Research On Single-phase Grounding Fault Line Selection In Resonant Grounding Distribution Network

The neutral point of distribution network in China is mainly ungrounded and grounded through arc suppression coil(resonant grounding).Among all kinds of faults in distribution network,the probability of single-phase grounding fault is over 80%.Due to the compensation effect of arc suppression coil and the interference of various external factors in single-phase grounding fault,the fault signal of neutral grounding through arc suppression coil is weak and the fault situation is complicated.In addition,in high-resistance grounding fault,the accuracy of line selection is low due to the influence of transition resistance.Therefore,it is particularly important to study a line selection method suitable for resonant grounding distribution network.Aiming at the shortcomings of existing fault line selection methods,this thesis proposes a single-phase grounding fault line selection method for resonant grounding distribution network based on distributed intelligent collaboration.The main contents are as follows:(1)Firstly,the characteristics of single-phase grounding fault in resonant grounding distribution network are analyzed,and combined with instantaneous zero-sequence power theory,Principal Component Analysis(PCA)is used to cluster analysis of instantaneous zero-sequence power curve clusters of feeders.According to PCA principal component distribution law,the fault line selection criterion based on cluster discrimination is determined.Secondly,according to the principle that the zero-sequence current of the faulty feeder and the sound feeder are in opposite directions after the fault of the distribution network,the characteristic frequency band of the fault current is extracted by wavelet transform,and the fault information on the characteristic frequency band is used to distinguish the faulty lines.Finally,aiming at the difficulty of line selection for high-resistance grounding fault in distribution network,the transient characteristics of high-resistance grounding process are analyzed,and the line selection criterion is formed by using the difference of impedance characteristics between high and low frequency bands of feeders,and a line selection method to deal with high-resistance grounding fault is proposed.(2)In view of the problems that a large amount of data is generated during the operation of the distribution network and the network structure is complex and changeable,which leads to the failure information exchange among the advanced applications of the distribution system in time,serious data waste and poor data processing capability,this thesis combines the data processing capability and storage function of cloud computing with fault line selection,integrates supervisory control and data acquisition(SCADA),wide area measurement system(WAMS),fault recording information system and fault line selection system,and proposes a fault line selection mode combining distributed intelligent collaboration with cloud computing.(3)The traditional fault line selection device starts by detecting whether the neutral point voltage of distribution network exceeds 15% of the phase voltage amplitude as the criterion of whether the ground fault occurs.However,the traditional method may fail under the faults of small fault closing angle and large transition resistance,with low sensitivity and long starting time.However,the resonant grounding system has zero-sequence voltage with small amplitude because the three-phase parameters are not symmetrical.After the fault occurs,the zero-sequence voltage increases significantly,so the zero-sequence voltage is an ideal starting amount.The sudden change of zero-sequence voltage is used as the starting amount of line selection device,which meets the requirements of quick action and sensitivity of the device.