USA converting back to Direct Current

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No Show

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Location
Texas
I was wondering what everyone thought about this? With the renewable energy advancements in solar, wind and the latest in battery and capacitors (super capacitors) technology and the energy crunch, global warming, and oil prices. And the fact that the only reason that we began using Alternating Current to began with was for the distribution of electricity accross the US. Thomas Edison ran electricity to the first city using Direct Current, because that was all he new, and that was where he was passed up in technology by Tesla and alternating current. Most of our small electronic devices are DC, all are cars use DC, cordless drills, saws, cell phones and as far as lighting, LED is efficient and the lamps last for decades, they also can use battery's as backup. There are already alot of advantages to using DC. Soon we will all have our own renewable power plants on our roofs of our buildings and houses that produce DC and we will be driving electric cars that are DC, so why would we ever convert DC it into AC at all?
 

boater bill

Senior Member
Location
Cape Coral, Fl.
This was covered in power systems EE301, distribution efficiency is everything.
How would we replace the generation facilities, equipment, switchgear, etc?
Sounds to me you want an intellectual discussion, not a practical one.
You asked for thoughts and there is mine.
 

nakulak

Senior Member
based on history, the interest in renewable energy will last until the current oil crunch is over, then they will forget about them/it again until the next energy crunch or global environmental disaster (which ever comes first)
 

dbuckley

Senior Member
nakulak said:
based on history, the interest in renewable energy will last until the current oil crunch is over, then they will forget about them/it again until the next energy crunch or global environmental disaster (which ever comes first)
I hope you are right. But I don't expect the current oil crunch to ever be over...

Back on topic: lots of nutters are putting DC distribution in their homes, as it saves on having dozens of wall warts about the place.
 

Energy-Miser

Senior Member
Location
Maryland
No Show said:
I was wondering what everyone thought about this? ...?
One advantage of DC is that because it does not incur capacitive losses in proximity of the earth, high voltage DC transmission is possible using towers that do not have to be so tall and massive. Solar and fuel cells too produce DC power. So DC might make a comback. Westinghouse and Edison were proponents of AC and DC respectively. Who knows it may be that we will be entering Edison's era again. e/m.
 

iwire

Moderator
Staff member
Location
Massachusetts
I don't see it changing at the end user anytime soon, but I think DC is already in use in some high voltage distribution systems.
 

dereckbc

Moderator
Staff member
Location
Plano, TX
iwire said:
I don't see it changing at the end user anytime soon, but I think DC is already in use in some high voltage distribution systems.

Bob you are right, but only in the confines of a sub-station yard. Here in Texas, the state is not allowed to sync or connect to the national grid. So in interstae connections the outside source must convert to DC, pass to Tx, then immediately converted back to Ac for transmission and distribution. However this all takes place with the confines of a sub-station or a few feet of space.
 

No Show

Member
Location
Texas
Net Metering

Net Metering

Texas has now excepted net metering. Meaning that in the event a coustumers renewable energy system produced to much electricity (AC) it would let the meter spin backwards in to the utility co. grid act as the storage(instead of battery back up) untill the demand returns and they settle up at the end of the month.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Dereck,
Bob you are right, but only in the confines of a sub-station yard. Here in Texas, the state is not allowed to sync or connect to the national grid. So in interstae connections the outside source must convert to DC, pass to Tx, then immediately converted back to Ac for transmission and distribution. However this all takes place with the confines of a sub-station or a few feet of space.
Siemens and ABB both say they use high voltage DC for long distance energy transmission.
The High Voltage Direct Current (HVDC) systems are used for energy transmission world-wide. They are a useful supplement or in some cases the only alternative for traditional High Voltage Alternating Current (HVAC) systems.
These HVDC Transmission systems are specifically used to:
economically transmit electrical energy long distances via overhead lines or cable,
connect asynchronous grids or grids with different frequencies.

Siemens has been one of the leading companies in the HVDC business for more than 25 years.
The use of HVDC at 800 kV, has been found efficient, environmentally friendly and economically attractive for large point-to-point power transmissions of the order of 6,400 MW and more, with distances of more than 1,000 km. Worldwide there is an increasing interest in the application of HVDC at 800 kV.
Don
 

dbuckley

Senior Member
DC transmission makes enormous sense, as the power level and distance goes up, DC becomes more economic, as the cost of the equipment required gets dwarfed by the losses on the AC line.

You guys have several HVDC systems, mostly back-to-back, like the Texas examples, and some over longer distances.

Just a couple of miles down the road from me passes the line of what was, at the time of comissioning (1965), the longest and biggest HVDC line in the world.

In terms of polarity: it is a bipole, so both +ve and -ve lines are overhead with the ground taking the balance...
 

Energy-Miser

Senior Member
Location
Maryland
dereckbc said:
Simple Dc cannot be distributed/transmitted with any efficiency known to man or physics.
Not sure what is meant by simple DC, but asdie from that DC can be transmitted at very high voltages, more efficiently than AC, and I don't see much difference in the way distribution is done for the two. It is true however that we have a lot of experience with stepping up and stepping down AC using very efficient transformers. Clearly magentic core transformers do not work with DC, and therefore expensive and less efficient solid state circuitry will have to be used with DC. However, I think the efficiency of DC transmission will make up for the added expense, as has been pointed out in another post. e/m
 

dereckbc

Moderator
Staff member
Location
Plano, TX
Don, High voltage direct current (HVDC) is used to transmit large amounts of power over long or short distances or for interconnections between asynchronous grids like TX. DC is way to expensive to regulate and change voltages which would require very expensive electronic converters, invertiers, and rectifiers. The conversion is also be very inefficient, and prone to failures.

Look at it another way from the POCO plant. The 1200 or 2400 VAC out of the generator would have to stepped up via transformer, rectified, transmitted to distribution, then at distribution converted back to AC, stepped down in voltage, rectified again to dc arriving at you interconnection, be converted to AC again, and stepped down to a usable lower voltage. Keeping it AC all the way is simple and cheap with transformers.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
dbuckley said:
In terms of polarity: it is a bipole, so both +ve and -ve lines are overhead with the ground taking the balance...
Wow. Just think of the audio amplifiers we'll be able to build. :smile:
 

Energy-Miser

Senior Member
Location
Maryland
hardworkingstiff said:
Or maybe an evolution of the best of both? We seem to be able to convert back and forth between AC and DC without difficulty.
I don't think either will ever go away, it is only a question of which may become more dominant. Right now almost all electronic devices run on DC. However most of the generation, transmission and distribution is done in AC. There is a lot of conversions from one to the other, which is fairly inefficient. Think of a battery in an RV (a DC source), powering an inverter to generate 60 hz AC, which is then used by the power supply of the computer you plug into it, converting it to DC again, so that it can power the circuitry of the computer. Clearly DC distribution within the RV would make better sense in this case. e/m.
 
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