Research On Line Selection Method Based On The ρ Plane For High Resistance Grounding Fault In Low Resistance System

The low-resistance grounding system can effectively suppress over-voltage and quickly remove faults.With the gradual increase in the scale of cables connected to the distribution network,with the effectiveness of suppressing overvoltages and the rapidness of removing faults,the operation mode of low resistance grounding is increasingly being applied to the distribution network of medium and large cities.Among.The low-resistance grounding system is generally equipped with zerosequence over-current protection,but due to its relatively high threshold of action,the current to ground when a single-phase high-resistance ground fault occurs is relatively weak,and the protection may refuse to operate.If the system runs with a fault for a long period of time,it may directly cause the insulation breakdown between the cable lines,which will expand the scope and nature of the fault.The fault line selection of 10 k V low resistance grounding system can g enerally be divided into the line selection method based on steady state quantity and the line selection method based on transient state quantity.When the transition resistance is large,the steady-state fault characteristic quantity and transient charact eristic quantity flowing through the grounding point are relatively weak,so the existing line selection method has poor ability to deal with high transition resistance.In addition,the asymmetry of line parameters and the saturation of zero-sequence current transformers will also have a negative impact on fault location and line selection.In view of the above problems,this paper studies the high-resistance grounding fault line selection method of this type of system.On the PSCAD/EMTDC simulation platfo rm,a 10 k V low-resistance grounding system single-phase high-resistance grounding fault model was built,and different types of single-phase high-resistance grounding faults were simulated using fixed-value transition resistance and Mayr arc models.Throug h theoretical analysis and digital simulation,the fault waveforms of two types of high-resistance grounding faults are given,and the fault characteristics of different types of high-resistance grounding faults are compared and analyzed,which provides a basis for the selection of highresistance grounding faults in low-resistance systems.A high-resistance fault line selection method based on ratio braking differential amplitude and phase plane is proposed.When a single-phase high-resistance grounding fault occurs,the zero sequence current of the faulted line has a relatively large projection component on the neutral line current as the reference axis,and is slightly larger than the current flowing through the neutral line;the zero sequence current of the normal operating line The projected component on the reference axis of the neutral line current is relatively small,much lower than the current flowing through the neutral line.Based on the characteristics of the zero-sequence current of this fault,a line selection criterion suitable for this type of fault is constructed and visualized.In order to ensure the sensitivity of the criterion,firstly,the fault action threshold is set according to the expected detected transition resistance resistance va lue,and the line selection procedure in the case of a fixed-value high-resistance ground fault is explained.Finally,the authenticity of the proposed method is verified by simulation.Sex and reliability.A scheme for setting the criterion of high-resistance ground fault line selection is proposed.The influence of measurement errors such as current transformer saturation and asymmetry of line parameters on the neutral line current after a fault is analyzed,and the plane is adjusted with the maximum poss ible amplitude and phase angle errors.The experimental results show that the method has a good effect.The fault tolerance.