6 ms·

One of the fascinating challenges with HVDC is that a circuit breaker - an off switch! - is a surprisingly complex and expensive piece of engineering. If the po

One of the fascinating challenges with HVDC is that a circuit breaker - an off switch! - is a surprisingly complex and expensive piece of engineering. If the poles aren’t separated quickly enough, an arc can form and current continues to flow. This is usually undesirable. (Technically AC has the same problem, but the problem is much more acute for DC at the same voltage.) You know the joke/story about how nasa spent millions of dollars developing a pen that can write in space, and the soviets used a pencil? Well, the circuit breaker version of this is that the west built crazy complex huge high voltage circuit breakers, and the Soviets just built, uh, “single use” circuit breakers. With explosives. (I don’t know if this is true, I have never found a source, but it feels true, it should be true, I so desperately want it to be true.)

jnsaff2 3y ago
Tesla has pyro-fuses in their newer inverters and I believe in some battery packs as well.
- londons_explore 3y ago
  Worth noting for each pyro fuse in the cars what it protects against. The fuse in the motor inverters protects against failure of the mosfets (switches) inside the motor inverter. If any one of those switches get stuck 'on', the motor ends up doing full-power braking. That happening while driving along the highway would be catastrophic - hence the pyro-fuse to prevent such things. The fuse in the battery pack is to prevent a short circuit anywhere in the high voltage system of the car short circuiting the battery. Obviously a short would cause some pretty huge currents to flow, probably causing the battery to overheat in a few seconds, giving out large amounts of flammable gas, which would immediately ignite (TV-style fireball explosion). And again, the pyro fuse prevents that.
deleted 3y ago
[deleted]
gnfargbl 3y ago
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...
stefan_ 3y ago
Nobody is confused about how to make a single use circuit breaker. But things like train stations have a need for repeated DC circuit breaking at high voltages.
genter 3y ago
What's the difference between a single use circuit breaker and a fuse?
- planede 3y ago
  A fuse is triggered by excessive current flow on the line that it breaks. A single use circuit breaker is triggered manually or by some external signal.
fsh 3y ago
Explosive circuit breakers are standard in electric car safety systems (in case the regular one fails). I can't imagine anyone using them in normal operation though. The space pen story is made up as well: https://www.snopes.com/fact-check/the-write-stuff/ https://www.snopes.com/fact-check/the-write-stuff/
- trelane 3y ago
  It's not quite wrong either. The truth is more complex. See https://www.scientificamerican.com/article/nasa-spent-millions-on-a-pen-able-t/ https://www.scientificamerican.com/article/nasa-spent-millio... and https://www.reuters.com/article/factcheck-nasa-pens-idUSL1N2MQ1RR https://www.reuters.com/article/factcheck-nasa-pens-idUSL1N2... I think any of us would balk at a government agency spending 1300 bucks on a single pencil (first link). And the graphite conductivity problem is a non sequitur, given that the Russians used wax (or grease) pencils, not graphite. This is really the point of the anecdote: wasteful government spending. Though apparently the Russians also find the pens useful and bought some as well.
  - kube-system 3y ago
    > I think any of us would balk at a government agency spending 1300 bucks on a single pencil (first link). Only people who don't understand how engineering and manufacturing projects work. $1300 is completely reasonable for a very low volume manufactured product, which was specified to meet specific criteria. The reason it sounds unreasonable is because it is being called a "pencil/pen", instead of what it actually was, which was speciality equipment designed to be compatible with the conditions inside of the spacecraft. At face value in meme format, the implied "free" solution would be buying a pen or pencil off the shelf, when in reality, that alone wouldn't have solved the problem. It is possible that someone could have evaluated off-the-shelf options to see if one would have met the criteria, but that would still have significant labor cost.
    - trelane 3y ago
      > which was speciality equipment designed to be compatible with the conditions inside of the spacecraft. Right, that's the point. It's also how you get the other very expensive things that the Pentagon gets dinged for.
asfginionio 3y ago
All switches have this problem, even low-voltage or AC ones. Slow switches, or switches that bounce, create arcs. This damages the contacts and can be hazardous. This is one reason switches are "clicky". The action of completing or breaking the circuit must happen quickly. Switches have springs in them, which ensure the switch goes between the two extremes as quickly as possible. The springs oppose the motion for first part of the travel. Partway through the travel, they suddenly start to assist the motion and force the switch the rest of the way.
Borg3 3y ago
Bzzzz :) https://www.youtube.com/watch?v=GMbN9nb3qyk https://www.youtube.com/watch?v=GMbN9nb3qyk
deleted 3y ago
[deleted]
tzs 3y ago
Would it be feasible to use induction to briefly induce a reverse current on a short section of the line that is of the same magnitude as the forward current so that there won't be arcing when you break the circuit there?
- namibj 3y ago
  Kinda; actively sucking current/voltage difference away from a circuit breaker can allow you to interrupt a long DC line/part of a larger DC mesh without interrupting sufficiently distant users. Think train line/streetcar grid.

jnsaff2 3y ago

Tesla has pyro-fuses in their newer inverters and I believe in some battery packs as well.

londons_explore 3y ago
Worth noting for each pyro fuse in the cars what it protects against. The fuse in the motor inverters protects against failure of the mosfets (switches) inside the motor inverter. If any one of those switches get stuck 'on', the motor ends up doing full-power braking. That happening while driving along the highway would be catastrophic - hence the pyro-fuse to prevent such things. The fuse in the battery pack is to prevent a short circuit anywhere in the high voltage system of the car short circuiting the battery. Obviously a short would cause some pretty huge currents to flow, probably causing the battery to overheat in a few seconds, giving out large amounts of flammable gas, which would immediately ignite (TV-style fireball explosion). And again, the pyro fuse prevents that.

deleted 3y ago

[deleted]

gnfargbl 3y ago

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...

stefan_ 3y ago

Nobody is confused about how to make a single use circuit breaker. But things like train stations have a need for repeated DC circuit breaking at high voltages.

genter 3y ago

What's the difference between a single use circuit breaker and a fuse?

planede 3y ago
A fuse is triggered by excessive current flow on the line that it breaks. A single use circuit breaker is triggered manually or by some external signal.

fsh 3y ago

Explosive circuit breakers are standard in electric car safety systems (in case the regular one fails). I can't imagine anyone using them in normal operation though. The space pen story is made up as well: https://www.snopes.com/fact-check/the-write-stuff/ https://www.snopes.com/fact-check/the-write-stuff/

trelane 3y ago
It's not quite wrong either. The truth is more complex. See https://www.scientificamerican.com/article/nasa-spent-millions-on-a-pen-able-t/ https://www.scientificamerican.com/article/nasa-spent-millio... and https://www.reuters.com/article/factcheck-nasa-pens-idUSL1N2MQ1RR https://www.reuters.com/article/factcheck-nasa-pens-idUSL1N2... I think any of us would balk at a government agency spending 1300 bucks on a single pencil (first link). And the graphite conductivity problem is a non sequitur, given that the Russians used wax (or grease) pencils, not graphite. This is really the point of the anecdote: wasteful government spending. Though apparently the Russians also find the pens useful and bought some as well.
- kube-system 3y ago
  > I think any of us would balk at a government agency spending 1300 bucks on a single pencil (first link). Only people who don't understand how engineering and manufacturing projects work. $1300 is completely reasonable for a very low volume manufactured product, which was specified to meet specific criteria. The reason it sounds unreasonable is because it is being called a "pencil/pen", instead of what it actually was, which was speciality equipment designed to be compatible with the conditions inside of the spacecraft. At face value in meme format, the implied "free" solution would be buying a pen or pencil off the shelf, when in reality, that alone wouldn't have solved the problem. It is possible that someone could have evaluated off-the-shelf options to see if one would have met the criteria, but that would still have significant labor cost.
  - trelane 3y ago
    > which was speciality equipment designed to be compatible with the conditions inside of the spacecraft. Right, that's the point. It's also how you get the other very expensive things that the Pentagon gets dinged for.

asfginionio 3y ago

All switches have this problem, even low-voltage or AC ones. Slow switches, or switches that bounce, create arcs. This damages the contacts and can be hazardous. This is one reason switches are "clicky". The action of completing or breaking the circuit must happen quickly. Switches have springs in them, which ensure the switch goes between the two extremes as quickly as possible. The springs oppose the motion for first part of the travel. Partway through the travel, they suddenly start to assist the motion and force the switch the rest of the way.

Borg3 3y ago

Bzzzz :) https://www.youtube.com/watch?v=GMbN9nb3qyk https://www.youtube.com/watch?v=GMbN9nb3qyk

deleted 3y ago

[deleted]

tzs 3y ago

Would it be feasible to use induction to briefly induce a reverse current on a short section of the line that is of the same magnitude as the forward current so that there won't be arcing when you break the circuit there?

namibj 3y ago
Kinda; actively sucking current/voltage difference away from a circuit breaker can allow you to interrupt a long DC line/part of a larger DC mesh without interrupting sufficiently distant users. Think train line/streetcar grid.