In this paper, the morphological changes of the vacuum arc with the breaking current at the intermediate frequency are observed and the volt-ampere characteristic of the vacuum arc at intermediate frequency is analyzed under transverse magnetic field (TMF). Volt-ampere characteristics of the vacuum arc are divided into three phases: the initial arcing phase, the transitional phase, the current decline phase. The thermal inertia is the important factor influencing the three phases. The change of arc mode correlates with arc volt-ampere characteristics that can be used as criteria of three phases. It can be used to infer the relationship between the frequency and the arc voltage. The higher the frequency, the greater the initial rate of rise of the arc voltage(du/dt) and the larger the area surrounded by arc volt-ampere characteristics will be, while the lower the frequency, the more linear the arc volt-ampere characteristics seem to be. In this paper, we give the correlations between the arc voltage and the amplitude and frequency of the current at the initial arcing phase.
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