Research On The Method Of Improving Ability To Endure Transition Resistance And Overload Of Distance Protection

Distance protection is an important part of line protection and has been widely used in the power system.But for single-phase high-resistance grounding and non-full-phase overload,the existing solutions are not effective enough.In this case,this paper studies how to improve the ability of distance protection to endure transition resistance and overload.The main research results and innovations are as follows:1.According to the characteristic that the transient quantity decays faster when grounding with high-resistance,the half-wave attenuation average ratio Wδ,half-wave singular value ratio W∧ and energy spectrum entropy WE,which can characterize the characteristics of the transient quantity,are defined.And combined with Bayesian classifier,a fault classifier is formed to distinguish low-resistance grounding and high-resistance grounding.2.The Ucosφ/U1 cosφ1 characteristic criterion is proposed,which is used to identify overload(including non-full-phase overload)and single-phase grounding.And the identification of phase-to-phase faults and single-phase high-resistance grounding is improved by combining the U cos φ and the classification information of the grounding faults.3.A new method for calculating transition resistance is proposed.The relationship between transition resistance,decay time constant and time delay coefficient is derived.Then,the decay time constant and time delay coefficient are extracted from the generalized S transform coefficient matrix by applying least square fitting and beat phenomenon.As a result,the third independent equation for high-resistance grounding is constructed(the classic scheme can only list two independent equations),and the solution of transition resistance is realized.4.The impedance characteristic adaptive setting method and the zero-sequence adaptive setting method based on the transition resistance value are proposed,and combined with the grounding fault classification method,an improved protection scheme is formed that the protection are opened directly when grounding with low-resistance while the calculated value of transition resistance is used to adjust the protection setting when grounding with high-resistance.Finally,the above scheme was verified by MATLAB/SIMULINK.The simulation results show that the improved scheme proposed in this paper can be activated by phase during grounding and be reliably blocked during overload when dealing with various overloads;When dealing with various types of grounding faults,it has the performance characteristics of "Start-up quickly when low-resistance grounding and endure high-resistance grounding wherever fault occurs".