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Some military equipment, especially naval, has something called a "battleshort" where electrical protections can be disabled during combat, where losing equipme
by jcrawfordor 6y ago
Some military equipment, especially naval, has something called a "battleshort" where electrical protections can be disabled during combat, where losing equipment could be more dangerous than electrical hazards. It's interesting to think about whether this could be applied to DC environments, but honestly, I think few DCs actually have this kind of risk aversion for downtime. Alternatives like precautionary replacement of generators that have been oversped probably come at too high of a cost, not to mention that many of those false-positive-prone protective devices are there to reduce risk of fire.
- captn3m0 6y agoAlso on aircrafts: https://en.wikipedia.org/wiki/War_emergency_power https://en.wikipedia.org/wiki/War_emergency_power
- irontinkerer 6y ago“ the P-51H Mustang was rated at 1,380 hp, but WEP would deliver up to 2,218 hp” Wow!
- linsomniac 6y agoIndeed. I forget where I read it, but it provides that power increase for (IIRC) some small double digits number of seconds before you need to throttle back, or the engine eats itself. If you are able to make it back to base, and that WEP wire is broken, the engine needs a rebuild before it flies again. Definitely an impressive power boost though.
- tomatotomato37 6y agoThe MiG-25 also have something similar where the engine redline is marked around Mach 2.8, but there's no system stopping the pilot from keeping it maxed to somewhere above Mach 3 but damaging the engine in the process. Funnily enough I believe the SR-71 has the opposite problem, where the engines would merrily go above Mach 3.5 with no issue but the airframe and everything attached to it would get torn apart by the intense heat if the pilot tried to go any faster
- chipsa 6y agoNo, SR-71s are still limited by engine temperature. They measure the Compressor Inlet Temperature, but I suspect that actual limitation is the turbine inlet temp. That said, it'll merrily try to go above that without issue if you don't throttle back. Additionally, there's the Mach Cone. The shock wave off the nose forms a cone shape, with the angle determined by the speed of the aircraft. From the nose to the wingtip forms an angle of about 17.5 degrees, which corresponds well with the max speed from the CIT of Mach 3.3. That both methods of determining max speed agree shouldn't be surprising. Skunk Works was filled with good engineers.
- p_l 6y agoMiG-31 has limiter on engine controls connected to airspeed and mach number indicators, because the engine will happily run above Ma 3, with no issues. The airframe, however, will get bent from temperature and you better hope the missile cooling loops don't fail. The power isn't dialed down at lower speeds in order to provide thrust for maneuvering and climb.
- Unklejoe 6y agoWe use something similar on turbocharged drag (grudge) racing cars. The boost controller has a "scramble" button which overrides the preset boost targets and allows you to run a higher (and unsafe) boost level as long as the button is pressed. This is useful when you're in the middle of a $10,000 race and you're losing by a few feet.
- segfaultbuserr 6y agoWhat, this is real?! I already thought it was a Hollywood movie plot.
- Unklejoe 6y agoYes, definitely real! Although what you're probably thinking of is nitrous oxide injection. One popular manufacturer of nitrous oxide systems is "NOS", which was featured heavily on the Fast & Furious movies. The "scramble" button I'm talking about is for "boost", which is the amount of positive air pressure inside the intake manifold. Both "boost" and nitrous can dramatically increase power by essentially getting more oxygen into the combustion chamber, but nitrous is a much more dramatic effect.
- bluGill 6y agoAll motorcycle mechanics have a sign "speed costs money, how fast do you want to go". It isn't a joke, most of them can get as much power out of a 500cc motor as industrial engines get out of 19 liters. The catch is that you have to rebuild the engine every 10 hours of operation, while the industrial engine will run non-stop for many years.
- blaser-waffle 6y agoThose industrial engines also don't turn you into a meat crayon if you make a minor screw-up.
- bluGill 6y agoSure they do, run away engines are a real problem. They will sometimes start using their own oil as fuel, and at that point you better run. (modern engines have safety air shutdowns)
- kitteh 6y agoA320 and B737 had special thrust bump modes for short fields like KSNA. Going back many years to the P&W JT8D you could operate in the red provided you did it for only a certain amount of seconds and logged it down.
- repiret 6y agoIn general aviation aircraft it’s quite common for there to be time limits on the highest power setting.
- p_l 6y agoThere's a maximum power mode selectable on the FADEC interface, which gives you at least 30 minutes of engine life - any use means the engine needs total overhaul. This mode is pretty much reserved for go around or post V1 takeoff when one engine on twin engined airliner had failed.
- wvh 6y agoMany years back I had the opportunity to visit one of those data centres at the heart of Europe's financial operations. In case of fire, you had a minute or so to get out, because then the place is pumped full of argon. I guess that's a DC variation of your "battleshort"...
- dividedbyzero 6y agoWhat would they do in case of injured/incapacitated people in there? Seems conceivable that some things that could start a fire might cause that as well.
- brewdad 6y agoName a server rack after those who gave the ultimate sacrifice.
- frabert 6y agoInteresting, one of the guys that worked on my Uni's DC told us that the fire suppressor system is interlocked: to enter the DC, you need to open a door using a key. Upon opening the door, the fire extinguishing system is disabled, and is only enabled when the door is closed. The people working in the DC are supposed to keep the key on themselves. Also, they used Halon 1301 instead of Argon as the gas.
- nine_k 6y agoMost of military equipment is built to be able to operate outside the safety bounds, because the enemy in a battle is actively trying to push it outside these safety bounds and outright destroy it. Burning down your afterburner chamber and winning a fight is better that preserving it and losing the whole aircraft. In a datacenter though your bets are usually much lower. Nobody is going to die, or lose many millions, if some of your equipment shuts down to prevent it from being damaged, catching a fire, etc. There are though high-stake situations where you want exactly that: spend the entire amount of the resources of certain hardware to prevent a loss of life, or of untold millions, when you are powering a surgery chamber, or a large stock trading operation. People who realize that do over-provision and pay top dollar for that when they can afford that. I remember that when a major fire occurred in one of the skyscrapers in the financial district of NYC, traders of a particular financial company were evacuated with their laptops into helicopters on the roof, and ferried to a spare office across Hudson river, in NJ. To minimize the impact of that, they connected to the corporate network via their phones as hotspots, and kept trading while airborne. Of course one cannot hope to pull such an operation off without extensive preparation and likely regular drills. Not preparing to a black swan event during a high-stakes event, like translation of a Superbowl match, sounds like either not having enough paranoia which is professionally required, or, more likely, as a cost-cutting after a wrong assessment of risks.
- brianwawok 6y agoThat sounds a lot harder than having half of each team in two separate buildings. If one needs to shut down the secondary team just takes the full load...
- nine_k 6y ago(1) I don't think the other building was an office they kept full-time; it could even have been a hotel. (2) Think about hiring twice as much senior programmes, just in case. Good day traders are even more expensive.
- blaser-waffle 6y ago
- btown 6y agohttps://en.wikipedia.org/wiki/Battleshort https://en.wikipedia.org/wiki/Battleshort > According to Allied Ordnance Publication AOP-38-3,[1] a NATO publication, a battleshort is "The capability to bypass certain safety features in a system to ensure completion of the mission without interruption due to the safety feature." It also says, "Examples of bypassed safety features are circuit overload protection, and protection against overheating". > For example, the electrical drives to elevate and traverse the guns of a combat warship may have "battleshort" fuses, which are simply copper bars of the correct size to fit the fuse holders, as failure to return fire in a combat situation is a greater threat to the ship and crew than damaging or overheating the electrical motors. > Battleshorts have been used in some non-combat situations as well, including the Firing Room/Mission Control spaces at NASA during the manned Apollo missions — specifically the Moon landings. As a side note, with great apology to those who may have lost their lives due to the consequences of real-world battleshorts - this is actually a really interesting analogy for the "war room" scenarios we find ourselves in at startups. Risking damage to morale and productivity can be acceptable if the alternative is irrecoverable loss of the startup's reputation. But this also can't be a sustained state of affairs - these types of procedures are meant for a battle, and risk compounds if you don't return to a steady state. Perhaps adding "battleshort" to our lexicon would make it clear that "doing things that don't scale" is often necessary but not without its costs.
- helldritch 6y agoThis is one of those comments I so rarely see where what I already know is put in to words I've never been able to find. Thank you for this, I'll be updating our documentation to include these concepts first thing tomorrow.
- vosper 6y ago> Perhaps adding "battleshort" to our lexicon would make it clear that "doing things that don't scale" is often necessary but not without its costs. ... And 6 months later marketing people will have commandeered it, without regard to the original meaning, and they’ll be asking people to battleshort so they can really be agile and lean in on providing air cover via the updated sales deck.
- imgabe 6y agoElectrical codes in the US are very clear that they care much, much more about preventing fires than preventing loss of power. The one exception is the fire pump that provides water pressure to the sprinkler system, since if that's running there's already a fire. The owner of the datacenter's aversion to downtime is not going to be a concern to the building inspector or the fire marshal.
- zaarn 6y agoFire supression systems basically run their own electrical code. At one of my previous workplaces I learned a bit about our local firecode in relation to electrical code. Mostly that firecode supersedes electrical code. The fire alarm is running of a 230V line (standard) without grounding (non-standard) via a special line from the upstream power transformer that has higher amperage tolerance. All the fire detectors are powered and wired from this at 40-70V, no ground or if there is a ground, it's grounded at the control panel of the fire alarm system. In the event of a fire, the entire system is rated about 10X over it's standard ratings. The wires that are allowed to handle 1 Amp before are now allowed to go to 10 Amps, just in case there is a short this might burn it out and allow other equipment to operate. I've seen some systems that are "optionally fused", they have an internal relais that's held by external power and if the fused lines fail, it automatically switches to unfused power, where the alarm system can evaluate the condition and decide to go back to the fused line if power returns. That's on top of having it's own backup batteries. Some of the more modern systems have watchdogs systems built in so that in case the fire alarm computer is on fire, it won't switch to the unfused line once the computer is no longer operational.
- angry_octet 6y agoI think you will find that those circuits use isolation transformers and have no path to earth normally -- if you touch active and normal building earth there is no circuit. At to amperage ratings, don't you just mean that they have a 10x safety factor? Probably using current limiting supplies that can handle a short circuit. Fire circuits (and the feed from the main panel) should use fire rated cabling -- generally mineral insulated copper sheathed cables. Most of the standards (NFPA 75/76) are moving away from being prescriptive to being risk or performance based though, so it is possible they used normal conduit if the overall risk was small. Incidentally, hospitals also make extensive use of isolation transformers for wet areas (like emergency / ICU), to provide a local point for resetting breakers (electronically), identifying which point is tripping, etc, see IEEE 602-2007. Much better filtering for medical equipment too. You also tend to see positive retention plugs (in the US, green dot UL 817).