3 ms·

Rather than separating the conductors more quickly, wouldn't it be preferable to replace the space they occupied with a material in which arcs cannot form? Or i

Rather than separating the conductors more quickly, wouldn't it be preferable to replace the space they occupied with a material in which arcs cannot form? Or is this a cost/risk thing? e.g. I know SF_6 is sometimes used for this purpose, but that is problematic as it is a potent greenhouse gas.

pmontra 3y ago
Like one metal blade that is placed in between the wires (current flows) and slid up to an insulating part (current does not flow) ?
- _trampeltier 3y ago
  Thats not that easy. As soon the two metals are seperated, there will be an arc. The arc is really, really hot and will burn everything and also as soont there is an arc, the arc stays can bee so much much longer in discance than just air. Since there is 0 in DC, large DC-switches are much more difficult to build. There are several options from SF6 (today no), to vacum or blowing magnets (blow the arc to cooling cambers).
- atoav 3y ago
  I am pretty sure if it was that simple it would have been done that way already. Breaking high currents is something we had to do for more than a hundred years. Arc flashes are no joke. We are talking about 2800 to 19000 degrees Celsius here. I don't know about your insulator but it has to survive a multiple of the surface temperature of the sun. And ideally it withstands that more than once or twice.
quickthrowman 3y ago
A typical miniature or molded case low-voltage (under 1000V) circuit breaker will have arc chutes to extinguish the arc. [0] Higher power low-voltage circuit breakers as well medium and high voltage breakers can use oil [3], (compressed) air [1], gas [4], and vacuum [2] to extinguish the arc flash. SF-6 is used for high voltage applications while vacuum and air are common for medium voltage gear installed indoors, oil breakers are used in outdoor installations at utility substations and similar installations. [0] https://wiraelectrical.com/what-is-an-arc-chute/ https://wiraelectrical.com/what-is-an-arc-chute/ [1] https://www.se.com/us/en/faqs/FA360729/ https://www.se.com/us/en/faqs/FA360729/ [2] https://en.m.wikipedia.org/wiki/Vacuum_interrupter https://en.m.wikipedia.org/wiki/Vacuum_interrupter [3] https://www.electricaltechnology.org/2021/08/ocb-oil-circuit-breaker.html/amp https://www.electricaltechnology.org/2021/08/ocb-oil-circuit... [4] https://www.electricaltechnology.org/2021/08/sf6-sulphur-hexaflouride-circuit-breaker.html/amp https://www.electricaltechnology.org/2021/08/sf6-sulphur-hex...
Gud 3y ago
Most high voltage breakers already are SF6. They rely on the 0-point crossing to quench the arc.
- Faaak 3y ago
  But is there not 0-point crossing in DC currents ?
  - eternityforest 3y ago
    The current is always positive except when it's turned off. It never reversed so it never passes through 0v to get to negative volts. Which is also the big advantage, since you're not spending part of the time at lower voltage.

pmontra 3y ago

Like one metal blade that is placed in between the wires (current flows) and slid up to an insulating part (current does not flow) ?

_trampeltier 3y ago
Thats not that easy. As soon the two metals are seperated, there will be an arc. The arc is really, really hot and will burn everything and also as soont there is an arc, the arc stays can bee so much much longer in discance than just air. Since there is 0 in DC, large DC-switches are much more difficult to build. There are several options from SF6 (today no), to vacum or blowing magnets (blow the arc to cooling cambers).
atoav 3y ago
I am pretty sure if it was that simple it would have been done that way already. Breaking high currents is something we had to do for more than a hundred years. Arc flashes are no joke. We are talking about 2800 to 19000 degrees Celsius here. I don't know about your insulator but it has to survive a multiple of the surface temperature of the sun. And ideally it withstands that more than once or twice.

quickthrowman 3y ago

A typical miniature or molded case low-voltage (under 1000V) circuit breaker will have arc chutes to extinguish the arc. [0] Higher power low-voltage circuit breakers as well medium and high voltage breakers can use oil [3], (compressed) air [1], gas [4], and vacuum [2] to extinguish the arc flash. SF-6 is used for high voltage applications while vacuum and air are common for medium voltage gear installed indoors, oil breakers are used in outdoor installations at utility substations and similar installations. [0] https://wiraelectrical.com/what-is-an-arc-chute/ https://wiraelectrical.com/what-is-an-arc-chute/ [1] https://www.se.com/us/en/faqs/FA360729/ https://www.se.com/us/en/faqs/FA360729/ [2] https://en.m.wikipedia.org/wiki/Vacuum_interrupter https://en.m.wikipedia.org/wiki/Vacuum_interrupter [3] https://www.electricaltechnology.org/2021/08/ocb-oil-circuit-breaker.html/amp https://www.electricaltechnology.org/2021/08/ocb-oil-circuit... [4] https://www.electricaltechnology.org/2021/08/sf6-sulphur-hexaflouride-circuit-breaker.html/amp https://www.electricaltechnology.org/2021/08/sf6-sulphur-hex...

Gud 3y ago

Most high voltage breakers already are SF6. They rely on the 0-point crossing to quench the arc.

Faaak 3y ago
But is there not 0-point crossing in DC currents ?
- eternityforest 3y ago
  The current is always positive except when it's turned off. It never reversed so it never passes through 0v to get to negative volts. Which is also the big advantage, since you're not spending part of the time at lower voltage.