Arc Modeling And Overvoltage Analysis In Non-solidly Earthed Network

With the expansion of distribution networks and popularity of cable lines,the current of ground capacitance gradually increases.When a single-phase arc grounding fault appears,it tends to be difficult for the arc to extinguish reliably,leading to the intermittent grounding fault.Overvoltage caused by intermittent arc grounding fault is one of the greatest threats in the non-solidly earthed network.It is of great significance to establish an accurate arc model and research the overvoltage characteristics for fundamentally restraining the overvoltage harm.First of all,an improved cybernetic arc model suitable for non-solidly earthed network is established in this paper,which can accurately demonstrate the arc development process through controlling arc length.By comparing the stable ignition voltage,air withstand voltage and system recovery voltage in different conditions,criteria of arc extinction and reignition are proposed.Considering the influence of wind speed on the real-time arc length and the air withstand voltage,simulation procedure of intermittent arc grounding fault is presented.Then,a typical simulation model of 10k V distribution network is built via PSCAD.Stable arc grounding fault is simulated in the non-solidly earthed network.Moreover,impacts of diverse arc model parameters on arc characteristics are analyzed.According to the power frequency arc extinction theory,the high frequency arc extinction theory and the arc extinction and reignition criteria,intermittent arc grounding faults of non-solidly earthed networks are simulated,respectively.Overvoltage differences are compared.Plus,influences of various arc model parameters,transition resistance and detuning degree on overvoltage characteristics are analyzed.Finally,comparison between simulation results and field data indicates the effectiveness of improved cybernetic arc model and the feasibility of arc extinction and reignition criteria.By further analysis,it can be obtained that in the arc model,constant parameter V_s0 determines the arc voltage amplitude;empirical parameterβdetermines the zero break time;arc length determines the arc transient current amplitude.For isolated neutral system,overvoltage caused by high frequency extinction basically increases,and its maximum value is higher than that of power frequency extinction theory or arc extinction and reignition criteria.For Petersen coil grounded system,maximum overvoltage generated by power frequency extinction and high frequency extinction is approximately equal,which is higher than that of arc extinction and reignition criteria.Overvoltage can be reduced and arc extinction can be accelerated through increasing V_s0,decreasingβ,adding wind speed,rising transition resistance,adopting overcompensation mode.This paper address the deficiency of arc modeling and overvoltage analysis in non-solidly earthed network,which makes it more precise to simulate the arc grounding fault and the intermittent arc grounding overvoltage.