| This topic focuses on the use of transmission line wave transmission equations to solve two major problems encountered with current sampling value differential protection in high voltage long distance transmission,one of which is distributed capacitive current and the other is current transformer saturation.Along with the development of high-voltage long-distance transmission,compared with the action time fixed phase differential protection,sampling value differential has the characteristics of fast action,less calculation,strong resistance to TA saturation,etc.,is more adaptable to the development of the power grid protection principle for ultra-high voltage and ultra-high voltage long-distance transmission lines,its distribution parameters characteristics are obvious,the distribution capacitance current is not negligible,resulting in normal operation of the line on both sides of a large differential current,which seriously limits the application of sampling value differential protection on high-voltage long-distance transmission lines.The differential current criterion based on the wave transmission equation takes into account the distribution characteristics of the line and naturally includes the distributed capacitance current and transmission time delay,which fundamentally solves the problem of distributed capacitance current on the line.MATLAB simulation results show that this method has better compensation effect than the traditional method of compensation with given distributed capacitance parameters.Current transformer saturation has been one of the main problems in current differential protection,and this thesis investigates the saturation of current transformers in ultra-high voltage networks.The characteristics of current transformer saturation and the impact of current transformer saturation on current differential protection are analyzed.Based on the time difference method,the auxiliary criterion based on wave transmission equation and fault ranging principle is introduced to improve the anti-TA saturation capability of the protection,so that the protection can meet the requirements of rapid fault determination in the TA linear transmission zone and no false operation of TA saturation outside the zone. |
