Design of Opening Velocity Characteristics for 2/3 Coil-Type Axial Magnetic-Field Contacts

The opening velocity characteristics significantly influence the short-circuit current breaking capability of a vacuum circuit breaker (VCB). This article aims to design the opening velocity characteristics for a pair of 2/3 coil-type axial magnetic field (AMF) contacts used in a 126-kV single-break VCB. The contact material we used was Cu50Cr50 (composed of 50 wt.% Cu and 50 wt.% Cr); the contact diameter was 100 mm. The initial opening velocity of the VCB,
$v_{1}$
, was defined as an average velocity in the first one-third of the full-contact gap
$d$
of 60 mm, while
$v_{2}$
was the average velocity of the first two-thirds of
$d$
. The threshold velocity,
$v_{\mathrm {1\_{}th}}$
, of 3.1 m/s was a lower limit for the
$v_{1}$
design to achieve high current-interruption performance within a short arcing time. The threshold velocity,
$v_{\mathrm {2\_{}th}}$
, of 3.1 m/s was an upper limit for the
$v_{2}$
design to achieve a high current-interruption capability over a long arcing time. The opening velocity characteristics were implemented via a spring-type operating mechanism a high
$v_{1}$
of 3.5 m/s ± 0.2 m/s, and a low
$v_{2}$
of 3.0 m/s ± 0.2 m/s, was achieved, respectively. The feasibility of the designed opening velocity characteristics adopted in the 126-kV VCB was demonstrated to be capable of handling a high short circuit breaking current and a small capacitive load switching current, by performing a series of type test duties. This contribution would be beneficial for the single-break VCBs at a transmission-voltage level to achieve high current-interruption performance.