The Woodruff School

SUMMARY

AgCdO is one of the most widely used contact materials in the world because of its outstanding performance. Nevertheless, due to environmental considerations, it will soon be completely forbidden by European environmental directives. Therefore, finding a good substitute is of crucial importance. Electrical arc erosion plays a crucial role in the reliability and life of power switching devices. Depending on the contact material�s behavior in response to an electrical arc, surface damage can induce severe changes in contact material properties that will impact the power switching device�s functioning. Consequently, electrical arc effects and consequences on the contact material surface are of first importance. In this context, we have focused our research activities on the following axes. First of all, in order to better understand AgCdO (Current contact material in aerospace industry) and AgSnO2 (Potential candidate to AgCdO substitution) arc erosion behaviors, arc erosion experiments, where the power switching devices have been subjected to different numbers of arc discharges, have been realized. Further, a general macroscopic electrical contact arc erosion model valid for low and high currents was developed. To compare model results to experimental data, this model describes the complete breaking process of electrical contacts and gives the total amount of material removed after one breaking operation. In parallel, arc erosion experiments on AgCdO power switching devices have been conducted at high currents (0 -> 1000 A) in order to validate the arc erosion model. Next, using the general arc erosion model, the properties having the greatest influence on the electrical arc erosion process have been determined through simulations on silver contact material. At this stage, ab-initio calculations were needed to obtain ranges of variation of certain silver contact material properties. Finally, an investigation of the trends of changing local contact material composition of AgSnO2 on these identified material properties was performed. This study was based on ab-initio calculations for two different oxide compositions of AgSnO2. These will allow us to give directions to aid the design of a good substitute for AgCdO, and therefore, to complete the main objective of this research work.

SUBJECT:	Ph.D. Dissertation Defense

BY:	Frederic Pons

TIME:	Monday, November 30, 2009, 9:00 a.m.

PLACE:	MRDC Building, 4115

TITLE:	Electrical Contact Material Arc Erosion: Experiments and Modeling Towards the Design of an AgCdO Substitute.

COMMITTEE:	Dr. Mohammed Cherkaoui, Chair (ME) Dr. Ting Zhu (ME) Dr. Erian Armanios (AE) Dr. Jianmin Qu (ME) Dr. Hanchen Huang (RPI-ME)

SUMMARY AgCdO is one of the most widely used contact materials in the world because of its outstanding performance. Nevertheless, due to environmental considerations, it will soon be completely forbidden by European environmental directives. Therefore, finding a good substitute is of crucial importance. Electrical arc erosion plays a crucial role in the reliability and life of power switching devices. Depending on the contact material�s behavior in response to an electrical arc, surface damage can induce severe changes in contact material properties that will impact the power switching device�s functioning. Consequently, electrical arc effects and consequences on the contact material surface are of first importance. In this context, we have focused our research activities on the following axes. First of all, in order to better understand AgCdO (Current contact material in aerospace industry) and AgSnO2 (Potential candidate to AgCdO substitution) arc erosion behaviors, arc erosion experiments, where the power switching devices have been subjected to different numbers of arc discharges, have been realized. Further, a general macroscopic electrical contact arc erosion model valid for low and high currents was developed. To compare model results to experimental data, this model describes the complete breaking process of electrical contacts and gives the total amount of material removed after one breaking operation. In parallel, arc erosion experiments on AgCdO power switching devices have been conducted at high currents (0 -> 1000 A) in order to validate the arc erosion model. Next, using the general arc erosion model, the properties having the greatest influence on the electrical arc erosion process have been determined through simulations on silver contact material. At this stage, ab-initio calculations were needed to obtain ranges of variation of certain silver contact material properties. Finally, an investigation of the trends of changing local contact material composition of AgSnO2 on these identified material properties was performed. This study was based on ab-initio calculations for two different oxide compositions of AgSnO2. These will allow us to give directions to aid the design of a good substitute for AgCdO, and therefore, to complete the main objective of this research work.