Sorry, dhoule, my computer has been in the shop for 10 days.
Basically, the contacts are mounted on the middle of curved strips called horns.
As the arc forms across the contacts the magnetic field of the blowout coil pushes it up the curved pieces of the horn, which, since they are curved outward from each other increasingly lengthens the arc to the point of which it can no longer sustain, and therefore extinguishes.
This is in the book, "Electric Motor Control" by Walter Alerich. Published by Delmar.
[This message has been edited by Redsy (edited 05-20-2005).]