my suggestion to you is to google the term "current source". Most sources you are familiar with like batteries and generators are more like voltage sources. A current source is in a way the opposite concept and you need to think about it for a while.) A grid tie inverter emulates a current source. It puts out at its terminals (within limits) whatever voltage is needed to cause the desired current to flow.
They all follow Ohms law I=E/R. With a voltage source, V is fixed and I varies with R. With a current source, I is fixed and V varies with R.
In a normal grid tie situation, the amount the V has to vary is very small probably 1 or 2 volts at the most. That is the detail of how it controls the current. The voltage will rise or fall as required such that the desired current flows.
You can Google the design of current sources for more detail.
It can take DC voltage and build a sin wave using PWM (Pulse Width Modulation)
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As shown on pg 74 that is smoothed and fed into a transformer. A feedback circuit measures the current flow and adjusts the voltage of the constructed wave as needed. Not sure what you want here. If you want the exact details about how each part works google is your friend. 30 years ago I was working with drive panels for large industrial DC motors that did all this to feed current back into the lines when doing regenerative braking. When they want to slow down they don't worry about sharing a load. They know there are loads out there and they just pump the power into the line. At that time it was all controlled using analog circuits.
Google "Norton and Thevinin Equivalency" or "Norton Thevinin Circuits".
You'll see that a resistive circuit can be modeled as either a current source or a voltage source together with a resistor and that they are interchangeable and equivalent in how they behave.
On 4/18/2011 7:02 PM snipped-for-privacy@optonline.net spake thus:
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Sorry, it's still a hopeless hash.
I really do want to follow your example, but I can't until I can see your circuit diagram properly. This ASCII-art thing clearly isn't working; any chance you can post a picture somewhere? Then I'll be able to follow along.
You need to change your "fixed spacing" font to one that is "fixed spacing"
I can even read it perfectly in your reply.
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On 4/18/2011 7:02 PM snipped-for-privacy@optonline.net spake thus:
Sorry, it's still a hopeless hash.
I really do want to follow your example, but I can't until I can see your circuit diagram properly. This ASCII-art thing clearly isn't working; any chance you can post a picture somewhere? Then I'll be able to follow along.
It's still all garbled. Line wrapping and all that. Your news client (Microsoft Windows Live Mail 15.4.3508.1109) probably behaves differently from mine (Thunderbird).
Like he said, if there is a change in the current flow there is a change in the voltage drop across each component between you and 'the grid'. The impedance of these components is small, but nevertheless it exists.
Besides, grid voltage regulation is not perfect. Those tap-changers you mentioned have discrete steps and most have time-delays in them with a dead-band around their set-point. These are designed so the thing doesn't wear out constantly stepping up and down when the voltage set-point is 'between' the tap settings.
On Apr 19, 3:33=A0pm, "Mho" wrote: It shows up perfect when I look at it in David's replies too. How about I just describe how to draw it on a piece of paper which should be easy. It's very similar to that example circuit Wilkins provided a while back
Left side is the PV array voltage source V1, which we will vary.
Right hand side is fixed voltage source V2=3D 240volts, representing the power company.
Now go across the top part of the circuit between V1 and V2 left to rightand draw a string of resistors connected in series that connects the two.
In order.....
R1 is the internal resistance of the PV array Rw is the resistance of the wire from the PV at the house to the grid Rg is the resistance of the grid as it goes down the block to the load Rg again is the resistance of the next piece of grid as it goes another block Rw is the resistance of the wire from the grid to the power company source R2 is the internal resistance of the power company source
For simplicity all these are 1 ohm each and per above connected look like this:
----R1-----Rw----Rg-----------Rg----Rw---R2----
Label the point between Rw and Rg on the left Vg. This is the connection point measurement voltage at the grid, where the PV array wire from the house attaches to the grid.
Connect the bottom of V1 to the bottom of V2
Add a load, Rload=3D100 ohms, one end connected between the two Rg resistors at the top and the other end connected to the bottom path between V1 and V2 that you drew in previous step
Here it is with the vertical connections left out:
--- R1 -- Rw ---Rg------Rg----Rw----R2----
V1 Rload=3D100 V2=3D240v
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Remember Vg is the voltage between Rw and Rg on the left.
Now you have amodel of two power sources driving a load. Follow the math I posted previously.
Yes, we'e on the same page. They are interchangeable, but I think Mark had a good idea in bringing up the idea of the current source, as conceptually it's a bit easier to understand. It appears to have got Smitty at least partly convinced.
.. twould be a strange grid/retic system indeed were tap change contacts found in the environment. Then again I am not surprised at anything uttered from those who feed the Gymmy Bob troll.
GB will be very busy searching his digests of "Popular Mechanics" for the term "dead-band" just to be sure it isn't an old Bob Marley joke:->
"Gymy Bob" /
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"John P. Bengi" /
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"Solar Flare" /
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"Pizzza Girl" /
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"Janice" /
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"Joesepi" /
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.. mind how you go. Don't want you bleeding all over the place:-D
The few tap-changers I've seen 'up close and personnel' are in sub-stations, not pole-mounted. The contacts are in oil-bath and arranged such that they don't open under appreciable current (multiple contacts, a center-tapped inductor and ingenious mechanism).
Similar experiences here.The contacts are usually just copper or copper plated with silver.
Many schemes are contrived to save the wear and tear on the contacts. On larger capacity units there are two sets of contacts, ones that take the arc and are easy to replace and a second set that can carry big currents, close last and open first.
Some use vacuum bottled contacts to eliminate arcing and most use an inductor or resistance not as good) to afford tap changing without ever breaking the circuit.
Oh, I have dealt with a few pole mounted units for inline use in the rural long lines to boost it back up a bit.
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-------------- On 4/19/2011 17:28 PM, Jim Wilkins wrote: Would the contacts be the tungsten (heavy) cylindrical slugs sometimes found below equipment-laden power poles?
Wikipedia is not a source of information (by their own definition). Do not use it for quotes. Now your information is a fourth hand paraphrasing, lower than a rumour level.
From Wikipedia: "In an electric power distribution system, voltage regulators may be installed at a substation or along distribution lines so that all customers receive steady voltage independent of how much power is drawn from the line."
Obviously when a local area is supplying power to the grid, power generation elsewhere will be reduced. And any voltage changes that results from that will be adjusted with line voltage regulators, if necessary.
How do you get the value 250-500W?
Motors will only increase their energy drain by raising the frequency, Plus a small loss due to internal resistance in the windings.
As for a resistive load, increasing the voltage from 120 to 125 volt will result in a power drain increase of about 8.5% or 8.5 W for a 100W light bulb, assuming 120V is the nominal voltage.
Remember though that the voltage increase on the step-down side of the transformer due to homeowners PV arrays will be less than 5 volt pretty much guaranteed. Local codes state a maximum voltage drop (7V in BC) over the lines to a house, at 80% load of service panel capacity.
Most households have a 200A service panel. A 10kW PV array is well below the service panel capacity.
And you cannot just look at the PV array output. You must take into account the local energy consumers as well. That will reduce the current going into the grid, and thus the voltage increase.
You claims are pretty vague, please explain what you mean by wasted.
By the way, there is some "waste" by just using the grid only as well. Losses everywhere in the grid.
What is your definition of worth while? And what do you know about the utility's voltage regulation policies?
The utilities _have_ to use voltage regulation due to demand changes.
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