Feeding solar power back into municipal grid: Issues and finger-pointing

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"bud--" wrote in message

This is a fatal flaw in your argument. Transformers are not infinite sources. A utility transformer might supply a fault current 20x the rated current (for a "5% impedance" transformer). (While a transformer will supply a fault current larger than the rated current that is not likely with PV. PV is basically a constant current source.)

Using a real transformer houses will have far less available fault current.

Cite where 100kA is required.

I agree that is very likely. One reason is that a higher rating is not necessary.
(SquareD, if I remember right, has a rating of 20kA downstream from both the main and branch circuit breaker.)
I doubt many Canadian house panels have fuse protection, or are different from US panels with circuit breaker protection rated around 10kA.

The interrupt rating required goes up with the service current rating. For a house, the utility is not likely to have over 10,000kA available fault current. The transformers become too large, many houses are supplied with longer wires and higher resistance losses, and the system is much less safe.
I believe it would take a rather massive amount of PV installations to cause a problem. The PV installations would all have to be on the secondary of the same utility transformer. The transformer is then not likely to support the PV current back to the grid. If the fault current is 20x the transformer full load current, and the PV current is equal to the transformer full load current, the PV supply would increase the fault current by about 5% (assuming the inverter doesn't shut down). If there were too many PV installations the utility could put fewer houses on a transformer. Seems like a problem that is not that hard to handle for the utility, at least until PV generation becomes rather common.
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On 11-04-12 09:58 AM, m II wrote:
Nothing.
Forgery reported to nntp provider
mike
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On 4/12/2011 10:58 AM, m II wrote:

bud--
----------------- |Perhaps re-read ( or just read ) the last few posts. Your objection is |mostly agreement with items already covered.
Perhaps you should take reading lessons. Maybe you and harry could get group rates.
- You said "considering the street transformer as an infinite current supply" which no one does. - As a result your calculation is meaningless. - You said Canadian house panels were protected with fuses. I disagree. Perhaps a cite? - You said "any approved O/C device in a panel these days is rated at 100kA". I asked for a cite - still missing.
- Daestrom said adding PV systems to residences could result in an available fault current larger than the rating of existing service panels. It is certainly an interesting point, but not likely for reasons stated.
I did agree with daestrom that most US house panels are likely to have a 10kA IR.
|Can you cite the percent impedance of the transformers
5% impedance would be common
| or the code rules you discuss?
I didn't discuss code rules.
Your 'newsreader' is incompetent at treating sigs.
--
bud--

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On 4/14/2011 10:33 AM, harry wrote:

Use of "per-unit" values for voltage, current, impedance, ... is common in the electric power field. It makes calculations easier, particularly as the system gets more extensive. One of the "per-unit" values is "% impedance".
A utility transformer is likely to be rated in "% impedance".
Daestrom has written about this. Looks like mII (or whoever) is familiar with it. That leaves you. If you knew as much as you think you know you would be familiar with % impedance.
You really need to go for some instruction. These things can't be worked out by lying on your bed and thinking about it.
--
bud--


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On 4/12/2011 11:59 AM, harry wrote:

If you are talking about normal load ratings - what a useful revelation. I am sure no one had any idea...

There is a limit on the normal current for a transformer? I had no idea....
But heating is not a limit on fault current (which my post was almost entirely about).

Earth is not calculated because it is such a poor conductor. It may be necessary in some of the screwier UK electrical systems with an RCD main.

With minimal reading ability it is obvious that daestrom, mII (or whoever) and I talked about the fault current ratings of circuit breakers or fuses. Or did you think that houses have 10,000A services?

I worked them out 40 years ago then worked with them the last 40 years.
You really should learn to read and think. Maybe when cows fly....
--
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daestrom wrote:

Please be informed that the Josepi clown has been forging my username for a few weeks now. His provider is doing nothing to stop the forgeries.
Check the headers when in doubt. It's times like these I wonder about the maturity levels of some, no doubt very ill, people.
mike
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daestrom wrote:

Please be informed that the Josepi clown has been forging my username for a few weeks now. His provider is doing nothing to stop the forgeries.
Check the headers when in doubt. It's times like these I wonder about the maturity levels of some, no doubt very ill, people.
mike
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Actually you can and do as I understand it. To pump power into the grid you supply a slightly higher voltage than what is in the line. When spread over all the loads on the grid the change in voltage is next to nothing. If enough inputs are made by others the voltage will rise, and it is allowed to so long as it stays within a certain range. If it is going to go too high it is up to the utility to reduce the input at sources they control.
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I have no idea how it works exactly, but here in North Jersey PSE&G has been putting up solar panels on their (I think) utility poles. Each one is maximum 200 Watts at 110V, feeding directly into the grid the poles carry. This is a link + picture in another town not too far away (1 line): <http://www.nj.com/hudson/index.ssf/2011/02/pseg_installing_solar_panels_ o.html> or: <http://tinyurl.com/3dvgy7r
--
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Han
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On 4/4/2011 6:16 AM Home Guy spake thus:

and
Are you sure about that first statement? Pardon me if I misunderstand what you wrote, but don't you only get paid for the *net current* leaving your meter? If you're generating 5KW but "sucking" 6KW into your AC, etc., then you have a 1KW net draw, so you're not gonna get paid anything, correct?
That second statement is correct: you can't "push" electrons into the grid. But it doesn't matter *how* your inverters are working; it's a basic law of physics.
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The 80c per kwh seems very high. But strange as it may seem, here in the Peoples Republic of NJ, you get paid for the total amount of electricity the solar array generates, not just the excess amount. It's not a direct payment per kwh though. That would be too easy.
The actual story goes something like this. Utilities are being forced by law to supply increasing amounts of renewable energy. They can meet that number through a variety of ways. They could buy it from wind sources on the grid, for example. But they can also buy certifcates from folks who generate solar at their homes or businesses. That certificate counts just like if they had bought energy from company X's windmill on the wholesale grid somewhere.
Every time the homeowner solar array generates a certain amount of KWH of energy, the homeowner gets one certificate. Then it gets more complicated. They have some kind of auction system that determines how much those certifcates are worth and how much your power company will pay for it. The amount has flucutated widely, for factors I don't understand. But in recent years the typical 8KW array could generate a couplel thousand dollars a year back to the homeowner.
Oh, and I think they will also actually pay you an additional small amount for any net amount you put into the grid once a year too.
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If you apply more volts to a line than what it is carrying what do you think happens? I run machines that use regenerative braking. They draw energy from the line to set things in motion. To slow or stop them the electric motor acts as a generator producing a higher voltage than the grid, forcing power back into the grid. An inverter can do the same thing using solid state circuits. The inverter in my Prius takes DC current from the battery and converts it to whatever voltage and frequency is needed at the time to run the variable frequency AC motor. When slowing down the motor becomes an AC generator and the inverter converts the output to a DC voltage just a bit higher than the battery, pumping charge back into it.
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On 4/10/2011 10:02 PM Bruce Richmond spake thus:

Sorry, I don't think you know what you're talking about.
You seem to think that you can "force" or push "voltage" into a line, by using a higher voltage than what's on the line.
That's not at all what's at work here when one has a photovoltaic system and an intertie feeding power back into "the grid".
The intertie and the house's power connection are going to be at pretty much exactly the same voltage. What happens is that the PV system is connected *in parallel* with the grid; it's dumping more *current* into the system, not more voltage.
You do understand the difference between current and voltage, don't you?
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<http://www.northjersey.com/news/116938343 _Municipal_officials_throw_wrench_in_PSE_G_s_solar_paneling_program.html>
or http://tinyurl.com/3tcv4le
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On 4/11/2011 3:57 AM Han spake thus:

1. So what in the world does that have to do with the point I stated? (Rhetorical question. Answer: nothing.)
2. Y'know, if you used a non-brain-damaged news client that didn't mangle long URLs (unlike your Xnews), you wouldn't have to dick around with those tinyurls.
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I was agreeing with your statement of parallel systems, and offered a picture to sort of substantiate.

Sorry, I'm staying with Xnews for a while longer.
Have a wonderful day, David ...
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I love how you can state that without any sort of qualification...
You seem to have forgotten about higher end bathroom fans which use an inverter to operate a DC motor which is much quieter than an AC motor...
AND
Light Rail vehicles are operated on DC systems which drive HUGE traction motors with either an overhead wire or third rail using the other rails as a one-way return path through the vehicle chassis...
This is 600VDC and up, and WILL kill you if you make any mistakes around it...
Those two quite common examples seem to refute your absolute determination that ALL rotating electric machinery is operated with AC motors...
~~ Evan
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wrote:

Those two quite common examples seem to refute your absolute determination that ALL rotating electric machinery is operated with AC motors...
How so?
Vaughn
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wrote:

Look deeper in the motor. It's all AC on the inside. ;-)
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Exactly!
Vaughn
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