Відео

Usually a big rotating mass, coupled to a generator and motor.

Sometimes you can hear the drop in frequency

No power company will let you connect a direct short 😊

@@brauchmernet Makes a lot of sense haha

Being very close to a step - down transformer for one, having very short (relatively) cables from source to consumer with low impedance that's two, being close to a massive generator like a turbine that's three, this was AC but DC may do just the same a d DC can be capacitively stored that's five... many scenarios. But such tests are proof of satisfactory operation for worst-case scenarios, where the clamps have to obviously perform as intended. Limits are intentionally pushed. This is, by all accounts, textbook definition of destructive testing.

Is Skin Effect really that shallow? at audio

@@jagmarc skin depth is around 0.5mm at 20k in copper

The power levels required for this tests are the main reason why the are only made in certain testing facilities.

So someone has jobs...

I would assume that the cables are sufficiently restrained and none of the clamps gives way during the short-circuit.

For 50/60 Hz AC 10 to 20ms is about one half or one whole cycle. I would be skeptical that overcurrent or other fault detection can interrupt fault current that quickly. Putting that aside, in the first clip with just cable ties, you can see that a lot of momentum is imparted to the cables even during the first one or two cycles. Based on this I would guess that this momentum would go on to break the cable ties, even if the fault current was interrupted and so no new acceleration was taking place. I would love to see this test though!

@@pierrekinbrand modern fast acting fuses can interrupt the overcurrents in such short time.

@artyomsyomushkin1104 thanks for sharing this fact, I was unaware. Frankly that's amazing.

I had to solve a problem like this in my electromagnetics class. Currents in the kA range can generate thousands of tons of reaction force as the gaussian loop "tries to" expand to admit more flux. You can integrate F over time but like @avoid3dsa says I think it all comes down to the mass of the cables and their momentum once they get moving. Copper is really dense! The answer to the problem my professor wrote was some insanely huge force that no clamp could withstand, but he wanted to make sure we were checking our work.

Yes, it's to retain the cables in the event of fault currents. The cables will whip about due to the extremely large magnetic forces that are generated when a very large fault current flow. Don't know if it's on UA-cam but I saw a film of some very high-capacity fuse tests in a high-voltage cabinet where the cables weren't secured sufficiently and the cables broke away and whipped about causing secondary flashover, short circuits and fire.

Most likely this was not 275 kV: the air-gaps between the conductors at the feeding end would be far too small to sustain that voltage. Short circuit tests like these are most likely more down to check if the cables sustain physical damage (or even total failure) in short circuit conditions considering the forces the cables, supports and cleats have to endure. Thus it's more about Amps than Volts.

Given the quality of the short, I’d assume on the order of 0.01 ohms, and 63kA, ignoring reactive components puts the voltage under 1kV ballpark. I’d guess for the 63kA desired fault current they used their 12-ish kV phase-phase transformer, whatever that is in 50Hz land, and interrupted its primary side to control the experiment, which was really well thought out though today would be worthy of 4K 120p, a photographic scale backdrop, and a nice 200mm lens. I’ve seen a small 2kA inrush make 4/0 awg (100-ish mm2) get up and dance in a 100 foot long aerial drop. Those clamps performed admirably!

@@swsuwaveI think so too. Conductor-to-conductor resistance is the most important factor here and most likely will have been accurately measured before testing commenced. Not only because it's a test, but because this is done in the field in real-world situations as well. Judging by the massive short they create and the slight decrease in frequency that can be heard, this was done using a rotary converter or even a flywheel-converter (They had one in the past if I remember it right, don't know if they still do). This all to keep the national grid from sustaining severe dips whenever they would perform a big short circuit test. You can hear the effect quite clearly in these videos: ua-cam.com/video/le3-fwsDxLs/v-deo.html and ua-cam.com/video/igh6Cj3C9pw/v-deo.html I have no idea if the clamps passed the test or not ;) sometimes tolerances are down to minimums we can hardly imagine considering the forces that strain those cables during a short. If you're in for a bit of a bang, this is definitely one to watch ;) ua-cam.com/video/avppv8ljRVo/v-deo.html

Video shows how two different bundling methods cope forces occuring during short circuit. Short circuit situation has multiple times more current going through cables than normally would. That generates electromagnetical forces that make those cables move like that.

@YAKUMO RAN Yeah!Me too! I think very strong transformer need be used too. Something with 1MW of power:)

@@joe125ful We have had a massive short circuit fault in The Netherlands in september 2022 that did this: ua-cam.com/video/9JKgGESux94/v-deo.html Some of the research indicated the distribution line that sagged carried 4 or even 6 times over it's maximum amount of current. At some points the lines were 50 cm's from the ground due to how exceptionally hot they became. This happened after a couple of safety systems had been deactivated for maintenance, and the last-resort type of system still active, failed spectacularly. Downstream city substations started noticing things were off due to stray voltages (a line contacted the ground and caused grounds in other systems to become disrupted) and voltages on phases that were way above normal (240V is normal, but some neighbourhoods saw 380 or more) and decided to kill power, eventually stopping the problem upstream. The sagging line also came into contact with the 1500VDC overhead wiring system that our regular trains run on, causing people to witness breakers in the poles to explode or catch fire, along with stray currents (and very high ones at that) trying to find their way from the rails into the ground making the ground smoke. We had a drought at the time and it we were INCREDIBLY lucky this didn't spawn several massive wildfires, nor were there any injuries.

In some cases, testing for the most common errors or types of short circuit. In other cases it is merely a case of: "So, we designed something according to what we know about material specifications, and now we want to know how it behaves when there are fault conditions. We want to know what safety precautions to take, or if it's a case of "back to the drawing board."

Mwah, toch moet je niet onderschatten hoe erg dat al fout kan gaan ;) Maar toch sluit ik nog liever een gewoon 16A beveiligd stopcontact kort dan een gemiddelde accu.

@@weeardguy Zeker, maar alles goed onderverdelen in lagere groepen...

And that's RMS, so at DC level. If they used 50Hz AC (which I assume), you'd see 63000 A * 1.41 = 88830 A peak current. Ouch.

@@adev8565 electric arc furnaces use 40,000+ amps and 80 MVA or more.

nah, not really

In a short circuit test the voltage would be theoretically zero.

Probably 275.000 volts KEMA can generate this voltage and current without any problems.

@@jameswest8280 That would only be if the cables were superconductors, so in theory it should not be zero but sure much lower than the power source voltage.

@@teresashinkansen9402 true, there would resistive and inductive losses. Not sure what the voltage drop would be, I imagine a few hundred volts.

The lower the voltage, the higher the short circuit amps, also the resictance Counts