PTFE Vapor Contribution to Pressure Changes in High-Voltage Circuit Breakers

Abstract

A transient magneto-hydrodynamic model based on @Ansys-Fluent software applied on a high-voltage circuit breaker (HVCB) geometry is presented. The model is turbulent (κ-ε realizable model), and radiation is taken into account by a hybrid model (Discrete Ordinates Method and P1). The insulating medium is SF 6 , and current I rms = 25 kA. An ablation model based on the literature was applied to represent the ablation of the Polytetrafluoroethylene (PTFE) walls. The theoretical and experimental results (pressure, ablation rate, and voltage drop variation) are presented and compared. Several cases were considered: no ablation (ceramic walls), ablation only from downstream parts, and ablation from upstream parts of HVCB walls. The corresponding pressure variations are presented. In order to explain the pressure increase, some additional quantities such as mass flow rate and energy integrated into one section of the heating channel are given. The results show that even if the mass of PTFE ablated is small, the pressure increase is due to the energy input from the vapor.Index Terms-Computational fluid dynamic (CFD) model, heating volume, high-voltage circuit breaker (HVCB), pressure increase, SF 6 and C 2 F 4 vapors.

A study on thermal‐interrupting performance improvement of SF6 gas circuit breaker by promotion of nozzle ablation

“…PTFE, which is typically used for GCB nozzles, is known to be ablated by the radiation power of the arc . For PTFE nozzles exposed to SF 6 arcs, we derived a formula for the arc radiation Φ rw absorbed by the surface of the nozzle .…”

Ablated mass of PTFE nozzle due to high‐current SF6 arc exposure: Formulation of ablated mass

“…When a nozzle is ablated, its throat diameter increases; as a result, the change in cross‐section area of gas channel may impair circuit breaking performance. On the other hand, nozzle ablation gases are known to contribute to arc cooling and blow strength due to higher pressure in the puffer chamber, thus improving GCB breaking performance …”

“…When developing high-performance, compact SF 6 gas circuit breakers (GCBs), numerical analysis of arc behavior is a useful tool to guide design of the arc-extinction chamber. [1][2][3][4][5][6][7] In order to improve accuracy of such numerical design, one must better understand arcs that occur during breaking; moreover, it is important to clarify hot gas flow and other phenomena that accompany arc ignition, and to incorporate them into analysis procedures. However, these phenomena are extremely complex, and few models can represent them in numerical analysis.…”

“…On the other hand, nozzle ablation gases are known to contribute to arc cooling and blow strength due to higher pressure in the puffer chamber, thus improving GCB breaking performance. [1][2][3][4]6,7 A number of methods were proposed to calculate nozzle's ablated mass during circuit breaking, and to represent the effect of puffer pressure growth due to nozzle ablation in arc behavior analysis. In such methods, nozzle's ablated mass is determined simply from arc current and empirical constants, 6 or PTFE thermolysis amount is calculated via radiation flux emitted from arc to the nozzle, 7 and so forth.…”

“…[1][2][3][4]6,7 A number of methods were proposed to calculate nozzle's ablated mass during circuit breaking, and to represent the effect of puffer pressure growth due to nozzle ablation in arc behavior analysis. In such methods, nozzle's ablated mass is determined simply from arc current and empirical constants, 6 or PTFE thermolysis amount is calculated via radiation flux emitted from arc to the nozzle, 7 and so forth. However, the former method disregards nozzle shape and cannot provide a versatile model for arc behavior analysis in arc-extinction chamber under various conditions including rated voltage and interrupting current.…”