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Mark J

Used SawStop

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On 6/4/2019 at 2:43 PM, drzaius said:

And there ain't no such thing as 110 either :)

I feel like we're making the world a better place here, 1 post at a time.

What if we say the intermediate and go 115/230?

My house measures out at 123 no load. The regulators on the sub down the street are set to deliver 125 so during summer AC loading the house never drops below the 5% code standard.

On 6/4/2019 at 10:22 PM, wtnhighlander said:

Did anyone happen to recall that Edison's original 110 volt distribution was a DC system? Imagine the number of generating plants needed to avoid distribution loss over distance! We should be grateful to Westinghouse and Tesla for bringing three-phase AC to the market.

Maybe Drzaius will correct me but I'm pretty sure we have a fair amount of DC transmission in the US and Canada. I know for a fact there is at least one that is feed from the Milton R Young Generation plant in Center, ND. It's the Square Butte HVDC line. One of my Christmas gifts when i was younger was wrapped in the wiring blueprints for the plant relay for the line. I don't know why i remember that.

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1 hour ago, Chestnut said:

What if we say the intermediate and go 115/230?

Inaccurate is still inaccurate

1 hour ago, Chestnut said:

Maybe Drzaius will correct me but I'm pretty sure we have a fair amount of DC transmission in the US and Canada. I know for a fact there is at least one that is feed from the Milton R Young Generation plant in Center, ND. It's the Square Butte HVDC line. One of my Christmas gifts when i was younger was wrapped in the wiring blueprints for the plant relay for the line. I don't know why i remember that.

Any DC transmission in Canada or US is experimental. There was the big fight about it back in the Edison days, but AC won out. Now DC is being looked at again. The biggest hurdle that DC has faced is the issue with transforming the voltage up for transmission & back down for end usage. No such thing as a DC transformer. Now, with the advance in electronics, that is becoming more viable. High voltage DC transmission is more energy efficient because there are no inductive or capacitive loses.

Edit: I just did a little reading & it seems that high voltage DC transmission has indeed moved beyond the experimental stage, at least for long distance lines. The majority is still AC though.

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That's why AC won out in the late 1800s, DC resistive losses are high in low volt/hi amp circuits. Before the advent of vacuum tube, and later solid-state rectifiers & transistors, there was no simple way to transform DC. Much of Tesla's high voltage / high frequency experimentation DID use DC supply, but required a mechanically complex rotary spark gap device to "chop" it into pulses, achieving a similar affect as AC.

One other problem with high voltage DC transmission is arc blast. AC crosses the zero-potental point every half-cycle, so any arc from a short-circuit extinguishes itself quickly. DC arcs will continue to grow until the air gap between contuctors increases beyond the potential ability to sustain the arc plasma, or some protective device interrupts the circuit. For the same reason, protective devices require much heavier shielding than similar devices in AC circuits.

Coincidentally, I drove past a local high school yesterday, just as some group was doing a ceremonial balloon release on the front lawn. 'Mylar' balloons. One of the aluminized plastic streamers hung the 3 phase powerline overhead, and created a briefly spectacular lighting flash, and dropped enough voltage to crash the traffic light controller at the next intersection. Had the line been DC, that arc would have looked more like a battle between Thor and Thanos.

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8 hours ago, wtnhighlander said:

That's why AC won out in the late 1800s, DC resistive losses are high in low volt/hi amp circuits. Before the advent of vacuum tube, and later solid-state rectifiers & transistors, there was no simple way to transform DC. Much of Tesla's high voltage / high frequency experimentation DID use DC supply, but required a mechanically complex rotary spark gap device to "chop" it into pulses, achieving a similar affect as AC.

One other problem with high voltage DC transmission is arc blast. AC crosses the zero-potental point every half-cycle, so any arc from a short-circuit extinguishes itself quickly. DC arcs will continue to grow until the air gap between contuctors increases beyond the potential ability to sustain the arc plasma, or some protective device interrupts the circuit. For the same reason, protective devices require much heavier shielding than similar devices in AC circuits.

Coincidentally, I drove past a local high school yesterday, just as some group was doing a ceremonial balloon release on the front lawn. 'Mylar' balloons. One of the aluminized plastic streamers hung the 3 phase powerline overhead, and created a briefly spectacular lighting flash, and dropped enough voltage to crash the traffic light controller at the next intersection. Had the line been DC, that arc would have looked more like a battle between Thor and Thanos.

The protection equipment on the DC lines are capable of tripping out in very few cycles. I don't remember the number or exactly how long a cycle is, i could find out if you'd like. The result is they are able to trip off DC lines as fast as AC lines so the arcs would for all intents and purposes look the same. You would never see DC in distribution lines though that is just too complicated. HVDC pretty much runs from generation to the first substation and then gets converted to AC for distribution. We're talking huge lines in the 500 Megawatt range. None of the lines this big ever make it close to a town or city but I know things are different out east.

10 hours ago, drzaius said:

Inaccurate is still inaccurate 

I was making a joke due to the short period in the US where the standard was 115/230. I'm that pedantic guy that corrects people when they say 110/220 as well. The people that bother me the most are the ones that say 120/220 .... how in the heck do you double 120 to get 220?

 

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Search youtube for high voltage arc flash & you'll see some spectacular results. A few years ago in downtown Calgary there was a failure in an under ground vault. It blew the manhole cover off & it looked like a giant blow torch shooting out of the hole. 

A DC arc is much harder to extinguish for reasons stated by @wtnhighlander. In school they had a test console for connecting simple lighting & switching circuits. The voltage was 120, but for some reason it was DC, not AC. When the instructor had his back turned, we'd hook up several 100W light bulbs in parallel & then slowly pull the wire away from the hot terminal. You could easily get an arc an inch or more long. Doing the same with AC will only yield an arc a fraction of an inch.

I had occasion to experience and arc flash up close & personal once. Not youtube worthy, but it was enough to leave my pants & shirt in tatters & my belt & tools plated with a coppery sheen. Very scary stuff & it profoundly changed my attitude about safety procedures.

What was this thread about? I think it's been well & truly derailed. Sorry OP.

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1 hour ago, drzaius said:

Search youtube for high voltage arc flash & you'll see some spectacular results. A few years ago in downtown Calgary there was a failure in an under ground vault. It blew the manhole cover off & it looked like a giant blow torch shooting out of the hole. 

A DC arc is much harder to extinguish for reasons stated by @wtnhighlander. In school they had a test console for connecting simple lighting & switching circuits. The voltage was 120, but for some reason it was DC, not AC. When the instructor had his back turned, we'd hook up several 100W light bulbs in parallel & then slowly pull the wire away from the hot terminal. You could easily get an arc an inch or more long. Doing the same with AC will only yield an arc a fraction of an inch.

I had occasion to experience and arc flash up close & personal once. Not youtube worthy, but it was enough to leave my pants & shirt in tatters & my belt & tools plated with a coppery sheen. Very scary stuff & it profoundly changed my attitude about safety procedures.

What was this thread about? I think it's been well & truly derailed. Sorry OP.

I wasn't saying anything about the dangers of DC arcs just that the relay and protection equipment will trip the line in milliseconds if a fault occurs on those lines. Hawks are a huge pita for the transmission lines as the defecate every time they take off which causes a lot of faults.

I think it was about someone buying an expensive saw and using it as a storage table.

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49 minutes ago, Chestnut said:

I wasn't saying anything about the dangers of DC arcs just that the relay and protection equipment will trip the line in milliseconds if a fault occurs on those lines

Yes, design of HVDC relays & circuit breakers is vastly more difficult than AC.

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1 hour ago, drzaius said:

What was this thread about? I think it's been well & truly derailed. Sorry OP.

Not at all!  As long as this doesn't turn into a power struggle (see what I did there).  I'm learning as much as anyone.  

I might have some other questions about that saw when I finally get around to tuning the arbor tilt, but that won't be for a while.  

48 minutes ago, Chestnut said:

I think it was about someone buying an expensive saw and using it as a storage table.

And for the record it was a discounted expensive saw being used as a storage table.  :rolleyes:

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1 minute ago, Mark J said:

I might have some other questions about that saw when I finally get around to tuning the arbor tilt, but that won't be for a while.  

If it didn't come with the manual, you can download it from the website. I know the PCS manual explains and illustrates things well. Were there shims under the top when you took it off?

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Nope, no shims.  The alignment with the miter slots was easy, but I have to read the manual on the tilt alignment.  It just hasn't gotten to the top of my to do list.

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