42 / 2024-03-29 16:14:32

Improved Mayr-Cassie Arc Model of Tree-Contact Incipient Fault Based on MHD Simulation

tree-contact incipient fault,Mayr-Cassie arc model,MHD simulation

Abstract- Overhead distribution lines are susceptible to climate and environment, short-term contact with the branches around the distribution lines will cause the grounding fault arc, describe as the tree-contact incipient fault. The intermittent and frequent occurrence of the tree-contact incipient fault can cause serious accidents such as disconnection of lines and fire, as shown in Fig.1(a). To realize the detection and identification of tree-contact incipient fault, the simulation of distribution line with arc black-box model is needed. This paper focused on establishing an improved Mayr-Cassie arc model based on magnetohydrodynamics (MHD) simulation to realize the simulation calculation of tree-contact incipient fault characteristics under 10 kV overhead lines. Firstly, based on the geometric structure of the tree-line and the real environmental conditions, a MHD model of tree-contact incipient fault arc is established, as shown in Fig.1(b), combined with the electromagnetic field control equation and the gas flow field control equation. According to the real situation, the arc current is 10 A, and the arc current waveform in half cycle is taken as the input of MHD model. Subsequently, the MHD model can make the development process of the tree line flashover arc visually studied and analyzed，by outputting the distribution changes of temperature, pressure, gas flow velocity, etc., the physical changes in the process of arc combustion are intuitively reflected. As shown in Fig.2, in the early stage of the development of the arc, the maximum temperature nearly remains constant, the high temperature area is expanded, the diameter of the arc column is increased. In the later stage, with the change of the input current, the arc column does not change significantly, and the overall temperature gradually decreases. According to intuitive physical changes, the prior probability of Mayr model and Cassie model for the contribution ratio of arc resistance can be obtained. Finally, through the MHD simulation, by traversing all the grids in the arc region, the total energy of the arc region at the current time can be calculated, and the arc voltage can be output by setting the detection point at the two poles of the arc. Then arc time constant, heat dissipation power and voltage constant, these key parameters in the Mayr-Cassie model can be obtained, then the dynamic conductivity characteristics of the arc are calculated, as shown in Fig.3. Combined with the prior probability, the function relationship between the above key parameters and arc conductance is established through parameter fitting, and then the improved Mayr-Cassie arc model is obtained. Then the tree-contact incipient fault simulation is carried out by using improved Mayr-Cassie arc model, the reliability of the model is verified by comparing the simulated results with the experimental results