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Broadband over Powerlines
scubacuda writes "Today's Bottom Line links to an article on Internet-over-powerline technology. St. Louis-based Ameren Corp and other utilities are testing are testing the technology, and, according to the article, "many consider it increasingly viable." Proponents claim the powergrid technology will bolster broadband competition, lower consumer prices and bridge the digital divide in rural areas. Skeptics say that few tests prove its financial and technical viability. Kludge, panacea, or hoax? (I'd think it was a total crock had I not personally known someone working in India with a PCL company)"
Didn't we have problems with this when it was trialed a few years back i nthe UK? i'm sure I heard reports of lamposts going haywire, any URL's?
The only problem I see is that every overhead power line is going to turn into a giant antenna picking up interference. My school got squeemish enough about a teacher with too long of an ethernet cable, what about miles and miles of power lines out in the open during an electrical storm?
In Israel the (single) power company used this technology for years for its own data communication.
I think the reason it never moved to other sectors involved both the high price of the required modems and the requirement for a licence (being a communication provider requires a licence, at least here in Israel) which was always a problem to gain here.
About a year ago German company RWE (big energy corporation) was cheered as the new leader in broadband connections via powerlines. It even was available to customers, but eventually they quit the powerline business in September 2002. Appearantly they had only 200 paying customers instead of the expected 120000.
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Heck, you could put this together in 5 minutes. http://www.knology.net/~bburdette/ethernet-over-ac .jpg
Try it on your work network!
In the energy services field it is common to send data up the drilling fluid on a drilling rig. They use a valve downhole to modulate pressure waves up the pressurized fluid in the pipe. This gives them details of the environment at the drilling bit. They data rate is quite low.
They had this when I lived in Germany. The deal isn't that they sent a signal over the HV wires. The HV wires come into the local tranformer and get stepped down to the right voltage and smoothed out. At that point you can have a bypass to filter out the higher frequency signal that carries your packets. So from the house to the transformer you can have one set of signals riding on a normal 220 V 50 Hz (+/-) power. At the bypass, you can change the frequency so it can travel over the high voltage lines or can send it over to fiber from the tranformer to a central location. The difference between Germany and the States is that in Germany, they have a transformer that services an entire neighborhood. So you can put in the equimpent at the transformer and have potentially thousands of customers to regain the costs. In the States, there may be a neighborhood transformer, but there are also generally transformers every few houses for the final conditioning. That means expensive equipment that needs to be recouped over a small number of people.
That's nice in theory, but totally inpractical. Basically, you'd have to sync both ends of the data transmission with frequency, except that the grid frequency is not a constant, and unpredictable...
The 60Hz frequency standard in the US is a "desired" point... everything, from turning on a blender at home, to firing up your local steam generator for the morning ramp, has an effect on the grid, from a minute twitch to a big swing. If there is more demand than generation, the frequency slows down as energy is sucked out of the grid; likewise, overproduction of electricity causes the frequency to speed up. Now, it takes many many MWatts to make a change, because so many loads & generators are wired in parallel, but it's still possible.
There are many companies operating in parallel across the USA (abbreviated RTOs & ISOs) that work to balance the supply & demand of electricity every second... we track the frequency (graph here) in an attempt to balance the whole thing out, by calling on more generation when the frequency is low, and telling the to back off when it is high...
Now, as far as sending data by modulating the AC wave, the problem here is the "scrubbing" effects of Transformers. The premise behind high voltage transfer of electricity is to use transformers to step up the voltage & lowering the current. Lower current equates to less heat loss, so you can send the energy more miles for the same loss. Now, the problem is the magnetic core does not have a good frequency response when converting E to M to E again... they're designed for a low frequency after all. So, you end up with every transformer removing all of the high-freq. oscillations.