Power Lines

MF294-4

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They are going to have meetings in our community for a proposed DC power transmission line that is going across IL from Ks to IN. News article says they will leave a smaller footprint than AC. It's been a long time since I have been in a electronics or AC class so I can't figure this out. DC? Smaller footprint?
 
So, Thomas Edison is finally getting his way? He killed a awful lot of poor circus elephants with AC power trying to convince people how evil it was.
 
We occasionally stop in at the lock on the north end of Cayuga Lake. One time the lock master was there with everything opened up. I was looking at the old, heavy, motors, gorgeous brass handles, switches, etc. still in excellent condition. All installed in the 20's by the (Edison) General Electric Co. All still DC. Lock master explained it was DC because it had more torque. I'm no electrical guru, but I'm thinking it was DC because Edison got the bid! I assume he got the bid to power the whole canal.
Somewhere I read that someone has come up with a way to transmit DC distances? We shall see.
 
AC has alternating magnetic fields around wires. You can hear them buzzing. DC will have a magnetic field too, but it's not changing. It may really screw up a compass.

I question if this will put an end to stray ground voltages.

If I recall, our overhead cranes at a steel mill were 440vac rectified, DC.
 
DC power transmission is more economical than AC over long distances. As far as a "smaller footprint", I'd say that's all relative. You only need two lines to transmit DC, versus four or more for AC. But you will still be looking at some very large towers to support those DC transmission lines.
 
It has to do with corona, hysteresis, and RF losses. It's more efficient and doesn't lose as much per wire mile even though it usually operates at a higher voltage.
 
DC does not travel long distances well. I don't know what kind of deal this is, but there is something wrong with this whole idea. YPOP is correct.
Richard in NW SC
 
DC power transmission is hardly new technology; it's been in use for over thirty years in the US, and much longer in Europe. European countries started using it to transmit power through underwater cables in the fifties.

Simply stated, there are fewer losses in a DC transmission line than in an AC line operating under the same conditions. The downside of DC is the cost of converting high voltage AC to high voltage DC, then back to AC at the other end. For this reason, overland DC transmission lines are typically over 300 miles long. The break-even point is much shorter for underwater transmission lines.
HVDC power transmission
 
DC allows higher voltage transmission.
Edison could not just jack up the voltage to transmit long distances in the early days of DC, because transformers only work on AC. So he was stuck with his 250 or 500 Volts and that is what limited the distance traveled. Now with modern technology (presumably Insulated Gate Bipolar Transistors, or IGBT's) you can convert DC to AC efficiently; at the transmission line voltage.
Another advantage of DC is that you do not have to synchronize the power stations because the convertors do that at the conversion stations on the receiving end.
HVDC
 
I googled "high voltage DC transmission lines" and National Geographic in 2012 had an article on it. Pretty interesting, but its all in the name of making renewable energy more useful. It sure goes against everything I've been taught but there is new technology changing old rules all the time.
 
George , The cranes at Bethlehem Steel were 250 volts DC , as were the big roll motors ie 4000 HP. They were all General Electric.Very smooth and better speed control. joe
 
From my research on the links you guys provided, looks like I am behind the Times but that is not unusual. Thanks.
 
The power line has made news in Indiana for some time. Some people in Ill were saying not in my back yard you don't, NIMBY, George Carlan. There are always NIMBYs.
 
For decades, DC was the current of choice if variable speed was needed because practical and cost effective speed control of AC machines was not developed until the introduction of high power semiconductors.

On the other hand, speed control of DC machines was easily achieved using the available technology of the era.

Modern high power electronics now allow VFAC control of AC induction motors, which are inherently more reliable and less expensive to manufacture and maintain. As a result, AC machines are continually encroaching into applications once exclusively the realm of DC.

Railroad locomotives are a case in point. Many modern diesel electric locomotives utilize induction traction motors controlled by high power VFAC control systems, so-called AC traction.

The trend will continue.

Dean
 
Not DC but a look at some other power lines in use.

Here in rural Oz the problem is big distances. So we get SWER (single wire earth return). Which has its limits at about 5 hp for motors but does the rest OK.

If you're flying they're hard to see though.
 
(quoted from post at 20:40:30 11/18/14) So, Thomas Edison is finally getting his way? He killed a awful lot of poor circus elephants with AC power trying to convince people how evil it was.

Edison really wasn't a very nice guy. There's a reason he and Henry Ford got along so well...

Now Tesla, there was an interesting guy.
 
Semiconductors have made it feasible for DC transmission, it is much more efficient to transmit on DC and reduced RF.

I think it is a good change.
 
(quoted from post at 09:02:12 11/19/14) Semiconductors have made it feasible for DC transmission, it is much more efficient to transmit on DC and reduced RF.

I think it is a good change.

Not much RF at 60 cycles.
 
I can just see Edison talking to a crowd. Just stand here ladies and gentleman and watch me let the smoke out of this elephant.
 
Is it going to be straight DC or pulsating DC? Pulsating DC can still be used with transformers. AC voltage goes positive and negative. DC always stays above zero voltage, however it can still have a sinusoidal waveform just like AC it just stays above zero volts. When passed thru a transformer it becomes AC if the centertap of the secondary winding is used as the ground reference point.
 
Pulsed direct current has all the disadvantages of a pure sine wave and then some. DC transmission lines need to have clean DC (meaning no AC component) for maximum efficiency. Unfortunately, when AC is rectified you don't get DC, you get full-wave rectified DC. Consequently the power must be filtered to remove the AC component before it goes to the transmission line.
 

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:>)
 

Higher average voltage . DC voltage and current stays at it's peak value. A 120V sin wave is at zero twice per cycle and peaks twice per cycle at 169.7 volts.
Now consider how much more power those same wires and same insulation could carry at a steady 169.7 VDC.
 
(quoted from post at 19:17:06 11/18/14) They are going to have meetings in our community for a proposed DC power transmission line that is going across IL from Ks to IN. News article says they will leave a smaller footprint than AC. It's been a long time since I have been in a electronics or AC class so I can't figure this out. DC? Smaller footprint?

There are new lines being installed across Minnesota right now. (CapX2020) The new lines are higher than the existing ones around here and are single steel towers rather than twin poles like the older transmission here.

A bit of the description from their website. "345 kV poles are typically between 140 and 170 tall and will be between 700 and 1,000 feet apart. Typically, a 150-foot right-of-way will be required."
 
(quoted from post at 14:57:14 11/24/14)
Higher average voltage . DC voltage and current stays at it's peak value. A 120V sin wave is at zero twice per cycle and peaks twice per cycle at 169.7 volts.
Now consider how much more power those same wires and same insulation could carry at a steady 169.7 VDC.
aaahhhhhh..........maybe 40% more?
 
(quoted from post at 15:55:04 11/24/14)
(quoted from post at 14:57:14 11/24/14)
Higher average voltage . DC voltage and current stays at it's peak value. A 120V sin wave is at zero twice per cycle and peaks twice per cycle at 169.7 volts.
Now consider how much more power those same wires and same insulation could carry at a steady 169.7 VDC.
aaahhhhhh..........maybe 40% more?
Pretty close, 2.225 times more power iirc.
 
(quoted from post at 18:21:09 11/24/14)
(quoted from post at 15:55:04 11/24/14)
(quoted from post at 14:57:14 11/24/14)
Higher average voltage . DC voltage and current stays at it's peak value. A 120V sin wave is at zero twice per cycle and peaks twice per cycle at 169.7 volts.
Now consider how much more power those same wires and same insulation could carry at a steady 169.7 VDC.
aaahhhhhh..........maybe 40% more?
Pretty close, 2.225 times more power iirc.

Or at the same level of power. the AC 120V line looses 1.85 times more power to waste heat than a 169.7VDC line.
 

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