Thought experiment - break 1000Vdc & 1000Arms in <1mS !! - Page 1
Forum section: electronics / projects

author: max_torque
author_rank: Super Contributor
timestamp: August 09, 2016, 06:00:41 pm
content: We were talking about how one would, practically, and for the lowest cost, build a high speed DC contactor, that can break 1000Vdc and 1000Arms in less than 1mS!!Size doesn't matter, but the on state resistance must be as low as is practical (obviously, with 1000Arms going through it!!) The "reset" can be manual, and the device can sustain a limited amount of damage in the act of breakiing the current, but the bits that get damaged must be relatively easy and relatively cheap to replace (say <$200 / £100 ish)We had lots of crazy ideas involving compress air, explosive bolts, large springs, electromagnets and also sorts of weird stuff!We also talked about how to snuff the arc, again involving sand, compressed air, large magnets and more explosions!So, how would you do it?

author: CM800
author_rank: Frequent Contributor
timestamp: August 09, 2016, 06:15:41 pm
content: 1mS.... well, why not just use a big ol' IGBT?

author: Dave
author_rank: Super Contributor
timestamp: August 09, 2016, 06:26:36 pm
content: 1ms != 1mSThe former is a millisecond, the latter is a millisiemens. Get the units right.I don't see how you could accomplish the switching time with a mechanical solution, much less do it cheaply. I second TCWilliamson's suggestion, go solid state.

author: PartialDischarge
author_rank: Super Contributor
timestamp: August 09, 2016, 06:27:25 pm
content: Since what you have is basically an uncontrolled short-circuit, where a LOT of current can flow (you expect 1000A but its going to be much more), you need a thyristor, any other semiconductor will break if you do those tests.A thyristor rated for 1000A rms continuous current may specify a non-repetitive peak current of 10kA over 10ms, and more in less time , no igbt can match that.You can fire them easily by the way with a 9V battery

author: Gyro
author_rank: Super Contributor
timestamp: August 09, 2016, 06:47:39 pm
content: A small but rather basic flaw.You can only turn-on a Thyristor, it won't turn off again until the current through it drops to zero. The OP wants to interrupt in <1ms.

author: Ian.M
author_rank: Super Contributor
timestamp: August 09, 2016, 06:53:24 pm
content: Hmm. What about a meter long 'fuse' carrying the current made of heavy wall copper pipe, packed with copper thermite and hermetically sealed, with det cord strung below it? Fire the thermite and the det cord, and the pipe departs explosively as copper vapour. while the blast from the det cord blows the vapour out of the gap.Here's 500g of Copper thermite blowing up:

author: PartialDischarge
author_rank: Super Contributor
timestamp: August 09, 2016, 06:53:43 pm
content: Quote from: Gyro on August 09, 2016, 06:47:39 pmI guess the OP is using capacitors as a source (unless he has a 1000V mains at home), and with a thyristor the stored energy will be long gone in less than 1 ms

author: max_torque
author_rank: Super Contributor
timestamp: August 09, 2016, 06:53:49 pm
content: I'm trying to break 1000Vdc and 1000Arms and there will be a large(not sure how big, but i can't control or specify it) inductance, which is going to pretty much fry any conventional solid state device when it tries to break it. Chances are, the upstream voltage will jump up to several thousand volts, and a nice fat arc will rip across the unit, driven by the 1000Arms that was flowing at the moment of breaking!To ensure a break i think there needs to be a large, definite, mechanical separation of large, contacts or similar (because the "closed" resistance must be low (probably <1mohm)I was thinking about firing a large charged capacitor, using a thyristor, though a coil, and using the resultant massive electo-motive force to spring apart a set of contacts for example?? After all F = MA, so if we get enough F, the A should be pretty big! Certainly, plenty of you-tube vids show people doing things like collapsing tin cans in short periods of time with high magnetic discharges etc?

author: max_torque
author_rank: Super Contributor
timestamp: August 09, 2016, 06:55:36 pm
content: Supply is either a 1000VDC DC powersupply or a large 1000Vdc battery! Both have enough stored charged, to really, really ruin your day....

author: max_torque
author_rank: Super Contributor
timestamp: August 09, 2016, 06:57:09 pm
content: Quote from: Ian.M on August 09, 2016, 06:53:24 pmInteresting idea, we though about something similar, but actually, we weren't sure how quickly something like that could be detonated? I know detcord burns at a fanastic rate (km/s iirc), but initiating it is actually quite slow i think? (speed for typical primer cap?)

author: Gyro
author_rank: Super Contributor
timestamp: August 09, 2016, 07:03:52 pm
content: Well if you want to break the arc then discharge horns (Jacob's ladder style), possibly in combination with magnetic blowout contacts should clear it. It will probably take longer than 1ms to clear it though and I wouldn't put anything you're sentimental about above the horns.

author: PartialDischarge
author_rank: Super Contributor
timestamp: August 09, 2016, 07:05:57 pm
content: max_torque, if I understood you well, you basically need a device to discharge a great deal amount of energy into "something" (and in the least amount of time so the power is even greater) to explode it , break it, burn it... is that so?By the way, attached is the discharge of some capacitors through a thyristor I did some time ago. From 1600V to 0 in 200us with more than 15000A in peak current.EDIT: Added the scope photo

author: Gyro
author_rank: Super Contributor
timestamp: August 09, 2016, 07:24:01 pm
content: An example of magnetic arc blowout for high current... Just don't be a di*k head and knacker it like the op did.https://www.eevblog.com/forum/reviews/photonicinduction-20-000-amp-breaker-switch/msg780848/

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: August 09, 2016, 07:32:41 pm
content: First you build a nice French Guillotine, but make the blade out of something non-conductive, maybe polycarbonate. Put a narrow metal cutting edge on it if you want to use it a lot. The blade has to be larger in both dimensions than the conductor. Place soft metal conductor where neck normally goes. Drop the blade from up high just the right number of milliseconds before you want to break the circuit. Be sure the blade stops with the conductor near the center. Hopefully the arc won't flash around the blade- make larger if needed.

author: oldway
author_rank: Super Contributor
timestamp: August 09, 2016, 07:47:42 pm
content: First thing to know: is it a resistive or an inductive circuit ?If it is an inductive circuit, you will have high overvoltage on the device who will break this current.dU = L dI/dt.In this case, you will need a big snubber to dissipate the inductive energy.For an inductive circuit, there are fast dc circuit breakers for metro third rail with such capacity (1000Vdc 1000A or more) but I don't thing they can interrupt the current as fast as 1ms.http://www.alstom.com/Global/Transport/Resources/Documents/Brochures%202015/ARC%20812andARC%201512%20High-Speed%20Circuit%20Breakers%20-Product%20sheet%20-%20English.pdf?epslanguage=tr-TRUsing semiconductors is possible: the different options are:- IGBT- GTO- Fast SCR's with forced comutation. (Mc Murray- Bedford).

author: Marco
author_rank: Super Contributor
timestamp: August 09, 2016, 08:10:01 pm
content: You're under specced, define a max inductance.If you want to do it for an unknown inductance you will have to destroy the universe when you want to break the current, it's the only way to be sure.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: August 10, 2016, 12:24:33 am
content: Hydrogen thyratron... or IGCT.https://library.e.abb.com/public/3ab5c20d7d104c9ec12579c9002e91c6/5SHY%2035L4522_5SYA1249-00Feb12.pdfImplementation is left as an exercise for the reader.

author: oldway
author_rank: Super Contributor
timestamp: August 10, 2016, 09:33:11 am
content: I really wonder how you would do this with an hydrogen thyratron .As far I know, the thyratron has no turn off capability, nor possibility to interrupt a dc current.It should be a forced comutation circuit as used for fast scr's, but deionizing time is greater than Toff of SCR's (Thyratrons :50 to 500s , fast SCR's 5 to 100µs)IGCT seems to be a GTO with his integrated gate pulse generator.

author: amyk
author_rank: Super Contributor
timestamp: August 10, 2016, 10:34:59 am
content: I also agree that the cheapest way would involve pyrotechnics.

author: oldway
author_rank: Super Contributor
timestamp: August 10, 2016, 10:57:22 am
content: Pyrotechnics produces plasma gaz and plasma is highly conducting.It does not seem to be a good idea.

author: Ian.M
author_rank: Super Contributor
timestamp: August 10, 2016, 11:13:30 am
content: That depends. If you can blow the plasma out of a big enough gap quickly enough, the plasma carrying the current for a few hunded microseconds isn't going to be a problem.I suspect its going to need an array of shaped charges probably with a gas Krytron tube triggered exploding wire detonators to sequence them quickly enough to create a coordinated hypersonic blast front to clear the gap of plasma from detonating the primary 'fuse' element. Optimum method for observing result - with a telescope in a bunker a mile away with *good* earplugs!Going back to mechanical means, even Conrad's French guillotine knife switch (above) would be more practical if driven by an over-grown Ramset cartridge!Classic SF reference:Quote from: E.E. 'Doc' SmithFrom'Grey Lensman', serialized in 'Astounding Science Fiction', Oct 1939-Jan 1940

author: mikerj
author_rank: Super Contributor
timestamp: August 10, 2016, 11:44:29 am
content: Quote from: Gyro on August 09, 2016, 06:47:39 pmThen use a Gate Turn-off Thyristor (GTO). They are a bit slow to turn off, but 1ms might be achievable.

author: zl2wrw
author_rank: Regular Contributor
timestamp: August 10, 2016, 11:59:43 am
content: I'd suggest that you use a suitably rated IGBT and commutation diode with a decent gatedrive circuit - this will easily turn off in less than 1ms.Use a suitable commutation diode to provide a path for the inductive current to flow after the IGBT is turned off, and at switch off, use a Vce clamping circuit to keep the IGBT on for the short time it takes for the diode to reverse recover and switch on. Exceeding rated Vce is bad (avalanche breakdown).Basically, a Vce clamping circuit monitors the voltage between the collector and emitter of the IGBT, and if it starts to approach the maximum Vce rating of the IGBT, it lets current flow into the gate of the IGBT to delay turn off (yes this produces high disipation in the IGBT by prolonging turn-off, but only for long enough for the diode to reverse recover).A "desaturation protection" circuit can be used to monitor Vce when the IGBT is turned on - if Vce is too high when the IGBT is turned on, then the load is probably drawing too much current (eg a short circuit), but the good news is that if you turn the IGBT off within a few us of desaturation, it will probably survive (provided that your circuit trips out and stops instead of hitting it with another desaturation event at the start of the next PWM pulse).Cheers

author: oldway
author_rank: Super Contributor
timestamp: August 10, 2016, 12:39:26 pm
content: In my opinion, to break 1000Vdc § 1000A (dc and not rms because rms is only if there is ac current or ac+dc current) in <1ms, that's means that this current must be interrupted in the load.Interrupted = no current at allThen you can'tUse a suitable commutation diode to provide a path for the inductive current to flow after the IGBT is turned off,(this what we call "free wheeling diode") because inductive current will flow in this diode and in the load still after IGBT has interrupted the current, during a time depending of the time constant L/R of the circuit.This can be more than 1ms.In an inductive circuit, you must make a "hard" breaking of the current to minimize the current breaking time.

author: CM800
author_rank: Frequent Contributor
timestamp: August 10, 2016, 01:15:37 pm
content: 4500V 1200A IGBT?http://www.infineon.com/cms/en/product/power/igbt/igbt-module/igbt-module-4500v-6500v/FZ1200R45KL3_B5/productType.html?productType=db3a30443dd17fb5013dd44a98aa02a5Fail that, yes, vacuum spark triggered spark gaps.

author: MagicSmoker
author_rank: Super Contributor
timestamp: August 10, 2016, 01:22:24 pm
content: Quote from: oldway on August 10, 2016, 12:39:26 pmYou can use a capacitor on the supply side of the IGBT to provide a pathway for energy stored in the supply inductance. On the load side a gas arrester tube or MOV or the like can be used to allow the flyback voltage to climb to a value that both the IGBT can tolerate and which provides for rapid demagnetization of the load side inductance.EDIT - corrected "freewheeling diode" to "capacitor"

author: oldway
author_rank: Super Contributor
timestamp: August 10, 2016, 01:33:13 pm
content: I agree but with 1000Vdc and 1000A, we deal with high power.I don't know if there are gas arresters tubes or MOV's for such a high voltage and high current.

author: MagicSmoker
author_rank: Super Contributor
timestamp: August 10, 2016, 06:10:53 pm
content: Quote from: oldway on August 10, 2016, 01:33:13 pmOh sure, there are plenty of MOVs and GDTs that can handle this level of power which you can buy straight from the usual distributors. E.g. - a Littelfuse BB60 series MOV or Bourns 2097 series GDT.

author: max_torque
author_rank: Super Contributor
timestamp: August 10, 2016, 06:35:26 pm
content: Lots of great ideas, and the testing of those ideas would be a LOT of fun! (from a suitable distance away!)The problem with the "explosive" options is sourcing the explosives, but then i wondered about using a gaseous explosive, say Hydrogen/oxygen or even easier to source Oxyacetylene. iirc, gaseous explosions can be very quick indeed, and are easily triggered, using perhaps a modified flash tube or something similar?Hows about a gaseous explosive ram, ie a piston in a cylinder, being used to fire a projectile through a conductor, or using it to break the conductor? A secondary compressed air blast could be used for arc extinguishant for a few sec after the conductor is severed?O0

author: MagicSmoker
author_rank: Super Contributor
timestamp: August 10, 2016, 07:43:24 pm
content: Quote from: max_torque on August 10, 2016, 06:35:26 pmI seem to vaguely recall that flame front propagation isn't nearly as fast in a gaseous mixture as it is in solid explosive compounds. Maybe somewhere around 20-40m/s inside a piston engine, depending on the fuel, compression ratio, etc.Also, I thought the whole point of this thought experiment was to completely disconnect a 1kV/1kA load in 1ms or less - I would think that any kind of chemical reaction - whether an explosion or merely "rapid deflagration" - would be too slow by an order of magnitude or two.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 11, 2016, 01:13:00 am
content: Quote from: oldway on August 10, 2016, 09:33:11 amFood for thought.But no, you don't use SCRs for this, you most likely use IGBTs, a clamp diode, and a large enough snubber cap and resistor.As mentioned earlier, the problem is underspecified.As soon as you have an estimated maximum inductance figure, we can choose the IGBT, diode, capacitor and resistor, and all that's left is for you to build it (and not screw it up by adding more inductance).Tim

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: August 11, 2016, 02:05:14 am
content: Quote from: oldway on August 10, 2016, 09:33:11 amAs a shunt, to short out whatever a slower pass-device won't cut. Thyratrons have tremendous peak current handling, subby didn't specify how often he wanted to do this...

author: Cerebus
author_rank: Super Contributor
timestamp: August 12, 2016, 01:06:11 am
content: Quote from: max_torque on August 09, 2016, 06:57:09 pmSearch for "exploding bridge wire detonator". Very fast and potentially very accurately timed. Will quite happily detonate high explosives like detcord directly without any intervening pyrotechnic help. Be aware though that this is exactly what you need to trigger the conventional explosives used to generate a compression wave for an atomic bomb. Hence the high voltage parts necessary to control triggering them are tightly controlled and trying to obtain them can bring you to the attention of the kind of three letter agencies you don't want looking at you!

author: LeonV
author_rank: Contributor
timestamp: August 12, 2016, 05:15:04 am
content: How about a large copper rod, say 1 or so meters long, clamped between two electrodes. And some impact device to whack it out.Like a rocket sled, but more practically, a spring loaded hammer.Or have the copper rod spring eject-able, and make a release mechanism on the electrodes.You could have the copper rod get slammed into the other current path, but the electrodes that it gets slammed into would need to be shock absorbed, with water barrels or something, Maybe a sand dune.

author: Ian.M
author_rank: Super Contributor
timestamp: August 12, 2016, 06:59:46 am
content: The problem with anything mechanical that doesn't involve lots of high explosives, is the acceleration required. To clear a 1m gap in 1ms, assuming uniform acceleration from rest requires a final velocity of 2000m/s (Mach 5.8 ), and an acceleration of 2*106m/s2(>200000g).Assuming there was some method of suppressing the arc so that a 10cm gap would be sufficient, the situation improves slightly, as the final velocity is now subsonic, and it *ONLY* requires a little over 20000g acceleration, comparable to a rifle bullet being fired.

author: tautech
author_rank: Super Contributor
timestamp: August 12, 2016, 07:10:31 am
content: Quote from: Ian.M on August 12, 2016, 06:59:46 amMost seem to have overlooked the old style of arc suppression using contacts immersed in an oil bath.

author: zl2wrw
author_rank: Regular Contributor
timestamp: August 12, 2016, 07:55:22 am
content: At least in this part of the world, "Exploding Bridge Wire" detonators (and explosives in general) are probably much harder to get hold of than the electronic components required to fire them.A big problem with anything explosive, or even high speed deflagration (eg "smokeless" gunpowder) is that the hot gas given off by the chemical reaction is already ionised, and thus electrically conductive (google "flame rod sensor"). The nitrogen gas released by an automotive airbag gas generator (decomposition of sodium azide) *might* be cool enough to not be ionised (relatively low energy reaction compared to other pyrotechnics), though an airbag inflator will likely be far too slow a source of gas:https://en.wikipedia.org/wiki/Airbag#Operation

author: Berni
author_rank: Super Contributor
timestamp: August 12, 2016, 10:27:35 am
content: Explosives are actually being used for interrupting large currents in certain fuses.Interrupting 20kV or more on high voltage lines is not an easy task for a fuse. To help it they put an explosive charge inside the fuse that upon tripping pushes the hot arc out the bottom of the fuse and away from the terminal on the other side. They are usually used on top of poles so that if it trips it wont hurt anythyng or anyone.Testing this is actually doable since a capacitor bank the size of a night stand could provide the juice, and more importantly it becomes empty at some point in case the device failed to interrupt as maintaining the 1000A for 1 second would be pretty spectacular.I been in a lab where they test fuses and similar high power equipment, they are next to a hydroelectric dam where they are wired in to there local substation where they can pull the huge thousands of amps currents. Or they can put the power in to a giant 2 or 3 story tall power supply that generates 100s of kV for insulation testing high voltage equipment.

author: LaserSteve
author_rank: Super Contributor
timestamp: August 12, 2016, 05:50:33 pm
content: A large array of "Hard" modulator tubes in parallel. As "Hard" modulators (Big Triode or Tetrode) are in the realm of accelerators, nuclear research, classified "old school" military widgets, and old style large radars, you may not find much on them these days.There are some other technologies that can do this. ;-)Steve