Study On Influencing Factors Of Current Distributions In 500kV Substations

One and a half main wiring connection is widely used in 500kV substations, which has large current safety margin for each device in strings. Therefore, currents in switches and buses are allowed to exceed ratings under certain operation circumstances for short time. Significance of increasing capacity of 500kV substations in East China Power Grid is taking advantages of current safety margin of one and a half main wiring connection, using devices which have lower current carrying capacity to push a higher current, which brings large economic and social benefits.Works have been done in this thesis:1. PSCAD simulation has been done under equal contact resistance circumstances. For simplicity, current distributions in 500kV substations are initially analyzed without considerations of influencing factors of currents, pressures, temperatures, numbers of breakers’ operations and different types of breakers. Preliminary law of current distributions in 500kV substations under equal contact resistance circumstances is analyzed and basic requirements of operations in 500kV substations are put forward.2. Actual measurements of current distributions in 500kV substations have been done. Actual measurements are carried out in Shandong Zibo Substation and Shanghai Huangdu Substation. Actual measurements are carried out under the same circumstances as simulation. Comparisons between results of actual measurements and simulation are made in order to judge the accuracy of simulation model.3. Experimental platform of influencing factors of contact resistance of breakers is made and relevant experiments are carried out. Influencing factors of contact resistance of breakers include currents, pressures, temperatures, numbers of breakers’ operations and different types of breakers. Experiments are carried out with only one variable of influencing factor. For example, experiments on influencing factor of currents are conducted with fixed amounts of pressures, temperatures, numbers of breakers’ operations and types of breakers. All influencing factors are experimented respectively. Experiment results of influencing factors of contact resistance of breakers are curve fitted via MATLAB curve fitting tool and fitting curves and fitting equations are gotten, which lay basic foundation for further research.4. PSCAD simulation has been done under varying contact resistances circumstances. Influencing factors of contact resistance of breakers include currents, pressures, temperatures, numbers of breakers’ operations and different types of breakers. Influences of contact resistance of breakers on current distributions in 500kV substations are taken under consideration. General suggestions for operations in 500kV substations are put forward.5. Coefficients of current distributions in 500kV substations are calculated. Transfer function matrix of substations is calculated in order to reveal quantitative relationship between currents in lines and those in breakers and find out influences of changes of currents in lines on currents in breakers.