Research On Phase Selection Of Single-phase To Ground Fault In 10kV Power Grid Based On Variance Theory

In China,the 10kV power grid is a key link in the power system.It is followed by the high-voltage transmission grid,and further constitutes the main framework of the distribution network.Its importance is self-evident.Therefore,the power system has extremely high requirements for the safe and reliable operation of the 10kV grid.The neutral point of 10kV power grid mostly adopts non-grounding and arc suppression coil grounding methods,both of which belong to the category of small current grounding methods,That is,when a single-phase ground fault occurs in the system,the fault current is small and the three-phase line voltage of the system still maintains a symmetrical relationship,so that the continuous power supply to users is not affected.With the development of economy and society,the rapid increase of electricity load,the scale of 10kV power grid has also expanded correspondingly,and there have been more and more problems with it,which is facing severe challenges in terms of safety and reliability.The single-phase grounding problem of 10kV power grid has been around for a long time.Current solutions mostly focus on fault line selection,and the understanding of fault phase selection is not deep.As a result,even if the existing line selection research reaches a technical bottleneck,it is unwilling to deny the past and think out of the box.The single-phase ground fault problem of small current grounding systems has become a problem in the industry.For the phase selection of single-phase ground faults,the traditional concept is only the phase voltage ratio method to determine the fault phase.However,as the ground resistance increases,the fault phase voltage is no longer easy to distinguish,and due to the asymmetry of the load,it often appears a situation where the fault phase voltage is higher than the normal phase voltage.When this happens,use the phase-voltage ratio-amplitude-phase method to confirm the fault phase,which will inevitably lead to miss election.On the basis of summarizing various fault handling methods,this paper presents a phase selection method based on variance theory.This method can effectively determine the fault phase under the conditions of high resistance grounding and unsymmetrical load.In theory,as long as the sampling frequency is sufficient,the criterion is not affected by the phase of the fault,the size of the transition resistance when the fault occurs,and the grounding method,and has good applicability.Finally,a simple 10kV power grid model with 3 outgoing lines was built using Matlab,and the single-phase grounding faults were simulated when the neutral point was not grounded and the neutral point was grounded through the arc suppression coil.The simulation was conducted through different grounding resistances.To verify the criteria of the phase selection method proposed in this paper,and the results show that the algorithm is accurate and reliable.