Integral methods of analysing electric arcs: II. Examples

It is shown that the arc model based on laminar flow cannot predict satisfactorily the voltage of an air arc burning in a supersonic nozzle. The Prandtl mixing length model (PML) and a modified k-epsilon turbulence model (MKE) are used to introduce turbulence enhanced momentum and energy transport. Arc voltages predicted by these two turbulence models are in good agreement with experiments at the stagnation pressure (P 0) of 10 bar. The predicted arc voltages by MKE for P 0 = 13 bar and 7 bar are in better agreement with experiments than those predicted by PML. MKE is therefore a preferred turbulence model for air nozzle arc. There are two peaks in ρC P of air at 4000 K and 7000 K due, respectively, to the dissociation of oxygen and that of nitrogen. These peaks produce corresponding peaks in turbulent thermal conductivity, which results in very broad radial temperature profile and a large arc radius. Thus, turbulence indirectly enhances axial enthalpy transport, which becomes the dominant energy transport process for the overall energy balance of the arc column at high currents. When the current reduces, turbulent thermal conduction gradually becomes dominant. The temperature dependence of ρC P has a decisive influence on the radial temperature profile of a turbulent arc, thus the thermal interruption capability of a gas. Comparison between ρC P for air and SF 6 shows that ρC P for SF 6 has peaks below 4000 K. This renders a distinctive arc core and a small arc radius for turbulent SF 6 , thus superior arc quenching capability. It is suggested, for the first time, that ρC P provides guidance for the search of a replacement switching gas for SF 6 .

Section: Computational Domain and Boundary Conditionsmentioning

confidence: 99%

“…Arc modelling at that time was mainly based on the integral method [5,[7][8][9]. This method of arc analysis has achieved considerable success in predicting the arc behaviour under steady state and for relatively high currents [5].…”

Section: Introductionmentioning

confidence: 99%

Analysis of the characteristics of DC nozzle arcs in air and guidance for the search of SF₆replacement gas

Liu¹,

Zhang²,

Yan³

et al. 2016

“…For a given gas and nozzle material, the behaviour of the arc in affinely related nozzles is fully determined by two non-dimensional parameters, one of which is similar to the nozzle coefficient first introduced by Cowley and Chan (1974). The other non-dimensional coefficient, the ablation coefficient, is similar to that of Fang and Newland (1983).…”

Section: Discussionmentioning

confidence: 99%

The behaviour of ablation-dominated DC nozzle arcs

Bu¹,

Fang²,

Guo³

1990

A mathematical model for the ablation-dominated arcs has been developed. The ablation is caused by arc radiation. It has been assumed that the ablated wall material mixes completely with the arc quenching gas to form a mixing layer surrounding the arc. It has been shown that for a given gas and nozzle material the arc behaviour in affinely related nozzles is fully determined by two non-dimensional parameters, one of which is the nozzle coefficient N. The other is the ablation coefficient determined by the arc radiation characteristics and the nozzle material. When the nozzle coefficient reaches a certain value, the flow of the arc quenching gas is entirely blocked. Further decreasing the value of N (i.e. increasing the current), a reverse flow is established and the arc burns in the ablated material. For a given tank pressure, the pressure within the nozzle, the reverse mass flow rate and enthalpy flux are proportional to the square of the current. This is consistent with the trend observed experimentally.

“…These predictions agree with weight loss measurements made following several tests. Both the thermal zone of heated gas and nozzle ablation become significant as the current approaches the nozzle blocking limit (estimated as 44 kA from the method of Cowley and Chan (1974)). Beyond this point the thermal 'bubble' has a considerable effect on the pressure estimation, and for peak currents of the number of 70 kA the heated gas fills the arcing space of the interrupter before being expelled through the nozzle when the current falls towards zero.…”

Section: Set Initial Conditions Lmentioning

confidence: 99%

Transient pressure variations in SF₆puffer circuit breakers

Shimmin¹,

Jones²,

Ali³

1990

The operation of the SF6 puffer circuit breaker relies on he pressurisation of gas by a combination of piston compression, nozzle blocking and gas heating. Theoretical modelling of the physical processes occurring during high-current interruption is important for mechanical design and for prediction of electrical performance. A high-current arc model has been developed, which takes account of observed gas behaviour throughout the arcing period and beyond current zero. The predicted pressurisation is compared with experimental work, and shows good agreement over a wide range of operating conditions. The theoretical model pays particular attention to the mechanisms of heat transfer within the upstream region of the interrupter, and incorporates a new description of the arc thermal boundary.