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cj1150gs

What if the power grid fails?

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>and the fans cannot be stopped by the VFD.

A little side explanation here -

VFD's are inverters; variable frequency drives that can synthesize drive waveforms to allow better control of AC induction motors. "Standard" induction motors spin at some multiple of 60hz (usually 3600 rpm) but they can waste a lot of power, since without direct control of the drive waveform you can't control speed and torque independently. You can still use them for tunnel motors in this mode of operation if you have adjustable pitch fans, so the motor RPM can stay constant while the fan pitch (and thus airspeed) changes.

VFD's allow you to do away with the variable pitch fans since they can be operated at any speed. They operate at the lowest possible voltage at a given speed (set by both voltage and frequency) to save power. Good VFD's do vector control, where the slip angle is controlled to maximize efficiency.

To stop the fan, you can just short all the motor leads together; the power is dissipated as heat and the motor stops quickly. A lot of systems use this as an emergency stop since it can be implemented as a fail-safe. To stop it even faster you can reverse the slip angle and actually torque the motor to a stop very rapidly. This wastes power so there's usually no good reason to do it. You can also regen the motor and change the slip angle so the motor is actually feeding power back to the inverter. Trains do this (to recapture some of the braking energy) but there's no reason for tunnel fans to do this because they spin down so fast on their own. Setting the motor to zero torque (effectively disconnecting it from power) is the "safest" way to shut down the motor since it doesn't stress the motor or the drives.

This is just an overview of what VFD's can do. Tunnel power systems can be programmed to do whatever you like with the VFD.

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I know I said I wouldn’t say anything else, but I just got off the phone with the company that designed and built the control system for SVCO, discussing other issues. Since I had them on the line, I brought this question up.

The fastest way to stop the wind is to either take the throttle to zero or hit the stop soft key on the screen. At that point, the motors are generating power, which is dissipated by the VFD’s through resistors converting the power to heat. This acts to brakes the motors or slow them down faster than if they were simply disconnected from the VFD’s. The next slower way for the wind to stop is to hit the e-stop. This stops power to the motors instantaneously. They are free to wind down without the braking action caused by converting the energy they are producing to heat though the VFD’s. The slowest way for the wind to stop is if the incoming power grid fails. The VFD’s sense the loss of power, use residue power to soften the power loss, keeping the motors going as long as possible and allowing the motors to wind down without the braking action caused by the VFD’s.

It takes about 15 seconds for the wind to reach 30-mph after taking the throttle from 90% to zero. It takes about 45 seconds for the wind to reach 30-mph using the e-stop from 90%. It would take even longer for the wind to reach 30-mph from 90% if the power grid failed. I am able to hop in, pop up to the bottom of the turn vanes (about 40-feeet), come back down, stop, and back out the door all after the throttle has been reduced from 84% to zero. If the power grid were to fail, there would be more wind, longer, since the braking action of the VFD’s wouldn’t happen. You would not crash into the net.

So there you have it. Testimonials from Instructors that have been flying when the tunnel shut down, testimonials from flying in the tunnel after the wind has been cut off, and information from the designer of the system.

If this doesn’t convince everyone that you are in no danger in the event of a power grid failure while flying at Skyventure Colorado, then I do not know what will.

So, Paulipod & JP, please stop trying to convince our clients that they are at risk.

Now I am going to go put on my snowboarding stuff and see of my street is steep enough to board down since there is 2 feet of snow out there.

Derek

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So, Paulipod & JP, please stop trying to convince our clients that they are at risk



Not at all at any point what I was saying.... and my reasoning for discussion isnt public perception or marketing.

All that aside I will just have to accept then that our air must have less mass to it... and our drive system must have less momentum although it weighs more... which explains why our air can decrease in speed so quickly

Been an intersting discussion though!

:)

Bodyflight Bedford
www.bodyflight.co.uk

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“So, Paulipod & JP, please stop trying to convince our clients that they are at risk”

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Not at all at any point what I was saying....



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As far as I am aware, a power outage in every tunnel built to date will result in almost instant air loss.



“how quickly will the air go from 120MPH to 0”

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Almost instantly...



You may not have intended it, but that is exactly how it came across.

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All that aside I will just have to accept then that our air must have less mass to it... and our drive system must have less momentum although it weighs more... which explains why our air can decrease in speed so quickly



I have no idea why the wind speed would decrease quicker at Bedford than at SVCO. I don’t even know that it does. What I do know is that it doesn’t decrease quickly or instantly if the power grid fails at SVCO.

I have explained that I am able to fly after the throttle is reduced to zero, and that the wind speed slows down faster with the throttle than during a power grid failure. This remains undisputed.

From looking at some pictures, I am curious what type of propeller your tunnel uses, fixed or variable pitch? How many blades? What material is it made from? How much does it weigh? What type of motor powers it?

SVCO and Bedford are very different tunnels and the wind flow reaction to a power outage is obviously very different. It would be interesting to compare the differences in rotating mass, air speeds through the air paths, air volume, and how the different drive systems react to a power loss. Clearly they are very different tunnels.

Derek

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Some things I'm curious about:
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The VFD’s sense the loss of power, use residue power to soften the power loss


In order to actually "feel" this effect, the capacitors in the VFDs would have to be huge (at a combined wattage of roughly 1 MW). Any chance to find out the capacity and voltage of them?

And another thing I'd like to know:
When I was at the Genting Skyventure a few years ago, I witnessed a power failure. Coincidently,at that time the General Manager of the Hotel/Theme Park was flying in the tunnel. He was bellyflying about 2m above the net and hit the net within a second.(Genting Skyventure is non-recirculating with "old" technology, and is therefore not comparable to the newer SV tunnels)
The power was out for at least 10 minutes, and during this time the GM was "locked" in the tunnel since the entrance door couldn't be opened. Of course, he didn't have his cellphone in the tunnel so he had no means of finding out how things proceed in "his" complex, which seemed to really piss him off...
Is this still the same, or can the door on newer SV tunnels be opened when the power is out ?

No.1 reason NOT to be an astronaut: ...You can't drink beer at zero gravity...

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Some things I'm curious about:
In Reply To
The VFD’s sense the loss of power, use residue power to soften the power loss
In order to actually "feel" this effect, the capacitors in the VFDs would have to be huge (at a combined wattage of roughly 1 MW). Any chance to find out the capacity and voltage of them?



Next time I talk to Bill, I'll ask.

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Is this still the same, or can the door on newer SV tunnels be opened when the power is out ?



At SVCO, the doors can be opened without power.

Derek

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So, Paulipod & JP, please stop trying to convince our clients that they are at risk.



Untill you said this I honestly thought you were not taking this personaly. Seems like the Colorado skydiver ego runs rampant even at the tunnel.

Re-read my posts, you'll find you've made two mistakes.

One, assuming I'm trying to convince your clients they are at risk. I've already stated the risks are minimal, though the fact you've bought into the "tunnel flying is safer than skydiving" myth is concerning.

Two, assuming no one but you or your "sources" have any experinence. I have experienced power failures in 3 different wind tunnels.

edit: spelling again
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You're not as good as you think you are. Seriously.

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I didnt want to read all the replies, just the first. but im bored and wil explain.

this all depends on the tunnel, recirculating tunnels you would probably be fine, air is really heavy, and it has a lot of inertia, so if the motors stopped generating airspeed through the fan and tunnels, the air would still have a lot of inertia, and would take a few seconds to slow and stop. i would say about 10 seconds. plenty of time for one to come back down to the net.

on a non-recurculatinf tunnel, there is still inertia, but not near as much. i would bet that there would still be enough air moving time to be lowered safely back to the net, at east at a non-injury causeing speed.

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jp you certainly have no room to talk about egos (i think you can single handedly prove beyond doubt that ego travels). leave that out of it. one of your posts clearly stated (i don't have the exact quote at this second) that a power outtage while freeflying would result in a serious potential for injury. Derek said nothing about tunnel flying being safer than skydiving. where did you come up with that? the only thing either of us has said is that a power loss at SVCO is going to be a non issue for nearly every single flier that will ever come here, in response to a post that suggested potential for serious injury. you seconded that idea (serious injury). you have not experienced a power outtage here. no one has. i don't even remember you flying in the tunnel after we cut the power using the stick. i can't speak for Derek (even though he's standing right here) but i feel that there's no need to scare anyone about a power loss. suggesting that anyone is going to be seriously hurt, with no experiential basis for that suggestion, is irresponsible. Shane has experienced a power outtage with fliers in Perris, and his experience does not match your story at all.
there's nothing personal about it, except that we work here and don't want the clients scared about something because of someone's need to post overly dramatic messages.



Say what you mean. Do what you say.

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Seems like the Colorado skydiver ego runs rampant even at the tunnel.



That statement is not only disappointing, it's untrue. JP, I thought better of you.

But I'm sure being the hot skydiver/tunnel rat that you are, you have no recollection whatsoever of who I am.[:/]

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Genting Skyventure is part of a large casino/theme park/shopping complex built on a mountain north of Kuala Lumpur, Malaysia.
http://www.genting.com.my/en/themepark/skyventure/index.htm
It was the first publicly accessible vwt in asia.


(edited for clicky)

No.1 reason NOT to be an astronaut: ...You can't drink beer at zero gravity...

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Boys and girls of all ages...

I have the perfect solution.

Twice I have made "boo-boos" (not my fault, I sware) that have resulted in the power grid faulting. The last time the power outage was from Yosemite to Quebec, Dry Creek to Arapahoe... So, just a small section of the grid in the big picture, but enough to make a statistical sample.

Granted, my boo-boos discovered maintenance issues in the grid slightly upstream of my connection to the grid, so we will have to recreate these problems, but the results usually equates to a square mile outage.

So, why don't I come to the tunnel and tinker with the grid while someone is flying, and we can see what happens!

Perhaps a little more "safe" approach would be just to flip off the service disconnect to the building and watch the results in the tunnel, however one would argue that this is not a true test as the disconnect would provide infinite resistance on the "grid" when turned off, whereas faulting the grid would provide the opposite, near zero resistance...

So the only true test would be to allow me to play.;)

Should I call Park Meadows Mall and tell them of the pending power outage the day before Christmas, or do you want to make the call?

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I for one have experienced many tunnels round the world and none of them compare to SVJP. This tunnel will never lose power, it's so good, just ask it. Unfortunately the air is the hottest of all the tunnels with the air being thick like poop. In order to fly in it you must wear boots the shit is so thick. This tunnel has a personality of it's own. The tunnel casts off an arrogance to it's flyers unequal to any other tunnel in the world. This tunnel is unbelieveably arrogant and condescending to everyone that flies around it. And this tunnel talks about ego? Give me a break, that's the tunnel calling the asphalt black. As pope said, insert state here. In this case, I think everyone in this thread is happy to not be in the presence of SVJP. SVJP needs to do a systems check and take a look at itself and realize, nobody likes the way it operates.
Don't understand what I'm saying, that's fine. Those that do unfortunately do.
Doing business as=SVJP There is only one person that will get that. let's keep that between the 2 of us, as my identity.

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So there you have it. Testimonials from Instructors that have been flying when the tunnel shut down, testimonials from flying in the tunnel after the wind has been cut off, and information from the designer of the system.



I thought I'd contribute a video I have to the discussion. A couple of years ago, and the very first time I got into a tunnel, the power failed right after I entered. I "heard" the power fail more than I felt it and knelt on the grate for a bit trying to figure out what I had done wrong before I figured it out. :$

As noted, after I captured and compressed the video it's a little choppy and not quite real-time, but it's only a little bit slower than the actual event. You can see that I get placed on the grate pretty gently.

The power fails about 10 seconds into the video.

http://www.youtube.com/watch?v=t0HYQlpV-wE
Owned by Remi #?

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A breaker tripped and the fans lost power.



The main supply to all 5 drive units failed? Or one drive unit had a fault, and the control computer told the other 4 drives to go into shutdown?
----------------------------------------------
You're not as good as you think you are. Seriously.

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I'm really not sure. We were there after a huge storm mid august 2004(hurricane charlie maybe?) and the folks at the tunnel said that they were having trouble getting a part for the motors because all the power outages and problems after the storm had caused huge demand. We waited through the night and into the next afternoon before they found one.

When they got the part and opened the tunnel it ran for about 5 minutes before the power failed.

They described the part as a breaker of some sort. When the motor(s) failed we were told that the breaker had failed. I didn't ask detailed questions.

It hadn't occured to me to worry about a power failure before it happened, and after it happened I didn't worry about it because it caused such a gradual decrease in speed.

Edit to add: That's Omar in the tunnel with me. He might remember (assuming there aren't many power failures at SVO)
Owned by Remi #?

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I didn't see the lights go out.***

it just doesn't matter what everyone else says, does it JP? even a video of someone flying in a non recirculating tunnel that loses power doesn't prove to you that the flight didn't "immediately" stop. you're so intent on finding a flaw in the power loss that makes it not qualify as the power loss you're looking for. what's the point of even having a conversation if there's no potential for change? the guy who actually experienced it said he heard the failure rather than felt it, and was gently set back down on the net. seems reasonable that a higher windspeed, like freeflying speed, would take even longer to set a person down. flying in a recirculating tunnel would take even longer.

if the lights had gone out, then you could say that there was no video to prove that he actually didn't crash to the net, huh?



Say what you mean. Do what you say.

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