Question about the Grid

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richxtlc said:
You are correct, the spinning reserve is the available generation in case of the loss of the largest unit or tie feeder. It is the capacity that is available, not excess MWs that are just hanging around on the grid.
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Yes, but the spinning reserve is mechanical, in the sense of generator inertia. There is extra ampacity in 'reserve,' not actually power that's being generated. The current, and thus the power, will still vary with changes in load.

It's impossible for more power to be generated than is consumed. Less current will flow, that's all. Power is still volts x amps. If the generators are unloaded some, they will spin easier, requiring a reduction in applied torque.
 
LarryFine said:
Yes, but the spinning reserve is mechanical, in the sense of generator inertia. There is extra ampacity in 'reserve,' not actually power that's being generated. The current, and thus the power, will still vary with changes in load.

It's impossible for more power to be generated than is consumed. Less current will flow, that's all. Power is still volts x amps. If the generators are unloaded some, they will spin easier, requiring a reduction in applied torque.
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nice one. so I can use the water-in-a-dam analogyhere: the water is still there and supplies only when there is consumption.
 
Dispach of generation

Dispach of generation

It seems to me that there are a lot of misnomers about utilities and their dispatch of generation. IE what turns on and when. I general there are 4 classes or resources that are necessary to run the grid efficiently.

Base loaded generation: any utility can tell you what the absolute minimum generation capacity they will need is. This is the generation that a utility will need at their minimum load this is usually late at night when everyone is in bed. the most common examples include Hydro, Coal, and Nuclear power plants these are the most efficient plants at converting one source of energy to another cheaply

Seasonal load shaping: This is generation adjusts for seasonal load changes for example in California in July the load is lot higher then in February due to the temperature. Examples of this type include Coal and Gas.

In day Load shaping: During a day load changes due to peoples habits for example people start getting up at 6:00 am therefore they turn on their lights take a shower and cook breakfast all of which need electricity. To deal with this we need quicker moving "chunks of power" Examples of this are mostly Gas and Hydro there are a few coal plants dispatched this way

Load Balancing: this is used for maintaining system frequency the because on the grid power in has to equal power out at any point in time or you get frequency deviations. this is the type of resource that has to respond to the turning on of lights etc. The resources usually used for this are Hydro and simple cycle Gas.

renewables: I had to give them their own area to deal with the special variability of renewables. Most renewables are dispatched when they are generating and not dispatched when they are not. when you see wind turbines that are not spinning while the wind is blowing there are several possibilities.

1. They have been displaced. usually this would be a regulatory requirement to run another resource IE Hydro resources during a high runoff period or during a fish migration.

2 They don't have transmission. There are too many reasons for this to discuss

3 Power costs are near 0 or even negative. In a lightly loaded condition this can be the case. For example on a spring day in the Pacific NW with high runoff the dams have a regulatory requirement and a physical constrain to run lots of water through their turbines sometime they can generate more energy then is needed in this case power will go negative so that people will turn off their 0 cost generation like PV to take that power at -1 $/MW

There are other issues that could cause people to not dispatch those renewables when they are available.

Anyway Just my 2 cents right now
 
LarryFine said:
Yes, but the spinning reserve is mechanical, in the sense of generator inertia. There is extra ampacity in 'reserve,' not actually power that's being generated. The current, and thus the power, will still vary with changes in load.
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The inertia has practically nothing to do with it. Inertia would be more like something that has already been generated and embedded in the system. Spinning reserves are just units that are already on line and can start generating more output within ten minutes.
 
mivey said:
The inertia has practically nothing to do with it. Inertia would be more like something that has already been generated and embedded in the system.
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If you mean stored excess energy, like a charged cap, it doesn't work that slowly. The grid is so large that most current changes are relatively miniscule, but a sudden large increase results in an instant increase in current generated, at (almost) the speed of light.

Changes in current flows don't have inertia in the weight-on-a-spring bouncing-for-several-seconds sense. A sudden current change doesn't result in a decaying oscillation like a rippling pond.

Spinning reserves are just units that are already on line and can start generating more output within ten minutes.
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That seems like a contradiction. If they're already online, that would mean the generators are less than fully loaded, and a sudden incease in consumption would merely result in an instant current increase.

Anything that takes 10 minutes to start generating doesn't sound like being on line to me. Now, having said all that, I could be way off base, but that's how I see it.
 
LarryFine said:
... If they're already online, that would mean the generators are less than fully loaded, and a sudden incease in consumption would merely result in an instant current increase.

Anything that takes 10 minutes to start generating doesn't sound like being on line to me. Now, having said all that, I could be way off base, but that's how I see it.
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I agree. As I understand it, the so-called spinning reserve is just online power plants operating at less than capacity. They can handle moderate surges on demand. Peakers, the standby plants that require minimal startup time, are brought online when the monitors indicate a possible to likely under-capacity situation.

I recall a time about two, two and half years ago when I was working at an AEP plant down for pollution control upgrades. Another AEP plant in the region also had two of three units down for the same. A third plant had an emergency shutdown, and peakers had to be brought online to make up for the reduced capacity. Because the plant I was at was closer to being online than the others (or so the engineers thought), we had to change gears over to getting the plant I was at back online in 24 hours. We didn't actually have to go online because the plant that had the emergency shutdown was able to get back online, but it showed me just how frantic AEP gets in reduced capacity situations.
 
richxtlc said:
You are correct, the spinning reserve is the available generation in case of the loss of the largest unit or tie feeder. ...
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Or, as in Fairbanks, there is no spinning reserve. They have a 40?MW (might be 20MW) battery bank tied to inverters - good to hold the load for 20 minutes. That's long enough to get the GTs started and online. They paid for it with the reduction in fuel costs, and maintenance. I've seen it - kind of neat.

cf
 
LarryFine said:
If you mean stored excess energy, like a charged cap, it doesn't work that slowly. The grid is so large that most current changes are relatively miniscule, but a sudden large increase results in an instant increase in current generated, at (almost) the speed of light.

Changes in current flows don't have inertia in the weight-on-a-spring bouncing-for-several-seconds sense. A sudden current change doesn't result in a decaying oscillation like a rippling pond.
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The point was that a spinning generator does not have the "inertia" in the sense that you would have with a big flywheel. It just ain't that big of a flywheel as compared to the reserve rating.
LarryFine said:
That seems like a contradiction. If they're already online, that would mean the generators are less than fully loaded, and a sudden incease in consumption would merely result in an instant current increase.

Anything that takes 10 minutes to start generating doesn't sound like being on line to me. Now, having said all that, I could be way off base, but that's how I see it.
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There is not much about a generator that is instantaneous in that sense. These units ramp up to load, they do not pick up the rated load "instantaneously". It does not take 10 minutes to start ramping up as they start ramping up without significant delay. The rule is to be able to pick up the rated reserve load in less than 10 minutes.

Add: The fault current delivered to the system could be classed as instantaneous but that is for a duration measured in cycles. Not the same as the times we are talking about for regular load changes.
 
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Cold Fusion said:
Or, as in Fairbanks, there is no spinning reserve. They have a 40?MW (might be 20MW) battery bank tied to inverters - good to hold the load for 20 minutes. That's long enough to get the GTs started and online. They paid for it with the reduction in fuel costs, and maintenance. I've seen it - kind of neat.

cf
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It would be cool if you could snag some pics.
 
The concept of "spinning reserve" is that there is enough capacity on the generators that are running (ergo spinning) that will enable them to pick up the load in the event of loss of a generator or major tie feeder. This is done by initiating a fast load pickup call to the generating stations. Depending on the type of prime mover, steam or gas, it could take 10-20 minutes to do so. The utilities test this fast load pickup periodically to insure that the generators and the station crew are able to do so in the required time, otherwise they are not considered part of the spinning reserve. The inertia (flywheel), storage batteries, pumped storage, etc are not what is called "spinning reserve.
 
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