetic phenomenon to setting computation of double lines and multi-lines in whi -ch strong mutual exists.What is more,Take much consideration to the modification and optimization of setting computation,which is also the emphases of research.In introduction of this dissertation,background,intention and significance of this problem are introducted.And then engineering application characteristic of EHV doub -le lines erected in the same towers and distance relaying characteristic are also concl -uded particularly.Finally,the content of this dissertation is including as follow:â‘ stu -dy on 220kV EHV double lines erected in the same towers;â‘¡study on 500kV EHV double lines erected in the same towers;â‘¢make a optimization principle and method of distance relaying setting computation,which can be applicated in setting computati -on of QingYuan PaJiang Grid.Chapter Two has introducted relaying protection schem -e and setting computation in parallel double lines of EHV power grid.Firstly,some distinctions between parallel double lines fault and single line fault are analysed concl -uded.And then study on relaying protection and reclosing are summarized,it also gives a prospect of the latest research trend of relaying protection in parallel double li -nes of EHV power grid—adaptive relaying protection and artificial nerve network application.Finally,with two parts of study on software and algorithm and problems and solutions,the study on relaying protection setting computation is comparatively roundly expounded,which establish a great base for study on the latter chapters.Chapter Three takes what pilot zero-sequence protection malfunction in "FushanZhongshan" line of GuangDong Power Grid which happened in Jan 19^th2006 as exam -ple,and gives a brief introduction of the principle of weak current and strong magnet -ic phenomenon.And then Chapter Three compares proper phasors of regional fault inside and regional fault outside with proper phasors which exist in weak current and strong magnetic phenomenon,it gives a result that the phases of 3I₀ and 3U₀ in both sides of non-fault line are both opposite.Chapter Three also introduces theoretical ana -lysis and computation of protection malfunction which is brought in by weak current and strong magnetic phenomenon deeply,which gives a result that current relation wea -ker,magnetic relation stronger,protection malfunction happens more possibly.In the last,Chapter Three establishs a model of weak current and strong magnetic phenomen -on in parallel double lines of 220kV power grid in PSASP,which indicates that the conclusion introduced above is right.Chapter Four calculates one phase equivalent zero-sequence impedance,one phase equivalent zero-sequence capacitance,one phase equivalent zero-sequence susceptanc -e of single line considering double overhead ground wires influencing factor and considering the other line influencing factor base on 500kV parallel double lines and double overhead ground wires model considering cyclic transposition factor,and Chap -ter Four also calculates mutual resistance,mutual inductance and mutual capacitance and one phase equivalent positive-sequence parameter of 500kV parallel double lines. Chapter Four takes all datas calculated above as distributed transmission lines compo -nent parameter of 500kV parallel double lines weak current and strong magnetic phenomenon simulation model considering double overhead ground wires influencing factor.Through analysis of simulation waveform,it can give a result that whether keep zero-sequence voltage both sides of non-fault line cophase in fault moment to the mo -ment which weak current and strong magnetic phenomenon brings zero-sequence vol -rage both sides of non-fault line opposite phase then protection malfunction is a key to make weak current and strong magnetic phenomenon lockout myself and make prot -ection judge it right as regional fault outside.In the last,Chapter Four proposes that it can adopt "memory component" to realize this process above,and Chapter Four also proposes some useful and perfect lockout measures.Chapter Five has introduced the the imagination and feasibility analysis of distanc -e protection setting optimization,and some correlation setting optimization principle, which are applicated in distance protection setting computation of several important lines of QingYuan PaJiang Area power grid.And then chapter five makes some theoret -ical analysis of two ground-fault distance protection setting method(based on assista -nce(branch)coefficient and based on detecting impedance),and studys the computati -on of zero-sequence current compensation coefficient under the influence of zero-seq -uence mutual inductance in double lines erected in the same towers.In the last,the typical single line and double lines(PaJiang Jia line,PaJiang Yi line)of PaJiang Area power grid are selected as the computation example,zero-sequence current cpmpesatio -n coefficient K is calculated,in a word,and it proves that the setting method based on detecting impedance has some advantages as high sensitivity and what could not be influenced by operation mode etc,which has some theoretical signficance and practica -1 value to enhance efficiency of distance protection setting coumputation in 110kV,220kV district power grid.Finally,this dissertation makes a detail conclusion of all research works and intro -duces the next problems which should be made more perfect and made intensively. And they give some thoughts for the next researchworks.