Transformation Characteristics of High-Current Vacuum Arcs With Still-Spaced Contacts Under TMF–AMF Combined Magnetic Fields

Abstract

A novel double-type contact system with still-spaced contacts was proposed to offer a better arc control and a electric field shielding effect to the eroded inner contacts, especially during the capacitive interrupting process. The experimental double-type contact system consisted of the inner moving transverse magnetic field (TMF) contacts and the outer still-spaced axial magnetic field (AMF) contacts, which was called as TMF–AMF contacts. The objective of this paper is to determine the transformation characteristics of high-current vacuum arcs with still-spaced contacts under TMF–AMF combined magnetic fields. The experimental investigation includes the vacuum arcing behaviors, the arc voltage, and the arc current transformation characteristics. The arc current in the tests varied over a range from 0 to 30 kA at 50 Hz. The contacts material was CuCr25 (25% Cr). A high-speed charge-coupled device video camera was used to record the vacuum arc appearance. The experiments indicate that the vacuum arc current can transform successfully from the inner TMF contacts to the outer still-spaced AMF contacts for the novel TMF–AMF double-type contacts. The partial arc current flowed through the outer still-spaced contacts was mainly at the latter half of the vacuum arc duration and less than 50% of the total arc current. The value and polarity of the arc current also play a significant role in the arc current transformation characteristics of the TMF–AMF contacts with still-spaced contacts. Moreover, with the vacuum arc expanding to the still-spaced contacts, the variation of the Lorentz force of the arc column would weaken the rotation of the arc column and strengthen the transformation characteristics of the vacuum arc column to the still-space AMF contacts significantly.