Abstract
The arc behavior during the closing and opening of electrical contacts not only influences the surface morphology, but also causes the erosion of contact material. The mechanical stresses, the molten bridge, and the arc cause this erosion. Consequently, the erosion mechanism is very complex. Therefore, to avoid the influences of mechanical stresses and numerous arc striking, static-gap experiments with a single arc discharge are conducted to investigate the effects of pulse voltage, gap distance, and arc duration on the erosion characteristics and mechanism of silver based contact materials. Moreover, this experimental result is verified by the finding of the dynamic testing of electrical contacts.
The results of the erosion characteristics show that the arcing and non-arcing regions have been distinguished at the supply voltage from 32 V to 500 V and the gap distance from 0.2 mm to 40 mm. The empirical formula for the minimum pulse voltage at arc initiation in terms of gap distance is established. When the pulse voltage is smaller than 200 V, the erosion area increases with increasing gap distance due to the action of the metallic-phase arc. However, when the pulse voltage is greater than 200 V, with increasing gap distance, the erosion area increases to a maxim, and finally diminishes due to the increase in the amount of gaseous-phase arc.
The results of the erosion mechanism show that the arcing region is classified into three erosion patterns, namely, the molten metal bridge (B), metallic-phase arc (M), and gaseous-phase arc (G). At the gap distance of 0.2 mm, the erosion pattern of anode silver is varied from B, through B+M, and, M, to M+G. According to the electron transfer across triangular potential barrier, the thermionic emission causes the erosion patterns of B, B+M, and M, and mixed thermionic and field emission results in the erosion pattern of M+G. When the pulse voltage is 500 V, with increasing gap distance, the splashing of metallic particles around the anode crater becomes more dispersed, shorter with more silver powder, and finally disappeared with a little silver powder due to the influence of the gaseous-phase arc.
The results of the anti-weld ability show that when the pulse voltage is 500 V and the arc energy is grater than 14 J at the static-gap experiments, the critical gap distance to produce welding for Ag-Ni, Ag-CdO, and Ag-SnO2 is 3 mm, 8 mm, and 15 mm, respectively. This indicates Ag-Ni contact possesses the best anti-weld ability. On the other hand, the results of dynamic testing of electrical contacts show that at the arc energy less than 10 J, the anti-erosion, anti-weld ability, and the welding area are seen to increase with contact materials in the following order: Ag-CdO > Ag-SnO2 > Ag-Ni. However, when the arc energy is greater than 10 J, the anti-erosion, anti-weld ability, and the erosion area are seen to increase in the reverse order: Ag-SnO2 < Ag-CdO < Ag-Ni, which are in very good agreement with the results of static-gap experiments.
Furthermore, the erosion surface of the silver-based contact materials can be observed and analyzed by using the X-ray diffraction method (XRD), differential thermal analysis (DTA), and gravitation thermal analyzer (GTA). Results show that when the arc energy is greater than 14 J, Ag-CdO and Ag-SnO2 have been decomposed into Ag-Cd and Ag-Sn alloys, respectively, which reduce their anti-weld ability. On the other hand, the welding trend has been reduced due to the dispersion of NiO on the surface of Ag-Ni contact. Consequently, the anti-erosion and anti-weld ability for the Ag-Ni contacts are better than those of the other Ag-MeO contact materials.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0725103-162528 |
| Date | 25 July 2003 |
| Creators | Chung, Ho-Hua |
| Contributors | HON SO, Chiou, Yuang-Cherng, none, Kuang, Jao-Hwa, none, none, Lee, Rong-Tsong, Tsai,Ying-Chien |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0725103-162528 |
| Rights | unrestricted, Copyright information available at source archive |
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