SHORT TERMHYDRO-THERMAL COORDINATION

Presented ByRajendra Narayan Senapati

Roll no-26243Regd. No.-0701105115

22nd MAR 2011

Outline1) Introduction2) Need of Hydrothermal Scheduling3) Classification of Hydro Plants4) Classification of Hydrothermal Scheduling Problem5) Solution for Short-term Scheduling Problem6) Conclusion7) References

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Introductiono Hydro-plants can be easily started and assigned load in

very short time.o Slow response of thermal power due to boiler, super

heater, and turbine system.o Thermal plant base load planto Hydro plant peak load plant

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Need of Hydrothermal Scheduling

•The optimal scheduling problem in a hydro-thermal system stated as to minimize the fuel cost of thermal plants under the constraint of water availability for hydro-generation over a given period of operation•To maintain an optimal balance between fuel cost and water storage level to maintain reliable and uninterrupted operation.• To test these techniques on different problems.

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Classification of Hydro Plants

•Classification1. Pumped storage plants2. Conventional plants

•Classification on the basis of location1. Hydro plants on different streams2. Hydro plants on the same stream3. Multi-chain hydro plants

•Classification on the basis of Quantity of Water Available1. Run-off- River Plants without Pondage2. Run-off River Plants with Pondage

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Classification of Hydrothermal Scheduling Problem

•Long range problemlong-range scheduling is validity ranges from 1 week to 1 year or several years.Long-term hydrothermal scheduling is used for breaking down the long-term problem into a number of midterm (e.g., monthly) problems.•Short range problemInvolves the hour-by-hour scheduling of all generation on a system to achieve minimum production cost for the given time period.The load, hydraulic inflows, and unit availabilities are assumed known.Reservoir levels is given 22nd MAR 2011

Scheduling problem consists of•Problem characteristics.•Problem formulation. •Solution approach

Scheduling Problems

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Two-unit hydrothermal systems

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For any time period j

However, the energy available from the hydro plant is insufficient to meet the load

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Use here the entire amount of energy from the hydro plant in such a way that the cost of running the steam plant is minimized. The steam-plant energy required is

i.e. (Load energy) - (Hydro energy) = (Steam energy)

It does not require the steam unit to run for the entire interval of Tmax hours. Therefore

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Where

= run period for steam plant Then

The scheduling problem becomes

Subject to

And the Lagrange function is

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Then

The total cost over the interval is

Where

Let the steam plant cost be expressed as

Then

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Also

Where = Optimum value of stem generated powerThen

= /

And

Now we can establish the value of Ps* by minimizing FT:

Or

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Which means the unit should be operated at its maximum efficiency point long enough to supply the energy needed, E.

IfWhere fc is the fuel cost

Now the heat rate is

And the heat rate has a minimum when

Giving best efficiency at

Solution for Short-term Scheduling Problem

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Fixed head hydro thermal scheduling

Variable head hydro thermal scheduling

Problem Characteristics

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Problem Formulation

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Thermal Model

operating cost

fuel cost

Hydro Model

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rate of discharge

Constraints

Classical Method

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Problem

Subject to

Let = length of jth interval

The loads are constant in each interval. Other constraints could be imposed, such as:

The Lagrange function is:

for a specific interval j =k,

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So

Suppose we add the network losses to the problem. Then at each hour

And the Lagrange function becomes

With resulting coordination equations (hour k):

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Flow Chart for Classical Method22nd MAR 2011

Conclusion

•Hydro-thermal scheduling is done when power demand is less than the maximum capacity of power generation by the hydro and thermal plants. The benefit of this scheduling is to save the cost of generation, in addition to meeting the agricultural and irrigational requirements.•The operating cost of thermal plant is very high, though their capital cost is low. On the other hand the operating cost of hydroelectric plant is low, though their capital cost is high. So it has become economical as well convenient to have both thermal and hydro plants in the same grid.

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Referrences•Kothari D.P., Dhillon J.S., “Power System Optimization”, Prentice Hall of IndiaPrivate Limited, New Delhi, 2004.•Elgerd O.I, “Electric Energy Systems theory, An Introduction”, Tata McGraw Hill Limited, New York, 1983.•Grainger J.J., Stevenson W.D., “Power System Analysis”, Tata McGraw Hill Limited, New York,2003.•Fabrício Y. K. Takigawa, Erlon C. Finardi, Edson L. da Silva, “A Decomposition Strategy to Solve the Short-Term Hydrothermal Scheduling Based on Lagrangian Relaxation”,2005.•Hota P.K., Barisal A.K., Chakrabarti R., “An improved PSO technique for short-term optimal hydrothermal scheduling”,2009.•Ramos L.M., Lora A.T., Santos J.R., “Short-term Hydro-thermal Coordination Based on Interior Point Nonlinear Programming and Genetic Algorithms”,2001.

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THANK YOU