Maloperation Risk Analyses And Novel Differential Protection Schemes Under The Scenario With Measurement Errors

Differential protection principle is considered superior with respect to selectivity,sensitivity,and speed of operation as as compared with directional comparison or stepped distance schemes.How to guarantee and enhance the correct action rate of differential protection in data synchronization error conditions and TA saturation scenarios remains to be problems in need of a solution within the field of main protection.However,existing researches on the abnormal operation behavior of the differential protection in data synchronization error conditions and TA saturation scenarios are quite rare.Especially,the mechanism of impact of disturbance under data synchronization error and TA saturation conditions on the performance of multi-terminal differential protection is unclear.Therefore,it is particularly important to thoroughly study the scenarios and mechanism of the abnormal actions of differential protection under data synchronization error and TA saturation disturbance,to seek out the pattern and characteristics of fault and disturbance,and accordingly put forward solutions to improve the correct action rate of the differential protection,which would further enhance the overall correct action rate of differential protection.Accordingly,this thesis focuses on the study of the mechanism of abnormal operation of differential protection caused by data synchronization error and TA saturation.Furthermore,and the corresponding protective strategies are surveyed as well.In this paper,the main sources of additional errors,including the unbalanced current caused by TA saturation and the data synchronization errors are analyzed.The effects of synchronization error and TA saturation disturbance on the amplitude and phase of the differential current and the restraint current are studied.The mechanism of the abnormal operation behavior of the differential protection in data synchronization error conditions and TA saturation scenarios are analyzed by employing ? plane analytic approach.The simulation results show that the existing two kinds differential protection criterions have defects in dealing with synchronization error and TA saturation.Moreover,according to the distribution characteristics of operating point under different synchronization errors and TA saturation disturbances,a method of dividing the restraint area and the action area suitable for the current differential protection is adopted.The crescent ideal restraint area is designed.Then,a novel criterion for multi-terminal protection,which takes account of both fault sensitivity in the region and the ability to withstand synchronization error,is advanced in this paper.In this method,two resistant coefficients are used to adjust the shape and size of the resistant region,and a setting method of restraint coefficients is obtained in this process.Compared with the traditional single restraint coefficient differential protection criterion,it is proved that the new criterion can improve the restraint ability of the criterion for the synchronization error and TA saturation error.Finally,the simulation model of medium and low voltage distribution network,multi terminal transmission lines and bus are constructed,and it is verified that the protection scheme composed of two resistant coefficients is more advantageous than the existing differential protection criterion in dealing with the synchronization error and TA saturation error.This provided a means for improving the correct action rate of differential protection under the disturbance of data synchronization error and TA saturation error,and the application range of proportional differential protection is expanded.