A Method Of Single Phase Grounding Fault Identification And Section Location Based On Compensation Degree Adjustment

10kV power system in our country is widely grounded through arc suppression coil,and single phase grounding fault accounts for the highest proportion of all faults.In order to shorten the operation time of single phase grounding fault,a new requirement of grounding fault section location is put forward on the basis of grounding fault line selection.Transient method is the mainstream method of single phase grounding fault location at present,but the transient signal has a short duration and is difficult to measure.This thesis presents a method of single phase grounding fault identification and section location based on compensation degree adjustment,which is a steady state method suitable for resonant grounding system.The single phase grounding fault location method in this thesis is mainly based on three theoretical foundations.The first is the distribution law of zero sequence current during single phase grounding fault in neutral point ungrounded system.That is,the closer the point downstream of the grounding point or in the non grounding line is to the end of the line,the smaller its zero sequence current amplitude is.The closer the point upstream of the grounding point is to the grounding point,the greater its zero sequence current amplitude is.The second is the distribution law of zero sequence current during single phase grounding fault in over compensation system.That is,the closer the point downstream of the grounding point or in the non grounding line is to the end of the line,the smaller its zero sequence current amplitude is.The closer the point upstream of the grounding point is to the grounding point,the smaller its zero sequence current amplitude is.The third is the change law of zero sequence current after changing the compensation degree during single phase grounding fault in over compensation system.That is,for the point upstream of the grounding point,its zero sequence current changes after conversion by zero sequence voltage.While for the point downstream of the grounding point or in the non grounding line,its zero sequence current remains unchanged after conversion by zero sequence voltage.The simulation shows that the correctness of the change law is not affected by grounding location,load,number of grounding lines,grounding resistance,distributed generation.The single phase grounding fault location method proposed in this thesis is:after the bus zero sequence voltage exceeds the limit,judge that the single phase disconnection,ferroresonance and single phase grounding through arc resistance do not occur according to the identification method to be proposed in this thesis,determine that the single phase grounding through stable resistance occurs.The location process starts.Change the compensation degree of the resonant grounding system.If the zero sequence current amplitude of a point changes after conversion by zero sequence voltage,the point is located upstream of the grounding point,otherwise the point is located downstream of the grounding point or in the non grounding line.Judge the grounding fault section according to the system topology.On this basis,several special issues are discussed.(1)How to improve the location reliability when single phase grounding through high resistance occurs.For the point upstream of the grounding point,its zero sequence current amplitude after conversion by zero sequence voltage has a limited range of change after changing the compensation degree during single phase grounding through high resistance,which is not obvious compared with the point downstream of the grounding point or in the non grounding line.The reliability of location by this method is not enough.In case of single phase grounding through high resistance,the system will temporarily become a neutral point ungrounded system after the grounding section is judged.According to the distribution law of zero sequence current along the line in neutral point ungrounded system,on the judged grounding line,if the amplitudes of zero sequence currents gradually increase in the process of approaching from the first and last ends of the line to the judged grounding section,it is proved that the section location is correct.In this way,the location reliability is improved in case of single phase grounding through high resistance.(2)Whether the distributed generation has an influence on the location method in this thesis.A large number of distributed generators are connected to the distribution system.The distribution network has changed from a traditional single power system to a multiple power system,which challenges the traditional single phase grounding fault location method.Considering the low voltage ride through control strategy,the distributed generator is modeled as a three phase current source controlled by positive sequence voltage.Theoretical analysis and simulation results show that whether in neutral point ungrounded system or over compensation system,distributed generation do not change the distribution law of zero sequence current during single phase grounding fault,and do not affect the correctness of the location method in this thesis.(3)How to ensure that the location process does not start when single phase disconnection,ferroresonance or single phase grounding through arc resistance occur.Most of the existing single phase grounding fault location methods start after the bus zero sequence voltage exceeds the limit.The single phase disconnection and ferroresonance will also increase the zero sequence voltage,causing the location process to start when it should not start.The location method in this thesis is not suitable for single phase grounding through arc resistance.The grounding fault section can not be correctly selected until single phase grounding through arc resistance develops into single phase grounding through stable resistance,which is the disadvantage of this method.In order to avoid the location process in this thesis starting in cases of single phase disconnection,ferroresonance and single phase grounding through arc resistance,it is necessary to study the identification methods of single phase disconnection,ferroresonance and single phase grounding through arc resistance.This thesis analyzes several cases of single phase disconnection with disconnection phase grounding composite fault by using phasor diagram,discusses the influence of power of distributed generators and grounding resistance on the zero sequence voltage on both sides of the disconnection point,and decides to distinguish single phase disconnection and single phase grounding by using the difference between the zero sequence voltage of the power side and the zero sequence voltage of the load side.Four classical arc models are modeled and simulated.The simulation results show that the zero sequence voltage distortion rate can be used to distinguish single phase grounding through arc resistance and single phase grounding through stable resistance.Several cases of fundamental frequency ferroresonance are analyzed by using phasor diagram.The processes of fundamental frequency,low frequency and high frequency ferroresonance are simulated.The simulation results show that some special phenomena of ferroresonance and zero sequence voltage distortion rate can be used to distinguish ferroresonance and single phase grounding.