Abstract
The objective of this paper is to propose a quantitative method to determine opening velocities for VCBs at transmission voltage. A couple of 2/3 coil-type axial magnetic field (AMF) contacts, which are used in a 126 kV vacuum interrupter, are arranged in a demountable vacuum chamber. The movable contact is opening with three different kinds of opening travel-curves. Each curve is adjusted by two opening velocities, v 1 and v 2 , respectively. The v 1 is an average opening velocity within 1/3 full contact gap, which is with 1.8 m/s, 2.4 m/s and 2.7 m/s, respectively. The v 2 is an average opening velocity within 2/3 full contact gap, which is with 2.4 m/s, 2.7 m/s, and 3.0 m/s, respectively. The test current ranges from 4 kA to 40 kA, stepped by 4 kA. When a VCB is used to interrupt a short-circuit current, the preferred opening velocity is determined by reducing the arcing interval t I for the intense arc mode and increasing the arcing interval t II until the formation of high-current anode mode (HAM). The preferred v 1 is higher than a threshold value v 1_th , at which there is a peak critical contact gap d I_peak , for the evolving from intense arc mode into diffuse arc mode. The preferred value v 2 is lower than another threshold value v 2_th , at which there also exists a peak critical contact gap d II_peak , for the evolving from diffuse arc mode into the footpoint mode and anode spot mode.
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