Small power plant vs grid-powr flow

[hansforum]

I have one beginner question.

If we connect small (micro) power plant (100kW) to the grid in the locality with thousand residents, how can we know if our small power plant will deliver all produced power to the grid? I mean, if in that locality at one moment is very low power demand how can we know what portion of that demand will supply grid and what portion will supply our small power plant? If small power plant is connected to the grid is it possible that it can't deliver all of it power so it has to reduce power production due to very low demand or if at one place demand is low, power is transferred elsewhere?

 

[byrdj]

the "Norm" is that generators connected to the grid will be loaded as per the the grid dispatcher. they request that you produce a given amount and be on a governoring system with a specified regulation so if the demand goes down, the grid frequecy goes up, then every unit shares the reduction as per thier regulation setting. If you do not comply with the dispatcher, you can set your governor for valves wide open so all you can produce will will be delievered to the grid and you will not share in the grids regulation

 

[cranky108]

First, why are you concerned about where the power goes? As long as you are being paid for it, why care?

Second, Why are you concerned about grid demand if the plant is so small?

Third, If you can't get the power out of the plant, and the grid is healthy, then you must be doing something wrong. Maybe not enough water, or pressure, or to many losses in your plant.

We have several so called "small hydro's" and have never had any of these problems. Now going on over 75 years.

The grid operators do a good job of keeping the grid healthy, and on frequency.

 

[Adam1980]

The power produced by the plant will flow according to load flow laws which are some how similar to a reservoir of water filling pots with the network impedance as the pipes slope.

The plant will serve the demand this is rule 1.
If there is no demand close to the plant, the closest demand (hence smallest impedance connection) will be served. However a 100 kW isnt that much to transfer along great distances or different voltage levels they will be gone as thermal losses (I2R).

To be economic the 100 kW generation should serve a nearby demand or the next household in a neighborhood.

 

[hansforum]

I am concerned with the situation when I have enough water to produce max power (100kW) and because of low demand in the grid due to higher freq of the grid I have to reduce power production because all generators have to reduce power. So there is possibility that I can deliver all I can produce and big generators will reduce power if power demand is reduced?

 

[rasevskii]

You do not seem to understand the basics of AC generation. If this is (likely) an induction generator, the power output will be determined by the turbine gate opening. IN other words the turbine will try to run the generator at a higher than normal speed, but the grid frequency will keep the unit at a nearly constant speed as if it were an ordinary induction motor, therefore power will be delivered to the grid. If it is a synchronous generator the same will happen but the unit will run in lockstep with the grid frequency. This assumes that you are in parallel with a large utility.

Most likely your small unit will not have a governor as such, but only an actuator controlled by (usually)a PLC control system. Is this unit already in operatio or still only in the planning stage?

Adam1980 above has it all wrong. THe KW flow has nothing to do with impedances. Only the kVAR flow is affected by these.

It is ridiculous to try to say where the power "goes to", the same argument is used by green power marketers to convince certain consumers (paying a higher rate)that "their" power only comes from renewable sources when it comes from the grid generally. Unless they have their own off grid private wind or hydro system, that is.

rasevskii

 

[rasevskii]

@hansforum:

It depends...if you are in fact on a small island system where the frequency can vary noticably, then you might have a problem getting full power output at times of low load on the system. But that would be quite a picturesque bush operation indeed. On large utilities in North America, Europe and elsewhere the system frequency is held to well within 0.1 HZ normally. The turbine governors on large hydro units usually have droop settings of not more than 4% which means the freq. has to vary by 4% on the system for the unit to go from no-load output to full output. In practice these units are usually block loaded by the dispatcher or local operators, by changing the speed setting on the governor, or running the unit close to the load limiter setting which is adjustable. On Kaplan and Francis turbines there is a cavitation area of loading that has to be avoided therefore these units are normally run at close to full output.

On your unit there might also be a cavitation area that has to be avoided at lower loadings. Vibration and some instability may occur. Depends on the type of turbine, submergance and other factors.

rasevskii

 

[DRWeig]

Of course, if the total load connected to the grid falls below 100 kW, you won't be able to push 100 kW into it...

Best to you,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies

 

[cranky108]

Does any body really believe a 100 kW unit will be controlled by the grid operator?

Most utilities (in the US) are required to purchase power from small producers like this, at there published rates. I.E. the small producer will not need to worry about lack of loading, frequency, voltage support, etc. They have a customer who is required to purchase the power at a fixed rate. Produce what you want, the large power company will just back down there large unit by 100 kW.

I know this for a fact, because that is what we do for solar farms.

However, there is a different story if you can produce more than 10 MW. Even at lower production rates there may be more requirements like voltage level you connect to.
But 100 kW is very small.

 

[waross]

A friend of mine bought and installed a 60 kW wind turbine in Central America. It took him quite a while to get it up and running. When he finally got it on-line he was surprised to find that as well as being billed for all the power that he had consumed when the wind turbine was not operating, he was also billed for all the power that he had delivered to the grid.
The National Electrical Energy administration demanded that he disconnect from the grid immediately. Before he could reconnect, he had to submit a study completed by a Registered Electrical Engineer. Then he would have to provide control and protection to standards set by the Utility. He had to follow the same steps for a 60 kW plant as he would have to follow for a 60 MW plant. There may also have been a requirement that the installation be reviewed by Congress. The wind turbine was dogged down and forgotten.
Another larger plant in the same country did proceed, went through all the steps and went online. The utility set limits on power factor and voltage. Unfortunately, the line capacity and characteristics at that point limited the output to about 80% of the plants capacity.
It's often hard on the financial picture when your revenue is artificially limited to about 80% of the amount that your financial planning was based on.
Moral:
Find out what the utility requirements are before proceeding.
Unless you are on a very very small island, the load on the grid will never drop below 100 kW.
Even on a small island, population 5000 to 10,000 the load will seldom drop that low.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[cranky108]

Good point waross. The maturity of several countries industries can be a problem.

Even sader is the number of electrical engineers world wide who graduate each year and can't find jobs. It makes you wonder about the quality of the universitys (in more than one respect).

Maybe one should ask what country this plant is to be installed.

And to qualify some of what I said above. There are limits of how much "non-utility generation" we allow on each feeder circuit. In general it is not to exceed 10% of the expected minimum load on that feeder. So 100 kW is not a big deal, unless you are the one who will exceed the 10% limit.