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| Study on Radiation Transport Characteristics of C4F7N Gaseous Arc |
| Zhong Linlin, Wang Yifan, Gu Qi |
| School of Electrical Engineering Southeast University Nanjing 210096 China |
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Abstract In order to reduce greenhouse gas emissions in power industry, more and more efforts are being made to discovery eco-friendly SF6 replacements. At the moment, SF6 alternatives are commonly used as insulating medium, but study on their arc extinguishing performance is insufficient and is still in the exploratory stage. An excellent interrupting medium should quickly cool the arc, and radiation as the main form of arc energy transport plays a key role in the arc interrupting process. Therefore, this paper performs a study on the radiation transport characteristics of C4F7N gaseous arc mixing with CO2 and N2 by combining numerical simulation and experiment, which can lay a theoretical foundation for the engineering application of eco-friendly arc extinguishing gases.
Firstly, a two-dimensional (2D) magnetohydrodynamics (MHD) model is established to describe the transport behavior of C4F7N gaseous arcs by coupling multi-physical field equations, including Navier-Stokes equations, Maxwell equations, and turbulence equations. In this MHD model, the radiation transport is described by the net emission model which is easy to implement and requires net emission coefficients (NEC) as input. Based on the MHD model, the time-dependent multi-physical fields, such as temperature and radiation energy of C4F7N gaseous arcs are obtained by the finite volume method (FVM). The radiation transport characteristics of C4F7N gaseous arcs are investigated during the opening of contacts, and the effects of current magnitude and mixing ratios on the arc shape, temperature distribution, and radiation energy distribution are discussed. It is found that due to the distribution of arc radiation energy along the x axis, the C4F7N arcs are gourd-shaped. As the current is raised, the arc radiation energy increases, leading to a clearer gourd shape. With the increase of gas content in C4F7N, the arcs gradually shrink by the action of radial Lorentz force.
Secondly, the experiment platform is constructed for the arc optical diagnosis. The arc shapes and spectrum information are collected by a high-speed camera and a spectrometer respectively. The experimental results show that there is randomness in the arc development, but the arc shape is basically similar to the simulation results. The arc brightness is heightened with the increase of current, indicating that the radiation transport energy is gradually enhanced. In addition, considering that the arc temperature is the macro indication of the radiation transport characteristics, the temperatures of C4F7N arcs are measured based on the spectral information. The results show that although the measured arc temperatures are slightly lower than the simulation results, the evolution trend of measured temperatures is consistent with the simulated ones, which verifies the effectiveness of the simulation model.
In general, both simulation and experiment results show that the radiation capability of C4F7N gaseous arcs is stronger than SF6 arcs. This indicates that C4F7N gas mixtures can be used as an arc extinguishing medium to accelerate the energy dissipation in the arc extinguishing process. However, the experimental results also show that there is solid material condensation (e.g. graphite) during the interrupting process of C4F7N arcs, which not only limits the self-recovery of C4F7N gas, but also brings insulation hazards. Therefore, follow-up work should focus on the radiation transport characteristics of C4F7N arcs under the premise of suppressing or reducing the condensation of solids (e.g., by adding O2).
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Received: 16 February 2023
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2023, Vol. 38 
