Current noise up to GHz band generated by slowly breaking silver-compound contacts with external dc magnetic field

Abstract

Since electromagnetic (EM) noise resulting from an arc discharge disturbs other electric devices, parameters on electromagnetic compatibility, as well as lifetime and reliability, are important properties for electrical contacts. To clarify the characteristics and the mechanism of the generation of the EM noise, the current noise up to GHz band frequency generated by slowly breaking contacts with external direct current (dc) magnetic field, up to 40 mT, was investigated experimentally using Ag and AgSnO 2 material. To reveal the characteristics as pure clean surface contact operation, the arc only at the operation of the first contact break was measured. Firstly, the effect of the external dc magnetic field on the duration and voltage fluctuation of the breaking arc of AgSnO 2 material, which has relatively longer arc duration, was quantified. The experimental results on AgSnO 2 material newly revealed that although applying external dc magnetic field is effective in reduction of duration of gaseous phase in arc discharge, higher variation of contact voltage in the gaseous phase which results in high frequency noise is caused. Secondly, the effect of the external dc magnetic field on the breaking arc of Ag was measured. It was found that larger current noise arises, when the contact voltage is rapidly varied at the arc discharge. There are two kinds of rapid changes, which cause high-frequency EMC problem, in the voltage waveform. One is at extinction of arc discharge. Other kind is short-duration arc (short-arc) before the ignition of the continuous metallic arc. Especially, we focused on the characteristics of the short-arc at the initial of the opening of the contact for clarifying the high frequency EMC problem. It was demonstrated that the spectrum of current noise in the case of B = 30 mT is smaller than that in the case of B = 0 mT. In addition, duration and fluctuation of short-arc is suppressed by the dc magnetic field. These results are basic and useful finding to know not only the noise generation in the contact-breaking phenomena but also the material dependency for EMC problems.