Energy Balance Of Arc Research Articles

Energy balance in MIG arcs

Recent studies of metal inert gas (MIG) processes by spectroscopy and fluid simulations have shown that metal evaporation causes a specific spatial structure of the arc, and among others a minimum of plasma temperature at the arc centre. Changes in the arc structure and in the heat transfer to the material are closely connected with the arc energy balance; its detailed analysis has not been carried out so far under the specific impact of metal vapour. In this paper, magnetohydrodynamic (MHD) simulations of an MIG arc in argon including iron evaporation at the wire tip are considered. The main terms in the energy balance are discussed focusing on a comparison of the arc regions with and without metal vapour. In addition, a simple approach of the energy balance at a cross section of the MIG arc is proposed where all details of the heat transport are neglected. The MHD model and the simplified approach are in good agreement and clearly demonstrate that the specific structure in an MIG arc is mainly caused by the different temperature dependence of the plasma radiation and the electrical conductivity in argon or in argon mixtures with iron vapour.

Calculation of laminar flows of plasma in the channel of a plasmatron with the self-adjusting length of the electric arc

A simplified method is suggested for the calculation of the parameters of laminar flows of plasma in the channel of a plasmatron. A new analytical solution of the Elenbaas–Heller equation is derived, which generalizes the channel model of electric arc to the case when the volume radiation makes a significant contribution to the electric arc energy balance. Numerical calculations are performed in order to determine the electric field intensity, the longitudinal pressure gradient, and the heat transfer to the electric arc channel wall depending on the working parameters of the plasmatron in a laminar flow of gas in a stabilized section. In determining the arc length, it is assumed that the electric arc is shifted downstream of the flow and, at the same time, performs random walks over the channel cross section. The walks occur under the effect of vortexes whose characteristic size is of the order of the arc diameter.

On axisymmetric deformations of the electric arc column in an accelerating flow

A review of axial flow arcs which exhibit well defined varicose oscillations suggests that, although these have frequently been attributed to shear instabilities, their observed phase speeds are an order of magnitude less than those expected for shear driven phenomena. It is suggested that the coupling between the energy balance of arc and the cold flow conditions the response of the arc column to oscillatory forcing, delaying the onset of shear instability. A linearized mathematical analysis of the thermal coupling alone confirms that, in common with many of the observations, such disturbances travel at the cold flow speed.

Practical Modeling of the Circuit Breaker ARC as a Short Line Fault Interrupter

The short-line fault interrupting ability of gas-blast circuit breakers is limited by arc energy balance processes very close to current zero. Practical calculation of the energy balance limit in a given circuit requires mathematical modeling of the arc as a circuit element. Using the combined Cassie-Mayr model, useful relations are derived for treating the limiting cases of the short-line fault both with and without capacitance shunting. Included are methods for approximate analysis and extrapolation of data from actual and simulated short-line fault tests with and without RRRV controlling resistance and capacitance shunts. In these analyses the arc is described by only two model parameters: a near-current-zero arc voltage Eo and an arc time constant 0, both definable as simple functions of the circuit di/dt. Examples are given of such analyses of high di/dt interrupting tests on actual and model SF6-blast interrupters.

Radiative energy losses from a high-current air-blast arc

The importance of total radiation losses from high-current arcs burning in highly accelerated air flows representative of conditions existing in commercial gas-blast switchgear has been investigated. Such losses have been measured both in the high-pressure region upstream of a shaped orifice, where gas velocities are low, and in the region downstream where velocities become supersonic and pressure conditions approach ambient. The dominance of upstream electrode vapor as the source of plasma radiation losses is demonstrated and the importance of radiated losses within the arc energy balance is examined using measured values of axial electric field. For upstream electrodes of elkonite (sintered copper/tungsten) as used in high-power gas-blast circuit breakers, it is shown that some 30–40% of the electrical energy input upstream of the orifice is lost as radiation, while downstream this figure becomes 10–20%. The effect of reservoir pressure on arc electric fields is examined and the contribution to this effect of radiation losses is quantified.

A study of the radiative energy losses from an arc in jet flow

Radiative energy losses from an arc in jet air flow have been studied. By confirming the importance of these losses, the author supplements a previous paper (see abstr. A82063 of 1974) in which a large discrepancy in the arc energy balance was attributed to them. For arcs burning to an upstream cathode of sintered copper (tungsten in an M=0.8 air flow, radiation is the major energy loss mechanism, accounting for more than 50% of the column voltage requirements. The presence of upstream electrode vapours in the arc column is responsible for the high values of the radiation loss.