Regulating Real Power

[skm]

Hi,

I have an interesting scenario which I would like to discuss / share with you all.

Our client is having a cement plant (peak demand of 20MW) which is presently being fed from the utility grid sunstation “A” through a tapping. They are planning to put up a power plant of 42MW at about 2-3 km away from the cement plant. A feeder from this power plant would be given to cement plant to meet its load and only minimum contractual demand (1MW) would be taken from the grid. Another feeder from this power plant shall be connected to the utility grid at their Station ‘A’ for wheeling of balance available generation so that the same can be utilized by client for another plant located some 50km away from this power plant. Utilitiy grid station “A” & “B” are about 100km from each other and connected to each other through a double circuit line.

In case of loss of power from the power plant, the cement plant load shall be met from the utility.

Now the question:

1. Is it possible to limit / control the power flow such that only 1MW is taken from grid at the cement plant and balance 20MW being imported from the power plant?
2. Is it possible to control the wheeling power to the grid so as to optimize the cost of importing power from the utility?
3. What happens should the power demand at the Utility station A or B increases?

I understand many of this can be understood by having a load flow done for the system. However I am putting this on the site so as to ensure that this philosophy of connection to grid at 2 places is basically not a correct solution. In my opinion a better solution is to remover the utility connection at the cement plant and connect the power plant only to the grid.

Hoping to get some advice from you guys soon.

 

[Alex68]

You could regulate the power flow in a line with a phase shift transformer. So you could limit the power flow from the grid.

 

[habor]

You can not control the power flow with the given conditions. Connection to the grid should be done at only 1 place.

 

[jghrist]

I agree with habor. Unless you can separate the load so only a small portion is connected to the grid, leave the grid connection open and pay the 1 MW minimum charge for the availability of a backup.

Otherwise, you could end up using some of your available generation balance feeding thru the bus at Plant A back into the grid.

 

[tommom]

You can not both draw one MW from the grid at your cement plant AND maximize the output of your power plant to the grid.

The power plant is your source of real power. Its output must be controlled to (Demand cement plant - 1 MW) in order to exactly control the draw from the grid. You can't control the output of the power plant's real power to two different control points (ie 1 MW draw plus say 22 MW output to the grid.)

Your best bet might be to re-negotiate your utility agreement to delete the 1 MW minimum draw, or separate out a 1 MW load and have that separately fed, with a transfer scheme to add the cement plant back onto the grid on failure of your power plant.

 

[NYedison]

1) You may have to segregate the 1 MW load in the cement plant and have it fed from utility. (Existing connection).
2)Balance of the load may be fed from new feeder of power plant.
3)Provide a transfer switch to feed 1MW Load.

4) Tarnasfer switch will have Normal feed from Utility and emergency feed from new powerr plant source.

5) If utilty power fails New plant will feed the load.

6) You can monitor the Power flow between the Utility and new Power Plant at the Substation A with a suitable bidirectional revenue meter.

 

[RRaghunath]

If I understand right, you are going to have two OHLs to cement plant once the power plant is commissioned. This means power plant output can flow to the cement plant directly in one line and through utility grid substation A busbars in the other case.

Distance from power plant to the cement plant is 2-3km, as mentined in the post. What is the distance (route length) from power plant to substation and substation to cement plant.

Here lies major problem for you, I think. You will be selling power from power plant at a lesser price and buying the same power at much higher price through the second line. Not a good one.

The simple solution to me, without getting in to hifi things such as phase shifting transformers, back-to-back DC links, seems to be maintaining connection with the grid at only one point (I see this is in line with your thinking).

I would think the best way to do this is to disconnect existing grid connection (it is only a TEE-OFF, I can see) and taking power from power plant busbars.

The power at power plant busbars can be pooled power, i.e. grid as well as generation connected to the same bus bars as the out going line to the cement plant. This ensures that power plant power is available at normal times and grid power is available when power plant is down.

The cement plant authorities may not relish this very much as loosing the grid connection at their cement plant busbars makes one feel insecure (especially after getting used to the arrangement for a long time).

The agreement with power plant agency can be made in such a way the responsibility of providing reliable power and penalties in case of shortfall are all included. I know it is easier said than done.

Best of luck.