Anybody know what a blowout is? I recently came across a symbol on an electrical print, very similar to a solenoid symbol labeled blowout. It is not a solenoid. What is it?

I have seen the term used to refer to a device that "blows out" or extinguishes an arc drawn between separating contacts, especially on DC systems.

I have seen them take the form of magnets along the sides of the arc chute, or a solenoid operated device that generates a short puff of air which is directed into the contact gap.

I believe a "blowout coil" uses the actual magnetic field generated by the coil to extinguish the arc by repeling or pushing it away from the contacts.
I have a detailed explanation in a book somewhere. I'll look it up.

[This message has been edited by Redsy (edited 05-10-2005).]

Thanks guys.

Redsy, I would appreciate any more info you might be able to come up with.

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).]

Thanks, Redsy!

Actually, if I understand things correctly there are several different patents for blow outs, and I believe the one you are describing is the most effective for most applications.

Here's some good pictures http://xnet.rrc.mb.ca/janaj/air_breakers.htm

An old (1920s) device had a spring loaded fuse-wire which was contained with carbon tetrachloride in a glass tube. The chemical vapor doused the arc as the melted fuse-ends were whipped apart. Used only on high voltage/low amps instrumentation transformers where the cost of a full breaker set was not economically justified.
Alan.

Thanks Alan,

That was a little bit before my time. I got started in 1960 and haven't had much experience on things pre WWII. I love this forum. I am learning a lot from it.

Ditto the learning comment -- I never realized how complex a high-voltage switch could get.

By the way, in case you guys have never seen it, this has got to be the coolest movie ever of a switch arc:
http://205.243.100.155/frames/longarc.htm#500_kV_Switch

John, Thanks for the arc presentation. They were great.