Magnetic blow-out arc extinguishing device

A magnetic blow-out arc extinguishing device comprising:

• two pairs of separable contacts connected electrically in series including a stationary contact having a ring-shaped contact surface, a movable contact having a ring-shaped contact surface and a semi-stationary support member interposed between said stationary and movable contacts and having a first ring-shaped semi-stationary contact surface confronting and cooperating with said ring-shaped contact surface of said stationary contact to form a first pair of contacts and a second ring-shaped semi-stationary contact surface cooperating with said ring-shaped contact surface of said movable contact to form a second pair of contacts, said first and second ring-shaped semi-stationary contact surfaces being connected electrically and mechanically to each other,
• actuating means for moving said movable contact towards the separated position of said pairs of separable contacts,
• means for moving said semi-stationary support member to follow said movable contact along a predetermined stroke for separating said first pair of contacts just before said second pair of contacts is separated and drawing arcs between both pairs of contacts,
• a blow-out coil having a longitudinal axis extending parallel to the path followed by said arcs, said coil having a pair of terminals connected across said first pair of contacts so as to be energized at the appearance of an arc-voltage between the contacts of said first pair and developing a magnetic blow-out field, said ring-shaped contact surfaces on said stationary, semi-stationary and movable contacts being disposed coaxially with the longitudinal axis and outside said coil so that said magnetic field directed substantially radially between said ring-shaped surfaces causes rotation of the arc drawn between the separated contacts of said first pair and of the arc drawn between said second pair of contacts.