Yes, interesting. The comment that ac can be transmitted more efficiently than dc I don't think is true anymore. It may have been the case before power electronics, when there was no easy way to transform the voltage of dc.
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Thanks Alehman.
For me, it's real news.
BTW, I heard about some very intresting project in the USA,
HVDC link between USA and Mexico. It's true?
Regards.
Slava
I had not heard about the Mexico project. We have a number of HVDC lines within the U.S. DC links are also used to interconnect our eastern and western grids in a few places.
So I guess maybe my I was too quick to declare Westinghouse the winner.
There are also a few projects (Nippon Telecom, French Telecom, intel and more) where DC distribution is used in "Local Area Power Systems" (LAPS). Computers and most other devices (including micro wave ovens, washing machines, lamps, drives etc) work well from DC.
Using DC distribution simplifies back-up power, eliminates harmonics problems, does away with rectifiers and electrolytic capacitors and has some other benefits, too.
I have visited two (test installation) sites where 350 V DC is being used throughout whole companies and has been so for over a year.
There is some interest in 350V+- DC power for large data centers in the U.S. The primary stated benefit being improved efficiency. I'm not yet convinced of that.
Of course 48VDC is still prevalent for telecommunications equipment as it always has been. Some of the new digital telecom equipment is shifting toward AC power.
One thing that must be considered when discussiong DC distribution is the limited nature of the application. It only works at very high voltages, too high to be safe at the "street level" where humans interract with electricity.
I think DC distribution in a building can make sense, especially with the more recent prevalence of electronic loads, and we already know that HVDC grid ties make sense. But there is a LOT of transmission and distribution in between where DC makes no sense at all.
As in all things, there is no one answer; it takes a lot of different instruments to make a good symphony. Edison should never have spurned Tesla, together they would have been able to realize the greatest potential from the outset.
Thanks Gunnar. I'm familiar with that study, but remain unconvinced.
No doubt there is room for considerable improvement of efficiency of typical switch-mode computer power supplies. Newer UPS's and computer power supplies are vastly improved over those of only a few years ago. Major server manufacturers have recognized the need for improvement and are providing much better power supplies and publish efficiency numbers. Inexpensive power supplies in typical desktop computers are still pretty miserable.
Regardless of which system is used, if the discussion results in improved overall efficiency, it is worthwhile.
Dear Gunnar, thanks a lot.
Actually, I don't know, what is very important in this forum:
Practical tips, like to setting of relay
or such topics. Lot of us are so closed with practical works
and don't know about other intresting projects and solutions.
Learn, Learn and Learn.
Best Regards.
Slava
In answer to your question regarding the connection to Mexico, that would be at any interface with the power grid of (most of) Texas which is referred to as ERCOT (Energy Reliability Council of Texas.)
Texas is asynchronously connected to the rest of the world. There are already two (and maybe more that I can't remember) HVDC connections to the rest of the world, one from Oklahoma and one at another point I can't remember and am too lazy to google.
HVDC transmission is the only way power can be sent into or out of the ERCOT grid, so any interconnects from Mexico to Texas will have to be HVDC. I would assume that connect points from Mexico to other points in the US grid (New Mexico, Arizona or California) would be AC.
This reminds me about the "zero miles" HVDC link in Japan. About half Japan has a 50 Hz grid and half has a 60 Hz grid. An HVDC link with "zero length" is used to connect these two blocks together.
Power transfer between between Texas and Mexico are mainly HVDC but they are planning on installing a Variable Frequency Transformer for a 100 MW capacity. It plays the same role as a back-to-back HVDC but with a motorized transformer instead of power electronics.
That VFT is a quite special but interesting equipment used for the first time here on Hydro-Quebec's network.
At first glance 'variable frequency' looks like a slight misnomer - 'variable phase' seems closer to the truth, although I can see how it might allow asynchronous operation of two discrete systems if it was continuously rotating at the slip frequency between systems. Maybe variable frequency is a fair name after all. Interesting design.
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If we learn from our mistakes I'm getting a great education!
O.K. It's very intresting design.
But several things, what I puted attention from first reading:
1. VFT, connection like to Japan - unvalible ( must be two grids with same freq.)
2. Only back to back connection possible. Not long transmission.
3. 100MW transmision only ( of course on this moment). Mexico link was 150MW.
4. Reference: only one project (no data about other).
5. No words like to "cost saving solution".
6. Place saving, need check with 100MW application of HVDC.
7. Low maintanance? I don't know, it's rotating and "small"
3000 HP DC motor.
Not clear something.
May be is good solution for interconnection of small grids.
I remember having read that link some time back and passing it up the management chain. I'd like to see a study of the heat loss in the VFT vs HVDC route.
My guess is that is why it is only a 100 MW device. Nice I guess if you only need to transmit 100MW.
