Naked Science Forum
Non Life Sciences => Technology => Topic started by: AlmostHuman on 08/10/2011 10:02:50
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Hey!
Has anyone worked with power line communication? I need some guidelines on what to look for and what to expect of things available on market.
Lets say that I need to control about 100 different appliances connected over 1000 meters long powerline. Laying new wires is not an option. Preferred solution is power line communication.
Is this possible with x10 home automation devices?
Thank you!
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Is that 1000 meters total? Or 1000 meters between devices?
That seems awfully ambitious.
Have you considered wireless? If you have several "nodes" that are separated by a km or so, but have "line of sight", then you could set up wireless bridges.
Or, if it is all within a single building, wireless still might be an option.
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1000 meters total. Wireless is pretty expensive, so I opted for power line comm.
To be exact, this is about street light control. So, about 30 to 50 lamps distributed over a 1000 meters. Every lamp has 2 modes, so it is about 60 to 100 outputs to be controlled. Wireless is nice, but I don't need that kind of comfort :).
Thank you
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Anyone?
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I believe that the off-the-shelf powerline data-comms units designed for home-broadband distribution will have a range limted to 50 metres or so (although it will depend significantly on the wiring). But these are designed for high data rates (Mbps) whereas for controlling streetlights the data rate you need is miniscule. As a general rule, low data-rate comms can be carried over long distances (or with weaker signals) much more easily than high data-rate systems.
I suspect a proprietary powerline comms system (or some specialised off-the-shelf system designed for this type of application) could meet your requirements.
I presume you are hoping to use existing mains wiring. Can you be sure that a single cable joins all the lamps? If the lamps just get wired into the local mains-distribution (as I believe happens in the UK) then the signal paths and other appliances on the wire (potentially loading or interfering with the signal) could be a show-stopper.
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Thank you techmind. Just a simple communication is needed, and the only showstopper left is... Well I can't find off-the-shelf simple comm device.
Everything I stumbled upon was for home use (1000 ft max), so I couldn't take it seriously.
Thank you, again!
PS If anyone have links to products I could consider, I'd be happy to have them :). Development platforms are welcome as well. Thank you!
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You might take a look at this. These things use two-way communication, but I'm really not sure how they do it.
http://en.wikipedia.org/wiki/Smart_meter
I have a sneaky suspicion that an over-the-wire solution will end up looking very similar to a radio solution in terms of cost and complexity, but that's just my guess.
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@Geezer
Your suspicion is a lot more than suspicion :)
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A couple of weeks ago, someone from the power company came to my house to do an evaluation for meter upgrades.
I asked about smart meters, and they said that they were considering wireless networking rather than power line networking. I would imagine that either way, they will end up with a lot of hubs and relays as "line of sight" gets broken up pretty badly. But, it should save significantly on the meter reading, and give me a stimulus to recharge my EV at off-peak hours.
As far as smart street lights. You might evaluate your goals.
Are they all wired in a string, or does each light connect independently to the main power?
If you have strings of lights, then you would likely turn them all on and off at the same time, and would treat several as a group.
If you want to know when a bulb goes out. Then, measure the power consumption of the whole string. If the string goes out of spec, then you have a problem, and need to check the lights.
You said 30 to 50 devices.
What is your budget per device?
$100? $500?
For wireless, Cisco is pretty expensive, but you might be able to find Linksys or similar wireless routers/bridges. And, they should be able to act as signal relays or boosters. You wouldn't need to go any faster than 802.11b (11 mbps). For 10+ yr old technology, there should be quite a few available on E-Bay or at your local computer recycler.
Linksys might be interesting because the routers run on Linux. I.E. They might be able to be able to be manipulated as mini-computers, or perhaps you could select a small single board computer and add a wireless card to get full featured computing.
Your problem is... if you had 1000 lights, you could afford to do customization. But, your system is small enough that a lot of custom development would be prohibitive. That is, unless you end up with a marketable product.
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Ahem!
We had an RF AMR (Automatic Meter Reading) module that used one entire transistor to transmit, and receive! The range was quite enough for "drive by" reading, although the "intelligence" was a bit limited.
Not only that, but the battery operated versions (for water and gas) had a demonstrated minimum life of ten years (no kidding).
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Yeah,
The added all that automated stuff when I was in St. Louis.
Then the Power company decided to shut off my power (despite the power bill being paid a couple of months in advance). Then they started charging an estimated billing because I wasn't using enough power (after they had disconnected my power).
The Gas company also started charging estimated billing because I wasn't using enough gas. Then, they sent a technician out to check the meter, check the seals, and run a sniffer around the pipes to verify that they hadn't been messed with. Then, they didn't believe their own technician's reading, and refused to credit the amount overpaid, and continued to charge an estimated reading since the usage was low.
I believe that at least the gas company is setup so they don't have to do drivebys, but rather use wireless hubs controlled through the central office, so they get readings several times a day (which they refuse to trust).
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One other thought about the electric power networking.
Does the system go through different transformers. I'm doubtful you would get a clean transmission through a transformer. That would be a blessing and a curse. It would naturally isolate different segments of your net. It might allow you to decrease the range of individual components. But, you would need to bridge between the transformers somehow.
This is probably why the power company doesn't like networking their meters over the power lines.
If everything is on the same side of a single transformer, you might just try it out. The ranges listed might be a little conservative... you said 1000 feet, and you need about 3000 feet.
Can you set up multiple subnets?
Say from A-->B-->C
Then from C-->D-->E
Using C as a bridge.
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Yeah,
The added all that automated stuff when I was in St. Louis.
Then the Power company decided to shut off my power (despite the power bill being paid a couple of months in advance). Then they started charging an estimated billing because I wasn't using enough power (after they had disconnected my power).
The Gas company also started charging estimated billing because I wasn't using enough gas. Then, they sent a technician out to check the meter, check the seals, and run a sniffer around the pipes to verify that they hadn't been messed with. Then, they didn't believe their own technician's reading, and refused to credit the amount overpaid, and continued to charge an estimated reading since the usage was low.
I believe that at least the gas company is setup so they don't have to do drivebys, but rather use wireless hubs controlled through the central office, so they get readings several times a day (which they refuse to trust).
Oh dear! I can assure you I had nothing to do with that, although I was involved in certain goings-on in Pittsburgh, but it's probably best if we don't go into that [:D].
We've had a driveby electric meter here for at least ten years, and it seems to do work just fine. (The propane comes in a tanker truck, and the water isn't metered (yet).)
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Here labour is still cheaper than automation, and meters are expensive. The regular reading also detects tampering.
As to street lighting, there are various options.
You can use a series setup where you pass a constant current though a wire and each lamp is designed to use a specific current, normally 6.6A. The lights have a failure mechanism that shorts the bulb, keeping the circuit intact. You do need a constant current transformer, and the voltage applied can be over 10kV at the supply end. Not used as new any more, but a lot of them are around. Control is from either a single photocell or a time switch next to the regulator
Otherwise you have a parallel system, where each individual lamp is run on either 120, 230, 277 or 400V, depending on the country and method of supply. You can have a dedicated wire for lamps, with a photocell or time switch acting as a group control, or each fixture will have it's own photocell, and be connected to the regular mains supply cabling.
Mains signalling is easy, if you want to do a simple system you just have to send audio tones ( normally around 10W via an isolating transformer and a pair of low value capacitors to both provide isolation and make a high pass filter) onto the mains, and at each point you recover the audio frequency and detect it to operate a switch. This is what X10 is, at least from the power line interface side. You could use X10 modules ( cheap and already type approved) and a few X10 range extenders if you go too far. Allows simple signalling, and does not generate too much interference. If you have a 3 phase or split phase supply there are X10 bridges to repeat the signal across the phases, and these can be very useful.
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That sounds like a pretty good solution Sean. What sort of distance can you get by injecting a 10W audio tone?
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We had this audio on power line system in Maidstone when I was a boy but I think it has long since gone, I think the power required would be quite high as the amplitude of the super imposed tone was about ten percent of the regular supply voltage.
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Good point that you only need a very crude signal. So, no need to fully support networking, if the signal required is just a few commands.
Lamp On Dim
Lamp On High
Lamp Off
(and perhaps an Error response).
A little more complex if individual lamps are treated independently.
"Tones" are regularly used as test equipment, and I believe are generally low power. I have ones that can plug into either phone lines, or even one to plug into 110V power lines, but unfortunately no digital detector or frequency detector.
It might be a problem if there was bleed-over into residential systems.
Transformers on the grid will likely isolate the signals and limit their scope.
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Of course, if the distribution for the lighting system was independent of everything else, you could transmit the power as high frequency "squarish" waves and PWM them to send the control signals.
That's how this works http://en.wikipedia.org/wiki/Digital_Command_Control
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Geezer,
Are you sure you don't work in Military Procurement?
AlmostHuman is looking for ways to save power and money. And, you come up with rebuilding the entire electrical grid.
How many devices are line frequency dependent? Older mechanical clocks? Analog TVs? I presume most of the new digital equipment run independent of the line frequency.
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Are you sure you don't work in Military Procurement?
Oh no, I'm really only interested in World domination.
Mind you, it does bring up an interesting question. What would happen if we actually did transmit power with higher frequency squarish waves? DC would probably be best for the long haul stuff, but there might actually be some advantages for local distribution. I should probably start another thread!
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Geezer, depends on where the first transformer is, as this will pretty much stop it going further upstream. It was used years ago to control street lights from a central control, bu injecting the tone into the high voltage system ( although at a much higher power as you were injecting into 33kV or more) and providing some oil filled capacitors at the substations to pass the tone through to the detector, before the transformer.
In a long line you would simply place a choke in the supply side ( if you want, as the supply transformer will do the same) and inject. The tone will be detectable to the end of the line, at least a kilometer or two if you use a tone of around 1kHz or so.
Injecting a 1kHz tone onto an active phone line is detectable for kilometers without doing anything more than coming close to the line with the detector. Works on any POTS line, though you do have issues with data lines that might take exception to the source and not work properly for data, though the tone is there if somewhat noisy.
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Street light control was done using cycle modulation and rythmatic relays woking at a few cycles per second around 50 years ago. About 28 years ago I invented and patented a spread spectrum communications system for electricity gas and water utilities http://worldwide.espacenet.com/publicationDetails/biblio?DB=EPODOC&II=3&adjacent=true&locale=en_gb&FT=D&date=19830911&CC=DK&NR=116383A&KC=A that went as far as a full scale trial but the british world beating technology was killed stone dead when the government decided to privatise the utilities.
DCC chips are easily available an used for lots of model railways but they are only good for low voltages.
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Street light control was done using cycle modulation and rythmatic relays woking at a few cycles per second around 50 years ago. About 28 years ago I invented and patented a spread spectrum communications system for electricity gas and water utilities
Oh yes! EMI, I remember them. Didn't they make gramaphone records? [;)]
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To (try to) cut long story short:
Let's say that right now I need off-the-shelf solution for testing and marketing purpose, and I think I've managed to find solution that we could try (there's a lot space for improvement in this phase, but it's not necessary).
As I said, that solution is going to be for marketing purposes only (to animate politician to install some level of energy saving street light system). On the other side, when the politicians take the bait and we get green light for this project, we will implement the solution that we find optimal.
As far as my planning goes, I think that we will take few development platforms for power line communication and develop system that will fit our needs when we are done with marketing (if our marketing is successful).
System implemented now is done with mercury bulbs and without any smart control. By some Kyoto agreement, mercury bulbs are to be replaced with something eco-friendly by 2013. So, our goal is to implement power saving system (we're not responsible for bulbs, but just for their control). New bulbs will have two modes: power saving and full power. Solution (that will be implemented) needed is one that could control any particular bulb at any time and (optional) have some feedback (is bulb turned on or off).
Every block has its own transformer (nothing else but the street lights is connected to that transformer). One power cable (one wire for each phase (R,S,T) and one for neutral (N) = 4 wires) goes from transformer to the end of the block and all lamps are connected to that power line (first bulb connected to R, second to S, third to T, fourth to R...) everything is weatherproof and dry. Control device should be able to communicate with main control via RS232 and to transmit commands to modules that control particular bulbs and to collect and dispatch data considering status of each bulb to main control. Size of any block isn't over 1000 meters, and there's 40 lamps max per block. So there's max of 80 outputs to control per block.
Project leaders are eager to experiment and find optimal solution (price per lamp should not be over 120 USD). IT support is probably the strongest link in our team, so there should be no problems as far as software is considered.
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To (try to) cut long story short:
Let's say that right now I need off-the-shelf solution for testing and marketing purpose, and I think I've managed to find solution that we could try (there's a lot space for improvement in this phase, but it's not necessary).
As I said, that solution is going to be for marketing purposes only (to animate politician to install some level of energy saving street light system). On the other side, when the politicians take the bait and we get green light for this project, we will implement the solution that we find optimal.
As far as my planning goes, I think that we will take few development platforms for power line communication and develop system that will fit our needs when we are done with marketing (if our marketing is successful).
System implemented now is done with mercury bulbs and without any smart control. By some Kyoto agreement, mercury bulbs are to be replaced with something eco-friendly by 2013. So, our goal is to implement power saving system (we're not responsible for bulbs, but just for their control). New bulbs will have two modes: power saving and full power. Solution (that will be implemented) needed is one that could control any particular bulb at any time and (optional) have some feedback (is bulb turned on or off).
Every block has its own transformer (nothing else but the street lights is connected to that transformer). One power cable (one wire for each phase (R,S,T) and one for neutral (N) = 4 wires) goes from transformer to the end of the block and all lamps are connected to that power line (first bulb connected to R, second to S, third to T, fourth to R...) everything is weatherproof and dry. Control device should be able to communicate with main control via RS232 and to transmit commands to modules that control particular bulbs and to collect and dispatch data considering status of each bulb to main control. Size of any block isn't over 1000 meters, and there's 40 lamps max per block. So there's max of 80 outputs to control per block.
Project leaders are eager to experiment and find optimal solution (price per lamp should not be over 120 USD). IT support is probably the strongest link in our team, so there should be no problems as far as software is considered.
What?! You mean you're actually looking for a practical solution? We're scientists! [;D] (er, well, some of us anyway)
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What?! You mean you're actually looking for a practical solution? We're scientists! [;D] (er, well, some of us anyway)
Not really. I am looking for hybrid solution (half practical, and half "unpractical" [;)] ). I am looking for development platforms on which solution to this "problem" could be based.
Thanks for help though!
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If the poles are all "line of sight", could you use IR communication (although it can be influenced by weather).
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Almost human. For a one off there are probably lots of basic digital communication chips that can be used to implement your system as you suggest simple microcontrollers or PGA can be used to do the logic. Any single cable has a reasonable characteristic impedence and a simple capacitance resistance circuit can be used to isolate the high voltage and protect the input. you might need a slightly more poweful driver than a simple communications line but they are available.
When I did the mainsborne telecontrol project we had only just started to use the simplest microprocessors. and the range of chips was very limited an mostly basic logic so you had to design most of it yourself!
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At this point the networking would be nice. However, I think I would avoid the temptation to do networking to every individual lamp.
If several lamps are wired together, then just treat the cluster as a single lamp, and design a dimming approach that can turn the string on and off, as well as dim them. The Cold Cathode Compact Florescent Lamps are low power, and dimmable, so you would just set the desired voltage at the source. I know the street lamps are bright... can the CCFL lamps put out enough light on high power? Mercury might be an issue, but the lamps should be able to be recycled, especially if you have a lot of them.
It is a bit confusing, but there are both PLC (programmable logic controllers), and PIC Controllers which are essentially a PLC on a single chip. You should be able to program a PIC to run independently based on the specified algorithm. It would take the inputs from a photo sensor to determine dawn and dusk. I would calculate noon and midnight based on halfway between dawn and dusk (good enough for the purposes of the system) to prevent time-drift. Then program each controller with the desired schedule for the individual lamp. If necessary, it should be able to guess within a week of the date based on the length of day.
Maintenance would have to be done at each lamp, or each PIC. However, it should have relatively lower power requirements, and would be unaffected by systemic issues. Did someone suggest that Fog & rain would interrupt IR? Is it possible to at least mount your control box at ground level? Anyway, if you create a good algorithm, then systemic upgrades should be rare. Keep in mind that with a networking approach, there are still needs for the initial installs, and periodic network repairs and upgrades.
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The dimming photocell has already been invented, and is quite common in Switzerland AFAIK, where you find a lot of fixtures that have 2 lamps, one high power and one low power. Both lamps are switched on at sunset, and at midnight the high power one is switched off, only coming on 2 hours before sunrise. The low power lamp is on all night. Generally implemented as a mercury lamp and a LPS lamp, as both have the distinct advantage of a lifetime measured in decades ( not like the current lighting that might make 5 years at best, more like 2 in most cases) and giving a good quality light when people are around ( MV lighted) and a lot of light the rest of the time ( LPS is really efficient at making light, though it is red) when there are not many people around. Otherwise 2 HPS lamps of different power in more recent installations.
They compensate for day length, and set themselves up automatically to switch at midnight.
Dimming is really only going to be feasable if you have high power LED lamp units, and you can integrate the controller into the power supply for the unit, along with the power line interface. Do not forget to make the power supply capable of surviving 5 years at 125C, and to be able to survive multiple simulated lightning spikes applied to the power supply terminals, along with being able to survive prolonged overvoltage ( at least capable to survive lost neutral on a 3 phase system without blowing up or popping a fuse) along with reliable startup at any point from -55 to 125C and any input voltage in the range at the same time. Self resetting thermal protection would also be good.
MV lamps are dimmable, simply by using a multitap ballast and dropping the current of the lit lamp to a lower level. Not going to give a big dimming range, but will offer savings without causing problems for the lamp in terms of life and poor operation. Most sodium and metal halide lamps are not dimmable, unless you use an electronic ballast to run them, and these are not going to survive in street lamp use.
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....and LED lights might not be such a good idea as someone is likely to purloin them [:D]
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I did look up LED street lights, and found some 100% LED street light bulbs, as well as complete lamp units with lower overall power consumption than the low-light versions of the standard bulbs. Since the LEDs use multiple bulbs, it should be easy to shut off 50% or more to run at half power.