Thermodynamic evaluation of oxidation during brazing process of medium-voltage electrical circuit breakers

¹ University Grenoble Alpes, SIMAP, 1130 rue de la piscine, BP 75, 38402 Saint-Martin-d’ Hères, France
e-mail: ioana.nuta@simap.grenoble-inp.fr
² CNRS, SIMAP (UMR-5266), 38000 Grenoble, France
³ Schneider Electric- SEA, ZI de Ripotier, BP 133, 07202 Aubenas Cedex, France
⁴ Schneider Electric- ZAC St Ange, 4 rue de l’Industrie, 38760 Varces-Allieres-et-Risset, France

Received: 11 February 2016
Accepted: 13 May 2016

Abstract

The present study is a thermodynamic analysis of the different molecular flows occurring during the vacuum brazing of electrical vacuum bottles also called Vacuum Interrupters (mentioned later as VI). Among the available impurities either coming from the Vacuum Interrupters components materials or from vacuum technology, the analysis is focused on the oxygen since this impurity leads to formation of the more stable compounds, i.e. oxides. During the brazing cycles the resistors of the vacuum furnace and the VI materials including some braze components are the main sources of vapours that partly escape or make deposits on colder parts of the furnace. Vaporization and condensation processes are evaluated, their matter flows quantified and finally their interaction with residual oxygen calculated through a balance between input oxygen from vacuum or neutral gas and the different sources of oxygen coming from the parts under treatment. The enrichment of the VI materials and deposits with oxygen is evaluated as well as the limits required for vacuum conditions. The main conclusion is that present vacuum conditions allow correct working of the brazing sequence but in any other temperature steps or ramps, oxygen is trapped as oxides at the surface of the parts or accumulated in the bulk materials of the furnace.