| The Chinese distribution network has a wide coverage and high fault rate which more than 80% faults are single-phase to ground fault.For a long time,the single-phase grounding fault feeder identification and fault location,single-phase high resistance grounding protection of distribution nework have not been solved effectively.The failure of fault feeder identification and fault location and the refusing operation of single-phase high impedance to ground protection will lead to system operation with faults for a long time,and thus damaging electrical equipment and expanding the scope of the fault and destroying the stable operation of system,and even causing personal injury and death.Therefore,it is of great significance for the safe and stable operation of the distribution network that the fault feeder and fault section are quickly determined and the fault is timely removed.In this paper,equivalent circuits and single-phase to ground fault characteristics for resonant grounding system(RGS)and low resistance grounded system(LRGS)are analysed.Faulty feeder identification and fault location methods of RGS,single-phase high impedance grounding protection methods for RGS and LRGS are researched.A method for faulty feeder identification of the RGS based on zero-sequence impedance characteristics of high and low frequency bands is proposed.Firstly,the high and low frequency bands of single-phase to ground fault in RGS are defined and the selection principle of the cutoff frequencies of high and low frequency bands is given.The zero-sequence impedance of healthy feeder presents capacitance characteristic in both high and low frequency bands while the equivalent zero-sequence impedance of faulty feeder presents capacitance characteri stic in high frequency band and inductance characteristic in low frequency band.So,the ratios of bus zero-sequence voltage derivative and zero-sequence current in high frequency band and low frequency band for healthy feeder are equal,and the actual difference of the ratios between high frequency band and low frequency band is approximately to zero.However,the ratios of bus zero-sequence voltage derivative and zero-sequence current in high frequency band and low frequency band for faulty feeder are not equal,and the difference is much greater than zero.Based on the distinguishing characteristic,criterion of faulty feeder identification can be obtained.Moreover,in order to realize the autonomous identification for faulty feeder,a method based on correlation analysis theory for faulty feeder identification is put forward by utilizing zero-sequence impedance characteristic,it identifies faulty feeder by comparing correlation coefficients of bus zero-sequence voltage derivative and zero-sequence current in high frequency band and low frequency band,without the needing of other feeders' information.Multiple imulation results demonstrate the feasibility of the proposed method which has been applied to the single-phase grounding protection demonstration project of the distribution network s of four cities built by the state grid Hunan power corporation.A single-phase to ground fault location method based on FastICA and Fuzzy C Means(FCM)clustering for RGS is proposed.In this method,the FastICA algorithm is used to extract the transient-state components and steady-state components of zero-sequence currents of feeder terminal units(FTUs)which are respectively expressed by transient-state factors and steady-state factors.Then,differential mode value(DMV)corresponding the section can be calculated by the difference of two transient-state factors and the difference of two steady-state factors between the two FTUs.Then,the all DMVs are imported to FCM algorithm in which the clustering number is set as two.One clustering indicates healthy section,the other clustering denotes faulty section.If the DMV of a section is divided into a clustering separately,the section is faulty section,all the rest sections are healthy sections.Theoretical analysis and simulation results show that the proposed method has the advantages of low transmission of data,small communication pressure,dispensing with checking the data synchronization and setting threshold.Actual wave data recorded verify further the reliability of the proposed method.The active method by adjusting the compensation de gree of arc-suppression coil for faulty feeder identification and fault location in RGS is presented.The transient variation component(TVC)of each feeder is contructed by bus zero-sequence voltages and zero-sequence currents of feeders before and after adjusting compensation degree of arc-suppression coil.The TVCs of healthy feeders are close to zero while the TVC of faulty feeder is a larger value.Therefore,an active faulty feeder identification method is designed.For a RGS having branches,if the fault occurs in the main section,the TVCs of the section and upstream main sections of fault point are large,the TVCs of others are close to zero;if the fault occurs in the branch section,the TVCs of the section and upstream main sections of fault point are large,the TVCs of others are close to zero.Based on the conclusion,a active method for fault location can be proposed.Meanwhile,making a little improvement of the fault location method by replacing the zero-sequence current of TVC with zerosequence current imcrement,the faulty section also can be identified by the improvement fault locaiton method.Moreover,the method is able to realize two or several faulty sections location.A single-phase HIF method for faulty feeder identification in RDS i s proposed.Firstly,the transient process is analysed under the over-damping state and under-damping state for the HIF in RDS.Transient zero-sequence current of healthy feeder is proportional to bus transient zero-sequence voltage derivative,and the proportional coefficient is feeder own capacitance value while transient zero-sequence current of faulty feeder is proportional to bus transient zero-sequence voltage and bus transient zero-sequence voltage derivative,and the proportional coefficients are the reciprocal of transition resistance and feeder own capacitance value respectively.Based on the least squares algorithm,feeder own capacitance parameter and transition resistance parameter of each feeder are estimated.Be means of comparing estimated transition resistance with the set threshold,the faulty feeder is able to be identified.Numerical simulation results and test results based on RTDS experiment platform have verified the effectiveness of the proposed method.A protection method that is suitable for the single-phase HIF in the LRGS is put forward.The method defines the composite power of each feeder which is used to contruct protection criterion.Through the derivation,it is found that for healthy feeder the phase angle of the feeder composite power is zero,and the amplitude is close to zero while for faulty feeder the phase angle of the feeder composite power is ?,and the amplitude is close to 2.On the basis of the above principle,the protection method for the single-phase HIF in the LRGS can be obtained.Numerical simulation results and test results based on RTDS experiment platform show that the proposed method does not need check the polarity of the voltage or current transformers,and have a good performance under the influence of transition resistance,noise interference and system unbalanced current. |
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