Establishment of Intermittent Reignition Arc Model and Analysis of Intermittent Arcing Ground Faults in Distribution Network
The intermittent reignition of electric arcs is the most typical characteristic of single-phase grounding faults in distribution networks.The existing electric arc models often overlook this intermittent reignition characteristic,resulting in the inaccurately description of the characteristics of discontinuous arc glow grounding faults,thus affecting the relay protection operations.To address this,the paper proposes a method for establishing an intermittent reignition electric arc model and analyzes the characteristics of discontinuous arc glow grounding faults based on this model.The random variation of arc impedance serves as an important indicator of intermittent reignitions,so the study focuses on the stochastic nature of arc impedance variations and the reignition time intervals in the intermittent reignition electric arc model.In the black box electric arc model,the Cassie-Mayr combined model accurately describes the transition of arc current from high to low values.However,there exist an issue of fuzzy criteria for transitioning from high to low currents and the abrupt changes during the transition process.To address these issues,the paper introduces a continuous transition function and utilizes the Fermi function to assign weights to the Mayr and Cassie models in the combined model to represent the changing chara-cteristics of arc resistance.Building upon the improved Cassie-Mayr single reignition arc model,the intermittent reignition electric arc model is established by incorporating the stochastic nature of intermittent reignition through the duration of arc reignition,as defined by the power-frequency arc extinguishing theory.Using this model,simulation and analysis of a typical 10 kV distribution network with single-radiation grid structure are conducted.The fault characteristics such as fault voltage,fault current,higher harmonics,zero-sequence components,and frequency distribution are extracted using the Fast Fourier Transform(FFT)and the wavelet packet analysis under different conditions.The research findings indicate that the improved Cassie-Mayr combined model not only resolves the issue of abrupt transitions in arc currents but also accurately represents the stochastic nature of the actual arc impedance variations by allocating weights to different models.By setting the duration of arc reignitions,the stochastic nature of intermittent reignition is accurately captured.The moments of arc interruption occur at non-integer cycles,resulting in overvoltage and overcurrent amplitudes higher than those at integer cycles.The cable lines increase the fault current in the faulted line,with overcurrent ranging from 3.81pu～7.20pu,making the arc extinguishing more difficult.The fundamental frequencies of phase zero-sequence currents in high-current system faults range from 0～400 Hz,while in the low-current system faults,they range from 1200～1600 Hz.
distribution networksingle-phase grounding faultintermittent reignition arc modelneutral point groundingwavelet packet analysis
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