Could Net Metering Endanger Line Workers?
May 12th, 2009
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There is a lot of whoey going around about how great it would be for everyone to have a little generator in their house instead of having a big generator in a power plant. Already utilities are being forced to offer so called “net metering” options which allow people to backfeed the power grid from their own electricity generating equipment. Often this is in the form of solar panels or small wind turbines, but it also can be found with larger “distributed generation” methods which have been promoted by government subsidies and mandates on electrical companies. Some end users may eventually generate several kilowatts by biomass burning, micro-hydroelectric or waste heat recovery systems.
There is one thing which has not been mentioned in this discussion and that is the possibility that a large number of end-user electricity generation could increase the risk to utility workers of electrocution when working on supposedly dead lines that are connected to a customer backfeeding the power grid. Normally, utilities work on power lines while they are in operation. Working on “hot” lines obviously has its dangers but can be done safely if the proper precautions are taken.
There is one exception to this rule, however, when line workers work on power lines “cold” and thus can touch the equipment directly. This happens during a power failure, such as those caused by a tree falling on electrical lines or wind blowing over transmission poles. In such cases, the lines must be shut down by a breaker or fuse at the nearest substation or they will arc dangerously on the ground, potentially starting fires or injuring those around. Additionally, these kind of ground faults would short circuit the flow of power in the area. Thus, the lines must be shut down and because of this the utility workers attempt to repair them as quickly as possible in order to restore service.
There is a danger to working with cold lines: every once in a while, lines which have fallen and been cut off to isolate the fault are actually being energized by an improperly hooked up standby generator. This can happen if the generator is simply plugged into the wall without a proper isolation switch or if the isolation switching mechanism somehow fails. This has happened and every once in a great while, due to a storm cutting off power and a homeowner improperly wiring their generator, a lineman is killed due to unexpected voltage on lines that are supposed to be cold.
In addition to this danger there are others including the possibility that the generator could damage power company equipment or that when the power does come back on, and the generator is suddenly hit by power that is not in phase with it, there could be severe damage to wiring or to the generator, or in the case of solar power, the inverter system. The inverters on net metered generation systems are designed to synchronize their phase with the mains AC, but it’s not entirely clear whether or not all of the systems out there would respond properly to power being cut and suddenly restored or the possibility of extremely high loads, as may be caused by downed lines.
The issue: if more and more end users start going for net-metering plans, then there could very well be an increase in incidents caused by either a faulty isolation mechanism or due to amateur installations or modifications, such as adding more capacity, which do not take into account the possibility that their setup may endup back-feeding during a power failure. Will this turn out to be a problem? Maybe or maybe not, but it is something worth considering.
This entry was posted on Tuesday, May 12th, 2009 at 8:47 pm and is filed under Enviornment, Misc, Politics. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
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May 12th, 2009 at 10:38 pm
You have touched on one issue, there are others For example much of the equipment of the present electricity networks was installed with a nominal design life of about 40 years. Increasingly this equipment is reaching the end of its life cycle. Consequently it is not able to bear much of what this two way traffic will demand of it.
Power quality (PQ) is also an item of steadily increasing concern in power transmission and distribution. The connection of distributed generation to the distribution grid may influence the stability of the power system, i.e. angle, frequency and voltage stability. It will also have an impact on the protection selectivity, and the frequency and voltage control in the system.
In a highly meshed transmission network the real limit in the transfer co-ordinated capacity between areas is by the speed of the controller. Corrective control control actions can be accomplished in an appropriate manner only if a developed coordinated control scheme is implemented. Coordinated control also implies that devices located somewhere in the interconnected network must actuate in a coordinated fashion with other controls to relieve overload or voltage limit constraint at some specific point after a contingency occurs. Coordinating the operation of multiple devices on such a time scale will require several technological advances that for the moment do not exist.
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May 12th, 2009 at 10:57 pm
DV82XL said:
Yes, but it’s not just an age issue. Two-way power flow when you have a lot of scattered little nodes of production is ALWAYS a difficult system to manage. The service lines are layed out to make for a stable system but you can’t have that when you have so much distribution and possible delays.
To make it work is not just an issue of getting more technology out there. Some of it comes down to just having more wire. If you want to switch from one area to another then you need more distribution circuits to rout the power. Making it “smart” only helps you so much. If you want to be able to transfer a load you need the capacity to transfer it.
I just don’t see any way this could be made to work with technical development. It requires stringing more lines. We need more lines anyway, but to go to decentralization would basically multiply the total complexity and size of the system by a factor of two at least.
The best way to coordinate the system is to have something that is just solid and has enough excess capacity to take up the slack when something fails. Our system was built like that and 40 years ago it had enough capacity and so (with a few isolated instances aside) it worked well. Today it still is the system we had and it still would work just as well if demand had not gone up. Demand has gone up and the system was upgraded, but not quite enough.
I would not knock the old equipment though, especially some of the passive components but also some of the things like the big transformers for high amperage voltage control or line isolation. Some of the old stuff is going to last damn near forever because if you have seen them they are built like a tank. If you look at some of the transformers and equipment from the 1940’s it is just very very well built, and that is part of the reason it has functioned well despite the fact that it has often been neglected or asked to do more than it was installed for. Some of the old equipment just has good thick gauge windings, big sturdy internals, thick solid housings and so on. You know, there’s really no substitute for that. It’s heavy though, but it’s very sturdy.
I think the original system was built very well and really the whole idea of reinventing the wheel on this one is not going to turn out to be the way to do it. I’m convinced distributed generation is a dead end, for many reasons, not the least is the fact that all the trouble you have to go to to accommodate it ends up getting you very little added power. A megawatt of home-based net-meter generation is the most expensive, problematic, headache-inducing, unreliable and difficult to work with megawatt you will find.
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May 12th, 2009 at 11:25 pm
Engineering Edgar said:
You’re right, I didn’t phrase that very well. I meant the network was not built for two-way traffic, and even in cases where bi-directional flow is physically possible it could be achieved only by overriding system fail-safes, and potentially compromising product integrity, and that this is as much due to the age of the design as the age of the equipment. Consequently all of this would have to be replaced. Nevertheless parts of the system are getting old and replacing them and as you rightly observed, expanding the network as well wold be horrendously expensive.
Also this doesn’t mean that we should not start building in Flexible AC Transmission Systems (FACTS) into the system as we go, because there is much about those protocols that will improve the grid and save power that is being lost (being turned into heat) for one network related reason or another. But anyone that thinks FACTS means we can all tie-in whatever random electrical generation we want into the system is dreaming in color. In SOME instances local generation when used only as an offset can be cost effective, solar-electric driven A/C would fall in that class, but feeding back into the lines is a lost cause and a danger that should be stopped.
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May 13th, 2009 at 3:14 am
The system needs to be upgraded and that’s a big task as is. We can maintain it as a system that is basically conventional and intended to deliver power to the end user, primarily in one direction, at least on the local leg of the system, so you’re not feeding power backwards through substations onto regional feeds and that kind of thing.
Just doing that is a big task. It is a big task just to upgrade it to better service and relibility.
Now lets consider we want to add on generators potentially in people’s homes? The big task now becomes HUGE because the system now needs localized routing in two directions and also the power needs to be conditioned at multiple points to stop someone’s bad inverter from putting unacceptable noise on the line. Now to get this to work the system is at least double the complexity and probably more.
What do you get for this, I ask you? You get very little.
The first thing anyone should realize about doing a project is the cost/benefit ratio. It’s the most important thing to consider because if you lose site of that, then you burn money and get nothing back.
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May 13th, 2009 at 11:07 am
If the big problem with the power grid has stayed the same and demand has gone up, why not try to get demand to go down again? Conservation has to be a big part of any energy policy and right now we are over consuming in horrendous amounts that is causing these problems. Maybe we’ll have to live without so much air conditioning but consumption I figure is the best way to help out.
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May 13th, 2009 at 12:51 pm
This actually brings up something I hadn’t put much thought into (and I don’t know many others have put as much as they should). A power grid is going to occasionally be impacted by natural events or system failures which are going to result in damage to the grid and force areas to be shutdown. In this circumstance, as is mentioned, there is the issue of getting the system repaired and service restored as quickly as possible. If you have power being fed from multiple directions even on the local medium voltage level, this is going to complicate the process and it could potentially make things very dangerous. If lines go down and not all the sources powering them disconnect then you can have a fire started or someone injured or killed.
The other issue is cold starting, which is a complex matter to begin with. When there is a regional power outage, the generators can’t be turned on all at once. Normally there is a designated power plant, or power connect to a functioning area of the grid, which starts first and then energizes the grid. This is followed by power plants that draw from the lines to spin up and match the phase. Some plants need to wait until there is enough power avaliable for them to draw several megawatts to power up equipment like blowers, fuel handling, pumps and so on. Those plants may need to draw power for a while before they build up enough steam to produce power independently.
The whole sequence is intended to keep things in proper phase and frequency and to prevent any spikes on the system while allowing the plants to come online from cold. Imagine how much more complex this could get with many source and some of them not even being under the direct control of the power system, it’s hard enough with a limited number of power plants.
Then add the control issue, which is always a big factor in the smart grid systems. You need to provide control commands to the generator sites to tell them to power down and when to power back on, which ones go first and so on. How can you do this if your infrastructure is not intact? If the wires are down how do you signal the generators to check that they’re functional and to assure they’re not backfeeding and then to coordinate the re-start? That would be extremely difficult.
I do think that most of the small inverters and such things do have some features to safe them in the case of a power failure or a disconnect, but with more and more of them being installed, the probability of a problem increases and they start to become more of a force in overall stability.
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May 13th, 2009 at 1:27 pm
Shoe Shine Charlie said:
Are we indeed consuming in such large amounts, or is this something you have been told? I would like to see some proof to back-up your statement, that it is consumption, not a lack of supply that is causing problems, and that the current grid cannot move enough current.
An Actual Scientist said:
You are right, an inherent risk of interconnected networks is a domino effect – that is a system failure in one part of the network can quickly spread, and cold-starts become very difficult. What the distributed gird folks want to deal with this is smart loads, where in individual loads will not draw power until instructed to by the grid. Not only will this increase the expense of such network, but it will increase the control issue by several orders of magnitude.
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May 13th, 2009 at 2:52 pm
Black starting a single power plant is not a huge deal, but black starts on a number of power stations around a region where there is a cold grid is a headache. Luckily this does not happen much. Cascading failures that take out big areas are rare but we’ve had a few.
Power failures of a small size are common. They happen a good few times a month in a utility district. Even in good weather tree limbs fall and cars hit poles, but usually these faults only hit a small neighborhood or at worst a small portion of a town. This is why emergency crews are on standby, because they do get the call and there is a hurry to restore service. Most outages are just a few homes or businesses and are simple enough to restore. They have to patch the wires that fell and either reset the breaker or replace a pole fuse.
This would be made a much more complex matter if instead of a neighborhood of consumers you have a neighborhood of net-metering homes because you’d have to do a lot like verify that the systems are all disconnected for safety and make sure none are trying to power the whole neighborhood and maybe overloading in the process. They might not shut down if there are multiple units in the same area because they could mistake the current from other units as a sign that the power is still functioning.
So in this circumstance, your job of restoring service becomes more difficult. All the systems need to be verified as shut down and they can’t come online when power starts because you could have a supply spike if there are enough. You would want to have them come on after the service was restored and to do it one at a time.
The control issue: Big problem here in case of a major failure. If you communicate with your devices via the power grid, then how can you communicate with them to make sure they are all in safe condition if lines are down? You can’t. Even if it’s radio based, if the devices don’t have power to receive or if they do but their antenna is damaged, how do you communicate and verify they’re all safed for the restart? You can’t and that could be a big issue. What happens if you are hit by a hurricane and the network is damaged? How can you be sure that all the micro generators are off line? How can you be sure all the nodes are reset and ready for a cold restart?
Basically a logistics nightmare when you’ve made it so that individual homes are now not just consumers but an actual power feeding part of the system.
Power systems do get decimated with multiple faults from natural disasters. Ice storms are some of the worst. Think about the potential danger of trying to restring wiring you think is dead when some rogue microgenerator has it powered on or if you have a grid that has thousands of generators which need to be given command authorization when to start and you can’t get it out because the system is in shambles.
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May 13th, 2009 at 3:03 pm
Engineering Edgar said:
They claim that this will be done by setting all devices to default off, not that I am defending this, in fact that just puts more of a burden on the C and C software that would now have to address and turn on each load individually. It doesn’t matter which way you look at it you lose.
According to Scientific American the U.S. Federal Energy Regulatory Commission just launched a six-month study today to determine how much renewable energy the electric grid can accommodate.
“We need a good metric – a good yardstick, a tool – to assess how much renewable energy can be injected into the bulk power … system,” said Joseph McClelland, director of FERC’s Office of Electric Reliability.
No kidding?
Can the Grid Handle Renewables? A new study aims to find out how much electricity from wind and sunshine the aging power grid can support
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May 13th, 2009 at 4:48 pm
You are talking about two different things here which are not necessarily mutually exclusive or inclusive:
Active “Smart” Grid Management – Useful if done properly
Net Metering/Distributed Generation (The idea of homes and buisinesses feeding the grid) – A dumb idea no matter how you slice it.
A smart grid has problems to be worked out but it has advantages too. Having people feed power from solar panels or whatever to the power grid has problems and basically no beneift except to the solar cell installer.
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May 13th, 2009 at 5:49 pm
Biff Henderson said:
For sure FACTS is going to be implemented over time because it’s the next step up in grid command and control and one way or the other this upgrade is needed. For one thing it can help reduce the electricity that gets lost in transit—some 7 percent of electricity gets lost that way—and to eliminate unnecessary fossil fuel burning by electric utilities. But can the network be made smart and robust enough to deal with a plethora of micro-generators – no, that’s just not going to happen. I will be very surprised if it is found that the grid can bear the 15% of this sort of power that politicians are talking about, and it’s safe to say that the 25% that supporters of green energy think we can do, is out of the question, smart grid or not.
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May 13th, 2009 at 8:00 pm
Being the mere computer programmer here, I guess I have to ask the dumb question:
Why can’t the “net metering” interface be set up such that if there is no power coming in from the grid, no power is fed back out?
http://www.lightheat.com/alt_power/net_metering.html
“The system also includes an on/off switch so the power can be shut down in case of a power failure: Otherwise, current flowing back into the system might electrocute someone working on the lines.
“If we lose power right now, it automatically shuts down,” Child said. “
If the systems work like this, it seems to address this problem in a natural way.
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May 13th, 2009 at 8:23 pm
mdf said:
It is supposed to do that. Automatic generators do too, but the problem is that the mechanism fails occasionally especially if it’s an amateur rig and there is reason to be concerned that if you have enough people doing it the odds are eventually one of them will fail, especially if it’s an amateur rig-up which is the kind of thing you might see on this.
There is a situation where the automated switching could be fooled too, and I don’t think it has been addressed. If it is a sunny day and the solar panels on your house are outputting and at the same time you have a couple of neighbors who also have solar panels outputting then what happens when a pole falls and the neighborhood is cut off? The disconnect switch is tripped by a failure of grid power, but your neighbors house is keeping voltage on the grid, so your switch detects voltage and assumes the power is still working. Your neighbor, meanwhile, detects positive voltage on the power grid from your output. Both are fooled into thinking the whole system is up.
This is not likely unless you have major proliferation of net metering. If there are a bunch of houses in an area that have voltage output the power line could be cut and there would still be enough output to make it appear to be live. even worse possibility: The power grid is cut off but an ‘island’ is energized by the net metering and the equipment sees that there is a voltage drop and mistakes it for a brownout. That could cause things to shut off or try to compensate and that would make it more dangerous.
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May 13th, 2009 at 10:07 pm
This is a topic I know a LOT about. I am a utility engineer, working mostly in distribution. Utiliies’ resistance to distributed generation has historically been based on safety concerns, but once the safety issues were addressed (and they have been, in many jurisdictions) distributed generation does not add risk to workers or power quality so long as a few things are looked after. First, the interconnection must meet the utility’s standards. A well written standard, and verification that the installation meets the standard, will look after most of the problems. Second, as long as DG remains piddle power with low penetration on the distribution system, there isn’t much to worry about. Most small PV and wind installations are inverter-based and there are no issues with modern grid-tie inverters, in small doses. Larger DG units, from hundreds of kW to a few megawatts, are a different story. While many are now inverter-based (wind turbines), they are often induction generators or synchronous generators that can pack a punch and absolutely must meet utility protection standards, including periodic testing. In our case, my utility usually insists on backup protection that we specify, install and maintain at the generator’s expense.
I sat through a presentation from a neighbouring utility just this morning that illustrated how difficult it was to accomodate a biomass-burning generator that was out at the end of a long feeder and somewhat larger than the local loads. Voltage control is going to be a little tricky because the generator expects to be able to generate at full load, even if the local load is light. A good amount of engineering work went into determining the least cost and best way to maintain voltage within limits for all customers along the feeder. During light load times, the utility is forced to purchase the energy generated at the end of the line, and about 8% is consumed in losses before it gets back to the substation and onto other feeders. The “accept all comers” approach often results in these aberrations.
Are linemen put at risk by DG or bad backup generator installations? I’d say moreso by bad generator installations than by DG. But their work practices have evolved to protect them from these threats; they aren’t new. No lineman should be touching a primary conductor without either grounding it first (installing a personal shunt in my lingo) or making sure he is treating it as energized, with the appropriate protections in place according to standard work practices. Every time there is a storm in our area, the reminder goes out to the crews at the morning tailgate meetings to always be looking out for backfeed. There’s always some a-hole out there who thought he’d save money on a proper transfer switch for his generator.
Regarding some of the commments about communicating with DG installations – we don’t. We generally don’t need to because they are so small. The larger ones are required to operate within parameters that can include how long they stay off after an outage. I could go on, but it’s time for bed.
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May 14th, 2009 at 1:09 am
At Brad: Understood these distributed sources are not a big deal because they’re not so common and don’t produce much power, but in case you didn’t know, there are politicians and activists who are talking about a near future where nearly everyone’s home is net metering and they’re even claiming that everyone’s car is going to be connected to the grid for bidirectional feed.
If that becomes the case you’re looking at thousands of locations accounting for many megawatts and that is a lot of place for something to go wrong. I think the idea is stupid anyway, but just one argument would be the issue of restoring power. Just imagine if you had damn near every home capable of backfeeding.
As for generator danger: Yes, I’m sure 99% of the time it’s an idiot who decides they have a great way to hook it up their own way and it comes down to an amateur causing the problems.
Brad F said:
Agreed, but this is the real current world and not the world that the Green Party suggested a while ago where I recalled them stating (to paraphrase) “The electric system of the future is one in which we all produce electricity and we exchange it with eachother as we need”
Pure fantasy, but think about the safety angle and the service restoration side: If you have hundreds of thousands of isolation switches, there’s a good chance one will fial and if you have hundreds of thousands of power generators, they might not all come back smoothly.
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May 14th, 2009 at 1:33 am
I have a question.
What would happen if you had a big power plant or generator and you suddenly switched it onto an ac system but there was a missmatch of the phases on the plant and the system so that when it was connected they did not have the same timing?
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May 14th, 2009 at 2:17 am
Seth Goldman said:
I saw a picture of that in the last couple months somewhere. It might have even been here. A quick googling does not find it though.
Anyway, short answer: The generators fly out through the wall. Phase mismatches with the grid are bad, crossing the streams bad. The grid is much, much bigger than you are and it [i]will[/i] win.
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May 14th, 2009 at 1:14 pm
grmann said:
If the generator does not get destroyed by it, something else will. It amounts to two huge forces opposing each other and it is a classic case of “something has got to give.” I think in most modern power plants the generator wouldn’t take a hit as hard as some of the regulators and transformers. When the opposing currents collide they amount to a very bad short circuit, so I think the transformers and the switches will probably melt before the generator has time to react.
If it does go all the way to the generator though, it will find overwhelming forces trying to change the synchronization on it. It will try to resync with one giant lurch. (The power trying to push the generator into phase all at once). I can’t imagine how stressful this would be, but I’d imagine shafts snapping and equipment breaking lose from its mounts. It might cause momentary overspin, and it could be even worse if the system auto deploys breaks or something to try to slow it because that’s just fighting the inevitable.
I imagine whatever happened it would include a very sharp loud noise followed by some very unpleasant events.
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May 14th, 2009 at 1:18 pm
Brad F said:
What about the idea that if you had enough net metering in a small area, like for example, if you had several vehicle-to-grid setups in a cluster of homes, that this could actually become a self-sustaining “island” of power where it would be disconnected but each car or inverter saw the grid as being on because of the others providing power?
I can’t see this happening as long as you put it ‘piddle power’ but if the decentralized nuts and the VTG groups have their way then it might be a concern.
I don’t think it will ever get to that point, despite all the propaganda that it is the way of the future, but I can see how the safety issue might be one of the concerns.
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May 14th, 2009 at 1:59 pm
Something like that should NEVER happen in a modern power plant. It is not hard to bring two systems into phase and to check for proper match. Each system is functioning at the same frequency (within very tight tolerance. 59 hz on one side and 61.5 on the other won’t do) then the hot lead on each one should be equal to zero in terms of voltage difference. Assuming they both have the same neutral, then you can just put a voltmeter across them and it will read zero if they are properly phased and also are operating on the same voltage (also important).
If the voltage potential is not zero on all legs (or very close to zero) then the two circuits should not be brought together. There are phase-loss breakers that stop this from happening automatically.
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May 14th, 2009 at 2:05 pm
This explains howsmall generators on a simple circuit can be phased:
http://yarchive.net/car/rv/generator_synchronization.html
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May 14th, 2009 at 3:50 pm
Not noticed with all the talk about DG and the smart grid is that the other side of the coin is load management and by the looks of it it may be easer to mandate smart loads, that is loads with controllers that can sense frequency and voltage drift, detect black-outs, etc. Without communicating directly with the grid these controllers would be programed to respond based on the general conditions that it detects on the line. This technology is well developed and could be implemented slowly by mandating these controllers into items like water heaters A/C and electric heating and similar big loads.
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May 14th, 2009 at 5:13 pm
About backfeeding in a power outage: Is it not sufficient when doing this to simply switch the Main Breaker to the OFF position, and not turn it back on until your generator is disconnected from the wall socket? Granted there are people who somehow forget to do this, though I can’t imagine why anyone would think his meger 4 or 5 kW can run his entire neighborhood…
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May 14th, 2009 at 5:18 pm
Seth Goldman said:
Paralleling a generator out of phase (which is what you’re talking about) drives ENORMOUS currents since on one side of the circuit breaker you might have a large positive voltage (1.73 times the nominal voltage) while on the other side of the breaker you might have an equally large Negative voltage. These currents are generally high enough to trip the output breaker on the offending generator though often not before some damage occurs.
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May 14th, 2009 at 7:13 pm
Net metering just requires proper safety methods to be used, I still think it’s a good idea.
Also, this is unrelated to the current post, but I wonder about your opinion:
http://www.guardian.co.uk/environment/2009/may/12/farmers-restricted-chernobyl-disaster
This really ought to make people think twice about nuclear power, I think.
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May 14th, 2009 at 7:35 pm
Bruce,
You’re a fool.
Chernobyl is a red herring as far as safety goes:
Designed by people that didn’t give a damn about safety,
Built by people that didn’t give a damn about safety,
Operated by people that didn’t give a damn about safety,
Administered by people that didn’t give a damn about safety,
The whole thing overseen by a government that didn’t give a damn about safety,
And even with all that, to qoute your link,
“237 people suffered from acute radiation sickness, of whom 31 died within the first three months.”
oh wait, can’t forget about the 4,225,000 sheep.
Do you know how may people are killed every year by coal emissions?
Do you care?
It’s over 30,000 in the US alone.
Do you know what you get if you don’t build nuclear plants?
You get coal produced electricity.
Not wind produced electricity, not solar produced electricity because they are both a joke.
You get coal.
Any questions, ask the Germans.
They build more windmills than just about anybody and it still comes down to nuclear vs. coal.
Wake up and smell the coal ash!
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May 14th, 2009 at 8:08 pm
Gordon said:
It is true this should never happen. The automatic synchronizer will ensure the slip is low (the generator and the power system are rotating at almost the same frequency), the voltages are within spec and the phase angles are within a few degrees of each other before allowing the generator breaker to close. It is not difficult for this to be done by hand (and eye) since that is how it was done for many years before high reliability electronics came along. Back then, and still today, the operator would watch the synchroscope and match his machine to the power system. A synchroscope is just a dial with one rotating hand to display the relative angles of the generator and the grid. When the synchroscope was rotating slowly and coming up on top dead center, the operator would push the button (or turn the pistol-grip handle) to close the breaker.
Here is situation in which the worst could happen: Let’s say an inexperienced technician or electrician is checking the wiring associated with the voltages to the synchronizer and disconnects some wiring to do his checks. If he mistakenly reinstalls the wires on the wrong terminals, the voltage presented to the synchronizer could be 120 or 180 degrees out of phase. The next time the generator is synchronized, everything looks correct but all hell breaks loose when the breaker closes.
Synchronizing isn’t just a case of checking the voltage across the breaker with a voltmeter, because the breaker might be operating at anywhere from 4 kV up to 500 kV. In order to measure voltage at these levels, voltage transformers are used and there is a lot of cabling between the VTs on the grid side of the generator breaker, and the control room where the synchronizer is. When the generator is new commissioning testing ensures that all the VT polarities are correct and that the phasing is correct, but it is possible to mess it up, even years down the road.
Having said all that, the worst almost never happens because of procedures and training based on many years of experience. I had a lot of fun being responsible for the first sync of a brand new generator back in 1991. Although it was a bit anticlimactic when the breaker closed and nothing much happened, there was a tremendous sense of accomplishment when we saw the first megawatts being generated after such a long construction period.
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May 14th, 2009 at 11:38 pm
Bruce said:
The article makes no sense to me. For one thing, the British Isles are a considerable distance from Ukraine and given the prevailing winds they would have gotten a minuscule dose even in 1986 and now, more than twenty years later, that tiny amount of fallout is well under .1% of the original activity.
It sounds from the article like there is less concern about the “Chernobyl fallout” than the radioactivity levels in general – even tiny ones. Sheep which test positive for “high radiation” are restricted as are sheep which grazed in the same area.
Okay… cesium-137 is about the only major gamma emitter from Chernobyl that would not have completely decayed to nothing, but it still would have been reduced signifficantly both by radioactive decay and weathering and sedimentation. That said, if there were levels of concern, it’s easy enough to reduce the plant uptake with some extra potassium fertalizer.
1000 barquells = 0.027 microcuries. So no more than .027 microcuries of radioactivity is allowed per kilogram of meet.
That is… not much… at all…
I believe Brazil Nuts are considerably more radioactive than that. Anyway, it would be dwarfed by the amount of exposure one gets from potassium-40 in foods.
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May 15th, 2009 at 12:44 am
Bruce said:
Pure unadulterated radiophobia exacerbated by bureaucratic overreaction.
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May 15th, 2009 at 11:57 am
Not noticed with all the talk about DG and the smart grid is that the other side of the coin is load management and by the looks of it it may be easer to mandate smart loads, that is loads with controllers that can sense frequency and voltage drift, detect black-outs, etc. Without communicating directly with the grid these controllers would be programed to respond based on the general conditions that it detects on the line. This technology is well developed and could be implemented slowly by mandating these controllers into items like water heaters A/C and electric heating and similar big loads.
Could the argument be made then, that the focus on microgeneration, which is clearly the most hyped aspect of the so-called ’smart grid’ is really just obscuring the actually useful portion of the plans? If we spend most of what we have on the idea of net generating and that kind of thing then it’s just taking away from a worthy portion.
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May 15th, 2009 at 4:25 pm
Cat Man Do said:
As I said up thread FACTS (and other modern control protocols) will be implemented on the grid because they are needed for reasons other than to allow DG.
As for passive load management, the technology is available Dynamic Demand in the UK has a ready-for-market device waiting to go.
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May 15th, 2009 at 4:34 pm
DV82XL said:
Right… but again, that’s a totally seperate issue than the whole idea of vehicle-to-grid or having thousands of microgenerators, having net metering as a major energy source etc. That stuff is all smoke and mirrors and smoke being blown around. Politicians and interest groups like to talk about things like solar roofs and wind turbines on apartment buildings and so on.
Those are basically worthless and only make the problems more difficult to deal with
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May 15th, 2009 at 4:57 pm
drbuzz0 said:
Absolutely no question, I just don’t want to throw the baby out with the bathwater here, in as much as there is a lot good about the ’smart grid’ that has nothing to do with net metering or distributed microgenerators.
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May 16th, 2009 at 10:14 am
DV82XL said:
That’s basically the way I see it too. I’m intrigued by the dynamic demand concept. I think it’s holds some promise, but I’m concerned about unintended consequences. Let’s say some manufacturers incorporate frequency response into their products, using the same, industry-standard control. All programmed with the same response characteristics. After a few years, millions of devices will react at the same time for a frequency drop, dropping more load than is required to compensate for the deficiency in generation, resulting in an overfrequency condition that may result in tripping some generation, and on and on. I’m pretty sure the guys who are pushing this concept are well-aware of these types of problems, but the implementation in low cost controls might not be so intelligent.
There are other aspects of the smart grid that are way cool and will help me to operate a more efficient and reliable power system. The trick is to demonstrate the economics in a cost-of-service regulation environment.
While I don’t see problems with low penetrations of DG, there is a lot of head-scratching going on in the industry about what’s going to happen as we get to high penetrations (if that ever happens). Certainly there are some model “green” (how I’ve come to despise that word) communities about, where some of these issues can be accurately analyzed. As some of that research is published we will learn more about larger-scale effects.
But the only way we’re going to see high penetrations of DG is if one of 2 things happen. Either DG will become economic, or it will acquire sufficient utility and status that it becomes a must-have, like dishwashers or cell phones. Either one of those events could happen, but I’m not holding my breath. That’s why my initial comments above only referred to low penetrations of DG. I’m watching for it,
I’m interested in the effects, but I won’t really believe it until I see it happening.
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May 16th, 2009 at 1:28 pm
Brad F said:
You raise an excellent point, which hasn’t really been addressed by dynamic demand supporters. Clearly this has to be dealt with or indeed one could see the grid going into a positive feedback of ‘interesting’ proportions.
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May 17th, 2009 at 10:57 pm
You know, the whole idea of a smart grid and dynamic demand can only get you so far. No amount of control or automation can help you if you just don’t have the generating capacity to provide for the demand. We (the US) along with much of the world is not in a circumstance where our installed generating capacity is getting stretched thin and it’s so bad that many plants that are designated as peakers or reserve are running nearly constalty as if they were base load and that leaves precious little room for increased demand or any kind of unplanned outage.
Even if you have good control of the grid, if you have a shortage of input then you are forced to consider either brownouts or cutting loads. This probablem may eventually equalize itself if things get so bad in terms of reliability and expense that industries start to jump ship (which some are doing as it is).
Few new plants are being built. About the only ones that even *can* be built (or more reasonably signifficantly upgraded) are gas and that is one of the more expensive and less price-reliable ways of doing it. Consequently old dirty coal plants are being run even though they’re dirty and past their prime, because they are what we have already and have to hold out as long as nothing else new comes around.
That is the bigger concern I think, the lack of power generating. If you don’t have power generators then your grid is not of that much use and net metering is never going to change this because it’s so tiny.
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May 18th, 2009 at 4:59 am
You guys are all too negative. We can solve all these problems by hooking the grid up to prayer wheels powered by hamsters. Very devout hamsters.
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