New perspectives on the dynamics of AC and DC plasma arcs exposed to cross-fields

AC electric air arcs in medium voltage (MV) distribution networks, including railway catenary, photovoltaic power generation systems, and traditional distribution networks, can cause insulation damage accidents. Although various studies have been performed on the macroscopic characteristics of the MV AC arc in the air, the research on the physical properties of the arc, such as temperature field and particle composition, is relatively lacking. This work deals with diagnosing the temperature and particle composition of the arc under laboratory conditions based on the arc generation and the moiré deflection diagnosis systems. Based on the experimental results, there are three typical stages in developing the MV AC arc: the initial, transition, and stable combustion. The temperature during the stable combustion of the arc is between 1500–2100 K, while the fluctuation period is half a power frequency cycle. The particle components of the arc are mainly composed of O2, N2, and O. Different from the DC arc, the AC arc exhibits a zero-crossing extinguishing phenomenon, while the gap temperature is still high after extinguishing the arc, and the insulation has not been fully restored. This research provides a method for diagnosing MV AC arcs in the air under laboratory conditions and initial values for the arc modeling.

Section: Temperature and Composition Diagnosis Of MV Ac Arc In The Airmentioning

confidence: 99%

Temperature and composition of AC arc plasma of medium voltage distribution networks in the air

Zhou¹,

Yuan²,

Wei³

et al. 2022

“…The radially symmetric channel arc model is illustrated in figure 1 along with the boundary conditions and a temperature profile for a given cross-section. Equation ( 1) can be further refined by making use of the following transform [13][14][15][16] :…”

Section: The Governing Equationsmentioning

confidence: 99%

“…The use of S greatly facilitates the convergence of the numerical solution. Upon applying expression (3) to equation (1), we obtain what is known as the Elenbaas-Heller equation [1,[13][14][15]:…”

Section: The Governing Equationsmentioning

confidence: 99%

An optimal method for the computation of the parameterR_sof the net emission coefficient approximation approach for determining the electrical and thermal characteristics of plasma arcs

Abdo¹,

Rohani²,

Fulcheri³

2017

Large-scale industrial plasma torches and processes use primarily high-current electric arcs. Therefore, their basic design must inevitably account for radiative transfer which becomes the prevailing heat loss mechanism at high currents. This heavily increases the complexity of the governing equations. Many approximate approaches have been proposed. The present work relies on the method of approximate average net emission coefficient (NEC) using the isothermal sphere approximation with a radius Rs to solve semi-analytically the Ellenbaas–Heller equation and compares it with exact calculations obtained using an iterative method. To our knowledge no study has provided yet a method to determine the most accurate value of Rs. In this paper, we present an optimal method for determining the best value of Rs that leads to the best agreement between the approximate and the exact methods. As a result, the complete electric characteristic has been obtained for hydrogen at 1 bar in a detailed case study.

“…Most researchers in the field of electric power engineering simplify an MV AC air arc using a nonlinear mathematical model, and there is a lack of understanding of the discharge mechanism of the arc. The plasma discharge mechanism based on the assumption of the local thermodynamic equilibrium (LTE), on the other hand, is relatively well understood and has been successfully applied to the modeling of high-current air arcs [4]. An arc is constantly arcing and extinguishing with the periodic change in the current [5], and its discharge mechanism is quite complex because of repeated restrikes and low-current characteristics.…”

Section: Introductionmentioning

confidence: 99%

Measurement of medium-voltage AC air arc temperature and particle number density based on dual-wavelength Moiré deflection technology

Zhou,

Yang,

Yuan

et al. 2024

AC air arcs are generated in medium-voltage (MV) power systems under the effect of harsh weather conditions, equipment aging, and high penetration of distributed generation, threatening equipment and public safety. The arc current and temperature are low due to the wide application of arc suppression devices. In this scenario, the MV AC air arc does not satisfy the local thermodynamic equilibrium (LTE) condition. In addition, the repeated arcing and extinguishing processes further complicate the arc discharge mechanism, which bring challenges in the modeling and detection of MV AC air arcs. Experimental methods are a direct and efficient approach to determine the properties of arc plasmas. In this study, a dual-wavelength moiré deflection diagnostic system was established to determine the time evolution of the particle density and radial distribution of the temperature in an MV AC air arc without relying on the LTE assumption. The electron number density and heavy particle number density change transiently during the arc discharge process and change gradient along the radial direction. The heavy particle temperature and electron temperature were then calculated based on the measured particle number density. During the arcing stage, the temperature of the electrons exceeded that of the heavy particles significantly, and the arc deviated from LTE. Finally, the limitations of the traditional single-wavelength moiré deflection method are analyzed. The classic single-wavelength moiré deflection method, while capable of estimating heavy particle temperature in plasma, exhibits a significant error in electron density estimation compared to the dual-wavelength moiré deflection method.