Where Does the High Voltage Originate?

The only plant I have figures for is Dinorwig, UK.

Motor/generators 18kV 330MVA (generating) 312MVA (motor)

Export voltage 400kV

Exactly what I wanted to know - the explanation of that figure in the article!

The document of which this drawing is a part is very informative, very interesting, and, being presented to "The Management", more or less couched in layperson's language (to be PC about it). As a result, and because it is a look at WHY, and HOW the grid failed in the entire Northeastern USA and parts of Canada in 2003, and what was done, and can be done in the future, both to keep this kind of failure from happening again, and to soften the blow of any future failure for whatever reason, it is a fascinating read.

Of course, the first couple of sections are all about the importance of the people presiding over the study, but once you get past that to the work the of contractors studying issue, it gets down to the meat, past the fluff, and gets very informative and interesting.

Good read, even if it does go WAY beyong Mikerho's original question. In fact, though it is a 50 page pdf, I archive it to my hard drive for further perusal. I found a LOT to learn from it. Thanks for posting the pic that led to it.

I apologize. To correct my own error (and perhaps not discourage others from downloading/reading the report) it is only a 30 page pdf, not the 50 I mistakenly cited.

And I'm on page 18, and still cranking. It makes VERY educational reading, IMHO.

Glad you liked it. That report is the summary report of a very large document. The complete report is a "must have" document for any insomniacs looking for a drug free treatment. The index at the front of my link refers to the over 200 pages of the full document.

And what it all boils down to is that the lines shorted out on adjacent untrimmed trees, but since no one told anyone else about it, and the management functions thus didn't know, and weren't watching independently for the related overloads to occur, nothing was done in the 30 minute window which COULD have fixed it before the cascade became catastrophic. So, trim the stinking vegetation. And watch your load indications. And communicate. And if you are supposed to be the "backstop", by being aware of what is happening, for Pete's Sake, BE AWARE!

Seems like a whole lot of folks had to fail at a whole lot of fairly small things, but all of them were the "We should have done this before, and then we wouldn't be here" variety, as opposed to the "What in the world just broke? We couldn't have seen that coming!" category of events.

This was all stuff that, reasonably, if the entities involved wanted to feel qualified to operate, they should have been doing it. And the policies and procedures were apparently in place and vetted, albeit the report acknowledges that some of the P&P were somewhat ambiguous.

I do note, though, that any wide-scale terrorist attack on the infrastructure is going to require a large group of very well coordinated teams working together to make any truly wide-ranging damage occur. This is due in part to the number of layers and the number of watchers it would be necessary to plan for, if any such attack were to succeed.

They key word is transformers. A transformer basically consists of two coils of wire and an iron core. When you put alternating current through one coil, it magnetizes the core and induces current in the other coil.

The more turns in the second coil, the higher the voltage and lower the current. Since power loss in transmission lines is due to current, transformers are used to step up the voltage (and lower the current) as high as practicable for transmission over long distances and step the voltage down at the user's end.

Already know transformer theory, but thanks anyway!

just another terrorist looking to know where to find our Achilles heel huh?here's a tidbit. AC and DC differ for some obvious reasons, as AC prefers to travel closer to the outside diameter of the wire rather than the center.transmission lines are often hollow at points of higher voltage to keep weight down

Thanks for that!

Slang of high voltage in naughty engineer's talk is an affair with one having an STD. -- Street talk, that is.

In Physics, it simply is a high pressure storage of charges.

HV AC is not an efficient means of transporting electricity. HV DC is far more efficient. and when moving HV AC at 50 or 60HZ there are many losses on the lines so, reducing the frequency to one third at 12-16.5Hz (50Hz cycles) or 20Hz for 60 Hz cycles is far more efficient and one can transmit approximately 3 times the distance with minimum losses on a line.

11kV/33kV generation into a step up Tfx (known as super grid Tfx), and then step down on the other side to the user defined voltages. Every country uses there own standard voltage which was and is set by the generator set output. Not all voltage systems are the same in transmission.

Australia uses SWER lines, (single wire earth return) at 20kV for distribution, long distance to out lying places, (farms and sheep stations). So that is a 20kV supply, Peanut Tfx at each home, stepping down to 220V.

UK uses 400kV for transmission and S Africa and much of Africa uses 765kV. China has a 1MV (1000kV), lines which transmits at +/-900kV. And Russia with the highest transmission voltage of 1150kV.

It may not be your answer bit it does can help in the direction right.

While it is true that there are less losses in DC than AC,the reason AC is dominant is the ease with which it is transformed to various voltage levels.

High temperature superconductors have made it possible now to transport very high amounts of energy with virtually no losses.

Even considering the overhead cost of refrigeration of the conductors, it is still more efficient.

Where the USA Eastern grid meets the Western grid,there is a phase difference,and the AC must be converted to DC,then reconverted to AC to match phases of the two grids.

The same where Canada and USA grid meet.

The Canada and US grids are now connected via superconductor DC.

There are several islands that are also connected to mainland grids using

superconductors now.

I am not sure,but it seems like one in New York,and one in Japan,and I am sure there are others.

Very informative.

Thank you!

More info than I originally wanted to know, but very useful nonetheless.

Thank you!

The reason for using high voltage for power transmission is simple - higher voltage means lower current for the same amount of power, and that means the wires can be a smaller gauge. In spacecraft, a 120VDC bus is used (instead of a 28VDC bus) because the wires can be smaller, and thus lighter. Same logic applies if you're building a power grid - wires are lighter, use less copper, require less structure to hold them up, etc. Also you'll see this in motor design - and electric car will typically use a high voltage motor so the winding doesn't have to be as massive. The downside is safety.

Mikerho,

You have a great opportunity to see the concept up close and personal about an hour from you in The Dalles, Or at the Celilo Converter Station. https://en.m.wikipedia.org/wiki/Celilo_Converter_Station

This is the northern terminus of what's called the Pacific Intertie system that sends HVDC power from the Bonneville Power System on the Columbia River down to Southern California. The dams on the Columbia generate at various voltages, but step to to one high voltage AC line, which goes to Celilo to be converted to 500KVDC and sent to SoCal, where it is converted back to AC again, then transmitted as AC to substations all over the area.

Can I thumb a ride?

500KVDC brings up a question in my mind. I always understood (maybe misunderstood) that DC was more "lossy" at high current than was AC, as long as the AC frequency was kept low (60 HZ, in my understanding, didn't really have "skin effect" issues) and that, along with the ability to step voltage up or down with transformers, was the prime reason we transmit AC long distances. But, if The Dalles transmits HVDC to Celilo, and the power from Columbia River is converted to HVDC, so that the whole stream can be sent to SoCal, there must be inherent efficiencies (besides not needing to synchronize phases), in HVDC transmission.

So, what don't I understand about power loss at 60HZ, vs power loss at DC levels, for similar voltage/power level transmission?

It is more "lossy" at high current, that's why you go with high voltage. Your losses in DC are just I squared R losses, so if your current is 1A, 1 squared is still one, so your losses are minimal. But 500,000V x 1A is still 500,000VA , that's a lot of energy.

OK, so, point taken. And I was aware of IsquaredR losses being much lower as current decreases. The math is simple, and clear. But I was under the (evidently mistaken) impression that these lines are routinely delivering at least MW, if not GW of power, which would obviously raise the I value to where squaring it would mean massive losses. And I know that even at 500KV, whether DC or low-freq AC, arc-over is much more prevalent than at lower voltages. Increase above 500KV and it probably gets exponentially uglier.

So, win some, lose some, and all engineering is trade-offs, but clearly, using your example limits, it would be the least "lossy" of the available solutions to run at 500KV at 1 AMP. I guess if you needed to be able to deliver 5 times the power, it MIGHT make sense to run 5 lines on the same towers, with appropriate build-out engineering.

And to avoid ANY skin effect, obviously DC is the source of choice.

Thanks.

Skin effect is just that, a known effect that if ignored can lead to unanticipated problems. It can also be used in a design to solve problems. The slightly higher resistivity and slightly paramagnetic property of aluminum allows for a significantly higher percentage of the aluminum area to conduct than copper when large core areas are needed. Additionally since the center of the cable does not conduct well anyway from this effect a steel center core can mechanically support and not add more resistance.

Thank you. I am learning a fascinating amount about power transmission. Since my training and experience was in communications system design and implementation, as well as component level troubleshooting and repair, my knowledge of High Voltage and High Current is minimal.

Except for the time I spent doing lightning dissipation and control engineering. But that is power, voltage, and current way beyond anything here. And as such, I'm guessing very little of what applies here for everyday control and delivery even comes close there.

Do not get confused here. What about AAAC on lines? They are slightly different to ASCR lines. The steel is there for a specific reason and it is not as a primary conductor but it does conduct.

Conductor weight affects tower strength, size, foundations, cost, span lengths, tensioning, and method and of course time to build the OH lines.